Diagnostic X-ray Beams Research Articles

Angular‐dependent coherent scatter measured with a diagnostic x‐ray image intensifier‐based imaging system

Low-angle scatter of x rays at diagnostic energies is primarily coherent. This coherence gives rise to interference effects resulting in x-ray diffraction patterns that are characteristic of the scattering material. A method is described of imaging these low-angle (0 degree-10 degrees) x-ray diffraction properties of tissue specimens using a diagnostic x-ray beam and image intensifier-based system. The coherent-scatter cross sections of several materials measured this way are presented. It is shown theoretically that the measurements made with this system can be expressed as the mono-energetic cross section "blurred" by the x-ray spectrum using a linear superposition integral. Experimental results using aluminum powder confirm this. Using a 70 kVp x-ray beam filtered with gadolinium to reduce the spectral width, materials such as water, Lucite, and hydroxyapatite all have significantly different diffraction patterns. The cross sections determined from this analysis from the basis of a unique method of characterizing and identifying tissue samples according to their atomic structure rather than x-ray attenuation properties.

Low-angle X-ray scattering signatures of urinary calculi.

This is the first reported use of low-angle X-ray scattering for the investigation of urinary calculi. Low-angle X-ray scattering (LAXS) measures the diffraction of a broad spectrum of X-rays at a single angle and uses a conventional diagnostic X-ray beam, and could thus be developed for use in vivo. A total of 45 calculi were investigated using this technique. Calcium oxalate stones showed a bimodal signature with peaks of almost even photon energies. Signatures for the other stone types were less well-defined. The results are discussed in more detail below. Our preliminary results show that the technique is capable of distinguishing between calcium oxalate stones and other stone types in vitro. Further work is in progress to correlate the results of this technique with objective parameters of stone hardness.

Experimental verification of reverse order of diagnostic X-ray beam quality in voltage-ripple dependence.

It has been generally expected that, as X-ray tube-voltage ripple increases, the X-ray spectrum shifts to the low photon-energy side, and therefore the mean energy decreases, i.e. the beam quality is softened. This is the normal order. Previous calculation (Birch et al., 1979), however, showed that the beam quality generated by 100% ripple was harder than that by 50% ripple. This is the reverse order, against general expectation. To verify the reverse order, X-ray spectra are measured using a germanium detector system. The measurements are performed with various thicknesses of aluminium object. To obtain large ripples at small tube currents, small-capacity high-voltage cables are made. To perform efficient measurements, the homogeneous sensitive region of the germanium crystal is determined, and detector-collimators with various diameters are prepared. As a result, experimental verification of the reverse order is performed for various thicknesses of object. The reverse order also appears in photon spectra and mean energies calculated using three models from previous work (Kramer, 1923; Birch and Marshall, 1979; Tucker et al., 1991) by inserting the tube-voltage waveforms measured with the authors' system. The experimental results agree well with the results using the Birch-Marshall model. Mean energies reach the minimum levels for the three models at 20-60% ripple, as do the experimental results. The reason for the phenomenon is clarified by qualitative illustration.

Microprocessor-based diagnostic X-ray beam quality assurance dosimeter using a photovoltaic detector/amplifier device

A novel instrument for non-invasive testing and quality assurance of diagnostic x-ray units, using a photovoltaic detector/amplifier device as a dosimeter is described. This small-size, fast, low power transducer has a uniform stable response (within ± 6%) of 3.7 V/(cGy min −1, air kerma rate) for 50–150 kV lightly filtered x-rays. A microprocessor based data acquisition system samples the x-ray intensities with an unshielded detector, or their ratio, with a pair of detectors shielded by differential filters and stores these data in memory; then evaluates and displays kVp, exposure time (number of x-ray pulses), beam output and waveform.

Shielding requirements for constant-potential diagnostic x-ray beams determined by a Monte Carlo calculation.

A Monte Carlo calculation has been performed to determine the transmission of broad constant-potential x-ray beams through Pb, concrete, gypsum wallboard, steel and plate glass. The EGS4 code system was used with a simple broad-beam geometric model to generate exposure transmission curves for published 70, 100, 120 and 140-kVcp x-ray spectra. These curves are compared to measured three-phase generated x-ray transmission data in the literature and found to be reasonable. For calculation ease the data are fit to an equation previously shown to describe such curves quite well. These calculated transmission data are then used to create three-phase shielding tables for Pb and concrete, as well as other materials not available in Report No. 49 of the NCRP.

Estimation of effective dose equivalent to staff in diagnostic radiology

The irradiation of staff in diagnostic radiology was simulated for conditions commonly encountered in fluoroscopy. Scattered radiation distributions were produced from diagnostic X-ray beams generated at tube potentials in the range 60-120 kVp, using the abdomen sections of a Rando phantom. Doses to a number of organs in the head and neck were measured using a Rando phantom loaded with lithium fluoride thermoluminescent dosemeters. The torso sections were placed on a water phantom on top of a stand, with film badge dosemeters positioned on the surface of the phantom at the forehead, neck, chest and waist, and the phantom was placed in the radiation field. The effective dose equivalent (EDE) to the phantom was calculated for various X-ray beam qualities and lead apron thicknesses and compared with the film badge doses. The results indicate that a dosemeter worn at the waist/chest level under a lead apron generally underestimates the EDE. Conversely, dosemeters worn at the forehead/neck tend to overestimate the EDE. It is recommended that a dosemeter is positioned under a lead apron, if worn.

Diagnostic X-ray spectra measurements using a silicon surface barrier detector

A silicon surface barrier detector is used to analyse diagnostic X-ray spectra. This detector, usually employed to detect charged particles, has a very low efficiency for X-ray. This characteristic is advantageous in overcoming experimental problems caused by the high fluence rates typical of diagnostic X-ray beams. The pulse height distribution obtained with silicon surface barrier detectors is very different from the true photon spectra because of the presence of escaped Compton photons and the fact that detection efficiency falls abruptly when photon energy increases. A detailed analysis of the spurious effects involved in detection is made by applying a Monte Carlo method. A stripping procedure is described for implementation on a personal computer. The validity of this method is finally tested by comparison with the experimental results obtained with a Ge detector. The spectra obtained with the Si detector are in fairly good agreement with the analogous spectra measured with a Ge detector. The advantages of using Si as opposed to Ge detectors in X-ray spectrometry can be summarised as: its simplicity of use, its greater economy for use in routine diagnostic X-ray spectroscopy and the possibility that the stripping procedure can be implemented on a personal computer.

Spectroscopic analysis and dosimetry of diagnostic X-ray beams filtered by rare earth materials., Tyndall D.A., Oral Surg. Oral Med. Oral Pathol., 62(2), 205-211, (1986). : [診断

Spectroscopic analysis and dosimetry of diagnostic X-ray beams filtered by rare earth materials., Tyndall D.A., Oral Surg. Oral Med. Oral Pathol., 62(2), 205-211, (1986). : [診断

Spectroscopic analysis and dosimetry of diagnostic x-ray beams filtered by rare earth materials

A laboratory investigation was carried out to assess the effect of various types of rare earth filter materials on the energy spectrum and concomitant reduced exposure values of diagnostic x-ray beams at 70, 80, and 90 kVp. An x-ray spectroscope was constructed and used to generate the energy spectra of beams passing through the various rare earth filter materials. Photographs were made of each spectrum, and live-time gross photon counts were recorded. Following spectral determinations, ionization chamber readings were generated for each filter material. Substantial effects on x-ray spectra and reduction of exposure values were noted. The degree of these effects were dependent on the atomic number, k-edge, and thickness of each filter. Metallic forms of rare earth materials proved to be more effective than the salt forms with erbium offering the greatest potential for reduction in exposures over the range of experimental kilovolt (peak) values.

A comparison of water equivalent thickness measurements: CT method vs. heavy ion beam technique

The purpose of this study was to evaluate existing X-ray CT methods for determining water-equivalent path length from body surface to a tumour site. In the method, the CT numbers are used to obtain linear attenuation coefficients which provide a measure of the electron density. These numbers are averaged over the energy spectrum of the diagnostic X-ray beam and other parameters which have a dependence on energy. From range measurements with heavy charged particles, it is also possible to obtain an independent and direct measure of electron density along the beam path. In the results reported here, the beam path electron density or water-equivalent path length was measured with charged particle beams, using radiation sensitive diodes as target markers. To minimise error which would be introduced by motion of the target volume, a frozen dog cadaver was used. Comparison was made between the water-equivalent path length measured with high energy particle beams, and the water-equivalent path length estimated from an X-ray CT image of the same target volume by the methods presently used in charged particle therapy (Chen et al. 1979). There was good agreement between the values determined directly with neon or helium ion beams, but when these values were compared with estimated path lengths derived from X-ray CT data, it was observed that the CT range could be in error by as much as 11% for adverse conditions of marked inhomogeneity and the presence of high atomic number bone. Under the best conditions of moderate inhomogeneity and absence of bone, the derived CT range values agreed reasonably well with the direct measurements.

Monte Carlo calculations of mammographic x-ray spectra

Knowledge of the photon energy spectra of diagnostic x-ray beams in general, and of mammographic x-ray beams in particular, is useful for calculating radiation dose and evaluating image quality. Mammographic x-ray spectra have been computed theoretically using the Monte Carlo method. Agreement with the experimentally determined spectra is not particularly good. The causes of the differences need to be investigated.

A simple method for measuring the quality of a diagnostic x-ray beam

A device can be constructed for kilovoltage measurement by taking the ratio of signals from an ionisation chamber and a sodium iodide crystal scintillator, with the crystal mounted behind the ionisation chamber. The ionisation chamber monitors the incident photon flux and the crystal measures the energy carried by the beam, the crystal being sufficiently thick almost completely to absorb diagnostic quality radiation incident upon it. The ratio of the signal from the scintillator divided by the ionisation chamber signal is a function of the mean photon energy which, in a heavily filtered beam, is a fixed proportion of the peak kilovoltage. 1.5 mm of copper placed over the ionisation chamber makes the ratio independent of tube filtration up to 140 kVp. Below 60 kVp, exposure factors become excessively large and a 0.5 mm copper filter may be substituted to extend the operating range downwards.

Calorimetric measurement of the energy fluence of diagnostic X-ray beams.

A method for measurement of the energy fluence of diagnostic X-ray beams is described, using total absorption calorimetry. Optimization of the absorbing element is discussed quantitatively, and it is shown that a lead plate of 1 mm is as sensitive as gold or platinum absorbers. Using Styrofoam insulation, semiadiabatic conditions pertain during the measurement time of 2-6 s. Use of the method is illustrated in measurement of energy fluence corresponding to tube voltages of 55-115 kVp. The results are in good agreement with those obtained from X-ray energy spectrum data.

Measurements of diagnostic x-ray backscatter by a novel ion chamber method.

There is a major gap in backscatter information for diagnostic x-ray beams. Such information is increasingly needed for dose measurements and calculations, as well as for designing devices and techniques. We have therefore carried out measurements on both low Z materials and metals, using an ion chamber method designed specifically for the purpose. Lucite and two D.R. White tissue substitutes were studied extensively (BR 12 "average breast" and MS 11 "water"). Measured percent backscatter (BS) was greatest for Lucite and least for MS 11, with BR 12 in between. Backscatter buildup is rapid: 50% of full backscatter is achieved with 6 mm thickness for all three materials using mammographic beams and with about 12 mm using general diagnostic beams. A simple relationship between BS and field area permits close estimates of BS values for fields for which measured data is not available. Among metals tested, copper exhibited greatest backscatter (39% BS maximum), aluminum least, and lead in between--information of potential importance in cassette design and similar applications.

Monte Carlo calculation of the dose distributions across a plane bone-marrow interface during diagnostic X-ray examinations.

The distribution of dose across a plane bone-marrow interface on irradiation with various diagnostic X-ray beams at a representative site have been determined using the Monte Carlo method. The site was in a dorsal vertebra near its surface and situated at a depth of 70 mm under the skin. The X-ray beams studied were generated at 100, 90, 80 and 70 kV with 2 mm aluminium added filter and at 55 kV with 1 mm aluminium added filter. It was found that the dose to bone marrow due to excess photoelectrons produced in bone falls off rapidly as the distance from the bone-marrow interface increases. Consequently, the percentage excess dose to a plane bone-marrow cavity, which is almost constant for the range of kV studied, is significant only if the cavity size is small.

Analytic formulae for estimation of dose along the central ray of diagnostic x-ray beams.

Empirically derived analytic formulae for estimation of dose delivered along the central ray by conventional diagnostic x‐ray procedures are presented. The formulae are based on a computational model employing tissue–air ratios along the central axis of beams with 2.5 and 3.5 mm Al filtration, and for 3φ waveform (15% ripple) throughout the range from 70 to 120 kVp.

A multiple exposure penetrameter cassette for measurement of effective kilovoltage.

The measurement of the effective kilovoltage of diagnostic X-ray beams by a penetrameter technique (Ardran and Crooks, 1968) has been in routine use for several years. Earlier designs of penetrameter have since been modified by various workers (Hospital Physicists' Association, 1977; Jacobson et al., 1976) so that multiple exposures may be made on a single film. All of these modifications have involved the use of a separate stepwedge for each kV determination, each wedge being fixed permanently to the front of the cassette and having its own set of reference holes. The device described in this note makes use of a single “stepwedge/reference unit” (15 × 5.9 × 0.9 cm) which is independent of the cassette. With the aid of two lead masks, four columns of images may be produced across the width of an 18 × 24 cm film. Up to three images may be produced in each column making a total of 12 exposures per film. The principles of operation are the same as those described by Ardran and Crooks. The stepwedge employed ...

Photon energy distribution of some typical diagnostic x-ray beams.

A high-purity germanium spectrometer system was used to determine primary x-ray spectra over the 45--90-kVp region. Methods were devised for producing and examining spectra stimulating diagnostic conditions without operating the x-ray generator at high current levels. The techniques used to correct the experimental data and produce a photon fluence spectrum are discussed. The results, presented graphically and in tables, have been normalized to yield the relative number of photons per 2-keV interval. Methods for converting a normalized spectrum into a photon fluence spectrum that will produce an exposure of 1 R are presented. The analytical model and procedures used to calculate the K-escape fraction are discussed.

Experimental test of a new method for kVp measurements.

We present the results of an experimental test of a new method for measuring the kVp of a diagnostic x-ray beam. The method involves measuring x-ray attenuation in copper or tin absorbers and plotting the attenuation curve in a new way. Our measurements were done at 60, 90, 100, and 120 kVp on a 3-phase, 12-pulse diagnostic generator. The kVp was measured with a calibrated voltage divider-oscilloscope system. Except at 90 kVp, excellent agreement was found, with precisions on the order of plus or minus 1%. The 90-kVp point appeared to be somewhat affected by characteristic tungsten radiation and gave agreement with a lower value of precision.

Book reviewsThe Physics of Radiodiagnosis. 1973 (London, The Hospital Physicists Association).Report A:An introduction to diagnostic radiological systems. 40 pp. H.P.A. Report Series No. 6. £2.Report B:Measurements referring to diagnostic X-ray Beams. 36 pp. H.P.A. Report Series No. 7. £2.Report C:The assessment of Image Intensifier and Television System Performance. 31 pp. H.P.A. Report Series No. 8. £2.

These short reports were prepared by the diagnostic radiology topic group of the H.P.A. The standing of the members of the topic group is sufficient to guarantee that the reports are of a very high standard. Only a very few experts working in this field would fail to learn much by the study of these reports and they will be undoubtedly of great value to all working in the fields covered, whether physicists, engineers, technicians or those radiologists and radiographers who take a serious interest in these matters.