H.J. van den Herik

Developments Towards an Expert System for the Quantitative Analysis of Thallium-201 Scintigrams

Sequential thallium-201 (Tl-201) scintigraphy has achieved widespread use for the assessment of exercise induced myocardial perfusion abnormalities (Pohost et al., 1977; Burrow et al., 1979; Simoons and Reiber, 1984). In this nuclear imaging technique, images of the myocard are acquired by means of a scintillation camera after intravenous administration of Tl-201. Thallium-201 is a radiopharmaceutical that distributes over the body as a function of distribution of cardiac output. Consequently, the Tl-201 accumulated in the myocard reflects regional myocardial blood flow. An area with reduced thallium-uptake early after exercise may be due to either transient uptake abnormalities (ischemia) or to previous myocardial infarction (scar). These possibilities can be distinguished by comparing the immediate post-exercise image with the late post-exercise or redistribution image taken between 3 and 4 hours later. An ischemic area is characterized by the fact that the thallium-uptake is reduced in the early image, but normal in the late post-exercise image. In the case of a scar, the uptake is low in both images. To minimize variations in the interpretation of the scintigrams and to quantify the perfusion abnormalities, the early and late post-exercise images must be compared in detail. This is only feasible by computer processing. Over the past years, we have developed an extensive software package for the quantitative analysis of thallium-201 scintigrams (Lie, et al., 1979; Lie, et al., 1981; Reiber et al., 1982).

Heuristics in the Abbot-Monk Problem

The future of expert systems lies in parallel processing. A combination of various AI techniques is considered for parallel knowledge-based systems. A careful examination of its organizational structure with respect to the relations between processes and data structures can result in a performance improvement. The appropriate tool for investigating parallel systems is simulation. In order to get some insight into the inter-dependency of the processes, a parallel computer simulator is constructed and tested.