Quantification of systolic count increase in technetium-99m-MIBI gated myocardial SPECT

This study was performed to clarify the validity of quantification of myocardial wall thickening by the count increase method using electrocardiography (ECG)-gated SPECT. Methods: We performed a phantom study to examine the quantification of this method and to clarify the relationship between the changes of relative counts and objective size (such as myocardial wall) under various conditions. In addition, in volunteers, the percent count increase (%Cl) was analyzed in left ventricular segments based on circumferential profile curve analysis by ECG-gated SPECT with ^99mTc-MIBI (methoxyisobutyl-isonitrile), and it was compared with the regional systolic wall thickness (%Th) assessed by echocardiography during lowdose dobutamine infusion. Results: In our phantom study, the relative count changes were correlated linearly with the object size only within less than 20 mm. Recovery coefficient curves were influenced by acquisition parameters such as type of collimator, diameter of camera rotation, counts and photon scattering. In ECG-gated SPECT, the %Cl value was increased gradually at each stage after dobutamine infusion, in relation to the increase of the %Th seen on echocardiography, although there are significant large deviations between these two parameters. Conclusion: In this study, quantitative analysis based on the %Cl in ECG-gated SPECT may underestimate regional wall thickening. These data should be considered in the evaluation of the %Cl as an index of myocardial function.