الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
The distribution of radioactivity in an object can be imaged using single photon emission computed tomography SPECT. According to this method, a gamma camera rotates around the objects, acquiring projection images. SPECT imaging has a number of potential advantage over conventional nuclear medicine planar imaging. However, special attention is needed, and aspect care is taken in both acquisition and reconstruction of the image. The present study investigates the various parameters affecting SPECT images and the experimental results demonstrate that, the uniformity of reconstructed images is very sensitive to scintillation camera. Contrast is an important aspect of SPECT because the removal of over and underlying activity improves contrast. The number of views required for SPECT should be carefully determined. If the number of views is less than the minimum, streak artifacts may appear in the reconstruction slices. The type of collimator is studied and we found that low energy ultrahigh resolution collimator is recommended compared to low energy high resolution collimator. Higher SPECT resolution will always be achieved with the smaller pixel size of 128 x 128 matrices. Concerning the used energy window width, we notice that there is an improvement in resolution with increasing signal to noise ratio and decreasing the total count of the reconstructed image. Bad contrast of the image is produced case of 10% and 15% energy windows in comparison with 20% energy window. We demonstrate that the standard 20% symmetric energy window around the 140 KeV photo peak of Tc99m produce adequate contrast and resolution for SPECT imaging. Analysis of the results obtained from different types of reconstruction filters, show that the best reconstruction filters is the ramp filter with prereconstruction Butterworth filter, and the best cutoff frequency for all reconstruction filter is 0.3 cm1 . Photon attenuation is an important factor affecting SPECT imaging. Although he conventional and the most widely used reconstruction technique in nuclear medicine is filtered back projection, its images are noisy, inaccurate, and contain unwanted streak artifacts. The diagnostic accuracy of SPECT imaging can be improved using iterative reconstruction methods. The contrast and resolution were improved with iterative reconstruction technique (OSEM). In conclusion, it can be stated that methodological comparisons and experimental, both with phantoms and human studies, show that iterative reconstruction and especially the OSEM method is a clear improvement of SPECT in clinical use and it represents advances in quantitative and qualitative SPECT imaging.