Fluss-sensitive 4D magnetresonanztomographie - Blutflusseigenschaften bei gesunden probanden und patienten mit erkrankungen der thorakalen aorta

Background: Modern magnetic resonance imaging (MRI) enables us to depict morphological details of the cardiovascular system using a three-dimensional (3D) data set. Phase contrast MRI (PC MRI) with its intrinsic sensitivity to flow and movement allows us to assess both vessel-morphology data and that of blood-flow velocities at the same time. The combination of time-resolved 3D imaging and acquisition of 3D blood-flow velocities (flow-sensitive 4D MRI) makes it possible to analyse blood-flow patterns in a highly detailed fashion. The acquired MRI-data includes three dimensions of velocity and one of time. Blood flow acceleration, antegrade and retrograde flow, helical flow and complex flow patterns can be depicted and interpreted in detail. The method has been introduced, it is validated in-vitro and first in-vivo results have been reported [1-9]. Data of healthy individuals with no known vascular pathologies [1, 2, 5, 8], of patients with defined pathologies of the thoracic aorta [3, 4, 6, 8, 9] and of those after surgical intervention [2, 6, 7, 9] were assessed. This article illustrates flow-sensitive 4D MRI and the method of 3D MR velocity mapping. The method's diagnostic and prognostic potential in aortic surgery is discussed below. Methods: For 3D MR velocity mapping a time-related 3D MRI dataset is acquired under ecg-gating and under respiration control. It provides both anatomical information and functional blood flow information. After data reconstruction and preprocessing, a software package (EnSight, Computational Engineering International, Apex, NC) allows blood flow visualisation in each part of the aorta using three different visualisation-modes: 2D velocity vector fields, 3D stream lines and 3D particle traces. Results: The assessed data show that flow-sensitive 4D MRI in combination with innovative methods of flow-visualisation makes it possible to visually interpret local and global blood flow patterns in healthy volunteers and patients in detail. Physiological blood flow patterns in normal aortas were visible. Aortic diseases such as aneurysms or dissections and graft replacement of the aorta are associated with major changes in local blood flow patterns. The presented method allows their qualitative characterisation on a highly-detailed level exceeding the possibilities offered by current standard procedures. Discussion: The method's potential for clinical application in aortic surgery must be evaluated in future studies. More patients and improved technical details and data quantification methods are therefore necessary.