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.

中文翻译：

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用于 1.5 T 全身扩散加权 MR 成像的集成切片特定动态匀场

客观的

将集成切片特定动态垫片 (iShim) 与失真校正后处理与传统 3D 体积垫片进行比较，以减少 1.5 T 全身扩散加权成像 (WB-DWI) 中的伪影和信号损失。

方法

十名志愿者使用传统的 3D 体积垫片和 iShim 进行了 WB-DWI。连续 48 名患者接受了 WB-DWI，仅使用体积垫片 ( n  = 24) 或 iShim ( n  = 24)。对于所有受试者，在合成的b  = 900 s/mm ²图像上测量成像站界面处的脊髓位移。在志愿者中比较信号强度比，计算为高敏感性梯度区域（胸骨）的平均信号强度除以低敏感性梯度区域（椎体）的平均信号强度。对于患者，图像质量从 1 级到 5 级（1 = 差，5 = 极好）。从 1 到 4（1 = 2 + 步，4 = 0 步）记录信号强度不连续性分数。一种< 0.05 的p值被认为是显着的。

结果

使用 iShim 在志愿者的胸椎交界处和在患者的颈椎和胸椎交界处( p < 0.05)，脊髓位移伪影较低( p  < 0.05)。与体积垫片序列相比，iShim 的健康志愿者胸骨/椎骨信号强度比更高 ( p  < 0.05)。体积匀场和 iShim 患者组在图像质量和信号强度不连续性评分方面没有显着差异。

结论

iShim 减少了成像站之间的脊髓位移伪影和磁敏感梯度引起的信号损失的程度。