Dynamic diffusion-tensor measurements in muscle tissue using the single-line multiple-echo diffusion-tensor acquisition technique at 3T

Abstract

When diffusion biomarkers display transient changes, i.e. in muscle following exercise, traditional diffusion tensor imaging (DTI) methods lack temporal resolution to resolve the dynamics. This paper presents an MRI method for dynamic diffusion tensor acquisitions on a clinical 3T scanner. This method, SL-MEDITATE (Single Line Multiple Echo Diffusion Tensor Acquisition Technique) achieves a high temporal resolution (4s) (1) by rapid diffusion encoding through the acquisition of multiple echoes with unique diffusion sensitization and (2) by limiting the readout to a single line volume. The method is demonstrated in a rotating anisotropic phantom, in a flow phantom with adjustable flow speed, and in in vivo skeletal calf muscle of healthy volunteers following a plantar flexion exercise. The rotating and flow-varying phantom experiments show that SL-MEDITATE correctly identifies the rotation of the first diffusion eigenvector and the changes in diffusion tensor parameter magnitudes, respectively. Immediately following exercise, the in vivo mean diffusivity (MD) time-courses show, before the well-known increase, an initial decrease which is not typically observed in traditional DTI. In conclusion, SL-MEDITATE can be used to capture transient changes in tissue anisotropy in a single line. Future progress might allow for dynamic DTI when combined with appropriate k-space trajectories and compressed sensing reconstruction.

Advanced MRI Techniques for Muscle Imaging

“…Muscle is an ordered fibrillar biological tissue that exhibits tissue anisotropy (i.e., diffusion of water is not unrestricted in all directions). [82][83][84][85][86] Muscular diffusion values also depend on the orientation of muscle fibers because the motion of water is least restricted parallel to fibers. Diffusion-weighted imaging (DWI) offers the opportunity to measure molecular diffusion noninvasively and to make meaningful inferences from such information in clinical contexts.…”

Spatially resolved kinetics of skeletal muscle exercise response and recovery with multiple echo diffusion tensor imaging (MEDITI): a feasibility study

“…One contributing factor to this discrepancy may be in effective diffusion time, which varies in the MEDITI echo train as opposed to the singular EPI-DTI value. We have previously noted this systematic error and studied it with simulations [27], finding the pre-exercise normalization, as employed in the present study, to dramatically reduce its influence on the signal kinetics. Also, the repeatability indicated by the ~5% coefficient of variation estimates over the dynamic series, which include multiple sources of variability (coil sensitivity, rotation artifact) in addition to the diffusion processing, is quite reasonable given the levels of activation in muscle shown in Figs 4-6.…”

“…Prior work has explored the diffusion-weighting pattern’s capturing of dynamic diffusion tensor behavior [24,27]; the current study focused upon spatially-resolved dynamic imaging. In this implementation, each of the 11 echoes in each MEDITI echo train was measured with a 5-petal Single TrAjectory radial (STAR) k-space acquisition [30].…”

“…The structure of the MEDITI pulse sequence and processing workflow is indicated in Figure 2; it was built on prior implementations of the MEDITATE approach [24,27], Multiple slice selective RF pulses (flip angles 61°/73°/85°/45°/85°) generated a train of 11 echoes (time to echo formation 90 to 245 ms; transverse relaxation encoding 18 to 108 ms; longitudinal relaxation encoding 0 to 183 ms) that was acquired alternately with low and high diffusion gradients that provided diffusion weighting from 145 to 718 (145, 225, 252, 337, 361, 389, 401, 521, 590, 633, 718) s/mm 2 over 11 different directions [24], Repetition time for each echo train was TR = 2 s. The sequence was prefaced by a spectrally adiabatic inversion recovery (SPAIR) fat suppression preparation. Prior work has explored the diffusion-weighting pattern’s capturing of dynamic diffusion tensor behavior [24,27]; the current study focused upon spatially-resolved dynamic imaging. In this implementation, each of the 11 echoes in each MEDITI echo train was measured with a 5-petal Single TrAjectory radial (STAR) k-space acquisition [30].…”

“…Recently, a new approach for compressing the required directional encodings has been demonstrated [24], titled “multiple echo diffusion tensor acquisition technique (MEDITATE)” and based on prior work in preclinical scanners [25,26], A single-voxel variant (SV-MEDITATE) has been applied to measure dynamic anisotropic diffusion exercise response in normal calf muscle [27] and thigh muscles in controls and dermatomyositis patients [28]. However, to produce a spatially-resolved variant of MEDITATE, k-space acquisition and reconstruction must be chosen to (a) include self-navigation of phase errors and (b) achieve sufficient temporal resolution to capture post-exercise recovery.…”