The aim of the research. Development and implementation of new methods for pre-operative staging of advanced ovarian, gastric and colorectal cancer to improve patient selection for cytoreductive surgery and increase its radicality.Materials and methods. Data from 120 patients with advanced ovarian cancer, 28 with advanced gastric cancer and 119 with advanced colorectal cancer were analyzed. Preoperative detection of the incidence of peritoneal carcinoma and the possibility of surgery in radical or cytoreductive volume performed by CT with intravenous contrast (72 patients with ovarian cancer, 17 patients with gastric cancer, and 69 patients with colorectal cancer), and MR T1 and T2, contrast-enhanced T1, and diffuse-weighted sequences (48 patients with ovarian cancer, 11 patients with gastric cancer, and 50 patients with colorectal cancer). Subsequently, preoperative and intraoperative assessment of the prevalence of the tumour process with peritoneal carcinoma index (PCI) by Sugarbaker was performed.Results. A statistically significant increase in the informativeness of the preoperative assessment of the incidence of tumour process in peritoneum and the presence of distant metastases using DWI / MRI compared with CT with intravenous contrast was determined. Patients from all groups were categorized according to the completeness index of cytoreduction achieved by preoperative staging and patient selection using DWI / MRI and CT. The use of DWI / MRI allowed to significantly reduce the number of suboptimal and non-optimal cytoreductive interventions.Conclusions. DWI / MRI has made it possible to significantly improve the preoperative incidence of advanced ovarian, gastric, and colorectal cancer compared to CT, predict the radicality of future surgery, and detect inoperable cases.