Diffusion-weighted echo planar imaging (DW-EPI) suffers from geometric distortion due to low phase-encoding bandwidth. Read-out segmented echo planar imaging (RS-EPI) reduces distortion but residual distortion remains in extreme cases. Additional corrections need to be applied, especially for radiotherapy applications where a high degree of accuracy is needed. In this study the use of magnetic field map corrections are assessed in DW-EPI and RS-EPI, to reduce geometric uncertainty for MRI-guided radiotherapy applications. Magnetic field maps were calculated from gradient echo images and distortion corrections were applied to RS-EPI images. Distortions were assessed in a prostate phantom by comparing to the known geometry, and in vivo using a modified Hausdorff distance metric using a T2-weighted spin echo as ground truth. Across 10 patients, field map-corrected RS-EPI reduced maximum distortion by 5 mm on average compared to DW-EPI (σ = 1.9 mm). Geometric distortions were also reduced significantly using field mapping with RS-EPI, compared to RS-EPI alone (p ≤ 0.05). The increased geometric accuracy of these techniques can potentially allow diffusion-weighted images to be fused with other MR or CT images for radiotherapy treatment purposes.

中文翻译：

---

读出的分段回波平面成像中的场图校正可减少MRI引导放射治疗中前列腺DWI中的空间畸变。

扩散加权回波平面成像（DW-EPI）由于相位编码带宽低而遭受几何失真。读出的分段回波平面成像（RS-EPI）可以减少失真，但在极端情况下仍会残留残余失真。需要进行其他更正，尤其是对于需要高度准确性的放疗应用。在这项研究中，在DW-EPI和RS-EPI中评估了磁场图校正的使用，以减少MRI指导的放射治疗应用的几何不确定性。从梯度回波图像计算出磁场图，并将畸变校正应用于RS-EPI图像。通过与已知几何体进行比较来评估前列腺体模中的畸变，并在体内使用修正的Hausdorff距离度量（使用T2加权自旋回波作为地面实况）进行评估。在10位患者中，经现场图校正的RS-EPI与DW-EPI（σ= 1.9 mm）相比，平均最大失真降低了5 mm。与单独使用RS-EPI相比，使用RS-EPI进行场映射还可以显着减少几何变形（p≤0.05）。这些技术的提高的几何精度可以潜在地使扩散加权图像与其他MR或CT图像融合，以进行放射治疗。