Positron camera with extended counting rate capability.

Positron emitters may be imaged using two opposing scintillation cameras without collimators. The counting rate limitation of this approach can be largely largely overcome by using graded absorbers to reduce scattered radiation from the patient and using not only photopeak events but Compton events in the scintillator as well. This increases the useful counting rate by more than a factor of 5. By combing this technique with the use of fast electronics, useful images have been obtained in the presence of scattering material at counting rates above 7,500 cps.