The Need for Standardized Methods for Measuring the Aorta: Multimodality Core Lab Experience From the GenTAC Registry

Abstract

Objectives: This study sought to evaluate variability in aortic measurements with multiple imaging modalities in clinical centers by comparing with a standardized measuring protocol implemented in a core laboratory.

Background: In patients with aortic disease, imaging of thoracic aorta plays a major role in risk stratifying individuals for life-threatening complications and in determining timing of surgical intervention. However, standardization of the procedures for performance of aortic measurements is lacking.

Methods: To characterize the diversity of methods used in clinical practice, we compared aortic measurements performed by echocardiography, computed tomography (CT), and magnetic resonance imaging (MRI) at the 6 GenTAC (National Registry of Genetically Triggered Thoracic Aortic Aneurysms and Cardiovascular Conditions) clinical centers to those performed at the imaging core laboratory in 965 studies. Each center acquired and analyzed their images according to local protocols. The same images were subsequently analyzed blindly by the core laboratory, on the basis of a standardized protocol for all imaging modalities. Paired measurements from clinical centers and core laboratory were compared by mean of differences and intraclass correlation coefficient (ICC).

Results: For all segments of the ascending aorta, echocardiography showed a higher ICC (0.84 to 0.93) than CT (0.84) and MRI (0.82 to 0.90), with smaller mean of differences. MRI showed higher ICC for the arch and descending aorta (0.91 and 0.93). In a mixed adjusted model, the different imaging modalities and clinical centers were identified as sources of variability between clinical and core laboratory measurements, whereas age groups or diagnosis at enrollment were not.

Conclusions: By comparing core laboratory with measurements from clinical centers, our study identified important sources of variability in aortic measurements. Furthermore, our findings with regard to CT and MRI suggest a need for imaging societies to work toward the development of unifying acquisition protocols and common measuring methods.

Keywords: CT; MRI; aortic measurements; core laboratory; echocardiography; standardization.

Figure 1. Adjusted Mean of Differences (in cm) by imaging modality at each aortic segment

In this model adjusted to age groups, enrollment diagnosis and clinical center, the mean of differences is closer to zero for echo than for CT and MRI at all segments and is statistically significant between the 3 imaging modalities for the sinus of Valsalva, ascending aorta and transverse arch. AVA, aortic valve annulus; SV, sinus of Valsalva;STJ, sino-tubular junction; Asc Ao, ascending aorta; T Arch, transverse arch; Desc T, mid-descending thoracic aorta. Mean of differences are reported as clinical center – iCORE, therefore a negative value reflects iCORE measurements larger than centers, and viceversa.

Figure 2. Adjusted Mean of Differences (in cm) by Clinical Center (CC 1-6) at each aortic segment

In this model adjusted to age groups, enrollment diagnosis and imaging modalities the mean of differences is statistically significant between different CC (p value for the F statistics <0.05) at the aortic valve annulus (AVA), sinus of Valsalva (SV), Ascending aorta (Asc Ao) and transverse arch (Tr Arch) segments. STJ, sino-tubular junction; Desc T, mid-descending thoracic aorta. Mean of differences are reported as CC – iCORE, therefore a negative value reflects iCORE measurements larger than centers, and viceversa.