ISMRM Honors 2017

RSL Celebrates Award Winning Research

Summa Cum Laude

2D Multi-Spectral Thermometry for Monitoring Focused-Ultrasound Sonications Near Metallic Hardware

Hans Weber, Pejman Ghanouni, Aurea Pascal-Tenorio, Kim Butts Pauly, Brian Hargreaves

The lack of a technique for MR thermometry near metallic hardware excludes a growing patient population from MR-guided focused ultrasound treatments. In this work, we explore the temperature-induced signal change in fast two-dimensional multi-spectral imaging for monitoring sonications near metallic hardware. We demonstrate initial feasibility in phantom and ex vivo experiments as well as a patient treatment.

Accelerated Imaging of Metallic Implants Using a Double-Peak-Model Constraint

Xinwei Shi, Evan Levine, Hans Weber, Brian Hargreaves

Multi-Spectral Imaging (MSI) enables MRI near metallic implants, but suffers from prolonged scan times. Model-based reconstruction accelerates MSI by enforcing a signal model along the spectral dimension to reduce the number of unknowns in image reconstruction. The previous signal model assumes that spins in one voxel have the same off-resonance frequency, which tends to fail where the off-resonance field changes rapidly. Here we propose a more flexible MSI signal model that allows multiple frequencies within a voxel, and demonstrate improvements with both simulated and in-vivo data. 3x net additional acceleration above partial-Fourier and parallel-imaging alone (20x in total) was achieved.

Differential Domain Analysis for 3D Cartesian Sampling

Evan Levine, Brian Hargreaves

Selection of arbitrary 3D Cartesian sampling patterns for support-contrained MRI, parallel MRI, and dynamic MRI can be heuristical, and g-factor calculations require a computationally expensive simulation. To provide theoretical guidance and a method to optimize 3D Cartesian sampling, a novel concept of a differential distribution is introduced to represent a distribution of pairwise differences between sample locations, and is related to point-spread-functions. Its relationship to noise amplification in a generalized sensitivity encoding model and linear reconstruction is then used to efficiently optimize multidimensional k-space sampling. Examples in support-constrained MRI, parallel MRI, and dynamic MRI demonstrate reduced noise amplification

Pile-up and Ripple Artifact Correction Near Metallic Implants by Alternating Gradients

Xinwei Shi, Brady Quist, Brian Hargreaves

Multi-Spectral Imaging techniques have been shown to significantly reduce metal-induced artifacts. However, they often suffer from residual pile-up and ripple artifacts in the vicinity of metal, where the metal-induced off-resonance gradient “cancels” the frequency-encoding gradient. Fully phase-encoded methods can overcome the drawbacks of frequency encoding, but usually incur prohibitively long scan times. Here we address this limitation by combining two acquisitions with alternating-sign readout and slice-select gradients. We demonstrate with simulations, phantom and in-vivo scans that the proposed method can effectively suppress pile-up and ripple artifacts, and reduce the signal loss areas near the implants. 

From Visualization to Quantification: Calibrating Motion Magnification by Amplified Magnetic Resonance Imaging

Wendy Ni, Maged Goubran, Greg Zaharchuk, Michael Moseley, Kristen Yeom, Samantha Holdsworth

The brain is constantly in motion.  Changes in the cardio-ballistic motion of brain structures can provide invaluable information on natural processes and pathology.  We have previously introduced a qualitative visualization technique, Amplified MRI (aMRI), to amplify subtle cardio-ballistic motion in the brain.  Now we attempt to quantify the underlying motion through simulation-based characterization of the aMRI technique.  By generating calibration curves for a range of motion parameters, we calculated the unamplified tissue displacement in two human subjects.  The estimated displacements are higher than literature values.  Nevertheless, our simulations are the first steps in benchmarking aMRI’s potential as a quantitative technique.

Cluster Analysis of Cartilage T2 and T1rho Relaxation Times: Can the Contralateral Knee be used as a Control in the ACL-injured population?

Uchechukwuka Monu, Emily McWalter, Caroline Jordan, Brian Hargreaves, Garry Gold

In an ACL-injured population, longitudinal studies that use advanced MRI techniques such as T2 and T1rho mapping to assess cartilage health, typically compare ACL-injured knees with a separate healthy group or the contralateral knees. It is still unclear whether the contralateral knees can be used as a control group. Using a cluster analysis-based technique, we identify in the contralateral knees, significant increase in T1rho relaxation times over 1-year that is comparable to the increase in the ACL-injured knees. These focal cluster areas may represent degenerative changes and demonstrate that the contralateral knees may not be good controls. 

Magna Cum Laude

Overcoming Limitations of Virtual Observation Points in pTx using IMPULSE

Mihir Pendse, Brian Rutt

We analyze the performance of the IMPULSE pTx optimization algorithm, which allows SAR-aware pulse design without virtual observation points (VOP) compression. We compare performance of IMPULSE with conventional optimization methods using VOPs and compare different values of the overestimation parameter. We show that IMPULSE results in elimination of the time-intensive compression step without significantly increasing the time for real-time optimization. Additionally by eliminating the overestimation error from the VOP compression, IMPULSE is able to achieve better mitigation of local SAR hotspots after optimization than VOP-based methods.

T1-T2 Shuffling: Multi-Contrast 3D Fast Spin-Echo with T1 and T2 Sensitivity

Jonathan Tamir, Valentina Taviani, Shreyas Vasanawala, Michael Lustig

Volumetric fast spin-echo (3DFSE) imaging is clinically desirable because of its robustness to off-resonance and its utility for obtaining many types of image contrasts at isotropic resolution. However, its routine clinical use is inhibited by blurring due to long echo trains needed to maintain scan efficiency. Her we present T1-T2 Shuffling, a 3DFSE-based acquisition and reconstruction scheme that mitigates image blur and retrospectively synthesize T1-weighted and T2-weighted image contrasts. The acquisition, an extension of T2 Shuffling, employs a randomizing echo train view ordering with variable repetition times (TRs). The use of short TRs increases scan efficiency while providing T1 sensitivity.

Accelerated 3D Multispectral MRI with Robust Principal Component Analysis for Separation of On and Off-resonance Signals

Evan Levine, Kathryn Stevens, Brian Hargreaves

3D multispectral imaging (MSI) corrects most distortion in MRI near metallic implants at the cost of prolonged scan time by phase encoding to resolve slice distortions. However, existing methods to accelerate 3D MSI do not exploit the redundancy of slice-phase encoding for the dominant on-resonance signal. A novel compact representation of 3D-MSI images based on a decomposition of on- and off-resonance via robust principal component analysis (RPCA) is introduced to exploit this redundancy in a calibration and model-free reconstruction and push the current limits of accelerated 3D MSI. A complementary randomized sampling strategy is used to vary undersampling in different spectral bins to enable the separation. Experiments with retrospective and prospective undersampling show comparable image quality between standard MSI images and 2.6-3.4-fold accelerated RPCA and improvement over bin-by-bin compressed sensing reconstruction.

Extreme ASL:  Challenges and Solutions to Improve Perfusion Imaging in Patients with Markedly Prolonged Arterial Transit Delays

Jia Guo, Audrey Fan, Marc Lebel, Samantha Holdsworth, Ajit shankaranarayanan, Greg Zaharchuk

It is known that if labeling parameters are not properly adjusted in the presence of prolonged arterial transit delays (ATDs), perfusion may be underestimated using arterial spin labeling (ASL), yielding false negatives and possibly unnecessary interventions. In this study we evaluate the cases where the prolonged ATDs due to cerebrovascular disease posed challenges to perfusion quantification using ASL. Some possible solutions, which we term ‘extreme ASL’, were explored and discussed.

Improved Short-T2* Estimation with Bloch Equation-Modeled Concurrent Excitation and Relaxation

Ethan Johnson, Kim Butts Pauly, John Pauly

Short-T2* magnetization (order of [0.1,1ms]) can relax appreciably during standard-rate excitation pulses, which can bias estimates of relaxation rates formed by fitting to observed signal decay.  The effect can, however, be included in an updated model to improve T2* estimation for fast-relaxing signals.  Here, a demonstration is presented.

Visualizing Axonal Damage in Multiple Sclerosis Using Double Diffusion Encoding MRI in a Clinical Setting

Grant Yang, Qiyuan Tian, Christoph Leuze, Max Wintermark, Jennifer McNab

Double diffusion encoding (DDE) measurements of microscopic anisotropy show promise as a method of assessing neurodegeneration. Unfortunately, DDE has yet to be demonstrated in a clinical setting due to constraints in SNR and scan time.  Here, we used an optimized gradient orientation scheme to show the first DDE measurements of microscopic anisotropy in multiple sclerosis (MS) patients. Five MS patients were scanned using a DDE sequence optimized to run in five minutes. The microscopic anisotropy maps show improved visualization of axonal damage compared to fractional anisotropy (FA) and may provide additional insight into changes in tissue microstructure.  

MR-Guided Mixed-Reality For Surgical Planning: Set-Up and Perceptual Accuracy

Subashini Srinivasan, Amanda Wheeler, Brian Hargreaves, Bruce Daniel

Microsoft HoloLens provides the ability to visualize 3D holograms of preoperative MRI in addition to the physical environment. In this work we have developed a HoloLens application that aligns these preoperative holograms to the patient. The accuracy of perceiving these holograms was evaluated by presenting different shapes of holograms in random locations and comparing their positions to ground truth. The current set-up enables visualization and perception of holograms with a margin tolerance of < 6 mm

Monolithic Transmit Line Resonator as a Combined B1/B0-shim Coil Element

Riccardo Stara, Mihir Pendse, Jason Stockmann, Brian Rutt

In this work we propose and evaluate, for the first time, the use of a single-turn-single-gap Transmit Line Resonator as a combined RF-transceive and B0-shim element. We compare this design to a standard loop in terms of both RF and B0-shimming performance. The benefits of our combined TLR/B0-shim design are improved RF performance due to the fixed and smaller number of lumped elements, and the increase in B0-shim efficiency. Our results show the TLR element design to be an ideal building block for high-channel-count integrated Parallel Reception, Excitation and Shimming (iPRES) arrays.

5 Minute Comprehensive Knee MRI with 3D Double-Echo Steady-State (DESS)

Akshay Chaudhari, Bragi Sveinsson, Jeff Wood, Dushyant Thakur, Kathryn Stevens, Chris Beaulieu, Marcus Alley, Curtis Abercrombie, Garry Gold, Brian Hargreaves

Knee MRI is performed commonly in the US for assessing acute injuries as well as degenerative diseases. However, current knee MRI protocols can require 25-30 minutes or more and cost approximately $1.1billion/year. In such instances, a short knee protocol could lower costs while increasing patient throughput, comfort, and access to care. In this study, we show that a five-minute double-echo steady-state (DESS) scan, with automatic T2 maps and fluid-nulled images, offers high efficacy and diagnostic utility compared to the standard knee protocol. These results suggest that a five-minute DESS scan could be used for comprehensive MRI of the knee. 

Young Investigator Award -cum laude
Traditional Poster

PET/MR Imaging of Metabolic Bone Activity in Osteoarthritis

Feliks Kogan, Audrey Fan, Emily McWalter, Uchechukwuka Monu, Edwin Oei, Andrew Quon, Garry Gold

Osteoarthritis (OA) is a leading cause of disability, resulting in reduced quality of life, at tremendous societal cost. New hybrid PET/MR systems allow for simultaneous, sensitive, and quantitative assessments of early bone activity in OA with PET, which can be correlated with high-resolution quantitative MR methods of soft tissues to study the pathogenesis of OA. We demonstrate promising initial results of simultaneous PET/MR hybrid imaging of knee OA. Results suggest that PET/MR may detect metabolic abnormalities in subchondral bone, which appear normal on MRI.  These advancements will allow us to detect and track early and reversible changes in OA.

Study Group Honors

Intervential MR

Hans Weber - Oral Presentation, 2nd place: "Artifact-Reduced Imaging of Biopsy Needles with 2D Multi-Spectral Imaging"

Subashini Srinivasan - Poster Presentation, 2nd place: "MR-Guided Mixed-Reality For Surgical Planning: Set-Up & Perceptual Accuracy"