Cross-sectional Imaging Identifies Flow-mediated Vasodilatation More Accurately Compared with Longitudinal Imaging

Objectives The purpose of this study was to evaluate cross-sectional imaging to longitudinal plane imaging for measurement of flow-mediated dilatation (FMD). Background Accurate and reproducible assessment of FMD as a measure of endothelial function has important implications. Conventional imaging of the brachial artery is in a longitudinal plane. However, the changes in vasodilatation seen are subtle and minimal (10%-20%) in healthy states with an even smaller change in diseased states, thus, affecting interobserver and intraobserver variability and reproducibility. Methods Nine healthy volunteers (5 men, 4 women) between the ages of 25 and 65 years had baseline FMD measurements done using both longitudinal and cross-sectional imaging. Brachial artery was occluded by inflating the sphygmomanometer cuff on the arm at a pressure of 150 mm Hg for 5 minutes. The artery was imaged continuously for 5 minutes postdeflation. The images were recorded digitally on a computer and analyzed for area and diameter changes by user-guided semiautomated boundary detection method described by our group earlier. Results The baseline measurements were normalized to 1.00 for both longitudinal and cross-sectional images. After cuff deflation, the mean longitudinal diameter increased to 1.10 ± 0.04 versus 1.30 ± 0.17 ( P = .007) for the cross-sectional method. The mean longitudinal measurements were 85.7 ± 13.9 pixels at baseline that increased to 94.3 ± 13.1 pixels for a mean change of 8.6 ± 3.1 pixels after cuff deflation, compared with a mean of 8577.4 ± 2950.8 pixels that increased to 11120.5 ± 3989.4 pixels for a mean change of 2543 ± 1552 pixels by the cross-sectional method ( P < .001). Conclusions Cross-sectional imaging produced a much larger change in area and pixels compared with longitudinal imaging. This translates into greater sensitivity in detecting small changes produced by FMD.