In silico study of quantitative digital subtraction angiography (qDSA) blood velocity measurements versus catheter geometry

Quantitative DSA (qDSA) is a method for measuring arterial blood velocity from a 2D digital subtraction angiography sequence acquired during an interventional radiology procedure. Previous investigations in swine models and phantoms have compared qDSA velocity to MRI or ultrasound velocity measurements. The purpose of this study was to develop a computational fluid dynamics (CFD) simulation platform with well-controlled conditions to investigate the dependence of qDSA results on catheter geometry, injection conditions, and blood velocities. The OpenFOAM CFD package was configured with a two-liquid mixing solver. Simulations were performed for injections of iohexol contrast (300 mgI/mL, 2 mL/s) through a 5 Fr catheter tip into a straight vessel (6-mm diameter, 20-cm length) with inlet arterial blood flow defined to follow a time-varying cardiac profile (1Hz). Varying inlet blood velocities (15-45 cm/s) and varying catheter tip orientations were simulated (0-45 deg bend relative to centerline; 0-180 deg rotation). X-ray projections of iodine concentration were simulated at 1/30s intervals and then time-attenuation maps (TAMs) were generated for a distal section of the vessel. qDSA velocity was measured from the TAMs by an established spatio-temporal frequency domain method. For a downstream vessel section (14.5-19.5 cm), the qDSA-based velocity was linearly related to the CFD average velocity in a central slice with a slope of 0.82 and an offset of 11.45 cm/s (R²=0.98). For a fixed inlet blood velocity (25 cm/s) and a 45-degree catheter tip bend, changes in catheter rotation resulted in 12.5% standard deviation in qDSA velocity.