PSPMT and photodiode designs of a small scintillation camera for imaging malignant breast tumors

We are investigating the concept of utilizing a small gamma ray scintillation camera to help identify and localize malignant breast tumors after a suspicious finding in a mammogram. Excellent sensitivity and specificity for malignant breast tumors has been achieved using conventional nuclear medicine scintillation cameras with certain Tc-99m labeled radiopharmaceuticals. However, because of the large size, low image resolution and high cost of these devices, they are not ideal for use in breast imaging in a mammography suite. A dedicated miniaturized camera would allow imaging at angles that are physically impossible with the standard camera. These lateral views would not include the background activity from the heart and liver. In addition, with a potentially higher intrinsic resolution, shorter collimator and if breast compression is applied, a small camera could significantly improve the sensitivity and signal to noise ratio for the scintillation imaging method. We are exploring two different photodetector technologies for a small prototype camera development. The first uses a position sensitive photomultiplier (PSPMT) as the photodetector, the second, an array of silicon PIN photodiodes (PD). In this report, we present imaging results obtained with a NaI(Tl)-PSPMT design, and the design features, expected performance and relevant energy and position measurements obtained for a test CsI(Tl)-PD device.