Objective: The aortic valve can be assessed using MDCT; however, measurements of the aortic opening area vary with the cardiac cycle. In this study, we sought to assess the optimal timing for measuring the area of the aortic opening with MDCT.
Materials and methods: Retrospectively gated MDCT was performed in 57 patients with the following parameters: gantry rotation time, 420 milliseconds; tube voltage, 120 kV; tube current, 550 mAs with tube current modulation; and slice collimation, 16 x 0.75 mm. From 72 to 100 mL of contrast agent (320 g/mL3) was injected i.v. at 4-5 mL/s. High-resolution data sets were obtained for planimetry at phase starts of 0, 50, 100, 150, and 200 milliseconds after the R wave peak and were assessed for aortic opening area and the presence of artifacts.
Results: In 41% of patients, the cardiac phase with the largest aortic opening area was at 50 milliseconds after the R wave peak. The area of the aortic opening measured at 0 milliseconds after the R peak was 2.7 +/- 0.8 cm2 (mean +/- SD); at 50 milliseconds, 2.9 +/- 0.2 cm2; at 100 milliseconds, 2.9 +/- 0.7 cm2; at 150 milliseconds, 2.8 +/- 0.7 cm2; and at 200 milliseconds, 2.4 +/- 0.8 cm2. The image quality was best at 50 milliseconds after the R peak in 42% of patients, 100 milliseconds in 29%, 150 milliseconds in 20%, 0 milliseconds in 7%, and 200 milliseconds in 2%. The aortic valve appeared closed in three patients at 0 milliseconds and in four patients at 200 milliseconds. Fewer artifacts were present in the midsystolic phases (i.e., 50-150 milliseconds) ("double-leaflet" artifact, 5-13%; "incomplete contour" artifact, 20-26%) than in the early (0 milliseconds) and late (200 milliseconds) systolic phases (double-leaflet artifact, 38% and 43% of patients; incomplete contour artifact, 76% and 73%, respectively).
Conclusion: Aortic valve planimetry is best performed at phase starts of 50-100 milliseconds after the R peak because the area of the aortic opening is widest and image quality is best at that phase.