new approach to scatter correction in SPECT images based on Klein_Nishina equation

Scattered photon is one of the main defects that degrade the quality and quantitative accuracy of nuclear medicine images. Accurate estimation of scatter in projection data of SPECT is computationally extremely demanding for activity distribution in uniform and non-uniform dense media. The objective of this paper is to develop and validate a scatter correction technique that use an accurate analytical model based on Klein_Nishina scatter equation and compare Klein_Nishina scatter estimation with triple energy window. In order to verify the proposed scattering model several cylindrical phantoms were simulated. The linear source in the cylindrical Phantoms was a hot rod filled with 99mTc. K factor defines as the ratio of scatter resulting from MC simulation to scatter estimated from Klein_Nishina formula. Also a SPECT/CT scan of the image quality phantom was acquired. Row data were transferred to a PC computer for scatter estimation and processing of the images using MLEM iterative algorithm in MATLAB software. The scatter and attenuation compensated images by the proposed model had better contrast than uncorrected and only attenuation corrected images. The K-factors that used in proposed model doesn't vary with different activities and diameters of linear source and they're just a function of depth and composition of pixels. Based on Mont Carlo simulation data, the K_N formula that used in this study demonstrates better estimation of scattered photons than TEW. Proposed scattered correction algorithm will improve 52.3% in the contrast of the attenuated corrected images of image quality phantom

Reducing the respiratory motion artifacts in pet cardiology: a simulation study

There are several technical features that make PET an ideal device for the noninvasive evaluation of cardiac physiology. Organ motion due to respiration is a major challenge in diagnostic imaging, especially in cardiac PET imaging. These motions reduce image quality by spreading the radiotracer activity over an increased volume, distorting apparent lesion size and shape and reducing both signal and signal-to-noise ratio levels 4D average male torso [2 cm diaphragmatic motion] produced by NCAT phantom was used for simulations. Emission sinograms generated by Eidolon PET simulator were reconstructed using iterative algorithm using STIR. The respiratory motion correction [RMC] applied to data sets using an automatic algorithm. Cross section views, activity profiles, contrast-to-noise ratios and left ventricle myocardium widths of corrected and non-corrected images were compared to investigate the effect of applied correction. Comparison of respiratory motion corrected and non corrected images showed that the algorithm properly restores the left ventricle myocardium width, activity profile and improves contrast-to-noise ratios in all cases. Comparing the contrast recovery coefficient []shows that the applied correction effected phases of number 7,8 and 9 of cardiac cycle more than the other 13 phases and the maximum value being 1.43 +/- 0.07 for phase number 8. The maximum value of ratio of the left ventricle myocardium width for non-RMC and RMC images along the line profile passing the apicobasal direction and along the line profile passing from the middle of the lateral wall of the left ventricle were 1.38 +/- 0.07 for phase number 9 and 1.12 +/- 0.03 for phases of number 8 and 9 respectively. Blurring and ghosting of each image depends on the speed of diaphragm during that respiratory phase. This simulation study demonstrates that respiratory motion correction has good overall effect on PET cardiac images and can reduces errors originating from diaphragmatic motion and deformation. Effect of such a correction varies from one cardiac phase to another and this depends on the blurring and ghosting of all respiratory phases used to form this cardiac phase. Using an automatic algorithm capable of correcting respiratory motion using full signal may be very useful to prevent lengthening of the overall scan time to obtain same motionless lesion signal levels