Accuracy of arterial pulse‐wave velocity measurement using MR

Abstract

The performance of a one-dimensional MR technique for the estimation of pulse-wave velocity in the aorta was evaluated. An expression for the error in this estimate was formulated and verified both by simulation and by experiment. On the basis of this formulation, guidelines for increasing the efficiency of the acquisition were established. The technique was further validated by comparison with pulse-wave velocity measurements made with a pressure catheter. All data were acquired from a latex tube driven by a pulsatile flow system. MR measurements of pulse-wave velocity in the tube were found to be very reproducible in the presence of white noise. Measurements by other techniques were in good agreement, falling within 2 SD of the mean. Because of its sensitivity and spatial resolution, this technique shows promise for making spatially resolved estimates of vessel distensibility. This would allow assessment of diseases, such as atherosclerosis, that cause local changes in the material properties of the vasculature. Index termsaortic compliance; pulse-wave velocity; MRI The distensibility of the aorta plays an important role in smoothing the blood flow delivered to the periphery and maintaining this flow during diastole (1). This is achieved by the reduction of the mechanical impedance seen by the ejecting left ventricle (2-4). Changes in aortic distensibility appear to correlate with age, coronary artery disease, and fitness (5-7). Specifically, particular changes have been attributed to the presence of atherosclerosis (8,9) or connective tissue disorders (10)(11)(12). Chronic increased vascular loading may lead to left ventricular hypertrophy and even heart failure, whereas changes in the material properties of the aortic wall and accompanying aneurysmal dilation commonly lead to sudden aortic dissection or rupture. An accurate, noninvasive method to estimate the material properties of the aortic wall could play an important role in the early diagnosis of vascular disease such as atherosclerosis and provide a guideline for surgical intervention in cases of aneurysmal dilation.The distensibility of blood vessels can be measured directly by imaging the fractional change in cross-sectional area of the vessel with given changes in pressure. This measurement has been made with cine x-ray angiography (13), ultrasound (14,15), x-ray CT (16), and MRI (6) coupled with either sphygmomanometer-or micromanometer-based blood pressure measurements. Low image resolution, motion, and the lack of local blood pressure measurements increase the error of these techniques. Estimates of blood vessel distensibility have also been obtained by measurements of pulse-wave velocity in the aorta. The pulse-wave Address reprint requests to E.A., Johns Hopkins Outpatient Center Room 4241, 601 N. Caroline Street, Baltimore, MD 21287-0845. E-mail: eatalar@mri.jhu.edu.. NIH Public Access NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript velocity is the rate at which a flow or pressure wave propagates down a vesse...

Estimation of left ventricular performance through temporal pressure variations measured by MR velocity and acceleration mappings

“…The aortic propagation pulse-wave was estimated from the ratio of the distance between two sections of the thoracic aorta (ascending and descending) over the time lag between the mean velocity curves vs. time obtained at these sections (12). This time lag (⌬t) was defined as the difference between two linear fittings of the velocity rise at the intersection of the time axis (Fig.…”

“…MRI methods of measuring blood flow velocity (7), total acceleration (8), pressure mapping (9 -11), and vessel compliance (12) have been well validated. Unlike other methods of measuring fluid motion, such as Doppler, MRI provides measurements of total acceleration (8), and indices for post-load (12).…”

“…Unlike other methods of measuring fluid motion, such as Doppler, MRI provides measurements of total acceleration (8), and indices for post-load (12). MRI is also capable of estimating the impulsive flow of the LV, which may be key in evaluating myocardial performances by MRI.…”

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

“…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 estimation but relied on 2D PC acquisitions in sagittal oblique slices exactly transecting the thoracic aorta (27,28). 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).…”

“…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)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(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).…”