Evaluation of Coronary Perfusion by Positron Emission Tomography
The methods used in positron emission tomography (PET) studies for the estimation of myocardial blood flow are based upon the principle of mass conservation; what goes in, must come out. Whether or not there are barriers, any nonmetabolized tracer has a mean transit time through each region that is exactly its volume of distribution divided by the flow. When retention is long, the tracer is almost an analog of a mechanically deposited microsphere. When the tracer is flow-limited in its exchange, the measurement of its mean transit time is most secure when the volume of distribution and mean transit time are large. Complicating factors, such as slow permeation across capillary and cell barriers and the metabolism of the tracer, require more detailed models for analysis. The movements of the heart and the fact that the spatial resolution of PET images is almost of the same magnitude as the thickness of the wall of the ventricle, complicate the form of the signal. Nevertheless, with the improved temporal and spatial resolution of newer tomographs, there are good prospects for the evolution of protocols that will give local metabolism and flow with usable accuracy.
KeywordsTransit Time Myocardial Blood Flow Coronary Perfusion Indicator Dilution Water Space
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