Bio

Academic Appointments


Honors & Awards


  • Stanford Medicine Faculty Innovation Program (Co-PI), Stanford University (2015)
  • Radiation Physics Impact Award, Stanford University (2014)
  • Scholarship for nanostorage research from Ministry of economic affairs, NTU (2004)
  • The AP-NFO student Award, 4th Asia-Pacific International Conference on near-field Optics (2003)

Professional Education


  • DABR, The American Board of Radiology, Therapeutic Medical Physics (2015)
  • Residency, Stanford University, Therapeutic Medical Physics (CAMPEP Accredited) (2014)
  • Ph.D., University of California, Los Angeles, Biomedical Physics (CAMPEP Accredited) (2011)

Publications

All Publications


  • Anatomic optimization of lung tumor stereotactic ablative radiation therapy. Practical radiation oncology Yu, A. S., von Eyben, R., Yamamoto, T., Diehn, M., Shultz, D. B., Loo, B. W., Maxim, P. G. 2015; 5 (6): e607-13

    Abstract

    The purpose of this study was to demonstrate that anatomic optimization through selection of the degree of breath hold that yields the largest separation between the target and nearby organ at risk could result in dosimetrically superior treatment plans.Thirty patients with 41 plans were included in this planned secondary analysis of a prospective trial. Fifteen plans were created for treatment with use of natural end exhale (NEE), and 26 plans used deep inspiration breath hold (DIBH). To evaluate whether the original plan was dosimetrically optimal, we replanned treatment using the opposite respiratory state with the same beam configuration as the original plan. A treatment plan was deemed superior if it met protocol constraints when the other did not. If both plans met or violated the constraints, the plans were deemed equivalent.Of the 26 plans originally planned with DIBH and replanned with NEE, 3 plans were dosimetrically superior with NEE, 1 plan was dosimetrically superior with DIBH, and 22 plans were dosimetrically equivalent. Of the 15 plans originally planned with NEE, 4 plans were dosimetrically superior with NEE, 2 plans were dosimetrically superior with DIBH, and 9 plans were dosimetrically equivalent.For 10 of 41 plans, planning with 1 respiratory state was superior. To obtain uniformly optimal plans, individual anatomic optimization would be needed.

    View details for DOI 10.1016/j.prro.2015.05.008

    View details for PubMedID 26231596

  • Monitoring external beam radiotherapy using real-time beam visualization MEDICAL PHYSICS Jenkins, C. H., Naczynski, D. J., Yu, S. S., Xing, L. 2015; 42 (1): 5-13

    Abstract

    To characterize the performance of a novel radiation therapy monitoring technique that utilizes a flexible scintillating film, common optical detectors, and image processing algorithms for real-time beam visualization (RT-BV).Scintillating films were formed by mixing Gd2O2S:Tb (GOS) with silicone and casting the mixture at room temperature. The films were placed in the path of therapeutic beams generated by medical linear accelerators (LINAC). The emitted light was subsequently captured using a CMOS digital camera. Image processing algorithms were used to extract the intensity, shape, and location of the radiation field at various beam energies, dose rates, and collimator locations. The measurement results were compared with known collimator settings to validate the performance of the imaging system.The RT-BV system achieved a sufficient contrast-to-noise ratio to enable real-time monitoring of the LINAC beam at 20 fps with normal ambient lighting in the LINAC room. The RT-BV system successfully identified collimator movements with sub-millimeter resolution.The RT-BV system is capable of localizing radiation therapy beams with sub-millimeter precision and tracking beam movement at video-rate exposure.

    View details for DOI 10.1118/1.4901255

    View details for Web of Science ID 000347957200002

    View details for PubMedID 25563243

  • Regional distribution of SGLT activity in rat brain in vivo AMERICAN JOURNAL OF PHYSIOLOGY-CELL PHYSIOLOGY Yu, A. S., Hirayama, B. A., Timbol, G., Liu, J., Diez-Sampedro, A., Kepe, V., Satyamurthy, N., Huang, S., Wright, E. M., Barrio, J. R. 2013; 304 (3): C240-C247

    Abstract

    Na(+)-glucose cotransporter (SGLT) mRNAs have been detected in many organs of the body, but, apart from kidney and intestine, transporter expression, localization, and functional activity, as well as physiological significance, remain elusive. Using a SGLT-specific molecular imaging probe, α-methyl-4-deoxy-4-[(18)F]fluoro-D-glucopyranoside (Me-4-FDG) with ex vivo autoradiography and immunohistochemistry, we mapped in vivo the regional distribution of functional SGLTs in rat brain. Since Me-4-FDG is not a substrate for GLUT1 at the blood-brain barrier (BBB), in vivo delivery of the probe into the brain was achieved after opening of the BBB by an established procedure, osmotic shock. Ex vivo autoradiography showed that Me-4-FDG accumulated in regions of the cerebellum, hippocampus, frontal cortex, caudate nucleus, putamen, amygdala, parietal cortex, and paraventricular nucleus of the hypothalamus. Little or no Me-4-FDG accumulated in the brain stem. The regional accumulation of Me-4-FDG overlapped the distribution of SGLT1 protein detected by immunohistochemistry. In summary, after the BBB is opened, the specific substrate for SGLTs, Me-4-FDG, enters the brain and accumulates in selected regions shown to express SGLT1 protein. This localization and the sensitivity of these neurons to anoxia prompt the speculation that SGLTs may play an essential role in glucose utilization under stress such as ischemia. The expression of SGLTs in the brain raises questions about the potential effects of SGLT inhibitors under development for the treatment of diabetes.

    View details for DOI 10.1152/ajpcell.00317.2012

    View details for Web of Science ID 000314632400005

    View details for PubMedID 23151803

  • Functional expression of SGLTs in rat brain AMERICAN JOURNAL OF PHYSIOLOGY-CELL PHYSIOLOGY Yu, A. S., Hirayama, B. A., Timbol, G., Liu, J., Basarah, E., Kepe, V., Satyamurthy, N., Huang, S., Wright, E. M., Barrio, J. R. 2010; 299 (6): C1277-C1284

    Abstract

    This work provides evidence of previously unrecognized uptake of glucose via sodium-coupled glucose transporters (SGLTs) in specific regions of the brain. The current understanding of functional glucose utilization in brain is largely based on studies using positron emission tomography (PET) with the glucose tracer 2-deoxy-2-[F-18]fluoro-D-glucose (2-FDG). However, 2-FDG is only a good substrate for facilitated-glucose transporters (GLUTs), not for SGLTs. Thus, glucose accumulation measured by 2-FDG omits the role of SGLTs. We designed and synthesized two high-affinity tracers: one, α-methyl-4-[F-18]fluoro-4-deoxy-D-glucopyranoside (Me-4FDG), is a highly specific SGLT substrate and not transported by GLUTs; the other one, 4-[F-18]fluoro-4-deoxy-D-glucose (4-FDG), is transported by both SGLTs and GLUTs and will pass through the blood brain barrier (BBB). In vitro Me-4FDG autoradiography was used to map the distribution of uptake by functional SGLTs in brain slices with a comparable result from in vitro 4-FDG autoradiography. Immunohistochemical assays showed that uptake was consistent with the distribution of SGLT protein. Ex vivo 4-FDG autoradiography showed that SGLTs in these areas are functionally active in the normal in vivo brain. The results establish that SGLTs are a normal part of the physiology of specific areas of the brain, including hippocampus, amygdala, hypothalamus, and cerebral cortices. 4-FDG PET imaging also established that this BBB-permeable SGLT tracer now offers a functional imaging approach in humans to assess regulation of SGLT activity in health and disease.

    View details for DOI 10.1152/ajpcell.00296.2010

    View details for Web of Science ID 000284822100008

    View details for PubMedID 20826762

  • Quantification of Cerebral Glucose Metabolic Rate in Mice Using F-18-FDG and Small-Animal PET JOURNAL OF NUCLEAR MEDICINE Yu, A. S., Lin, H., Huang, S., Phelps, M. E., Wu, H. 2009; 50 (6): 966-973

    Abstract

    The aim of this study was to evaluate various methods for estimating the metabolic rate of glucose utilization in the mouse brain (cMR(glc)) using small-animal PET and reliable blood curves derived by a microfluidic blood sampler. Typical values of (18)F-FDG rate constants of normal mouse cerebral cortex were estimated and used for cMR(glc) calculations. The feasibility of using the image-derived liver time-activity curve as a surrogate input function in various quantification methods was also evaluated.Thirteen normoglycemic C57BL/6 mice were studied. Eighteen blood samples were taken from the femoral artery by the microfluidic blood sampler. Tissue time-activity curves were derived from PET images. cMR(glc) values were calculated using 2 different input functions (one derived from the blood samples [IF(blood)] and the other from the liver time-activity curve [IF(liver)]) in various quantification methods, which included the 3-compartment (18)F-FDG model (from which the (18)F-FDG rate constants were derived), the Patlak analysis, and operational equations. The estimated cMR(glc) value based on IF(blood) and the 3-compartment model served as a standard for comparisons with the cMR(glc) values calculated by the other methods.The values of K(1), k(2), k(3), k(4), and K(FDG) estimated by IF(blood) and the 3-compartment model were 0.22 +/- 0.05 mL/min/g, 0.48 +/- 0.09 min(-1), 0.06 +/- 0.02 min(-1), 0.025 +/- 0.010 min(-1), and 0.024 +/- 0.007 mL/min/g, respectively. The standard cMR(glc) value was, therefore, 40.6 +/- 13.3 micromol/100 g/min (lumped constant = 0.6). No significant difference between the standard cMR(glc) and the cMR(glc) estimated by the operational equation that includes k(4) was observed. The standard cMR(glc) was also found to have strong correlations (r > 0.8) with the cMR(glc) value estimated by the use of IF(liver) in the 3-compartment model and with those estimated by the Patlak analysis (using either IF(blood) or IF(liver)).The (18)F-FDG rate constants of normal mouse cerebral cortex were determined. These values can be used in the k(4)-included operational equation to calculate cMR(glc). IF(liver) can be used to estimate cMR(glc) in most methods included in this study, with proper linear corrections applied. The validity of using the Patlak analysis for estimating cMR(glc) in mouse PET studies was also confirmed.

    View details for DOI 10.2967/jnumed.108.060533

    View details for Web of Science ID 000272488000026

    View details for PubMedID 19443595

  • In vivo quantitation of glucose metabolism in mice using small-animal PET and a microfluidic device JOURNAL OF NUCLEAR MEDICINE Wu, H., Sui, G., Lee, C., Prins, M. L., Ladno, W., Lin, H., Yu, A. S., Phelps, M. E., Huang, S. 2007; 48 (5): 837-845

    Abstract

    The challenge of sampling blood from small animals has hampered the realization of quantitative small-animal PET. Difficulties associated with the conventional blood-sampling procedure need to be overcome to facilitate the full use of this technique in mice.We developed an automated blood-sampling device on an integrated microfluidic platform to withdraw small blood samples from mice. We demonstrate the feasibility of performing quantitative small-animal PET studies using (18)F-FDG and input functions derived from the blood samples taken by the new device. (18)F-FDG kinetics in the mouse brain and myocardial tissues were analyzed.The studies showed that small ( approximately 220 nL) blood samples can be taken accurately in volume and precisely in time from the mouse without direct user intervention. The total blood loss in the animal was <0.5% of the body weight, and radiation exposure to the investigators was minimized. Good model fittings to the brain and the myocardial tissue time-activity curves were obtained when the input functions were derived from the 18 serial blood samples. The R(2) values of the curve fittings are >0.90 using a (18)F-FDG 3-compartment model and >0.99 for Patlak analysis. The (18)F-FDG rate constants K(1)(*), k(2)(*), k(3)(*), and k(4)(*), obtained for the 4 mouse brains, were comparable. The cerebral glucose metabolic rates obtained from 4 normoglycemic mice were 21.5 +/- 4.3 mumol/min/100 g (mean +/- SD) under the influence of 1.5% isoflurane. By generating the whole-body parametric images of K(FDG)(*) (mL/min/g), the uptake constant of (18)F-FDG, we obtained similar pixel values as those obtained from the conventional regional analysis using tissue time-activity curves.With an automated microfluidic blood-sampling device, our studies showed that quantitative small-animal PET can be performed in mice routinely, reliably, and safely in a small-animal PET facility.

    View details for DOI 10.2967/jnumed.106.038182

    View details for Web of Science ID 000246326100031

    View details for PubMedID 17475972

  • Bright fluorescent nanodiamonds: No photobleaching and low cytotoxicity JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Yu, S. J., Kang, M. W., Chang, H. C., Chen, K. M., Yu, Y. C. 2005; 127 (50): 17604-17605

    Abstract

    Diamond nanocrystals emit bright fluorescence at 600-800 nm after irradiation by a 3 MeV proton beam (5 x 1015 ions/cm2) and annealing at 800 degrees C (2 h) in vacuum. The irradiation/annealing process yields high concentrations of nitrogen-vacancy defect centers ( approximately 107 centers/mum3), making possible visualization of the individual 100 nm diamond crystallites using a fluorescence microscope. The fluorescent nanodiamonds (FND) show no sign of photobleaching and can be taken up by mammalian cells with minimal cytotoxicity. The nanomaterial can have far-reaching biological applications.

    View details for DOI 10.1021/ja0567081

    View details for Web of Science ID 000234008900018

    View details for PubMedID 16351080