## 3 Results
### Quantitative Image Quality Analysis  
The SNR and CNR on DWI images were significantly different among three rs-EPI sequences (all \(p\) < 0.001), while these were not significantly different between 2 \(\times\) SMS rs-EPI and rs-EPI (all \(p\) > 0.001). Geometric distortions on DWI images were statistically different among the three groups of sequences and the geometric distortion of 2 \(\times\) SMS rs-EPI was the lowest (Table 4).  
The inter-observer agreement was excellent for ADC\({}_{\rm lesion}\) (ICC = 0.931 (0.895, 0.955), 0.963 (0.942, 0.976), and 0.854 (0.775, 0.906)) for rs-EPI, 2 \(\times\) SMS rs-EPI, and 3 \(\times\) SMS rs-EPI, respectively. The inter-observer agreement was excellent for ADC\({}_{\rm normalized}\) (ICC = 0.889 (0.825, 0.930), 0.885 (0.760, 0.938), and 0.854 (0.775, 0.906)) for rs-EPI, 2 \(\times\) SMS rs-EPI, and 3 \(\times\) SMS rs-EPI, respectively.  
In the comparison between rectal tumor tissues of ADC values, there was a significant difference among three rs-EPI sequences (1.19 \(\pm\) 0.21 vs.1.18 \(\pm\) 0.22 vs.1.10 \(\pm\) 0.26, \(p\) < 0.001). In the comparison between rectal normal tissues of ADC values, there was a significant difference among three rs-EPI sequences (1.68 \(\pm\) 0.13 vs. 1.66 \(\pm\) 0.14 vs. 1.54 \(\pm\) 0.20, \(p\) < 0.001). For rectal tumor tissue and normal rectal tissue, there were no significant differences between the 2 \(\times\) SMS rs-EPI and rs-EPI sequences (\(p\) = 0.068/\(p\) = 0.066); There was a significant difference of ADC values between 3 \(\times\) SMS rs-EPI and 2 \(\times\) SMS rs-EPI, 3 \(\times\) SMS rs-EPI and rs-EPI (all \(p\) < 0.001). With the increase of the acceleration factor, the ADC values of both normal rectal tissue and tumor tissue decreased, as shown in Table 5 and Figure 4.  
\begin{table}
\begin{tabular}{c c c c c c} \hline  & **Rs-EPI** & **2 \(\times\) SMS rs-EPI** & **3 \(\times\) SMS rs-EPI** & **\(X^{2}\) Value** & **\(p\) Value** \\ \hline SNR & & & & \\ b = 0 s/mm\({}^{2}\) & 120.95 \(\pm\) 21.66 & 119.52 \(\pm\) 23.27 & 111.88 \(\pm\) 19.31 ab & 36.105 & \textless{}0.001 \\ b = 1000 s/mm\({}^{2}\) & 53.31 \(\pm\) 7.15 & 52.79 \(\pm\) 7.58 & 52.42 \(\pm\) 8.09 ab & 13.040 & 0.001 \\ CNR & & & & & \\ b = 0 s/mm\({}^{2}\) & 4.84 \(\pm\) 0.47 & 4.88 \(\pm\) 0.47 & 4.74 \(\pm\) 0.55 ab & 32.109 & \textless{}0.001 \\ b = 1000 s/mm\({}^{2}\) & 4.26 \(\pm\) 0.67 & 4.31 \(\pm\) 0.67 & 4.18 \(\pm\) 0.75 ab & 18.588 & \textless{}0.001 \\ Geometric distortion & & & & & \\ b = 0 s/mm\({}^{2}\) & 3.49 \(\pm\) 0.32 & 3.47 \(\pm\) 0.32 & 3.51 \(\pm\) 0.33 ab & 13.231 & 0.001 \\ b = 1000 s/mm\({}^{2}\) & 3.57 \(\pm\) 0.38 & 3.52 \(\pm\) 0.33 & 3.61 \(\pm\) 0.43 ab & 25.529 & \textless{}0.001 \\ \hline \end{tabular} Note: a compared with rs-EPI, \(p\) < 0.05; b compared with 2 \(\times\) SMS rs-EPI, \(p\) < 0.05.  
\end{table}
Table 4: Comparison of quantitative evaluation indexes of three EPI sequences.  
\begin{table}
\begin{tabular}{c c c c c} \hline  & **rs-EPI** & **2 \(\times\) SMS rs-EPI** & **3 \(\times\) SMS rs-EPI** & **\(X^{2}\) Value** & **\(p\) Value** \\ \hline ADC\({}_{\rm lesion}\) (10\({}^{-3}\) mm\({}^{2}\)/s) & 1.19 \(\pm\) 0.21 & 1.18 \(\pm\) 0.22 & 1.10 \(\pm\) 0.26 ab & 40.582 & \textless{}0.001 \\ ADC\({}_{\rm Normalized}\) (10\({}^{-3}\) mm\({}^{2}\)/s) & 1.68 \(\pm\) 0.13 & 1.66 \(\pm\) 0.14 & 1.54 \(\pm\) 0.20 ab & 51.835 & \textless{}0.001 \\ \hline \end{tabular} Note: a compared with rs-EPI, \(p\) < 0.05; b compared with 2 \(\times\) SMS rs-EPI, \(p\) < 0.05.  
\end{table}
Table 5: The comparison of ADC value between three EPI sequences.