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iShim and Water Excitation Improves the Signal-to-Noise Ratio on q-Space Imaging

The qualitative evaluation of the central nervous system (CNS) using magnetic resonance imaging (MRI) has recently become possible owing to the introduction of diffusion-weighted imaging (DWI). This study aimed to examine whether the signal-to-noise ratio (SNR) could be increased by combining integrated slice-by-slice shimming (iShim) with a fat suppression (FS) method other than short-tau inversion recovery (STIR) in diffusion-weighted imaging (DWI) and q-space imaging (qsi).

A cross-sectional study was conducted and 10 Japanese non-symptomatic volunteers (mean [standard deviation (SD)] age, 33.5 [9.2] years; 8 males, 2 females) were included. All participants underwent imaging of the cervical-upper thoracic spine. The authors acquired DWI images (b-values: 0 and nine steps from 400 to 10,000 s/mm2 for six axes) using a prototypical single-shot echo planar imaging sequence by combining two types of shimming (3D Shim and iShim) and two types of FS (STIR and water excitation [WE]) in 10 volunteers. In the DWI study, the SNR for each b-value, FS effect in the b0 image, and distortion in the added image (b0 - b10,000) were evaluated for the above-mentioned four imaging methods. qsi involved original DWI images. In the qsi study, the SNR was evaluated.

The results showed that with regard to both 3D Shim and iShim, the SNRs were significantly higher when using WE than when using STIR in b0 - b900 images (p < 0.01). For 3D Shim, however, the SNR increase effect of WE disappeared (p < 0.01) at b1600 or higher. For iShim, the SNR increase effect of WE was maintained up to b3600 (p < 0.01). The FS effect of STIR was superior to that of WE (p < 0.01). Although WE had a weak FS effect, its FS effect was greater with iShim than with 3D Shim (p < 0.01). In added images, with iShim, the spinal cord area became significantly smaller (p < 0.05), resulting in a less distorted image when compared with the 3D shim image. On qsi, with regard to both 3D Shim and iShim, the SNRs were significantly higher when using WE than when using STIR (3D Shim: p < 0.05; iShim: p < 0.01). The SNR of iShim/WE was superior to that of 3D Shim/WE (p < 0.05). 

In conclusion, the combination of iShim and WE has a high SNR on qsi. iShim might show improved clinical performance with regard to the detection of suspicious lesions in the neck region.


Article by Yoshifumi Sone, et al, from Japan and Germany.

Full access: http://mrw.so/4y8aGV

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