ABSTRACT: The role of MR imaging in rectal cancer is well established in clinical practice but standard assessment has limitations. This thesis investigates new MR imaging methods and their diagnostic relevance in patient staging and management. It is divided in 2 parts: Part I focuses on lymph node staging and Part II focuses on the patterns of sustained clinical complete response after neoadjuvant therapy in locally-advanced rectal cancer patients. Part I: Pelvic MR imaging is the pillar of rectal cancer staging and the basis for optimal multidisciplinary patient management. A thorough and systematic knowledge of the relevant anatomy, the key staging features and the particularities of early, low and mucinous tumours is mandatory for MR imaging interpretation and is provided as an educational review. Lymph node status is one of the key staging features for risk stratification, but evaluation is hampered by limited MR imaging accuracy. Two new methodologies - Susceptibility Perturbation MR Imaging and Higher-order Diffusion MR Imaging - are introduced as original research. These methods were tested ex-vivo at ultra-high field (16.4 Tesla) in mesorectal lymph nodes and the mechanisms underlying the emerging contrasts were elucidated using quantitative histology. The experiments were then translated in-vivo upon patient staging in a clinical scanner (1.5 Tesla) and confronted with standard visual analysis by specialized radiologists. Part 2: Locally-advanced rectal cancer patients may have no signs of viable tumour after neoadjuvant therapy. “Watch-and-Wait” programs were developed to place such patients under strict surveillance instead of submitting them to likely unnecessary mutilating surgery. MR imaging plays a fundamental role in the selection and follow-up of such patients and an educational review of the methods upon which they rely is provided. To identify a clinical complete response in the early period after neoadjuvant therapy may be less important than to identify a clinical complete response that will be sustained over time, given complete responders that regrow present with a higher rate of distant metastases. Three new imaging patterns were reported for that purpose and are presented as original research – the split scar sign, the tumour scar depth angle difference and the scar thickness at second assessment. Susceptibility Perturbation MR Imaging and Higher-order Diffusion MR Imaging may allow more accurate lymph node staging. As such, they may have the potential to improve risk stratification and patient selection for neoadjuvant therapy. The split scar sign, the scar depth angle difference and the scar thickness at second assessment are simple tools to analyze on post-neoadjuvant therapy MR imaging that may aid in patient selection for “Watch-and-Wait” versus curative resection.