THE IMPACT OF VESSEL ORIENTATION IN-SPACE ON DENSITOMETRIC MEASUREMENTS OF CROSS-SECTIONAL AREAS OF CORONARY-ARTERIES

Under ideal conditions, densitometric measurement of a coronary arteri al cross section in biplane angiographic images should result in nearl y equal cross sectional areas for both planes. However, quite apprecia ble discrepancies have been found by some authors in patients. In this study, the role of inadequate spatial orientation of the vessel axes relatively to the x-rays was assessed by use of a 3D technique applied to 60 stenoses (45 pre PTCA and 15 post PTCA) in simultaneously acqui red digital biplane coronary angiograms of 27 CAD patients. The 3D tec hnique yields two radius values per projection directly in mm at any a rterial cross section of interest. This was used to determine the area s A(r)(in mm(2)) of the reference cross sections. As with catheter cal ibration, these cross sections were thus assumed to be more or less ci rcular, but out-of-plane effects and errors due to a catheter diameter determination in pixels were avoided. The areas of the stenotic secti ons were then determined densitometrically (in mm(2)) from the two pro jections (1 and 2) according to A(s1) = A(r)D(s1)/D-r1, resp. A(s2) = A(r)D(s2)/D-r2, where D-r1, D-r2, D-s1 and D-s2 are the conventional d ensitometric areas of the reference and stenotic cross sections measur ed in planes 1 and 2. As expected, the areas A(s1) and A(s2) correlate d only moderately: A(s2) = 0.92 A(s1) + 0.7 mm(2), r = 0.82, n = 60, S EE = 1.4 mm(2). The 3D method also yielded the two spatial angles betw een the local vessel axis and the x-rays of both planes. These two ang les were then used to correct each densitometric area for inadequate o rientation. With the corrected densitometric areas A(s1c) and A(s2c), the correlation improved to: A(s2c) = 1.05 A(s1c) + 0.03 mm(2), r = 0. 93, n = 60, SEE = 0.8 mm(2). Inadequate orientation of the cross secti ons in space thus appears to be an important factor of inaccuracy in d ensitometric measurements of stenotic cross sections in patients.