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

Abstract

The aim of this study was to determine the value of flow-sensitive four-dimensional MRI for the assessment of pulse wave velocity as a measure of vessel compliance in the thoracic aorta. Findings in 12 young healthy volunteers were compared with those in 25 stroke patients with aortic atherosclerosis and an age-matched normal control group (n 5 9). Results from pulse wave velocity calculations incorporated velocity data from the entire aorta and were compared to those of standard methods based on flow waveforms at only two specific anatomic landmarks. Global aortic pulse wave velocity was higher in patients with atherosclerosis (7.03 6 0.24 m/ sec) compared to age-matched controls (6.40 6 0.32 m/sec). Both were significantly (P < 0.001) increased compared to younger volunteers (4.39 6 0.32 m/sec). Global aortic pulse wave velocity in young volunteers was in good agreement with previously reported MRI studies and catheter measurements. Estimation of measurement inaccuracies and error propagation analysis demonstrated only minor uncertainties in measured flow waveforms and moderate relative errors below 16% for aortic compliance in all 46 subjects. These results demonstrate the feasibility of pulse wave velocity calculation based on fourdimensional MRI data by exploiting its full volumetric coverage, which may also be an advantage over standard two-dimensional techniques in the often-distorted route of the aorta in patients with atherosclerosis. Magn Reson Med 63:1575-1582, 2010. V C 2010 Wiley-Liss, Inc. Key words: pulse wave velocity; compliance; phase contrast; atherosclerosis; aorta Increased pulse wave velocity (PWV) as a measure of aortic stiffness is an important marker for both agerelated changes in aortic compliance and the presence of atherosclerosis (1,2) and is an independent predictor of cardiovascular mortality and stroke (3,4). Reliable measurement of PWV is of particular interest for monitoring the progression or regression of vessel compliance during therapy (5,6).Pressure catheter measurements can be considered the gold standard for the assessment of the development of aortic pressure wave, but their use is limited due to the invasiveness of the procedure (7). To provide a noninvasive estimate of PWV, phase contrast (PC) MRI has been applied in a number of in vivo studies determining blood flow based on flow waveform measurements in single two-dimensional (2D) planes transecting the aorta (8-10). For PWV estimation, typically transit-time methods are employed estimating temporal differences of specific features of blood flow waveforms, e.g., time from foot to foot or peak to peak, between two locations of the vessel with known distance (11-24). However, the precision of this method highly depends on the exact calculation of flow difference and distance between only two measuring points (16,25,26).Methodological improvements include a more continuous evaluation along a vessel center line and cross-correlation (XCor) analysis for the estimation of waveform delays, which improved the accuracy of PWV...

Pulse wave velocity with 4D flow MRI: Systematic differences and age-related regional vascular stiffness

“…An age-based comparison of our results on global PWV in the descending aorta corresponding high-temporal resolution PWV data available in the literature provides complementary support of the promising performance of 4D flow MRI (see Table 3). This accord well with previous comparisons between 4D flow MRI and methods with higher temporal resolution 14,18 . Nevertheless, further studies are needed to assess the impact of temporal resolution, as well as spatial resolution, on PWV estimates.…”

“…if temporal resolution is low, or if data is noisy) directly impacts the precision of the PWV estimate. The situation becomes different when the distance in not regarded as fixed, as in the present study and previous 4D flow MRI studies 14,18 . Treating distance as a continuous variable enables the use of analysis locations along the entire aorta.…”

“…The approach used here is similar to that used in previous 4D flow MRI studies in that is exploits the volumetric nature of the data and extracts complete pulsatile flow waveforms at multiple locations 14,18 . Similar methods have also been used with 2D in-plane PC-MRI and 1D FVE, where velocity-time profiles rather than complete pulsatile flow waveforms are measured 8,26 .…”

“…The invasiveness of the gold standard technique and the limitations of the current clinical approach have prompted the development of alternative means of estimating PWV 5 . Notably, MRI has evolved as a promising method [6][7][8][9][10][11][12][13][14][15][16][17][18] The merits of MRI for the estimation of PWV include the capabilities of obtaining: 1) angiographic images that permit accurate determination of vascular distance and 2) an arbitrary number of velocity or flow waveforms at any location in the body. MRbased PWV estimation has primarily been done with 2D cine phase-contrast (PC) MRI 6,9-11, 13 .…”

“…Recently, some studies have explored PWV estimation based on 3D cine PC-MRI ("4D flow MRI") 14,17,18 . The most interesting feature of 4D flow MRI for PWV estimation is its full 4D spatiotemporal coverage of velocity data.…”