A NEW TECHNIQUE FOR IMPROVED DENSITOMETRIC QUANTIFICATION OF CORONARY-ARTERY STENOSES IN ANGIOGRAPHIC IMAGES

In vitro studies have demonstrated that densitometric quantification o f coronary artery stenoses is superior to geometric methods to assess non-circular lumens. However, in patients, several authors have report ed significant discrepancies between area reduction percentages obtain ed densitometrically from two different imaging projections, Some of t he factors causing the discrepancies can be reduced by simple precauti ons taken during image acquisition. Some others may be compensated for during analysis. Nevertheless, two factors remain problematic. The fi rst is the inadequate spatial orientation of the vessel axes at the st enotic and reference cross sections with respect to the x-rays. The se cond is the difficulty in identifying the same vessel cross section in both planes at the time of analysis. We have designed a new densitome tric technique that eliminates the error contributions of these two fa ctors. The technique requires simultaneously acquired biplane coronary angiograms and biplane images of a translucent cube bearing steel mar kers acquired in exactly the same biplane geometry. Using the two proj ection matrices calculated from the images of the cube, the centreline s and the edges of the coronary arteries can be reconstructed in space from the biplane angiograms. The angles between the vessel axes and t he x-ray beams can be determined and the densitometric cross sections can be corrected accordingly. Moreover, the 3D reconstruction allows t he identification of the same cross section in the two planes for the determination of the area reduction percentages. Validation measuremen ts were performed on a Perspex phantom and in patients, before and aft er angioplasty. In both types of measurement, the interplane discrepan cies could be roughly halved. The densitometric technique presented ca n be incorporated into routine angiography and could become a strong a lternative to the geometric approach that is presently dominating this field.