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

Abstract

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 of 2-3cm distal to the flow divider for avoiding multi-directional blood flow yet lack experimental evidence to support this recommendation. This study aimed to determine the minimum distance required to avoid multi-directional 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±4yrs) participated in this study. Ultrasound VFI was employed to visualize blood flow patterns, quantify flow uniformity via vector concentration coefficient (VCC), and multi-directional flow length was quantified at rest in triplicate (n=20), post-isometric contraction (n=20), and during thigh cuffing (n=10). At rest, the mean multi-directional flow length was 3.12±0.59cm, which decreased to 2.80±0.66cm post-contraction (P=0.02). Thigh cuffing (80mmHg) resulted in a multi-directional flow length of 2.75±0.64cm, not significantly different from rest (P=0.69). Males exhibited a shorter multi-directional flow length compared to females (mean difference: 0.31±0.71cm, P=0.05). The VCC increased from 0.39±0.08 at rest to 0.57±0.15 post-contraction (P<0.01), indicating increased flow uniformity. Reliability metrics demonstrated good-to-excellent reproducibility at rest, with ICC(3,1)=0.85 and 0.84 and CV%=7.1±6.2% and 7.5±4.5% for multi-directional flow length and VCC, respectively. Our data suggest a minimum scanning proximity of 3.5cm to the femoral bifurcation to ensure blood flow assessments are free of multi-directional flow, and invite further study in different body positions and arteries of interest to increase rigour in this area.