Development of a small gamma camera using wavelength-shifting fibres coupled to inorganic scintillation crystals for imaging 140 keV gamma rays

We are developing a small gamma camera for scintimammography with Tc/sup 99m/ (140 keV). The camera is based on coupling wavelength-shifting fibres (WSF) to the surface of an inorganic scintillation crystal-CsI(Na)-in order to obtain information about the position of interaction of the gamma rays. We have performed experimental measurements on the light output of 1 mm round multi-clad WSFs coupled to two CsI(Na) slabs, 3 and 5 mm thick. The results show a mean of 3.8 photoelectrons per gamma ray interaction of Co/sup 57/ 122 keV, with a mean of 1 photoelectron at the fibre located nearest the collimated beam of gamma rays, for the 3 mm thick crystal. Simulations based on the single electron response of photomultiplier tubes show that a 1.7 mm FWHM spatial resolution can be achieved with this camera design. The camera can be shaped to suit any application, it is compact and has low cost, which, together with its predicted performance in terms of spatial resolution, makes this concept very promising as a small gamma camera for 140 keV.