Investigating the effect and photon scattering correction in isotopic scanning with gamma and SPECT

Nowdays medical imaging systems has been become a very important tool in medicine, both in diagnosis and treatment. With the fast improvement in the computer sciences in the last three decades, three dimensional imaging systems or topographic systems has been developed for the daily applications. Among the different methods, for now X-ray Computerized tomography scanning, Magnetic Resonance Imaging, Single Photon Emission Computerized Tomography and Positron Emission tomography have been found many clinical application. SPECT and PET imaging systems are working with the use of emitting photons from special radioisotopes. In these two systems, image is reconstructed from a distribution of radioisotope in the human body's organs. In SPECT accuracy of data quantification for image reconstruction has influenced from photon attenuation, photon scattering, statistical noises and variation in detector response due to distance. Except scattering other three factors could be modeled and compensated with relatively simple models. Photon scattering is a complex process and usually semiemperical methods is used for its modeling. The effect of scattering photons on images was considered. This survey was done in both lab and clinical cases. Radioisotopes were 192 Ir and 99m Tc. 192 Ir is a solid source with the half-life of 73 days and is used at industrial radiography application. At the beginning, models and methods, were established by the help of 192 Ir. Then at the final stage, they were developed to use for 99m Tc. There are different methods for the error correction of scattered photons. A method from the 'window subtraction' group has been developed for lab cases. Generally, in this method with the use of adjacent window of the photopeak window, scattered photons are subtracted from the original count. A Monte Carlo simulation is used for better evaluation of results. In the clinical section , a dual head SPECT system was (ADAC system of Shariati hospital at Tehran). The phantom was elliptical Jaszczak (or Carlson Phantom). The effect of different adjustment of system on scattering were considered. For qualitative comparison in each case, line Spread Function and Modulating Transfer Function were measured and extracted, respectively. This comparison were done for both lab and clinical systems in different experiments, with and without scatter correction. Also image reconstruction with filtered back projection algorithm were performed in both cases (with and without scatter correction) and results has been surveyed. The final result was: scattering has a major rules in degrading of reconstructed images and with scatter correction, it is possible to compensate error and increase image quality