Transmission Radiography Research Articles

High-energy photon radiography system using laser-Compton scattering for inspection of bulk materials

Transmission radiography of bulk materials using continuously energy-tunable quasimonochromatic photon beams has been performed with the photons of a few tens MeV. The photon beam is generated with the laser-Compton scattering of the 300–800 MeV electrons in the electron storage ring “TERAS” with laser lights. The present radiography system is applicable to an inspection of bulk materials and to nondestructive testing of large industrial products. The effectiveness of the method has been examined using metals, ceramics, and concrete blocks. The spatial resolution of the radiography system was measured to be 650 μm using a 1 mm collimator system.

Dosimetric characteristics of the DRAXIMAGE model LS-1 1-125 interstitial brachytherapy source design: a Monte Carlo investigation.

(Received 5 June 2001; accepted for publication 26 December 2001; published 19 March 2002) We have used Monte Carlo photon transport simulations to evaluate dosimetric characteristics of a new 125I seed, the DRAXIMAGE BrachySeed (model LS-1) source for interstitial brachytherapy and to calculate the dosimetric parameters recommended by the AAPM Task Group 43 (TG-43). To eliminate thick end welds, preformed closed-ended Ti shells are welded together near the transverse plane. The radioactivity is localized near the seed ends in order to maximize isotropy at typical prescription distances. Transmission radiography reveals that its internal components can move by as much as 200 microm under the influence of gravitational forces affecting the dose-rate constant and relative dose distribution by as much as 5% and 10%, respectively. However, the clinical dose distribution can be well represented by a weighted average of dose distributions corresponding to three different orientation-dependent internal geometry configurations. This average dose distribution agrees closely (within 1% at 1 cm) with that derived from the geometry specified by the vendor model (seed components uniformly spaced), from which the recommended relative dosimetry parameters were derived. An average dose-rate constant of 0.935 cGy h(-1) U(-1) is recommended for clinical application and values of 0.919, 0.963, and 0.920 for vertical orientation, horizontal orientation, and the vendor specified geometries, respectively. The NIST wide-angle free-air chamber realization of the air-kerma strength primary standard, SKN99, was explicitly simulated. We show that the output of Ag characteristic x rays is about half that of the model 6711 source resulting in a relative dose distribution between that of the model 6711 source and pure 125I x-ray emitters. Finally, it is demonstrated that the TG-43 point-source formalism more accurately estimates solid-angle weighted dose at small distances if one uses a radial dose function data prepared using a point-source, rather than line-source, geometry factor.

Diffraction contrast in X-ray radiographic images of octahedrite meteorites

Slices of ∼12 mm thickness cut out of an octahedritic iron–nickel meteorite of the Gibeon shower were investigated by conventional X-ray transmission radiography. When the direction of the incident X-ray beam is parallel to one or two of the four habit planes of the kamacite lamellae, black–white contrast lines are observed in the radiographs. These lines are attributed to Bragg reflection, at lattice planes parallel to the lamellae planes, of a narrow band of wavelengths filtered out of the incident white spectrum by absorption in the sample.

Using photoelectron emission microscopy with hard-X-rays

We present several successful test cases of using photoelectron emission microscopy (PEEM) for photon energy up to 25 keV. First, the full extended X-ray absorption fine structure analysis was implemented in areas as small as 100 μm 2 for transition-metal K edge absorption spectra and, therefore, demonstrated the feasibility of combining structural and chemical analysis with hard-X-ray absorption spectroscopy with high lateral resolution. We also show that PEEM can be used in a transmission (radiography) mode as an imaging detector for hard-X-ray. This approach again leads to the unprecedented 0.3 μm lateral resolution, particularly critical for the use of coherence-based phase contrast techniques in real time X-ray radiology.

PROPERTIES OF THE RADIOGRAPHY FACILITY NEUTRA AT SINQ AND ITS POTENTIAL FOR USE AS EUROPEAN REFERENCE FACILITY

At December 3rd 1996, the spallation neutron source SINQ had its first proton beam onthe target. With a steady-state proton beam of 850 IlA this facility is now the strongest of its kind in the world. One of the first experimental facilities in operation was theradiography station NEUTRA (for NEUtron Transmission Radiography). The designwas described at earlier meetings [1,2] and the first validation measurements werereported [3]. There are some advantages in comparison to other radiography stations atresearch reactors. This will be demonstrated in detail by means of the measured valuesand examples of practical applications. The use as reference facility will be envisagedwithin an European project (COST-524).

Noninvasive Tomographic and Velocimetric Monitoring of Multiphase Flows

A condensed review of recent advances accomplished in the development and the applications of noninvasive tomographic and velocimetric measurement techniques to multiphase flows and systems is presented. In recent years utilization of such noninvasive techniques has become widespread in many engineering disciplines that deal with systems involving two immiscible phases or more. Tomography provides concentration, holdup, or 2D or 3D density distribution of at least one component of the multiphase system, whereas velocimetry provides the dynamic features of the phase of interest such as the flow pattern, the velocity field, the 2D or 3D instantaneous movements, etc. The following review is divided into two parts. The first part summarizes progress and developments in flow imaging techniques using γ-ray and X-ray transmission tomography; X-ray radiography; neutron transmission tomography and radiography; positron emission tomography; X-ray diffraction tomography; nuclear magnetic resonance imaging; electrica...

Inelastic photon scattering: Effects and applications in biomedical science and industry

Compton scattering is widely used to analyse electron momentum distributions in solid state systems. Perhaps less well-known is its role as the major cause of image contrast in medical and industrial radiography. This article discusses the principles and applications of a technique, known as Compton scatter imaging (CSI), which is based on direct registration of the Compton scatter radiation. Following a historical survey of the major developments in this field, the strengths and weaknesses of transmission radiography and Compton scatter imaging are compared in order to determine those measurement situations to which the latter is best suited. A description is given of several disturbing effects to which CSI is prone and ways in which these may be accounted for to yield quantitative density data are presented. The most important types of imaging system based on Compton scatter are discussed and compared. The ComScan (an acronym for Compton scatter scanner) is a commercially-available backscatter imaging system which is discussed here in some detail. ComScan images taken from applications of topical and historical interest are presented.

Quantitative verification of 192Ir PDR and HDR source structure by pin-hole autoradiography.

For precise localization of the center and determination of the dimensions of the radioactive material within the capsule of brachytherapy sources, we have developed a method based on simultaneous pin-hole autoradiography of two sources. We constructed a variable magnification pin-hole camera consisting of two telescopically fitted Plexiglas cylinders which can accommodate two radioactive sources on the plate covering the top cylinder. The 192Ir pulsed and high dose-rate sources were studied and an 192Ir seed was used as a reference source. The magnification factor was determined from the dimensions of the 192Ir seed image, which was geometrically well defined by a separate transmission radiography experiment. The observed position for the center of radioactivity in the PDR and the HDR source capsules are in agreement with the vendor specifications. The distance from the tip of the PDR capsule to its center of radioactivity was found in this way to be 0.79 +/- 0.21 mm, which agrees with the position (0.85 mm) of the pellet situated closer to the tip as specified by the vendor. Quantitative verification of the internal source structure using this method enhances the accuracy with which the dose distribution near brachytherapy sources can be predicted by three-dimensional Monte Carlo calculations.

Monte Carlo studies of x-ray energy absorption and quantum noise in megavoltage transmission radiography.

The subject contrast of bony anatomy in megavoltage medical radiographs is very low, making detection of bony landmarks difficult if additional noise sources are introduced into the images. One source of noise, which is inherent to the x-ray detection process, is x-ray energy absorption noise. X-ray energy absorption noise results from variations in the amount of energy deposited in the imaging detector per interacting x ray. These variations increase the noise content of the image. In this study, EGS4 Monte Carlo simulations of x-ray interactions in metal plate phosphor screen detectors have been performed to determine the distribution of energy absorption events within the phosphor screen. From these "absorbed energy distributions (AEDs)", the x-ray energy absorption noise and the quantum absorption efficiency of the detector are determined. These calculations are performed for a range of detector thicknesses (0.1-4 mm) and x-ray energies (0.1-10 MeV). A number of conclusions can be drawn from these investigations. (i) The x-ray absorption noise reduces the detective quantum efficiency (DQE) of metal plate/phosphor screen detectors by as much as 50% at energies used in megavoltage imaging (1-10 MeV). (ii) It is important to include secondary particle (electron) transport in estimating the quantum absorption efficiency of these detectors. For instance, the quantum efficiency of a typical portal detector is approximately 2%, even though 4%-5% of the incident photons are attenuated. (iii) The metal "conversion" plate commonly used in megavoltage imaging enhances the DQE of the phosphor screen by increasing the quantum absorption efficiency and reducing the magnitude of the x-ray absorption noise.

Applications of Rayleigh scattered photons to substance identification

The advantages of Rayleigh scatter techniques over conventional X-ray methods for the detection of low- Z materials within a low- Z matrix have been demonstrated. Radiographs obtained by normal transmission methods and by a Rayleigh scattering technique have been recorded for several representative test objects and the resulting contrasts compared. Materials which are indistinguishable in the transmission images become apparent in the scatter images simply by taking the measurement at an appropriate scatter angle determined by the X-ray diffraction pattern of the material of interest. Inclusions which are undetectable in the transmission radiographs have been identified with contrasts of up to 28% which may be further increased with simple contrast enhancement procedures. This techniques has applications in any system that currently uses conventional transmission radiography, such as on line security screening or quality control monitoring, and may in principle be used in tandem which such a system.

X-ray scatter in megavoltage transmission radiography: physical characteristics and influence on image quality.

The physical characteristics of x rays scattered by the patient and reaching the imaging detector, as well as their effect on verification (portal) image quality, were investigated for megavoltage (0.1-20 MeV) x-ray beams. Monte Carlo calculations and experimental measurements were used to characterize how the scatter and primary fluences at the detector plane were influenced by scattering geometry and the energy spectrum of the incident beam. The calculated scatter fluences were differentiated according to photon energy and scattering process. Scatter fractions were measured on a medical linear accelerator (Clinac 2100c, 6 MV) for a typical imaging geometry using an ionization chamber and a silicon diode. After correction for the energy dependence of the chamber and diode, the scatter fractions generated by the Monte Carlo simulations were found to be in excellent agreement with the measured results. In order to estimate the effect of scatter on image quality, the scatter and primary signals (i.e., energy deposited) produced in five different types of portal imaging detectors (lead plate/film, storage phosphor alone, lead plate/storage phosphor, compton recoil-electron detector, and a copper plate/Gd2O2S phosphor) were calculated. The results show that, for a specified geometry, the scatter fraction can vary by an order of magnitude, depending on the sensitivity of the imaging detector to low-energy (< 1 MeV) scattered radiation. For a common portal imaging detector (copper plate/Gd2O2S phosphor), the scattered radiation (i) reduced contrast by much as 50% for a fixed display-contrast system, and (ii) decreased the differential-signal-to-noise ratio (DSNR) by 10%-20% for a quantum-noise-limited portal imaging system. For currently available TV-camera-based portal imaging systems, which have variable display contrast, the reduction in DSNR depends on the light collection efficiency and the noise characteristics of the TV camera. Overall, these results show that scattered radiation can reduce contrast significantly in portal films while deteriorating image quality only moderately in on-line systems.

Evaluation of X-ray beam quality and film-screen combinations for detection of small low-contrast objects

The detection of small low-contrast objects in transmission radiography has been simulated by phantom experiments for specific anatomical regions (phantom thicknesses). Improvement of image quality in combination with a low patient dose is addressed to a complicated optimization problem. It has been shown that in the low-contrast case, the image resolution is largely determined by the low-frequency part of the noise spectrum and by the absorption contrast between detail of interest and surrounding medium. Improvement of image resolution is performed more efficiently via beam quality (by enhancement of absorption contrast). This is also true in the case of photoelectrically recorded photons (DLR). Conversely, the detector MTF (modulation transfer function) is of minor importance for the low-contrast case. The role of X-ray scattering in the phantom as well as light propagation in the phosphor is outlined. Numerous commercially available film-screen combinations of different speed and phosphors have been tested. In summary, fast screens of Gd2O2S phosphors are most appropriate for detection of low-contrast objects.

Three-dimensional information from real-time encoded images

The real-time neutron radiography facility at the University of Virginia has been used for both transmission radiography and computed tomography. Recently, a coded aperture system has been developed to permit the extraction of three-dimensional information from a low intensity field of radiation scattered by an extended object. A technique was developed to permit retrieval of information by decoding two-dimensional coded aperture images collected with a real-time video system. An RCA video camera and a DEC PDP-1 1 computer in a network with a Convex-i parallel processing mainframe were employed. This system coupled with theoretical extensions and improvements allowed retrieval of information unobtainable by earlier optical methods. The effects of thermal noise, shot noise, and aperture related artifacts were examined so that better digital filtering techniques could be constructed and implemented. The application and advantages of this imaging technique to the field of thermal neutron imaging are discussed.

Three-dimensional information from real-time encoded images

The real-time neutron radiography facility at the University of Virginia has been used for both transmission radiography and computed tomography. Recently, a coded aperture system has been developed to permit the extraction of three-dimensional information from a low intensity field of radiation scattered by an extended object. A technique was developed to permit retrieval of information by decoding two-dimensional coded aperture images collected with a real-time video system. An RCA video camera and a DEC PDP-1 1 computer in a network with a Convex-i parallel processing mainframe were employed. This system coupled with theoretical extensions and improvements allowed retrieval of information unobtainable by earlier optical methods. The effects of thermal noise, shot noise, and aperture related artifacts were examined so that better digital filtering techniques could be constructed and implemented. The application and advantages of this imaging technique to the field of thermal neutron imaging are discussed.

Quantitative stereology and radiologic image analysis. Part II: Transmission (projection) radiography.

This paper extends the results of Part I to estimates of three-dimensional anatomy and morphology obtained form measurements on a projection plane. Ambiguities and overlap obscuration in projections are discussed. Estimates of vascular (angiography) network geometry are easily obtained and applications to particle volume, surface area, spacing, and number are possible.

Gamma-ray scattering studies of composition variations in alloys

The physical principles underlying the use of gamma-ray scattering to detect composition variations in bulk alloy samples are described and the sensitivity of the method, which is an alternative to conventional transmission radiography, is evaluated for titanium alloys. The elastic (Rayleigh) and inelastic (Compton) scattered beams are recorded separately and their intensities used to monitor composition changes collectively and individually. The sensitivity of the method is illustrated by measurements on titanium alloys containing aluminium and zirconium.

On the Sensitivity and Application Possibilities of a Novel Compton Scatter Imaging System

A novel type of Compton scatter imaging system is described having the following features: maximum possible use is made of the available scatter radiation; and mechanical constraints permit millisecond 2-D scan times. The sensitivity of this type of scatter system is compared with that of transmission radiography, and it is found that the former is to be preferred for `radiologically thin' objects. An important medical example is the imaging in back scatter mode of radiation-sensitive organs lying near the surface of the body. Some industrial applications of the scatter technique also suggest themselves: e.g. for section imaging of `thin' sheets, plastic components, or back scatter imaging of surface regions of bulky objects, for which the conventional transmission technique gives inadequate penetration. Data correction for attenuation effects and multiple scatter radiation is illustrated using scatter images of objects drawn from the fields of medical and industrial radiology.

X-ray scatter background signals in transmission radiography.

With monoenergetic x-ray beams incident on polystyrene phantoms, the spectra of the tramsmitted x rays were measured with a scintillation spectrometer. The scattered and unscattered components of the transmitted x-ray fluence at a point on the beam axis were determined as a function of (i) the incident x-ray energy (18, 22, 32, 49, 58, 69, and 660 keV), (ii) the phantom thickness (5.3, 10, and 21 cm), (iii) the scatter solid angle determined by the exposed area of the phantom and the separation distance of the image plane (0.090, 0.31, 0.66, 1.8, 3.5 4.3, 4.8, and 5.1 sr), and (iv) the beam diameter at the image plane (25, 17, and 10 cm). The results indicate that, as the incident x-ray energy decreases from 660 to 30 keV, the contribution of the scattered component to the transmitted fluence increases from approximately 50% to 90% for the 21-cm phantom and from 21% to 50% for the 5.3-cm phantom. For typical cases, the data show the effect of the scatter component on the ratio of the image to the background signals. In addition, the examples show that optimum conditions for maximizing this signal ratio may be obtained by a careful selection of the incident x-ray energy for low-, medium, and high-contrast objects.

Three-dimensional reconstruction in nuclear medicine emission imaging

The study presents application of methods of ascertaining the three-dimensional distribution of isotope concentration or density in nuclear medicine, and differs from previous three-dimensional reconstruction efforts of astrophysics, electron microscopy, and X-ray radiology in that statistically poor measurements and photon attenuation are taken into account by the algorithm. The methods discussed are applicable to photon or heavy ion transmission radiography as well as emission imaging.

Photons and physiology. New Horizons for Radiologist Lecture.

HomeRadiologyVol. 103, No. 1 PreviousNext New HorizonsPhotons and PhysiologyNew Horizons for Radiologists Lecture1E. James PotchenE. James PotchenAuthor Affiliations Mallinckrodt Institute of Radiology 510 South KingshighwaySt. Louis, Mo. 63110E. James PotchenPublished Online:Apr 1 1972https://doi.org/10.1148/103.1.1MoreSectionsPDF ToolsImage ViewerAdd to favoritesCiteTrack CitationsPermissionsReprints ShareShare onFacebookTwitterLinked In AbstractIn his New Horizons for Radiologists Lecture, the author points to a synergy between radiology and physiology. He first emphasizes radiology's role in applying photons to develop our knowledge of cardiovascular pathophysiology, particularly the cardiac ejection fraction and myocardial dyssynergy. He then turns to the microvascular system. Subtopics under this heading include radiologic measurement of blood flow, radiologic assessment of vascular permeability, and brain, pulmonary, and tumor microvasculature. He concludes that emission and transmission radiography, using tracers and standard radiology will afford much information about phenomena that have hitherto been obscure.Article HistoryPublished in print: Apr 1972 FiguresReferencesRelatedDetailsRecommended Articles RSNA Education Exhibits RSNA Case Collection Vol. 103, No. 1 Metrics Altmetric Score PDF download