1989 Volume 26 Issue 6 Pages 571-576
Clinical evaluation of aortic atherosclerosis has been most commonly performed by visual analysis of aortic calcification on conventional radiographs or X-ray CT. However, precise evaluation of the degree of calcification or mild changes with increasing age can be difficult by these methods of visual analysis. A new quantitative method of evaluating the abdominal aortic atherosclerosis using CT is reported. Target CT scans of the abdominal aorta were performed at the level of the 1st, 3rd and 4th lumbar vertebrae. Two circular regions of interest (ROI) were selected along the outer margin and inner margin of the abdominal aortic wall on CT images, since it was difficult to precisely trace the aortic wall. Histograms of CT value for each pixel were made from two ROIs. A histogram at the ROI of the outer margin was depicted using class values over the maximum CT value in histogram at the ROI of inner margin which indicated flowing blood. A sum of products of the value in each class by the number in that class was divided by the aortic diameter. The value thus obtained was defined as the atherosclerotic index (S.I.). Forty-five cases were studied with this method. Six cases were excluded because of artifacts. The remaining 39 cases (16 males, 23 females) were analyzed. S.I. increased with aging and was higher in men than in women. However, it increased more rapidly in women (8.68/year) than in men (2.73/year). Because this new method employed the CT value, it is more objectively quantitative than previous methods of visual analysis in evaluating abdominal aortic atherosclerosis. This method has potential for the analysis of slight changes with increasing age or for therapeutic effects in cases of atherosclerosis.
