This study evaluates the reliability of functional MRI measurements in pelvic disease through quantifying repeatability and reproducibility, using healthy volunteers. The aim is to provide insights into the consistency of results across sessions and observers, informing the trustworthiness of functional MRI in assessing pelvic disease and particularly rectal cancers and guiding protocol optimization.

Volunteers will be required to complete a questionnaire to ensure their eligibility and safety for undergoing an MRI. This questionnaire, along with safety information, will be reviewed before each MR session.

Subsequently, volunteers will undergo three MRI sessions, ideally two on the same day, with the last session scheduled 10 to 17 days apart from the previous ones. Each session is expected to last approximately 60 minutes (several sequences), and no contrast agent will be injected at any point.

On the first day, volunteers will have an MRI on the 1.5 Tesla MR-Linac Unity (Elekta device) and an MRI on a standard 1.5 Tesla MRI (Siemens). Between days 10 to 17, they will exclusively undergo an MR-Linac session.

Inclusion Criteria:

• ≥ 18 yo
• Healthy
• Volunteer
• Ability to undergo an MRI

Exclusion Criteria:

• < 18yo
• Contraindication to undergoing an MRI (see safety questionnaire)
• Previous pelvic irradiation
• Pelvic pathology