| Summary: | 碩士 === 國立清華大學 === 生醫工程與環境科學系 === 102 === Single photon emission computed tomography (SPECT), an important technique in nuclear medicine, can collect the emitted photons of the radionuclide and reconstruct the images of radionuclide distribution inside body through computer calculation. However, attenuation and scatter effect occurs when photon passing through the body and will reduce quantitative accuracy of measured radioactivity concentration. In order to achieve the quantitative accuracy, it is necessary to compensate the photon attenuation in the object. The most used attenuation correction method in SPECT is Chang’s method. In this study, we proposed a method called Improved Attenuation Correction (IAC) method. The IAC method estimates the ACF map by calculating the equivalent linear attenuation coefficient based on the attenuation map and the activity map. The attenuation map can be calculated from CT images, while the activity map can be assumed uniform in the initial step. After attenuation correction using the calculated ACF map of IAC, the image can be reconstructed by filter back-projection algorithm and the activity map for next iteration. The iteration stops when the difference between the reconstructed images of two successive iterations is smaller than a predefined criterion. The performance was evaluated by using Monte Carlo simulations of two digital phantoms (brain phantom and thorax phantom). The simulated results demonstrated that the proposed method achieved better image quality and quantitative accuracy than Chang’s method. We concluded that the proposed attenuation correction method could effectively restore the activity concentration and is potential for clinical uses.
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