RESUMO
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.
