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The effect of 7 days of continuous capacitive electrical stimulation on bone growth around titanium implants placed in the tibiae of adult male rats, was evaluated in this study. The animals were 'hooked-up' to an external power supply, emitting a symmetrical sinusoidal wave form with an amplitude of 2.0 volt p-p and a frequency of 60 kHz. The current values tested were 20muA, 30muA and 60muA. In surgery I, a head cap was affixed to the animal's skull with stainless-steel screws and an acrylic resin. The head cap was connected to the external power supply by an electrical stimulation wire, encased in a stainless-steel spring. Two electrical leads were subcutaneously tunneled from the head cap to the future tibial implant site, and sutured to the soft tissues. After a one week acclimatization period, a second surgical procedure, surgery II, involved the placement of titanium implants proximal to the tibial tuberosity in each tibiae. Electrodes were then sutured one on either side of the implant, thus 'cuffing' the implant, and the current was then applied to one implant site with the other acting as a control. / After seven days of continuous capacitive electrical stimulation, a biomechanical pull-out test was carried out to measure the force in Newtons (N) of implant extraction. (Abstract shortened by UMI.)

Attenuation and scatter are limiting factors in image quality and quantitation of organ function by single photon emission computed tomography (SPECT). To correct brain images for attenuation an effective water/tissue attenuation coefficient of 0.12 cm$ sp{-1}$ (at 140 keV) or larger has been recommended in order to compensate for the additional bone (skull) attenuation. / It has been determined that the reconstructed images are overcorrected in the centre by 5%, and the optimum correction occurs for a reduced coefficient of 0.09 cm$ sp{-1}$. The overcorrection is due to increased attenuation at the edges of all projections where the path length through the bone is greater, although the bone also increases the scatter at the projection edges. / A correction scheme which uses effective bone and water coefficients was developed to compensate for the attenuation. Alternatively, prior to attenuation correction, a common scatter correction was found to be effective in explicitly removing the bone and water scatter.

The work reported in this thesis is motivated by the need for new screening techniques for detecting early-stage breast tumors. In recent years, pulsed microwave imaging in the gigahertz range has been suggested as a promising complementing methodology to the currently existing detection and imaging modalities. This technique is based on significant electrical contrast between the cancerous and healthy breast tissue in the microwave range. To exploit this electrical contrast for imaging purposes, a broadband trans-receiving antenna is placed near the breast surface. The antenna launches a pulse and then collects the backscattered response, used for detection of the potentially underlying tumor. In our work, we examine tumor detection capabilities of the "Dark Eyes" antenna, recently reported in the literature and suggested as antenna of choice for pulsed microwave breast imaging due to its compact size, ease of fabrication and cost-effectiveness. The simulation tool, SEMCAD-X, is based on the finite-different time-domain method and is used throughout this work to construct the realistic hemi-spherical breast model and analyze its interaction with the microwave radiated from the antenna source.

Our group studies the interaction between antibiotic peptides and phospholipids. These peptides are known to form channels in the lipid membrane. With X-ray diffraction, oriented circular dichroism and in-plane neutron scattering measurements, and evidences from experiments done by others, we have established channel models for alamethicin and magainin, and measured the channel sizes. In this thesis, neutron off-plane scattering of aligned peptide-lipid samples is discussed. Compared to in-plane scattering, this new technique provides a much richer structural information of the sample. We therefore are able to easily distinguish different structures based on the scattering pattern, and, ideally, reconstruct the channel scattering length density in real space. Inter-membrane correlation was observed in the magainin samples.

This thesis proposes models for the calculation of upper and lower limiting values to the backscatter factor (BSF) that can be used to evaluate measured and modelled BSF values. The upper limit to the BSF is obtained from a Monte Carlo simulation of an infinite parallel beam incident on a semi-infinite phantom in which the dose contribution from all orders of photon scatter is considered. The lower limit is calculated using an analytical photon transport model which considers only the primary dose and the scatter dose from photons that have undergone a single scattering interaction in the phantom. A parametrization of the limiting values in terms of photon energy and irradiation field size is presented and comparisons are made with BSF's from the literature. To further illustrate the utility of the limiting BSF's, comparisons are also made with current TLD-measured BSF's and Monte Carlo simulations of the BSF.

A computer program was developed during the course of this work to calculate electron arc dose distributions with the angle $ beta$ concept. The angle $ beta$ uniquely describes the dependence of radial percentage depth doses an electron arc therapy on the nominal field width, isocenter depth, and virtual source-axis distance. The $ beta$ concept can be used in clinical situations to determine the field width when the isocenter depth and the required radial percentage depth dose are known. This thesis presents an overview of the physical properties of electron arc therapy and describes in detail the angle $ beta$ pseudo-arc technique used at McGill. A description of the algorithms used in the computer program is given the $ beta$ technique is compared to measurements and other calculation methods.

This thesis is concerned with the creation, verification and implementation of a computer programme for simulating photon transport in diagnostic radiology. The programme is based on the Monte Carlo technique in which probabilistic problems are solved using random numbers. For this reason mathematical number generators along with a few standard tests which enable the randomness of the numbers to be evaluated are introduced. A discussion on sampling from probability distributions is presented with emphasis on the physical aspects of the Monte Carlo technique applied to low energy photon transport. The validity of the computer programme is established by comparisons with previously published Monte Carlo work, with predictions from an analytical photon transport model and with experimental measurements. The application of Monte Carlo simulations to specific radiographic problems are illustrated by the modeling of percent depth doses.

The spin-spin and spin-lattice relaxation times of protons on polymers, T$ sb{ rm 1p}$ and T$ sb{ rm 2p}$, respectively, have been used to probe the absorbed dose of irradiated polymer solutions in which radiation-induced changes in polymer molecular weight, M$ sb{ rm n}$, occur. The M$ sb{ rm n}$ dependencies of T$ sb{ rm 1p}$ and T$ sb{ rm 2p}$, and of the water proton T$ sb{ rm 1w}$ for solutions of poly(ethylene oxide) (PEO) in D$ sb2$O and H$ sb2$O are presented. T$ sb{ rm 1p}$ and T$ sb{ rm 1w}$ are independent of M$ sb{ rm n},$ and T$ sb{ rm 2p}$ varies with M$ sb{ rm n}$ according to a specific inverse power dependence until low M$ sb{ rm n}$ when T$ sb2$ saturation occurs. The dose dependence of T$ sb{ rm 1p}$ and T$ sb{ rm 2p}$ measured for dilute solutions of PEO in D$ sb2$O reflects the dependence of M$ sb{ rm n}$ on dose. A novel semi-empirical model is proposed for the dose dependence of T$ sb{ rm 2p}$ which incorporates the measured M$ sb{ rm n}$ power dependence of T$ sb{ rm 2p}$ into a theoretical expression of the dose dependence of the M$ sb{ rm n}$. This expression is based on previous bulk polymer work and has been modified to hold for polymers in solution. The model can be fitted well to the T$ sb{ rm 2p}$ data measured for different doses, and the values of the fitting parameters agree with those expected from independent measurements. Practical aspects of the NMR/polymer dosimetry technique are also addressed.

The measurement and analysis of the human diaphragm electromyogram (EMGdi), as obtained with an esophageal electrode, requires objective control of the disturbances and filtering effects which can influence the signal. One issue of importance is that an increase in the muscle-to-electrode distance (MEdist) acts as a low-pass filter, filtering out the high frequency components of the EMG power spectrum (the MEdist filter). Due to the numerous factors which can influence the EMGdi, control of signal quality is also of utmost importance. The aims of this study were: (1) to evaluate the effect of the MEdist filter on EMGdi, as measured with a multiple array esophageal electrode, (2) to take advantage of the MEdist filter in order to locate the position of the diaphragm with respect to the electrodes, and (3) to evaluate the influence of changes in chest wall configuration on EMGdi center frequency (CF) values, while controlling for both signal quality and the MEdist filter. / Five normal male subjects performed static contractions of the diaphragm at seven predetermined chest wall configurations. The EMGdi was measured with an array of eight steel rings mounted on a catheter, forming seven sequential pairs of electrodes, with an interelectrode distance of 10 mm. EMGdi signal quality was evaluated by computer algorithms. The pair of electrodes whose EMGdi signals (and power spectrums) were the least influenced by the MEdist filter was assumed to be closest to the diaphragm. / The results of the study indicated (1) EMGdi power spectrums and their associated CF values were strongly affected by the position of the diaphragm with respect to the multiple array esophageal electrode. CF decreased by approximately 1 Hz per mm displacement away from the diaphragm. (2) By controlling for the MEdist filter, there was no relationship found between changes in chest wall configuration and CF values. These data demonstrate that changes in chest wall configuration, and hence diaphragm length, do not influence the CF values of the EMGdi, if the distance between the electrodes and the diaphragm and signal quality are controlled for.