Evaluation of the effect of the Wolfmet collimator on the detection capability of the SPECT imaging system

Abstract

Collimator is one of the important parts in the single photon emission computed tomography (SPECT) imaging system and plays an effective role in imaging quality. In this study, the effect of parallel hole collimator material on quality of radioisotopic images and functional parameters of the imaging system was evaluated. Materials and methods: SIMIND Monte Carlo program, version 6.1, was used to simulate a Siemens e.cam SPECT imaging system equipped with a "Low Energy-High Resolution" (LEHR) parallel hole collimator. 99mTc radioisotope was used for a point source and also Jaszczak phantom imaging in the both simulated and experimental systems. Nine tungsten alloys with high atomic number (composed of tungsten, nickel, copper and iron) were investigated as the LEHR collimator material. In this study, a 99mTc point source, a Jaszczak phantom and also XCAT voxelized human phantom were used to investigate the effect of the collimator material on the functional parameters of the imaging system, including spatial resolution, sensitivity and characteristics parameters of the collimator. Structural similarity index (SSIM) and medical image diagnosis were used to evaluate detectability and image quality parameters including contrast and spatial resolution. Results: Verification of the imaging system simulation was confirmed by comparing the functional and imaging parameters obtained from the both simulated and experimental systems. Improved image quality including contrast of hot and cold lesions in liver of XCAT phantom and cold spheres of the Jaszack phantom was found by the W_ha193 collimator composing 93% tungsten, 3.5% nickel and 3.5% copper, compared to the conventional lead and lead-antimony collimators. The alloy improved spatial and energy resolution without reducing sensitivity and percentage of collimator induced x-rays and also the penetrated rays was significantly reduced without reducing the primary gamma rays compared to the Lead.