Evaluation of quality of images reconstructed from the data acquired in narrow (15%) and standard (20%) symmetrical energy window in conjunction with physical filter in tc-99m spect

Single Photon Emission Computed Tomography (SPECT) is a very useful medical imaging modality for detecting various diseases. However, relative to other medical imaging specialties, such as X-ray and Magnetic Resonance Imaging it has some limitations in terms of dgradation of image quality. Photopeak energy window width and scatter radiation are the factors among others in SPECT imaging that affect the image quality. This study is aimed at evaluating the narrow (15%) and standard (20%) energy window data images with and without physical filter (Zinc (Zn) 0.2mm thick) as scatter radiation absorber. Philips ADAC/Forte dual head SPECT system was used. Carlson’s phantom consisting of cold and hot region inserts, filled with water was scanned. Tc-99m radionuclide (21mCi) was distributed homogeneously into the phantom. Data were acquired by setting 15% and 20% energy windows with and without physical filter. Images were reconstructed using filtered back projection technique with a Butterworth filter of cut-off frequency 0.35/cm and order 5. Chang’s attenuation correction method was applied using 0.12 and 0.13/cm linear attenuation coefficient (LAC) values. Reconstructed images were investigated both qualitatively and quantitatively. Cold and hot region image results indicated that the physical filter improved the contrast and SNR of narrow energy window data images with a 0.13/cm LAC value as compared to standard energy window data images. Furthermore, the detectability of smaller cold and hot regions was enhanced. In conclusion, the use of a physical filter with a narrow energy window provided improved image quality as compared to standard energy window data images. Therefore, it is suggested that further studies should be conducted for the implementation of physical filter technique with narrow energy window in clinical examinations