Detection of Acute Graft Rejection in Heart Transplant Patients by Estimation of T2

MRI acquisitions will be performed according to the already described method based on conventional Fast Spin Echo sequences and with an additional calibration pad positioned on the patient thorax (dedicated pad made by the Nancy CIC-IT with stable and adapted T2). MRI will be performed if possible before the biopsy and otherwise the radiologist will be kept blinded of the biopsy results.