Associate Professor, Biomedical Data Science
Master of Science, Nankai University, Mathematics (1998)
Doctor of Science, Harvard University, Biostatistics (2002)
My research interest includes
(1) Survival Analysis and Semiparametric Modeling;
(2) Resampling Method ;
(3) Meta Analysis ;
(4) High Dimensional Data Analysis;
(5) Personalized Medicine for Disease Diagnosis, Prognosis and Treatment.
Although AKI is common among hospitalized children, comprehensive epidemiologic data are lacking. This study characterizes pediatric AKI across the United States and identifies AKI risk factors using high-content/high-throughput analytic techniques.For the cross-sectional analysis of the 2009 Kids Inpatient Database, AKI events were identified using International Classification of Diseases, Ninth Revision, Clinical Modification codes. Demographics, incident rates, and outcome data were analyzed and reported for the entire AKI cohort as well as AKI subsets. Statistical learning methods were applied to the highly imbalanced dataset to derive AKI-related risk factors.Of 2,644,263 children, 10,322 children developed AKI (3.9/1000 admissions). Although 19% of the AKI cohort was ≤1 month old, the highest incidence was seen in children 15-18 years old (6.6/1000 admissions); 49% of the AKI cohort was white, but AKI incidence was higher among African Americans (4.5 versus 3.8/1000 admissions). In-hospital mortality among patients with AKI was 15.3% but higher among children ≤1 month old (31.3% versus 10.1%, P<0.001) and children requiring critical care (32.8% versus 9.4%, P<0.001) or dialysis (27.1% versus 14.2%, P<0.001). Shock (odds ratio, 2.15; 95% confidence interval, 1.95 to 2.36), septicemia (odds ratio, 1.37; 95% confidence interval, 1.32 to 1.43), intubation/mechanical ventilation (odds ratio, 1.2; 95% confidence interval, 1.16 to 1.25), circulatory disease (odds ratio, 1.47; 95% confidence interval, 1.32 to 1.65), cardiac congenital anomalies (odds ratio, 1.2; 95% confidence interval, 1.13 to 1.23), and extracorporeal support (odds ratio, 2.58; 95% confidence interval, 2.04 to 3.26) were associated with AKI.AKI occurs in 3.9/1000 at-risk US pediatric hospitalizations. Mortality is highest among neonates and children requiring critical care or dialysis. Identified risk factors suggest that AKI occurs in association with systemic/multiorgan disease more commonly than primary renal disease.
View details for DOI 10.2215/CJN.00270113
View details for PubMedID 23833312
Early detection of pancreatic ductal adenocarcinoma (PDAC) allows for surgical resection and increases patient survival times. Imaging agents that bind and amplify the signal of neovascular proteins in neoplasms can be detected by ultrasound, enabling accurate detection of small lesions. We searched for new markers of neovasculature in PDAC and assessed their potential for tumor detection by ultrasound molecular imaging.Thymocyte Differentiation Antigen 1 (Thy1) was identified as a specific biomarker of PDAC neovasculature by proteomic analysis. Upregulation in PDAC was validated by immunohistochemical analysis of pancreatic tissue samples from 28 healthy individuals, 15 with primary chronic pancreatitis tissues, and 196 with PDAC. Binding of Thy1-targeted contrast microbubbles was assessed in cultured cells, in mice with orthotopic PDAC xenograft tumors expressing human Thy1 on the neovasculature, and on the neovasculature of a genetic mouse model of PDAC.Based on immunohistochemical analyses, levels of Thy1 were significantly higher in the vascular of human PDAC than chronic pancreatitis (P=.007) or normal tissue samples (P<.0001). In mice, ultrasound imaging accurately detected human Thy1-positive PDAC xenografts, as well as PDACs that express endogenous Thy1 in genetic mouse models of PDAC.We have identified and validated Thy1 as a marker of PDAC that can be detected by ultrasound molecular imaging in mice. The development of a specific imaging agent and identification of Thy1 as a new biomarker could aid in the diagnosis of this cancer and management of patients.
View details for DOI 10.1053/j.gastro.2013.06.011
View details for PubMedID 23791701
Clinical practice guidelines state there is insufficient evidence to support advising patients with peripheral artery disease (PAD) to participate in a home-based walking exercise program.To determine whether a home-based walking exercise program that uses a group-mediated cognitive behavioral intervention, incorporating both group support and self-regulatory skills, can improve functional performance compared with a health education control group in patients with PAD with and without intermittent claudication.Randomized controlled clinical trial of 194 patients with PAD, including 72.2% without classic symptoms of intermittent claudication, performed in Chicago, Illinois between July 22, 2008, and December 14, 2012.Participants were randomized to 1 of 2 parallel groups: a home-based group-mediated cognitive behavioral walking intervention or an attention control condition.The primary outcome was 6-month change in 6-minute walk performance. Secondary outcomes included 6-month change in treadmill walking, physical activity, the Walking Impairment Questionnaire (WIQ), and Physical and Mental Health Composite Scores from the 12-item Short-Form Health Survey.Participants randomized to the intervention group significantly increased their 6-minute walk distance ([reported in meters] 357.4 to 399.8 vs 353.3 to 342.2 for those in the control group; mean difference, 53.5 [95% CI, 33.2 to 73.8]; P < .001), maximal treadmill walking time (intervention, 7.91 to 9.44 minutes vs control, 7.56 to 8.09; mean difference, 1.01 minutes [95% CI, 0.07 to 1.95]; P = .04), accelerometer-measured physical activity over 7 days (intervention, 778.0 to 866.1 vs control, 671.6 to 645.0; mean difference, 114.7 activity units [95% CI, 12.82 to 216.5]; P = .03), WIQ distance score (intervention, 35.3 to 47.4 vs control, 33.3 to 34.4; mean difference, 11.1 [95% CI, 3.9 to 18.1]; P = .003), and WIQ speed score (intervention, 36.1 to 47.7 vs control, 35.3-36.6; mean difference, 10.4 [95% CI, 3.4 to 17.4]; P = .004).A home-based walking exercise program significantly improved walking endurance, physical activity, and patient-perceived walking endurance and speed in PAD participants with and without classic claudication symptoms. These findings have implications for the large number of patients with PAD who are unable or unwilling to participate in supervised exercise programs.clinicaltrials.gov Identifier: NCT00693940.
View details for Web of Science ID 000321253000023
View details for PubMedID 23821089
Chronic graft-versus-host disease (GVHD) results in significant morbidity and mortality, limiting the benefit of allogeneic hematopoietic cell transplantation (HCT). Peripheral blood gene expression profiling of the donor immune repertoire following HCT may provide associated genes and pathways thereby improving the pathophysiologic understanding of chronic GVHD. We profiled 70 patients and identified candidate genes that provided mechanistic insight in the biologic pathways that underlie chronic GVHD. Our data revealed that the dominant gene signature in patients with chronic GVHD represented compensatory responses that control inflammation and included the interleukin-1 decoy receptor, IL-1 receptor type II, and genes that were profibrotic and associated with the IL-4, IL-6 and IL-10 signaling pathways. In addition, we identified three genes that were important regulators of extracellular matrix. Validation of this discovery phase study will determine if the identified genes have diagnostic, prognostic or therapeutic implications.
View details for DOI 10.1016/j.clim.2013.04.013
View details for PubMedID 23685278
Risk prediction procedures can be quite useful for the patient's treatment selection, prevention strategy, or disease management in evidence-based medicine. Often, potentially important new predictors are available in addition to the conventional markers. The question is how to quantify the improvement from the new markers for prediction of the patient's risk in order to aid cost-benefit decisions. The standard method, using the area under the receiver operating characteristic curve, to measure the added value may not be sensitive enough to capture incremental improvements from the new markers. Recently, some novel alternatives to area under the receiver operating characteristic curve, such as integrated discrimination improvement and net reclassification improvement, were proposed. In this paper, we consider a class of measures for evaluating the incremental values of new markers, which includes the preceding two as special cases. We present a unified procedure for making inferences about measures in the class with censored event time data. The large sample properties of our procedures are theoretically justified. We illustrate the new proposal with data from a cancer study to evaluate a new gene score for prediction of the patient's survival.
View details for DOI 10.1002/sim.5647
View details for Web of Science ID 000319880100008
View details for PubMedID 23037800
Purpose: To develop and test a molecular imaging approach that uses ultrasonography (US) and a clinically translatable dual-targeted (P- and E-selectin) contrast agent (MBSelectin) in the quantification of inflammation at the molecular level and to quantitatively correlate selectin-targeted US with fluorodeoxyglucose (FDG) combined positron emission tomography (PET) and computed tomography (CT) in terms of visualization and quantification of different levels of inflammation in a murine acute colitis model. Materials and Methods: Animal studies were approved by the Institutional Administrative Panel on Laboratory Animal Care at Stanford University. MBSelectin was developed by covalently binding an analog of the naturally occurring binding ligand P-selectin glycoprotein ligand 1 fused to a human fragment crystallizable(or Fc) domain onto the lipid shell of perfluorobutane and nitrogen-containing MBs. Binding specificity of MBSelectin was assessed in vitro with a flow chamber assay and in vivo with a chemically induced acute colitis murine model. US signal was quantitatively correlated with FDG uptake at PET/CT and histologic grade. Statistical analysis was performed with the Student t test, analysis of variance, and Pearson correlation analysis. Results: MBSelectin showed strong attachment to both human and mouse P- and E-selectin compared with MBControl in vitro (P ≤ .002). In vivo, US signal was significantly increased (P < .001) in mice with acute colitis (173.8 arbitrary units [au] ± 134.8 [standard deviation]) compared with control mice (5.0 au ± 4.5). US imaging signal strongly correlated with FDG uptake on PET/CT images (ρ = 0.89, P < .001). Ex vivo analysis enabled confirmation of inflammation in mice with acute colitis and high expression levels of P- and E-selectin in mucosal capillaries (P = .014). Conclusion: US with MBSelectin specifically enables detection and quantification of inflammation in a murine acute colitis model, leveraging the natural pathway of leukocyte recruitment in inflammatory tissue. US imaging with MBSelectin correlates well with FDG uptake at PET/CT imaging. © RSNA, 2013 Supplemental material: http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.13122509/-/DC1.
View details for DOI 10.1148/radiol.13122509
View details for PubMedID 23371306
View details for PubMedCentralID PMC3662899
The Vitamin D Standardization Program (VDSP) has developed protocols for standardizing procedures of 25-hydroxyvitamin D [25(OH)D] measurement in National Health/Nutrition Surveys to promote 25(OH)D measurements that are accurate and comparable over time, location, and laboratory procedure to improve public health practice.We applied VDSP protocols to existing ELISA-derived serum 25(OH)D data from the Irish National Adult Nutrition Survey (NANS) as a case-study survey and evaluated their effectiveness by comparison of the protocol-projected estimates with those from a reanalysis of survey serums by using liquid chromatography-tandem mass spectrometry (LC-tandem MS).The VDSP reference system and protocols were applied to ELISA-based serum 25(OH)D data from the representative NANS sample (n = 1118). A reanalysis of 99 stored serums by using standardized LC-tandem MS and resulting regression equations yielded predicted standardized serum 25(OH)D values, which were then compared with LC-tandem MS reanalyzed values for all serums.Year-round prevalence rates for serum 25(OH)D concentrations <30, <40, and <50 nmol/L were 6.5%, 21.9%, and 40.0%, respectively, via original ELISA measurements and 11.4%, 25.3%, and 43.7%, respectively, when VDSP protocols were applied. Differences in estimates at <30- and <40-nmol/L thresholds, but not at the <50-nmol/L threshold, were significant (P < 0.05). A reanalysis of all serums by using LC-tandem MS confirmed prevalence estimates as 11.2%, 27.2%, and 45.0%, respectively. Prevalences of serum 25(OH)D concentrations >125 nmol/L were 1.2%, 0.3%, and 0.6% by means of ELISA, VDSP protocols, and LC-tandem MS, respectively.VDSP protocols hold a major potential for national nutrition and health surveys in terms of the standardization of serum 25(OH)D data.
View details for DOI 10.3945/ajcn.112.057182
View details for Web of Science ID 000319371500012
View details for PubMedID 23615829
We studied associations of magnetic resonance imaging (MRI)-measured superficial femoral artery (SFA) occlusions with functional performance, leg symptoms, and collateral vessel number in peripheral artery disease (PAD). We studied associations of collateral vessel number with functional performance in PAD.Associations of MRI-detected SFA occlusion and collateral vessel number with functional performance among individuals with PAD have not been reported.A total of 457 participants with an ankle brachial index (ABI) <1.00 had MRI measurement of the proximal SFA with 12 consecutive 2.5-μm cross-sectional images. An occluded SFA was defined as an SFA in which at least 1 segment was occluded. A nonoccluded SFA was defined as absence of any occluded slices. Collateral vessels were visualized with magnetic resonance angiography. Lower extremity functional performance was measured with the 6-min walk, 4-m walking velocity at usual and fastest pace, and the Short Physical Performance Battery (SPPB) (0 to 12 scale, 12 = best).Adjusting for age, sex, race, comorbidities, and other confounders, the presence of an SFA occlusion was associated with poorer 6-min walk performance (1,031 vs. 1,169 feet, p = 0.006), slower fast-paced walking velocity (1.15 vs. 1.22 m/s, p = 0.042), and lower SPPB score (9.07 vs. 9.75, p = 0.038) compared with the absence of an SFA occlusion. More numerous collateral vessels were associated with better 6-min walk performance (0 to 3 collaterals-1,064 feet, 4 to 7 collaterals-1,165 feet, ≥8 collaterals-1,246 feet, p trend = 0.007), faster usual-paced walking speed (0 to 3 collaterals-0.84 m/s, 4 to 7 collaterals-0.88 m/s, ≥8 collaterals-0.91 m/s, p trend = 0.029), and faster rapid-paced walking speed (0 to 3 collaterals-1.17 m/s, 4 to 7 collaterals-1.22 m/s, ≥8 collaterals-1.29 m/s, p trend = 0.002), adjusting for age, sex, race, comorbidities, ABI, and other confounders.Among PAD participants, MRI-visualized occlusions in the proximal SFA are associated with poorer functional performance, whereas more numerous collaterals are associated with better functional performance. (Magnetic Resonance Imaging to Identify Characteristics of Plaque Build-Up in People With Peripheral Arterial Disease; NCT00520312).
View details for DOI 10.1016/j.jcmg.2012.10.024
View details for Web of Science ID 000320977200008
View details for PubMedID 23647796
This study determined whether greater 2-year declines in Walking Impairment Questionnaire (WIQ) stair climbing, distance, or speed scores were associated with higher all-cause and cardiovascular disease (CVD) mortality among men and women with lower extremity peripheral artery disease (PAD).Associations of decline in the WIQ with mortality among people with PAD are unknown.Participants were 442 men and women with PAD identified from Chicago area medical centers. The WIQ was completed at baseline and at 2-year follow-up. Cox proportional hazard models were used to assess associations across categories of 2-year changes in WIQ stair climbing, WIQ distance, and WIQ speed scores with subsequent all-cause and CVD mortality, adjusting for age, sex, race, ankle-brachial index, body mass index, smoking, comorbidities, and other covariates.One hundred twenty-three participants (27.8%) died during a median follow-up of 4.7 years after the 2-year change in WIQ score measurements. Forty-five participants died from CVD. Adjusting for covariates, participants with WIQ score declines ≥20.0 points had higher all-cause mortality (hazard ratio [HR]: 1.93, 95% confidence interval [CI]: 1.01 to 3.68 for WIQ stair climbing; HR: 2.34, 95% CI: 1.15 to 4.75 for WIQ distance; and HR: 3.55, 95% CI: 1.57 to 8.04 for WIQ speed, respectively) compared with participants with ≥20.0 point improvement in each of the corresponding WIQ categories. Participants with ≥20.0 point declines in the WIQ distance score had higher CVD mortality (HR: 4.56, 95% CI: 1.30 to 16.01) compared with those with ≥20.0 point improvement in the WIQ distance score.Patients with PAD who experienced ≥20.0 point declines in the WIQ stair climbing, distance, and speed scores had a higher rate of all-cause mortality compared with those with less declines in each WIQ score.
View details for DOI 10.1016/j.jacc.2013.01.060
View details for Web of Science ID 000317842200011
View details for PubMedID 23500321
Among individuals with peripheral artery disease (PAD), we compared annual change in 6-minute walk performance between participants who neither underwent lower extremity revascularization nor walked for exercise (group 1, reference), those who walked regularly for exercise (group 2), and those who underwent lower extremity revascularization (group 3).Participants were recruited from Chicago-area vascular laboratories and followed annually. Change in 6-minute walk was calculated beginning at the study visit preceding lower extremity revascularization or exercise behavior and continuing for 1 additional year after the therapy was reported. Results are adjusted for age, sex, race, comorbidities, and other confounders.Of 348 PAD participants, 43 underwent revascularization during median follow-up of 84 months. Adjusted annual declines in 6-minute walk were -96.6 feet/year for group 1, -49.9 feet/year for group 2, and -32.6 feet/year for group 3 (P < .001). Forty-one percent of revascularizations were not associated with ankle-brachial index (ABI) improvement. When group 3 was limited to participants with ABI improvement ≥0.15 after revascularization, annual adjusted changes in 6-minute walk were -97.7 feet/year for group 1, -46.5 feet/year for group 2, and +68.1 feet/year for group 3 (P < .001). When group 3 was limited to participants without ABI improvement ≥0.15 after revascularization, annual adjusted changes in 6-minute walk were -99.2 feet/year for group 1, -48.0 feet/year for group 2, and -61.7 feet/year for group 3 (P < .001).A large proportion of PAD participants did not have ABI improvement of at least 0.15 at follow-up study visit after revascularization. The benefits of lower extremity revascularization in patients with PAD appear closely tied to improvements in the ABI after revascularization.
View details for DOI 10.1016/j.jvs.2012.09.068
View details for Web of Science ID 000317187900013
View details for PubMedID 23352363
While there is an increasing role of ultrasound for breast cancer screening in patients with dense breast, conventional anatomical ultrasound lacks sensitivity and specificity for early breast cancer detection. In this study, we assessed the potential of ultrasound molecular imaging using clinically translatable vascular endothelial growth factor receptor type 2 (VEGFR2)-targeted microbubbles (MB(VEGFR2)) to improve the diagnostic accuracy of ultrasound in earlier detection of breast cancer and ductal carcinoma in situ (DCIS) in a transgenic mouse model [FVB/N-Tg(MMTV-PyMT)634Mul]. In vivo binding specificity studies (n = 26 tumors) showed that ultrasound imaging signal was significantly higher (P < 0.001) using MB(VEGFR2) than nontargeted microbubbles and imaging signal significantly decreased (P < 0.001) by blocking antibodies. Ultrasound molecular imaging signal significantly increased (P < 0.001) when breast tissue (n = 315 glands) progressed from normal [1.65 ± 0.17 arbitrary units (a.u.)] to hyperplasia (4.21 ± 1.16), DCIS (15.95 ± 1.31), and invasive cancer (78.1 ± 6.31) and highly correlated with ex vivo VEGFR2 expression [R(2) = 0.84; 95% confidence interval (CI), 0.72-0.91; P < 0.001]. At an imaging signal threshold of 4.6 a.u., ultrasound molecular imaging differentiated benign from malignant entities with a sensitivity of 84% (95% CI, 78-88) and specificity of 89% (95% CI, 81-94). In a prospective screening trail (n = 63 glands), diagnostic performance of detecting DCIS and breast cancer was assessed and two independent readers correctly diagnosed malignant disease in more than 95% of cases and highly agreed between each other [intraclass correlation coefficient (ICC) = 0.98; 95% CI, 97-99]. These results suggest that VEGFR2-targeted ultrasound molecular imaging allows highly accurate detection of DCIS and breast cancer in transgenic mice and may be a promising approach for early breast cancer detection in women.
View details for DOI 10.1158/0008-5472.CAN-12-3391
View details for Web of Science ID 000316187500006
View details for PubMedID 23328585
View details for PubMedCentralID PMC3602408
Obstructive sleep apnea (OSA) is characterized by recurrent nocturnal hypoxia and sleep disruption. Sleep fragmentation caused hyperalgesia in volunteers, while nocturnal hypoxemia enhanced morphine analgesic potency in children with OSA. This evidence directly relates to surgical OSA patients who are at risk for airway compromise due to postoperative use of opioids. Using accepted experimental pain models, we characterized pain processing and opioid analgesia in male volunteers recruited based on their risk for OSA.After approval from the Intitutional Review Board and informed consent, we assessed heat and cold pain thresholds and tolerances in volunteers after overnight polysomnography (PSG). Three pro-inflammatory and 3 hypoxia markers were determined in the serum. Pain tests were performed at baseline, placebo, and two effect site concentrations of remifentanil (1 and 2 µg/ml), an μ-opioid agonist. Linear mixed effects regression models were employed to evaluate the association of 3 PSG descriptors [wake after sleep onset, number of sleep stage shifts, and lowest oxyhemoglobin saturation (SaO(2)) during sleep] and all serum markers with pain thresholds and tolerances at baseline, as well as their changes under remifentanil.Forty-three volunteers (12 normal and 31 with a PSG-based diagnosis of OSA) were included in the analysis. The lower nadir SaO(2) and higher insulin growth factor binding protein-1 (IGFBP-1) were associated with higher analgesic sensitivity to remifentanil (SaO(2), P = 0.0440; IGFBP-1, P = 0.0013). Other pro-inflammatory mediators like interleukin-1β and tumor necrosis factor-α (TNF-α) were associated with an enhanced sensitivity to the opioid analgesic effect (IL-1β, P = 0.0218; TNF-α, P = 0.0276).Nocturnal hypoxemia in subjects at high risk for OSA was associated with an increased potency of opioid analgesia. A serum hypoxia marker (IGFBP-1) was associated with hypoalgesia and increased potency to opioid analgesia; other pro-inflammatory mediators also predicted an enhanced opioid potency.Clinicaltrials.gov NCT00672737.
View details for DOI 10.1371/journal.pone.0054807
View details for PubMedID 23382975
Mass spectrometry (MS) has evolved to become the primary high throughput tool for proteomics based biomarker discovery. Until now, multiple challenges in protein MS data analysis remain: large-scale and complex data set management; MS peak identification, indexing; and high dimensional peak differential analysis with the concurrent statistical tests based false discovery rate (FDR). "Turnkey" solutions are needed for biomarker investigations to rapidly process MS data sets to identify statistically significant peaks for subsequent validation.Here we present an efficient and effective solution, which provides experimental biologists easy access to "cloud" computing capabilities to analyze MS data. The web portal can be accessed at http://transmed.stanford.edu/ssa/.Presented web application supplies large scale MS data online uploading and analysis with a simple user interface. This bioinformatic tool will facilitate the discovery of the potential protein biomarkers using MS.
View details for DOI 10.1186/1756-0500-6-109
View details for PubMedID 23522030
People with lower extremity peripheral artery disease (PAD) have greater functional impairment and faster functional decline than those without PAD. We describe methods for the Group Oriented Arterial Leg Study (GOALS), an ongoing randomized controlled clinical trial designed to determine whether a Group-Mediated Cognitive Behavioral (GMCB) intervention improves functional performance in PAD participants, compared to a health education control condition. In GOALS, PAD participants were randomized to either an intervention or a health education control condition in a parallel design. Both conditions consist of weekly group sessions with other PAD participants. In the intervention, cognitive behavioral techniques are used to assist participants in setting and adhering to home-based walking exercise goals. Participants are encouraged to walk for exercise at home at least 5 days/week. In the control condition, participants receive lectures on health-related topics. After 6 months of on-site weekly sessions, participants are transitioned to telephone follow-up for another 6 months. Participants in the intervention are asked to continue home walking exercise. The primary outcome is change in six-minute walk performance between baseline and six-month follow-up. Secondary outcomes include change in six-minute walk performance at 12-month follow-up, and change in treadmill walking performance, the Walking Impairment Questionnaire, quality of life, and physical activity at six and 12-month follow-up. In conclusion, if our group-mediated cognitive behavioral intervention is associated with improved walking performance in individuals with PAD, results will have major public health implications for the large and growing number of people with PAD.
View details for DOI 10.1016/j.cct.2012.08.001
View details for Web of Science ID 000310825400025
View details for PubMedID 23158112
Consider a comparative, randomized clinical study with a specific event time as the primary end point. In the presence of censoring, standard methods of summarizing the treatment difference are based on Kaplan-Meier curves, the logrank test, and the point and interval estimates via Cox's procedure. Moreover, for designing and monitoring the study, one usually utilizes an event-driven scheme to determine the sample sizes and interim analysis time points.When the proportional hazards (PHs) assumption is violated, the logrank test may not have sufficient power to detect the difference between two event time distributions. The resulting hazard ratio estimate is difficult, if not impossible, to interpret as a treatment contrast. When the event rates are low, the corresponding interval estimate for the 'hazard ratio' can be quite large due to the fact that the interval length depends on the observed numbers of events. This may indicate that there is not enough information for making inferences about the treatment comparison even when there is no difference between two groups. This situation is quite common for a postmarketing safety study. We need an alternative way to quantify the group difference.Instead of quantifying the treatment group difference using the hazard ratio, we consider an easily interpretable and model-free parameter, the integrated survival rate difference over a prespecified time interval, as an alternative. We present the inference procedures for such a treatment contrast. This approach is purely nonparametric and does not need any model assumption such as the PHs. Moreover, when we deal with equivalence or noninferiority studies and the event rates are low, our procedure would provide more information about the treatment difference. We used a cardiovascular trial data set to illustrate our approach.The results using the integrated event rate differences have a heuristic interpretation for the treatment difference even when the PHs assumption is not valid. When the event rates are low, for example, for the cardiovascular study discussed in this article, the procedure for the integrated event rate difference provides tight interval estimates in contrast to those based on the event-driven inference method.The design of a trial with the integrated event rate difference may be more complicated than that using the event-driven procedure. One may use simulation to determine the sample size and the estimated duration of the study.The procedure discussed in this article can be a useful alternative to the standard PHs method in the survival analysis.
View details for DOI 10.1177/1740774512455464
View details for Web of Science ID 000309730200002
View details for PubMedID 22914867
The clinical implications of low vitamin D in peripheral artery disease (PAD) are unknown. We hypothesized that among individuals with PAD, lower levels of 25-hydroxyvitamin D would be associated with poorer functional performance, more adverse calf muscle characteristics, and poorer peripheral nerve function. Participants were 402 men and women with PAD who underwent measurement of 25-hydroxyvitamin D (DiaSorin radioimmunoassay) along with 6-minute walk testing, measurement of walking velocity at usual and fastest pace, computed tomography-measured calf muscle density, and peripheral nerve conduction velocity (NCV). Among PAD participants, 20.4% had 25-hydroxyvitamin D levels < 30 nmol/L, consistent with deficient vitamin D status. Adjusting for age, sex, and race, lower 25-hydroxyvitamin D levels were associated with poorer 6-minute walk performance (p trend = 0.002), slower usual-paced 4-meter walking velocity (p trend = 0.031), slower fast-paced 4-meter walking velocity (p trend = 0.043), and lower calf muscle density (p trend = 0.031). After additional adjustment for body mass index (BMI) and diabetes, none of these associations remained statistically significant. However, lower levels of 25-hydroxyvitamin D were associated with poorer peroneal NCV (p trend = 0.013) and poorer sural NCV (p trend = 0.039), even after adjusting for age, sex, race, BMI, comorbidities, smoking, physical activity, and other confounders. In conclusion, vitamin D deficiency is common among people with PAD encountered in clinical settings. After adjusting for BMI and diabetes mellitus, we found no significant associations of lower levels of 25-hydroxyvitamin D with poorer functional performance or calf muscle characteristics. Associations of low vitamin D levels with poorer peripheral nerve function require further study.
View details for DOI 10.1177/1358863X12448457
View details for Web of Science ID 000309358900002
View details for PubMedID 22814997
To develop and test a real-time motion compensation algorithm for contrast-enhanced ultrasound imaging of tumor angiogenesis on a clinical ultrasound system.The Administrative Institutional Panel on Laboratory Animal Care approved all experiments. A new motion correction algorithm measuring the sum of absolute differences in pixel displacements within a designated tracking box was implemented in a clinical ultrasound machine. In vivo angiogenesis measurements (expressed as percent contrast area) with and without motion compensated maximum intensity persistence (MIP) ultrasound imaging were analyzed in human colon cancer xenografts (n = 64) in mice. Differences in MIP ultrasound imaging signal with and without motion compensation were compared and correlated with displacements in x- and y-directions. The algorithm was tested in an additional twelve colon cancer xenograft-bearing mice with (n = 6) and without (n = 6) anti-vascular therapy (ASA-404). In vivo MIP percent contrast area measurements were quantitatively correlated with ex vivo microvessel density (MVD) analysis.MIP percent contrast area was significantly different (P < 0.001) with and without motion compensation. Differences in percent contrast area correlated significantly (P < 0.001) with x- and y-displacements. MIP percent contrast area measurements were more reproducible with motion compensation (ICC = 0.69) than without (ICC = 0.51) on two consecutive ultrasound scans. Following anti-vascular therapy, motion-compensated MIP percent contrast area significantly (P = 0.03) decreased by 39.4 ± 14.6 % compared to non-treated mice and correlated well with ex vivo MVD analysis (Rho = 0.70; P = 0.05).Real-time motion-compensated MIP ultrasound imaging allows reliable and accurate quantification and monitoring of angiogenesis in tumors exposed to breathing-induced motion artifacts.
View details for DOI 10.1007/s10456-012-9271-3
View details for Web of Science ID 000307272200009
View details for PubMedID 22535383
The Walking Impairment Questionnaire (WIQ) measures self-reported walking distance, walking speed, and stair-climbing ability in men and women with lower extremity peripheral arterial disease (PAD). We determined whether poorer WIQ scores are associated with higher all-cause and cardiovascular disease (CVD) mortality in individuals with and without PAD.We identified 1048 men and women with and without PAD from Chicago-area medical centers. Participants completed the WIQ at baseline and were monitored for a median of 4.5 years. Cox proportional hazards models were used to relate baseline WIQ scores with death, adjusting for age, sex, race, the ankle-brachial index (ABI), comorbidities, and other covariates.During follow-up, 461 participants (44.0%) died, including 158 deaths from CVD. PAD participants in the lowest baseline quartile of the WIQ stair-climbing scores had higher all-cause mortality (hazard ratio, 1.70; 95% confidence interval, 1.08-2.66, P = .02) and higher CVD mortality (hazard ratio, 3.11; 95% confidence interval, 1.30-7.47, P = .01) compared with those with the highest baseline WIQ stair-climbing score. Among PAD participants, there were no significant associations of lower baseline WIQ distance or speed scores with rates of all-cause mortality (P = .20 and P = .07 for trend, respectively) or CVD mortality (P = .51 and P = .33 for trend, respectively). Among non-PAD participants there were no significant associations of lower baseline WIQ stair-climbing, distance, or speed score with rates of all-cause mortality (P = .94, P = .69, and P = .26, for trend, respectively) or CVD mortality (P = .28, P = .68, and P = .78, for trend, respectively).Among participants with PAD, lower WIQ stair-climbing scores are associated with higher all-cause and CVD mortality, independently of the ABI and other covariates.
View details for DOI 10.1016/j.jvs.2011.12.010
View details for Web of Science ID 000304206000017
View details for PubMedID 22608041
PURPOSE: To develop and test a fast ultrasonic molecular imaging technique for quantification and monitoring of angiogenesis in cancer. MATERIALS AND METHODS: A new software algorithm measuring the dwell time of contrast microbubbles in near real-time (henceforth, fast method) was developed and integrated in a clinical ultrasound system. In vivo quantification and monitoring of tumor angiogenesis during anti-VEGF antibody therapy was performed in human colon cancer xenografts in mice (n=20) using the new fast method following administration of vascular endothelial growth factor receptor 2 (VEGFR2)-targeted contrast microbubbles. Imaging results were compared with a traditional destruction/replenishment approach (henceforth, traditional method) in an intra-animal comparison. RESULTS: There was excellent correlation (R(2)=0.93; P<0.001) between the fast method and the traditional method in terms of VEGFR2-targeted in vivo ultrasonic molecular imaging with significantly higher (P=0.002) imaging signal in colon cancer xenografts using VEGFR2-targeted compared to control non-targeted contrast microbubbles. The new fast method was highly reproducible (ICC=0.87). Following anti-angiogenic therapy, ultrasonic molecular imaging signal decreased by an average of 41±10%, whereas imaging signal increased by an average of 54±8% in non-treated tumors over a 72-hour period. Decreased VEGFR2 expression levels following anti-VEGF therapy were confirmed on ex vivo immunofluorescent staining. CONCLUSIONS: Fast ultrasonic molecular imaging based on dwell time microbubble signal measurements correlates well with the traditional measurement method, and allows reliable in vivo monitoring of anti-angiogenic therapy in human colon cancer xenografts. The improved work-flow afforded by the new quantification approach may facilitate clinical translation of ultrasonic molecular imaging.
View details for PubMedID 22943043
To estimate an overall treatment difference with data from a randomized comparative clinical study, baseline covariates are often utilized to increase the estimation precision. Using the standard analysis of covariance technique for making inferences about such an average treatment difference may not be appropriate, especially when the fitted model is nonlinear. On the other hand, the novel augmentation procedure recently studied, for example, by Zhang and others (2008. Improving efficiency of inferences in randomized clinical trials using auxiliary covariates. Biometrics 64, 707-715) is quite flexible. However, in general, it is not clear how to select covariates for augmentation effectively. An overly adjusted estimator may inflate the variance and in some cases be biased. Furthermore, the results from the standard inference procedure by ignoring the sampling variation from the variable selection process may not be valid. In this paper, we first propose an estimation procedure, which augments the simple treatment contrast estimator directly with covariates. The new proposal is asymptotically equivalent to the aforementioned augmentation method. To select covariates, we utilize the standard lasso procedure. Furthermore, to make valid inference from the resulting lasso-type estimator, a cross validation method is used. The validity of the new proposal is justified theoretically and empirically. We illustrate the procedure extensively with a well-known primary biliary cirrhosis clinical trial data set.
View details for DOI 10.1093/biostatistics/kxr050
View details for Web of Science ID 000301293800006
View details for PubMedID 22294672
View details for PubMedCentralID PMC3297822
This study investigated whether higher body mass index (BMI) is associated with more adverse lower extremity muscle characteristics at baseline and more adverse changes in muscle over time among participants with lower extremity peripheral arterial disease (PAD).This was a longitudinal, observational study of 425 men and women with PAD and 261 without PAD. Computed tomography was used to measure calf muscle characteristics at baseline and every 2 years. Knee extension isometric strength, power, and 6-minute walk distance were measured at baseline and annually. Baseline BMI (kg/m(2)) categories were ideal (20-25), overweight (>25-30), and obese (>30). Analyses adjust for age, race, sex, ankle brachial index, comorbidities, and other covariates.At baseline, higher BMI among participants with PAD was associated with greater calf muscle area (ideal BMI: 5181 mm(2); overweight: 5513 mm(2); obese: 5695 mm(2); P = .0009 for trend), higher calf muscle percentage of fat (6.38%, 10.28%, 17.44%, respectively, P < .0001 for trend), lower calf muscle density (P < .0001 for trend), and higher isometric knee extension strength (P = .015 for trend). Among participants with PAD, higher BMI was associated with greater declines in calf muscle area (P = .030 for trend) and greater increases in calf muscle percentage of fat (P = .023 for trend). Among participants without PAD, there were no significant associations of baseline BMI with changes in lower extremity muscle outcomes over time.Among PAD participants, higher BMI is associated with greater calf muscle area at baseline. However, higher BMI is associated with more adverse calf muscle density and calf muscle percentage of fat at baseline and greater declines in calf muscle area over time.
View details for DOI 10.1016/j.jvs.2011.10.105
View details for Web of Science ID 000302145700016
View details for PubMedID 22365177
This study analyzed whether lower calf muscle density and poorer upper and lower extremity strength are associated with higher mortality rates in men and women with peripheral arterial disease (PAD).Men and women with lower extremity PAD have lower calf muscle density and reduced lower extremity strength compared with individuals without PAD.At baseline, participants underwent measurement of calf muscle density with computed tomography in addition to knee extension power and isometric knee extension, plantar flexion, and hand grip strength measures. Participants were followed up annually for up to 4 years. Results were adjusted for age, sex, race, body mass index, ankle-brachial index, smoking, physical activity, and comorbidities.Among 434 PAD participants, 103 (24%) died during a mean follow-up of 47.6 months. Lower calf muscle density was associated with higher all-cause mortality (lowest density tertile hazard ratio [HR]: 1.80 [95% confidence interval (CI): 1.07 to 3.03], second tertile HR: 0.91 (95% CI: 0.51 to 1.62); highest density tertile HR: 1.00; p trend = 0.020) and higher cardiovascular disease mortality (lowest density tertile HR: 2.39 [95% CI: 0.90 to 6.30], second tertile HR: 0.85 [95% CI: 0.27 to 2.71]; highest density tertile HR: 1.00; p trend = 0.047). Poorer plantar flexion strength (p trend = 0.004), lower baseline leg power (p trend = 0.046), and poorer handgrip (p trend = 0.005) were associated with higher all-cause mortality.These data demonstrate that lower calf muscle density and weaker plantar flexion strength, knee extension power, and hand grip were associated with increased mortality in these participants with PAD, independently of the ankle-brachial index and other confounders.
View details for DOI 10.1016/j.jacc.2011.12.019
View details for Web of Science ID 000301950300006
View details for PubMedID 22440216
RNA polymerase II (PolII) is essential in gene transcription and ChIP-seq experiments have been used to study PolII binding patterns over the entire genome. However, since PolII enriched regions in the genome can be very long, existing peak finding algorithms for ChIP-seq data are not adequate for identifying such long regions.Here we propose an enriched region detection method for ChIP-seq data to identify long enriched regions by combining a signal denoising algorithm with a false discovery rate (FDR) approach. The binned ChIP-seq data for PolII are first processed using a non-local means (NL-means) algorithm for purposes of denoising. Then, a FDR approach is developed to determine the threshold for marking enriched regions in the binned histogram.We first test our method using a public PolII ChIP-seq dataset and compare our results with published results obtained using the published algorithm HPeak. Our results show a high consistency with the published results (80-100%). Then, we apply our proposed method on PolII ChIP-seq data generated in our own study on the effects of hormone on the breast cancer cell line MCF7. The results demonstrate that our method can effectively identify long enriched regions in ChIP-seq datasets. Specifically, pertaining to MCF7 control samples we identified 5,911 segments with length of at least 4 Kbp (maximum 233,000 bp); and in MCF7 treated with E2 samples, we identified 6,200 such segments (maximum 325,000 bp).We demonstrated the effectiveness of this method in studying binding patterns of PolII in cancer cells which enables further deep analysis in transcription regulation and epigenetics. Our method complements existing peak detection algorithms for ChIP-seq experiments.
View details for DOI 10.1186/1471-2105-13-S2-S2
View details for Web of Science ID 000303936000003
View details for PubMedID 22536865
View details for PubMedCentralID PMC3375632
To evaluate ultrasonography (US) by using contrast agent microbubbles (MBs) targeted to P-selectin (MB(P-selectin)) to quantify P-selectin expression levels in inflamed tissue and to monitor response to therapy in a murine model of chemically induced inflammatory bowel disease (IBD).All procedures in which laboratory animals were used were approved by the institutional administrative panel on laboratory animal care. Binding affinity and specificity of MB(P-selectin) were tested in cell culture experiments under flow shear stress conditions and compared with control MBs (MB(Control)). In vivo binding specificity of MB(P-selectin) to P-selectin was tested in mice with trinitrobenzenesulfonic acid-induced colitis (n = 22) and control mice (n = 10). Monitoring of anti-tumor necrosis factor α antibody therapy was performed over 5 days in an additional 30 mice with colitis by using P-selectin-targeted US imaging, by measuring bowel wall thickness and perfusion, and by using a clinical disease activity index score. In vivo targeted contrast material-enhanced US signal was quantitatively correlated with ex vivo expression levels of P-selectin as assessed by quantitative immunofluorescence.Attachment of MB(P-selectin) to endothelial cells was significantly (P = .0001) higher than attachment of MB(Control) and significantly (ρ = 0.83, P = .04) correlated with expression levels of P-selectin on endothelial cells. In vivo US signal in mice with colitis was significantly higher (P = .0001) with MB(P-selectin) than with MB(Control). In treated mice, in vivo US signal decreased significantly (P = .0001) compared with that in nontreated mice and correlated well with ex vivo P-selectin expression levels (ρ = 0.69; P = .04). Colonic wall thickness (P ≥ .06), bowel wall perfusion (P ≥ .85), and clinical disease activity scoring (P ≥ .06) were not significantly different between treated and nontreated mice at any time.Targeted contrast-enhanced US imaging enables noninvasive in vivo quantification and monitoring of P-selectin expression in inflammation in murine IBD.
View details for DOI 10.1148/radiol.11110323
View details for Web of Science ID 000298611500021
View details for PubMedID 22056689
Recent withdrawals of major drugs have highlighted the critical importance of drug safety surveillance in the postmarketing phase. Limitations of spontaneous report data have led drug safety professionals to pursue alternative postmarketing surveillance approaches based on healthcare administrative claims data. These data are typically analysed by comparing the adverse event rates associated with a drug of interest to those of a single comparable reference drug.The aim of this study was to determine whether adverse event detection can be improved by incorporating information from multiple reference drugs. We developed a pharmacological network model that implemented this approach and evaluated its performance.We studied whether adverse event detection can be improved by incorporating information from multiple reference drugs, and describe two approaches for doing so. The first, reported previously, combines a set of related drugs into a single reference cohort. The second is a novel pharmacoepidemiological network model, which integrates multiple pair-wise comparisons across an entire set of related drugs into a unified consensus safety score for each drug. We also implemented a single reference drug approach for comparison with both multi-drug approaches. All approaches were applied within a sequential analysis framework, incorporating new information as it became available and addressing the issue of multiple testing over time. We evaluated all these approaches using statin (HMG-CoA reductase inhibitors) safety data from a large healthcare insurer in the US covering April 2000 through March 2005.We found that both multiple reference drug approaches offer earlier detection (6-13 months) than the single reference drug approach, without triggering additional false positives.Such combined approaches have the potential to be used with existing healthcare databases to improve the surveillance of therapeutics in the postmarketing phase over single-comparator methods. The proposed network approach also provides an integrated visualization framework enabling decision makers to understand the key high-level safety relationships amongst a group of related drugs.
View details for Web of Science ID 000303692300005
View details for PubMedID 22506565
To assess the effect of varying microbubble (MB) and DNA doses on the overall and comparative efficiencies of ultrasound (US)-mediated gene delivery (UMGD) to murine hindlimb skeletal muscle using cationic versus neutral MBs.Cationic and control neutral MBs were characterized for size, charge, plasmid DNA binding, and ability to protect DNA against endonuclease degradation. UMGD of a codon optimized firefly luciferase (Fluc) reporter plasmid to endothelial cells (1 MHz, 1 W/cm², 20% duty cycle, 1 min) was performed in cell culture using cationic, neutral, or no MBs. In vivo UMGD to mouse hindlimb muscle was performed by insonation (1 MHz, 2 W/cm², 50% duty cycle, 5 min) after intravenous administration of Fluc combined with cationic, neutral, or no MBs. Gene delivery efficiency was assessed by serial in vivo bioluminescence imaging. Efficiency of in vivo UMGD with cationic versus neutral MBs was systematically evaluated by varying plasmid DNA dose (10, 17.5, 25, 37.5, and 50 µg) while maintaining a constant MB dose of 1x10(8) MBs and by changing MB dose (1x10(7), 5x10(7), 1x10(8), or 5x10(8) MBs) while keeping a constant DNA dose of 50 µg.Cationic and size-matched control neutral MBs differed significantly in zeta potential with cationic MBs being able to bind plasmid DNA (binding capacity of 0.03 pg/MB) and partially protect DNA from nuclease degradation while neutral MBs could not. Cationic MBs enhanced UMGD compared to neutral MBs as well as no MB and no US controls both in cell culture (P < 0.001) and in vivo (P < 0.05). Regardless of MB type, in vivo UMGD efficiency increased dose-dependently with DNA dose and showed overall maximum transfection with 50 µg DNA. However, there was an inverse correlation (ρ = -0.90; P = 0.02) between DNA dose and the degree of enhanced UMGD efficiency observed with using cationic MBs instead of neutral MBs. The delivery efficiency advantage associated with cationic MBs was most prominent at the lowest investigated DNA dose (7.5-fold increase with cationic versus neutral MBs at a DNA dose of 10 µg; P = 0.02) compared to only a 1.4-fold increase at a DNA dose of 50 µg (P < 0.01). With increasing MB dose, overall in vivo UMGD efficiency increased dose-dependently with a maximum reached at a dose of 1x10(8) MBs with no further significant increase with 5x10(8) MBs (P = 0.97). However, compared to neutral MBs, cationic MBs enhanced UMGD efficiency the most at low MB doses. Relative enhancement of UMGD efficiency using cationic over neutral MBs decreased from a factor of 27 for 1x10(7) MBs (P = 0.02) to a factor of 1.4 for 1x10(8) MBs (P < 0.01) and no significant difference for 5x10(8) MBs.Cationic MBs enhance UMGD to mouse skeletal muscle relative to neutral MBs but this is dependent on MB and DNA dose. The enhancement effect of cationic MBs on UMGD efficiency is more evident when lower doses of MBs or DNA are used, whereas the advantage of cationic MBs over neutral MBs is substantially reduced in the presence of excess MBs or DNA.
View details for DOI 10.7150/thno.4240
View details for Web of Science ID 000312955800005
View details for PubMedID 23227124
View details for PubMedCentralID PMC3516840
To assess early treatment effects on computed tomography (CT) perfusion parameters after antiangiogenic and radiation therapy in subcutaneously implanted, human colon cancer xenografts in mice and to correlate in vivo CT perfusion parameters with ex vivo assays of tumor vascularity and hypoxia.Dynamic contrast-enhanced CT (perfusion CT, 129 mAs, 80 kV, 12 slices × 2.4 mm; 150 μL iodinated contrast agent injected at a rate of 1 mL/min intravenously) was performed in 100 subcutaneous human colon cancer xenografts on baseline day 0. Mice in group 1 (n=32) received a single dose of the antiangiogenic agent bevacizumab (10 mg/kg body weight), mice in group 2 (n=32) underwent a single radiation treatment (12 Gy), and mice in group 3 (n=32) remained untreated. On days 1, 3, 5, and 7 after treatment, 8 mice from each group underwent a second CT perfusion scan, respectively, after which tumors were excised for ex vivo analysis. Four mice were killed after baseline scanning on day 0 for ex vivo analysis. Blood flow (BF), blood volume (BV), and flow extraction product were calculated using the left ventricle as an arterial input function. Correlation of in vivo CT perfusion parameters with ex vivo microvessel density and extent of tumor hypoxia were assessed by immunofluorescence. Reproducibility of CT perfusion parameter measurements was calculated in an additional 8 tumor-bearing mice scanned twice within 5 hours with the same CT perfusion imaging protocol.The intraclass correlation coefficients for BF, BV, and flow extraction product from repeated CT perfusion scans were 0.93 (95% confidence interval: 0.78, 0.97), 0.88 (0.66, 0.95), and 0.88 (0.56, 0.95), respectively. Changes in perfusion parameters and tumor volumes over time were different between treatments. After bevacizumab treatment, all 3 perfusion parameters significantly decreased from day 1 (P ≤ 0.006) and remained significantly decreased until day 7 (P ≤ 0.008); tumor volume increased significantly only on day 7 (P=0.04). After radiation treatment, all 3 perfusion parameters decreased significantly on day 1 (P < 0.001); BF and flow extraction product increased again on day 3 and 5, although without reaching statistically significant difference; and tumor volumes did not change significantly at all time points (P ≥ 0.3). In the control group, all 3 perfusion parameters did not change significantly, whereas tumor volume increased significantly at all the time points, compared with baseline (P ≤ 0.04). Ex vivo immunofluorescent staining showed good correlation between all 3 perfusion parameters and microvessel density (ρ=0.71, 0.66, and 0.69 for BF, BV, and flow extraction product, respectively; P < 0.001). There was a trend toward negative correlation between extent of hypoxia and all 3 perfusion parameters (ρ=-0.53, -0.47, and -0.40 for BF, BV, and flow extraction product, respectively; P ≥ 0.05).CT perfusion allows a reproducible, noninvasive assessment of tumor vascularity in human colon cancer xenografts in mice. After antiangiogenic and radiation therapy, BF, BV, and flow extraction product significantly decrease and change faster than the tumor volume.
View details for DOI 10.1097/RLI.0b013e31823a82f6
View details for Web of Science ID 000298400100006
View details for PubMedID 22178893
Quantitative procedures for evaluating added values from new markers over a conventional risk scoring system for predicting event rates at specific time points have been extensively studied. However, a single summary statistic, for example, the area under the receiver operating characteristic curve or its derivatives, may not provide a clear picture about the relationship between the conventional and the new risk scoring systems. When there are no censored event time observations in the data, two simple scatterplots with individual conventional and new scores for "cases" and "controls" provide valuable information regarding the overall and the subject-specific level incremental values from the new markers. Unfortunately, in the presence of censoring, it is not clear how to construct such plots. In this article, we propose a nonparametric estimation procedure for the distributions of the differences between two risk scores conditional on the conventional score. The resulting quantile curves of these differences over the subject-specific conventional score provide extra information about the overall added value from the new marker. They also help us to identify a subgroup of future subjects who need the new predictors, especially when there is no unified utility function available for cost-risk-benefit decision making. The procedure is illustrated with two data sets. The first is from a well-known Mayo Clinic primary biliary cirrhosis liver study. The second is from a recent breast cancer study on evaluating the added value from a gene score, which is relatively expensive to measure compared with the routinely used clinical biomarkers for predicting the patient's survival after surgery.
View details for DOI 10.1111/j.1541-0420.2011.01600.x
View details for Web of Science ID 000298095900022
View details for PubMedID 21504421
Accurate risk prediction is an important step in developing optimal strategies for disease prevention and treatment. Based on the predicted risks, patients can be stratified to different risk categories where each category corresponds to a particular clinical intervention. Incorrect or suboptimal interventions are likely to result in unnecessary financial and medical consequences. It is thus essential to account for the costs associated with the clinical interventions when developing and evaluating risk stratification (RS) rules for clinical use. In this article, we propose to quantify the value of an RS rule based on the total expected cost attributed to incorrect assignment of risk groups due to the rule. We have established the relationship between cost parameters and optimal threshold values used in the stratification rule that minimizes the total expected cost over the entire population of interest. Statistical inference procedures are developed for evaluating and comparing given RS rules and examined through simulation studies. The proposed procedures are illustrated with an example from the Cardiovascular Health Study.
View details for DOI 10.1093/biostatistics/kxr001
View details for Web of Science ID 000294806800001
View details for PubMedID 21415016
To determine whether poor lower extremity nerve function is associated with less-favorable calf muscle characteristics and greater functional impairment in people with and without peripheral arterial disease (PAD).Cross-sectional.Three Chicago-area medical centers.Four hundred thirteen participants with PAD (ankle-brachial index (ABI) < 0.90) and 255 without.Electrodiagnostic testing of the peroneal nerve was performed. Calf muscle cross-sectional area and percentage fat were measured using computed tomography at 66.7% of the distance between the distal and proximal tibia. Six-minute walk performance was measured.Adjusting for age, sex, race, ABI, leg symptoms, smoking, physical activity, comorbidities, and other covariates, lower peroneal nerve conduction velocity (NCV) was associated with lower calf muscle area (first quartile 4,770.3 mm(2) , fourth quartile 5,571 mm(2) , P < .001) and poorer 6-minute walk distance (first quartile 989.2 feet, fourth quartile 1,210.8 feet, P < .001) in participants without diabetes mellitus with PAD. Lower peroneal NCV was associated with lower calf muscle area (first quartile 5,166.0 mm(2) , fourth quartile 6,003.8 mm(2) , P = .01) and poorer 6-minute walk distance (first quartile 866.4 feet, fourth quartile 1,082.5 feet, P = .01) in participants with diabetes mellitus and PAD as well. In participants without PAD, lower peroneal NCV was not associated with lower calf muscle area but was associated with poorer 6-minute walk distance only in participants without diabetes mellitus (first quartile 1,317.0 feet, fourth quartile 1,570.4 feet, P-trend < .001).Lower peroneal nerve function is associated with smaller calf muscle area and greater functional impairment in individuals with PAD. Future study is needed to determine whether improving peroneal NCV prevents loss of calf muscle and functional decline in people with PAD.
View details for DOI 10.1111/j.1532-5415.2011.03600.x
View details for Web of Science ID 000296449300010
View details for PubMedID 22091499
Successful management of pediatric arteriovenous malformations (AVMs) often requires a balanced application of embolization, surgery, and radiosurgery.To describe our experience treating pediatric AVMs.We analyzed 120 pediatric patients (< 18 years of age) with AVMs treated with various combinations of radiosurgery, surgery, and endovascular techniques.Between 1985 and 2009, 76 children with low Spetzler-Martin grade (1-3) and 44 with high-grade (4-5) AVMs were treated. Annual risk of hemorrhage from presentation to initial treatment was 4.0%, decreasing to 3.2% after treatment initiation until confirmed obliteration. Results for AVM obliteration were available in 101 patients. Initial single-modality therapy led to AVM obliteration in 51 of 67 low-grade (76%) and 3 of 34 high-grade (9%) AVMs, improving to 58 of 67 (87%) and 9 of 34 (26%), respectively, with further treatment. Mean time to obliteration was 1.8 years for low-grade and 6.4 years for high-grade AVMs. Disabling neurological complications occurred in 4 of 77 low-grade (5%) and 12 of 43 high-grade (28%) AVMs. At the final clinical follow-up (mean, 9.2 years), 48 of 67 patients (72%) with low-grade lesions had a modified Rankin Scale score (mRS) of 0 to 1 compared with 12 of 34 patients (35%) with high-grade AVMs. On multivariate analysis, significant risk factors for poor final clinical outcome (mRS ≥ 2) included baseline mRS ≥ 2 (odds ratio, 9.51; 95% confidence interval, 3.31-27.37; P < .01), left-sided location (odds ratio, 3.03; 95% confidence interval, 1.11-8.33; P = .03), and high AVM grade (odds ratio, 4.35; 95% confidence interval, 1.28-14.28; P = .02).Treatment of pediatric AVMs with multimodality therapy can substantially improve obliteration rates and may decrease AVM hemorrhage rates. The poor natural history and risks of intervention must be carefully considered when deciding to treat high-grade pediatric AVMs.
View details for DOI 10.1227/NEU.0b013e3182181c00
View details for Web of Science ID 000293586200005
View details for PubMedID 21430584
Cystic fibrosis (CF) carrier screening guidelines have been in place for almost a decade. The purpose of this study was to determine the current awareness by obstetricians of the existence and content of practice guidelines, the variety in practice regarding CF carrier screening, and the level of knowledge regarding CF genetics and screening result interpretation. We also explored potential barriers to offering screening and whether academic affiliation or type of practice influenced outcome.An online survey program was used to deliver a questionnaire to obstetricians throughout the United States. One hundred fifty-six respondents participated, with 143 answering all questions in the survey.Although most obstetricians are aware of screening guidelines and have accurate knowledge about CF carrier screening, 12.3% were not aware of carrier screening guidelines, 17.7% were unable to interpret basic results, 16.5% experienced barriers to offering screening, and 43% lacked information regarding carrier rates, screening sensitivity, and residual risk.Most obstetricians offer CF carrier screening and will refer to genetic counseling services at times. However, we identified a deficiency of information in a concerning percentage of practitioners. This deficiency could be improved by targeted and readily accessible educational efforts, especially for obstetricians not affiliated with academia.
View details for DOI 10.1089/gtmb.2010.0228
View details for Web of Science ID 000292773700011
View details for PubMedID 21453058
To present an analysis of glycemic control before and after introduction of a dedicated glucose management service (GMS) and outcomes within 1 year after liver transplantation (LT).We conducted a retrospective review of patients undergoing LT, who were treated with insulin infusions after LT, before and after introduction of a GMS. Outcome measures within 1 year after LT included graft rejection, infection, prolonged ventilation (>48 hours on a ventilator), and graft survival. A multiple logistic regression was used to examine the relationship between GMS use and outcomes.This study consisted of 73 (35 GMS and 38 non-GMS) organ transplant recipients. The mean perioperative blood glucose level in the GMS group was lower than in the non-GMS group: unadjusted, by 31.1 mg/dL (P = .001); adjusted for pre-insulin drip glucose, age, sex, Model for End-Stage Liver Disease (MELD) score, and type of transplant, by 23.4 mg/dL (P = .020). There were 27 rejection episodes, 48 infections, 26 episodes of prolonged ventilation, and 64 patients with graft survival at 1 year. The infection rate was lower in the GMS group than in the non-GMS group: the unadjusted odds ratio was 0.28 (P = .015); when adjustments were made for pre-insulin drip glucose, pretransplant glucose, age, sex, MELD score, type of transplant, and diabetes status before transplantation, the odds ratio was 0.24 (95% confidence interval, 0.06 to 0.97; P = .045). No significant associations were noted between GMS group and rejection rates, prolonged ventilation, or graft survival.In this study of LT patients, a GMS was associated with improved glycemic control and reduced postoperative infections. Further studies investigating effects of strict glycemic control after LT are warranted.
View details for DOI 10.4158/EP10343.OR
View details for Web of Science ID 000294276000002
View details for PubMedID 21324822
View details for PubMedCentralID PMC3158277
We studied associations of magnetic resonance imaging measurements of plaque area and relative percent lumen reduction in the proximal superficial femoral artery with functional performance among participants with peripheral arterial disease.The clinical significance of directly imaged plaque characteristics in lower extremity arteries is not well established.A total of 454 participants with an ankle brachial index <1.00 underwent magnetic resonance cross-sectional imaging of the proximal superficial femoral artery and completed a 6-min walk test, measurement of 4-m walking velocity at usual and fastest pace, and measurement of physical activity with a vertical accelerometer.Adjusting for age, sex, race, body mass index, smoking, statin use, comorbidities, and other covariates, higher mean plaque area (1st quintile [least plaque]: 394 m, 2nd quintile: 360 m, 3rd quintile: 359 m, 4th quintile: 329 m, 5th quintile [greatest plaque]: 311 m; p trend <0.001) and smaller mean percent lumen area (1st quintile [greatest plaque]: 319 m, 2nd quintile: 330 m, 3rd quintile: 364 m, 4th quintile: 350 m, 5th quintile: 390 m; p trend <0.001) were associated with shorter distance achieved in the 6-min walk test. Greater mean plaque area was also associated with slower usual-paced walking velocity (p trend = 0.006) and slower fastest-paced 4-m walking velocity (p trend = 0.003). Associations of mean plaque area and mean lumen area with 6-min walk distance remained statistically significant even after additional adjustment for the ankle brachial index and leg symptoms.Among participants with peripheral arterial disease, greater plaque burden and smaller lumen area in the proximal superficial femoral artery are associated independently with poorer functional performance, even after adjusting for the ankle brachial index and leg symptoms.
View details for DOI 10.1016/j.jcmg.2011.04.009
View details for Web of Science ID 000293180100007
View details for PubMedID 21757163
Male sex is an independent risk factor for long-term neurologic deficits in human preterm infants. Using a chronic, sublethal hypoxia (CSH) mouse model of preterm brain injury, we recently demonstrated acute brain volume loss with an increased male susceptibility to hippocampal volume loss and hypomyelination. We now characterize the long-term, sex-specific effects of CSH on cognition and brain growth. Neonatal mice were treated with CSH for 8 d, raised in normoxia thereafter and underwent behavioral testing at 6 wk of age. Behavioral assays sensitive to hippocampal function were chosen. CSH-treated males had impairments in associative learning, spatial memory, and long-term social memory compared with control males. In contrast, CSH-treated females were less impaired. Persistent reductions in hippocampal and cerebellar volumes were found in adult CSH-treated males, whereas regional brain volumes in adult CSH-treated females were indistinguishable from controls. Similar to human preterm infants, males exposed to hypoxia are especially vulnerable to short-term and long-term deficits in cognition and brain growth.
View details for Web of Science ID 000292015100004
View details for PubMedID 21436761
In participants with peripheral arterial disease (PAD), we determined whether more sedentary behavior and slower outdoor walking speed were associated with faster functional decline and more adverse changes in calf muscle characteristics over time.Modifiable behaviors associated with faster functional decline in lower-extremity PAD are understudied.Participants were 384 men and women with an ankle brachial index <0.90 followed for a median of 47 months. At baseline, participants reported the number of hours they spent sitting per day and their walking speeds outside their homes. Participants underwent baseline and annual measures of objective functional performance. Calf muscle characteristics were measured with computed tomography at baseline and every 2 years subsequently. Analyses were adjusted for age, sex, race, comorbidities, ankle brachial index, and other confounders.Slower walking speed outside the home was associated with faster annual decline in calf muscle density (brisk/striding pace -0.32 g/cm(3), average pace -0.46 g/cm(3), casual strolling -1.03 g/cm(3), no walking at all -1.43 g/cm(3), p trend <0.001). Greater hours sitting per day were associated with faster decline in 6-min walk (<4 h: -35.8 feet/year; 4 to <7 h: -41.1 feet/year; 8 to <11 h: -68.7 feet; ≥12 h: -78.0 feet; p trend = 0.008). Similar associations were observed for greater hours sitting per day and faster declines in fast-paced (p trend = 0.018) and usual-paced (p trend < 0.001) 4-m walking velocity.Greater sedentary hours per day and slower outdoor walking speed are modifiable behaviors that are associated with faster functional decline and greater decline in calf muscle density, respectively, in patients with PAD.
View details for DOI 10.1016/j.jacc.2010.12.038
View details for Web of Science ID 000291147200009
View details for PubMedID 21636037
Suppose that we are interested in making joint inferences about a set of constrained parameters. Confidence regions for these parameters are often constructed via a normal approximation of the distribution of a consistent estimator for a transformation of the parameters. In this article, we utilize the confidence distribution, a frequentist counterpart to the posterior distribution in Bayesian statistics, to obtain optimal confidence regions for the parameters. Members of such a region can be generated efficiently via a standard Markov chain Monte Carlo algorithm. We then apply this technique to draw inferences about the temporal profile of the survival function with censored observations. We illustrate the new proposal with the survival data from the well-known Mayo primary biliary cirrhosis study and show that the volume of the new 0.95 confidence region is only one thirty-fourth of that of the conventional confidence band.
View details for DOI 10.1111/j.1541-0420.2010.01486.x
View details for Web of Science ID 000292504000028
View details for PubMedID 20825392
We hypothesized that, in the absence of clinically recognized dementia, cognitive dysfunction measured by the clock draw test (CDT) is associated with greater functional impairment in men and women with peripheral artery disease (PAD). Participants were men and women aged 60 years and older with Mini-Mental Status Examination scores ≥ 24 with PAD (n = 335) and without PAD (n = 234). We evaluated the 6-minute walk test, 4-meter walking velocity at usual and fastest pace, the Short Physical Performance Battery (SPPB), and accelerometer-measured physical activity. CDTs were scored using the Shulman system as follows: Category 1 (worst): CDT score 0-2; Category 2: CDT score 3; Category 3 (best): CDT score 4-5. Results were adjusted for age, sex, race, education, ankle-brachial index (ABI), and comorbidities. In individuals with PAD, lower CDT scores were associated with slower 4-meter usual-paced walking velocity (Category 1: 0.78 meters/second; Category 2: 0.83 meters/second; Category 3: 0.86 meters/second; p-trend = 0.025) and lower physical activity (Category 1: 420 activity units; Category 2: 677 activity units; Category 3: 701 activity units; p-trend = 0.045). Poorer CDT scores were also associated with worse functional performance in individuals without PAD (usual and fast-paced walking velocity and SPPB, p-trend = 0.022, 0.043, and 0.031, respectively). In conclusion, cognitive impairment identified with CDT is independently associated with greater functional impairment in older, dementia-free individuals with and without PAD. Longitudinal studies are necessary to explore whether baseline CDT scores and changes in CDT scores over time can predict long-term decline in functional performance in individuals with and without PAD.
View details for DOI 10.1177/1358863X11407109
View details for Web of Science ID 000291218600002
View details for PubMedID 21636676
In a longitudinal study, suppose that the primary endpoint is the time to a specific event. This response variable, however, may be censored by an independent censoring variable or by the occurrence of one of several dependent competing events. For each study subject, a set of baseline covariates is collected. The question is how to construct a reliable prediction rule for the future subject's profile of all competing risks of interest at a specific time point for risk-benefit decision making. In this article, we propose a two-stage procedure to make inferences about such subject-specific profiles. For the first step, we use a parametric model to obtain a univariate risk index score system. We then estimate consistently the average competing risks for subjects who have the same parametric index score via a nonparametric function estimation procedure. We illustrate this new proposal with the data from a randomized clinical trial for evaluating the efficacy of a treatment for prostate cancer. The primary endpoint for this study was the time to prostate cancer death, but had two types of dependent competing events, one from cardiovascular death and the other from death of other causes.
View details for DOI 10.1111/j.1541-0420.2010.01456.x
View details for Web of Science ID 000292504000010
View details for PubMedID 20618311
View details for PubMedCentralID PMC2970653
The aim of this study was to determine whether persistently high levels of interleukin-6 (IL-6) or soluble vascular adhesion molecule-1 (sVCAM-1) are associated with faster functional decline compared to fluctuating or persistently low biomarker levels in 255 participants with peripheral arterial disease. Participants underwent baseline and ≥2 annual follow-up measures of IL-6 and sVCAM-1. Participants were categorized as follows: category 1, annual levels of IL-6 (or sVCAM-1) were in the lowest tertile for ≥3 study visits; category 3, annual levels of IL-6 (or sVCAM-1) were in the highest tertile for ≥3 visits. Category 2 levels of IL-6 (or sVCAM-1) did not meet criteria for group 1 or 3. Six-minute walking distance, fastest paced 4-m walking velocity, and the Short Physical Performance Battery were measured annually. Results were adjusted for age, gender, race, co-morbidities, statin use, physical activity, the ankle-brachial index, and other confounders. Across IL-6 categories, average annual decreases in 6-minute walking distance were -21.4 feet in category 1, -49.2 feet in category 2, and -76.8 feet in category 3 (p for trend = 0.013), and average annual decreases in Short Physical Performance Battery score were -0.18, -0.45, and -0.62, respectively (p for trend = 0.022). Similar associations of IL-6 categories with decrease in fastest paced walking velocity were observed (p for trend = 0.034). There were no significant associations of sVCAM-1 categories with functional decline. In conclusion, in participants with peripheral arterial disease, persistently high IL-6 levels are associated with faster functional decline compared to those with fluctuating or persistently low IL-6 levels.
View details for DOI 10.1016/j.amjcard.2011.01.007
View details for Web of Science ID 000290605600023
View details for PubMedID 21371679
The clinical significance of magnetic resonance-imaged plaque characteristics in the superficial femoral artery (SFA) is not well established. We studied associations of the ankle-brachial index (ABI) and leg symptoms with MRI-measured plaque area and percent lumen area in the SFA in participants with and without lower-extremity peripheral arterial disease (PAD).Four hundred twenty-seven participants (393 with PAD) underwent plaque imaging of the first 30 mm of the SFA. Twelve 2.5-mm cross-sectional images of the SFA were obtained. Outcomes were normalized plaque area, adjusted for artery size (0 to 1 scale, 1=greatest plaque), and lumen area, expressed as a percent of the total artery area. Adjusting for age, sex, race, smoking, statins, cholesterol, and other covariates, lower ABI values were associated with higher normalized mean plaque area (ABI <0.50:0.79; ABI 0.50 to 0.69:0.73; ABI 0.70 to 0.89:0.65; ABI 0.90 to 0.99:0.62; ABI 1.00 to 1.09:0.48; ABI 1.10 to 1.30:0.47 (P trend <0.001)) and smaller mean percent lumen area (P trend <0.001). Compared with PAD participants with intermittent claudication, asymptomatic PAD participants had lower normalized mean plaque area (0.72 versus 0.65, P=0.005) and larger mean percent lumen area (0.30 versus 0.36, P=0.01), adjusting for the ABI and other confounders.Lower ABI values are associated with greater MRI-measured plaque burden and smaller lumen area in the first 30 mm of the SFA. Compared with PAD participants with claudication, asymptomatic PAD participants have smaller plaque area and larger lumen area in the SFA. Clinical Trial Registration- URL: http://www.clinicaltrials.gov. Unique identifier: NCT00520312.
View details for DOI 10.1161/CIRCIMAGING.110.962183
View details for Web of Science ID 000290715800010
View details for PubMedID 21436300
Zinc is a trace element that is essential for innate and adaptive immune responses. In addition to being a structural element of many proteins, zinc also functions as a neurotransmitter and an intracellular messenger. Temporal or spatial changes in bioavailable zinc may influence the activity of several enzymes, including kinases and phosphatases. We provide evidence that zinc functions as an ionic signaling molecule after T cell activation. Cytoplasmic zinc concentrations increased within 1 min after T cell receptor (TCR) triggering, in particular in the subsynaptic compartment. The increase depended on the extracellular zinc concentrations and was inhibited by silencing zinc transporter Zip6. Increased zinc influx reduced the recruitment of SHP-1 to the TCR activation complex, augmented ZAP70 phosphorylation and sustained calcium influx. By calibrating TCR activation thresholds, increased extracellular zinc bioavailability facilitated the induction of T cell proliferative responses to suboptimal stimuli.
View details for DOI 10.1084/jem.20100031
View details for Web of Science ID 000289404800012
View details for PubMedID 21422171
Risk factors for poor outcome in the treatment of very large (≥20-24 mm) and giant (≥25 mm) intracranial aneurysms remain incompletely defined.To present an aggregate clinical series detailing a 24-year experience with very large and giant aneurysms to identify and assess the relative importance of various patient, aneurysm, and treatment-specific characteristics associated with clinical and angiographic outcomes.The authors retrospectively identified 184 aneurysms measuring 20 mm or larger (85 very large, 99 giant) treated at Stanford University Medical Center between 1984 and 2008. Clinical data including age, presentation, and modified Rankin Scale (mRS) score were recorded, along with aneurysm size, location, and morphology. Type of treatment was noted and clinical outcome measured using the mRS score at final follow-up. Angiographic outcomes were completely occluded, occluded with residual neck, partly obliterated, or patent with modified flow.After multivariate analysis, risk factors for poor clinical outcome included a baseline mRS score of 2 or higher (odds ratio [OR], 0.23; 95% confidence interval [CI]: 0.08-0.66; P = .01), aneurysm size of 25 mm or larger (OR, 3.32; 95% CI: 1.51-7.28; P < .01), and posterior circulation location (OR, 0.18; 95% CI: 0.07-0.43; P < .01). Risk factors for incomplete angiographic obliteration included fusiform morphology (OR, 0.25; 95% CI: 0.10-0.66; P < .01), posterior circulation location (OR, 0.33; 95% CI: 0.13-0.83; P = .02), and endovascular treatment (OR, 0.14; 95% CI: 0.06-0.32; P < .01). Patients with incompletely occluded aneurysms experienced higher rates of posttreatment subarachnoid hemorrhage and had increased mortality compared with those with completely obliterated aneurysms.Our results suggest that patients with poor baseline functional status, giant aneurysms, and aneurysms in the posterior circulation had a significantly higher proportion of poor outcomes at final follow-up. Fusiform morphology, posterior circulation location, and endovascular treatment were risk factors for incompletely obliterated aneurysms.
View details for DOI 10.1227/NEU.0b013e3182098ad0
View details for Web of Science ID 000288123100038
View details for PubMedID 21221025
Suppose that under the conventional randomized clinical trial setting, a new therapy is compared with a standard treatment. In this article, we propose a systematic, 2-stage estimation procedure for the subject-level treatment differences for future patient's disease management and treatment selections. To construct this procedure, we first utilize a parametric or semiparametric method to estimate individual-level treatment differences, and use these estimates to create an index scoring system for grouping patients. We then consistently estimate the average treatment difference for each subgroup of subjects via a nonparametric function estimation method. Furthermore, pointwise and simultaneous interval estimates are constructed to make inferences about such subgroup-specific treatment differences. The new proposal is illustrated with the data from a clinical trial for evaluating the efficacy and toxicity of a 3-drug combination versus a standard 2-drug combination for treating HIV-1-infected patients.
View details for DOI 10.1093/biostatistics/kxq060
View details for Web of Science ID 000288800600007
View details for PubMedID 20876663
Contrast-enhanced ultrasound imaging is increasingly being used in the clinic for assessment of tissue vascularity. The purpose of our study was to evaluate the effect of different contrast administration parameters on the in vivo ultrasound imaging signal in tumor-bearing mice using a maximum intensity persistence (MIP) algorithm and to evaluate the reliability of in vivo MIP imaging in assessing tumor vascularity. The potential of in vivo MIP imaging for monitoring tumor vascularity during antiangiogenic cancer treatment was further evaluated.In intraindividual experiments, varying contrast microbubble concentrations (5 × 10⁵, 5 × 10⁶, 5 × 10⁷, 5 × 10⁸ microbubbles in 100 μL saline) and contrast injection rates (0.6, 1.2, and 2.4 mL/min) in subcutaneous tumor-bearing mice were applied and their effects on in vivo contrast-enhanced ultrasound MIP imaging plateau values were obtained using a dedicated small animal ultrasound imaging system (40 MHz). Reliability of MIP ultrasound imaging was tested following 2 injections of the same microbubble concentration (5 × 10⁷ microbubbles at 1.2 mL/min) in the same tumors. In mice with subcutaneous human colon cancer xenografts, longitudinal contrast-enhanced ultrasound MIP imaging plateau values (baseline and at 48 hours) were compared between mice with and without antiangiogenic treatment (antivascular endothelial growth factor antibody). Ex vivo CD31 immunostaining of tumor tissue was used to correlate in vivo MIP imaging plateau values with microvessel density analysis.In vivo MIP imaging plateau values correlated significantly (P = 0.001) with contrast microbubble doses. At 3 different injection rates of 0.6, 1.2, and 2.4 mL/min, MIP imaging plateau values did not change significantly (P = 0.61). Following 2 injections with the same microbubble dose and injection rate, MIP imaging plateau values were obtained with high reliability with an intraclass correlation coefficient of 0.82 (95% confidence interval: 0.64, 0.94). In addition, in vivo MIP imaging plateau values significantly correlated (P = 0.01; R² = 0.77) with ex vivo microvessel density analysis. Tumor volumes in treated and nontreated mice did not change significantly (P = 0.22) within 48 hours. In contrast, the change of in vivo MIP imaging plateau values from baseline to 48 hours was significantly different (P = 0.01) in treated versus nontreated mice.Contrast-enhanced ultrasound MIP imaging allows reliable assessment of tumor vascularity and monitoring of antiangiogenic cancer therapy in vivo, provided that a constant microbubble dose is administered.
View details for DOI 10.1097/RLI.0b013e3181f9202d
View details for Web of Science ID 000286971700006
View details for PubMedID 21150790
We hypothesized that a greater 2-year decline in office-based functional performance measures would be associated with greater mobility loss and mortality in people with peripheral arterial disease (PAD).Associations of decline in functional performance with clinically important outcomes in patients with PAD are unknown.A total of 440 men and women with PAD completed the 6-min walk test and measures of walking velocity at baseline and annually for 2 years. Participants were categorized into tertiles according to their functional decline between baseline and 2-year follow-up and were followed annually after the functional change assessment. Cox proportional hazard models were used to assess relations between the 2-year change in functional performance with later mortality and mobility loss, with adjustments for age, sex, race, ankle brachial index, comorbidities, and other confounders.A total of 102 participants (23.2%) died during a median follow-up of 44.5 months after functional change was assessed. Of 319 participants without baseline mobility disability, 60 (18.8%) developed mobility loss after functional change was assessed. Participants in the tertile with the greatest 6-min walk decline had the highest subsequent mobility loss (hazard ratio [HR]: 3.50; 95% confidence interval [CI]: 1.56 to 7.85; p = 0.002), all-cause mortality (HR: 2.16; 95% CI: 1.28 to 3.64; p = 0.004), and cardiovascular disease mortality (HR: 2.45; 95% CI: 1.08 to 5.54; p = 0.031), compared with those with the smallest 6-min walk decline. Greater declines in fastest-paced 4-m walking velocity were associated with higher mobility loss (p trend = 0.018), all-cause mortality (p trend = 0.01), and cardiovascular mortality (p trend = 0.004).Participants with PAD with declining functional performance are at increased risk for later mobility loss and mortality.
View details for DOI 10.1016/j.jacc.2010.09.053
View details for Web of Science ID 000287650900012
View details for PubMedID 21329843
We hypothesized that women with lower extremity peripheral arterial disease (PAD) would have greater mobility loss and faster functional decline than men with PAD.Whether rates of mobility loss or functional decline differ between men and women with PAD is currently unknown.Three hundred eighty men and women with PAD completed the 6-min walk, were assessed for mobility disability, and underwent measures of 4-m walking velocity at baseline and annually for up to 4 years. Computed tomography-assessed calf muscle characteristics were measured biannually. Outcomes included becoming unable to walk for 6 min continuously among participants who walked continuously for 6 min at baseline. Mobility loss was defined as becoming unable to walk for a quarter mile or to walk up and down 1 flight of stairs without assistance among those without baseline mobility disability. Results were adjusted for age, race, body mass index, physical activity, the ankle brachial index, comorbidities, and other confounders.At 4 years of follow-up, women were more likely to become unable to walk for 6 min continuously (hazard ratio: 2.30, 95% confidence interval: 1.30 to 4.06, p = 0.004), more likely to develop mobility disability (hazard ratio: 1.79, 95% confidence interval: 1.30 to 3.03, p = 0.030), and had faster declines in walking velocity (p = 0.022) and the distance achieved in the 6-min walk (p = 0.041) compared with men. Sex differences in functional decline were attenuated after additional adjustment for baseline sex differences in calf muscle area.Women with PAD have faster functional decline and greater mobility loss than men with PAD. These sex differences may be attributable to smaller baseline calf muscle area among women with PAD.
View details for DOI 10.1016/j.jacc.2010.09.042
View details for Web of Science ID 000286880100011
View details for PubMedID 21292130
We determined whether more adverse calf muscle characteristics and poorer peripheral nerve function were associated with impairments in self-perceived physical functioning and walking ability in persons with lower extremity peripheral artery disease (PAD). Participants included 462 persons with PAD; measures included the ankle-brachial index (ABI), medical history, electrophysiologic characteristics of nerves, and computed tomography of calf muscle. Self-perceived physical functioning and walking ability were assessed using the 36-Item Short Form Health Survey (SF-36) and the Walking Impairment Questionnaire (WIQ). Results were adjusted for age, sex, race, ABI, body mass index, comorbidities, and other confounders. Lower calf muscle area was associated with a poorer SF-36 physical function (PF) score (overall p-trend < 0.001, 33.76 PF score for the lowest quartile versus 59.74 for the highest, pairwise p < 0.001) and a poorer WIQ walking distance score (p-trend = 0.001, 29.71 WIQ score for the lowest quartile versus 48.43 for the highest, pairwise p < 0.001). Higher calf muscle percent fat was associated with a poorer SF-36 PF score (p-trend < 0.001, 53.76 PF score for the lowest quartile versus 40.28 for the highest, pairwise p = 0.009). Slower peroneal nerve conduction velocity was associated with a poorer WIQ speed score ( p-trend = 0.023, 30.49 WIQ score for the lowest quartile versus 40.48 for the highest, pairwise p = 0.031). In summary, adverse calf muscle characteristics and poorer peripheral nerve function are associated significantly and independently with impairments in self-perceived physical functioning and walking ability in PAD persons.
View details for DOI 10.1177/1358863X10395656
View details for Web of Science ID 000289198700001
View details for PubMedID 21471147
We use the term "index predictor" to denote a score that consists of K binary rules such as "age > 60" or "blood pressure > 120 mm Hg." The index predictor is the sum of these binary scores, yielding a value from 0 to K. Such indices as often used in clinical studies to stratify population risk: They are usually derived from subject area considerations. In this paper, we propose a fast data-driven procedure for automatically constructing such indices for linear, logistic, and Cox regression models. We also extend the procedure to create indices for detecting treatment-marker interactions. The methods are illustrated on a study with protein biomarkers as well as a large microarray gene expression study.
View details for DOI 10.1093/biostatistics/kxq047
View details for Web of Science ID 000285625800005
View details for PubMedID 20663850
To establish associations between leg strength and mortality in men and women with lower extremity peripheral arterial disease (PAD).This was an observational, prospective study of 410 men and women with PAD aged 55 and older recruited from Chicago-area medical centers and followed for a mean of 60 months. The participants were followed for a mean of 60.0 months. Isometric knee extension, knee flexion, hip extension, and hip flexion were measured at baseline. Primary outcomes were all-cause and cardiovascular disease mortality. Cox proportional hazards models were used to assess relations between leg strength and all-cause and cardiovascular disease mortality among men and women, adjusting for age, race, comorbidities, physical activity, smoking, body mass index, and the ankle brachial index.Among the 246 male participants, poorer baseline strength for knee flexion (P trend = .029), knee extension (P trend =.010), and hip extension (P trend = .013) were each associated independently with higher all-cause mortality. Poorer strength for knee flexion (P trend = .042) and hip extension (P trend = .029) were associated with higher cardiovascular mortality. Compared with those in the fourth (best) baseline knee flexion quartile, hazard ratios for all-cause and cardiovascular disease mortality among men in the first (poorest) knee flexion quartile were 2.23 (95% confidence interval [CI], 1.02-4.87; P = .045) and 4.20 (95% CI, 1.12-15.79; P = .044), respectively. No significant associations of leg strength and all-cause mortality were identified among women.Poorer leg strength is associated with increased mortality in men, but not women, with PAD. Future study is needed to determine whether interventions that increase leg strength improve survival in men with PAD.
View details for DOI 10.1016/j.jvs.2010.03.066
View details for Web of Science ID 000281570100013
View details for PubMedID 20598471
To determine whether asymptomatic lower extremity peripheral arterial disease (PAD) and leg symptoms other than intermittent claudication (IC) in PAD are associated with faster functional decline than in people with both PAD and IC.Prospective, observational study.Chicago-area medical center.Four hundred fifteen people with PAD followed annually for up to 7 years.At baseline, patients with PAD were categorized into symptom categories, including IC; leg pain on exertion and rest; participants who could walk through exertional leg pain (pain/carry on); and participants who never experienced exertional leg pain, even during the 6-minute walk (always asymptomatic). Outcomes included mobility loss (becoming unable to walk one-quarter of a mile or walk up and down one flight of stairs without assistance) and becoming unable to complete the 6-minute walk without stopping. Analyses adjusted for age, sex, comorbidities, ankle brachial index, and other confounders.Always-asymptomatic participants (hazard ratio (HR)=2.94, 95% confidence interval (CI)=1.39-6.19, P=.005) and those with leg pain on exertion and rest (HR=2.89, 95% CI=1.47-5.68, P=.002) had greater mobility loss than participants with IC. Participants with PAD with leg pain/carry on were less likely (P=.047) to become unable to walk for 6 minutes continuously without stopping than participants with IC.The ABI identifies patients with asymptomatic PAD and those with atypical leg symptoms who are at risk for greater mobility decline than participants without PAD and participants with PAD with IC.
View details for DOI 10.1111/j.1532-5415.2010.02941.x
View details for Web of Science ID 000279448500005
View details for PubMedID 20550604
We determined whether statin use was associated with lower all-cause and cardiovascular disease (CVD) mortality in 579 participants with lower extremity peripheral arterial disease (PAD) according to the presence and absence of elevated C-reactive protein (CRP) and D-dimer levels. Statin use was determined at baseline and at each annual visit. The CRP and D-dimer levels were measured at baseline. The mean follow-up was 3.7 years. The analyses were adjusted for age, gender, race, co-morbidities, ankle brachial index, cholesterol, and other confounders. Of the 579 participants, 242 (42%) were taking a statin at baseline and 129 (22%) died during follow-up. Statin use was associated with lower all-cause mortality (hazard ratio 0.51, 95% confidence interval [CI] 0.30 to 0.86, p = 0.012) and CVD mortality (hazard ratio 0.36, 95% CI 0.14 to 0.89, p = 0.027) compared to statin nonuse. No statistically significant interaction was found for the baseline CRP or D-dimer level with the association of statin use and mortality. However, statin therapy was associated with significantly lower all-cause and total mortality only among participants with baseline CRP values greater than the median and not among those with CRP values less than the median (hazard ratio 0.44, 95% CI 0.23 to 0.88 vs hazard ratio 0.73, 95% CI 0.31 to 1.75 for all-cause mortality and hazard ratio 0.20, 95% CI 0.063 to 0.65 vs hazard ratio 0.59, 95% CI 0.093 to 3.79 for CVD mortality). In conclusion, among those with PAD, statin use was associated with lower all-cause and CVD mortality compared to no statin use. The favorable association of statin use with mortality was not influenced significantly by the baseline CRP or D-dimer level.
View details for DOI 10.1016/j.amjcard.2009.12.054
View details for Web of Science ID 000277579600025
View details for PubMedID 20403491
To evaluate associations between baseline lower extremity strength and decline in functional performance over 6 years of follow-up in men and women with lower extremity peripheral arterial disease (PAD).Prospective observational study.Three Chicago-area hospitals.Three hundred seventy-four men and women with PAD.Baseline isometric hip extension, hip flexion, knee flexion, and knee extension strength were measured using a musculoskeletal fitness evaluation chair. Usual and fastest-paced 4-m walking speed, 6-minute walk, and Short Physical Performance Battery (SPPB) were assessed at baseline and annually thereafter. Analyses were adjusted for age, sex, race, ankle-brachial index (ABI), comorbidities, and other confounders.In women with PAD, weaker baseline hip and knee flexion strength were associated with faster average annual decline in usual-pace 4-m walking speed (P trend <.001 and .02, respectively) and SPPB (P trend=.02 and .01, respectively). In women, weaker hip extension strength was associated with faster decline in usual-pace 4-m walking speed and SPPB (P trend=.01 and <.01, respectively). There were no significant associations between baseline strength and decline in 6-minute walk in women. There were no significant associations between any baseline strength measure and functional decline in men.Weaker baseline leg strength is associated with faster functional decline in nonendurance measures of functional performance in women with PAD but not in men with PAD.
View details for DOI 10.1111/j.1532-5415.2009.02562.x
View details for Web of Science ID 000272976400009
View details for PubMedID 19874404
Associations of pathophysiological calf muscle characteristics with functional decline in people with lower extremity peripheral arterial disease are unknown.Three hundred seventy participants with peripheral arterial disease underwent baseline measurement of calf muscle area, density, and percent fat with the use of computed tomography. Participants were followed up annually for 2 years. The outcome of mobility loss was defined as becoming unable to walk 1/4 mile or walk up and down 1 flight of stairs without assistance among those without baseline mobility limitations. Additional outcomes were > or =20% decline in 6-minute walk distance and becoming unable to walk for 6 minutes continuously among participants who walked continuously for 6 minutes at baseline. With adjustment for age, sex, race, body mass index, the ankle-brachial index, smoking, physical activity, relevant medications, and comorbidities, lower calf muscle density (P for trend <0.001) and lower calf muscle area (P for trend=0.039) were each associated with increased mobility loss rates. Compared with participants in the highest baseline tertiles, participants in the lowest tertile of calf muscle percent fat had a hazard ratio of 0.18 for incident mobility loss (95% confidence interval, 0.06 to 0.55; P=0.003), and participants in the lowest tertile of muscle density had a 3.50 hazard ratio for incident mobility loss (95% confidence interval, 1.28 to 9.57; P=0.015). No significant associations of calf muscle characteristics with 6-minute walk outcomes were observed.Our findings suggest that interventions to prevent mobility loss in peripheral arterial disease should focus on reversing pathophysiological findings in calf muscle.
View details for DOI 10.1161/CIRCULATIONAHA.108.842328
View details for Web of Science ID 000270015600006
View details for PubMedID 19738138