Flow measurements with digital subtraction densitometry in a steady flow experimental model

Computerized densitometry was applied on digital subtraction series for measuring flow rates, 600 to 2 000 ml/min, in model experiments, using contrast medium as indicator substance. A total of 962 measurements were performed, employing the Stewart-Hamilton dilution technique, as well as direct measurements of velocity of the indicator bolus between 2 measuring sites. Results with the dilution technique were closely correlated with true values, but slightly lower (mean 8%), presumably because of sedimentation of contrast medium. Measurements based on bolus velocity were most accurate when the bolus passage was defined by points near the gravity line of the area under the concentration curve. Use of more easily identified curve points, e.g. the time of curve maximum, tended to yield too high values due to flow laminarity with a high-velocity leading edge of the indicator. Variation in repeated measurements on any single image series was attributed to the low sampling rate.