Hokkaido University (北海道大学) / 博士 / 医学

Since the beginning of space exploration in last century, several kinds of devices from passive and active dosimeters to radiation environment monitors have been used to measure radiation levels onboard different space crafts and shuttles allowing the space community to identify and quantify space radiation. The recent construction of several laboratories on the International Space Station (ISS) has confirmed that prolonged duration space missions are now becoming standard practice and as such, the need to better understand the potential risk of space radiation to Astronaut’s health, has become a priority for long mission planner. The complex internal radiation environment created within the ISS is due to high-energy particle interactions within the ISS shielded environment. As a result, a large number of secondary particles, that pose specific health risks, are created. Neutrons are one important component of this mixed radiation field due to their high LET. Therefore, the assessment of the neutron dose contribution has become an important part of the safety and monitoring program onboard the ISS. The need to determine whether neutron dose measured externally to the human body give an accurate and conservative estimate of the dose received internally is of paramount importance for long term manned space missions. This thesis presents a part of an ongoing large research program on radiation monitoring on ISS called Matroshka-R Project that was established to analyze the radiation exposure levels onboard the ISS using different radiation instruments and a spherical phantom to simulate human body. Monte Carlo transport code was used to simulate the interaction of high energy protons and neutrons with the spherical phantom currently onboard ISS. A Monte Carlo model of the phantom has been built, and it consists of seven spherical layers presenting different depths of the simulated tissue. The phantom has been exposed to individual proton energies and to a spectrum of neutrons. The flux of the created neutrons inside the phantom has been calculated. The internal to external neutron flux ratio was calculated and compared to the experimental data, recently, measured on three separate expeditions of the ISS. The results from the calculations showed that the value of the neutron fluxes inside and outside the phantom is different from the data recently measured with bubble detectors. / UOIT

Continuous monitoring of blood perfusion and oxygenation is essential in assessing the health of a transplanted organ. Particularly, monitoring the perfusion and oxygenation of the organ during the two-week period after the transplant procedure is crucial in detecting a sustained loss in perfusion or a reduction in oxygen saturation before these changes render irreversible damage to the organ or patient. Pulse oximetry is a clinically accepted method of monitoring the arterial oxygen saturation of a patient in a non-invasive manner. Pulse oximeters exploit the wavelength-dependent absorption of oxygenated and deoxygenated hemoglobin to measure a patient's arterial oxygen saturation. However, traditional pulse oximeters do not provide perfusion information and produce erroneous oxygen saturation measurements under low perfusion levels. An optical blood perfusion and oxygenation sensor, based on a modified reflectance pulse oximeter, has been developed for in situ monitoring of transplanted organs. To reduce the number of animal experiments, phantoms that mimic the optical and anatomical properties of liver parenchyma have also been developed. In this work, in vitro data was gathered from dye solutions mimicking oxygenated blood that were pumped through single and multi-layer phantoms mimicking liver parenchyma and through a phantom mimicking the portal vein. A portion of the phantom data was compared to data collected from in vivo occlusion studies performed on female swine to assess the ability of the phantoms to mimic the response observed with changes in blood perfusion through liver parenchyma. Both the single layer and multilayer phantoms showed a similar response to changes in perfusion as the in vivo case. With each phantom, the signal increased linearly with increases in perfusion, but the multilayer phantom showed a higher sensitivity (approximately 30% higher) to changes in perfusion than the single layer phantom. This higher sensitivity would provide the ability to measure smaller changes in perfusion and increase the resolution of the sensor. Also, both parenchymal phantoms showed similar trends in the oxygenation studies, with the R value decreasing with increasing oxygenation. While the observations in this research demonstrate the ability to use both phantoms for in vitro experiments, the results show the multilayer phantom is a better option for mimicking perfusion because it displays similar occlusion patterns as the liver parenchyma in vivo, a higher sensitivity to changes in perfusion than the single layer phantom, and it is only slightly more complex in design (contains only two more layers of sinusoids) than the single layer phantom.

The objective of this work is to estimate and simulate organ uptake variability and correlations using measured data from the FastSPECT II Single Photon Emission Computed Tomography (SPECT) imaging system. We will investigate various methods that attempt to determine organ-uptake within a set of organs in a digital phantom; these methods include Region-of-Interest, Gauss-Markov, Wiener, and Reconstruction Estimation algorithms. In addition to the estimators, we will also test whether moving the phantom with respect to the imaging system and gathering multiple images from different positions will improve the performance of our estimators. The variations and correlations in the object will be modeled using Gaussian distributions with first and second-order statistics known exactly. We will present a mathematical formulation of this model, in a texture-free context, as well as some results on image-quality assessment. The object model will be the MOBY digital mouse phantom; the 4-D MOBY Mouse Model is a digital phantom developed by Paul Segars\citep{moby}, which provides a useful digital model for nuclear-medicine and CT imaging.

Explaining false memory has been a strong resource to understand how memory works in general. More than two decades of research on false memories show that false memories are a complex phenomenon that made most of the established theories of memory insufficient. Phantom recollection is a specific part of the false memory phenomena that consists of a memory illusion in which subjects have a false recollective phenomenology that resembles true recollections. Two experiments following DRM's paradigm served to study phantom recollection in adults, manipulating variables such as Level of processing, Type of voice, Retrieval time and Repetition. The three proper instructions of a mathematical model named Conjoint Recall were applied in order to have separate measures of the phantom recollection manifestations. Ninety American and 90 Mexican university students participated. The results of the experiments disconfirm IAR explanations of phantom recollection, but confirm most of Fuzzy-trace-theory's assumptions on this phenomenon (Brainerd, Payne, Wright, and Reyna, 2003).

Masters Research - Masters of Philosophy / INTRODUCTION: Level III dosimetric intercomparison studies test the entire radiotherapy patient treatment chain from diagnostic imaging to treatment delivery and verification imaging at multiple radiotherapy centres. The anthropomorphic phantom employed in an intercomparison needs to meet specific criteria including portability, tissue equivalence and accommodation of radiation detectors to ensure clinical relevance and dosimetric accuracy. The proposition that a purpose-built phantom can encompass all the attributes necessary for precise Level III dosimetric intercomparisons for prostate cancer is the premise of this body of work. METHODS: Organ outlines were generated from a human computed tomography image set and incorporated into the phantom design to replicate human anatomy as closely as possible. Twenty-five points of interest were located throughout the dataset to identify where point-dose values could be measured with thermoluminescence dosimeters. The centre of the prostate was identified as the location for measurement with a small-volume ionization chamber. The materials used in this phantom were tested against water to determine relative attenuation, density and Hounsfield Units. Three materials were chosen to mimic bone, organs, and a backfill material and the phantom was manufactured using modern prototyping techniques into five separate coronal slices. Time lines and resource requirements for the phantom design and manufacture were recorded. The ability of the phantom to mimic the entire treatment chain was tested at the Calvary Mater Newcastle Hospital. RESULTS: The phantom CT images indicated the densities and organ geometries were comparable to the original patient. The phantom proved simple to load for dosimetry and rapid to assemble. Measurements indicated the reproducibility to be in the order of 1% for the ionization chamber measurement and within 3% for thermoluminescence dosimeters. Due to heat release during manufacture, small airgaps were present throughout the phantom producing artifacts on lateral images. The overall cost for production of the prototype phantom was comparable to other commercial anthropomorphic phantoms ($AU45,000). The phantom was shown to be suitable for use as a “patient” to mimic the entire treatment chain for typical external beam radiotherapy for prostate and rectal cancer. Outlining of relevant structures by a radiation oncologist was uncomplicated and the computerised treatment plan compared well with the dose measured using ionisation chambers and thermoluminescence dosimeters. DISCUSSION & CONCLUSIONS: The phantom constructed for the present study incorporates all characteristics necessary for accurate Level III intercomparison studies and will be an effective tool for an intercomparison of pelvic treatments in Australasia. These results may benefit analysis of outcomes for prostate cancer treatments, especially in the clinical trial environment. It will be of significant interest in the future to use the phantom to assess advanced radiotherapy delivery techniques such as Intensity Modulated Radiation Therapy (IMRT).

Mammographic techniques used for screening programmes need to be of the highest quality; hence, the need of a good phantom to mimic breast response to radiation. The phantom materials must be sensitive to small changes in the mammography system and provide a means of evaluating the absorbed dose to the breast. These materials have to provide the same attenuation properties as the real tissues being simulated, for the radiation modalities being investigated. Cross-linked hydrophilic copolymers have the potential to be good phantom materials for the breast as their elemental compositions are similar to soft tissue. Two types of hydrophilic copolymer materials used in this study were designated as ED1S and ED4C. They were made from a certain proportionate mixture of methyl methacrylate and vinyl pyrrolidone. The physical properties of the materials such as liquid uptake and dimensional changes in hydration and dehydration processes were studied. The equilibrium water content of ED1S and ED4C fully hydrated in water was 55% and 70% respectively. The samples underwent distortion when dehydrated and a volume approximation formula for the dehydrated samples was derived. The linear attenuation coefficient and the mass attenuation coefficient of the hydrophilic copolymer materials at photon energies in the mammographic energy region were determined. Both a single beam transmission method and a photon transmission tomography method were used. The results were compared with XCOM calculated attenuation coefficients of water and average breasts using the elemental composition found in the literature. It was found that the mass attenuation coefficient of dry hydrophilic copolymer samples closely fit the XCOM calculated old-age breast (Breast 3) and samples fully hydrated in water fit the calculated young-age breast (Breast 1). Measurements were also carried out to determine the linear attenuation coefficient of normal and abnormal breast tissues at four photon energies in the mammographic energy region. The values found were in good accord with calculated average breast values. However, more studies need to be done as only three samples were used. The electron density of the hydrophilic copolymer materials was determined by using the Compton scattering technique. The electron density for dry ED1S sample was (3.1 +/- 0.4) x 1023 electrons per cm3 and for dry ED4C was (4.4 +/- 0.4) x 1023 electrons per cm3.

Master of Science / Department of Mechanical and Nuclear Engineering / William L. Dunn / Neutron dosimeters measure neutron doses but portable, real time, high efficiency, and gamma insensitive neutron dosimeters are not commonly available. Characterization of a newly invented neutron dosimeter, based on perforated semiconductor neutron detectors (SNDs) whose perforations are filled with neutron reactive material, was the main purpose of this research study. The characterization procedure was performed by both simulation and experiment. The Monte Carlo N-Particle (MCNP) transport code was used to model a boron-filled dosimeter and to study the responses when the dosimeter was located on the surfaces of a water phantom and an anthropomorphic phantom for parallel beams of neutrons having various energy spectra. A pair of detectors was modeled: one bare and one Cd-filtered. Dosimeter responses were normalized for a beam that would produce 1 mSv ambient dose equivalent if incident on the ICRU sphere phantom. Dosimeter responses were estimated at different positions on the torso and it was found that the responses are relatively insensitive to the placement on the torso. For 100% efficient detectors and for beam with a Watt spectrum incident from front to back of the phantom, the bare detector produces about 140 counts per [Mu]Sv and the Cd-filtered detector produces about 80 counts per [Mu]Sv. The experimental characterization study involves observing SND counts with the dosimeter placed on an anthropomorphic torso phantom and determining the corresponding neutron dose. A TLD pair method was used to determine the neutron dose on the surface of the phantom. The neutron reactive material of the dosimeter was [superscript]6LiF, which is different from that assumed for the modeled dosimeter. A bare dosimeter response collected over 10 min was 25113 [plus or minus] 158 counts and the corresponding neutron dose was measured to be 2.57 mSv. The Cd-filtered dosimeter response collected over 10 min was 23886 [plus or minus] 155 counts and the corresponding neutron dose was measured to be 2.32 mSv. The neutron dosimeters are capable of detecting doses in the [Mu]Sv range and above, and are anticipated to provide direct read-out in dose units in future using count-to-dose conversion factors for bare and Cd-filtered SNDs.

No description available.

Phantom Limb pain (PLP) affects up to 85% of all patients following an amputation, causing debilitating effects on their quality of life. Mirror Therapy (MT) has been reported to have potential success for the alleviation of PLP. Current understanding of PLP and the efficacy of MT for its alleviation are still unclear, therefore guidelines for treatment protocols are lacking. This literature review assesses the current best evidence for using MT to alleviate PLP of patients with amputation. Method: The authors systematically searched the academic databases Medline, Amed, CINAHL and Google Scholar, using key search terms with inclusion and exclusion criteria to identify relevant articles on the use of MT in populations of patients suffering PLP after unilateral limb amputation. Findings: Seven primary papers were identified and appraised. All the articles reported significant PLP alleviation after using MT with a trend for achieving phantom limb movement (PLM) prior to pain relief. Conclusions: Mirror Therapy is a promising intervention for PLP. Regular MT sessions are required to maintain treatment effect. Causes of PLP and pathways to its alleviation may be multifactorial; therefore further well-conducted RCTs are required to identify best practice.