Response

Abstract

We greatly appreciate the interest in our Technical Note on the measurement of eccentric blood flow in the ascending aorta (1), and applaud Dr.Della Corte et al (2) on their recent publication regarding restricted aortic cusp motion with bicuspid aortic valve (BAV). We believe that this type of correlation between aortic valve imaging features and concrete endpoints like interval aortic growth is exactly the direction this field needs to head. Regarding our group's recent article on wall shear stress (WSS) in the context of BAV, the data demonstrate that flow eccentricity is associated with marked skewing of systolic WSS profiles and focally increased WSS at the aortic convexity (3). The Technical Note in question, however, does not attempt to make a direct correlation with WSS in patients, but instead suggests that a straightforward parameter like flow displacement may prove to be a useful surrogate for the more complex and difficult to measure parameter of WSS. Second, we apologize if our equation regarding “center of velocity” was unclear. Our data are volumetric with three-directional velocity information. From this larger dataset, we exported a plane at a standardized level for the analysis we describe. Ultimately, this type of evaluation could be performed with conventional 2D phase contrast MRI, but we consider this a strength rather than a weakness of the approach. We agree that the cause versus consequence of aortic dilation issue is problematic, and caution against using aortic diameter for “in vivo validation” in the table reviewing imaging parameters of flow eccentricity. As pointed out, a proper evaluation of these parameters would require a systematic, prospective study. The goal of our Technical Note was more modest: to show that the flow displacement parameter we propose is simple, reliable, and reproducible. (We would strongly encourage adding a column for reproducibility in the aforementioned table.) More recently, we have started to investigate the relationship between flow displacement and key clinical endpoints, and are soon to publish our preliminary results (4). Michael D. Hope MD*, Monica Sigovan PhD*, Petter Dyverfeldt PhD*, David Saloner PhD*, * Department of Radiology, University of California, San Francisco, San Francisco, California.