Lag correction in amorphous silicon flat-panel x-ray computed tomography
Abstract/Contents
- Abstract
- Cone-beam computed tomography (CBCT), which uses much of the same hardware as traditional 2-D x-ray fluoroscopy, is now being used during patient treatment. The ability to perform CBCT scans has been driven by the development of amorphous silicon (a-Si) digital flat-panel (FP) x-ray detector technology. These detectors were originally designed for radiography and fluoroscopy, but because of their compactness, flexibility, low spatial distortion, and relative low-cost, are also practical for CBCT. One factor limiting the CBCT image quality for a-Si x-ray detectors is detector lag, stemming from charge trapping in the a-Si layer. Lag is defined as residual signal present in the detector, and can lead to a range of image artifacts in CBCT reconstructions, such as severe image shading for elliptical or off-center objects that could potentially obscure anatomy of interest. Current lag correction methods for a-Si FP detectors assume that the detector is linear and time invariant (LTI) and determine a temporal impulse response for the system. The detector output is deconvolved with the measured impulse response to compute the lag-corrected data. However a conventional FP is neither linear nor time invariant. Different techniques for measuring the FP impulse response are examined, as well as their effect on the final CBCT image reconstruction. A range of results are achieved by the different techniques, highlighting the non-linearity and time variance of the system. A novel non-LTI algorithm is then presented that better describes the x-ray detector dynamics, gives exposure independent results, and provides significant error reduction in CBCT for large objects where lag artifacts are most severe. A second method to reduce lag based on a hardware change to the a-Si detector is also described in this dissertation. The photodiode at each detector pixel is briefly operated in a forward bias mode to maintain saturation of charge trap states. Detector measurements and CBCT scans with and without the detector forward biasing are made to show image improvement and the trade-offs of using the hardware method.
Description
| Type of resource | text |
|---|---|
| Form | electronic; electronic resource; remote |
| Extent | 1 online resource. |
| Copyright date | 2011 |
| Publication date | 2010, c2011; 2010 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Associated with | Starman, Jared Daniel |
|---|---|
| Associated with | Stanford University, Department of Electrical Engineering |
| Primary advisor | Fahrig, Rebecca |
| Thesis advisor | Fahrig, Rebecca |
| Thesis advisor | Pauly, John (John M.) |
| Thesis advisor | Pelc, Norbert J |
| Advisor | Pauly, John (John M.) |
| Advisor | Pelc, Norbert J |
Subjects
| Genre | Theses |
|---|
Bibliographic information
| Statement of responsibility | Jared Starman. |
|---|---|
| Note | Submitted to the Department of Electrical Engineering. |
| Thesis | Thesis (Ph.D.)--Stanford University, 2011. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2011 by Jared Daniel Starman
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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