Feasibility study on multi-gamma-source CT imaging

Abstract

This study was performed to test a feasibility of multi-gamma-source CT imaging system. Gamma-source CT imaging system employs a radioisotope that emits monochromatic energy gamma-rays. The advantages of gamma-source CT include its immunity to beam hardening artifacts, its capacity of quantitative CT imaging, and its higher performance in low contrast imaging compared to conventional x-ray CT systems. Radioisotope should be blocked by use of a pin-hole collimator so as to make a fine focal spot. Due to its low flux in general, the reconstructed image from a single gamma-source CT would suffer from high noise. To address this problem, our study proposed a multi-gamma source CT imaging system and developed an iterative image reconstruction algorithm accordingly. Conventional imaging model assumes a single source position and image reconstruction algorithm accordingly constructs the ray tracing along a single ray per given detector pixel. In an iterative reconstruction framework, Mf=g provides the imaging model where f is the image vector, M is the system matrix, and g is the projection data. In a multi-gamma-source CT system however, such a single linear system would not describe the imaging model appropriately. Since one cannot separate a detector pixel value into multiple ones that are corresponding each rays from the sources, the inversion problem is not any more a single linear system. Instead, the imaging model can be constructed by a set of linear system models each of which assumes an estimated measurement $\tilde{g}$. Based on this model, the proposed algorithm has a weighting step which distributes each projection data into multiple estimated measurements. We used two gamma sources at various positions and with varying intensities in this numerical study to demonstrate its feasibility. Therefore, the measured projection data(g) is separated into each estimated projection data($\tilde{g_1}$),($\tilde{g_2}$ ). Image update is simultaneously performed. Our preliminary study successfully demonstrated the feasibility of using multi-gamma-sources for CT imaging. The proposed imaging protocol is believed to contribute to both medical and industrial applications.