Despite that most vestibular schwannomas are successfully treated with radiotherapy, current follow-up protocols entail years of serial magnetic resonance imaging (MRI) scans to ensure cessation of growth. This pilot study sought to identify early predictors of radiation treatment response using a non-invasive multi-modality imaging approach. We hypothesized that by combining information acquired from dynamic contrast-enhanced MRI (DCE-MRI), diffusion tensor imaging (DTI), and L-¹¹C-methionine positron emission tomography (MET-PET) treatment response could be identified sooner than the current several year waiting period. This thesis presents the baseline MRI and MET-PET results of the pilot study acquired to-date with follow-up data to be acquired in the next six months. Baseline results suggest that DTI and DCE-MRI yield information that may be useful in identifying the response of vestibular schwannomas to radiotherapy. In particular, vestibular schwannomas display elevated mean diffusion coefficients relative to the contra-lateral cerebellum. Also, the novel use of arterial input functions derived from the anterior inferior cerebellar arteries has led to the successful implementation of DCE-MRI pharmaco-kinetic models which may be used to quantitatively monitor tumor response to radiotherapy. Furthermore, MET-PET has shown promise as a tool for evaluating response as all tumors exhibited enhancement under this modality as compared to the contra-lateral side of the brain. Single-voxel spectroscopy with 3T MRI has proven to be a poor technique with which to examine vestibular schwannomas since only two of eight spectra were acquired successfully. All of the techniques that have shown promise as investigatory tools of tumor response can potentially be implemented clinically in the near future.

Despite that most vestibular schwannomas are successfully treated with radiotherapy, current follow-up protocols entail years of serial magnetic resonance imaging (MRI) scans to ensure cessation of growth. This pilot study sought to identify early predictors of radiation treatment response using a non-invasive multi-modality imaging approach. We hypothesized that by combining information acquired from dynamic contrast-enhanced MRI (DCE-MRI), diffusion tensor imaging (DTI), and L-¹¹C-methionine positron emission tomography (MET-PET) treatment response could be identified sooner than the current several year waiting period. This thesis presents the baseline MRI and MET-PET results of the pilot study acquired to-date with follow-up data to be acquired in the next six months. Baseline results suggest that DTI and DCE-MRI yield information that may be useful in identifying the response of vestibular schwannomas to radiotherapy. In particular, vestibular schwannomas display elevated mean diffusion coefficients relative to the contra-lateral cerebellum. Also, the novel use of arterial input functions derived from the anterior inferior cerebellar arteries has led to the successful implementation of DCE-MRI pharmaco-kinetic models which may be used to quantitatively monitor tumor response to radiotherapy. Furthermore, MET-PET has shown promise as a tool for evaluating response as all tumors exhibited enhancement under this modality as compared to the contra-lateral side of the brain. Single-voxel spectroscopy with 3T MRI has proven to be a poor technique with which to examine vestibular schwannomas since only two of eight spectra were acquired successfully. All of the techniques that have shown promise as investigatory tools of tumor response can potentially be implemented clinically in the near future.

No description available.

The Biomedical Imaging Lab at the University of Manitoba is building an MR compatible PET insert system. The detectors include SensL SPM ArraySB-4 SiPMs and dual layer offset LYSO crystal blocks with 409 total crystals. The detectors’ gain varies with temperature and bias voltage. Measurements inside the MR magnet revealed that the equilibrium temperature was around 30°C. The photopeak amplitude, energy resolution and events per crystal were studied at 30°C and also at temperatures from 20°C to 40°C with a fixed overvoltage of 2.5V and with a fixed bias voltage of 27.95V. It was determined that a fixed overvoltage helps stabilize detector output but is not sufficient. A study of detector characteristics versus overvoltage was subsequently conducted and a lookup table was constructed to adjust bias voltage. A distributed network-based control system was developed in this thesis project to monitor the operating parameters of the detectors.

The attenuation of photons within the body has been recognised as the major limiting factor hindering the ability of single photon emission computed tomography (SPECT) as a quantitative technique. This thesis investigates several aspects of an emission-transmission SPECT system using the Monte Carlo method and experimental techniques. The system was based on a rotating gamma camera fitted with a parallel hole collimator. The simulation of a transmission study was performed using a simple non-uniform mathematical phantom with two different external sources, a collimated line source and a flood source. The results showed that the attenuation maps were highly dependent on the geometry and photon energy of the source. The collimated line source produced improved image quality with lower statistical noise than the flood source. The results showed that, when high atomic number elements are present in the tissue composition, the attenuation coefficients at different energies are related through a second order polynomial transformation. If the object under study is formed of soft tissue equivalent materials, a linear transformation holds. The attenuation maps generated in the transmission study were used to correct for non-uniform attenuation compensation of an emission phantom. The results showed that non-uniform attenuation compensation improved image quality and reduced noise when compared to data without attenuation compensation. The presence of scattered photons in the emission data reduced the quality of the images and precluded accurate quantification. Absolute quantification was performed using the percent air sensitivity criterion. The largest difference between the theoretical and the Monte Carlo simulated images was approximately 8%. An emission-transmission myocardial perfusion study was simulated using an anthropomorphic phantom. Two photon energies of clinical interest were used, 75 keV and 140 keV, corresponding to the main photon emission energies of 201Tl and 99mTC. The results showed that 99mTc provided better image quality than 201Tl. Non-uniform attenuation compensation produced a very good agreement between the theoretical prediction and the simulation when scatter-free data were considered. The results presented in this thesis indicate that it is not possible to accomplish accurate attenuation compensation in general situations if scatter correction is not applied.

No description available.

<p> <b>Objectives:</b> We ought to compare the effect of transcatheter aortic valve replacement (TAVR) and surgical aortic valve replacement (SAVR) on right ventricular systolic function (RVSF) in high risk patients with severe aortic stenosis (AS). <b>Methodology: Data Source</b>. PubMed, EMBASE, Cochrane library, and references of selected articles. Study Endpoints. Transthoracic echocardiography was utilized to assess the change in RVSF post TAVR versus SAVR using tricuspid annular plane systolic excursion (TAPSE), and Fractional area change (RVFAC). <b>Statistical analyses</b>. Random effect model on standardized mean difference (Hedges; g) were used together with heterogeneity assessment. <b>Result:</b> We included 485 patients from five single-center observational studies. Comparing TAVR with SAVR, TAVR resulted in better improvement in RVSF [TAPSE (<i>g</i>=2.88, SE=0.63, <i>P</i>&lt;0.001, Q=73.18, /²=94.53, r=0.65), and RVFAC (<i>g</i>=0.91, SE=0.16, <i>P</i>&lt;0.001, Q=2.39, /²=16.61), r=0.65]. <b> Conclusion:</b> Compared with SAVR, TAVR is preferred aortic intervention in patients with severe symptomatic AS and RV systolic dysfunction.</p>

<p> The purpose of this study was to develop an assessment tool to measure musical training and experiences for grouping participants in human neuroimaging research studies. To fulfill the purpose of this study, the researcher: 1. Completed a comprehensive review of the research literature to establish the essential content of the assessment tool; 2. Developed an assessment tool to survey subjects about their musical training and experiences; 3. Pilot tested the assessment tool, and revised the tool according to the preliminary analyses of the validity, reliability, and usefulness of the assessment tool; 4. Established the content validity and reliability of the assessment tool with subjects participating in a neuroimaging study designed to analyze the influences of musical training and experiences on brain structures and functions, and 5. Determined if the assessment tool function effectively in the selection and grouping of musically and musically untrained subjects for neuroimaging studies. </p><p> The assessment tool was administered to a purposive sample (<i> N</i> = 42) in the southeastern region of the United States. Participants were recruited on the basis of musical training, both the existence and lack thereof. The assessment was completed via the web-based platform, Qualtrics. Coding of survey responses indicated differences in the participant pool that resulted in two groups: Musicians and Non-musicians. Further investigation yielded two subgroups within the Musician participant group: Moderate and Advanced. </p><p> Validity of the assessment tool was established using a three-step construction process, (a) development of a draft based on the existing literature and the musical training knowledge of the researcher, (b) a review of the assessment tool by five music educators and performers, and (c) administration to a pilot group of five additional people with varying levels of musicianship. Additional content validity was completed by external reviewers by rating each assessment item using a Likert-type scale: 1&ndash;<i>Not important </i>, 2&ndash;<i>Slightly important</i>, 3&ndash;<i>Fairly important</i>, 4&ndash;<i>Important</i>, and 5&ndash;<i> Very important</i>. Reliability was established using interrater reliability and was determined to be 88.9%. </p><p> A discussion was presented that included the differences among participants that made their musical training and experiences unique compared with other participants. Implications were discussed regarding the usage possibilities for the survey, as well as the potential effects of the survey on human neuroimaging research.</p><p>

Despite that most vestibular schwannomas are successfully treated with radiotherapy, current follow-up protocols entail years of serial magnetic resonance imaging (MRI) scans to ensure cessation of growth. This pilot study sought to identify early predictors of radiation treatment response using a non-invasive multi-modality imaging approach. We hypothesized that by combining information acquired from dynamic contrast-enhanced MRI (DCE-MRI), diffusion tensor imaging (DTI), and L-¹¹C-methionine positron emission tomography (MET-PET) treatment response could be identified sooner than the current several year waiting period. This thesis presents the baseline MRI and MET-PET results of the pilot study acquired to-date with follow-up data to be acquired in the next six months. Baseline results suggest that DTI and DCE-MRI yield information that may be useful in identifying the response of vestibular schwannomas to radiotherapy. In particular, vestibular schwannomas display elevated mean diffusion coefficients relative to the contra-lateral cerebellum. Also, the novel use of arterial input functions derived from the anterior inferior cerebellar arteries has led to the successful implementation of DCE-MRI pharmaco-kinetic models which may be used to quantitatively monitor tumor response to radiotherapy. Furthermore, MET-PET has shown promise as a tool for evaluating response as all tumors exhibited enhancement under this modality as compared to the contra-lateral side of the brain. Single-voxel spectroscopy with 3T MRI has proven to be a poor technique with which to examine vestibular schwannomas since only two of eight spectra were acquired successfully. All of the techniques that have shown promise as investigatory tools of tumor response can potentially be implemented clinically in the near future. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

<p> Although 1.5 and 3 Tesla (T) magnetic resonance (MR) systems remain the clinical standard, the number of 7 T MR systems has increased over the past decade because of the promise of higher signal-to-noise ratio (SNR), which can translate to images with higher resolution, improved image quality and faster acquisition times. However, there are a number of technical challenges that have prevented exploiting the full potential of ultra-high field (&ge; 7 T) MR imaging (MRI), such as the inhomogeneous distribution of the radiofrequency (RF) electromagnetic field and specific energy absorption rate (SAR), which can compromise image quality and patient safety. </p><p> To better understand the origin of these issues, we first investigated the dependence of the spatial distribution of the magnetic field associated with a surface RF coil on the operating frequency and electrical properties of the sample. Our results demonstrated that the asymmetries between the transmit (<i>B</i>₁⁺) and receive (<i>B</i>₁^&ndash;) circularly polarized components of the magnetic field, which are in part responsible for RF inhomogeneity, depend on the electric conductivity of the sample. On the other hand, when sample conductivity is low, a high relative permittivity can result in an inhomogeneous RF field distribution, due to significant constructive and destructive interference patterns between forward and reflected propagating magnetic field within the sample. </p><p> We then investigated the use of high permittivity materials (HPMs) as a method to alter the field distribution and improve transmit and receive coil performance in MRI. We showed that HPM placed at a distance from an RF loop coil can passively shape the field within the sample. Our results showed improvement in transmit and receive sensitivity overlap, extension of coil field-of-view, and enhancement in transmit/receive efficiency. We demonstrated the utility of this concept by employing HPM to improve performance of an existing commercial head coil for the inferior regions of the brain, where the specific coil&rsquo;s imaging efficiency was inherently poor. Results showed a gain in SNR, while the maximum local and head SAR values remained below the prescribed limits. We showed that increasing coil performance with HPM could improve detection of functional MR activation during a motor-based task for whole brain fMRI. </p><p> Finally, to gain an intuitive understanding of how HPM improves coil performance, we investigated how HPM separately affects signal and noise sensitivity to improve SNR. For this purpose, we employed a theoretical model based on dyadic Green&rsquo;s functions to compare the characteristics of current patterns, i.e. the optimal spatial distribution of coil conductors, that would either maximize SNR (ideal current patterns), maximize signal reception (signal-only optimal current patterns), or minimize sample noise (dark mode current patterns). Our results demonstrated that the presence of a lossless HPM changed the relative balance of signal-only optimal and dark mode current patterns. For a given relative permittivity, increasing the thickness of the HPM altered the magnitude of the currents required to optimize signal sensitivity at the voxel of interest as well as decreased the net electric field in the sample, which is associated, via reciprocity, to the noise received from the sample. Our results also suggested that signal-only current patterns could be used to identify HPM configurations that lead to high SNR gain for RF coil arrays. We anticipate that physical insights from this work could be utilized to build the next generation of high performing RF coils integrated with HPM.</p><p>