Age-related changes of regional pulse wave velocity in the descending aorta using Fourier velocity encoded M-mode.
ABSTRACT Aortic pulse wave velocity (PWV) is an independent determinant of cardiovascular risk. Although aortic stiffening with age is well documented, the interaction between aging and regional aortic PWV is still a debated question. We measured global and regional PWV in the descending aorta of 56 healthy subjects aged 25-76 years using a one-dimensional, interleaved, Fourier velocity encoded pulse sequence with cylindrical excitation. Repeatability across two magnetic resonance examinations (n = 19) and accuracy against intravascular pressure measurements (n = 4) were assessed. The global PWV was found to increase nonlinearly with age. The thoracic aorta was found to stiffen the most with age (PWV [thoracic, 20-40 years] = 4.7 ± 1.1 m/s; PWV [thoracic, 60-80 years] = 7.9 ± 1.5 m/s), followed by the mid- (PWV [mid-abdominal, 20-40 years] = 4.9 ± 1.3 m/s; PWV [mid-abdominal, 60-80 years] = 7.4 ± 1.9 m/s) and distal abdominal aorta (PWV [distal abdominal, 20-40 years] = 4.8 ± 1.4 m/s; PWV [distal abdominal, 60-80 years] = 5.7 ± 1.4 m/s). Good agreement was found between repeated magnetic resonance measurements and between magnetic resonance PWVs and the gold-standard. Fourier velocity encoded M-mode allowed to measure global and regional PWV in the descending aorta. There was a preferential stiffening of the thoracic aorta with age, which may be due to progressive fragmentation of elastin fibers in this region.
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ABSTRACT: The Bramwell-Hill model describes the relation between vascular wall stiffness expressed in aortic distensibility and the pulse wave velocity (PWV), which is the propagation speed of the systolic pressure wave through the aorta. The main objective of this study was to test the validity of this model locally in the aorta by using PWV-assessments based on in-plane velocity-encoded cardiovascular magnetic resonance (CMR), with invasive pressure measurements serving as the gold standard. Seventeen patients (14 male, 3 female, mean age ± standard deviation = 57 ± 9 years) awaiting cardiac catheterization were prospectively included. During catheterization, intra-arterial pressure measurements were obtained in the aorta at multiple locations 5.8 cm apart. PWV was determined regionally over the aortic arch and locally in the proximal descending aorta. Subsequently, patients underwent a CMR examination to measure aortic PWV and aortic distention. Distensibility was determined locally from the aortic distension at the proximal descending aorta and the pulse pressure measured invasively during catheterization and non-invasively from brachial cuff-assessment. PWV was determined regionally in the aortic arch using through-plane and in-plane velocity-encoded CMR, and locally at the proximal descending aorta using in-plane velocity-encoded CMR. Validity of the Bramwell-Hill model was tested by evaluating associations between distensibility and PWV. Also, theoretical PWV was calculated from distensibility measurements and compared with pressure-assessed PWV. In-plane velocity-encoded CMR provides stronger correlation (p = 0.02) between CMR and pressure-assessed PWV than through-plane velocity-encoded CMR (r = 0.69 versus r = 0.26), with a non-significant mean error of 0.2 ± 1.6 m/s for in-plane versus a significant (p = 0.006) error of 1.3 ± 1.7 m/s for through-plane velocity-encoded CMR. The Bramwell-Hill model shows a significantly (p = 0.01) stronger association between distensibility and PWV for local assessment (r = 0.8) than for regional assessment (r = 0.7), both for CMR and for pressure-assessed PWV. Theoretical PWV is strongly correlated (r = 0.8) with pressure-assessed PWV, with a statistically significant (p = 0.04) mean underestimation of 0.6 ± 1.1 m/s. This theoretical PWV-estimation is more accurate when invasively-assessed pulse pressure is used instead of brachial cuff-assessment (p = 0.03). CMR with in-plane velocity-encoding is the optimal approach for studying Bramwell-Hill associations between local PWV and aortic distensibility. This approach enables non-invasive estimation of local pulse pressure and distensibility.Journal of Cardiovascular Magnetic Resonance 01/2012; 14:2. · 4.44 Impact Factor
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ABSTRACT: Quantification of the age- and gender-specific in vivo mechanical characteristics of the ascending aorta (AA) will allow for identification of abnormalities aside from changes brought on by aging alone. Multiphase clinical CT scans of 45 male patients between the ages of 30 and 79 years were analyzed to assess age-dependent in vivo AA characteristics. The three-dimensional AA geometry for each patient was reconstructed from the CT scans for 9-10 phases throughout the cardiac cycle. The AA circumference was measured during each phase and was used to determine the corresponding diameter, circumferential strain, and wall tension at each phase. The pressure-strain modulus was also determined for each patient. The mean diastolic AA diameter was significantly smaller among young (42.6 ± 5.2 years) at 29.9 ± 2.8 mm than old patients (69.0 ± 5.2 years) at 33.2 ± 3.2 mm. The circumferential AA strain from end-diastole to peak-systole decreased from 0.092 ± 0.03 in young to 0.056 ± 0.03 in old patients. The pressure-strain modulus increased two-fold from 68.4 ± 30.5 kPa in young to 162.0 ± 93.5 kPa in old patients, and the systolic AA wall tension increased from 268.5 ± 31.3 kPa in young to 304.9 ± 49.2 kPa in old patients. The AA dilates and stiffens with aging which increases the vessel wall tension, likely predisposing aneurysm and dissection.Annals of Biomedical Engineering 07/2013; · 3.23 Impact Factor
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ABSTRACT: To assess the difference between thoracic and abdominal aortic pulse wave velocity (PWV) in apparently healthy subjects including young adults to elderly subjects. We performed PWV and distensibility measurements and analysis of thoracic and abdominal aortic segments in 96 apparently normal subjects aged 20-80 years with magnetic resonance (MR). Both unadjusted correlation and General Linear Model (GLM) analysis of log-transformed PWV (thoracic and abdominal aorta) and distensibility (four aortic cross-sections) were performed. Both thoracic and abdominal PWV values and distensibility values increased with age. In unadjusted analyses the correlation between the ln(thoracic PWV) and age (r = 0.71; P < 0.001) was stronger than between ln(abdominal PWV) and age (r = 0.50; P < 0.001). In GLM analysis, the only determinant of thoracic and abdominal PWV was age (F = 42.5 and F = 14.8, respectively; both P < 0.001). Similarly, correlation between ln(distensibility) and age was strong (r = -0.79, r = -0.67, r = -0.71, and r = -0.65 for ascending, descending, diaphragmatic, and low abdominal aorta, respectively; all P < 0.001). In GLM analysis, age was the major determinant for distensibility of the ascending aorta (F = 81.7; P < 0.001), descending aorta (F = 42.2; P < 0.001), diaphragmatic aorta (F = 39.2; P < 0.001), and low abdominal aorta (F = 32.8; P < 0.001). The thoracic aorta is less stiff than the abdominal aorta in young and middle-aged subjects, and stiffens more rapidly with age than the abdominal aorta, resulting in a stiffer thoracic than abdominal aorta at older age. J. Magn. Reson. Imaging 2014. © 2014 Wiley Periodicals, Inc.Journal of Magnetic Resonance Imaging 02/2014; · 2.57 Impact Factor
Age-related changes of regional pulse wave velocity in the descending aorta using Fourier velocity encoded MR M-mode
V. Taviani1, S. S. Hickson2, C. J. Hardy3, A. J. Patterson1, C. M. McEniery2, I. B. Wilkinson2, J. H. Gillard1, and M. J. Graves1
1Department of Radiology, University of Cambridge, Addenbrooke's Hospital, Cambridge, United Kingdom, 2Clinical Pharmacology Unit, University of Cambridge,
Addenbrooke's Hospital, Cambridge, United Kingdom, 3GE Global Research, Niskayuna, New York, United States
Central arteries, like the aorta, play a crucial role in buffering and attenuating the pulsatile nature of blood flow. Aging is the most important process involved in altering
arterial compliance. Over time, stiffening of the aorta reduces its buffering function, with adverse consequences on the left ventricle  and more peripheral arteries .
Although aortic stiffening with age has been extensively documented , the interplay between aging and regional arterial compliance is still a debated question, with
major implications for therapeutic interventions.
Previous MR studies have addressed the problem of quantifying regional arterial compliance either by direct measurement of arterial distensibility  or by pulse wave
velocity (PWV) measurement using cine phase contrast (CPC) with through-plane velocity encoding . Direct measurements of arterial distensibility are limited by the
fact that local pulse pressure is difficult to evaluate. The accuracy of PWV measurements by PC with through-plane velocity encoding can be degraded when short
arterial segments are considered. Fourier velocity encoded (FVE) M-mode can produce time-velocity profiles with high temporal and spatial resolution along a
relatively straight arterial segment . The aim of this work was to measure regional PWV in the descending aorta using FVE M-mode in a large cohort of healthy
subjects and to investigate the interplay between regional aortic stiffening and age.
Fifty-six healthy subjects (age range: 25-76 years, mean age: 53.1 years) participated in the study after providing written informed consent. All subjects were
normotensive and free from cardiovascular disease and medication. Images were acquired on a 1.5T whole-body imaging system (Signa HDx, GE Healthcare,
Waukesha, WI) using an 8-channel abdo-torso phased-array surface coil.
An ECG-triggered, oblique-sagittal double inversion recovery prepared fast spin-echo (FSE) sequence was used to localize the descending aorta (Figure 1a). The FVE
M-mode sequence consisted of a cylindrical excitation pulse, followed by a bipolar velocity-encoding gradient and a readout gradient applied along the axis of the
cylinder (pencil) . The sequence was gated to the cardiac R-wave and executed 32 times per heart cycle with the bipolar gradient amplitude stepped to a new value on
each new trigger. To increase the effective temporal resolution to 3.5ms, four interleaves were acquired, with the ECG trigger delay incremented by 3.5ms each time,
resulting in 128 time frames covering the first 450ms of the cardiac cycle. Thirty-two velocity-encoding steps were used, yielding a true velocity resolution of 9.4cm/s,
which resulted in aliasing of velocities greater than 150cm/s. A 24cm readout field of view (matrix size = 256×32) and a 2cm diameter cylindrical excitation pulse were
prescribed. Cylindrical excitation was achieved through an 8-cycle spiral trajectory which resulted in an inner aliasing ring diameter of 28.5cm.
FVE M-mode images (Figure 1b) were reformatted to yield Doppler-like time-velocity images (Figure 1c) along the length of the pencil . An automatic line detector
was used to extract the velocity profile as a function of time from each of the time-velocity images. The velocity profiles extracted from the time-velocity images at
different spatial positions were visualized as a velocity surface, each point of which represented velocity at a given time and position. Bilinear interpolation and the
gradient-based regularization technique, implemented in the Matlab (The Mathworks, Inc., Natick, MA) function gridfit , were used to smooth the obtained velocity
surface, with the smoothing parameter chosen for each subject on the basis of visual comparison with the original data points. The foot of the velocity wave was defined
at each spatial location as the intersection between a line fitted to the early systolic upslope (10% to 40% of peak velocity) and the zero velocity line.
Four planes, orthogonal to the descending aorta, were defined on the FSE scout image: 1) 2cm distal to the aortic valve; 2) at the level of the diaphragm; 3) midway
between location 2) and a location 3cm proximal to the aortic bifurcation; 4) 3cm above the aortic bifurcation (Figure 1a). PWV was computed over the entire length of
the pencil and for the three segments delimited by these planes, by linear regression of the foot of the wave at each position along the vessel as a function of the
corresponding location along the aorta (Figure 1d). Repeatability of segmental PWV was evaluated on a smaller cohort of 10 volunteers over two visits, a week apart.
Repeated regional PWVs were in good agreement (mean difference=0.19±0.82cm/s). A significant nonlinear relationship between overall PWV and age was found (2nd
order polynomial regression: r2=0.73, p<0.001) (Figure 2), confirming previous results . Overall PWV was found to decrease along the aorta (PWV1=6.4±2.1m/s;
PWV2=6.0±1.9m/s; PWV3=5.2±1.5m/s), with PWV3 significantly lower than both PWV1 and PWV2 (p<0.05). Two-way ANOVA showed a significant interplay
between age and position (p<0.01) (Figure 3). The distal thoracic aorta was found to stiffen the most with age (Seg1, PWV1(20-40ys)=4.7±1.1m/s; PWV1(60-
80ys)=7.9±1.5m/s), followed by the proximal (Seg2, PWV1(20-40ys)=4.9±1.3m/s; PWV1(60-80ys)=7.4±1.9m/s) and distal abdominal aorta (Seg3, PWV1(20-
Although peripheral arteries have been found to be stiffer than central arteries , the existing data concerning the descending part of the aorta are contradictory,
probably due to the small sample size and the different techniques used. Our results are in agreement with the two major MR studies conducted to date [4,5] and support
the well-known hypothesis of age-related degradation of elastin , mainly found in the thoracic aorta, as the major determinant of vascular stiffening.
In conclusion, we used the high spatial and temporal resolutions achievable with FVE M-mode to evaluate regional PWV in a large cohort of healthy subjects. We
found a nonlinear relationship between overall PWV and age and a preferential stiffening of the thoracic aorta with age.
Position along the vessel
Position of the foot of the wave
203040 506070 80
PWV [m/s] = 0.002·Age [ys]2 - 0.11·Age [ys] + 5.94
20-40ys 40-60ys 60-80ys
Figure 1 Figure 2 Figure 3
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