Keywords: DWI/DTI/DKI, Diffusion/other diffusion imaging techniques, Cardiac diffusion MRI, microscopic anisotropy, strong gradients, tensor-valued diffusion encoding, Diffusion Kurtosis imaging

Motivation: Tensor-valued diffusion encoding has been shown to provide more information on tissue microstructure than conventional diffusion weighting/tensor imaging.

Goal(s): Quantifying microscopic anisotropy, isotropic and anisotropic kurtosis in a human heart in vivo with a TE commonly used for DTI.

Approach: We used strong gradients ($$$\mathrm{G_{max}=300\,mT/m}$$$) in combination with linear, planar, and spherical tensor encoding with up to second-order motion compensation to achieve $$$\mathrm{b_{max} = 1500\,s/mm^2}$$$ with a TE of 74 ms.

Results: Estimated diffusion metrics matched the values reported in the literature while a shorter echo time was achieved due to the strong gradients used resulting in increased SNR and therefore image quality.

Impact: We implemented tensor-valued diffusion encoding with ultra-strong gradients for in vivo cardiac diffusion MRI in humans. This allows us to quantify microscopic anisotropy and kurtosis. 

Keywords: DWI/DTI/DKI, Diffusion Tensor Imaging

Motivation: SNR and parameter map accuracy in cardiac DTI are limited by maximum gradient strength related to motion-compensation and diffusion encoding time, precluding evaluation of helical cardiomyocyte structure.

Goal(s): Our goal was to improve SNR and cardiac DTI tissue microstructure characterization using an MR system capable of 200mT/m maximum gradient strength.

Approach: DTI was performed in human and swine subjects using standard (40mT/m), performance (80mT/m), and ultra-high-performance (200mT/m) maximum gradient strengths, with zeroth, first, and second-order motion compensating gradients.

Results: SNR and DTI tissue characterization were improved with ultra-high-performance gradients, however second-order motion compensation continued to be required to prevent motion artifacts.

Impact: Ultra-high performance 200mT/m gradients enable high SNR cardiac DTI with improved characterization of helical cardiomyocytes, potentially addressing the clinical need for noninvasive cardiac microstructure evaluation.  

Keywords: Diffusion Acquisition, Diffusion Tensor Imaging, Cardiac diffusion MRI, strong gradients, ZOOM, reduced field of view, non co-planar rf

Motivation: Cardiac diffusion tensor imaging (cDTI) with echo-planar imaging (EPI) requires long readouts to avoid aliasing artefacts if 2D-selective rf-pulses are not available. These prolong the echo time (TE) and increasing sensitivity to off-resonance artefacts.

Goal(s): The reduction of the excited and refocused field of view in the phase direction to reduce TE and sensitivity to image artefacts in cDTI.

Approach: We combine ZOnally-magnified Oblique Multi-slice (ZOOM) EPI (i.e. tilting the slice orientation of the refocussing rf-pulse) with ultra-strong gradients.  

Results: We were able to reduce TE (from ~70 ms to 59 ms) in cDTI considerably by reducing the FoV and using strong gradients. 

Impact: We reduced the echo time in cDTI with ultra-strong gradients which will allow us to use more advanced diffusion acquisitions (higher b-values and/or different gradient waveforms) in the heart in vivo.  

Keywords: Microstructure, Gradients

Motivation: Noninvasive quantification of axon diameter in the living human brain offers valuable insights into the mesoscopic organization of white matter. Current methods for mapping axon diameter using diffusion MRI are limited by gradient strength.

Goal(s): To evaluate the sensitivity of axon diameter mapping to small diameter axons on the Connectome 2.0 scanner (Gmax=500mT/m) compared to the original Connectome scanner (Gmax=300mT/m).

Approach: The AxCaliber-SMT model was fitted to diffusion MRI data in 10 healthy subjects scanned on Connectome 2.0 and Connectome 1.0.

Results: Median axon diameter in the corticospinal tract was 2.63um on Connectome 2.0 and 4.00um on Connectome 1.0.

Impact: Connectome 2.0 pushes the resolution limit and signal-to-noise ratio of axonal diameter mapping, allowing for greater sensitivity toward small diameter axons at the individual level for a variety of neuroscientific and clinical applications.

Keywords: Microstructure, Diffusion/other diffusion imaging techniques, High-performance head-only Gradient

Motivation: Detect a mild traumatic brain injury with a reliable diagnostic for staging disease state and the testing therapies for treating the malady in acute and long term phase. 

Goal(s): Develop a MRI biomarker that can be repeated used on patients especially in the warfighter population which have more that 500,000 diagnosed mTBI over the past 30 year.

Approach: Use of diffusion MRI to determine the white matter microstructural state namely the axon diameter.

Results: MAGNUS SE-DWI high-B can detect changes in axon diameter and follow these changes in single subject over time.

Impact: High B-value diffusion imaging (b > 30000 mm2/sec) can detect changes in mild TBI subjects that can be seen to progress through the recovery process.  The high-performance gradient system, MAGNUS, (200mT/m, 500T/m/s) scanning without peripheral nerve stimulation in the subject.

Keywords: Diffusion Analysis & Visualization, Diffusion/other diffusion imaging techniques, Gradient nonlinearity correction

Motivation: Correction of gradient nonlinearity effects on diffusion-sensitization is important. However, not all software packages and/or diffusion models can incorporate spatially-varying bvals/bvecs information.

Goal(s): Determine how significant nonlinearities are in the Human Connectome Project(HCP) dataset and investigate the feasibility of a spherical harmonics (SH)-based signal regeneration technique to directly incorporate nonlinearity effects and eliminate the need for additional information sharing.

Approach: FA, MD and angular error maps from 200 subjects were compared using different formats of correction.

Results: Nonlinearities are significant on HCP-dMRI data. The proposed SH-based signal regeneration approach allows the use of spatially invariant diffusion gradient tables with substantially reduced residual error.

Impact: Diffusion models and software not designed to incorporate spatially-varying bvals/bvecs can now take advantage of gradient nonlinearity correction. A reprocessed version of HCP dMRI dataset will be made publicly available in this format, along with the conventional gradient deviation tensors.

Keywords: Diffusion Acquisition, Diffusion Tensor Imaging, DW-SSFP

Motivation: At 7T the conventional spin-echo EPI diffusion sequence suffers from the B1+ inhomogeneity and geometric distortion due to refocusing RF pulses and EPI readout.

Goal(s): To develop a diffusion imaging sequence without refocusing RF pulses and EPI readout at 7T.

Approach: Develop a 3-dimensional DW-SSFP sequence with a spiral readout to reduce the geometric distortion, to maximize the diffusion gradient time, and to reduce susceptibility effect.

Results: The proposed DW-SSFP sequence was successful in reducing the B1+ inhomogeneity, the geometric distortion, and the susceptibility effect compared to the spin-echo EPI diffusion sequence using cadaveric head specimens at 7T.

Impact: This sequence enables the acquisition of high-resolution diffusion images that do not suffer from the B1+ inhomogeneity and geometric distortion often observed at 7T. It provides good quality fiber tracts and fractional anisotropy maps of the brain.

Keywords: DWI/DTI/DKI, Diffusion Tensor Imaging

Motivation: In neuroscientific researches, 3T DWI provides limited resolution while 7T DWI suffers from challenges such as shorter relaxation time and increased field inhomogeneity.

Goal(s): To evaluate the performance of 5T in high-resolution whole brain multi-shell DWI.

Approach: 1.1 mm-isotropic whole brain DWI with 2 shells was acquired using multi-band single-shot 2D EPI on 5T. DTI metrics and MSMT-CSD model were computed. The nearly identical acquisition parameters and data processing were applied to the same subject on 3T.

Results: 5T DWI resolved brain structural connectivity more accurately than 3T. Better FA contrast was observed at 5T, demonstrating higher SNR achieved at 5T.

Impact: The feasibility of simultaneously achieving high spatial resolution and adequate q-space sampling in practical acquisition time at 5T demonstrated its potential as a new tool in DWI-based neuroscientific studies.

Keywords: DWI/DTI/DKI, Low-Field MRI, Tetrahedral Encoding

Motivation: The project aimed to tackle extended DTI scan durations, worsened by low SNR at low fields, striving to boost efficiency while preserving results' accuracy at lower SNR levels.

Goal(s): The study sought to create an ML-based approach to shorten DT-MRI scans while ensuring reliable tensor estimation despite low SNR challenges at ULF.

Approach: ML models, trained on synthetic data, predicted diffusivities and principal eigenvectors from four diffusion-weighted images, factoring in simulated noise and gradient rotations for noise and motion.

Results: The models estimated diffusivities and fibre orientations with fewer data, showing promise for ULF tractography. Suggesting shorter DTI scans are possible at ULF.

Impact: Our results are relevant to clinicians and researchers using low-field MRI, potentially enabling faster DT-MRI scans, opening avenues for efficient DTI in challenging settings, and making fibre mapping more accessible with reduced acquisition scan times.

Keywords: DWI/DTI/DKI, Diffusion Tensor Imaging

Motivation: The employment of DTI in ULF MRI systems demonstrates considerable potential for examining microstructural variations in neuropathology and therapy. Although confronted with the inherent obstacle of low SNR at ULF, incorporating DTI yields an array of benefits. These advantages involve heightened accessibility, diminished costs, and superior patient care, while simultaneously extending the range of application possibilities for this crucial imaging modality throughout diverse healthcare contexts.

Goal(s): The implementation of DTI on an ULF MRI scanner.

Approach: DTI protocol was successfully implemented at 0.05 T.

Results: This study demonstrated the successful implementation of DTI protocol on an ULF MRI system.

Impact: This study explored the potential of a 0.05 T MRI system to increase MRI accessibility. Successful DTI implementation demonstrated the scanner's capacity to examine microstructural changes, highlighting its promising application in this field.