The availability of accurately aligned, whole body, functional PET images has a significant impact on the diagnosis of malignant disease and on identifying and localizing metastasis. Gamma ray attenuation correction is essential in all quantitative PET studies. / The object of this study was to explore the possibility of using beta-gamma coincidence as an attenuation correction technique in order to improve transmission scan image quality. / This study consisted of testing and implementing a beta-gamma attenuation correction technique on an animal PET scanner. In its final form the system uses 68Ge sources enclosed in plastic scintillator cylinders coupled to PMTs. The detection of positrons is activated by the energy loss in the scintillator medium. This system is used in coincidence with one of the animal PET scanner's BGO crystal detectors in order to acquire transmission scans.

Two ultrasound systems were studied to investigate the effects of positional and volumetric prostate variations on dosimetry over the course of external radiation therapy. A 2D system, currently used at the Montreal General Hospital for patient repositioning, was compared to a 3D system invented recently. Prostate variations were quantified from ultrasound images acquired daily during a 2003 clinical study. A method was devised to introduce ultrasound information in a Monte Carlo Treatment Planning System previously developed at McGill. Patient repositioning was evaluated for both systems using dose-volume histograms of Voxel Monte Carlo dose calculation. Repositioning with the 3D system, neglecting volume changes, was found to bring the target dose to within 1 % of the planned dose, rather than the 12 % of the clinical 2D system. However, when considering the varying 3D volumes, the dose could only be corrected to within 7 %. These results indicate that the 3D system provides not only a more accurate assessment of prostate displacements, but also volumetric information that significantly affects the dosimetry.

This thesis relates to the study of rapid ionic currents in single cells using a single electrode voltage clamp amplifier (SEVC). The practical limitations inherent with the SEW, primarily the effects of series resistance (R s) which dominate when attempting to record rapid ionic currents, are outlined. The various methods in use to compensate for Rs are explored. A novel method of Rs compensation is described which overcomes the stability limitations of conventional designs. / To illustrate the advantages of this new Rs compensation, a voltage clamp amplifier implementing this Rs compensation is used to record rapid Na+ current in rat Superior Cervical Ganglia (SCG) neurons and human ventricular myocytes which could not be resolved with conventional equipment. Data obtained using partial Rs compensation is compared to that obtained with full Rs compensation using the new voltage clamp amplifier. Criteria for adequate voltage control of voltage clamped Na+ currents are developed and illustrated.

A new paradigm for the characterization of structure appearance is proposed, based on a combination of grey-level intensity data and a shape descriptor derived from a priori Principal Components Analysis of 3D deformation vector fields. Generated without external intervention, it extends more classical, 2D manual landmark-based shape models. Application of this novel concept leads to a method for the segmentation of medial temporal lobe structures from brain magnetic resonance images. The strategy employed for segmentation is similar to that used in other appearance-based approaches, while the resulting output data is identical to ANIMAL, a non-linear registration and segmentation technique. The proposed method was tested on a data set of 80 normal subjects for which manual and ANIMAL segmentated structures were available. Experimental results demonstrated the robustness and flexibility of this method. Segmentation accuracy, measured by overlap statistics, is marginally lower (<2%) than ANIMAL, while processing time is 6 times faster. Finally, the applicability of this concept towards shape deformation analysis is presented.

The brain can be explored while a subject executes different tasks. Such techniques are commonly referred as activation studies. The regions of the brain involved in a particular task can be located by comparing regional differences in tracer concentration to a control state. Group of neurons in the brain form complex logical circuits and their activities increase while they interpret a stimulation. These neuronal activities require glucose and oxygen and these substances travel in the blood following hemodynamic rules. Many factors influence the hemodynamic response induced by brain activation (FRIBA), but certain aspects of its temporal behavior are still unclear. A special technique was implemented with an ECAT EXACT HR+ (CTI/Siemens) to fulfil this lack in PET activation studies. The new HR+ has this 3D option, which can help to evaluate the FRIBA with a tracer (11C-CO) that remains in the blood vessels to measure the cerebral blood volume (CBV) differences. Only CBV studies can appreciate the temporal course of the FRIBA in PET. The resulting images are, however, very noisy and many pitfalls are present during their analysis. (Abstract shortened by UMI.)

The block effect in Positron Emission Tomography (PET) is the degradation in spatial resolution that is seen when there are more scintillation crystals than photomultiplier tubes in a detector. / We measured the block effect in detectors from three PET scanners: the Siemens-CTI HR+, the GE Advance, and the Siemens-CTI HI-REZ. In the CTI HR+ the block effect was 0.7 mm in the central crystals, and negligible for the edge crystals. In the GE Advance the block effect was 0.6 mm for the central crystals, and 0.5 mm for the edge crystals. In the CTI HI-REZ detector the block effect varied from 0.5 mm to 2.1 mm depending on the crystal location. / The effect of changing the depth of the first point of gamma-ray interaction in the block detectors was examined. The gamma-ray interaction depth was varied, and the event position in the crystal identification image was examined. If the events were positioned inconsistently with gamma-ray interaction depth, this might be a cause of the block effect. / In the CTI HR+ detector and the CTI HI-REZ detector, the positioning of events in the crystal identification image was dependent both on the crystal depth of the first point of interaction and the crystal location. In the GE Advance block detector the positioning of events in the crystal identification image was consistent for varying gamma-ray interaction depth, and crystal position. / In crystals where the positioning of events is not consistent with interaction depth, the block effect is larger. In the GE Advance block detector, another cause of the block effect may exist.

This thesis provides the first systematic measurements of respiratory mechanics in humans anesthetized with halothane. Measurements were made both in anesthetized and anesthetized-paralyzed states. Both active and passive elastance and flow resistance values of the total respiratory system are presented. Next, the passive mechanics data are partitioned into lung and chest wall components. As this partitioning is based on measurements of esophageal pressure, a simple method for validating the esophageal balloon-catheter technique for indirect measurement of pleural surface pressure has also been developed, and applied to anesthetized subjects. In addition, lung mechanics has been studied in awake normal subjects in different body postures (sitting, supine, right and left lateral decubitus). The present approach can be readily extended to investigate the effects of other anesthetics and drugs used in conjunction with anesthesia on respiratory mechanics.

Electron arc therapy is the treatment modality for superficial tumors involving large curved surfaces. At the McGill University Health Centre, the characteristic angle beta concept was developed for the dosimetry and treatment planning of electron arc therapy. In this work, this concept was verified in dynamic mode with the new generation linac of Varian(TM), the Clinac-21 EX. / Radial PDDs were measured for beta angles varying from 60º--120º of electron arc beams with energies of 6 MeV, 9 MeV, and 12 MeV and 2-D isodose distributions of electron arc beams were studied as well. Dose penumbral regions exist at the beam start area and stop area, and the size of these regions is a function of the beam energy and the field width. When shielded with a tertiary collimator, the size of the penumbral regions and the dose levels in the penumbral regions were reduced significantly, and it is sufficient for the shielding to cover exactly the start field and the stop field of the arc beam in a clinical setting. / The dose rate of the electron arc beam was investigated. It was found that the dose rate at the depth of dose maximum linearly increased with the arc beam field width and was independent of the arc angle.

A commercial electron dose calculation software (Eclipse TM) implementation based on the Macro Monte Carlo algorithm has been introduced. Eclipse™ initial configurations were performed for all available electron beam energies 6, 9, 12, 16, and 20 MeV. We evaluated the electron Monte Carlo (eMC) module of the Eclipse™ using a verification data set comprised of depth dose curves, profiles, Relative Output Factors (ROF), and 2-0 dose distributions in the transverse plane in a homogeneous phantom. The verification data set was comprised of measurements performed for combinations of 6, 9, 12, 16, and 20 MeV beam energies with five standard field sizes and thirteen irregularly shaped fields under three phantom setups. The phantom setups were normal beam incidence at source-to-surface distance (SSO) = 100cm, normal incidence with extended SSO=11 Ocm, and oblique incidence with extended SSO=11 Ocm. Calculations were performed in a digital phantom with the maximum number of particles accepted by Eclipse ™ with a grid spacing that was no larger than approximately one-tenth the distal falloff distance of the electron depth dose curve from 80% to 20% of the maximum dose. Overall, the agreement between the calculated dose distributions and measured on es was good for fields larger than 2 cm to better than 3% dose difference and 3 mm distance-to-agreement.

It is standard practice in radiation therapy to have two independent calculations for the number of monitor units used in patient treatment plans. The relationship between monitor units and absorbed dose to water is sophisticated for MLC-based IMRT. Verification measurements of absorbed dose to water with ionization chambers in MLC-based IMRT fields remains uncertain and the accuracy of computer modeling is limited by the physics assumptions used. In this thesis, point dose measurements from three cylindrical ionization chambers of different collecting volumes are evaluated against the CORVUS (NOMOS Corporation, Cranberry, PA) finite-size pencil beam algorithm and the PEREGRINE (NOMOS Corporation, Cranberry, PA) Monte Carlo calculation engine. After establishing the characteristics of the chambers and treatment planning system under various beam geometries, dynamic and step and shoot MLC deliveries were evaluated. Between detectors, the smallest volume chamber measured the greatest dose. Compared to measurements, CORVUS and PEREGRINE both underestimated the dose in IMRT fields by approximately 5%. On average PEREGRINE yielded better agreement than CORVUS by 2%.