Effect of contrast injection on angiographic measurements

Angiographic determinations of blood flow, based on either contrast wavefront velocity or appearance time, are subject to methodological inaccuracy. The inaccuracies due to variable injection flow rates, contrast reflux from a vessel orifice and location of the measurement site were studied in an in vitro model. Contrast boluses of varying volumes and rates were introduced into a nonpulsatile flow stream of normal saline. Variable-size venting needles were also inserted to permit controlled reflux. Transarterial flow was measured with both an electromagnetic flow probe and digital subtraction angiography. Regression equations relating angiographic and electromagnetic flow measurements to underlying steady-state saline, superimposed contrast injectate, and contrast reflux flows were obtained. More accurate angiographic measurements were obtained when the measurement site was moved away from the injection site, since this avoids the turbulent effects of the contrast injection. The results also indicate that for accurate contrast transit flow determinations, the amount of contrast injected and the friction lost in reflux, must be accounted for