The apparent diffusion coefficient (ADC) is a quantitative measure of water diffusion in tissue which is sensitive to the microstructural features of brain tissue and can be measured non-invasively with diffusion-weighted MRI (DWMRI). Within minutes after the onset of ischemic stroke, the ADC of water decreases 30-50% within the affected tissue. Although this was initially discovered nearly two decades ago, there is no consensus on the biophysical mechanisms responsible for the drop in ADC after ischemia. This dissertation investigates the biophysical mechanisms which determine the ADC through mathematical models of water diffusion in tissue as well as experiments in hollow fiber bioreactor (HFBR) cell cultures.The mathematical model of water diffusion in tissue predicts that the biophysical mechanisms which affect the ADC are diffusion time dependent. At short diffusion times, the ADC is sensitive to the intrinsic diffusivity of intracellular water, while at long diffusion times, the ADC is sensitive to changes in the intracellular volume fraction. Furthermore, the ADC changes associated with ischemia can be account for completely by a change in the intracellular cell volume fraction when the intracellular T2 is allowed to be lower than the extracellular T2.A unique feature of the HFBR bioreactor cell culture system is that it allows the diffusive properties of intracellular water to be investigated individually. The change after ischemia in the ADC measured from intracellular water (iADC) is dependent upon the diffusion time used to collect iADC measurements. At short diffusion times, the iADC decreases after ischemia, which is likely due to a decrease in the energy dependent movement of water within the cell. At long diffusion times, the iADC increases after ischemia, which is related to cell swelling. The results from the HFBR experiments are consistent with the mathematical model and provide a clear picture of the biophysical mechanisms important to measurements of water diffusion in living and ischemic tissue with DWMRI.

Niemann Pick Type C (NPC) disease is a rare genetic disease which is most often diagnosed in children, causes tragic irreversible neurologic deterioration, and is universally fatal. Many therapies and treatments are in development and would benefit from improved methods of assessing disease progression and treatment response. A large amount of NPC research is carried out in animal models such as the Npc1^(-/-) mouse model of the most common type of NPC disease, NPC1. This dissertation investigates three methods of noninvasive assessments of disease state in the Npc1^(-/-) mouse model with the use of magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS).MRI and MRS provide safe and widely available methods of measuring and visualizing internal tissue characteristics, suitable for longitudinal studies of disease progression and response to therapy. In this work, disease-associated dysmyelination of white matter tracts in the brain of Npc1^(-/-) mice was quantitatively measured at multiple time points with MRI methods of diffusion tensor imaging (DTI) and T2-mapping. These quantitative in vivo measures of disease status show promise as biomarkers for use in future studies of disease progression and treatment response in NPC disease models. High resolution MRI data was also collected and analyzed at multiple time points to quantify differences in both global and regional brain volumes in the Npc1^(-/-) mice as brain atrophy develops with disease progression. MRS was utilized to quantitatively examine changes in brain metabolite levels previously reported in clinical NPC disease studies. The results of the MRI and MRS studies in the Npc1^(-/-) mouse model demonstrate the ability to quantify changes in the brain due to neurodegeneration at multiple time points along the progression of neurological Npc1^(-/-) disease. MRI methods of quantifying white matter pathology with currently available DTI and T2-mapping techniques appear to be promising in vivo biomarkers of disease in the brain for future studies, while quantification of volumetric changes due to brain atrophy currently shows changes only at later disease stages. In vivo MRS with currently available methodology provides insight into the neurodegenerative disease pathology in the Npc1^(-/-) mouse but appears to lack sensitivity as a biomarker.

Nuclear spin polarization <em>P</em> is a key factor in overall Magnetic Resonance (MR) sensitivity, and conventionally is of order 10^-6 owing to the tyranny of its induction by the strength of the detection magnetic field. But various hyperpolarization mechanisms applied externally to the detection field can temporarily increase nuclear spin polarization to near unity (<em>P</em> = 1). The resulting increased MR signal enables a variety of applications, including biomedical use of hyperpolarized (HP) contrast agents to assay cellular metabolism via Magnetic Resonance Imaging (MRI), typically ¹³C-labeled metabolites reporting on abnormal metabolism. In this work optimization of radiofrequency (RF) coils and hyperpolarizer automation are used to increase the detection sensitivity of hyperpolarized contrast agents (HCA) and improve their production. It is shown that low-field imaging can be more sensitive than corresponding high-field detection when using RF coils optimized to the resonant frequency. The feasibility of low-field molecular imaging of ¹H and ¹³C HCA with high spatial resolution (as fine as 94&#x00D7;94 &mu;m²) is demonstrated with low-field 38 mm inner diameter RF coils at a static magnetic field strength <em>B</em>₀ = 0.0475 T, achieving signal-to-noise ratios suitable for <em>in vivo</em> imaging studies.

Ultrasound is an imaging modality which provides spatial measurements of subsurface targets during surgical interventions without the radiation or logistical concerns of CT or MR imaging, respectively. However, image interpretation is known to be a challenging task without other sources of information. This is not only because of the noise characteristics of ultrasound, but also because manipulation and compression of soft tissue during imaging with an ultrasound probe can distort the size and position of targets. A system for tracking ultrasound images in 3D space was implemented with a novel framework for addressing these issues. A novel laser range scanner was first characterized with respect to its ability to create textured point clouds tracked in physical space. The geometric point cloud accuracy was determined using phantoms to be submillimetric, and the tracking accuracy of the system was found to be similar to other passive optical tracking tools. This study established a gold standard registration and surface measurement tool to be used in the tracked ultrasound framework. A strategy was developed for correcting tissue compression by using the pose of the ultrasound probe within the tissue. An initial image-to-physical registration of the tracked ultrasound to a patient-specific model was done to calculate this pose. After registration, the pose of the probe was used to assign boundary conditions to the tissue model. The solution of the model was then reversed to estimate the tissue in the uncompressed state. This strategy was found to be capable of reducing errors of approximately 1 cm to 2-3 mm. The correction strategy was then generalized to use a block mesh calibrated to the tip of the ultrasound probe. This strategy did not require a patient-specific mesh, and only required an intraoperative measurement of compression depth. The formulation of the generic model was also significantly faster than the patient-specific method and gave nearly the same correction accuracy. Future work will involve incorporation of accurate material properties into the model correction, as well as real-time surface point cloud information from stereovision cameras.

Novel dosimetric materials to ensure properly calibrated x-ray beam profiles are required to facilitate the implementation of Microbeam Radiation Therapy in cancer treatment. Indirect conversion dosimetric materials are explored for possible future applications in Microbeam Radiation Therapy devices. The indirect conversion materials barium borophosphates, barium fluorophosphates with sodium ion modifier, and barium aluminosilicates were synthesized and studied. Each synthesized compound was also doped (or additionally co-doped) with a rare-earth compound. The rare-earth compounds used for doping included samarium (III) oxide, and samarium (III) fluoride. Codoping was explored with the compound erbium (III) chloride. Synthesized samples were x-ray irradiated at the Biomedical Imaging and Therapy beamline of the Canadian Light Source and also at the University of Saskatchewan. Experimental characterization methods of dosimetric material samples included x-ray luminescence, photoluminescence, electron spin resonance, Raman spectroscopy, absorbance spectroscopy, x-ray diffraction, differential scanning calorimetry, and modulated differential scanning calorimetry. The materials are experimentally characterized and determined for their merit in further research and development. All materials were found to scintillate, and some were found to function as x-ray storage phosphors as well. The barium borophosphates and also the barium fluorophosphates with sodium ion modifier possessed x-ray storage functionality according to photoluminescence spectra. An absorbance peak was observed after x-ray irradiation for barium fluorophosphates. Electron spin resonance data suggest that x-ray irradiation forms two similar types of paramagnetic defects for barium borophosphates. It appears that these defects are oxygen hole centres, which form during the indirect conversion process of samarium dopant cations. Indirect conversion involves samarium cation valency change from the 3+ to 2+ oxidation state, occurring when an electron is captured by the cation. Thermal analysis of the barium fluorophosphates by differential scanning calorimetry and modulated scanning calorimetry indicate preferential properties and moderate glass forming ability for manufacturing processes. It is concluded that barium fluorophosphates are best suited for dosimetric detectors, and secondly, barium borophosphates. Finally, future studies on materials for dosimetry in Microbeam Radiation Therapy are recommended.

<p>We have yet to establish the optimum combination of hyperthermia with radiation and/or chemotherapy for effective treatment of bladder cancer. Convenient and affordable microwave applicators capable of well-localized non-invasive heating of murine, canine and human bladder cancers is essential for logical progression of studies from pre-clinical to multi-institution clinical trials, as needed to investigate the effects of hyperthermia as an adjuvant treatment for bladder cancer. </p><p>The primary objective of this research was to utilize state-of-the art segmentation and simulation software to optimize target-specific microwave antennas for more uniform heating in pre-clinical and clinical investigations of bladder hyperthermia.</p><p>The results of this research are:</p><p>1. The development of a reliable simulation-based approach for optimizing microwave applicators;</p><p>2. The design, construction and testing of an applicator for heating murine bladder to 40-43°C while maintaining surface and core temperatures normothermic;</p><p>3. The optimization, construction and testing of a fundamentally different type of antenna (metamaterial) for heating pediatric and/or canine bladder;</p><p>4. A preliminary effort towards the optimization, construction and testing of a metamaterial antennas for heating adult bladder.</p><p>One significant implication of this work is to enable essential pre-clinical bladder hyperthermia studies with the development of a reliable microwave applicator for heating murine bladder to 40-43°C while maintaining surface and core temperatures normothermic. It is clear that hyperthermia enhances the effects of chemo- and radio- therapies, and this device will allow scientists to investigate the basic principles underlying this phenomenon more systematically.</p><p>Another significant contribution of this work is the development of metamaterial antennas for deep tissue hyperthermia. These antennas decrease the cost and increase the comfort and portability of bladder hyperthermia devices. These improvements will enable the multi-institutional clinical trials required to apply for insurance reimbursement of deep-tissue thermal therapy and the subsequent widespread use of hyperthermia as an adjuvant to current cancer therapies.</p> / Dissertation

Regenerative medicine has the potential to revolutionize how medical professionals approach combating and treating disease. Over the past several decades, human mesenchymal stem cells (hMSCs) have become one of the most promising cell sources for regenerative medicine due to their autologous availability, self-renewal capacity, angiogenic effect, immunomodulatory effects, and multi-lineage differentiation potential. However, the individuals who would gain the most from stem cell-based therapies are typically those of advanced age, and the hMSCs they would otherwise provide are accompanied by detrimental abnormalities such as reduced self-renewal and differentiation potentials, thereby limiting their therapeutic efficacy. Furthermore, hMSC-mediated tissue regeneration would require exhaustive in vitro expansion to achieve sufficient numbers, and serially-expanded hMSCs demonstrate passage-associated abnormalities. This dissertation project aimed at tackling a significant issue in clinical translation of hMSCs, namely looking for material compositions that promote hMSC stem cell health for ex vivo expansion. A library of combinatorial copolymers utilizing FDA-approved synthetic polymers poly(ε-caprolactone) (PCL) and poly(ethylene glycol) (PEG) was synthesized and then fabricated into thin spin-coated films for cell culture. hMSC phenotype was characterized across the copolymer library and the copolymer surface features were interrogated by x-ray scattering and super resolution imaging methods. An ideal candidate copolymer was identified followed by verifying a molecular mechanism for the pro-therapeutic hMSC phenotype and demonstrating the universal effect of the copolymer by culturing patient-derived hMSC instead of commercial hMSCs. These findings will contribute to future biomaterial design to enable effective translation and scalability of regenerative medicine strategies using autologous hMSCs.

Cancer immunotherapies, which seek to arm the patient&rsquo;s own immune system for personalized therapy, are a promising option for effective elimination of tumors. Focused ultrasound (FUS) is one propitious method for generating anti-tumor immunotherapy, advantageous in its capacity to deliver non-ionizing, non-invasive, tumor-localized treatment; this involves the transdermal deposition of sonic energy at a focal point in the tumor, which induces acute inflammation capable of activating an anti-tumor immune response. Here, we characterize, <em>in vivo</em>, the early (48 hours) adaptive anti-tumor immune responses induced by FUS treatment of tumors. Compared to untreated tumors, tumors treated with mechanical FUS (mFUS) demonstrated increased NF-&kappa;B activation in local and distant tumors. Additionally, a &ldquo;responder&rdquo; subset of mFUS-treated mice was identified and mFUS-treated tumors exhibited an increased percent of CD4+ T cells and an increased CD4+/CD8+ T cell ratio, as compared to untreated tumors. Immunohistochemical analysis of CD4+ T cells revealed a higher presence of immunostimulatory phenotypes in mFUS-treated tumors compared to untreated tumors. Taken together, these results suggested a FUS-induced shift towards anti-tumor immune activity.

Magnetization transfer (MT) imaging has emerged as a viable alternative to conventional structural MRI indices. It has been shown to be remarkably sensitive to changes in myelin associated with pathologies such as multiple sclerosis (MS). Previous work has built a solid foundation to study the MT effect in vivo, however, the existing literature falls short of developing methods that may help provide solutions to elucidating the clinical problems associated with MS. Therefore, the overall goal of this dissertation was to further the understanding of quantitative magnetization transfer (qMT) imaging at clinical MRI field strengths to provide solutions to these clinical problems. Since qMT imaging has been shown to be sensitive to myelin pathology, these metrics were translated to areas outside of the brain, into the optic nerve and spinal cord, where radiological changes may be better correlated with clinical disability. Next, the coverage of a new MT imaging method, inhomogeneous magnetization transfer (ihMT) was expanded to cover a large 3D volume in a clinically reasonable scan time. This new acquisition strategy has been shown to be specific to WM, and thus, may provide a better indicator of changes in myelin than traditional MT imaging over a large volume. Finally, the two pool MT model was investigated to devise several different methods â one based on a new acquisition strategy, and one based on a new modeling methodology â to remove effects that confound the signal of interest in chemical exchange saturation transfer (CEST) spectra. In conclusion, qMT has been shown to be a remarkably important technique towards understanding the properties of myelin. Gaining a fundamental understanding of how myelin is affected by pathologies which affect the macromolecular structure of neural tissues may facilitate advances in the way we diagnose, treat, and hopefully cure disease. qMT may provide key contributions to this puzzle, and the studies described here have hopefully laid a foundation to drive these future discoveries.

Due to the need to acquire a series of T2-weighted images, quantitative T2 mapping protocols in magnetic resonance imaging (MRI) suffer from long scan times. In order to alleviate this problem, fast spin-echo (FSE) imaging protocols can be employed, but the resulting images contain errors in the form of smoothing and ghosting artifacts which propagate to T2 maps. This dissertation presents a new method, dubbed Multiple Echo, Caesar Cipher Acquisition and Model-Based Reconstruction (ME-CAMBREC), which explicitly accounts for k-space signal attenuation during the reconstruction step. T2 maps generated by ME-CAMBREC contained reduced artifact compared to those generated by FSE methods, while requiring only a fraction of the scan time of a multiple spin-echo protocol. For moderate-to-high acceleration factors, ME-CAMBREC outperformed parallel imaging and steady-state T2 mapping techniques. Data suitable for ME-CAMBREC can be acquired in multi-slice mode using pulse sequence interleafs, but a slice gap should be employed to limit T2 bias caused by radiofrequency profile effects. Although ME-CAMBREC can be used to generate accurate T2s in the presence of flip angle errors, it was shown that the use of an independent measure of the transmit field (B1+) will improve fitted T2 precision.