VALIDATION OF A QUANTITATIVE RADIOGRAPHIC TECHNIQUE TO ESTIMATE PULSATILE BLOOD-FLOW WAVE-FORMS USING DIGITAL SUBTRACTION ANGIOGRAPHIC DATA.
JOURNAL OF BIOMEDICAL ENGINEERING
225 - 233.
We have validated a new radiographic technique for determining pulsatile volume flow in arteries following an intraarterial injection of contrast material. Instantaneous blood velocities were estimated by generating a parametric image from dynamic angiographic images in which the image grey level represents contrast material concentration as a function of time and distance along a vessel segment. Adjacent concentration-distance profiles in the parametric image were shifted with respect to distance until a match occurred. A match was defined as the point where the sum of squares of the differences in the two profiles was a minimum. The distance translated per frame interval gives the instantaneous contrast material bolus velocity. We have validated the technique using an experimental phantom of blood circulation, consisting of a pump, flexible plastic tubing, the tubular probe of an electromagnetic flowereter (EMF) and a solenoid, to simulate a pulsatile flow waveform, which includes reverse flow. Small boluses of contrast material can be injected at various positions in the circuit. Measurements of pulsatile velocity flow were taken at 40 ms intervals, using a tube of 6.6 mm internal diameter and an imaged tube length of 200 mm. The shape of the flow velocity waveform was faithfully reproduced but there was an overstimation of peak velocity of 40% at low velocities (peak velocity of 540 mm s-1), reducing to 19% at peak velocities of 964 mm s-1 with an underestimation of 16% at the peak velocities of 1899 mm s-1. The validation was repeated for distances ranging from 130 to 230 mm between injection and measurement sites and for imaged tube lengths varying from 200 to 20 mm. Calculation of the mean difference and standard deviation of the difference between angiographic velocities and velocities calculated from EMF readings confirmed that the technique was independent of catheter position over this range, but that reduction of tube length resulted in a systematic reduction in mean flow velocity measurements. To demonstrate the use of this technique in a clinical context, we have measured blood flow waveforms in a patient immediately before and after percutaneous transluminal angiplasty of a stenosis in the superficial femoral artery.
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