Digital autoradiography: film and electronic multitracer techniques for heart imaging

A multitracer digital film autoradiography (DFA) and a single-tracer multiwire proportional chamber autoradiography (MWPCA) have been developed for the simultaneous study of regional myocardial blood flow and metabolism in the canine heart. Radioactive indicators of flow (plastic microspheres), metabolism (deoxy-2-D-glucose labeled either with (14)C or (3)H), and flow and metabolism ((201)T1), were used in the same experiment. Multiple tracers were discriminated by film autoradiography on the basis of their properties (particulate or nonparticulate, short or long half-life), and by multiple film exposure. A multiwire chamber was used for (3)H detection. Perfusional and metabolic maps were obtained in transverse microslices of the heart (40 mum thick) by digital image processing. The operation, the advantages and limits of the single techniques as well as their combined use are described. The two techniques are complementary: DFA, although time consuming and proportionality limited, allows the use of multiple tracers and it is mandatory for particulate tracer detection due to its high spatial resolution; MWPCA, in spite of a lower resolution provides a very fast and proportional detection as compared to DFA, but limited to only one tracer at the time.