Incidence of MRI Sacro-Iliac Joint Anomalies in Young Women

500 women aged of 18 to 50 years old, including 100 women who gave birth within the year, referred to the Imaging department for pelvic MRI for the exploration of pelvic or gynecologic pathology will be recruited consecutively. MRI will be performed on a 1.5 T MRI according to standardized exploration of the pelvis and will include axial T1-weighted sequences and T2STIR (or T2 fat sat or T2 Dixon) of maximum 6 mm thickness . An additional Axial STIR sequence may be added as part of the research (duration 3 minutes), if the standard protocol does not include any STIR, T2 fat sat T2 or T2 Dixon sequence. SI lesions will be assessed in a centralized randomized and independent review of all MR images by 2 musculoskeletal radiologists according to ASAS criteria. Patients will complete a standardized questionnaire on the day of MRI to collect the following data : patient's and family history of chronic inflammatory disease, number and date of pregnancies, practice of sports, back pain, joint pain.