Developing a dual energy x-ray source for low-cost spectral CT

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ABSTRACT Dual energy computed tomography (DECT) provides significantly more information compared to a regular CT. It is increasingly used for a variety of clinical tasks including tissue differentiation, metal artifact reduction, automatic bone removal, contrast enhancement, and iodine quantification. Although several technologies have been developed for DECT, a major limitation is a significantly increased equipment cost, which has hindered the more widespread clinical use. The goal of this project is to develop a new x-ray source technology to reduce the cost and to enhance the performances of DECT. Specifically, we propose a dual energy x-ray source that emits radiations with two distinct energy spectra with an increased energy separation compared to those obtained by spectral filtration or the rapid kVp switching method alone. This will be accomplished by utilizing two cathode-anode pairs and a voltage divider to reduce the effective voltage of one of the anodes, at a constant applied tube voltage. The radiations from the two anodes are further optimized to reduce the spectral overlap by incorporating two individualized spectral filters. For DECT, x-ray radiation is emitted alternately from the two anodes by selectively activating the corresponding cathode. The carbon nanotube (CNT) field emission cathodes are used to enable rapid switching and intensity modulation of the two beams with micro-second accuracy. The advantages of the proposed source compared the current technologies are: 1) Significantly reduced equipment cost – no rapid kVp switching, energy sensitive detector or two sets of source/detector is required; 2) Increased energy separation and reduced overlap which will lead to an enhanced DECT performance; 3) Independent control of the exposures of the two x-ray beams to minimize image noise; 4) Enabling DE-CBCT imaging in one gantry rotation; and 5) Instantaneous switching of the energy spectrum with micro-second response time resulting in improved accuracy and reliable in the dose profile. This feasibility study will focus on a fixed-anode x-ray source for dual-energy cone-beam CT (DE-CBCT) for maxillofacial and head imaging, the technology developed can be applied to other areas of medical imaging where CBCT is currently deployed such as image guided radiation therapy, interventional radiology and extremity imaging. The approach can also be extended to multi-energy (3 or more) for advanced spectral imaging. It can be used for spatially distributed x-ray source array that emits photons with 2 or more energy spectra from for fixed-gantry dual energy tomosynthesis and CT. The Specific Aims are: 1) Demonstrating the feasibility of a dual energy x-ray source for low-cost DE-CBCT; and 2) Demonstrating DE-CBCT imaging using a prototype dual energy x-ray source.