Readout-segmented echo-planar imaging in diffusion-weighted imaging of the kidney: comparison with single-shot echo-planar imaging in image quality

Objective: The purpose of this study was to compare the image quality of readout-segmented echo-planar imaging (RS-EPI) and that of standard single-shot echo-planar imaging (SS-EPI) in the kidney in a rat model. Materials and methods: Twelve Wistar rats undergoing MRI examinations were imaged with two diffusion-weighted (DW) imaging protocols: a standard SS-EPI and a new RS-EPI protocol, both with a 1.0 x 1.0 x 3.0 mm voxel. The two groups of diffusion-weighted images were independently scored on geometric distortion, image blurring, signal dropout, and the overall image quality by two radiologists. Signal-to-noise ratio (SNR) and apparent diffusion coefficient (ADC) were measured on both sequences. Inter-rater agreement (IRA) was evaluated by Fleiss kappa (kappa) and inter-class correlation coefficient (ICC) statistics. Comparisons of image qualities were made by Wilcoxon signed-rank test and paired-sample t test. Results: Both RS-EPI and SS-EPI had good IRAs in scoring image qualities (kappa = 0.607-0.833) and measuring renal ADCs (ICC = 0.828-0.945). Compared to SSEPI, RS-EPI produced less geometric distortion (median score 1.5 versus 2.5, p < 0.0001), less image blurring (1.75 versus 2.0, p = 0.0003), less signal dropout (1.0 versus 3.0, p = 0.0001), and a lower score in overall image artifacts (4.25 versus 7.25; p < 0.0001). RS-EPI had higher SNR of renal DW images than SS-EPI (p < 0.001). The intra-variability of ADCs in cortex, outer medulla, and inner medulla ranged from 9.6 % to 11.1 % (Pearson correlation coefficient q = 0.6750.729; p < 0.001) between the two protocols. Conclusion: We showed that for DWI of the kidney at 1.0 x 1.0 x 3.0 mm(3) voxel sizes, the new protocol provided better image quality than standard SS-EPI protocol.