Abstract
In single photon emission computed tomography (SPECT) imaging, the choice of a suitable filter and its parameters for noise reduction purposes is a big challenge. Adverse effects on image quality arise if an improper filter is selected. Filtered back projection (FBP) is the most popular technique for image reconstruction in SPECT. With this technique, different types of reconstruction filters are used, such as the Butterworth and the Hamming. In this study, the effects on the quality of reconstructed images of the Butterworth filter were compared with the ones of the Hamming filter. A Philips ADAC forte gamma camera was used. A low-energy, high-resolution collimator was installed on the gamma camera. SPECT data were acquired by scanning a phantom with an insert composed of hot and cold regions. A Technetium-99m radioactive solution was homogenously mixed into the phantom. Furthermore, a symmetrical energy window (20%) centered at 140 keV was adjusted. Images were reconstructed by the FBP method. Various cutoff frequency values, namely, 0.35, 0.40, 0.45, and 0.50 cycles/cm, were selected for both filters, whereas for the Butterworth filter, the order was set at 7. Images of hot and cold regions were analyzed in terms of detectability, contrast, and signal-to-noise ratio (SNR). The findings of our study indicate that the Butterworth filter was able to expose more hot and cold regions in reconstructed images. In addition, higher contrast values were recorded, as compared to the Hamming filter. However, with the Butterworth filter, the decrease in SNR for both types of regions with the increase in cutoff frequency as compared to the Hamming filter was obtained. Overall, the Butterworth filter under investigation provided superior results than the Hamming filter. Effects of both filters on the quality of hot and cold region images varied with the change in cutoff frequency.
Highlights
In single photon emission computed tomography (SPECT), image noise is an important factor may degrade the image quality
The structured noise may occur from imaging system artefacts, the nonuniformities in gamma camera images, such as ring or streak artefacts produced during the image reconstruction process which interferes with the visibility of the structure of the region of interest [8]
These mathematical filters are categorized as passive filters which allow low frequencies to pass and are most commonly used in SPECT hot and cold region images used for analysis are shown in Figures 2 and 3, respectively
Summary
In SPECT, image noise is an important factor may degrade the image quality. Noise is more common in nuclear medicine imaging [1, 2] which can be reduced by using digital filters [3,4,5,6]. In this context, different types of filters, such as high-pass, low-pass, and band-pass, are used. In SPECT, filtering of the image data is done in order to suppress the noise signals. The structured noise may occur from imaging system artefacts, the nonuniformities in gamma camera images, such as ring or streak artefacts produced during the image reconstruction process which interferes with the visibility of the structure of the region of interest [8]
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