Rapid sequence computed tomography (CT) scanning has many potential applications in studying intracranial physiologic events. However, visual inspection of these rapid sequence scans fails to extract the large amount of information inherent in the digital data. The concept of corrected mean transit time applied to rapid sequence scans after intravenous bolus injection of contrast material provides quantitative data on relative hemispheric flow. Use of histogram-based areas of interest permits accurate and reproducible identification of anatomic structures including arteries and gray and white matter. Gamma variate curve fit techniques reduce statistical noise. The concept of transit time can be expanded to the creation of functional CT images.
Changes in regional myocardial perfusion were measured using rapid sequence dynamic transmission tomography to detect differences in the initial distribution of contrast medium injected as an intravenous bolus. The experiments were carried out on 8 mongrel dogs instrumented with flow probes and vascular occluders around the coronary arteries. Flow reductions of 50 per cent or more were detected as regions of myocardium with less contrast enhancement than those with normal perfusion. Reactive hyperemia induced by transient ischemia was detected as areas of relatively increased contrast enhancement. These changes could be demonstrated on the images and quantitated using data depicting changes in HU (Hounsfield units) with time to develop an index of perfusion. The images obtained were of satisfactory quality and differences between the underperfused and normal myocardium were made more prominent by using dipyridamole infusions.
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