Spatial and temporal quantitation of plane thallium myocardial images.

A computer method has been developed to determine the relative initial uptake and segmental washout rates of thallium-201 from sequential myocardial images. Initial images in multiple projections are obtained at 10 min after thallium-201 injection, and delayed images 2-3 hr after injection. A modified interpolative method was used to construct a background reference plane, and net myocardial counts was used to construct a background reference plane, and net myocardial counts above this reference plane were determined from multiple count profiles. Washout rates were determined by linear regression of time-activity curves constructed from the sequential images. In this approach, both relative temporal as well as relative spatial quantitation is performed. Data from 25 normal subjects were used to establish numerical criteria and normal ranges for relative focal defects and abnormal segmental washout slopes. Normal ranges were set to include the 90-percentile limits of the distribution of values obtained from the normal population. From these values we derived a quantitative criterion for thallium scan interpretation that can be used for analysis and interpretation of scintigrams in clinical situations.