Development and application of advanced cone-beam CT acquisition strategies for image-guided therapies
In addition to its traditional role in diagnostics, CT has recently been increasingly utilized as a guidance tool in therapeutic procedures. This has been driven, in a large part, by advances in flat-panel x-ray detector technologies that have enabled the rapid development of flat-panel cone-beam CT...
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| Format: | Thesis Book |
| Language: | English |
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2013
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| Summary: | In addition to its traditional role in diagnostics, CT has recently been increasingly utilized as a guidance tool in therapeutic procedures. This has been driven, in a large part, by advances in flat-panel x-ray detector technologies that have enabled the rapid development of flat-panel cone-beam CT (CBCT). Guidance systems typically consist of a flat panel detector mounted opposite a kilovoltage x ray tube often on a C-arm in interventional radiology or image-guided surgery or mounted directly to linear accelerator for image-guided radiation therapy (IGRT). These systems have enabled new therapies and made existing therapies more accurate and safer for the patient. However, CT imaging involves additional x ray exposure to the patient and we must consider the "As low as reasonably achievable" (ALARA) principle of the USNRC and the AAPM Task Group 75 report that states it is no longer safe to consider imaging dose negligible and "that strategies for reducing the imaging dose and volume of exposed anatomy be pursued wherever possible, even when they require developing new image acquisition and reconstruction techniques." In that regard we have developed four targeted image acquisition strategies, enabled by a custom dynamic collimation device, that contain sufficient information to have clinical utility with substantially lower dose away from the target region than conventional methods. The design, development and verification of the dynamic collimator are described followed by the first imaging strategy, dynamic collimation of fluoroscopy for tracking implanted lung fiducials. The second imaging application, conformal ROI imaging in CBCT, reconstructs a region of interest (ROI) from restricted illumination data with the chord based BPF algorithm. This approach accurately recovers the ROI, but only the ROI, with highly targeted imaging dose. Additionally this approach is limited to certain peripheral ROIs To overcome these limitations we developed the intensity weighted ROI (IWROI) imaging method that uses filters to spatially vary the intensity of the beam instead of opaque blades to collimate the beam. In this way we acquire complete data of the patient that allows for reconstruction of the whole volume with standard reconstruction algorithms and is not limited to peripheral regions. However, the parts of the projection data measured with the low intensity (filtered) beam have higher noise which propagates back in to the reconstructed image during reconstruct resulting in a high quality image within the ROI and a lower quality, noisy image of the rest of the patient. The lower quality region can still be useful in image guidance, e.g. for alignment to high contrast structures such as bone or the skin surface. This technique has been developed with both statically mounted filters on the x ray source and with dynamic filtration with the collimator |
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| Item Description: | Advisors: Charles Pelizzari; Xiaochuan Pan |
| Physical Description: | 196 p |
| ISBN: | 9781303231711 |