The aim of this study was to compare the value of two magnitude-based MR sequences, a contrast-enhanced ultrafast MR sequence and a cine MR sequence, for the detection of flow around the graft in the postoperative ascending thoracic aorta. Thirteen patients who underwent ascending aortic surgery for dissection (n = 11) and aneurysm (n = 2) were enrolled. They were referred to MRI for mediastinum enlargement on the chest x-ray or mediastinal symptoms. All patients had replacement of the diseased ascending aorta using a graft-inclusion technique (with wrapping of the native aorta over the graft). Delays between surgery and MRI ranged from 15 days to 8 years (mean: 10 months). All patients were examined using a T1-weighted spin-echo sequence, a magnitude-based cine gradient-echo sequence, and an ultrafast contrast-enhanced MR sequence. MR images of the cine and the contrast-enhanced sequences were retrospectively and independently analyzed by two qualified radiologists for evidence of flow or thrombus around the graft, including perigraft structure and aneurysmal formations. Evidence of flow was detected by both methods in all aneurysmal formations of the ascending aorta located at suture level (n = 6). Evidence of flow in the perigraft structure was found in seven cases by contrast-enhanced MR sequence and in only four cases by cine MR sequence. Contrast-enhanced ultrafast MR sequence could be proposed as a minimally invasive and fast modality for assessing the perigraft structure, in graft-inclusion surgical procedures of the ascending aorta, when noncontrast enhanced MR sequences do not exclude the possibility of flowing blood in this structure.