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Dissertation
Dose reduction through variable dose scanning: optimality of the filtered back projection algorithm
Doctor of Philosophy (Ph.D.), Drexel University
Jun 1982
DOI:
https://doi.org/10.17918/00008350
Abstract
This thesis proposes and evaluates a novel approach to patient radiation dose reduction in x-ray C. T. scanning, Variable Dose Scanning. This technique spares radiosensitive tissues from the insult of unnecessary radiation when they are not in the area of immediate clinical interest. Specifically evaluated is the potential for reduction of dose to the eye and active bone marrow in head transmission computerized tomography. Using computer simulations, doses are calculated for an easily implementable two level exposure variation, and results are discussed for the fully optimized case where the intensities of all pencil beams are independently variable. The dose reduction possible for one case is 65% and another, 78%. This thesis then determines whether the current conventional reconstruction algorithms in C. T. (filtered back projection or Fourier reconstruction) are optimal in terms of signal to noise ratio of the final images for this novel scanning technique. To do this, a Cramer-Rao lower bound to noise in the image which is independent of reconstruction algorithm is derived and calculated for several types of scan. Input to this calculation comprises optimized photon distributions in the sense that the minimum dose is given while constraining the noise in the region of clinical interest. The bound uses the photon distributions determined from this mathematical optimization and is compared with the actual noise of these reconstructions. The comparison indicates that little if any improvement can be expected in signal to noise ratio using reconstruction algorithms other than the filtered back projection. The conclusion is that Variable Dose Scanning is a clinically useful technique of regional scanning which does not adversely effect image noise while it significantly reduces the radiation dose to the patient.
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Details
- Title
- Dose reduction through variable dose scanning
- Creators
- Robert Edward Stanton
- Awarding Institution
- Drexel University
- Degree Awarded
- Doctor of Philosophy (Ph.D.)
- Publisher
- Drexel University; Philadelphia, Pennsylvania
- Number of pages
- xi, 140 pages
- Resource Type
- Dissertation
- Language
- English
- Academic Unit
- Drexel University
- Other Identifier
- 991021888768104721