Diffusion-weighted imaging (DWI) has shown promisting in detecting small lesions, staging, evaluating treatment response in the rectal tumors. However, geometric distortions, imaging blurring and ghosting artifacts in single-shot echo-planar imaging (ss-EPI) make DWI difficult to interpret. Readout-segment EPI (rs-EPI) is a new approach to reduce susceptibility artifacts and blurring in DWI. In this study, we qualitatively and quantitatively compare the images quality of ss-EPI and rs-EPI for rectal cancer DWI. This study was approved by the institutional review board, and written informed consent was obtained from all participants before imaging. 61 patients (40 males and 21 females; average age, 56.4 ± 12.9 years old) with rectal caner were enrolled in this study. All MR imaging were performed on a 3T MR scanner (MAGNETOM Skyra, Siemens AG, Erlangen, Germany) with 18-channel soft coil. DWI was acquired using ss-EPI (FOV of 216×216 mm2, matrix of 128×128, TR/TE of 5000/88 ms, 25 slices, slice thickness of 4 mm, 2 b values of 0 and 1000 s/mm2, iPAT of 2, average is 1 for b=0 and 3 for b=1000) and rs-EPI (FOV of 216×216 mm2, matrix of 160×160, TR/TE1/TE2 of 5000/66/108 ms, 25 slices, slice thickness of 4 mm, 2 b values of 0 and 1000 s/mm2, iPAT of 2, average is 1 for b=0 and 3 for b=1000) with a segmentation of 5 shots in readout. One radiologist with the experience of 5 years evaluated the image quality based on the geometric distortions, blurring, and identification of lesion using a five point scale. Regions of interest (ROIs) were drawn in the central slice of the tumor on the ADC maps. The scores of image quality, SNR of tumor, SNR of healthy tissue, CNR between tumor and healthy tissue, and ADC values of tumor, ADC values of healthy tissue of the ss-EPI and rs-EPI using student’s t-test.An example case of a patient with rectal tumor was shown in figure 1. The score of image quality is higher in rs-EPI than ss-EPI (3.9±0.7 vs. 3.1±0.8, P <0.05). The SNR of tumor and healthy tissue are higher in rs-EPI than ss-EPI (tumor: 210.5±94.2 vs. 38.9±18.1; healthy tissue: 91.2±46.0 vs. 18.6±7.2; P <0.001 for both). The CNR is higher in rs-EPI than ss-EPI (119.2±62.6 vs. 20.3±13.9, P <0.001). The ADC value of tumor is similar in rs-EPI and ss-EPI (1.10×10-3 mm2/s±0.23 vs. 1.10×10-3 mm2/s±0.21, P >0.05), but of healthy tissue is higher in rs-EPI than ss-EPI (1.72×10-3 mm2/s±0.34 vs. 1.59×10-3 mm2/s±0.37, P <0.001). In both rs-EPI and ss-EPI, the tumor area has lower ADC values than healthy tissue (Figure 2).DWI is a promising method to differentiate pathological from healthy tissues in rectal tumorss. rs-EPI is based on a segmentation of k-space into several shots along the readout direction to shorten the ecaho spacing for higher resolution and lower susceptibility in DWI. In our studies, the DWI image quality was significantly improved by using rs-EPI than ss-EPI sequences in retal tumors in both qualitative and quantitative analysis. rs-EPI sequence is useful for DWI to improve the image quality for evlauting leisions in the patients with rectal tumors.