School of Biomedical Engineering, Southern Medical University, Guangzhou, China.
Guangdong Provincial Key Laboratory of Medical Image Processing & Guangdong Province Engineering Laboratory for Medical Imaging and Diagnostic Technology, Southern Medical University, Guangzhou, China.
NMR Biomed. 2022 May;35(5):e4652. doi: 10.1002/nbm.4652. Epub 2021 Nov 24.
The purpose of this study was to investigate the feasibility of two-dimensional (2D) navigated, interleaved multishot echo-planar imaging (EPI) to enhance kidney diffusion-weighted imaging (DWI) in rats at 7.0 T. Fully sampled interleaved four-shot EPI with 2D navigators was tailored for kidney DWI (Sprague-Dawley rats, n = 7) on a 7.0-T small bore preclinical scanner. The image quality of four-shot EPI was compared with T -weighted rapid acquisition with relaxation enhancement (RARE) (reference) and single-shot EPI (ss-EPI) without and with parallel imaging (PI). The contrast-to-noise ratio (CNR) was examined to assess the image quality for the EPI approaches. The Dice similarity coefficient and the Hausdorff distance were used for evaluation of image distortion. Mean diffusivity (MD) and fractional anisotropy (FA) were calculated for renal cortex and medulla for all DWI approaches. The corticomedullary difference of MD and FA were assessed by Wilcoxon signed-rank test. Four-shot EPI showed the highest CNR among the three EPI variants and lowest geometric distortion versus T -weighted RARE (mean Dice: 0.77 for ss-EPI without PI, 0.88 for ss-EPI with twofold undersampling, and 0.92 for four-shot EPI). The FA map derived from four-shot EPI clearly identified a highly anisotropic region corresponding to the inner stripe of the outer medulla. Four-shot EPI successfully discerned differences in both MD and FA between renal cortex and medulla. In conclusion, 2D navigated, interleaved multishot EPI facilitates high-quality rat kidney DWI with clearly depicted intralayer and interlayer structure and substantially reduced image distortion. This approach enables the anatomic integrity of DWI-MRI in small rodents and has the potential to benefit the characterization of renal microstructure in preclinical studies.
本研究旨在探讨二维（2D）导航交错多发回波平面成像（EPI）在 7.0T 大鼠肾脏弥散加权成像（DWI）中的可行性。在 7.0T 小口径临床前扫描仪上，对 Sprague-Dawley 大鼠（n=7）的肾脏 DWI 进行了全采样交错四发 EPI 和 2D 导航定制。将四发 EPI 的图像质量与 T2 加权快速采集弛豫增强（RARE）（参考）和无并行成像（PI）及有并行成像（PI）的单次激发 EPI（ss-EPI）进行了比较。采用对比噪声比（CNR）评估 EPI 方法的图像质量。采用 Dice 相似系数和 Hausdorff 距离评估图像失真。对所有 DWI 方法的肾皮质和髓质进行平均扩散系数（MD）和各向异性分数（FA）的计算。采用 Wilcoxon 符号秩检验评估 MD 和 FA 的皮质-髓质差异。四发 EPI 在三种 EPI 变体中具有最高的 CNR，与 T 加权 RARE 相比具有最低的几何失真（平均 Dice：无 PI 的 ss-EPI 为 0.77，双二倍体采样的 ss-EPI 为 0.88，四发 EPI 为 0.92）。四发 EPI 衍生的 FA 图清楚地识别出与外髓内层内条纹相对应的高度各向异性区域。四发 EPI 成功区分了肾皮质和髓质之间的 MD 和 FA 差异。总之，2D 导航交错多发 EPI 可实现高质量的大鼠肾脏 DWI，清晰描绘层内和层间结构，大幅降低图像失真。该方法可保持小啮齿动物 DWI-MRI 的解剖完整性，并有望有益于临床前研究中对肾脏微观结构的特征描述。
