A5090829577- Advanced MRI Techniques and Applications
- Advanced Neuroimaging Techniques and Applications
- Medical Imaging Techniques and Applications
- Atomic and Subatomic Physics Research
- MRI in cancer diagnosis
- Advanced NMR Techniques and Applications
- Sparse and Compressive Sensing Techniques
- NMR spectroscopy and applications
- Cancer Diagnosis and Treatment
- Functional Brain Connectivity Studies
- Electron Spin Resonance Studies
- Lanthanide and Transition Metal Complexes
- Fetal and Pediatric Neurological Disorders
- Bone and Joint Diseases
- Nuclear Physics and Applications
- Photoacoustic and Ultrasonic Imaging
- Non-Destructive Testing Techniques
- Seismic Imaging and Inversion Techniques
- Bladder and Urothelial Cancer Treatments
- Advanced X-ray and CT Imaging
- Image and Signal Denoising Methods
- Cerebrospinal fluid and hydrocephalus
- Numerical methods in inverse problems
- Medical Image Segmentation Techniques
- Cancer Genomics and Diagnostics
Stanford University
2021-2025
University Radiology
2023
Athinoula A. Martinos Center for Biomedical Imaging
2013-2022
Harvard University
2013-2022
Massachusetts General Hospital
2013-2022
Harvard–MIT Division of Health Sciences and Technology
2017-2022
Massachusetts Institute of Technology
2006-2021
Chiang Mai University
2021
United States Nuclear Regulatory Commission
2021
Stanford Medicine
2021
Simultaneous multislice Echo Planar Imaging (EPI) acquisition using parallel imaging can decrease the time for diffusion and allow full-brain, high-resolution functional MRI (fMRI) acquisitions at a reduced repetition (TR). However, unaliasing of simultaneously acquired, closely spaced slices be difficult, leading to high g-factor penalty. We introduce method create interslice image shifts in phase encoding direction increase distance between aliasing pixels. The shift is induced sign-...
Sleep is essential for both cognition and maintenance of healthy brain function. Slow waves in neural activity contribute to memory consolidation, whereas cerebrospinal fluid (CSF) clears metabolic waste products from the brain. Whether these two processes are related not known. We used accelerated neuroimaging measure physiological dynamics human discovered a coherent pattern oscillating electrophysiological, hemodynamic, CSF that appears during non-rapid eye movement sleep. Neural slow...
Controlled aliasing techniques for simultaneously acquired echo-planar imaging slices have been shown to significantly increase the temporal efficiency both diffusion-weighted and functional magnetic resonance studies. The "slice-GRAPPA" (SG) method has widely used reconstruct such data. We investigate robust optimization SG ensure image reconstruction accuracy through a reduction of leakage artifacts.
Abstract A 64‐channel brain array coil was developed and compared to a 32‐channel constructed with the same former geometry precisely isolate benefit of 2‐fold increase in elements. The coils were for standard clinical 3T MRI scanner used contoured head‐shaped curved around occipital pole tapered at neck both improve sensitivity patient comfort. Additionally, design is compact, split‐former intended robust daily use. Signal‐to‐noise ratio noise amplification ( G ‐factor) parallel imaging...
Purpose To introduce the wave‐CAIPI (controlled aliasing in parallel imaging) acquisition and reconstruction technique for highly accelerated 3D imaging with negligible g‐factor artifact penalties. Methods The involves playing sinusoidal gradients during readout of each encoding line while modifying phase strategy to incur interslice shifts as 2D‐CAIPI acquisitions. resulting spreads evenly all spatial directions, thereby taking full advantage coil sensitivity distribution. By expressing...
Significance A major challenge in neuroscience is our limited ability to image neural signals noninvasively humans. Oscillations brain activity are important for perception, attention, and awareness, progress cognitive depends on localizing these patterns. fMRI thought be too slow measure oscillations because it changes blood flow. Here, we use recently developed imaging techniques show that can faster than previously thought, responses 10 times larger expected. With computational modeling...
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...
Abstract Spatially tailored radio frequency (RF) excitations accelerated with parallel transmit systems provide the opportunity to create shaped volume or mitigate inhomogeneous B 1 excitation profiles clinically relevant pulse lengths. While such are often designed as a least‐squares optimized approximation target magnitude and phase profile, adherence profile is usually not important long slowly varying compared voxel dimension. In this work, we demonstrate method for least squares...
Purpose To examine the effects of reconstruction algorithm magnitude images from multichannel diffusion MRI on fiber orientation estimation. Theory and Methods It is well established that method used to combine signals different coil elements in can have an impact properties reconstructed image. Using a root‐sum‐of‐squares approach results signal follows effective noncentral‐χ distribution. As result, noise floor, minimum measurable absence any true signal, elevated. This particularly...
Purpose We introduce L2‐regularized reconstruction algorithms with closed‐form solutions that achieve dramatic computational speed‐up relative to state of the art L1‐ and L2‐based iterative while maintaining similar image quality for various applications in MRI reconstruction. Materials Methods compare fast methods employing L2‐regularization numerical phantom vivo data three applications; (i) Fast Quantitative Susceptibility Mapping (QSM), (ii) Lipid artifact suppression Magnetic Resonance...
Purpose To develop an efficient acquisition for high‐resolution diffusion imaging and allow in vivo whole‐brain acquisitions at 600‐ to 700‐μm isotropic resolution. Methods We combine blipped‐controlled aliasing parallel simultaneous multislice (SMS) with a novel slab radiofrequency (RF) encoding gSlider (generalized slice‐dithered enhanced resolution) form signal‐to‐noise ratio–efficient volumetric multislab acquisition. Here, multiple thin slabs are acquired simultaneously controlled...
This article introduces a constrained imaging method based on low-rank and subspace modeling to improve the accuracy speed of MR fingerprinting (MRF).A new model-based is developed for MRF reconstruct high-quality time-series images accurate tissue parameter maps (e.g., T1 , T2 spin density maps). Specifically, proposed exploits approximations images, further enforces temporal constraints capture magnetization dynamics. allows image reconstruction problem be formulated as simple linear...
Abstract Slice‐selective RF waveforms that mitigate severe B inhomogeneity at 7 Tesla using parallel excitation were designed and validated in a water phantom human studies on six subjects 16‐element degenerate stripline array coil driven with butler matrix to utilize the eight most favorable birdcage modes. The waveform design applied magnitude least‐squares (MLS) criteria an optimized k ‐space trajectory significantly improve profile uniformity compared conventional (LS) designs. Parallel...
Magnetic resonance (MR) fingerprinting is a new quantitative imaging paradigm, which simultaneously acquires multiple MR tissue parameter maps in single experiment. In this paper, we present an estimation-theoretic framework to perform experiment design for fingerprinting. Specifically, describe discrete-time dynamic system model spin dynamics, and derive bound, i.e., the Cramér-Rao characterize signal-to-noise ratio (SNR) efficiency of We then formulate optimal problem, determines sequence...
Purpose To enable fast reconstruction of quantitative susceptibility maps with total variation penalty and automatic regularization parameter selection. Methods ℓ 1 ‐Regularized mapping is accelerated by variable splitting, which allows closed‐form evaluation each iteration the algorithm soft thresholding Fourier transforms. This also renders estimation practical. A weighting mask derived from magnitude signal can be incorporated to allow edge‐aware regularization. Results Compared nonlinear...
We add user-controllable direct currents (DC) to the individual elements of a 32-channel radio-frequency (RF) receive array provide B0 shimming ability while preserving array's reception sensitivity and parallel imaging performance.
This paper introduces a statistical estimation framework for magnetic resonance (MR) fingerprinting, recently proposed quantitative imaging paradigm. Within this framework, we present maximum likelihood (ML) formalism to estimate multiple MR tissue parameter maps directly from highly undersampled, noisy k-space data. A novel algorithm, based on variable splitting, the alternating direction method of multipliers, and projection method, is developed solve resulting optimization problem....
Purpose MR fingerprinting (MRF) is a technique for quantitative tissue mapping using pseudorandom measurements. To estimate properties such as T 1 , 2 proton density, and B 0 the rapidly acquired data are compared against large dictionary of Bloch simulations. This matching process can be very computationally demanding portion MRF reconstruction. Theory Methods We introduce fast group algorithm (GRM) that exploits inherent correlation within dictionaries to create highly clustered groupings...