 Patients are sometimes needlessly left on long term medical therapy when their pCD has reached a chronic, fibrotic and irreversible stage. This practice needlessly exposes patients to clinical risk and health care systems to the financial expense of up to 20kpatientyear. More commonly, medical therapies are stopped prematurely, leading to prompt disease recurrence and chronic fistulisation with a major impact on quality of life. Importantly, it is very difficult to optimise therapies for pCD due to the absence of reliable disease measures. It is not possible to reliably correlate therapeutic drug monitoring to disease activity states. Due to all these limitations there has been an alarming paucity of well-designed randomised clinical trials. To this effect, both the 5th Scientific Workshop on pCD of the European Crohns and Colitis Organisation and the global consensus on the classification, diagnosis and treatment of pCD by the international Organisation of Inflammatory Bowel disease, have highlighted the urgent need of more sensitive and specific MR-markers of disease activity in pCD. Once reliable MR measures of disease activity have been validated then these can be used to design appropriate, inexpensive, sensitive and non-invasive MR based clinical activity scores. 