ABSTRACT
The use of electron paramagnetic resonance (EPR) tooth dosimetry for calculation of organ doses requires conversion of the measured absorbed dose in enamel. Before deriving conversion factors from simulation calculations with a realistic anthropomorphic human phantom, in the current study a simplified phantom was chosen to compare EPR measurement and Monte Carlo calculation. The dose response of tooth enamel of molars at various positions inside a cylindrical Plexiglas phantom of head-size was calculated hy Monte Carlo modelling in parallel photon beams of X rays of 63 keV equivalent energy and 60Co gamma rays (1.25 Mev). For X ray exposure, preliminary results of EPR dosimetry with tooth enamel samples prepared from molars irradiated in the phantom were in agreement with calculation. The mean value of the ratio of the measured to the calculated dose was 0.93 +/- 0.08.
Subject(s)
Dental Enamel/radiation effects , Photons , Adult , Humans , Molar/radiation effects , Monte Carlo Method , Phantoms, Imaging , Polymethyl Methacrylate , Reproducibility of Results , X-RaysABSTRACT
Conventional radiographic techniques have strong limitations when low-absorption contrast samples are imaged. Phase contrast radiography has been shown to produce high-quality images of soft tissues. In this technique the recorded intensity patterns are related to gradients in the refractive index of the sample. A critical point of this new technique is the need to employ crystal analysers, which results in an appreciable reduction in the beam intensity and consequently in rather long exposure times. In this paper the use of focused beams is suggested to overcome this aspect. Biological samples with small structures and low absorption variations were imaged using both flat and curved monochromator crystals, demonstrating that the use of curved optics leads to a decrease in the exposure time with only a limited degradation of the spatial resolution. This opens up the possibility of using the phase contrast technique with laboratory sources.
Subject(s)
Diagnostic Imaging/instrumentation , Diagnostic Imaging/methods , Synchrotrons , Tomography, X-Ray Computed/methods , Animals , Butterflies , Microscopy, Phase-Contrast/methods , Time Factors , X-RaysABSTRACT
The use of a dual K-edge filter (niobium-molybdenum) with a Mo anode x-ray tube for application to mammography is investigated. The incident and transmitted energy spectral distributions are compared with those provided by a molybdenum anode molybdenum filter tube (standard source). The imaging characteristics in terms of contrast and mean glandular dose have been evaluated for various phantom thicknesses. The niobium filtration removes the molybdenum K beta line almost completely from the beam spectrum whereas a Mo filtration is needed to avoid the increases both in the low-energy component of the incident beam and in the higher energy component of the transmitted one. The contrast is improved with respect to the standard source and the mean glandular dose is only slightly increased for moderate transmission phantoms (thickness 2-4 cm).
Subject(s)
Breast/anatomy & histology , Mammography/instrumentation , Phantoms, Imaging , Equipment Design , Female , Humans , Mammography/methods , Mammography/standards , Molybdenum , Niobium , Photons , Sensitivity and Specificity , X-RaysABSTRACT
Solid thermoluminescent CaSO4:Dy (TLD-900) has been recently put on the market by Harshaw Chemical Co. Preliminary results on annealing, glow-curve, short-time fading, dose and energy response and reproducibility of TLD-900 ribbons are presented.