Contrast flow velocity quantification from time-resolved CT angiography, a phantom study

In recent years, there has been an increasing interest in replacing digital subtraction angiography (DSA) as method of choice for the diagnostic imaging of patients suffering from lower extremity peripheral arterial disease (PAD). Due to small vessel diameters and suboptimal resolution, examinations of below-the-knee arteries however remain extremely challenging. The advent of wide beam CT scanners allows to perform multiple CT acquisitions over a wide patient volume. A sequence of these CT acquisitions at timed intervals could provide additional hemodynamic information, and as such allows to track a contrast bolus that propagates through the arterial conduit. The aim of this study was to evaluate the accuracy and precision of flow velocity measurements using time-resolved computed tomography angiography (CTA). To this end, we constructed a mechanical flow phantom (single lumen, 6 mm inner-diameter). Six consecutive time-resolved CTA acquisitions were performed at a constant flow rate to achieve six reference velocities (21.2 mm/s, 38.9 mm/s, 60.1 mm/s, 81.4 mm/s, 99.0 mm/s and 120.3 mm/s). The mean centerline flow velocity was obtained from the contrast propagation over three different segmental lengths (160 mm, 80 mm and 40 mm) and then compared to the reference flow velocity. The results of this study suggest that mean flow velocities within the range of typical blood flow velocities in the below-the-knee arteries (40 mm/s - 70 mm/s), can be accurately measured with high precision in a 6 mm flow phantom using time-resolved CTA when considering a minimal path length of 80 mm.