Attenuation and scatter correction in SPECT for sources in a nonhomogeneous object: a monte Carlo study

Single-photon emission computed tomography (SPECT) is important for imaging radioactivity distributions in vivo. Quantitative SPECT is limited due to attenuation and scatter contribution. Approximations such as constant attenuation and mono-exponential scatter functions will not be valid for non-homogeneous regions. A correction method is described where non-uniform density-maps are used in the attenuation correction. Correction for non-uniform scatter is made by a convolution technique based on scatter line-spread functions (SLSF) calculated for different locations inside a clinically realistic, nonhomogeneous, computer phantom. Calculations have been made for a myocardiac source, a uniform source in the lungs and a tumor located in the lungs. Projections were simulated for photon energies corresponding to 201Tl, 99mTc, and 111In. The results show that quantitative images can be obtained in nonhomogeneous regions. An increased contrast has also been demonstrated in the SLSF-corrected images. Comparison with measurements have been made to validate the Monte Carlo code and the scatter and attenuation method.