Simulation study of the influence of collimator material on image quality improvement for high energy photons in nuclear medicine using MCNP code

Performance of a single photon emission imaging system (SPECT) is determined more by the collimator than any other components. In high energy septal penetration and parallax error increases and the quality of image decreases. For reduction of the artifacts, high-z materials with high density such as depleted Uranium, Gold and Tungsten can be used instead of lead. In this work, the effect of collimator material has been evaluated. Also the dimensions (Septa thickness, Hole length, MTF (Modulation Transfer Function), Septal penetration and hole pattern) of the collimators has been investigated. MCNP Monte Carlo code has been used for our simulations. In order to benchmark, the HEGP and UHEGP collimators of GE Company are selected and FWHM values of the collimators calculated and compared with GE Company reported data. The effect of three materials (Tungsten, depleted Uranium and Gold) instead of lead has been investigated. The comparison showed good agreement between the simulation results and GE reported data. Performance of the collimator improved by increasing the atomic number of the collimator material. The collimators made of Uranium, Gold, Tungsten and Lead have better performance respectively with the same geometry. All results showed that, in addition to collimator dimensions, the effect of material has great influence on the quality of the image and collimator performance.