[How strongly does the radiation burden of diagnostic x-ray studies depend on the imaging technic?]

The radiation burden of an individual patient caused by a radiological examination depends strongly on the technical parameters, such as kV and mAs. As an inquiry among 150 swiss physicians showed, rather different irradiation techniques are used for the same examination. Depending on these irradiation techniques, the doses may vary by almost a factor of ten. These large variations in dose indicate that in some clinics or hospitals the radiographic techniques and the film processing are at fault. This fact has to be accounted for by future efforts of quality assurance in diagnostic radiology.

[Exposure of the Swiss population to radiation from diagnostic x-ray studies]

A new study is presently being conducted on the exposure of the Swiss population to radiation by diagnostic measures. This study is performed by the Department of Medical Radiation Physics of the University of Berne in collaboration with the Federal Health Bureau and the Swiss Institute for Health and Hospital Matters. In earlier studies the genetically significant exposure of the population and subsequently the median exposure of the red bone marrow had been investigated, whereas now the risk exposure to radiation of as far as possible practically all the risk-relevant organs will be studied. Prior to the initiation of the study, all results of earlier investigations during 1957, 1971 and 1978 were collected and analysed. It was found that the published results are hardly comparable, since the first study was based on individual X-ray examinations and the two subsequent studies on the localised X-ray examinations. To ensure that all data are now comparable, the results of the three studies were appropriately recalculated. Although certain assumptions had to be made that cannot be fully verified any more in view of the time that has elapsed, the collected results will provide a fairly reliable overview of the present-day state of knowledge in this particular field.

BRH routine compliance testing for diagnostic x-ray systems or components of diagnostic x-ray systems to which 21 CFR subchapter J is applicable.

Supersedes HEW publication (FDA) 75-8012.

Assembler's guide to diagnostic x-ray equipment under the Federal Performance Standard.

Mode of access: Internet.

Two thermal methods to measure the energy fluence of a brief exposure of diagnostic x rays

This paper describes two simple thermal methods for measuring the energy fluence in J/cm 2 from a diagnostic x-ray exposure. Both detectors absorb essentially 100% of the radiation and give a signal that is directly proportional to the energy fluence of the x-ray beam. One detector measures the thermal effect when a pulse of x rays is totally absorbed in the pyroelectric detector of lead-zirconium-titanate (PZT). The other detector measures the expansion of a gas surrounding a lead disk detector in a photoacoustic chamber. The increased pressure of the gas is transmitted through a 1-mm duct to a sensitive microphone. Both detectors have previously been used to measure the energy fluence rate of continuous x-ray beams in the same energy region using a chopped beam and a lock-in amplifier. Measurement of the energy fluence of a pulse of radiation eliminates the need for the beam chopper and lock-in amplifier and results in a simple, rugged, and inexpensive dosimeter. Either method can be combined with the area of the beam to give an estimate of the imparted energy to the patient from a diagnostic x-ray exposure.

Microcontrolled pyro-electric instrument for measuring X-ray intensity in mammography

A novel instrument for measurement of X-ray intensity from mammography consists of a sensitive pyro-electric detector, a high-sensitivity, low-noise current-to-voltage converter, a microcontroller and a digital display. The heart of this device, and what makes it unique is the pyro-electric detector, which measures radiation by converting heat from absorbed incident X-rays into an electric current. This current is then converted to a voltage and digitised. The detector consists of a ferro-electric crystal; two types were tested; lithium tantalate and lithium niobate. X-ray measurement in mammography is challenging because of its relatively low photon energy range, from 11 keV to 15 keV equivalent mean energy, corresponding to a peak tube potential from 22 to 36 kV. Consequently, energy fluence rate or intensity is low compared with that of common diagnostic X-ray. The instrument is capable of measuring intensities as low as 0.25 mWm -2 with precision greater than 99%. Not only was the instrument capable of performing in the clinical environment, with high background electromagnetic interference and vibration, but its performance was not degraded after being subjected to 140 roentgen (3.6 × 10 -2 C kg -2 air) as measured by piezo-electric (d 33) or pyro-electric coefficients. © IFMBE 2005.

Monte Carlo simulation applied in total reflection X-ray fluorescence: Preliminary results

The X-ray Fluorescence (XRF) analysis is a technique for the qualitative and quantitative determination of chemical constituents in a sample. This method is based on detection of the characteristic radiation intensities emitted by the elements of the sample, when properly excited. A variant of this technique is the Total Reflection X-ray Fluorescence (TXRF) that utilizes electromagnetic radiation as excitation source. In total reflection of X-ray, the angle of refraction of the incident beam tends to zero and the refracted beam is tangent to the sample support interface. Thus, there is a minimum angle of incidence at which no refracted beam exists and all incident radiation undergoes total reflection. In this study, we evaluated the influence of the energy variation of the beam of incident x-rays, using the MCNPX code (Monte Carlo NParticle) based on Monte Carlo method. © 2013 AIP Publishing LLC.

Development of an X-ray spectrometric system and feasibility tests of Silicon Drift Detector for medical and space applications

The thesis work concerns X-ray spectrometry for both medical and space applications and is divided into two sections. The first section addresses an X-ray spectrometric system designed to study radiological beams and is devoted to the optimization of diagnostic procedures in medicine. A parametric semi-empirical model capable of efficiently reconstructing diagnostic X-ray spectra in 'middle power' computers was developed and tested. In addition, different silicon diode detectors were tested as real-time detectors in order to provide a real-time evaluation of the spectrum during diagnostic procedures. This project contributes to the field by presenting an improved simulation of a realistic X-ray beam emerging from a common X-ray tube with a complete and detailed spectrum that lends itself to further studies of added filtration, thus providing an optimized beam for different diagnostic applications in medicine. The second section describes the preliminary tests that have been carried out on the first version of an Application Specific Integrated Circuit (ASIC), integrated with large area position-sensitive Silicon Drift Detector (SDD) to be used on board future space missions. This technology has been developed for the ESA project: LOFT (Large Observatory for X-ray Timing), a new medium-class space mission that the European Space Agency has been assessing since February of 2011. The LOFT project was proposed as part of the Cosmic Vision Program (2015-2025).

A LAPLACE TRANSFORM PAIR MODEL TO DETERMINE BREMSSTRAHLUNG SPECTRA FROM ATTENUATION DATA (RADIATION, X-RAY, SPECTRAL MODELING)

Every x-ray attenuation curve inherently contains all the information necessary to extract the complete energy spectrum of a beam. To date, attempts to obtain accurate spectral information from attenuation data have been inadequate.^ This investigation presents a mathematical pair model, grounded in physical reality by the Laplace Transformation, to describe the attenuation of a photon beam and the corresponding bremsstrahlung spectral distribution. In addition the Laplace model has been mathematically extended to include characteristic radiation in a physically meaningful way. A method to determine the fraction of characteristic radiation in any diagnostic x-ray beam was introduced for use with the extended model.^ This work has examined the reconstructive capability of the Laplace pair model for a photon beam range of from 50 kVp to 25 MV, using both theoretical and experimental methods.^ In the diagnostic region, excellent agreement between a wide variety of experimental spectra and those reconstructed with the Laplace model was obtained when the atomic composition of the attenuators was accurately known. The model successfully reproduced a 2 MV spectrum but demonstrated difficulty in accurately reconstructing orthovoltage and 6 MV spectra. The 25 MV spectrum was successfully reconstructed although poor agreement with the spectrum obtained by Levy was found.^ The analysis of errors, performed with diagnostic energy data, demonstrated the relative insensitivity of the model to typical experimental errors and confirmed that the model can be successfully used to theoretically derive accurate spectral information from experimental attenuation data. ^

Local liquid holdups and hysteresis in a 2-D packed bed using X-ray radiography

An X-ray visualization technique has been used for the quantitative determination of local liquid holdups distribution and liquid holdup hysteresis in a nonwetting two-dimensional (2-D) packed bed. A medical diagnostic X-ray unit has been used to image the local holdups in a 2-D cold model having a random packing of expanded polystyrene beads. An aqueous barium chloride solution was used as a fluid to achieve good contrast on X-ray images. To quantify the local liquid holdup, a simple calibration technique has been developed that can be used for most of the radiological methods such as gamma ray and neutron radiography. The global value of total liquid holdup, obtained by X-ray method, has been compared with two conventional methods: drainage and tracer response. The X-ray technique, after validation, has been used to visualize and quantify, the liquid hysteresis phenomena in a packed bed. The liquid flows in preferred paths or channels that carry droplets/rivulets of increasing size and number as the liquid flow rate is increased. When the flow is reduced, these paths are retained and the higher liquid holdup that persists in these regions leads to the holdup hysteresis effect. Holdup in some regions of the packed bed may be an order of magnitude higher than average at a particular flow rate. (c) 2005 American Institute of Chemical Engineers

The effects of radiative cascades on the x-ray diagnostic lines of Fe16+

We present complete collisional-radiative modelling results for the soft x-ray emission lines of Fe16+ in the 15 Å–17 Å range. These lines have been the subject of much controversy in the astrophysical and laboratory plasma community. Radiative transition rates are generated from fully relativistic atomic structure calculations. Electron-impact excitation cross sections are determined using a fully relativistic R-matrix method employing 139 coupled atomic levels through n = 5. We find that, in all cases, using a simple ratio of the collisional rate coefficient times a radiative branching factor is not sufficient to model the widely used diagnostic line ratios. One has to include the effects of collisional-radiative cascades in a population model to achieve accurate line ratios. Our line ratio results agree well with several previous calculations and reasonably well with tokamak experimental measurements, assuming a Maxwellian electron-energy distribution. Our modelling results for four EBIT line ratios, assuming a narrow Gaussian electron-energy distribution, are in generally poor agreement with all four NIST measurements but are in better agreement with the two LLNL measurements. These results suggest the need for an investigation of the theoretical polarization calculations that are required to interpret the EBIT line ratio measurements.