GEANT4/GATE Simulations

Collimator and gamma-Camera system simulations with GEANT4/GATE.

Front structure (photograph detail) of the hexagonal, parallel hole Pb-collimator used with the gamma-Camera system. Its main characteristics are: Face area: 59.5 x 60.4 mm2 Thickness: 26.8 mm Circumscribed Circle: R=0.75 mm Septum (Pb): 0.25 mm Number of holes along X: Nx=32 Number of holes along Y: Ny=23

Fig. 1: The collimator and the scintillation crystal of the gamma-Camera system have been properly modeled within the GATE simulation environment. The left part of this figure shows the hexagonal detail of the collimator structure. The simulated experimental setup is shown in the central part. The radiation source consists of four capillaries filled with water solution of 99mTc with the geometry shown in the right part of the figure. The capillaries are placed parallel to the collimator face and in various distances from it.

Fig. 2: Planar image projection of the 4-capillaries phantom as captured with the gamma-Camera system (dark blue) and directly compared with the simulated results (light blue). The distance phantom-collimator in this case is 5 mm.

Fig. 3: Left: The simulated gamma-Camera system repeated 36 times in a ring around the phantom to allow simultaneous data accumulation for SPECT analysis. Right: Simulation results of a MIRD type anthropomorphic head phantom with three ellipsoidal sources in the center and collimator geometry D/T=0.02 (D: Hole Diameter, T: Collimator Thickness).

Fig. 4: GATE simulated energy spectra for the IASA gamma-Camera, obtained for a 99mTc point source at 12cm from the collimator under a water thickness of (a) 0cm, (b) 4cm and (c) 10cm.

• Validation of the GATE Monte Carlo simulation platform for modelling a CsI(Tl) scintillation camera dedicated to small-animal imaging Phys.Med.Biol. 49 (2004) 271 (D. Lazaro et al.)
• Collimator Study of a gamma-Camera System using GATE IEEE MIC09 M13-369 (M. Mikeli et al.).

Fig. 5: Optical photon simulation with the program DETECT2000: The isotropically generated optical photons inside the scintillation crystal are propagated to the detective surface of the photomultiplier. Their ditribution is normally fitted with two Gauss shaped curves, where the red curve represents the photons that have not been reflected and the blue the reflected ones.

Further reading in:

• Study of the optical properties of continuous and pixelated scintillation crystals Jinst 4 (2009) P09002 (A. Polychronopoulou et al.)