Abstract
In SPECT, noise is one of the major limitations that degrade image quality. To suppress the noisy signals in an image, digital filters are most commonly applied. However, in SPECT image reconstruction, selection of an appropriate filter and its functions has always remained a difficult task. In this work an attempt was made to investigate the effects of varying cut-off frequencies and in keeping the order of Butterworth filter constant on detectability and contrast of hot and cold re-gions images. A new insert simulating hot and cold regions which provides similar views in a reconstructed image was placed in the phantom’s cylindrical source tank and imaged. Tc-99m radionuclide was distributed uniformly in the phantom. SPECT data were collected in a 20% energy window centered at 140 keV by a Philips ADAC Forte dual head gamma camera mounted with a LEHR collimator. Images were generated by using the filtered backprojection technique. A Butterworth filter of order 5 with cut-off frequencies 0.35 and 0.45 cycles·cm-1 was applied. Images were examined in terms of hot and cold regions, detectability and contrast. Results show that the hot and cold regions’ detectability and contrast vary with the change of cut-off frequency. With a 0.45 cycles·cm-1 cut-off frequency, a significant enhancement in contrast of cold regions was achieved as compared to a 0.35 cycles·cm-1 cut-off frequency. Furthermore, the detectability of hot and cold regions improved with the use of a 0.45 cycles·cm-1 cut-off frequency. In conclusion, image quality of hot and cold regions affected in a different way with a change of cut-off frequency. Thus, care should be taken in selecting the filter cut-off frequency prior to reconstruction of images; particularly, when both types of regions are expected in the reconstructed image.
Highlights
In clinical single photon emission computed tomography (SPECT), the quality of an image plays a significant role in diagnosing abnormalities and in the proper management of patients
The selection of filter in SPECT reconstruction depends on many factors, for example, type of patient study, energy of gamma ray photon, image count density, dose administered into the patient, statistical noise, amount of background noise, type of collimator and the information desired by a clinician as well as the preference of the interpreting physician in routine clinical studies [2] [7] [17]
Our study explored the effects on detectability, shape and image quality of hot and cold regions’ pairs with different sizes and at different locations in the phan
Summary
In clinical single photon emission computed tomography (SPECT), the quality of an image plays a significant role in diagnosing abnormalities and in the proper management of patients. SPECT images are reconstructed using filtered back projection and iterative techniques where the filtering is an important part of the image reconstruction process for addressing noisy signals which affect the quality of images to a greater extent [6]. In this regard, a variety of mathematical filters have been applied for various purposes, e.g., removal of star artifacts, statistical noise reduction, signal enhancement and restoration of image resolution. The disadvantage of low pass filters is a decrease in image contrast
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