The continual need for more accurate and effective techniques in radiation therapy makes it necessary to devise new control means combining high spatial resolution as well as high dose accuracy. Intensity modulated radio therapy (IMRT) allows highly conformed fields with high spatial gradient and therefore requires a precise monitoring of all the multileaf positions. In response to this need, the authors have developed a new 2D tissue equivalent dosimeter with high spatial resolution. A plastic scintillator sheet is sandwiched between two polystyrene blocks and the emitted light is captured by a high resolution camera. A newly developed procedure described herein allows efficient discrimination of the scintillation from the parasitic Cerenkov radiation. This processing is applied on the cumulated image from a sequence of images taken during an irradiation field at a rate of 10 images/s. It provides a high resolution mapping of the cumulated dose in quasireal time. The dosimeter is tissue equivalent (ICRU-44) and works both for electrons and photons without complex parameter adjustment since phantom and detector materials are identical. Instrument calibration is simple and independent of the irradiation conditions (energy, fluence, quality, ...). In this article, the authors present the principle of the dosimeter and its calibration procedure. They compare the results obtained for photons and electron beams with ionization chamber measurements in polystyrene. Technical specifications such as accuracy and repeatability are precisely evaluated and discussed. Finally, they present different IMRT field measurements and compare DOSIMAP measurements to TPS simulations and dosimetric film profiles. The results confirm the excellent spatial resolution of the instrument and its capacity to inspect the leaf positions for each segment of a given field.
In this paper we propose a method to characterize polarization based stereoscopic 3D displays using multispectral Fourier optics viewing angle measurements. Full polarization analysis of the light emitted by the display in the full viewing cone is made at 31 wavelengths in the visible range. Vertical modulation of the polarization state is observed and explained by the position of the phase shift filter into the display structure. In addition, strong spectral dependence of the ellipticity and polarization degree is observed. These features come from the strong spectral dependence of the phase shift film and introduce some imperfections (color shifts and reduced contrast). Using the measured transmission properties of the two glasses filters, the resulting luminance across each filter is computed for left and right eye views. Monocular contrast for each eye and binocular contrasts are performed in the observer space, and Qualified Monocular and Binocular Viewing Spaces (QMVS and QBVS) can be deduced in the same way as auto-stereoscopic 3D displays allowing direct comparison of the performances.
-Multispectral viewing angle and imaging characterization have been applied to different organic light-emitting diode (OLED) displays. Angular dependence of the OLED emission is always complex because of its multilayer structure. Spectral information is also related to the geometry of Fabry-Perot-like structure of each OLED. High-resolution viewing angle measurements of different OLED displays are reported and compared. Multispectral viewing angle polarization properties are also reported. Imaging measurements allow to detect wavelength shift on the surface of the displays probably related to thickness non-uniformities. Local radiance fluctuations from one pixel to the other more related to driving problems due to the dispersion of the electric properties of the driving thin-film transistors are also detected.
Viewing angle properties are certainly among the most common characteristics measured on any type of displays and in particular on LCDs. Historically, goniometers have first been used for this task. In 1993 ELDIM has introduced Fourier optics instruments (conoscopes) that are now widely used by many display makers. More recently an imaging technique based on the use of a low reflectance hemisphere has been introduced. All these approaches have their inner advantages and drawbacks depending on the optical setup and the measurements constraints. We present a comparison of these three systems based on their theoretical specifications.
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