Performance estimation of high resolution SPECT for the human brain by Monte Carlo simulation of scintillation lights

We developed the high resolution SPECT for the human brain. The SPECT has two kinds of detectors. One middle-size detector views whole a head. The other small detector which has extremely resolution (~1 mm) views localized region. These detectors are rotated simultaneously. The large detector consists of Nal(Tl) scintillator (15 cm×20 cm), 15 flat panel type multi-anode PMTs (H8500 Hamamatsu). The performance evaluation, spatial and energy resolution, has performed. The obtained spatial resolutions of X-direction and Y-direction are 2.4 mm and 2.1 mm(FWHM), respectively, and 10%@140 keV (FWHM) of the energy resolution was obtained. On the other hand, the small detector for the regional field of view is under the development. We will use the LaBr₃(Ce) as the scintillator which has large amount of scintillation lights lather than that of Nal(Tl). The performance of LaBr₃(Ce) has estimated by the Monte Carlo simulation of scintillation lights after the comparing the result of the experiments of the middle-size detector with that of the simulation. In this simulation, many optical properties of materials are considered. Using this simulation, the influence of the scintillator thickness on the spatial resolution has investigated. Also, main contribution is given to spatial resolution has been investigated by changing some optical properties such as the amount of emission lights, the refractive index of optical coupling grease and the index of reflector in this simulations. The small detector will be used with a pin-hole collimator, therefore gamma-rays obliquely enter the detector. The spatial resolutions of oblique and parallel incident are also compared.