22 research outputs found
Correction to strength and symmetry of the third-order nonlinearity during poling of glass waveguides
No full textNegative thermal poling introduces second-order nonlinear effects into silica glass. The effects are studied using the charge separation model allowing for the third-order nonlinear effect to be anisotropic. The second-order nonlinear coefficient χ(2) is found to be consistent with the results reported previously by Arentoft et al. (1999), Ren et al. (2002), and Marckmann et al. (2001) and the third-order nonlinear coefficient χ(3) is found to be anisotropic but constant during poling
Influence of the stem effect on radioluminescence signals from optical fibre Al<sub>2</sub>O<sub>3</sub>:C dosemeters
No full textThis paper analyses the influence of the Cerenkov radiation and other noise sources, the so-called stem effect, on radioluminescence (RL) signals generated in optical fibre Al2O3:C dosemeters used in medical dosimetry. The optical fibre dosemeter consists of a sensitive Al2O3:C crystal coupled to an optical fibre cable that carries the RL and optically stimulated luminescence (OSL) signals generated in the Al2O3:C crystal. During irradiation of the dosemeter, the real-time dose rate can be determined from the RL signal and after irradiation the total dose absorbed is determined from the OSL signal stimulated using a focused green solid-state laser. In particular, the components of the stem effect generated in the fibres were analysed to determine their impact on the RL signal
Optical fibre dosemeter systems for clinical applications based on radioluminescence and optically stimulated luminescence from Al<sub>2</sub>O<sub>3</sub>:C
No full textOptical fibre dosemeter systems based on radioluminescence and optically stimulated luminescence (OSL) from carbon-doped aluminium oxide (Al2O3:C) crystals were developed for in vivo real-time dose rate and absorbed dose measurements in radiotherapy and mammography. A technique was also developed for making ultra-small dosemeter probes that can easily be placed inside patients in radiation treatment. These probes have shown excellent properties in both head and neck intensity-modulated radiation therapy treatment and in mammography. The dose-response of the OSL signal for the new optical fibre dosemeter system showed a repeatability within 0.15% at a dose level of 60 mGy when integrated over 100 s. The temperature dependence in the range 0-45 degrees C showed a reproducibility within 1.3% when the OSL signal was integrated over 100 s
Poling effect of a charge-trapping layer in glass waveguides
No full textGermanium-doped multi-layer waveguides containing a silicon oxy-nitride layer as a charge trapper are thermally poled in an air environment. Compared to the waveguides without the trapping layer, the induced linear electro-optic coefficient increases more than 20%. A comparable rise in the internal field is found. Our results demonstrate an optimization of the optical nonlinearity by shaping the built-in internal field with the charge-trapping layer
Udvikling af et in vivo IMRT dosimetrisystem baseret på luminescens fra Al203:C og udlæsning via tynde lyslederkabler
No full textCW-OSL measurement protocols using optical fibre Al<sub>2</sub>O<sub>3</sub>:C dosemeters
No full textA new system for in vivo dosimetry during radiotherapy has been introduced. Luminescence signals from a small crystal of carbon-doped aluminium oxide (Al2O3:C) are transmitted through an optical fibre cable to an instrument that contains optical filters, a photomultiplier tube and a green (532 nm) laser. The prime output is continuous wave optically stimulated luminescence (CW-OSL) used for the measurement of the integrated dose. We demonstrate a measurement protocol with high reproducibility and improved linearity, which is suitable for clinical dosimetry. A crystal-specific minimum pre-dose is necessary for signal stabilisation. Simple background subtraction only partially removes the residual signal present at long integration times. Instead, the measurement protocol separates the decay curve into three individual components and only the fast and medium components were used
Is There an Age Pattern in the Treatment of AMI? Evidence from Ontario
No full textIn this article we analyse the rates at which those admitted to hospital with acute myocardial infarction (AMI) receive aggressive treatment, assess how those rates have changed over time, and ask whether there is evidence of age discrepancies. Estimates made on the basis of data from an administrative database that includes discharges from all acute care hospitals in Ontario for selected years, from 1995 to 2005, indicate that there are strong and persistent age patterns in the application of medical technology. Results showed that to be true even after controlling for the higher rates of co-morbidities among older patients and variations across hospitals in practice patterns.treatment of AMI, age pattern
Is There an Age Pattern in the Treatment of AMI? Evidence from Ontario
No full textIn this article we analyse the rates at which those admitted to hospital with acute myocardial infarction (AMI) receive aggressive treatment, assess how those rates have changed over time, and ask whether there is evidence of age discrepancies. Estimates made on the basis of data from an administrative database that includes discharges from all acute care hospitals in Ontario for selected years, from 1995 to 2005, indicate that there are strong and persistent age patterns in the application of medical technology. Results showed that to be true even after controlling for the higher rates of co-morbidities among older patients and variations across hospitals in practice patterns.treatment of AMI, age pattern
Ce doped SiO<sub>2</sub> optical fibers for remote radiation sensing and measurement
No full textScintillating materials, able to efficiently operate the conversion of energy absorbed in the form of ionizing radiation into light in the visible UV interval, are presently used in a wide class of applications as medical imaging, industrial inspection, security controls and high energy physics detector. In the last few years we studied and developed a new radiation sensor based on silica-glass fiber-optic technology. In its simplest configuration such device is composed by a short portion (about 10 mm) of scintillating fiber coupled to a photomultiplier by a suitably long passive silica fiber.At the early stage of its market introduction it is the smallest radiation sensor, also with respect to MOSFET and diode technology and it appears to be the ideal choice for in vivo measurements in medical field or remote sensing
