Key Points
- The joint annual meeting of ISMRM and ISMRT was held June 3–8 in Toronto.
- Focused ultrasound abstracts described three new devices and recent advances in brain treatments, epilepsy neuromodulation, and MRI innovations.
The joint annual meeting of the International Society for Magnetic Resonance in Medicine (ISMRM) and the International Society of MR Radiographers & Technologists (ISMRT) was held in Toronto June 3–8, 2023.
This scientific and clinical meeting, which highlights research, development, and applications of MRI in medicine and biology, included many abstracts that may be of interest to the focused ultrasound community. The oral and poster presentations described recent advances in Parkinson’s and essential tremor brain treatments, epilepsy neuromodulation, and MRI innovations.
In addition to the scientific sessions, an ISMRT educational session on interventional MRI featured presentations on Parkinson’s disease and prostate cancer by focused ultrasound experts Kullervo Hynynen, PhD, and Sangeet Ghai, MD, FRCR, respectively.
Notably, data from three new focused ultrasound devices were presented, including the Arrayus device, a mock transcranial MR-guided focused ultrasound system with improved signal-to-noise ratio (SNR), and an implantable neural interface powered by focused ultrasound.
The Foundation thanks Dennis Parker, PhD, the Mark H. Huntsman endowed professor in the Departments of Radiology and Imaging Sciences and Biomedical Informatics, and Henrik Odéen, PhD, MS, assistant professor in the Department of Radiology and Imaging Sciences, both at the University of Utah, for collecting the conference’s focused ultrasound—related content, which is summarized below.
Educational Session
ISMRT Education Session on Interventional MR
- MRgUS Brain: Parkinson’s Disease by Kullervo Hynynen, PhD
- MR-guided Focused Ultrasound Surgery (MRgFUS) for Prostate Cancer by Sangeet Ghai, MD, FRCS
New Devices for Intervention & Sensing Oral Presentation Session
0744: A Flat, Fully Populated MR-Guided Focused Ultrasound Phased Array Body System by Ryan M Jones, Yuexi Huang, Benjamin BC Lucht, Samuel T Gunaseelan, Tyler Portelli, Elizabeth David, and Kullervo Hynynen at Sunnybrook Research Institute, Toronto, ON, Canada; Arrayus Technologies Inc., Burlington, ON, Canada; Sunnybrook Health Sciences Centre, Toronto, ON, Canada; and the University of Toronto, Toronto, ON, Canada
Abstract: Existing commercial body MR-guided focused ultrasound (MRgFUS) systems have limited electronic steering ranges and rely on mechanical translation/rotation to ablate large tissue volumes. Here, we describe a flat, fully populated MRgFUS phased array body system with increased electronic steering capabilities. Following extensive benchtop and preclinical testing, the device was evaluated in a pilot clinical trial of MRgFUS for the treatment of uterine fibroids, which demonstrated the feasibilty and safety of the approach. The technology is extensible, stackable, and modular, allowing custom MRgFUS device development tailored to any indication.
Comments from D. Parker: Representing these authors from the group led by Kullervo Hynynen at Sunnybrook Health Science Center in Toronto, Ryan Jones presented results from pilot clinical trials of their fully populated, 6000-element phase array. The array operates at 500kHz and has element spacing less than half the wavelength, thereby allowing wide angle steering while avoiding grating lobes.
0745: Improvement of Experimental SNR in Mock Transcranial MRgFUS System with Strategic Design of Transfer Medium and Transducer Ground Plane at 3T by Karthik Lakshmanan, Ryan Brown, Giuseppe Carluccio, and Christopher M Collins at NYU Grossman School of Medicine, New York, NY, United States and the Center for Advanced Imaging Innovation and Research (CAIR), New York University, New York, NY, United States
Abstract: We show that novel modifications to a mock Transcranial MR-guided Focused Ultrasound (TMRgFUS) system show the potential to greatly improve MR performance. By using a transfer medium with reduced electric permittivity combined with slots in the transducer array ground plane, we measure a 2- to 3-fold increase in SNR across the middle of a head phantom portion of a mock TMRgFUS system.
Comments from D. Parker: In this talk presented by Chris Collins, the authors demonstrated that they could greatly reduce the banding artifact that is inherent in most Insightec Exablate neuro-ablation transducers by combining cuts in the transducer ground plane to electrically separate the transducer into a number of isolated segments with an acoustic transfer medium with reduced electric permittivity. The improvement in field uniformity around the focus was much greater than that obtained with either method alone.
0746: The MRDust: An Implantable Neural Interface Powered Via Focused Ultrasound With Data Communication Via MR Image Modulation by Biqi Rebekah Zhao, Yuhan Wen, Alexander Chou, Elad Alon, Rikky Muller, Chunlei Liu, and Michael Lustig from the Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, Berkeley, CA, United States
Abstract: We propose a new device for neuroscience studies: the MRDust, a sub-millimeter, wireless, programmable neural recording mote with on-device memory and compute. It receives power via focused ultrasound, records neural signals in burst mode, and uses a micro-coil to perturb local magnetic fields to achieve data uplink via dynamic MRI signal modulation. We demonstrate proof-of-concept experiments in which digital information is encoded in images of an SE-EPI dynamic sequence, and in which a piezoelectric harvester can harvest enough ultrasonic power to sustain device operation and receive control signals through amplitude modulation.
Comments from D. Parker: In this unique application, focused ultrasound is used to deliver power to an implanted device that then interacts locally with the tissue. The MR signal from the local tissue can be modulated by the local device.
Parkinson’s Disease Oral Presentation Session
1387: Enzyme Delivery to the Putamen in Parkinson’s Disease Patients by MR-Guided Focused Ultrasound by Yuexi Huang, Ying Meng, Christopher B. Pople, Allison Bethune, Ryan M. Jones, Agessandro Abrahao, Clement Hamani, Suneil K. Kalia, Lorraine V. Kalia, Nir Lipsman, and Kullervo Hynynen from Physical Sciences, Neurosurgery, and the Hurvitz Brain Sciences Research Program at Sunnybrook Research Institute in Toronto, ON, Canada; the Department of Medicine at the University of Toronto in Toronto, ON, Canada; the Krembil Research Institute at University Health Network in Toronto, ON, Canada; the Divisions of Neurosurgery and Neurology at Toronto Western Hospital in Toronto, ON, Canada; and the Department of Medical Biophysics and Institute of Biomedical Engineering at the University of Toronto in Toronto, ON, Canada
Synopsis: The phase I clinical trial demonstrated the successful application of microbubble-assisted MR-guided Focused Ultrasound for blood-brain barrier (BBB) opening in the putamen to facilitate biweekly therapeutic drug delivery in patients with Parkinson’s disease. BBB permeability within the targeted putamen was elevated successfully in all treatments, as revealed by Gd-enhanced T1-weighted MRI immediately post treatment. No contrast enhancement was observed in the treated putamen on MR imaging scans acquired one day following each treatment session, indicating closure of the BBB. FDG-PET revealed a reduction of glucose metabolism of the treated putamen relative to the contralateral putamen in all patients.
Comments from H. Odéen: Beta-glucocerebrosidase was successfully delivered to the putamen during three bi-weekly treatments in four Parkinson’s disease patients after MRgFUS BBB opening using Definity microbubbles. BBB opening was verified by CE T1w imaging directly after treatment, and closure was verified 24 hours post-treatment. Glucose metabolism was shown to decrease post-treatment in all cases.
Neuro Poster Session
5322: Effects of MR-Guided Focused Ultrasound Pallidotomy on Dyskinesia and Cerebral Regional Homogeneity in Parkinson’s Disease by Andrew Furman, Li Jiang, Justin Schumacher, Ziachen Zhuo, Howard Eisenberg, Paul Fishman, Dheeraj Ghandi, and Rao Gullapalli from Diagnostic Radiology and Nuclear Medicine, Neurosurgery, and Neurology in the School of Medicine, at the University of Maryland, Baltimore, MD, United States
Synopsis: MR-guided Focused Ultrasound (MRgFUS) pallidotomy is a promising, noninvasive neurosurgical approach for treating the primary and secondary symptoms, such as levodopa-induced dyskinesia, of Parkinson’s Disease (PD). While the behavioral effects of MRgFUS pallidotomy in PD have been previously established, its impacts on brain circuity and how these changes relate to symptom resolution are currently unclear. In the current study, we compared measures of Regional Homogeneity (ReHo), a metric of spatiotemporal correlation thought to reflect the integrity and modularity of mesoscopic circuity, before and after FUS lesion of the Globus Pallidus internus (GPi).
5346: Differential Lesion Volume Progression Following MR-Guided Focused Ultrasound Thalamotomy For Essential Tremor by Conrad P Rockel, Sarah Scott, Erin L Mazerolle, Samuel Pichardo, Davide Martino, Tejas Sankar, Zelma Kiss, and Bruce Pike from Radiology and Clinical Neurosciences, the Hotchkiss Brain Institute, and the Department of Surgery at the University of Calgary Cumming School of Medicine in Calgary, AB, Canada; the Department of Psychology at St. Francis Xavier University in Antigonish, NS, Canada; and the Department of Surgery at the University of Alberta in Edmonton, AB, Canada
Synopsis: Following MRgFUS thalamotomy for essential tremor, T1-weighted MRI images showed that lesions in some patients re-enlarged after the 3-month timepoint. After grouping patients as non-enlargers and enlargers based on this observation, we did not observe significant between-group differences in clinical measures of tremor beyond the 3-month timepoint. Patient demographic- and MRgFUS-related factors did not differ between groups. However, patients in the non-enlarger group demonstrated significantly greater tremor severity prior to and in early timepoints following MRgFUS thalamotomy, suggesting that the relationship between tremor severity and longitudinal lesion progression may be worthy of further investigation.
Connectivity & Tractography Digital Poster Session
3026: Alterations of White Matter Connectivity in Essential Tremor with MR-Guided Focused Ultrasound Thalamotomy by Xiaoyu Wang and Xin Lou from the Department of Radiology at Chinese PLA General Hospital in Beijing, China, and Nankai University in Tianjing, China
Synopsis: This research assessed the effects of MRgFUS thalamotomy on white matter connectivity in patients with essential tremor (ET). Results showed that MRgFUS might act on the topologic properties on brain networks. Rich-club and small-world organizations exist in healthy controls and patients with ET. The right orbital part of the superior frontal gyrus and right putamen were identified as a hub in the ET group only, whereas the left putamen identified as hubs in the group only. Importantly, gamma and sigma correlated with tremor improvement after MRgFUS thalamotomy, playing a role in reflecting tremor improvement for clinical treatment.
Advances in RF Coil Arrays Oral Presentation Session
1068: A Modular Sparse Hemispherical Transmit/Receive Phased Array for Microbubble-Mediated MR-Guided Focused Ultrasound Brain Therapy by Ryan M Jones, Dallan McMahon, Dallas Leavitt, Rohan Ramdoyal, Kang U Lee, Wai M Kan, Steven D Yang, Yi-Shiuan Chen, Chris Adams, and Kullervo Hynynen from Sunnybrook Research Institute in Toronto, ON, Canada, and the University of Toronto in Toronto, ON, Canada
Synopsis: MRI is commonly employed to assess microbubble-mediated focused ultrasound (FUS) treatment outcomes but is restricted to post-treatment evaluations due to its low temporal resolution. Here, we describe a modular, sparse, hemispherical transmit/receive phased array for microbubble-mediated FUS brain therapy and simultaneous 3D passive cavitation imaging (PCI) for real-time intraoperative treatment monitoring and control. The device was evaluated via MR-guided FUS experiments in rabbits. The utility of 3D PCI in calibrating FUS exposure levels and predicting MRI-inferred tissue damage volume distributions resulting from high target level sonications was demonstrated.
Comments from H. Odéen: Demonstration of BBB opening in a rabbit model was done using a novel modular spare hemispherical focused ultrasound array. The array consists of 64 modules, each with 64 elements in 8×8 grids, for a total of 4,096 elements. In each module, 60 elements are used for transmit (f = 258 kHz) and 4 corner elements are used for receive (f = 387 kHz). 3D passive cavitation imaging (PCI) was used to monitor the treatments and correlated with MRI-assessed tissue damage (signal hypointensities in T2*w MRI associated with RBC extravasations). 3D ultraharmonic imaging is a promising approach to calibrate exposure levels for MRgFUS BBB opening.
Thermometry Digital Poster Session
4993: Validation of an MR Thermometry Motion Compensation Algorithm For Periodic Motion During MR Guided High Intensity Focused Ultrasound (MRgHIFU) by Suzanne M Wong, Craig A. Macsemchuk, Andrew Headrick, Phoebe Luo, Arthur Akbulatov, James M. Drake, and Adam C. Waspe from Posluns Centre for Image Guided Innovation & Therapeutic Interventions at the Hospital for Sick Children in Toronto, ON, Canada, and the Departments of Biomedical Engineering and Medical Imaging at the University of Toronto in Toronto, ON, Canada
Synopsis: Magnetic resonance–guided high-intensity focused ultrasound (MRgHIFU) can noninvasively administer controlled hyperthermia as an adjuvant cancer therapy. For clinical translation, one of the main challenges is the sensitivity of MR thermometry to motion artifacts. This work aimed to validate a real-time hybrid principal component analysis and projection onto dipole fields (PCA-PDF) motion compensation algorithm on a clinical MRgHIFU system during reproducible motion profiles. The real-time PCA-PDF algorithm maintained a temperature standard deviation of < 1°C in a phantom while the periodic motion was induced on a phantom using an MR-compatible robot.
Conclusion: The results demonstrated that the PCA-PDF algorithm’s real-time capabilities were comparable to retrospective analysis, where the algorithm reduced temperature uncertainty to <1°C. Results also verified that the algorithm successfully distinguished heating from motion artifacts. Future work includes expanding the types of motion profiles to recreate more sporadic or arbitrary movements and further validation of the PCA-PDF algorithm.
5006: Accelerated MRI Thermometry Guidance for Transurethral Ultrasound Ablation of the Prostate Using Locally Low Rank Reconstruction by Ben YC Leung, Robert M. Staruch, and Mark Chiew from Profound Medical, Mississauga, ON, Canada; Medical Biophysics, University of Toronto, Toronto, ON, Canada; and Physical Sciences, Sunnybrook Research Institute, Toronto, ON, Canada
Synopsis: MRI-guided transurethral ultrasound ablation (TULSA) of the prostate control is based on dynamic proton resonance frequency shift MR temperature imaging. Given the localized, but spatio-temporally coherent heating pattern, locally low rank (LLR) reconstruction could facilitate accelerated thermometry. Images acquired during TULSA in a phantom were retrospectively under-sampled by acceleration factors of R=3, 4, and 6 by randomly sub-sampling EPI segments and reconstructed using LLR constraints with non-overlapping 4D patches and cycle-spinning patch shifts. LLR reconstruction demonstrated lower variance than GRAPPA reconstructions in unheated regions, but increasing measurement bias was found at R≥4. In vivo investigation of LLR reconstruction of MR thermometry for TULSA is warranted.
Epilepsy Digital Poster Session
5212: Focused Ultrasound Neuromodulation Combined with rs-fMRI and EEG as a Preclinical Tool to Investigate and Intervene Drug-Induced Epilepsy by Yi-Jing Juan, Xiao Zhen, PoChun Chu, You-Yin Chen, Hao-Li Liu, and Jyh-Horng Chen from the Graduate Institute of Biomedical Electronics and Bioinformatics and the Department of Electrical Engineering at National Taiwan University in Taipei City, Taiwan, and the Department of Biomedical Engineering at National Yang Ming Chiao Tung University in Hsinchu City, Taiwan
Conclusion: Focused ultrasound pulsations provide great potential to serve as an effective intervention tool to modulate the brain neuroactivity and have the possibility to suppress epilepsy. We demonstrated that the approach utilizing intracranial neural recording and rs-fMRI to assist the evaluation of anti-epileptic effect introduced by focused ultrasound pulsations is feasible. We also showed that longitudinal rs-fMRI monitoring and neural recording in the same epilepsy animal model have been successfully integrated to evaluate the drug-induced epileptic signal after PTZ injection. Focused ultrasound–induced neuromodulation induced region-to-region brain functional connectivity change; however, further interpretation is necessary to understand the linkage behind the mechanism in using ultrasound to interfere epilepsy.
Stretch, Rotate & Twist: New RF Coil Designs Digital Poster Session
3721: A Tailored Coil for Sensitive Detection of MRI Signals in Modulating the Rat’s Blood-Brain Barrier by Focused Ultrasound and Microbubbles at 7T by Sheng-Kai Wu, Alessandro De Maio, Hsin-Ju Lee, Kullervo Hynynen, Meaghan O’Reilly, and Fa-Hsuan Lin from Sunnybrook Research Institute in Toronto, ON, Canada, and the University of Toronto in Toronto, ON, Canada
Synopsis: Imaging-guided focused ultrasound using MRI can modulate the permeability of blood-brain barrier with high spatial accuracy. However, many MRI-guided FUS studies rely on either a body coil or head coil poorly suited to the FUS system geometry. We developed a tailored receiver coil to improve the sensitivity of 7T MRI for rats. The tailored geometry allows for a 30% SNR increase in a study modulating the blood-brain barrier permeability with microbubbles.
Phantoms & Repeatability Digital Poster Session
5097: Validation of the Single Reference Variable Flip Angle T1 Mapping Method in an Innovative Phantom by Michael Malmberg, Henrik Odéen, and Dennis L. Parker from Biomedical Engineering and Radiology and Imaging Sciences at the University of Utah in Salt Lake City, UT, United States
Synopsis: An innovative cylindrical phantom is used to mimic a dynamic acquisition with temperature-induced changes in T1. Single reference (SR) variable flip angle (VFA) T1 maps are acquired at several rotational positions of this phantom and are compared to corresponding T1 values acquired with the dual-angle variable flip angle and inversion recovery T1 mapping methods. The SR-VFA method of T1 mapping is shown to produce T1 accuracy within 4-10% of both inversion recovery and dual-angle VFA T1 measurements.
Comments by D. Parker: We believe that hybrid methods for measuring the longitudinal relaxation time, T1, in conjunction with the well-studied proton resonance frequency (PRF) shift method offer excellent potential in the simultaneous monitoring of temperature in fat and aqueous (glandular) tissue (e.g., breast tissue). The single reference variable flip angle method has the potential for T1 measurements at the same rate as the PRF measurements, but the accuracy of the method has not been validated. Validation of dynamic T1 measurement changes is difficult because it is nearly impossible to obtain reference T1 values. This work addressed this problem by constructing a cylindrical phantom where the T1 at a radius change smoothly with angle. When the cylinder is rotated, a stationary region of interest sees a dynamically change T1. When not rotating, slower inversion recovery methods can be used to obtain accurate, reference measurements. Motion is controlled accurately by a novel MRI-compatible motor, where the magnetic field of the scanner is used at the Stator field.
Thermometry Digital Poster Session
4994: Deep Learning–Based Drift Field Correction for MR Thermometry in the Upper Leg at 7T by E.F. Meliadò, M.W.I. Kikken, B.R. Steensma, C.A.T van den Berg, and A.J.E. Raaijmakers from the Department of Radiology, University Medical Center Utrecht, Utrecht, the Netherlands; Computational Imaging Group for MR Diagnostics & Therapy, Center for Image Sciences, University Medical Center Utrecht, Utrecht, the Netherlands; Tesla Dynamic Coils BV, Zaltbommel, the Netherlands; Department of Radiotherapy, University Medical Center Utrecht, Utrecht, the Netherlands; and Biomedical Image Analysis, Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, the Netherlands
Synopsis: PRFS-based MR Thermometry (MRT) bears strong potential for RF safety assessment. However, PRFS-MRT is impaired by external sources of frequency shift. It is hypothesized that deep learning will be able to separate the PRFS signal from these other sources of frequency shift. This study tested this concept on drift field correction for MRT in the human thigh at 7T. A convolutional neural network was trained using synthetic phase difference images based on measured drift fields and simulated temperature distributions. Results showed that the proposed deep-learning approach was able to correctly predict both simulated and measured temperature rise distributions.
4992: Compensation for Sporadic Motion in MR Thermometry Though a Hybrid Augmented Multi-Baseline and Near-Referenceless Approach by Arthur Akbulatov, Suzanne M. Wong, Craig A. Macsemchuk, Andrew Headrick, James M. Drake, and Adam C. Waspe from Posluns Centre for Image Guided Innovation & Therapeutic Intervention at The Hospital for Sick Children, Toronto, ON, Canada; Institute of Biomedical Engineering at the University of Toronto, Toronto, ON, Canada; and the Department of Medical Imaging at the University of Toronto, Toronto, ON, Canada
Synopsis: Magnetic resonance-guided high-intensity focused ultrasound (MRgHIFU) treatments are limited by motion artifacts introduced into MR thermometry calculations by large sporadic motions. A hybrid principal component analysis and projection onto dipole fields (PCA-PDF) motion compensation algorithm was expanded upon to include predicted motion using image augmentation techniques. When tested on MR images from a gelatin phantom being translated in the coronal plane, the improved PCA-PDF algorithm yielded a temperature standard deviation of 0.4 ± 0.1 °C, which is a 3.7 ± 0.1 °C reduction from an unmodified PCA-PDF approach, indicating that thermometry artifacts induced by motion were significantly reduced.
4987: Dynamic 3D Stack-of-Radial Multi-Baseline PRF MR Thermometry using Compressed Sensing Reconstruction and Image-Based Navigation by Qing Dai, Shu-Fu Shih, Jiaqi Zhou, Le Zhang, and Holden H. Wu from Radiological Sciences at the University of California, Los Angeles, in Los Angeles, CA, United States; Bioengineering at the University of California, Los Angeles, in Los Angeles, CA, United States; and the Department of Engineering Physics at Tsinghua University in Beijing, China
Synopsis: Multi-baseline proton resonance frequency (PRF) shift MR thermometry can reduce motion-induced temperature errors in moving organs during MR-guided thermal therapy. However, previous methods had to compromise the spatial coverage to increase the temporal resolution for resolving motion. This study developed a dynamic 3D stack-of-radial MRI method using compressed sensing reconstruction and image-based navigation to enable motion-resolved multi-baseline PRF thermometry with 1.4-sec true temporal resolution. The proposed method achieved stable thermometry with volumetric coverage in free-breathing liver MRI without heating.
4224: Magnetic resonance fingerprinting thermometry (MRFT) versus PRFS thermometry: comparative temperature prediction in ex vivo bovine muscle by Enlin Qian, Pavan Poojar, Maggie Fung, Zhezhen Jin, John Thomas Vaughan, Devashish Shrivastava, David Gultekin, and Sairam Geethanath from the Columbia Magnetic Resonance Research Center at Columbia University in New York, NY, United States; the Accessible MR Laboratory at the Biomedical Engineering and Imaging Institute’s Department of Diagnostic, Molecular, and Interventional Radiology at the Icahn School of Medicine at Mt. Sinai in New York, NY, United States; GE Healthcare in New York, NY, United States; and the Department of Biostatistics at Columbia University in New York, NY, United States
Synopsis: We explored T1-based magnetic resonance fingerprinting thermometry (MRFT) and compared it with proton resonance frequency shift (PRFS) thermometry in ex vivo bovine muscle data. We conducted temperature sensitivity calibration experiments for both methods. We compared MRFT and PRFS thermometry predicted temperatures in bovine muscles, validated by fluoroptic probe measurements. We observed strong correlation in temperature sensitivity calibration experiments (R2>0.958). Both methods predicted temperature accurately (RMSE<1.37 ℃ and RMSE<0.93 ℃ for MRFT and PRFS, over a range of 25 ℃). We observed a strong correlation between PRFS- and MRFT-predicted temperature in heated bovine muscle (R2>0.93).