Pitfalls in the Display of Color Doppler Jet Areas: Combined Variability Due to Doppler Angle, Frame Rate, and Scanning Direction

Abstract

The Doppler color jet area depicting a regurgitant or shunt lesion may be useful in estimating its severity. However, color jet area may be affected by technical factors. We studied the combined effects of Doppler angle, frame rate, and scanning direction on the Doppler color jet area of a free jet with 10-mL injection. Results: (1) Angle effects: color flow area was 11.7 ± 2.0 cm² at a Doppler angle of 20°, and 2.3 ± 1.2 cm² at an angle of 60°, when other parameters were kept constant (frame rate=12 frames/sec, reverse scanning direction). (2) Frame rate effects: with other parameters kept constant (Doppler angle = 20°, reverse scanning direction), color flow area was 11.7 ± 2.0 cm² at a rate of 12 frames/sec and 6.5 ± 1.8 cm² at 6 frames/sec. (3) Scanning direction effects: with other parameters kept constant (Doppler angle=20°, frame rate = 9 frames/sec), color flow area was 7.3 ± 1.1 cm² with scanning in the reverse direction, and 20.5 ± 1.6 cm² with scanning in the forward direction. (4) Combined effects: In our in vitro studies, the maximum color flow area was 20.5 ± 1.6 cm², and the minimum area was 1.5 ± 0.2 cm² (nearly twelve-fold). Conclusions: Doppler color jet area correlated inversely with Doppler angle (P<0.01) and directly with frame rate (P<0.01). Color jet area was increased in the forward (following flow), compared with the reverse (against flow) scanning direction (P<0.01). These machine factors must be considered clinically in quantitating color Doppler jet area.