Abstract:Objecitve To compare the value of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) and diffusion-weighted imaging (DWI) in evaluating the efficacy of neoadjuvant chemoradiotherapy (NCRT) for advanced rectal cancer. Methods Seventy-nine patients with rectal cancer undergoing total mesorectal excision (TME) after NCRT from January 2015 to June 2019 were selected for retrospective study.Pelvic MRI conventional plain scan combined with DWI or DCE-MRI were performed before and after NCRT, and their films for T and N staging before NCRT were compared with the postoperative pathological T and N staging.According to the postoperative pathology of TME, the patients were divided into pathological complete response (pCR) group and non-pCR group.DCE-MRI quantitative perfusion parameters, including transfer constant(K_trans), extravascular extracellular space volume ratio (V_e), efflux rate constant (K_ep) and apparent diffusion coefficient(ADC) value before and after NCRT were compared between pCR group and npCR group. Results Out of 79 patients after NCRT, 60 (75.9%) got T-stage reduction (histological tumor regression grading), 25 (31.6%) got N-stage reduction and 23 (29.1%) got pathologic complete remission.Before NCRT, K_trans, V_e and K_ep values were higher than those after NCRT, and ADC value was lower than that after NCRT; K_trans, V_e and K_ep values in pCR group were statistically higher than those in non-pCR group, and ADC value was lower than that in non-pCR group.After NCRT, K_trans value decreased, and ADC value increased in pCR group compared with non-pCR group(P<0.05，P<0.01). Conclusion Conventional MRI plain scan combined with DWI and DCE-MRI can accurately indicate the tumor stage of advanced rectal cancer.K_trans, V_e, K_ep and ADC values can quantitatively evaluate the efficacy of NCRT in advanced rectal cancer from a functional perspective.K_trans value and ADC value can predict the pathological remission of tumor.