Use of electron-multiplying charge-coupled device based micro-CT system for pre-clinical medical imaging applications
Podgorsak, Alexander Rudolf
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Computed Tomography (CT) is the current standard method for the visualization of internal structures of objects through the use of ionizing radiation. Micro-CT makes use of a small focal spot x-ray source and small field-of-view (FOV) detector to achieve unparalleled spatial resolution, allowing for the testing of pre-clinical imaging techniques on small animal samples and phantoms. However, there are disadvantages inherent with the use of such a small focal spot x-ray tube, such as the limited photon output. A detector with high sensitivity is needed for proper object visualization. One such detector that meets this criterion is an electron-multiplying charged coupled device (EMCCD) based detector system. The on-chip gain feature of the EMCCD allows for operation of the detector at low exposure levels without being electronic noise-limited. Using an EMCCD based detector coupled with the micro-CT system assembled at the University at Buffalo’s Toshiba Stroke and Vascular Research Center, two different imaging techniques were implemented; photon counting and material decomposition, and assessed them versus energy integrated CT. It was found that there was some improvement over energy integration that could be achieved through the use of photon counting. These gains were in terms of an increase in the sharpness of the edges of the scanned objects, a reduction in the streaking artifacts resulting from beam hardening, and a reduction in the measured radiation exposure the scanned object receives. The computed signal-to-noise ratio (SNR) at the edges of the scanned object was higher than that from energy integration as well. Additionally, it was found that it was possible to successfully decompose similar materials using data acquired from an EMCCD based micro-CT system. Knowledge was gained regarding the decomposition process that will be invaluable in further implementation of this process into specific anatomical regions of the body such as the neurovascular space. Both of these methods were enhanced through the use of the EMCCD detector. The low exposure levels required for a photon counting scheme are achievable using the gain electronics of an EMCCD, and its wide range of operation in terms of tube voltage allows for an effective decomposition. It seems likely that there are applications in a clinical system that could be bettered using a detector possessing the favorable features of the EMCCD detector.