EFFECTIVENESS OF A COMBINATION OF ML-EM AND STIM-CT IN PIXE-CT FOR BIOLOGICAL SPECIMEN

Abstract

In this study, we applied ML-EM (maximum likelihood expectation maximization) iterative algorithm and STIM-CT to a three dimension imaging technique of PIXE -CT for cellular analysis using 3 MeV proton microbeam with a diameter of 1 μm at TIARA (Takasaki Ion Accelerators for Advanced Radiation Application). The algorithm had been applied to tomography such as SPECT (Single Photon Emission Computed Tomography). It is also possible and suitable to apply the algorithm to PIXE-CT because the algorithm can be used to project images taking into account errors due to rare events. Energy loss of incident particles and absorption of X-rays, however, affect quantitative values dramatically in the case of PIXE -CT. We estimated those effects from density distribution of major elements measured by STIM-CT in this work. In order to show the appropriateness of this method, X-ray yield and absorption were calculated using density distribution of two-dimensional Shepp phantom. The PIXE-CT experiments were carried out using a dried unicellulate as a test sample placed on an automatic rotation stage, which made a full turn by rotating 360° at each step of 18° in vacuum. The results of those simulation and experiments have proved that this method is effective.