bluuebunny/crossref_metadata_2025 huggingface dataset:
Large‐area contrast of a fiber‐optic coupled x‐ray image intensifier
Authors: Davis V. L. , Glascock Homer H.
Published: August 2003

Large‐area contrast measurements have been made upon a fiber‐optic x‐ray image intensifier with an external input phosphor. Both photometric and photographic techniques were used. For a shadowed area of 10% of the input window area, a contrast ratio in excess of 150 was determined. This is a factor of 5 higher than previously reported for any x‐ray image intensifier. The improved contrast in the device is attributed to (1) reduced effect of x‐ray Compton scattering in the input window; (2) less cross‐chord light at the photocathode; and (3) greatly reduced light scattering and reflecting in output phosphor and window.
Computer‐compatible patient contour plotter
Authors: Simpson Larry D. , Mohan Radhe , Henderson Rolland
Published: August 2003

The use of a compact, mobile, relatively inexpensive electromechanical patient‐contouring mechanism is described. The system utilizes a Numonics Model 224 graphics digitizer suspended over the patient. The digital X and Y coordinates of the patient contour in either of multiple, parallel transverse, or sagittal planes are inherently accurate to within ±0.25 mm over a total reading area of 60×90 cm. Display features include the interface to an analog 11‐in.×17‐in. X–Y plotter with a variable scale‐down factor for those contours which would otherwise be larger than the plotting surface. The system is easy to use and may also be readily interfaced for on‐line entry of patient contours to calculator‐ or minicomputer‐based treatment‐planning systems.
Reconstruction of objects from diverging x rays
Authors: Edelheit Lewis S. , Herman Gabor T. , Lakshminarayanan Arasanipalai V.
Published: August 2003

Rotation of a system consisting of a single x‐ray source and a linear detector array allows rapid collection of x‐ray projection data from which transaxial cross sections can be reconstructed. In this paper, we present an algorithm which makes possible rapid computerized reconstruction from such data. We describe some experiments aimed at investigating the optimal choice of some of the parameters associated with the algorithm. We report on reconstructions using our algorithm of the intact thorax of a dog and also of cross sections of the human female breast from x‐ray data obtained by a computerized mammography machine.
Designing a wax phantom to simulate a flat tumor with diffuse edges
Authors: Ort Michael G. , Gregg Earle C.
Published: August 2003

A suitable wax phantom was designed for evaluating various film techniques used in subtraction radiography. Holes are drilled in a slab of wax and filled with various concentrations of iodinated wax, producing disk‐shaped regions with diffuse borders. The technical details of construction and a representative application are described.
Effective size of the transverse dimension of x‐ray‐tube focal spots
Authors: Prasad Satish C. , Hendee William R.
Published: August 2003

Corrections for nonuniform x‐ray intensity distributions have been computed for the dimension perpendicular to the anode–cathode axis of x‐ray‐tube focal spots. These correction factors were developed from comparison of OTFs for focal spots with uniform intensity distributions to those for focal spots with symmetric double‐peaked intensity distributions.
Energy absorbed in calcium tungstate x‐ray screens
Authors: Shuping Ralph E. , Judy Philip F.
Published: August 2003

The energy which must be absorbed in a CaWO4 x‐ray intensifying screen to produce unit net optical density on a film has been evaluated by measurement and calculation for a screen–film system over a range of beam qualities (1.4–7.4 mm Al HVL) spanning the diagnostic x‐ray region. It was found to be constant within experimental error. The absorbed‐energy constant for three additional CaWO4 screens is presented for a single beam quality. To correct the estimation of absorbed energy, the fractional escape of tungsten K x rays has been evaluated and the results are presented as a function of phosphor loading. The absorbed‐energy constant is useful for predicting optical density for variable beam conditions; a family of characteristic curves based on exposure is reduced to one curve for a particular film–screen system, expressed as optical density as a function of absorbed energy.
Relative properties of tomography, K‐edge imaging, and K‐edge tomography
Authors: Kruger R. A. , Riederer S. J. , Mistretta C. A.
Published: August 2003

The properties of tomography, K‐edge imaging, and K‐edge tomography are discussed in relation to the imaging of small concentrations of elements such as iodine and xenon and are compared by means of phantom images. It is demonstrated that the complementary selectivities provided by depth and energy subtraction are combined in K‐edge tomography. Using a three‐spectrum subtraction technique, the iodine difference signal predicted by computer calculations is on the order of 8000 times that of an equal concentration of bone. The corresponding ratio in tomography without energy subtraction is 20:1. It is argued that K‐edge tomography can successfully eliminate artifacts due to tissue inhomogeneities which presently enable 0.6% variations in tissue attenuation to mimic minimum detectable iodine signals in conventional computed tomography. Various instrumentation possibilities and energy subtraction techniques are discussed.
Ultrasonic pulse‐echo determination of thermal injury in deep dermal burns
Authors: Goans Ronald E. , Cantrell John H. , Meyers F. Bradford
Published: August 2003

Burns of all kinds represent a serious class of traumatic injury, affecting over two million people annually in the United States alone. Of this number, over 70 000 are serious enough to require extended hospitalization. Currently, there is no sensitive, quantitative technique for measuring the depth of thermal damage in such injuries. An ultrasonic pulse‐echo technique is described here whereby such information can be obtained within a few minutes postburn. Results from model porcine experiments are given to illustrate the usefulness of the method, and implications for the clinical care of human burn victims are discussed.
Interpretation of star test pattern images
Authors: Burgess A. E.
Published: August 2003

The star test pattern image contains a large amount of information about the focus OTF which is not presently used. A mathematical analysis of these images for the special case of separable and symmetrical focal spots is presented. Circular blur loci are identified and their changes over the imaging field are described. Harmonic distortion and its application are described. Sources of measurement error are discussed.
Composition of A‐150 tissue‐equivalent plastic
Authors: Smathers James B. , Otte Victor A. , Smith Alfred R. , Almond Peter R. , Attix Frank H. , Spokas John J. , Quam William M. , Goodman Leon J.
Published: August 2003

In recent years, the use of tissue‐equivalent materials has become quite common in fast‐neutron dosimetry, with the A‐150 plastic developed by Shonka et al. probably the most popular. Information on this specific plastic is scantily reported in the literature and as a consequence a preponderance of authors unknowingly reference an article by Shonka describing an early version of a tissue substitute plastic but having a different elemental composition than the present A‐150 formulation. We have reviewed the results of 21 chemical analyses which have occurred over a time span of four years on a total of 14 samples of A‐150 plastic and based on these data and the formulation of the plastic, have arrived at a suggested composition for A‐150 tissue‐equivalent plastic. The ambiguities of water absorption by nylon, one of the components of of the plastic, and the uncertainty this reflects in the composition of the plastic were evaluated.
Comparison of convolution and ray‐tracing methods for computing small blood vessel images in angiography
Authors: Doi Kunio , Rossmann Kurt
Published: August 2003

Two methods for computing x‐ray images of small blood vessels in angiography are presently available, namely, convolution and ray tracing. The convolution method, which is simpler and more powerful than the ray‐tracing method, is based on the assumption that blood vessel imaging is isoplanatic, whereas ray tracing is considered to provide correct images. In this study, the approximation error (difference between two images, normalized by the maximum value) due to nonisoplanatic imaging was determined by computation of blood vessel images according to both methods. The approximation error for geometric conditions normally encountered in angiography was less than 0.01. It is concluded that an approximation error of this magnitude is negligible and that the convolution method can be applied instead of the ray‐tracing method for the computation of images of small blood vessels.
Amplification and entailed resolution degradation in high‐pressure gas ionography
Authors: Peschmann K. R. , Grosche G.
Published: August 2003

This work deals with the introduction of a gas electronic gain factor in high‐pressure ionography (or “electron radiography”). The purpose is to check the possibility of a further reduction of radiation dose per radiograph. It is shown that xenon or krypton can be mixed with special molecular gases in order to achieve charge‐carrier multiplication at comparatively weak electrostatic fields and in an easily controllable manner. Some radiographs are reproduced which have been obtained in the amplifying working modes of the system. Relevant image characteristics and their limits are discussed. The obtainable resolution is limited by electron diffusion and by quantum noise (lowering of the effective quantum‐detection efficiency).
Experimental tests of proton beam localization
Authors: Bennett Gerald W. , Archambeau John O.
Published: August 2003

The depth of penetration of heavy charged‐particle therapy beams is sensitive to the density of tissues traversed. Maximum depth of dose contours will vary appreciably as the beam passes through bone, muscle, lung, and air or gas. Calculations suggest that beam activation of the short‐lived positron‐emitting isotope 15O in vivo will permit localization of proton therapy beams with reasonable detected‐event density and dose. Preliminary tests of this method indicate that the beam can be located at depth with a typical dose of 15 rad, using a large field‐of‐view positron camera on‐line. This technique is also applicable to other heavy charged‐particle beams, negative pions, and heavy ions.
On the choice of material for half‐value‐layer measurements for megavoltage x rays
Authors: Nath Ravinder , Schulz R. J.
Published: August 2003

The relative sensitivity of various materials for the measurement of half‐value‐layer thickness has been calculated for bremsstrahlung x‐ray spectra in the energy range 5–40 MeV. It is concluded that low‐atomic‐number materials such as water are more sensitive to changes in spectral quality of megavoltage x rays than high‐atomic‐number materials such as lead.
Physical characterization of 45‐MV photon beams for use in treatment planning
Authors: Suntharalingam N. , Steben John D.
Published: August 2003

Central‐axis percentage depth doses and tissue–maximum ratios (TMR) for 45‐MV photon beams from a betatron have been measured in water. Also the influence of field size and collimator scatter on the dose in the buildup region have been investigated. The maximum dose for TMR has been shown to occur at a point about 2 cm deeper than the maximum dose for percentage depth dose. This difference is significant in the characterization of the photon beam at this high energy. The measured physical data have been computerized for use in routine treatment planning. Computer‐generated beams have been found to be in close agreement with measured isodose curves. Computer‐generated isodose distributions for typical clinical irradiation techniques have been verified using RP/V film in an Alderson phantom.
Neutron energy spectra and dose‐distribution spectra of cyclotron‐produced neutron beams
Authors: Heintz P. H. , Johnsen S. W. , Peek N. F.
Published: August 2003

Neutron energy spectra and spectra of dose deposition in tissue‐equivalent material have been measured for neutron sources produced by 16‐, 22‐, 35‐, and 45.5‐MeV deuterons and 22.5‐, 35‐, 45‐, and 65.5‐MeV protons incident upon a thick beryllium target. Neutron spectra were measured using time‐of‐flight techniques and the dose distribution was measured using a 1/2 in. spherical “tissue‐equivalent” proportional counter filled with “tissue‐equivalent” gas.
Treatment planning in Cobalt‐60 radiotherapy using computerized tomography techniques
Authors: Payne William H. , Waggener Robert G. , McDavid William D. , Dennis Michael J.
Published: August 2003

Cobalt‐60 transmission measurements were made through an Alderson phantom utilizing a transverse axial tomographic device and a NaI (Tl) detector. Measurements were made on different sections of the phantom for as many as 162 angles and 120 linear increments. The attenuation coefficients were reconstructed using both convolution and algebraic reconstruction techniques. Three‐dimensional isodose distributions were obtained using the reconstructed attenuation coefficients. Comparison with standard treatment plans and measured isodose distribution using TLD techniques suggest that a more accurate isodose distribution may be obtained using the reconstructed attenuation coefficients, particularly in regions involving tissue heterogeneities.
Behavior of p–n junction silicon radiation detectors in a temperature‐compensated direct‐current circuit
Authors: Klevenhagen S. C.
Published: August 2003

The behavior of silicon p–n junction radiation detectors used in the direct‐current short‐circuit mode without bias was examined under such load resistance which ensures operation in a temperature‐compensated state. The objective was twofold; to check whether the compensation is achieved and to investigate the extent of compensation shown at temperatures other than that initially selected as the operation point. It was found that the detector performance in various thermal conditions can be predicted from a knowledge of the behavior of the individual detector and circuit parameters and that it is possible to stabilize the detector response within ±2% over a relatively wide temperature range: 18°–40°C. However, in the case of devices which show thermal currents of large temperature sensitivity, compensation at small and at large dose rates needs to be considered separately.
Empirical formula for 60Co axial depth doses
Authors: Fox John G. , Fox Paul G.
Published: August 2003

An empirical formula has been developed to approximate the published axial depth doses of 60Co radiation with greater accuracy than available hitherto. With sets of nine constants, varying slightly with SSD, a total of 2100 percentage depth doses are reproduced with root‐mean‐square deviations ranging from 0.13 to 0.16 for four values of SSD from 50 to 100 cm.
Single‐step calculation of the MTF from the ERF
Authors: Schneiders Nicholas J. , Bushong Stewart C.
Published: August 2003

A method is presented whereby the modulation transfer function can be calculated directly from the edge response function without having to find the line spread function as an intermediate step.
New method for the experimental evaluation of x‐ray grids
Authors: Dick C. E. , Motz J. W.
Published: August 2003

This work describes a new method for the experimental evaluation of antiscatter x‐ray grids in radiography. Five commercial grids are evaluated in terms of two parameters which are determined only by the construction of the grid and the x‐ray energy. A comparison of the grid performances was made for the x‐ray energies and scatter conditions that usually apply to chest radiography and mammography. The results show that for maximum scatter conditions the grid enhances the subject contrast by factors of approximately 6 and 2 in chest radiography and mammography, respectively, and that the contrast increases as the grid ratio increases. Also, in these examinations, the results show that, with improved grids, it is possible to reduce the patient exposures required for the no‐grid case by approximately one‐half without loss of the image‐information content (signal‐to‐noise ratio).
Theoretical considerations of effects of x‐ray film–screen characteristics on threshold detectability of small low‐contrast objects
Authors: Lassen Margit , Bloch Peter
Published: August 2003

An expression is derived for visual contrast of a radiographed small object that takes into account the proportion of scattered radiation as well as the shape of the sensitometric curve of the film–screen combination. Based on this expression for visual contrast applied to two different film–screen systems, predictions are made for threshold perceptability of low‐contrast objects radiographed with the two imaging systems in the presence of scattered radiation and at different points on the sensitometric curves.
Measurements of the effects of x‐ray film–screen characteristics on threshold detectability of small low‐contrast objects
Authors: Lassen Margit , Bloch Peter
Published: August 2003

Experiments were performed to test threshold detectability of a small nylon bead radiographed with two different image receptors and under different scattering conditions. In another paper, the present authors predicted, on theoretical grounds, the visibility of small low‐contrast objects radiographed in the presence of scattered radiation. The experiments discussed in this paper tested these predictions using an observer‐testing method resulting in Receiver Operating Characteristic (ROC) curves. In addition to the rigidly controlled experiments from which the ROC curves were obtained, another experiment was performed in which a human phantom was used and the radiographs rated as to the visibility of small artificial lesions. By and large, the experiments confirmed the predictions made from the theoretical analysis, using visual contrast as a measure of detectability.
Ionization collection efficiencies of some ionization chambers in pulsed and continuous radiation beams
Authors: Holt J. G. , Stanton R. E. , Sell R. E.
Published: August 2003

The most commonly used method of calibrating high‐energy photon or electron beams consists in converting cavity ionization to dose by the application of the appropriate Cλ or CE multiplied by the 60Co correction factor. The correct interpretation of calibration data for pulsed photon or electron beams requires a knowledge of the charge collection efficiencies of the ionization chambers used. The results are presented of efficiency measurements for both pulsed and continuous beams made with these chambers: 0.6‐cm3 Farmer, 0.5‐cm3 Spokas, 3‐cm3 Shonka, 1‐cm3 PTW, and 1‐cm3 Memorial pancake. The dependence of collection efficiency on collection voltage, dose rate, and dose per pulse is demonstrated. These results are shown to agree with Boag's formulas for collection efficiency. Attention is drawn to the fact that several kinds of dosimeters provide only minimal collection voltages for efficient collection of charge at high dose rates, especially in Linac electron beams. It is recommended to check the collection efficiency of chambers which are to be used at high dose rates, and a simple method for this purpose is described.
Development of Bragg diffraction imaging for medical use
Authors: Frieda D. , Spiegler P. , Kearly F. , Greenfield M. , Stern R.
Published: August 2003

Experience gained in developing a real‐time acoustical imaging system using Bragg diffraction is presented. Particular emphasis has been placed on medical applications. We have studied the difficulties in assembling a system capable of producing high‐quality images. Engineering data on the optical mounting and on the design of the transducer along with representative images are presented and discussed.
Importance of geometry in biological sample analysis by x‐ray fluorescence
Authors: Vañó E. , González L.
Published: August 2003

The determining factors of a good analysis by x‐ray fluorescence are discussed, emphasizing the importance of the geometrical arrangement, especially the excitation‐source to analysis‐material distance. The variation of the peak area of the Kα x‐ray of Fe is evaluated as a function of the distance. Precautions are given for the analysis of low concentration samples as well as for obtaining the relative concentration of an element in a specific material or organ.
Magnetic field modification of electron‐beam dose distributions in inhomogeneous media
Authors: Paliwal Bhudatt R. , Wiley Albert L. , Wessels B. W. , Choi M. C.
Published: August 2003

Modern curative radiotherapy requires higher doses to the tumor volume and, necessarily, minimal doses to the surrounding normal tissues. Attempts to use heavy charged particles to achieve such optimization are currently under investigation in many centers. Our data indicate that a static, superimposed magnetic field on a clinical electron‐therapy beam also offers the capability of some ’'tailoring” of isodose distributions. Furthermore, a variable, superimposed magnetic field minimizes those tissue‐generated dose heterogeneities which are inherent with all charged‐particle beams. We suggest that magnetically modified, clinically available electron beams also offer a practical and less expensive means of achieving tailored, heterogeneity‐corrected isodose distributions.
Monte Carlo calculation of the wall correction factors for ionization chambers and Aeq for 60Co γ rays
Authors: Bond J. E. , Nath Ravinder , Schulz R. J.
Published: August 2003

The application of cavity‐ionizaion chambers to the standadization of 60Co γ‐ray beams, in terms of exposure, requires that the specific ionization of air Jg, be corrected for the attenuation and scatter of the incident rays by the wall, central electrode, and suporting stem of the chamber. A Monte Carlo photon–electron transport code has been developed for the purpose of calculating this correction for spherical and cylindrical chambers. The code has been applied to a spherical graphite chamber having dimensions typical of the chambers used by the NBS, the calculated wall‐correction factor is in close agreement with the average of the NBS factors which were determined experimentally. The code was also used to calculate Aeq, which is central to the determination of tissue‐air ratios. The calculated value, 0.989±0.003, is very close to the generally accepted value, 0.985.
Noise characteristics of a microchannel plate x‐ray image intensifier
Authors: Gould Robert G. , Judy Philip F. , Bjärngard Bengt E.
Published: August 2003

The noise performance of an experimental microchannel plate x‐ray image intensifier has been evaluated. The intensifier, constructed for use with photons of energies between 20 and 150 keV, uses an MCP as the photon‐to‐electron converter. The influence of noise was determined by analysis of the optical‐density fluctuations of a photograph of the viewing screen of the intensifier when the conversion layer was exposed to between 1 and 60 mR. Additionally, the contrast‐detail performance of the experimental device was determined. The influence of both stochastic noise, due to quantum mottle and pulse‐height variations, and structural noise, due to fluctuations in inherent gain from point to point, have been considered by using a model that adds these components.
Tissue mimicking materials for ultrasound phantoms
Authors: Madsen Ernest L. , Zagzebski James A. , Banjavie Richard A. , Jutila Ronald E.
Published: August 2003

Up until now, no material has been found whose attenuation and speed of sound properties not only mimic those of human soft tissue, but are controllable in magnitude. We have discovered such a material in the form of water‐based pharmaceutical gels containing uniform distributions of graphite powder and known concentrations of alcohol. The magnitude of the attenuation coefficient can be controlled easily between 0.2 and 1.5 dB/cm at 1 MHz, by varying the concentration of graphite. These attenuation coefficients are nearly proportional to the frequency. The speed of sound varies between 1520 and 1650 m/s at room temperature, depending primarily upon the concentration of alcohol. Bacterial invasion has been prevented by sterilization procedures and the introduction of appropriate preservatives. The ultrasonic properties exhibit temporal stability and change little over the range of room temperatures.
Evaluation of observer performance in detecting blood vessels on simulated angiographic images
Authors: Sandor Tamas , Swensson Richard G.
Published: August 2003

This paper presents methods for evaluating the effects of technical factors on observers’ detection of small blood vessels in angiographic images. A fixed set of physical parameters was used to generate computer‐simulated angiographs that contained blood vessels of various diameters. Observers’ judgments about each set of images permitted estimation of the receiver operating characateristic (ROC) curves for vessel detection and of the probability of correctly locating the vessels. Both parametric and nonparametric methods were used to characerize the ROC curves. Three different, but theoretically related, measures of vessel detectability varied systematically with changes in the blood vessel's diameter, reflecting changes in observer performance.
Processing of incomplete measurement data in computed tomography
Authors: Lewitt Robert M.
Published: August 2003

Conventional approaches to computed tomography involve scanning the entire cross section and producing an image whose spatial and density resolution is uniform over its entire area. If the extent of each scan is restricted to the width of the lesion being investigated, then the x‐ray dose is reduced, but a set of incomplete “truncated” projections is measured. Conversely, projections are “hollow” when their inner parts cannot be measured, e.g., when there is a metallic object within the body cross section. We present procedures for preprocessing incomplete projections so that images can be reconstructed from them using the convolution/back projection method.
Noise considerations in dual energy CT scanning
Authors: Kelcz Frederick , Joseph Peter M. , Hilal Sadek K.
Published: August 2003

Dual energy CT scanning (tomochemistry) has been proposed as a method for determining various parameters relating to the elemental composition of the tissues. In this paper, our aim is to study the relative noise inherent in two proposed techniques for dual energy scanning: a “two crystal” technique and a “two kV” technique. In the two crystal technique, a split crystal detector is used to simultaneously obtain the high and low energy data during one scan at high kV. The two kV technique requires two scans taken with widely different kV settings. We first review three commonly used approaches for utilizing the scan data to compute the relevant parameters. A theoretical formalism is constructed which aids in understanding these methods. Then this formalism is used to study the influence of CT image noise on measurement precision in the case where the unknown parameters are densities. It is shown that, (1) the unavoidable overlap in the spectral data obtained by the two crystal technique results in a much lower signal‐to‐noise ratio than can be obtained by using the two kV technique, (2) the necessity for hard filtration of the high energy beam in the two kV technique has not heretofore been appreciated, and (3) the dose for a given x‐ray tube heat load is also lower with the two kV technique.
Attenuation in Lipowitz's metal of x rays produced at 2, 4, 10, and 18 MV and gamma rays from cobalt‐60
Authors: Huen Albert , Findley David O. , Skov David D.
Published: August 2003

Attenuation in Lipowitz's metal of x rays produced at 2, 4, 10, and 18 MV and gamma rays from cobalt 60 were measured to the 1% level with a narrow beam geometry. Blocks made from standard styrofoam mold (7.6 cm thick) would reduce these primary beams by 95% to 99%.
Neutron spectra from 35 and 46 MeV protons, 16 and 28 MeV deuterons, and 44 MeV 3He ions on thick beryllium
Authors: Waterman F. M. , Kuchnir F. T. , Skaggs L. S. , Kouzes R. T. , Moore W. H.
Published: August 2003

The energy spectra of neutrons produced by 35 and 46 MeV protons, 16 and 28 MeV deuterons, and 44 MeV 3He ions on thick beryllium were measured at angles of 0°, 15°, and 45° with respect to the incident beams. The spectra were measured by the time‐of‐flight method for neutrons from the maximum energy down to 1 MeV. Neutron dose rates obtained from the zero‐degree spectra by use of available tissue kerma factors agree with TE–TE ionization chamber measurements.
Stereo‐photogrammetry for the determination of patient surface geometry
Authors: Velkley D. E. , Oliver G. D.
Published: August 2003

A stereo‐photographic system has been developed with which surface contours of a human subject may be obtained rapidly and objectively. Nonmetric cameras are used and the results are obtained from direct measurements of the photographs. Software has been developed for interpretation of the photographic data with the asistance of a small computer and desk‐top digitizer such as those routinely used in radiotherapy treatment planning. With this system the coordinates of a point on the subject may be determined with an accuracy of ±1–2 mm.
Analysis of the significance of scattered radiation in reduced dose mammography, including magnification effects, scatter suppression, and focal spot and detector blurring
Authors: Muntz E. P.
Published: August 2003

A systems analysis of reduced dose mammography with scatter removal has quantitatively specified the relationships between the several parameters in mammography systems. While the results are only preliminary in the sense that they need to be proven experimentally, they do seem to provide a good feel for the nature of the important trade‐offs. The major uncertainties in the analysis probably have to do with the formal equivalence, that is implicit in the aperture theory, between large area and detail contrast, as well as the output versus focal spot relationship that was adopted. Also, there are important questions about specifying motion unsharpness as a function of exposure time in mammography examinations.
Computerized system for the measurement of gallstone volume, in vivo
Authors: Baily Norman A. , Keller Robert A. , Lasser Elliott C.
Published: August 2003

Instrumentation and methodology for the determination of gallstone volume from standard roentgenographic views have been developed. Evaluation of size is made by using video viewing, an operator‐set electronic window, intercept registers, and the programming of a PDP/8E for handling the data. The programming makes corrections for geometric factors arising from anatomical variations, corrections for variations in technique, roentgenographic magnification, and provides for the use of several roentgenographic views. The precision of the measuring (video) technique is ∼0.5 mm as measured on the roentgenogram. Estimates and test data indicate that this system should be capable of an absolute accuracy within 10% of the true volume.
Relative measurements of fast neutron contamination in 18‐MV photon beams from two linear accelerators and a betatron
Authors: Gur D. , Bukovitz A. G. , Rosen J. C. , Holmes B. G.
Published: August 2003

Fast neutron contamination in photon beams in the 20 MV range have been reported in recent years. In order to determine if the variations were due mainly to differences in measurement procedures, or inherent in the design of the accelerators, three different 18‐MV (BJR) photon beams were compared using identical analytical techniques. The units studied were a Philips SL/75‐20 and a Siemens Mevatron‐20 linear accelerators and a Schimadzu betatron. Gamma spectroscopy of an activated aluminum foil was the method used. By comparing the relative amounts of neutron contamination, errors associated with absolute measurements such as detector efficiency and differences in activation foils were eliminated. Fast neutron contaminations per rad of x rays in a ratio of 6.7:3.7:1 were found for the Philips, Schimadzu and Siemens accelerators, respectively.
Characterization of Clinac‐18 electron‐beam energy using a magnetic analysis method
Authors: Wessels B. W. , Paliwal B. R. , Parrott M. J. , Choi M. C.
Published: August 2003

Clinac‐18 electron‐beam energies and spectral energy distributions were measured by a magnetic analysis method to verify results obtained by the standard range method. A comparison of these measurements with nominal energies quoted by the manufacturer indicates that electron‐beam energies measured by both methods are in agreement with the manufacturer's specifications to ±0.6 MeV. Spectral energy distribution of the electron beam was measured to be approximately 1 MeV (FWHM) at all energies.
Specific γ‐ray constant and exposure rate constant of 192Ir
Authors: Glasgow Glenn P. , Dillman L. T.
Published: August 2003

Calculated values of the 192Ir specific γ‐ray constant Γ, range from the low value of 3.948 R cm2h−1mCi−1 recommended in NCRP No. 41 to a high of 4.89 R cm2h−1mCi−1. Measured values of Γ range only from 4.85 to 5.0 R cm2h−1mCi−1. Discrepancies in reported calculated values exist because the isotope decay scheme and other nuclear spectroscopy data pertinent to these calculations were not well known. Using the 28 γ rays and relative intensities from the most recent Evaluated Nuclear Structure Data File (ENSDF), Γ is calculated to be 4.62±0.05 R cm2h−1mCi−1 and the exposure rate constant Γδ is 4.69±0.05 R cm2h−1mCi−1. These new calculations are presented and previously reported values of Γ and Γδ are reviewed.
Disturbing diffraction phenomena observed in roentgen diagnostic practice
Authors: Carlsson Carl A. , Edholm Paul R. , Ericsson Torsten
Published: August 2003

The use of aluminum attenuation‐equalizing filters in diagnostic radiology may lead to the introduction of intensity blotches inside and outside the image area on the x‐ray film. These blotches are shown to be Laué diffraction spots; the effect can be minimized by selecting filter material with grain size less than about 10−3 mm3.
Technique for evaluating radiation beam and image slice parameters of CT scanners
Authors: Sorenson James A.
Published: August 2003

A technique is described for determining in a single scan three important CT scan parameters: beam localizer accuracy, image slice width, and radiation beam width.
X‐ray depth‐dose characteristics of the Toshiba LMR‐16
Authors: Mantel Joseph , Perry Harold , Weinkam James J.
Published: August 2003

The depth‐dose characteristics of the Toshiba LMR‐16 linear accelerator for 14‐MeV x rays have been measured at an SSD of 100 cm using diodes and ion chambers. The surface dose and build‐up depth both exhibit a considerable variation with field size. A new central axis model has been developed which takes account of these variations, and the agreement between the measured and computed data using this model is found to be excellent. Formulas are also presented to estimate the surface dose, buildup depth, and output factor as a function of field size.
Multiple window rectilinear scanner modification
Authors: Tatarczuk J. R. , Flesh L. H. , Kihm R. H. , Senecal J. A.
Published: August 2003

Although the gamma camera and multi‐crystal scanner have largely replaced the old dual probe rectilinear scanners in the larger hospitals, a large number of such scanners are still in use today. Modifications to these units can greatly enhance their usefulness. This paper describes the addition of dual SCA windows to each probe of a rectilinear scanner to increase sensitivity to multiple gamma‐ray isotopes such as 67Ga. This method allows increased information density and/or decreased scanning time without degrading image quality. NIM electronics are used to keep down capital costs, as these modules can be shared with other counting systems when multiple‐peak isotopes are not being scanned. A simple connection to an Ohio Nuclear Mdl 84 dual probe scanner is described. For other scanners, a slight modification would be necessary.
The early history of radiological physics: “A fourth state of matter”
Authors: Lerch Irving A.
Published: August 2003

This paper traces the development of the early history of radiological physics beginning with the early speculations of Faraday that “...matter may be classed into four states, solid, liquid, gaseous, and radiant,” and concluding just before the discovery of x‐rays. Throughout the main theme of the narrative is the discovery of the properties of cathode rays and changing contemporary explanations of their nature. The interaction between the experimental and theoretical work of such well‐known scientists as Faraday, Dalton, Hertz, and Maxwell is also stressed. (AIP)
Monte Carlo advice
Authors: Morin R. L. , Raeside D. E. , Goin J. E. , Widman J. C.
Published: August 2003

The generation of long, high quality random number sequences for Monte Carlo simulations using minicomputers is considered. The importance of the thorough testing of Monte Carlo random number generators is emphasized. A recommendation is given to authors of Monte Carlo papers to specify their random number generator and to describe the randomness testing which that generator has undergone.
Improving the buildup and depth‐dose characteristics of high energy photon beams by using electron filters
Authors: Ling C. Clifton , Biggs Peter J.
Published: August 2003

The attributes of high energy photon beams, i.e., low surface dose, large dmax and improved %DD, are compromised with increase in field size. This is due to the relative increase with field size of the electron component in the beam, as shown by recent experiments done here using a sweeping magnet. The present study shows that the advantages can be partially regained with the use of foils to remove electrons. Various thicknesses of Al, Cu, Sn, and Pb were placed in a 25‐MV linac x‐ray beam at several sites in the treatment head. Buildup curves were measured with a “pancake” chamber for various SSD and field sizes. The magnitude of improvement achieved is dependent upon field size, SSD, the atomic number of the foil material, and foil thickness. Pb foil (0.55 g cm−2) provided the best overall improvement. Surface dose reduction of 10%–20% can be achieved along with significant increase in dmax and %DD. These findings suggest a new design feature for the next generation of high energy linacs.
Assessment of errors in intensity measurements of pulse echo ultrasound using miniature hydrophones
Authors: Fischella P. S. , Carson P. L.
Published: August 2003

Total transmitted power and intensity distributions from diagnostic ultrasound systems have been measured with a radiation force balance and with a miniature hydrophone and instrumentation available in many medical centers. In assessing the accuracy of absolute intensity and power determinations from measurements of acoustic pressure with a hydrophone, ultrasonic power was computed from hydrophone measurements. This power value was compared with the power determined by a radiation force technique. On five pulse echo ultrasound systems, the ratio of the power measured with a radiation force balance to the power determined with the hydrophone varied from 0.25 to 5.5. These differences are attributed mainly to the known large variations in hydrophone response as a function of frequency, and possibly time, since several other possible sources of error were evaluated and estimated to have a reasonably small net effect of 25%. The errors evaluated were those dealing primarily with measurement procedures.
Choice of reference point in megavoltage dosimetry
Authors: Bagne Farideh
Published: August 2003

This work considers the problems associated in megavoltage x‐ray dosimetry concepts with the current techniques used for normalizing the various dose parameters. The depth of transient charged particle equilibrium (CPE) is introduced as the optimum choice of the normalization point. Properties of this depth are discussed and its uniqueness as a measure of beam quality is illustrated.
Geometrical considerations for Compton scatter densitometry
Authors: Huddleston Alan L. , Bhaduri Debabrata , Weaver John
Published: August 2003

The determination of the physical density by Compton scatter densitometry is dependent upon the geometry used for the measurement. The diameter of the sample, the density range, and the scattering volume size and shape influence the relative electron density values obtained by such a system. This work presents the results of an experimental analysis of these parameters in which the importance of each is evaluated for samples of known density. A bias in the computed Compton density, due to multiple scattering and attenuation, is defined; and an expression relating the density bias to these geometrical parameters is presented. The importance of applying corrections to the computed physical density for samples of large diameter and/or high density (cortical bone tissue and large diameter cancellous bone tissue) is discussed.
Accuracy of a two‐sensor sonic digitizer
Authors: Rosen I. I. , Lane R. G. , Kelsey C. A.
Published: August 2003

Digitizing devices are typically used in radiotherapy computer treatment planning for entering patient anatomy, the locations of internal radioactive source, and the outlines of irregularly shaped external beams. The errors encountered in the use of a large‐area two‐sensor sonic digitizer for computer input have been studied. Conversion of data from triangular to Cartesian coordinates makes the precision of the digitizer nonuniform over the sensitive area. The response of each sensor has been measured and found to be a nonlinear function of distance. The assumption of linearity in computing the triangular distances from the sensor readings produces errors in the computed distances of up to 0.8%. An alternative method of computing the distances using a fitted cubic function reduces the errors to less than 0.1%. For a test pattern, the maximum position error was reduced from 0.5 to 0.1 cm.
On optimizing the xeromammographic image
Authors: Fatouros Panos P. , Rao G. U. V.
Published: August 2003

This work undertakes a detailed systems‐based analysis of the xeromammographic process starting from basic considerations. Both the edge enhancement and wide‐recording latitude, the two principal characteristics of xeroradiography, are shown to bear an intimate relationship to the electric‐field distribution. Criteria and methods are formulated for optimizing xeromammographic image quality and a procedure is developed for calculating the white gap. Densitometric curves are derived for both positive‐ and negative‐mode xeroradiography and found to be in excellent agreement with experiment. The question of image linearity is examined carefully and a threshold value for the electrostatic contrast is established, which sets a natural criterion for the application of Fourier analysis. Furthermore, it is shown that, in xeromammography with its inherently low‐contrast structures, an optimal exposure exists which optimizes simultaneously all low‐contrast edges. This last finding, coupled with experimental results, suggests immediately the possibility of an automatic exposure termination in xeromammography. Beam hardening is also investigated and it is shown that increased filtration combined with a lower bias potential leads to substantial dose reduction without significant loss of image quality. The paper concludes with a discussion of scattered radiation and how it affects xeromammographic image quality.
Isolated iodine images using spatial‐frequency encoding
Authors: Macovski A. , Harrel G. , Strul B. , Yeh P.‐S. , Chan J. L.‐H.
Published: August 2003

A system has been implemented for imaging subtle amounts of iodine. Using a grating, information is encoded representing the transmission on either side of the iodine K edge. The information is decoded by filtering and processing the signal on a drum scanner. Experimental results are shown using a thyroid phantom and a rat. This system can be used in a number of studies including hepatography, the radiographic visualization of the liver.
Cobalt‐60 dose calibration: A comparison of methods
Authors: Freim John O. , Feldman Arnold
Published: August 2003

Cobalt‐60 dose determination can be accomplished by a variety of methods. This study investigates dose determination by actual “at‐depth” measurement for the depths and field sizes desired as well as by “in‐air” or “in‐water” calibration measurements for both constant SSD and isocentric techniques. Comparison of the above dose determination methods reveals the existence of both depth‐dependent and field size‐dependent dose discrepancies between the individual methods studied. For many teletherapy units, the source of these discrepancies lies in the inapplicability of the tabulated percent depth dose and tissue‐air ratio values employed. Appropriate percent depth dose and tissue‐air ratios can be obtained by performing a series of at‐depth dose determinations for a variety of depths and field sizes. When the appropriate values are employed, excellent agreement is found between all of the dose determination methods investigated.
Revision of tissue‐maximum ratio and scatter‐maximum ratio concepts for cobalt 60 and higher energy x‐ray beams
Authors: Khan Faiz M. , Sewchand Wilfred , Lee Joseph , Williamson Jeffrey F.
Published: August 2003

The concept of tissue‐maximum ratios (TMR) as a basis of dose computations has posed problems when applied to the whole range of clinically used megavoltage beams. Another problem is the definition of scatter‐maximum ratio (SMR) which assumes a value of zero at the depth of maximum dose. This paper describes new methods of measuring collimator and phantom scatter correction factors. The definitions of TMR and SMR are modified in order to compute phantom scatter at any depth, including depth of maximum dose. The revised concept is basic and general enough that it can be applied to x‐ray beams of any energy, fields of any shape and isocentric as well as non‐isocentric modes of treatment.
Determination of bone density by coherent–Compton scattering
Authors: Stalp John T. , Mazess Richard B.
Published: August 2003

Bone density previously has been determined by counting the number of Compton and coherently scattered photons using incident radiation from 241Am (60 keV). We have improved this technique by using more nearly optimal scattering angles and a higher incident beam energy. Three factors make this method clinically attractive; (a) sensitivity to changes in both bone density and elemental composition, (b) elimination of attenuation corrections for overlaying structures, and (c) the ability to measure the axial skeleton. An intrinsic Ge detector with high resolution (500 eV at 100 keV) allowed measurement of forward scatter at angles as low as 30 ° (from the incident beam), thereby maximizing the fluence of the coherent photons which are highly forward directed. Preliminary results showed high correlations (r=0.97–0.99) between the coherent–Compton ratio and density of bone phantoms using both 241Am and 153Gd sources. The skin dose for a measurement using 153Gd was calculated to be 1.5 cGy at 3% counting precision.
Dosimetric evaluation of a variable field electron beam applicator
Authors: Bukovitz A. G. , Saini D. , Gur D. , Sweeney L. E.
Published: August 2003

A commercially available variable electron beam applicator designed for the Philips SL‐75/20 linear accelerator was tested for possible clinical use. The basic design of this collimator consists of four movable L‐shaped stainless steel blades forming the corners. In addition, four smaller fixed blades of the same material and thickness fill in the sides. Film placed in polystyrene phantoms were exposed in all experiments. Field size, field flatness, beam homogeneity and penumbra measurements, all indicated that the applicator is acceptable for clinical use. However, for use with large field sizes and/or high energy electron beams some minor modifications are suggested.