Several new results are presented for applications involving the restoration of coherent signals and images from incomplete Fourier data. A closed form solution is derived for a class of iterative restoration algorithms. The closed form result may be used as a non-iterative implementation of the iterative algorithm. The closed form solution is also used to develop a simple, effective termination rule for the iterative algorithm. The utility of the new termination rule is demonstrated using simulated and experimental data. A solution technique is proposed for efficient restoration of bounded signals. The efficiency of the proposed technique is demonstrated via a one-dimensional slab dielectric profile inversion example. Finally, a difference image approach is proposed as a way to reduce the data requirements for 4-D magnetic resonance imaging of the cardiac cycle. The proposed technique is successfully applied to experimental MRI data, and future prospects for the approach are discussed.

A practical, field-capable, 3.0 to 5.0 μm mid-wave infrared Computed-Tomography Imaging Spectrometer (CTIS) has been demonstrated. The CTIS employs a simple optical system in order to measure the object cube without any scanning . The data is not measured directly, but in a manner which requires complicated post-processing to extract an estimate of the object's spectral radiance. The advantage of a snapshot imaging spectrometer is that it can collect information about a dynamic event which a standard scanning spectrometer could either miss or corrupt with temporal artifacts. Results were presented for reconstructions of laboratory targets with sampling up to 46 x 46 x 21 voxels over a variable field-of-view, or 0.1 μm spectral sampling. Demonstration of the snapshot capability has been performed on both static targets and targets with rapidly varying content. The contents of this dissertation are directed towards two ends. The primary undertaking is a realization of the theoretical model of the CTIS is a practical, field-capable MWIR instrument. The design, calibration, and operation of the MWIR CTIS are explained in detail in the text and appendices. Of additional interest is the advancement of the theory to improve the design and functionality of the spectrometer. A new algorithm for design of the holographic disperser component of the CTIS is introduced. The design process dramatically extends the set of possibilities for the disperser. In order to improve the reconstruction potential of the spectrometer, the analytic expressions which describe the CTIS have been expanded into a principal component basis set. The result is a technique for creating an initial estimate of the object and a technique for improving the reconstruction algorithm.

Current electron beam treatment planning algorithms are inadequate to calculate dose distributions in heterogeneous phantoms. Fast Monte Carlo algorithms are accurate in general but their clinical implementation needs validation. Calculations of electron beam dose distributions performed using the fast Monte Carlo system XVMC and the well-benchmarked general-purpose Monte Carlo code EGSnrc were compared with measurements. Irradiations were performed using the 9 MeV and 15 MeV beams from the Clinac 18 accelerator with standard conditions. Percent depth doses and lateral profiles were measured with thermoluminescent dosimeter and electron diode respectively. The accelerator was modelled using EGS4/BEAM, and using an experiment-based beam model. All measurements were corrected by EGSnrc calculated stopping power ratios. Overall, the agreement between measurement and calculation is excellent. Small remaining discrepancies can be attributed to the non-equivalence between physical and simulated lung material, precision in energy tuning, beam model parameters optimisation and detector fluence perturbation effects.

The technique of functional magnetic resonance imaging (fMRI) is rapidly developing from one of technical interest to wide clinical application. fMRI exploits the fact that brain neural activity produces a change in blood oxygenation level dependent (BOLD) response which is recorded at each point in the brain. In a typical experiment, a subject is given a stimulus or cognitive task, and the statistical question is to relate it to the BOLD response, usually via a linear model. The BOLD response is not instantaneous; it is delayed and smoothed by about 6 seconds. In this thesis we propose a rapid method of estimating and making inference about this delay. Our method is compared to other alternatives, and validated on an fMRI data set from an experiment in pain perception.

In positron emission mammography, the use of planar detector limits the angular coverage and introduces more noise than conventional positron emission tomography. / We first studied the sampling artifacts introduced from the use of discrete crystals. The images are reconstructed by back-projecting lines of response from and to the centroid of interaction within the crystal. We postulate that the sampling artifact should be reduced by allowing the lines of response to shift away from the centroid towards the next most probable crystal element. / We then studied noise in the peripheral region of the images. The solid angle function is an image uniformity correction function. The solid angle function is the last thing applied before the images are displayed. We postulate that image quality should improve by re-ordering the solid angle function and the smoothing algorithm. / These two techniques have shown an improvement in contrast, resolution, and noise. An ROC curve analysis showed an improvement of 9.5 % in accuracy.

The goal of Total Skin Electron Therapy (TSET) is to deliver a uniform dose to the patient's entire skin to a limited depth while sparing the body organs. Due to the laborious commissioning process, it is helpful to use the Monte Carlo (MC) method for the procedure and treatment planning. Calculations of dosimetric quantities were performed with EGSnrc/BEAM MC codes as well as with the fast MC code XVMC. The linac model for a 6 MeV Varian CL21EX accelerator was established by measuring the electron focal spot size with a slit camera. Using this measured focal spot value in our proposed divergent beam model, an improved result for large field profiles can be achieved. Measured PDDs and profiles under standard set-up and TSET conditions were compared to MC calculations. Overall, satisfactory results were obtained except for simulations with an additional scattering filter, suggesting the composition, density and dimensions of the filter need to be confirmed.

The goal of conformal radiation techniques is to improve local tumor control through dose escalation to target volumes while at the same time sparing surrounding healthy tissue. Accurate target volume delineation is essential in achieving this goal to avoid inadequate tumor coverage and/or irradiation of an unnecessary volume of healthy tissue. Respiratory motion is known to be the largest intra-fractional organ motion and the most significant source of uncertainty in treatment planning for chest lesions. A method to minimize effects of respiratory motion is to use four-dimensional (4D) radiotherapy. / A novel scanning procedure for 4D CT data acquisition is described in this work. Three single-slice helical scans are acquired simultaneously with the real-time tracking of several markers placed on a moving phantom. At the end of the three scans. CT data is binned into different respiratory phases according to the externally recorded respiratory signal and the scanned volume is reconstructed for several respiratory phases. The 4D CT images obtained show an overall improvement when compared to conventional CT images of a moving phantom.

<p> Accurate, cross-scanner assessment of in-vivo air density used to quantitatively assess amount and distribution of emphysema in COPD subjects has remained elusive. Hounsfield units (HU) within tracheal air can be considerably more positive than -1000 HU. With the advent of new dual-source scanners which employ dedicated scatter correction techniques, it is of interest to evaluate how the quantitative measures of lung density compare between dual-source and single-source scan modes. This study has sought to characterize in-vivo and phantom-based air metrics using dual-energy computed tomography technology where the nature of the technology has required adjustments to scatter correction. </p><p> Anesthetized ovine (N=6), swine (N=13: more human-like rib cage shape), lung phantom and a thoracic phantom were studied using a dual-source MDCT scanner (Siemens Definition Flash. Multiple dual-source dual-energy (DSDE) and single-source (SS) scans taken at different energy levels and scan settings were acquired for direct quantitative comparison. Density histograms were evaluated for the lung, tracheal, water and blood segments. Image data were obtained at 80, 100, 120, and 140 kVp in the SS mode (B35f kernel) and at 80, 100, 140, and 140-Sn (tin filtered) kVp in the DSDE mode (B35f and D30f kernels), in addition to variations in dose, rotation time, and pitch. To minimize the effect of cross-scatter, the phantom scans in the DSDE mode was obtained by reducing the tube current of one of the tubes to its minimum (near zero) value.</p><p> When using image data obtained in the DSDE mode, the median HU values in the tracheal regions of all animals and the phantom were consistently closer to -1000 HU regardless of reconstruction kernel (chapters 3 and 4). Similarly, HU values of water and blood were consistently closer to their nominal values of 0 HU and 55 HU respectively. When using image data obtained in the SS mode the air CT numbers demonstrated a consistent positive shift of up to 35 HU with respect to the nominal -1000 HU value. In vivo data demonstrated considerable variability in tracheal, influenced by local anatomy with SS mode scanning while tracheal air was more consistent with DSDE imaging. Scatter effects in the lung parenchyma differed from adjacent tracheal measures.</p><p> In summary, data suggest that enhanced scatter correction serves to provide more accurate CT lung density measures sought to quantitatively assess the presence and distribution of emphysema in COPD subjects. Data further suggest that CT images, acquired without adequate scatter correction, cannot be corrected by linear algorithms given the variability in tracheal air HU values and the independent scatter effects on lung parenchyma.</p>

Synthetic dyes, including thiazines, acridines, xanthenes, and a phenazine, were used as models for studying the photodynamic effect. In the presence of physiological reductants, the illuminated dyes produced superoxide (O$\sb2\sp-$), hydrogen peroxide (H$\sb2$O$\sb2$), and hydroxyl free radical (OH). Suitable reductants included NADH, glutathione, GMP, cysteine, tryptophan, and tyrosine. The production of OH$\cdot$ was dependent on chelated iron or on copper. Effective iron chelators included EDTA, DTPA, dipyridyl, and phenanthroline, and biologically significant compounds such as ATP, ADP, succinate, citrate, and DNA. DNA intercalation of the dyes did not prevent oxidization of NADH or the production of O$\sb2\sp-$ or OH$\cdot$. Hydroxyl radical scavengers competed effectively in the assays for the OH$\cdot$. While in the Haber-Weiss reaction superoxide reduces iron, which is oxidized by H$\sb2$O$\sb2$ to produce OH$\cdot$, excited state reduced dyes appeared capable of reducing the iron, so that SOD was only partially inhibitory of OH$\cdot$ production. Catalase prevented production of OH$\cdot$. Similar results were found for substrates and metals in an assay of single strand scission of DNA mediated by the dyes. Amounts of strand scission seen were dependent on concentrations of iron or dye. Cysteine, NADH, GTP, dGMP, tryptophan, and tyrosine were all able to provide electrons for the strand scission reaction. Furthermore, the single strand scission of DNA by the dyes was prevented by scavengers of O$\sb2\sp-$, H$\sb2$O$\sb2$ or OH$\cdot$ which are poor scavengers for singlet oxygen ($\sp1$O$\sb2$), and substitution of deuterium oxide for water, which exacerbates any damage produced by $\sp1$O$\sb2$, did not increase damage. The physiological reductant glutathione in E. coli was depleted by exposure to illuminated dye. Lethality of the dyes was reduced by enhanced levels of catalase or endonulcease IV provided by plasmid-coded genes, indicating that H$\sb2$O$\sb2$ is an important mediator of toxicity and that DNA is an important target, while OH$\cdot$ scavengers prevented kill, indicating that the OH$\cdot$ is also an important mediator of phototoxicity. Finally, DNA damage in vivo was reduced by an OH$\cdot$ scavenger. In conclusion, toxicity in the photodynamic effect is mediated by reduced oxygen species, particularly OH$\cdot$, and DNA damage probably underlies this toxicity.

Oblique-incidence, fiber-optic reflectometry is a simple and accurate method for measuring the absorption and reduced scattering coefficients, $\mu\sb{a}$ and $\mu\sb{s}\sp\prime ,$ of semi-infinite turbid media. Obliquely incident light produces a spatial distribution of diffuse reflectance that is not centered about the point of light entry. The shift in the center of diffuse reflectance is related to the medium's diffusion coefficient, D. We developed a fiber-optic probe to deliver light obliquely and sample the profile of diffuse reflectance. From a relative profile, we measure D, deduce the effective attenuation coefficient, $\mu\sb{eff},$ then calculate $\mu\sb{a}$ and $\mu\sb{s}\sp\prime .$ This method was verified with Monte Carlo simulations and tested on tissue phantoms. Measurements at 632.8 nm were accurate to within 5% for D and $\mu\sb{eff},$ resulting in 10% and 5% accuracy for $\mu\sb{a}$ and $\mu\sb{s}\sp\prime .$ In addition, $\mu\sb{a}$ and $\mu\sb{s}\sp\prime$ spectra were deduced from wavelength-resolved measurements of the diffuse reflectance from a white light source.