Aortic Root Volume and Geometry: Ready for Clinical Application?

Real-time 3-dimensional echocardiography (RT3DE) is a useful imaging modality that can be easily performed in the clinical practice, and has been proven to be applicable in measuring the real volumes of cardiac chambers such as left ven-tricle, 1-3) left atrium, 4)5) and right ventricle, 6)7) without geometric assumption. The volumes measured using RT3DE are well correlated with volumes assessed using other imaging tools such as cardiac magnetic resonance imaging (MRI) and multi-detector computed tomography (CT). However, volumes calculated using RT3DE tend to be smaller than those obtained using cardiac MRI, and this discrepancy might be attributed to a low spatial resolution of RT3DE. It was reported that minimal changes in endocardial surface position (1 mm) resulted in significant differences in measured volumes (11%) in measuring left ventricular volume using RT3DE. 1) Therefore, guidelines for measuring volumes using RT3DE is necessary to avoid volume underestimations and to reduce inter-and in-tra-observer variabilities. The authors of the study titled " Validation of three-dimensional echocardiography for quantification of aortic root geometry ; Comparison with multi-detector computed tomography " demonstrated 3-dimensional aortic root shape and excellent correlation between aortic root volumes measured using RT3DE and multi-detector CT. 8) This is another application of volume measurement using RT3DE. They found that aortic root volumes at end-diastole measured by RT3DE correlated well with those by multi-detector CT, and the agreement between the two was excellent. The results of this study showed feasibility and accuracy of RT3DE for clinical assessment of geometry and volume of aortic root. There are however several issues to resolve before applying these findings to clinical practice. First, analyses of RT3DE images are time-consuming. Although authors of this study did not present the time duration required for the image analysis, 20-30 minutes would be necessary to analyze one image including time needed for manual border correction. Therefore, automatic border detection protocol with higher accuracy, which can obviate time-consuming process of manual correction, should be developed for more universal clinical usage. Second, a low spatial resolution of RT3DE and tracing inner border of aortic wall might underestimate aortic root volume. Although there was no significant difference between aortic root volumes measured using RT3DE and multi-detector CT in this study, there was a tendency that the former is smaller than the latter. Therefore, tracing more outer dense line rather than tracing inner border of the aortic wall may be a better method. Last but not least, …