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Normal Thoracic Aorta Diameter on Cardiac Computed Tomography in Healthy Asymptomatic Adults

Rationale and Objectives

To establish the normal criterion of ascending aortic diameter (AAOD) measured by 64 multidetector computed tomography (MDCT) and electron beam computed tomography (EBT) based on gender and age.

Materials and Methods

A total of 1442 consecutive subjects who were referred for evaluation of possible coronary artery disease underwent coronary computed tomographic (CT) angiography (CTA) and coronary artery calcium scanning (CACS) (55 + 11 years, 65% male) without known coronary heart disease, hypertension, chronic pulmonary and renal disease, diabetes, and severe aortic calcification. The AAOD aortic diameter, descending aortic diameter (DAOD), pulmonary artery (PAD), and chest anteroposterior diameter (CAPD), posterior border of the sternal bone to the anterior border of the spine, were measured at the slice level of mid-right pulmonary artery using end systolic trigger imaging. The volume of four chambers, ejection fraction of left ventricle, and cardiac output were measured in 56% of the patients. Patients’ demographic information, age, gender, weight, height, and body surface area were recorded. The mean value and age-specific and gender-adjusted upper normal limits (mean ± 2 standard deviation) were calculated. The linear correlation analysis was done between AAOD and all parameters. The reproducibility, wall thickness, and difference between end-systole and end-diastole were calculated.

Results

AAOD has significant linear association with age, gender, DAOD, and pulmonary artery diameter ( P < .05). There is no significant correlation between AAOD and body surface area, four-chamber volume, left ventricular ejection fraction, cardiac output, and CAPD. The mean intraluminal AAOD was 31.1 ± 3.9 and 33.6 ± 4.1 mm in females and males, respectively. The upper normal limits (mean ± 2 standard deviations) of intraluminal AAOD, were 35.6, 38.3, and 40 mm for females and 37.8, 40.5, and 42.6 mm for males in age groups 20–40, 41–60, and older than 60 years, respectively. Intraluminal aortic diameters should parallel echocardiography and invasive angiography. Traditional cross-sectional imaging (with CT and magnetic resonance imaging) includes the vessel wall. The mean total AAOD was 33.5 and 36.0 mm in females and males, respectively. The upper normal limits (mean ± 2 standard deviations) of intraluminal AAOD were 38.0, 40.7 and 42.4 mm for females and 40.2, 42.9, and 45.0 mm for males in age group 20 to 40, 41 to 60, and older than 60 years, respectively. The inter- and intraobserver, scanner, and repeated measurement variabilities were low ( r value >0.91, P < .001, coefficient variation <3.2%). AAOD was 1.7 mm smaller in end-diastole than end-systole ( P < .001).

Conclusions

The AAOD increases with age and male gender. Gender-specific and age-adjusted normal values for aortic diameters are necessary to differentiate pathologic atherosclerotic changes in the ascending aorta. Use of intraluminal or total aortic diameter values depends on the comparison study employed.

Atherosclerosis is a generalized process that may involve the aorta and the coronary arteries. Atherosclerotic disease of the aorta has been demonstrated to increase the risk for ischemic stroke ( ) and been demonstrated to be associated with coronary artery disease (CAD) ( ). Ascending aortic atherosclerosis has also been associated with aortic valve disease, Marfan syndrome, and aortic aneurysms. Aortic root changes resulting from aging, involving aortic distensibility, is the most common cause of aortic regurgitation ( ). Early detection of aortic atherosclerosis before the onset of clinical symptoms may improve both the diagnosis and therapeutic interventions.

There have been some reports of the importance of aging on this process and gender-related differences in aortic diameters ( ). With more application of cardiac computed tomography (CT) and thoracic CT, it is essential to define the normal thoracic aortic diameter changes with aging in both genders. To date, most CT studies that have evaluated the thoracic aorta diameters in adults have been small in size ( ). We sought to evaluate the thoracic aortic diameters in a large population of patients without known diseases to establish normal values based on age and gender using high-resolution cardiac CT.

Materials and methods

Study Population

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Table 1

Profile in Clinical Parameters

Gender n Age BSA (m 2 ) LVEF CO/Beat AP Chest Diameter Female 500 56.3 (19–92) 1.73 67.5% 73.4 mL 110.2 mm Male 942 54.5 (19–93) 2.02 66.4% 83.8 mL 127.2 mm

All P values > .05 comparing both genders.

n, number of subjects; BSA, body surface area; LVEF, left ventricular ejection fraction; CO, cardiac output; AP, anteroposterior.

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EBT Study Protocol

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MDCT Study Protocol

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Measurements

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Analysis

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Results

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Table 2

Association Between AAOD and Factors

Factors Ascending Aorta Diameter Female Male n_r_ Value n_r_ Value Gender 487 0.28 487 0.28 Age 500 0.26 942 0.31 DAOD 500 0.48 942 0.43 PAD 500 0.21 942 0.21

DAOD, descending aortic diameter; n, number of subjects; PAD, pulmonary artery diameter.

All P < .05.

Table 3

Normal Ascending Aorta Diameter Measured with Echocardiography and CT

Authors Ascending Aorta Diameter Method Trigger Time Female Male n Age M ± SD (mm) n Age M ± SD (mm) Mao 500 56 31.1 ± 3.9 942 54 33.6 ± 4.1 CVCT End-systolic Mao 28 20–40 29.0 ± 3.3 80 20–40 30.8 ± 3.5 CVCT End-systolic Mao 305 41–60 30.7 ± 3.8 595 41–60 33.3 ± 3.6 CVCT End-systolic Mao 167 >60 32.2 ± 3.9 267 >60 35.0 ± 3.8 CVCT End-systolic Vasan ( ) 1816 46 28 ± 3 1473 47 32 ± 3 Echo End-diastolic Roman ( ) 67 43 27 ± 3 68 43 30 ± 4 Echo End-diastolic Sochowski ( ) 33 45 28 ± 3 27 45 28 ± 3 Echo End-systolic Reed ( ) 46 ⁎ 21 33 ± 4 45 ⁎ 21 32 ± 4 Echo — Reed ( ) 44 † 21 27 ± 3 46 † 21 31 ± 3 Echo — Aronberg ( ) 36 ‡ 20–40 33.6 36 ‡ 20–40 34.7 CT No trigger time Aronberg ( ) 33 ‡ 41–60 37.2 33 ‡ 41–60 36.3 CT No trigger time Aronberg ( ) 33 ‡ >61 35 33 ‡ >61 39.1 CT No trigger time Pearce ( ) 24 49 29 ± 3.4 46 50 32 ± 5.2 CT No trigger time

M, mean; SD, standard deviation; echo, echocardiography; CVCT, cardiovascular computed tomography.

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Table 4

Changes in Ascending Aorta Diameter with Different Trigger Time and Method of Ascending Aortic Diameter Measurement

Trigger Time n 35% phase 75% phase 95% phase 107 33.9 ± 4.1 32.9 ± 4.1 32.2 ± 3.9 ⁎

Imaging and Measuring Method (64 MDCT) n CTA (lumen) CTA (lumen + wall) CACS (lumen + wall) 85 32.8 ± 3.8 35.2 ± 3.8 ⁎⁎ 35.1 ± 3.8 ⁎⁎

MDCT, multidetector computed tomography; CTA, computed tomography angiography; CACS, coronary artery calcium scanning.

Compared with 35% phase for trigger time and CTA lumen for method.

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Table 5

Interobserver, Intermeasurement, Interscanner, Interphase, and Intermethod Variabilities

Measurements n_r_ CV (%) Bland Altman Plot Ratio 95% CI limit Interobserver variability 144 0.91 3.2 1.00, 95% CI 0.99–1.01 Inter-reader variability 140 0.92 3.0 1.01, 95% CI 0.99–1.01 Interscanner variability 100 0.91 3.2 1.01, 95% CI 0.99–1.02 Interphase variability (35% vs. 75% phase) 107 0.98 2.3 1.03, 95% CI 1.02–1.04 Interphase variability (35% and 95% phase) 107 0.97 2.4 1.05, 95% CI 1.05–1.06 Interlumen and (lumen + wall) CTA variability 85 0.98 3.3 0.93, 95% CI 0.92–0.93 Interwall CTA and CACS (lumen + wall) variability 85 0.99 1.7 1.00, 95% CI 1.00–1.01

n, number of subjects; CV, coefficient of variation; CTA, computed tomography angiography; CACS, coronary artery calcium scanning.

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Discussion

Aging Process: Aortic Histology, Anatomy, and Function

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Figure 1, Left, 64 multidetector computed tomography angiographic image. Right, coronary artery calcium (CACS) image. AAO, DAO, RPA, and PA represent the ascending aorta, descending aorta, right pulmonary, and pulmonary artery on the CACS scanning image. Lines A, B, C, and D represent AAOD, DAOD, PAD, and CAPD on the angiographic image. White arrow depicts the calcium foci and the black arrow points to the sclerosis aortic wall. D, diameter; AAO, ascending aorta; DAO, descending aorta; PA, pulmonary artery; RPA, right pulmonary artery; CAPD, chest anteroposterior diameter.

Figure 2, Changes in the aortic location, shape, and size within the RR interval. Four panel images of a multidetector computed tomography scan display the reconstructed images of the 15%, 25%, 35%, and 95% phase of the RR interval. The 35% phase is end-systolic and 95% phase is end-diastolic. The 25% phase has the most motion artifact (white arrows) and 35% phase has the most anterior location, cyclical shape, and the fewest motion artifacts. The distance between the aorta and sternal bone was 3.5 and 6.5 mm; the diameter was 31 and 29 mm in 35% and 95%, respectively (white dual arrow).

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Correlation Between AAOD and Parameters

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Difference of Aortic Diameter by Authors

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Reproducibility

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Definition

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Figure 3, Optimal sites to measure AAOD. Right superior panel was axial image at LM level (dual white arrow). Right inferior panel was RPA mid-slice level. Left superior and inferior panel were coronal and sagittal images at AAO mid-plane. White dot line shows the RPA slice level at coronal and sagittal image, which was about 16 mm superior to the LM ostium. AAO, ascending aorta; D, diameter; RPA, right pulmonary artery; LM, left main coronary artery; PA, main pulmonary artery.

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Limitations

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Conclusion

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