Integrated slice-specific dynamic shimming for whole-body diffusion-weighted MR imaging at 1.5 T

Abstract

Objective To compare integrated slice-specific dynamic shim (iShim) with distortion correction post-processing to conventional 3D volume shim for the reduction of artefacts and signal loss in 1.5 T whole-body diffusion-weighted imaging (WB-DWI). Methods Ten volunteers underwent WB-DWI using conventional 3D volume shim and iShim. Forty-eight consecutive patients underwent WB-DWI with either volume shim (n = 24) or iShim (n = 24) only. For all subjects, displacement of the spinal cord at imaging station interfaces was measured on composed b = 900 s/mm2 images. The signal intensity ratios, computed as the average signal intensity in a region of high susceptibility gradient (sternum) divided by the average signal intensity in a region of low susceptibility gradient (vertebral body), were compared in volunteers. For patients, image quality was graded from 1 to 5 (1 = Poor, 5 = Excellent). Signal intensity discontinuity scores were recorded from 1 to 4 (1 = 2 + steps, 4 = 0 steps). A p value of < 0.05 was considered significant. Results Spinal cord displacement artefacts were lower with iShim (p < 0.05) at the thoracic junction in volunteers and at the cervical and thoracic junctions in patients (p < 0.05). The sternum/vertebra signal intensity ratio in healthy volunteers was higher with iShim compared with the volume shim sequence (p < 0.05). There were no significant differences between the volume shim and iShim patient groups in terms of image quality and signal intensity discontinuity scores. Conclusion iShim reduced the degree of spinal cord displacement artefact between imaging stations and susceptibility-gradient-induced signal loss.

Diffusion Tensor Imaging of Peripheral Nerves: Current Status and New Developments

“…Adjustment of linear shimming for individual slice locations, so-called dynamic shimming, 30 demonstrated the improvement of off-resonance correction in body diffusion MRI. 31 32 High-order shimming 33 to correct for beyond zeroth (constant offset) and first-order (linear) components of the off-resonance pattern has been well adopted in brain diffusion MRI, but it has not yet been thoroughly investigated in body diffusion MRI or peripheral nerve diffusion MRI.…”