This CMR study describes the quantile distribution of cross-sectional areas, distensibility and PWV of the thoracic aorta in heart-healthy children and young adults between their 3rd and 29th year of life. Defining the normal range for aortic size and bio-elastic properties is an important aid in the early detection of adverse aortic changes.
Knowledge of the size of the thoracic aorta is important for the treatment of patients with congenital and acquired cardiovascular diseases. CMR allows an exact assessment of the aortic anatomy, independent of acoustic windows, and is therefore an optimal tool to detect anatomic abnormalities of the aorta such as dilatation or aneurysm formation
. We provide normal data for aortic cross-sectional areas in the form of percentile curves by age and gender. Normal data for aortic dimensions in children have been reported in various echocardiographic
[19, 20] and CMR studies
The CMR study from Kaiser et al.
 reported aortic diameters measured by contrast-enhanced (CE) CMR angiography in 53 children. This method was limited by the fact that CE-CMR images are static and represent a summation of all cardiac phases which may affect a comparison to ECG-gated acquisitions such as in echocardiography or in our study. Furthermore, they measured aortic diameters instead of cross-sectional areas.
Another early CMR-study from Mohiaddin et al.
 assessed aortic cross-sectional areas from enddiastolic spin echo images in 70 predominantly adult volunteers between the ages of 10 and 83 years. We confirmed their finding that aortic dimensions are positively correlated with age, but our study also covers children younger than 10 years, an age range where aortic dimensions and cardiac structures change rapidly according to somatic growth in prepubertal children
. Normal data for aortic cross-sectional areas have been reported by Rammos et al using angiocardiography
. As in our study, they showed a good correlation between BSA and aortic cross-sectional areas. However, their reported data are smaller than in our study, which may be mainly caused by the different technique.
However, the data from the mentioned studies are not exactly comparable to our measurements. Most studies used different imaging modalities
[18–20]. Furthermore, they report aortic diameters, or measured them in order to calculate cross-sectional areas
. CMR allows a direct measurement of aortic cross-sectional areas which is a more accurate approach to assess aortic size, since vessels are not circular in all segments and show an inter-individual anatomic variability.
The observed quantile distributions for aortic dimensions are of clinical value to detect pathologic anatomical changes of the aorta in children and young adults and will serve as reference values for future CMR research studies.
Aortic distensibility and PWV
This is the first study to provide reference CMR values for aortic distensibility and PWV in children and young adults, in conjunction with measurements of aortic size. The percentile ranges show that aortic distensibility decreases with age, whereas PWV increases with age. Age-associated changes and reference values of aortic distensibility and PWV in children and adults have also been reported in studies using different techniques. Senzaki et al. examined 112 patients with an age range from 6 months to 20 years by cardiac catherization. They showed that the arterial compliance normalized to body surface area significantly decreased with age
. The study by Avioli et al. used transcutaneous Doppler techniques to assess aortic PWV in subjects with an age range from 3 to 89 years. In their study aortic PWV significantly increased with age
. Another study measured PWV with ultrasound methods in 206 patients aged 0–15 years. Their median PWV was 3.04 m/s which is comparable to our data. However, in contrast to our study PWV was independent of age, which may be caused by the young age of their study group
. CMR assessment of aortic PWV showed good agreement with PWV obtained from invasive pressure measurements as the gold standard
. Unlike in ultrasound CMR is not limited to acoustic windows and does not only provide an estimation of aortic PWV
The aorta acts as a conduit delivering blood to the peripheral organs and transforms the pulsatile effect caused by ventricular ejection into a continuous blood flow
. As shown aortic distensibility decreases and PWV increases during age. The decreasing aortic elasticity observed in our young cohort may be related to normal structural wall changes during aging
. An increase in intimal-medial thickness after birth has been demonstrated in an earlier study
. The aortic elastic properties depend largely on the presence of elastic fibres in the vessel wall, which have a maximum rate in the perinatal period followed by a fast decrease already during childhood
. Besides these developmental changes aortic wall mechanics and stress seems to play an important role in aortic stiffening. In the course of a lifetime the human aorta will undergo billions of cycles of expansion and contractions. This cyclic mechanical stress leads to fragmentation of elastic fibres and causes a transfer of stress to the stiffer collagen fibres. The loss of elastin results in a reduction of aortic elasticity
. In adults, decreased aortic elasticity has adverse effects on cardiac systolic and diastolic function, due to increased left ventricular afterload and myocardial oxygen consumption as well as impaired coronary perfusion
Our data may be of interest in various diseases and pathological conditions that can affect aortic bioelasticity already in children and young adults. Impaired aortic bioelasticity has been reported for instance in patients with Marfan syndrome
, tetralogy of Fallot
, Turner’s syndrome
 and aortic coarctation
. In a recently published study we could show that patients with hypoplastic left heart syndrome have severly reduced aortic distensibility
. Furthermore, some functional vascular parameters are impaired in obese children
. Considering the increasing use of CMR for non-invasive scientific and clinical studies, the presented data may help in evaluating aortic bioelastic function and cardiovascular risk stratification with these diseases.
As it is difficult to recruit healthy children as volunteers for a CMR study, the sample size of our cohort is small in comparison to echocardiographic studies but fulfills the demand for statistical evaluation.