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Unlabelled: Carbon-11-labeled acetate is a unique tracer for noninvasive assessment of myocardial oxidative metabolism with PET. Because adequate kinetic models have been missing, data evaluation in the past was performed mostly with phenomenological approaches such as mono- or biexponential fitting which cannot account for the influence of finite input duration and blood volume encountered in noninvasive PET investigations., Methods: To investigate to what extent the current data evaluation schemes are justified, we developed a comprehensive model of [1-11C]-acetate kinetics in the myocardium which incorporates five tissue compartments: free acetate, activated acetate, CO2 precursors, amino acids and CO2. We derived the analytical solution of the model equations which is used for simulations and data fitting., Results: The five-compartment model can reproduce in detail known experimental data. The resulting values of the eight model parameters compare favorably with existing biochemical facts. We have established the relation between parameters of the detailed model and one- and two-compartment models used for the evaluation of PET investigations., Conclusion: The kinetics of [1-11C]-acetate are adequately described by a five-compartment model. One- and two-compartment models are sufficient for simultaneous quantitative assessment of myocardial oxidative metabolism and perfusion with [1-11C]-acetate and PET.

Methodological and technical aspects as well as application and results of the precordial Xenon-residue-detection technique are critically reviewed. The results concern mainly normal flow in various regions of the heart esp. in the free wall of the right and left ventricle, poststenotic flow in patients with coronary artery disease in relation to the degree of proximal narrowings as well as wall motion of the corresponding LV segment, bypassgraft flow and flow after drug interventions esp. nitrates, betablockers, the calcium-antagonist Nifedipine and the coronary dilator Dipyridamole. In spite of its serious limitations (high affinity of Xenon for fatty tissue, geometrical problems in the assessment of flow and its relation to anatomy, gas exchange in situations of high flow etc.), the technique is found to be a useful investigatory tool. Due to its technical display and the related high costs routine application is, however, prohibitive.

A patient-specific three-dimensional rotational ellipsoidal shell was reconstructed from planar myocardial scintigrams. This model was homogeneously filled with radioactivity ('ideal') and then projected onto the same planes as the actual scintigrams, including the absorption of heart and background. After normalization and inhomogeneous background correction, the actual and 'ideal' images were compared in order to quantify the myocardial, ischemic and infarcted volumes (difference quantitation). 201Tl defects appeared as hot spots. The a priori three-dimensional model was cut into 14 segments by six planes. Tomographic sectional views in any desired plane made possible the identification of the 14 spatial myocardial segments on slice images for difference quantitation. The orientation of the long axis of the left heart responsible for different inseparable overprojections of segments was accounted for. The mathematics of segmentation and reconstructive three-dimensional modelling is described. Computed examples are given. A total of 624 201Tl scintigrams from 78 patients were analysed according to this method. The results obtained for the myocardial, ischemic and infarcted volumes, the orientation of the left heart's axis in the thorax and the identification of spatial myocardial segments on projected and tomographic images, as well as the global myocardial and background kinetics of 201Tl are discussed. The procedure of reference modelling and difference quantitation might also be useful in other imaging modalities, such as emission-computed tomography, single-photon emission computed tomography, computed tomography or nuclear magnetic resonance.