Role of Iodinated Contrast Material in the Evaluation of Myocardial Infarction by Computerized Transmission Tomography

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Abstract
In vivo and in vitro studies have shown that areas of myocardial infarctions can be delineated on CT scans after intravenous administration of iodinated contrast material to dogs with experimental myocardial infarctions. Within the first minute after intravenous administration of contrast material (initial myocardial perfusion phase), the infarct appears an as area of decreased x-ray attenuation (cold spot image). Studies using radiolabeled microspheres indicate that the relative attenuation numbers throughout the myocardium in this phase reflect myocardial perfusion (Hessel et al, 1978). Delayed scans obtained at 5 minutes and later showed a reversal in the attenuation values of normal and infarcted myocardium with the infarct appearing as an area of homogeneous or mottled increase in x-ray density compared to normal myocardium. (Siemers et al, 1978; Carlsson et al, 1977; Higgins et al, 1979). This phenomenon of delayed contrast enhancement of myocardial infarctions ensues as early as 8 hours after coronary occlusion (Higgins et al, 1979) and is present in evolved infarcts as old as 51 days (Newell et al, 1979). Direct measurements of iodine concentration in infarcts, normal myocardium, and organs surrounding the heart were performed in dogs with 48-hour-old myocardial infarctions using fluorescent excitation analysis (Higgins et al, 1978, 1979). These measurements of iodine concentration in tissue samples obtained at 10-180 minutes after intravenous administration of contrast material indicated that the highest iodine concentration in the infarct was at 10 minutes, but the highest ratio of iodine concentration of the infarct to normal myocardium was at 180 minutes. At all time intervals, the concentration of iodine within the infarct was fivefold greater than in the normal myocardium.

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