4D magnetic resonance velocity mapping of blood flow patterns in the aorta in young vs. elderly normal subjects

Abstract

Four-dimensional magnetic resonance MR velocity mapping was developed to study normal flow patterns in the thoracic aorta using time-resolved cardiac gated threedirectional velocity data. Sixteen normal subjects were studied, one young group (average age 31 years) and one group with elderly people (average age 72 years). Blood flowed in a right-handed helix from the ascending aorta to the aortic arch. A straight flow pattern or a left-handed helix was seen in the descending aorta. Blood flow was never parabolic. Blood flowed forward in early systole, retrograde in mid-to-end systole, and forward again in diastole in all subjects as a basic pattern. Continuous retrograde flow over a long distance was not seen, but blood entered a retrograde flow column at various levels. In young people blood passed from the aortic valve to the mid-descending aorta in less than one heartbeat. In people in their sixties it took two heartbeats and in people older than 78 years, it took three heartbeats. The maximum systolic forward velocities were higher in young subjects than in elderly while the retrograde velocities were lower. J. Magn. Reson. Imaging 1999;10:861-869.1999 Wiley-Liss, Inc.Index terms: magnetic resonance velocity mapping; 4D aortic blood flow; blood flow in elderly; helical blood flow; blood flow patterns in one heartbeat THE FEASIBILITY of MR blood flow studies was suggested by Moran (1) and van Dijk (2). Clinical studies and verifications by Bryant et al (3), Nayler et al (4), and Firmin et al (5) followed soon thereafter. Klipstein et al (6) described blood flow patterns in the aorta with detailed velocity profiles, and Bogren et al (7) quantified ante-and retrograde flow. Two-directional velocity maps can be displayed as vector maps after computer animation of time-dependent flow fields in vessels or in the heart (8-14). Vector mapping has been used to describe the central flow fields in the normal aorta (15), in the pulmonary artery, in coarctation (14), and in aneurysms and grafts (16), and to analyze senescent blood flow changes and those caused by atherosclerosis (17). Vector mapping was performed in one slice only in the middle of the vessel to be examined, and each vector map represented the two-dimensional (2D) flow field in one slice of the imaged vessel during approximately 60-120 msec. Vector maps can be displayed in cine format. Even if 3D velocity mapping is performed and the third direction displayed separately, it is not a true 4D technique, since only one slice of the vasculature has been acquired and the data are not truly time resolved. Arrow maps reveal snap shots of the spatial organization of flow within the entire field. Streamline visualization was first used with non-gated 3D phase contrast angiography in the internal carotid artery and showed average flow trajectories and filling-time relationships (10). The method was subsequently improved by Buonocore (13), who later (18) described particle path visualization for time-resolved three-directional data sets in continuous slices covering t...

Three‐dimensional analysis of segmental wall shear stress in the aorta by flow‐sensitive four‐dimensional‐MRI

“…Findings from previous qualitative analyses of flow patterns showed righthanded helical flow patterns in the AAo and left-handed helicity in the DAo (17,19,20,23,38). Our data suggests that this helicity, which is derived from the in-plane component of the flow direction, is reflected by the distribution of WSS circ as shown in Fig.…”

Estimation of global aortic pulse wave velocity by flow‐sensitive 4D MRI

“…6a. In this case, previously reported methods relying on in-plane velocity measurements and evaluation of PWV along a vessel centerline (29)(30)(31)(32)(33)(34) are no longer applicable. Note also that the complex aortic shape and in particular the sharp bending of the distal descending aorta in this patient (see Fig.…”

“…Recently, more comprehensive three-dimensional (3D) CINE techniques in combination with three-directionally encoded velocities (flow-sensitive four-dimensional [4D] MRI) have been reported that provide information on multidirectional in vivo blood flow with full volumetric coverage of the vessel of interest (29)(30)(31)(32)(33)(34). It was the purpose of this study to investigate if PWV can be reliably estimated from 3D CINE PC data despite its lower temporal resolution by exploiting its full volumetric coverage.…”

Volumetric velocity measurements in restricted geometries using spiral sampling: a phantom study

“…Hence, in several 2D throughplane PC studies of maximum velocity and flow determinations in stenotic vessels, a multi-slice procedure was used [11,20]. With the advent of three-dimensional, three-directional velocity encoding sequences (here denoted 4D PC) [21][22][23], the possibility has emerged to quantify velocity and flow in multiple 4 dimensions, and in addition to visualize blood flow by streamlines and pathlines. These powerful possibilities offered by 4D PC have found a number of applications, and 4D PC has started to go beyond a visualization tool into a quantitative technique for extraction of velocity, flow and hemodynamically derived parameters such as wall shear stress [24] and kinetic energy [25].…”