The Influence of Inter-Crystal Scattering on Detection Efficiency of Dedicated Breast Gamma Camera: A Monte Carlo Study

Abstract

-Dedicated gamma cameras based on Photodiodes coupled to pixellated small size scintillators, is suitable for high resolution imaging such as small animal and breast cancer imaging. It is well known that inter-crystal scattering (ICS) is of the major resolution degradation factors in the system with small crystal size. The aim of this study is to quantitatively calculate the ICS events in different types of crystal material (CsI, NaI and LaBr 3 ) and size (0.5×0.5, 1×1, 1.5×1.5 and 3×3 mm 2 ) using Monte Carlo simulation. The simulations were designed to optimize camera design particularly for crystal pixel size and scintillation material. Three types of scintillation crystal were exposed by 140 keV photons of a point source as a pencil beam in orthogonal and oblique incidences. In oblique incidence, detected events in central pixel of crystal array decreased in small angles slowly and then decreased rapidly by increasing of incidence angle. In orthogonal incidence in four different pixel sizes, the percentage of photons encounters the ICS event in CsI crystal was 1.82%, 3.76%, 4.94% and 6.49% events for 3×3, 1.5×1.5, 1×1 and 0.5×0.5 mm 2 crystal pixel size respectively, that were less than NaI and LaBr 3 crystals. Also in the oblique incidence, in all pixel sizes of CsI crystal the photons encountered ICS events were less than NaI and LaBr 3 . According to our results, The CsI crystal from the point of view of higher detection efficiency and position detection accuracy (PDA) and lower ICS is preferable. However, the optimal crystal material and size for high resolution breast imaging are still open questions which require further research and development efforts.

Quantification of Inter-crystal Scattering and Parallax Effect in Pixelated High Resolution Small Animal Gamma Camera: A Monte Carlo Study

“…However, the use of smaller pixel size brings disadvantages, such as: the fraction of penetrated and scattered photons increases and this may have a detrimental impact on the quality of the final image because they cause some photons to be detected in crystals not corresponding to original position from which the photon was emitted and this leads to remarkable error in position estimation (mispositioning) [3]. Although Both intercrystal scattering(ICS) and penetration have been matters of concern in PET imaging [4], but it seems small crystal size in high resolution small animal gamma camera cause the imager suffer from ICS events even when using low energy photons such as 140KeV [5].…”

Effects of Crystal Pixel Size and Collimator Geometry on the Performance of a Pixelated Crystal -Camera Using Monte Carlo Simulation

“…Our object was to calculate the contribution of ICS events in 3 sizes of crystals and find the best crystal pixel size and geometry of hexagonalhole collimators to achieve higher PDA, CNR, and DE and lower full width at half maximum (FWHM) and ICS events. We performed these simulations without a collimator in a previous study and obtained good results (14). In this study, we wanted to determine the effects of a collimator on our results and camera performance.…”