## 4 Discussions
They reported that, on T2 images, the expert reader achieved an AUC of 0.92 with a sensitivity of 89%, and specificity of 76% while DWI significantly improved the AUC value to 0.999. They concluded that DWI increased diagnostic performance for LCR diagnosis compared to T2 imaging alone. To the best of our knowledge, this is the first study that assess DWI and DKI derived parameters performance in the differentiation of locally recurrent rectal cancer from scar/fibrosis tissue in patients subjected to TME after CRT. Our study showed that a single parameter of diffusion and perfusion was not able to identify local recurrent rectal cancer with high accuracy. However, the best results were obtained using the mean value of Kurtosis with an AUC of 0.72 and an accuracy of 75%. Considering a multivariate regression analysis (with the mean values of ADC, Kurtosis, fp, and Dp), a model mainly weighted by ADC and Kurtosis mean values obtained an AUC of 0.82 with an accuracy of 81%. Therefore, our results support the hypothesis that kurtosis effects could has a better performance in the differentiation of locally recurrent rectal cancer from scar/fibrosis tissue although DKI data were acquired with a maximum b value of 1000 s/mm\({}^{2}\). In general, high b-values are suggested in brain applications for the non-Gaussian kurtosis effect assessment [18] while in abdominal applications, for the lower signal-to-noise ratio due to the lower sensitivity of flexible surface coils compared with the head coil and lower T2 relaxation times, very high b-values are not usually applied. [PERSON] et al. [37] reported that the \"faster signal decay precludes the application of such high b-values in the body trunk because of 2 effects: (1) the long echo time of the echo-planar imaging sequence due to the longer application of the diffusion gradients and (2) the strong signal attenuation in DWI using high b-values. Furthermore, many tissues exhibit higher ADC values compared with the brain, again resulting in faster signal decay\". Some authors have shown that kurtosis effects could be measured in abdominal and whole-body using 800 s/mm\({}^{2}\) as maximum b-values or less at 3T [12; 38; 39; 40; 41]. We acquired DKI using multiple b-values with a maximum of 1000 s/mm\({}^{2}\) that, coupled with the parallel imaging factor use, resulted in images with acceptable SNR. Our results of univariate analysis were not completely in agreement with the results presented by the [PERSON] et al. [24] that reported for the ADC value an accuracy of 93%, a sensitivity of 91%, and a specificity of 92% in the differentiating of locally recurrent rectal cancer from scar tissue with a cut-off ADC value of \(1.34\times 10^{-3}\) mm\({}^{2}\)/s. Some limitations of the study are the measurement of diffusion and perfusion parameters by manually drawing a ROIs slice by slice along tumor or scar/fibrosis tissue contours; this technique may entail an inter-observer variability. A reproducibility analysis of MR derived parameters was not performed, however the use of mean values for extracted parameter by volume of interest allows to obtain more robust measures. Moreover, the number of recruited patients is non-negligible, but not conspicuous. The retrospective nature of study may predispose to selection bias. Considering that the study is retrospective, the radiologists were not blinded by the radiological report, but were blinded by the histological and/or clinical follow-up results. However, it must be clearly stated that the purpose of this study was not to assess the influence of DWI on the diagnostic quality of observers, but to determine DWI ability to discriminate LCR against scar/fibrosis tissue. The calculation of DKI parameters may be suboptimal for the use of an acquisition protocol with 1000 m/s\({}^{2}\) as a maximum b value.