The Measurement of Blood Flow from Dynamic Digital X-Ray Images Using a Weighted Optical Flow Algorithm: Validation in a Moving-Vessel Flow Phantom

Abstract. We have developed an algorithm based on optical flow for the extraction of flow waveforms from dynamic digital x-ray images. The aim of this study was to extend the validation of this technique to blood flow measurement in moving vessels. A pulsatile blood flow circuit was constructed to simulate the human arterial circulation using a length of silicone tubing as a model artery. A computer-programmable manipulator was used to move the model artery. Instantaneous recording of flow from an electromagnetic flow meter (EMF) provided the “gold standard ” measurement. Dynamic biplane x-ray images with injection of iodine contrast medium were acquired for different flow rates. The image data were formed into parametric images in which grey level represents contrast medium concentration as a function of time and distance along the vessel. The blood flow velocities were calculated as the ratio of temporal and spatial derivatives in the parametric image and then averaged along the vessel length using a weighting scheme based on the magnitude of the spatial derivative. The correlation coefficient between x-ray and EMF measurements was 0.922 (p<0.001) for instantaneous flows and 0.891 (p<0.001) for average flows. The mean difference (X-ray-EMF) was –15.8 ml/min for instantaneous flows and 0.3 ml/min for average flows.