Iranian Journal of Medical Physics

Iranian Journal of Medical Physics

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

Document Type : Original Paper

Authors
Jalil Pirayesh Islamian 1
Mohammad Taghi Bahreyni Toossi 2
Mahdi Momennezhad 3
Seyyed Rasool Zakavi 3
Ramin Sadeghi 3
1 Medical Physics Department, Faculty of Medicine, Tabriz University of Medical Sciences, Tabriz, Iran.
2 Medical Physics Research Center, Medical Physics Department, Mashhad University of Medical Sciences, Mashhad, Iran
3 Nuclear Medicine Department, Imam Reza Hospital, Mashhad University of Medical Sciences, Mashhad, Iran
10.22038/ijmp.2013.920
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.
Keywords
Backscatter Media
Image Quality
Resolution
SIMIND Monte Carlo
Single Photon Emission Computed Tomography
Subjects
Iranian Journal of Medical Physics
Volume 10, Issue 1 - Serial Number 1
Winter & Spring 2013
March and April 2013
Pages 69-77

  • Receive Date 10 July 2013
  • Revise Date 29 November 2012
  • Accept Date 21 April 2013