A5050731684- Advanced MRI Techniques and Applications
- Neurological disorders and treatments
- Transcranial Magnetic Stimulation Studies
- Advanced NMR Techniques and Applications
- Neuroscience and Neural Engineering
- Functional Brain Connectivity Studies
- Cardiac electrophysiology and arrhythmias
- Cardiac Imaging and Diagnostics
- Advanced Neuroimaging Techniques and Applications
- Atomic and Subatomic Physics Research
- Medical Imaging Techniques and Applications
- Wireless Body Area Networks
- MRI in cancer diagnosis
- Ultrasound and Hyperthermia Applications
- Electron Spin Resonance Studies
- Characterization and Applications of Magnetic Nanoparticles
- Muscle activation and electromyography studies
- Electromagnetic Fields and Biological Effects
- Ultrasound Imaging and Elastography
- Vagus Nerve Stimulation Research
- Magnetic Properties of Alloys
- Anesthesia and Sedative Agents
- Wireless Power Transfer Systems
- Ion channel regulation and function
- Electrical and Bioimpedance Tomography
Massachusetts General Hospital
2015-2024
Athinoula A. Martinos Center for Biomedical Imaging
2015-2024
Harvard University
2019-2024
Harvard–MIT Division of Health Sciences and Technology
2023
University Medical Centre Mannheim
2015-2022
Heidelberg University
2014-2022
University Hospital Heidelberg
2014-2022
Heidelberg University
2014
Abstract To increase granularity in human neuroimaging science, we designed and built a next-generation 7 Tesla magnetic resonance imaging scanner to reach ultra-high resolution by implementing several advances hardware. improve spatial encoding the image signal-to-noise ratio, developed head-only asymmetric gradient coil (200 mT m −1 , 900 T s ) with an additional third layer of windings. We integrated 128-channel receiver system 64- 96-channel arrays boost signal cerebral cortex while...
Purpose As gradient performance increases, peripheral nerve stimulation (PNS) is becoming a significant constraint for fast MRI. Despite its impact, PNS not directly included in the coil design process. Instead, characteristics of are assessed on healthy subjects after prototype construction. We attempt to develop tool inform by predicting thresholds and activation locations human body using electromagnetic field simulations coupled neurodynamic model. validate approach comparing simulated...
Abstract Rapid switching of applied magnetic fields in the kilohertz frequency range human body induces electric powerful enough to cause Peripheral Nerve Stimulation (PNS). PNS has become one main constraints on use high gradient for fast imaging with latest MRI technology. In recent gradients, are that limits their application sequences like echo-planar imaging. Application Magnetic Particle Imaging (MPI) humans is similarly constrained. Despite its role as a major constraint,...
Purpose Peripheral nerve stimulation (PNS) limits the image encoding performance of both body gradient coils and latest generation head gradients. We analyze a variety design aspects using detailed PNS model to guide process new high‐performance asymmetric raise thresholds maximize usable image‐encoding performance. Methods A novel three‐layer coil underwent optimization involving predictions series candidate designs. The PNS‐informed sought parameter space with <10% nonlinearity in 22 cm...
Peripheral Nerve Stimulation (PNS) limits the acquisition rate of Magnetic Resonance Imaging data for fast sequences employing powerful gradient systems. The PNS characteristics are currently assessed after coil design phase in experimental stimulation studies using constructed prototypes. This makes it difficult to find modifications that can reduce PNS. Here, we demonstrate a direct approach incorporation effects into optimization process. Knowledge about interactions between applied...
Purpose To test an integrated “AC/DC” array approach at 7T, where B 0 inhomogeneity poses obstacle for functional imaging, diffusion‐weighted MRI, MR spectroscopy, and other applications. Methods A close‐fitting 7T 31‐channel (31‐ch) brain was constructed tested using combined Rx ΔB shim channels driven by a set of rapidly switchable current amplifiers. The coil compared to shape‐matched 31‐ch reference receive‐only RF safety, signal‐to‐noise ratio (SNR), inter‐element noise correlation. We...
Objective. We present a PNS oracle, which solves these computation time and linearity problems is, therefore, well-suited for fast optimization of voltage distributions in contact electrode arrays current drive patterns non-contact magnetic coil arrays. Approach. The oracle metric nerve fiber is computed from an electric field map using only linear operations (projection, differentiation, convolution, scaling). Due to its linearity, this can be precomputed set or segments, allowing rapid...
Purpose To design short parallel transmission (pTx) pulses for excitation of arbitrary three‐dimensional (3D) magnetization patterns. Methods We propose a joint optimization the pTx radiofrequency (RF) and gradient waveforms 3D Our is based on parameterization k‐space trajectories (3D shells, stack‐of‐spirals, cross) using small number shape parameters that are well‐suited optimization. The resulting smooth sample efficiently with few turns while system at maximum performance. Within each...
We design, develop, and disseminate a 'virtual population' of five realistic computational models deep brain stimulation (DBS) patients for electromagnetic (EM) analysis. found DBS in our institution' research patient database who received high quality post-DBS surgery computer tomography (CT) examinations the head neck. Three have single implanted pulse generator (IPG) two others IPGs (one each lead). Moreover, one has abandoned leads on side head. For patient, we combined neck volumes into...
Purpose Cardiac stimulation (CS) limits to gradient coil switching speed are difficult measure in humans; instead, current regulatory guidelines (IEC 60601‐2‐33) based on animal experiments and electric field–to‐dB/dt conversion factors computed for a simple, homogeneous body model. We propose improvement this methodology by using more detailed CS modeling realistic models electrophysiological of excitable cardiac fibers. Methods compute fields induced solenoid, coplanar loops, commercial...
Peripheral nerve stimulation (PNS) has become an important limitation for fast MR imaging using the latest gradient hardware. We have recently developed a simulation framework to predict PNS thresholds and locations in body arbitrary coil geometries inform optimization process. Our approach couples electromagnetic field simulations realistic models neurodynamic model of peripheral fibers. In this work, we systematically analyze impact key parameters on predicted assess robustness results....
Many applications in MRI such as accelerated receive and transmit sequences require the synthesis of nonuniform 3-D gradient trajectories. Several methods have been proposed to design these trajectories a time-optimal manner, subject hardware specific magnitude slew rate constraints. In this work novel method is derived that designs trajectories, solely based on set arbitrarily chosen control points k-space. particular, no path constraint required for k-space trajectory. It shown above...
Abstract Purpose Peripheral nerve stimulation (PNS) limits the usability of state‐of‐the‐art whole‐body and head‐only MRI gradient coils. We used detailed electromagnetic neurodynamic modeling to set an explicit PNS constraint during design a coil constructed it compare predicted experimentally measured thresholds those matched without constraints. Methods designed, constructed, tested two actively shielded Y‐axis winding patterns: YG1 is conventional symmetric PNS‐optimization, whereas...
Abstract Objective. Rapid switching of magnetic resonance imaging (MRI) gradient fields induces electric that can cause peripheral nerve stimulation (PNS) and so accurate characterization PNS is required to maintain patient safety comfort while maximizing MRI performance. The minimum amplitude causes stimulation, the threshold, depends on intrinsic axon properties spatial temporal induced field. strength–duration curve widely used characterize simulation thresholds for periodic waveforms...
Purpose Peripheral nerve stimulation (PNS) modeling has a potential role in designing and operating MRI gradient coils but requires computationally demanding simulations of electromagnetic fields neural responses. We demonstrate compression an neurodynamic model into single versatile PNS matrix (P‐matrix) defined on intermediary Huygens’ surface to allow fast characterization arbitrary coil geometries body positions. Methods The approach divides prediction extensive pre‐computation phase the...
We calculate the impact of peripheral nerve geometry (bend angle, radius curvature, and axon diameter) electric field characteristics (hot-spot amplitude extent) on chronaxie stimulation to better understand variability in experimental values seen with MRI gradient coils.
Powerful MRI gradient systems can surpass the International Electrotechnical Commission (IEC) 60601-2-33 limit for cardiac stimulation (CS), which was determined by simple electromagnetic simulations and electrode experiments. Only a few canine studies measured magnetically induced CS thresholds in vivo extrapolating them to human safety limits be challenging.We magnetostimulation 10 healthy, anesthetized pigs using capacitors discharged into flat spiral coil produce damped sinusoidal...
We use a combined electromagnetic-electrophysiological modeling framework to predict cardiac stimulation (CS) thresholds in individualized porcine body models and compare those simulations measured eight pigs using strong dB/dt pulses. For all pigs, the simulated agree within 30%, no significant differences between measurements were detected (p<0.05, paired t-test). The threshold model uncertainty was found be ~25% sensitivity analysis of relevant parameters. A well-validated may help...
We report experimental PNS threshold measurements of an asymmetric optimized whole-body gradient coil and compare it to a standard symmetric designed without optimization. Stimulation thresholds were measured in 10 healthy adult subjects for five clinically relevant scan positions. The design raised by up 47% four out the studied positions (head, cardiac, pelvic, knee imaging positions). These results support potential value PNS-optimized gradients maximizing image encoding performance
High-amplitude gradient systems can surpass the IEC regulatory limit for cardiac stimulation (CS), which is based on animal electrostimulation data and simplified electromagnetic modeling. We assess CS in MRI by performing first magnetostimulation threshold measurements pigs, primary model of human cardiovascular system. use to validate a detailed modeling pipeline applicable both pigs humans. Experimental thresholds predictions porcine-specific models agree within 19% NRMSE. body indicates...