Abstract
The quantitative accuracy of SPECT is limited by photon attenuation and scatter effect when photons interact with atoms. In this study, we developed a new attenuation correction (AC) method, CT-based mean attenuation correction (CTMAC) method, and compared it with various methods that were often used currently to assess the AC phenomenon by using the small-animal SPECT/CT data that were acquired from various physical phantoms and a rat. The physical phantoms and an SD rat, which were injected with 99mTc, were scanned by a parallel-hole small-animal SPECT, and then they were imaged by the 80 kVp micro-CT. Scatter was estimated and corrected by the triple-energy window (TEW) method. Absolute quantification was derived from a known activity point source scan. In the physical-phantom studies, we compared the images with original, scatter correction (SC) only, and the scatter-corrected images with AC performed by using Chang's method, CT-based attenuation correction (CTAC), CT-based iterative attenuation compensation during reconstruction (CTIACR), and the CTMAC. From the correction results, we find out that the errors of the previous six configurations are mostly quite similar. The CTMAC needs the shortest correction time while obtaining good AC results.
Highlights
In order to improve the image quality of SPECT in clinical practice and the quantitative accuracy, photon attenuation correction (AC) has been broadly studied
The activity per unit volume in the central region of the phantom that was underestimated had flattened out, the overall activity concentration was pulled to close to the true value, and this is able to reflect the real situation of the homogenous distribution of radionuclide inside the ratsized phantom
The quantification corrected by CT-based mean attenuation correction (CTMAC) in combination with scatter correction is the same as those attenuation correction methods that are broadly applied currently, the errors are within the acceptable range, and the time required for correction is shortest
Summary
In order to improve the image quality of SPECT in clinical practice and the quantitative accuracy, photon attenuation correction (AC) has been broadly studied. It has been applied in territories, such as cardiac imaging, brain functional imaging, and cancer imaging. The photon energy emitted from the radioisotopes used for SPECT is mostly less than 400 keV. There are three factors affecting photon attenuation. It is energy, which is the characteristic of the radiation itself. The photon of higher energy is not easier to be attenuated and is easier to penetrate materials.
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