[Evaluation of Resolution Correction in Single Photon Emission Computed Tomography Reconstruction Method Using a Body Phantom: Study of Three Different Models].

PURPOSE: The aim of this study was to evaluate the resolution recovery techniques of Flash3D, Astonish, and Evolution in single photon emission computed tomography(SPECT) using a body phantom. METHODS: We scanned a National Electrical Manufactures Association body phantom filled with 99mTc. The body of the phantom with radioactive sphere and background was filled with either water or radioactive solution. We investigated image quality using profile curves, recovery coefficient, and image contrast. RESULTS: The profile curve at the edge of the hot sphere showed artifact due to Gibbs oscillation for all techniques, and also over estimation of recovery coefficient was seen in the hot sphere, as had been previously reported in a simulation study. These phenomena were more remarkable than Evolution in the Flash3D and Astonish techniques. For the contrast between hot sphere and background, the contrast recover was enough for the <17-mm hot spheres. These results showed that the effect of contrast correction was less as the radius of rotation diameter became large. CONCLUSION: In the present study using the body phantom, overestimated counts and edge artifacts due to Gibbs oscillation were shown. These phenomena were different by each resolution correction algorithms. Also, there were limitation regarding image quality improvement by resolution correction depending on sphere size and length of radius of rotation.

[Comparison of FBP and ML-EM reconstruction used by simulation data; effect of the projection number for the SPECT image].

PURPOSE: The influence of the numbers of projection of SPECT exerting on a re-constructed image cannot be strictly evaluated by phantom studies. Therefore, we compared re-constructed images of the FBP method and the ML-EM method by using simulation data. METHODS: Simulation data was entered in the image processing software, and the projection data that changed the numbers of projection was made. Afterwards, reconstructed images of the FBP and the ML-EM methods were compared with respect to contrast, %COV, and the NMSE value. RESULT: When the numbers of projection of the FBP and the ML-EM method were decreased, all of the contrast, %COV, and the NMSE value were more deteriorated than that of the ideal image. Therefore, the image quality of SPECT improves with both FBP and ML-EM methods when there are many numbers of projection. Moreover, the FBP method was excellent in a cold contrast, and the ML-EM method was uniformly excellent. Therefore, an understanding of features and their inspection are effective for the selection of each image reconstruction method.