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4D Flow MR Imaging

Magnetic Resonance Imaging (MRI) techniques provide non-invasive, highly accurate anatomic depictions of the heart and vessels. The intrinsic motion sensitivity of MRI can be used to image vessels with phase contrast (PC) MRangiography, or to quantify blood flow [1–3]. Traditionally, MR imaging of flow is accomplished using methods that resolve two spatial dimensions (2D) in individual slices [4]. Alternatively, 3D spatial encoding offers the possibility of isotropic high spatial resolution and thus the ability to measure and visualize the temporal evolution of complex flow patterns in a 3D-volume. In this context, ECG synchronized flow-sensitive 3D MRI using 3-directional velocity encoding (also termed ‘flow-sensitive 4D MRI‘, ‘4D Flow MRI‘, ‘time-resolved 3D velocity mapping‘ or ‘4D PC-MRI‘) can be employed to detect and visualize global and local blood flow characteristics in targeted vascular regions (aorta, cranial arteries, carotid arteries, etc.) [5, 6]. The nature of such datasets (3 spatial dimensions, 3 blood flow velocity directions, and time) points towards the potential of flow-sensitive 4D MRI to provide detailed quantitative flow and vessel wall parameters with complete vascular coverage. A number of recent studies have indicated the potential of flow-sensitive 4D-MRI for the detailed visualization of complex flow patterns associated with healthy and pathologic hemodynamics [7–12]. Over the past few years, flow-sensitive 4D MR imaging has systematically improved to the point that it is possible to reliably acquire comprehensive flow information within reasonable scan times on routine clinical MR systems. However, the subsequent analysis and visualization of complex, three-directional blood flow within a 3D volume is still time consuming, and advanced data processing and 3D visualization tools are necessary. In this article we report the first experiences with a new software prototype* for analysis of 4D Flow data, developed by Siemens Healthcare in cooperation with the Medical Physics group at the University Hospital Freiburg, Germany. After a brief overview of MR imaging and data analysis methods, we present their application for the evaluation of flow-sensitive 4D MRI in different vascular territories in the human body. 4D Flow MR Imaging