In PET activation studies, brain function is detected by identifying regional differences in tracer concentration between images acquired while a subject(s) executes different tasks. When imaging volunteers or patients, the differences produced by executing higher-order cognitive processes have magnitudes similar to those of the noise found in the measurements. Therefore, the development of techniques that enhance the signal to noise (S/N) of activation images is of great importance. / The work described here was performed to investigate and evaluate three strategies designed to enhance the S/N in activation images of cognitive function. / First, the applicability of switched protocols to the study of cognitive paradigms was analysed. Switched protocols enhance the S/N of subtracted images by manipulating tracer kinetics during the washout phase of the input function. This allows the acquisition of images up to 4-min long. Activation foci detected with switched and standard rCBF protocols were compared using two language tasks. The switched protocol improved the signal statistical significance up to 38% by reducing image noise. / Second, a protocol designed to augment the S/N enhancements yielded by switched protocols was evaluated. This protocol enhances the S/N of H 215O bolus PET activation images by altering the relative distribution of tracer in the uptake and washout phases of the input function. The protocol combines task-switching with the release of a large pool of activity-free blood (cold-bolus). The combined protocol was first tested using computer simulations of the uptake of H215O into the brain and then evaluated by imaging subjects performing two language tasks. In the PET experiments, activation foci obtained using the combined protocol had significantly higher t-statistic values than equivalent foci detected using a conventional switched protocol (mean improvement 36%). The improvements resulted from increases in signal magnitude. / Third, the performance of the ECAT EXACT HR + 3D PET scanner when employed to measure brain function using H215O bolus activation protocols in single sessions was evaluated. Using two sensory tasks and rCBF measurements, the scanner Performance was studied at different count-rates. Optimal dose fractionation strategies for one session imaging studies employing standard rCBF, switched, and cold-bolus/switched protocols were determined.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.34760 |
| Date | January 1997 |
| Creators | Moreno-Cantú, Jorge J. |
| Contributors | Thompson, Christopher (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Neurology and Neurosurgery.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001601766, proquestno: NQ44521, Theses scanned by UMI/ProQuest. |
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