Quantitative autoradiography using a radioimager based on a multiwire proportional chamber

Determination of the biodistribution of radiopharmaceuticals is an importan t issue for the evaluation of their performance in diagnosis and therapy. I n this study, we evaluated a digital radioimager (RI) based on a multiwire proportional chamber for quantitative autoradiography (AR). The RI allows d irect detection of electronic emissions of gamma emitters. Its qualitative and quantitative performances were tested on Tc-99m and In-111 labelled sec tions and compared with conventional film AR. Linearity of count rate versu s activity was verified over a 10(4) range of activity. As compared with fi lm AR, a substantial improvement of the detection limit was obtained even f or acquisition periods up to 20 times less than film exposure times. We pro vided the basis for quantitative analysis with tissue equivalent paste stan dards: the Tc-99m and In-111 RI counting efficiencies were respectively 1.1 9% and 2.35%. We illustrated the respective values of RI and film AR in two rat studies: Tc-99m-DMSA in kidney and dual-isotope Tc-99m-MIBI and In-111 -antimyosin in heart. Calculated activity concentrations on sections of rat organs confirmed good correlation to gamma counting (deviation less than 1 2%). We suggest RI as a convenient technique for fast localization of singl e or dual-isotope tracers and determination of activity distribution.