Special projections

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Selective coronary arteriography by the Sones technique was started at the Toronto General Hospital in 1960. A then “standard” x-ray system with the image intensifier above and the x-ray tube mounted below the table was used, which essentially limits projections to the transverse plane. With growing experience, it became clear that diagnostic accuracy was being compromised by the limitations posed by such an x-ray system. The transverse plane often foreshortened the proximal left anterior descending and circumflex arteries in the left anterior oblique view and the distal right coronary artery in the right anterior oblique view. Overlap, especially when a narrow divergent angle was present, obscured the origin of branches of the left anterior descending artery in the right anterior oblique view and in the distal right coronary artery and the origin of the posterior ventricular branch in the left anterior oblique view. Foreshortening and overlap were further complicated by asymmetry of the lesion, i.e., eccentric, crescentic, or even multiluminal obstruction.

In 1973 we installed a U-arm with a table rotating horizontally through the isocentric cardiac axis, the first Cardoskop-U, built to our design aspirations by Siemens. Thus, cranial and caudal angles could be easily added to the transverse plane, quickly confirming that routine use of these projections increased diagnostic accuracy in a substantial number of studies.

Analysis of 100 consecutive studies highlighted the magnitude of the problem in showing that an improved diagnosis was obtained in 54% of the studies. In 33.5%, the lesions had to be upgraded. . .



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