Monte Carlo Study of the Effect of Backscatter Materail Thickness on 99mTc Source Response in Single Photon Emission Computed Tomography

Authors

  • Jalil Pirayesh Islamian Medical Physics Department, Faculty of Medicine, Tabriz University of Medical Sciences, Tabriz, Iran.
  • Mahdi Momennezhad Nuclear Medicine Department, Imam Reza Hospital, Mashhad University of Medical Sciences, Mashhad, Iran
  • Ramin Sadeghi Nuclear Medicine Department, Imam Reza Hospital, Mashhad University of Medical Sciences, Mashhad, Iran
  • Seyyed Rasool Zakavi Nuclear Medicine Department, Imam Reza Hospital, Mashhad University of Medical Sciences, Mashhad, Iran
Abstract:

Introduction SPECT projections are contaminated by scatter radiation, resulting in reduced image contrast and quantitative errors. Backscatter constitutes a major part of the scatter contamination in lower energy windows. The current study is an evaluation of the effect of backscatter material on FWHM and image quality investigated by Monte Carlo simulation. Materials and Methods SIMIND program was used for simulation of a Siemen’s dual-head variable angle scintillation gamma camera. Planar and SPECT scanning of a 99mTc source and a Jaszczak phantom for varying thicknesses of Perspex slabs, as a backscatter media, were analyzed using the photopeak and scatter windows. Simulated planar images and reconstructed tomographic images were evaluated qualitatively, by two nuclear medicine specialists, and quantitatively, by Structural Similarity (SSIM) Index. Results In the 99mTc photopeak window, no significant change in total counts due to backscatter material was measured. In the scatter windows, scattering was overestimated compared with a simulated backscatter free SPECT system. For instance, at a thickness of 10 cm, total counts of a 99mTc source detected in the 72 keV windows eventually doubled with increasing backscatter material, compared with the situation without backscatter material. The backscatter contribution plateaued when more than 7 cm of scatter material was placed but there were optimized results for a backscatter thickness of 4.5 cm. Better image quality for the thickness was confirmed by the results of eye interpretation and also by SSIM algorithm. Conclusion Backscatter should be taken into account, particularly in model-based scatter correction methods in SPECT for an accurate simulation system optimization.

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Journal title

volume 10  issue 1

pages  69- 77

publication date 2013-03-01

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