Multidirectional blood flow in the femoral artery via vector flow imaging: Doppler ultrasound imaging insights.

The accuracy of femoral artery blood flow measurements via Doppler ultrasound hinges on assumptions of laminar flow upstream of the femoral bifurcation. Existing scanning guidelines recommend a minimum proximity to the flow divider of 2-3 cm for avoiding multidirectional blood flow yet lack experimental evidence to support this recommendation. This study aimed to determine the minimum distance required to avoid multidirectional flow contamination near the femoral bifurcation and to assess the reliability of vector flow imaging (VFI) in these measurements. Twenty healthy adults (10 females, 25 ± 4 yr) participated in this study. Ultrasound VFI was used to visualize blood flow patterns and quantify flow uniformity via vector concentration coefficient (VCC), and multidirectional flow length was quantified at rest in triplicate (n = 20), postisometric contraction (n = 20), and during thigh cuffing (n = 10). At rest, the mean multidirectional flow length was 3.12 ± 0.59 cm, which decreased to 2.80 ± 0.66 cm postcontraction (P = 0.02). Thigh cuffing (80 mmHg) resulted in a multidirectional flow length of 2.75 ± 0.64 cm, not significantly different from rest (P = 0.69). Males exhibited a shorter multidirectional flow length compared with females (mean difference: 0.31 ± 0.71 cm, P = 0.05). The VCC increased from 0.39 ± 0.08 at rest to 0.57 ± 0.15 postcontraction (P < 0.01), indicating increased flow uniformity. Reliability metrics demonstrated good-to-excellent reproducibility at rest, with intraclass correlation coefficient [ICC(3,1)] = 0.85 and 0.84 and coefficient of variation (CV)% = 7.1 ± 6.2% and 7.5 ± 4.5% for multidirectional flow length and VCC, respectively. Our data suggest a minimum scanning proximity of 3.5 cm to the femoral bifurcation to ensure that blood flow assessments are free of multidirectional flow and invite further study in different body positions and arteries of interest to increase rigor in this area.NEW & NOTEWORTHY Current ultrasound scanning guidelines to avoid multidirectional flow contamination in the femoral artery of 2-3 cm lack supporting evidence. We used vector flow imaging to report the multidirectional flow length during rest and manipulation of downstream vessel resistance in males and females. We suggest measurements at least 3.5 cm upstream from the femoral bifurcation to minimize multidirectional flows. This study also supports reliability of vector flow imaging for femoral artery assessments, with good-to-excellent reproducibility of results.