[Automatic quantitative analysis of vascular stenosis. Experimental study of a digital angiography system applied to...

The purpose of this study was to test the measurement reliability of the automatic stenosis quantitation program present in a digital angiography system (DG 300 General Electric CGR SA). The experimental study was performed on models mimicking circular, elliptic and irregular stenoses; it made it possible to measure the percentage of stenosis by geometric and densitometric methods. The parameters studied were the size and shape of the stenoses, the contrast medium concentration, the positioning of the stenosis in relation to the image intensifier, the number of Kvp and the angle of projection of X-ray beams in the case of elliptic and irregular stenoses. The results showed a perfect linear correlation between the thickness traversed by the X-ray beams and the value in grey level at the output of the optico-radiological chain (r between 0.987 and 0.997, p less than 0.001), using different Kvp (65 Kvp, 85 Kvp, 90 Kvp) and different X-ray doses (1 milliRoentgen and 80 microRoentgen). With all concentrations of contrast medium (320 mg I/ml to 5 mg I/ml), the values of the circular stenoses measured were very close to real values (75 p. 100) for vessels of all diameters, except those of 1.5 mm in a 22 cm field. When 16 cm and 11 cm fields were used, the results were very close to the 75 p. 100 real value (3 to 4 p. 100 of relative error), even with the 1.5 mm diameter. The values of elliptic stenoses measured by densitometry were very close to real values (1 to 4 p. 100 of relative error) with contrast medium concentrations ranging from 320 mg I/ml to 20 mg I/ml) and with three angles of projection (0 degrees, 30 degrees, 60 degrees). In contrast, the geometric method gave very different results with the three angles of projection. In the case of irregular stenosis (17 percentages of stenosis ranging from 26.2 p. 100 to 77.1 p. 100) the real values correlated very well with the estimated values (r = 0.999, p less than 0.0001). Some of the results were compared with those obtained with a digital cineradiology system (Pie Data) and were found to be equivalent.