Imaging Insights on the Aorta in Aging

Abstract

The aorta has 2 main functions, conduit and cushion, and is designed to transmit blood to the periphery and buffer pulsatile stress from ventricular contraction. In the interaction between the structural and functional changes of the aorta, aging and disease processes impact on aortic material properties and hemodynamics. For a comprehensive assessment of changes in aortic structure and function associated with aging and disease, noninvasive cardiovascular imaging techniques, especially magnetic resonance imaging, have recently been developed. Magnetic resonance imaging allows for direct and accurate measurement of different aortic characteristics including structural measures such as aortic area or volume, aortic length, curvature, and aortic wall thickness and functional measures such as aortic strain, distensibility, and pulse wave velocity. Excellent reproducibility of magnetic resonance imaging methods allows us to assess the response of the whole aorta to both pharmacological and nonpharmacological therapies. Aortic flow and functional assessment could be added to clinical routine cardiac magnetic resonance as a comprehensive imaging modality primarily performed for the noninvasive evaluation of left ventricular function, left ventricular load, and vascular/ventricular coupling. New techniques such as 4-dimensional flow could provide and further elucidate the combined age-related effects of altered aortic geometry and function. This following review will describe the pathophysiological aspects of the aorta and the ability, value, and prospects of cardiovascular imaging, especially magnetic resonance imaging, to study age-related changes in aortic structure and function and assess the relationship between these alterations and cardiovascular disease.

Keywords: aorta; cardiovascular disease; hemodynamics; magnetic resonance imaging.

Figure 1

Morphological evolution of the human aorta with age. Note that early modification of the aorta include widening of the aorta, particularly the ascending segment accompanied by widening of the arch and finally marked tortuosity. Automated segmentation of aortic volume on isotropic 3D-SSFP MRI ECG and respiratory gated acquisitions.

Figure 2

Black-blood spin echo T1-weighted image to measure aortic wall thickness. The thickness of descending aortic wall was measured using electronic calipers at 4 standard positions: 12, 3, 6, and 9 o'clock, and calculated as the average value of these 4 measurement.

Figure 3

Measurement of aortic distensibility in MRI. (A) Magnetic resonance imaging (MRI) shows 3-dimensional reconstruction of the thoracic aorta with transverse aortic dynamic acquisition plane (red). (B) Result of the semi-automated segmentation of the ascending aorta (green contour). (C) Resulting cross-sectional area to cardiac cycle time curve; Reprinted from Redheuil et al with permission of the publisher.

Figure 4

The change in ascending aortic distensibility with aging. (A) Ascending aorta strain (dot) and distensiblity (squares) by decades of age. (B) Ascending aortic distensibility (age<50=red dots and >50 years=blue dots);Reprinted from Redheuil et al with permission of the publisher.

Figure 5

Measurement of arch PWV in MRI using ARTFUN software (LIB, INSERM 1146, France). (A) Phase contrast cine transverse view. (B) Aortic arch view with steady state free precession sequence. (C) Measurement of the transit distance in the aortic arch. Numbers correspond to those in A and B. (D) Flow wave curves of ascending aorta and descending aorta after peak flow normalization. Transit time is measured as the average time shift that minimizes the least squares difference between systolic upslope data points of the ascending and descending aortic flow curves;Reprinted from Ohyama et al with permission of the publisher.

Figure 6

The change in arch PWV with aging in MESA study. Dots indicate median values and bars indicate 25%ile and 75%ile for each age decade. Lines connect each dots;Reprinted from Ohyama et al with permission of the publisher.

Figure 7

4D flow images of an 80-year-old subject free from overt cardiovascular disease.