Cross-sectional area measurements by digital subtraction videodensitometry.

A method for measurement of absolute cross-section areas in digital images of iodine-opacified vessels was tested in phantoms containing "normal" segments of circular cross-section and either circular or noncircular "stenoses" over a wide range of iodine concentrations. Accuracy varied with iodine concentration, with a slight tendency to overestimate the area at high concentration (185 mg I/ml) and to underestimate at low concentration (23 mg I/ml). Reproducibility was improved at the higher concentrations, with standard deviation ranging from 2% to 7% of the measured value, compared with 7% to 27% at the lowest concentration. Accuracy and reproducibility of area measurements on either normal or stenotic segments were unchanged by rotation of the vessel by up to 25 degrees out of the plane of the image. This method is easily implemented using computerized image processing techniques and has advantages over either manual or automated edge detection because it eliminates the need for an edge criterion and is independent of the viewing projection.