QUANTITATIVE-EVALUATION OF REGIONAL MYOCARDIAL PERFUSION USING FAST X-RAY COMPUTED-TOMOGRAPHY

Clinical quantitation of regional myocardial perfusion using a minimal ly invasive and easily applied technique could allow for ready quantit ation of the functional significance of coronary disease, allow for fu rther understanding of flow reserve in various cardiomyopathic and hem odynamic overload (pressure versus volume) conditions, and possibly pr ovide basic information needed regarding the development and clinical significance of coronary collateral vessels and diseases of the myocar dial microcirculation. Electron beam CT (EBCT) is a unique cardiac ima ging modality that allows for rapid acquisition tomographic slices of the heart with excellent spatial resolution. It has been demonstrated to provide accurate measurements of cardiac anatomy, biventricular fun ction, myocardial mass, and estimates of mural atherosclerotic plaque burden via quantification of coronary calcium. The application of clas sical indicator techniques for use by fast x-ray computed tomography t echniques such as electron beam CT has been shown to allow quantitativ e analysis of regional myocardial perfusion throughout the myocardium. Initial studies using central intravenous contrast injection in exper imental animals showed a close correlation of regional myocardial perf usion as quantitated by electron beam CT with measurements using radio labeled microspheres at resting and moderately increased now states. A t high now states, however, electron beam CT significantly underestima ted absolute myocardial perfusion and thus myocardial now reserve. Usi ng another fast CT device, the Dynamic Spatial Reconstructor (DSR), co ncepts of intramyocardial vascular blood volume and its relation to my ocardial now have been established. By adapting these concepts to elec tron beam CT scanning and accounting for the increase in intramyocardi al vascular blood volume at vasodilatation, the ability to correctly q uantitate perfusion states up to approximately 400 mt . min(-1) . 100 g(-1) using central intravenous contrast administration was demonstrat ed. This implies that studies can be done with intravenous injection m ethods for characterization of regional myocardial perfusion up to the normal flow reserve of approximately 4.1. Important physiologic and c linical abnormalities in flow reserve generally result in a ratio < 3: 1. Electron beam CT offers the capability to quantitate regional myoca rdial perfusion in both the clinical and research setting. Of particul ar interest is the ability to provide quantitative regional myocardial perfusion which can be coupled to the evaluation of cardiac anatomy a nd function as well as mural coronary atherosclerotic calcium burden d uring the same scanning session. Thus, electron beam CT has the potent ial to become a valuable, minimally invasive clinical tool for compreh ensive analysis of cardiac function and coronary status.