bluuebunny/crossref_metadata_2025 huggingface dataset:
Linear accelerator calibration monitor with a memory
Authors: Dixon Robert L. , Ekstrand Kenneth E.
Published: August 2003

A calibration monitor has been designed for measuring the constancy of linear accelerator or cobalt unit output between full calibrations. This monitor is battery‐operated, light‐weight, and slides into the shadow tray attachment on a linear accelerator or cobalt unit for easy setup. It provides a digital readout of the dose delivered, and a consistency check can be made in less than two minutes. The precision of the monitor, determined by cobalt‐60 irradiations over a 2 1/2 month period, is±0.6% (standard deviation). The monitor also retains the dose reading in a CMOS digital counter indefinitely, hence it can be used in the same fashion as mailed thermoluminescent dosimeters (TLD) for calibration checks at remote facilities without the complicated readout procedures associated with TLD. The monitor can be mailed to a remote facility, positioned without ambiguity, and irradiated; and the reading can be verified on return to the originating center simply by pressing a switch. The monitor can easily be set up to carry out a ’'blind” check in which the reading obtained is not known to the remote facility.
Direct data link between a CT scanner and a radiation treatment planning system
Authors: Abel Roland N. , Buhler Lester A. , Chu William T. , Slater James M. , Neilsen Ivan R. , Zimmerman Duane C.
Published: August 2003

A direct data link between a CT scanner and a radiation treatment planning system has been developed. The link transmits the data serially over a coaxial cable using the pseudo‐paper‐tape punch and reader (serial PIO) interfaces. The data transmission rate with error‐check is approximately 25 000 8‐bit bytes/s. This translates to about 7 s for transferring a CT scan with a 320‐pixel diameter.
Neutron energy spectra of d (49)‐Be and p (41)‐Be neutron radiotherapy sources
Authors: Graves Robert G. , Smathers James B. , Almond Peter R. , Grant Walter H. , Otte Victor A.
Published: August 2003

Zero‐degree neutron energy spectra for the p (41)‐Be and d (49)‐Be reactions were measured by time‐of‐flight for neutrons with energies above 1.9 and 1.4 MeV, respectively. Spectral changes resulting from the addition of copper, aluminum, and polyethylene filters to unfiltered beams were determined. Integral yields, average energies, filter material attenuation coefficients, and kerma fractions were computed for these spectra. Calculated spectra for neutron beams filtered by various thicknesses of polyethylene compared favorably with experimental results.
Correction factors for neutron dose changes caused by inhomogeneities
Authors: Weaver K. A. , Eenmaa J. , Wootton P.
Published: August 2003

A technique is presented for calculating correction factors for neutron dose changes caused by inhomogeneities. The technique is particularly applicable to geometries in which the inhomogeneity lies adjacent to, but not on, a direct path from the radiation source to the point of dosimetric interest; it yields results accurate to a few percent. Best results are obtained for inhomogeneities located at shallow depths.
Application of information theory to the assessment of computed tomography
Authors: Wagner Robert F. , Brown David G. , Pastel Mary S.
Published: August 2003

The imaging process has two fundamental stages: detection and display. The detection stage can be quantified rigorously using Shannon's information theory. This requires the contrast scale (CS), modulation transfer function (MTF), and noise power spectrum [N (f)] to be combined into a signal‐to‐noise ratio (SNR). This results in two fundamental summary figures of merit: the density of noise equivalent quanta (NEQ) in the image and the information bandwidth integral (IBWI). These algorithm‐independent measures are used to quantify the recording stage. The display stage is less well understood since it couples to an external observer. Several types of decision makers are treated. Examples are drawn from first and second generation CT, demonstrating that they are nearly quantum limited for large signals, indicating how their algorithms are matched or mismatched to the geometry, and calculating the contrast‐detail diagrams for those decision makers.
The design and performance of a scanning multiple slit assembly
Authors: Barnes Gary T. , Brezovich Ivan A.
Published: August 2003

A scanning multiple slit assembly (SMSA) has been constructed for the purpose of reducing scatter in medical radiography. The SMSA consists of a series of long, narrow beam‐defining slits above the patient that are aligned and synchronously moved with scatter‐eliminating slots beneath the patient during an exposure. Evidence, based on measurements of the ratio of scattered‐to‐primary radiation imaged and radiographs of patients, is presented indicating that such a device is a practical and efficient method of reducing scatter and improving contrast compared to conventional grids. The design considerations and trade‐offs associated with the choice of slit width, slit separation distance, and aft slot depth are discussed along with the effect of these parameters on the SMSA's performance. The various problems encountered in obtaining a uniform scan and the manner in which they were handled are also discussed.
Absorbed dose comparison: positron emitters 11C, 13N, and 15O versus gamma‐ray emitters
Authors: Feller Paul A. , Sodd Vincent J. , Nishiyama Hiroshi
Published: August 2003

Absorbed doses were calculated or taken from the literature for various compounds of 11C, 13N, and 15O, and compared to those of presently used gamma‐ray‐emitting nuclear medicine radiopharmaceuticals. As a rule of thumb, the doses per millicurie of the injectable positron‐emitting compounds are of the same order of magnitude as the dose per millicurie of 99mTc compounds. The absorbed doses from the injectable positron emitters are nearly one or more orders of magnitude lower on a per millicurie basis than those from the other injectable gamma emitters that were investigated.
A megavoltage MTF measurement technique for metal screen‐film detectors
Authors: Droege Ronald T.
Published: August 2003

A technique to measure the MTF of metal screen‐film detectors at megavoltage x‐ray energies has been devised. It employs an exposure through a slit 25 μm wide and a method to average numerous line spread functions from a single film image. That the slit is wide compared to those used at diagnostic x‐ray energies serves two purposes: it facilitates the use of a laser alignment procedure designed to ensure correct orientation of the slit‐forming tungsten blocks in the x‐ray beam, and it also increases the contrast in the slit image, thereby reducing the data analysis problems caused by film noise. Further reduction in the effects of film noise is accomplished by the averaging method. A correction is made to account for the effect of the wide slit on the MTF. The validity of this correction, the laser alignment, and the averaging method have been confirmed by simulations.
Physical factors affecting absorbed dose to the skin from cobalt‐60 gamma rays and 25‐MV x rays
Authors: Gagnon William F. , Horton John L.
Published: August 2003

When there is an absence of scattering material adjacent to the skin on the exit side of a megavoltage beam the dose to the skin is less than would be calculated using depth dose tables or isodose distributions measured in “semi‐infinite” phantoms. Ionization measurements using a thin‐window parallel‐plate chamber show that the dose at 4 mg/cm2 from the exit surface is 14% to 16% less for cobalt‐60 gamma rays and about 8% less for 25‐MV x rays compared to the dose with full backscatter. As the angle of incidence increases the skin dose increases due to radiation scattered toward the surface. A method for the calculation of skin doses from tangential therapy beams is described.
Calculating dose from remaining body activity: A comparison of two methods
Authors: Coffey Jack L. , Watson Evelyn E.
Published: August 2003

Two methods for calculating the radiation dose from remaining body activity have been suggested. One requires correction of the cumulated activities so that they reflect the activity uniformly distributed in the total body. The other method requires correction of the S values so that a value of S for the target organ from the remainder of the body is obtained. These two methods give the same answer. We have examined these methods and the number of steps required to calculate the radiation dose in each case. Our results show that the method of correcting the cumulated activities is preferred, especially if the number of source and target organs is large and a computer equipped with the necessary software is not available.
Microwave scattering parameter imagery of an isolated canine kidney
Authors: Larsen Lawrence E. , Jacobi John H.
Published: August 2003

This paper describes a method for imaging biosystems using radiation in the microwave frequency range (3.9 GHz). The advantages of interrogation with microwave radiation are discussed in terms of its physiological significance. An electromechanical scanning system for imaging isolated organs and the subsequent image processing techniques are described. Imagery is presented for a phantom target and an isolated canine kidney. The kidney images are interpreted in terms of the known anatomical and functional organization of the organ. It does appear to be possible to distinguish cortex corticis corresponding to a high proportion of proximal and distal convoluted tubules, deeper cortical layers corresponding to a high population density of glomeri, a medullary outer zone corresponding to the loops of Henle as well as the collecting system, and the region of calyces/renal pelvis.
Problem encountered in using the Siemens Mevatron‐VI linac for total body irradiation
Authors: Annett Clarence H.
Published: August 2003

This paper describes a serious problem that was encountered when the Siemens Mevatron VI, 6 MeV linear acceleration was used for whole body irradiation at the University of Kansas Medical Center. The problem can be prevented by interrupting whole body irradiation with short periods of cooling. (AIP)
Effect of x‐ray source filtration on dose and image performance of CT scanners
Authors: Szulc Massimiliano , Judy Philip F.
Published: August 2003

X‐ray source filtration as a means to reduce patient dose while maintaining image quality was investigated for CT scanners. The CT values, their variances for various materials, and the surface dose to a cylindrical phantom were calculated for different filter thicknesses and composition as well as for different tube potentials. Thermoluminescent dosimetry indicated that the maximum dose could be predicted by calculation with an accuracy of 10% (±2 s.d.). The product of the variance of the CT values times surface dose was used to establish the appropriate thickness and composition of the filter, a figure of merit that was independent of dose and noise when the sole source of noise was Poisson statistics. This analysis indicated that source filter materials with an atomic number from 29 to 40 are optimum, and if aluminum is used, the minimum thickness, at 120 kVp, should be 4 mm.
Influence of metal screens on contrast in megavoltage x‐ray imaging
Authors: Droege Ronald T. , Bjärngard Bengt E.
Published: August 2003

The radiographic contrast of metal screen‐film detectors was investigated in order to determine the contrast capabilities of these detectors applied to megavoltage x‐ray imaging. The film contrast γ was found to be independent of the metal screen composition. Measurement of the scatter‐to‐primary film dose ratio in contact geometry demonstrated that a thick front screen of either 1.5 g/cm2 copper or 2.5 g/cm2 lead provides optimum contrast for the photon energies studied (60Co and 4‐ and 8‐MV x rays). The same thicknesses were also found to be suitable in an air gap geometry which significantly improved the contrast compared to the contact geometry. Rear lead screens were found to provide no contrast improvement.
The effect of phosphor K x‐rays on the MTF of rare‐earth screens
Authors: Arnold Ben A. , Bjärngard Bengt E.
Published: August 2003

The LSF's and MTF's of two high resolution rare‐earth screen‐film combinations were measured at two beam qualities. The two beam qualities were chosen to provide x‐ray spectral distributions either above or below the K‐edge of the screen phosphor. The LSF's were found to be photon energy dependent. This energy dependence is attributed to the generation and reabsorption of phosphor K x‐rays resulting in a broadening of the LSF.
Metal screen‐film detector MTF at megavoltage x‐ray energies
Authors: Droege Ronald T. , Bjärngard Bengt E.
Published: August 2003

The MTF of metal screen film detectors used in radiation treatment verification has been measured at 4 and 8 MV x‐ray energies. The results show that lead screens provide better resolution than copper screens, and a single‐emulsion film offers considerable advantage over the traditional double‐emulsion film. A rear lead screen was found to seriously degrade the resolution properties of a front lead screen single‐emulsion film detector. The detector MTF was found to be energy dependent. In general, both the low and the high spatial frequency response decreased with increasing x‐ray energy. This, in part, accounts for the noticeable image quality difference between 4 and 8 MV radiographs.
Laser fluorescence bronchoscope for localization of occult lung tumors
Authors: Profio A. Edward , Doiron Daniel R. , King E. G.
Published: August 2003

A system for imaging occult bronchogenic carcinoma by the fluorescence of previously‐injected, tumor‐specific compound hematoporphyrin‐derivative has been assembled and successfully used to locate a tumor l mm thick. The violet excitation source is a krypton ion laser coupled to fused quartz fiber light conductor. An electrostatic image intensifier attached to a standard flexible fiberoptic bronchoscope provides a bright image even at relatively low irradiance. A red secondary filter rejects most reflected background and autofluorescence. Sensitivity and contrast capability of the system should permit detection of a tumor less than 0.1 mm thick.
A feasibility study of prompt capture gamma in vivo neutron activation analysis
Authors: Zamenhof Robert G. , Deutsch Owen L. , Murray Brian W.
Published: August 2003

The feasibility of using the information contained in the radiative capture gamma ray spectrum of the neutron‐irradiated human body to measure quantitatively total body elemental compositioninvivo has been investigated. Results of time dependent Monte Carlo simulations have shown that spectral interference of nonradiative capture origin can be completely eliminated by pulsing the detector/spectrometer system in anticoincidence with the neutron source. Calculations based on the results of the Monte Carlo simulation and on an experimental measurement of the efficiency versus energy characteristics of a Ge(Li) detector suggest that the primary limitation of the proposed technique would be inter‐element spectral interference rather than inadequate detector sensitivity. Experimental measurements using a pulsed 14‐MeV neutron generator and Ge(Li) gamma‐ray spectrometer have produced results that are consistent with the predictions of the theoretical model. A radiative capture gamma‐ray spectrum of a tissue‐equivalent phantom was measured in pulsed mode and analyzed off‐line using a computerized spectral analysis procedure. The results were scaled to a proposed facility consisting of a 2.5‐MeV pulsed neutron source and a detection system comprising two 50‐cm3 Ge(Li) detectors past which the subject would be scanned. It has been shown that in principle the elements hydrogen, chlorine, calcium, and nitrogen [the latter using large NaI (T1) detectors] could be measured with such a facility at an average body dose level of 0.1 rad. At this dose level the coefficients of variation based on counting statistics alone would be ±2%, or better, for these four elements. With an improvement in the detector/spectrometer energy resolution, the elements sulfur and carbon might also be measurable. It is also shown that by modifying the pulsing sequence appropriately and using 14‐MeV neutrons, total body oxygen could also be measured at the 0.1 rad dose level via its inelastic neutron scattering deexcitation gamma activity.
Dose distribution from a Delta‐25 head scanner
Authors: Agarwal S. K. , Friesen E. J. , Bhaduri D. , Courlas G.
Published: August 2003

The dose distribution pattern from a Delta‐25 head scanner was evaluated experimentally in a 17.5‐cm‐diam cylinder water phantom for different scan speed and slice thickness combinations. TLD chips were used to measure the dose at different points across the scan section. The isodose curves thus obtained were found to be asymmetric, with the regions of maximum and minimum dose near the surface on the opposite sides of the phantom. The effect of changing the scan thickness and speed on dose was evaluated and a linear increase in dose with the increase of slice thickness was observed. This was consistent with the design of the line focus and the beam collimators used in this system. The effect of multiple slice scan on the dose was also evaluated.
High‐LET pion dose contours under the LAMPF biomedical channel by plastic track detector scanning
Authors: Knowles H. B. , Ruddy F. H. , West G. W. , Kligerman M. M.
Published: August 2003

Cellulose‐nitrate plastic track detectors have been tested as high spatial‐resolution dosimeters at the Biomedical Channel of the Clinton P. Anderson Meson Physics Facility (LAMPF) at the Los Alamos Scientific Laboratory during pilot clinical trials with negative pi mesons (pions). Six plots of dose contours are presented. Reliable macrodosimetry with track detectors would in principle require detector calibration for the particular conditions of geometry and beam parameters in every case but it is interesting that absolute dose values, estimated from data taken with a quite different calibration geometry, were within 20% of agreement with dose values obtained by electronic dosimetry methods. The track detectors measure only the high linear energy transfer (LET) components produced by the pion beam; it is these components which are of special interest in the negative‐pion therapy program. Plastic track detectors appear to have many favorable properties for pion dosimetry.
Computer interface for a linear accelerator
Authors: Rosen I. I. , Stevens M. D. , Somers J. W. , Lane R. G. , Kelsey C. A.
Published: August 2003

A computer interface for the Clinac‐18 linear accelerator has been developed, using a standard CAMAC interface plus buffer amplifiers to isolate the CAMAC from the accelerator electronics. Buffer amplifiers are employed because direct connection of the CAMAC system to the accelerator was found to affect accelerator operation. The total interface accommodates the four gantry position analog signals and thirteen digital signals describing all available treatment options. The interface also allows the computer to inhibit beam operation.
Simulator mounted Moiré topography camera for constructing compensating filters
Authors: Boyer Arthur L. , Goitein Michael
Published: August 2003

A technique has been developed and implemented by which individualized Ellis compensating filters can be rapidly and accurately produced from Moiré topographic photographs. A novel Moiré camera has been designed such that it has been possible to mount it on a radiotherapy simulator. The camera does not interfere with normal use of the simulator but can be deployed as needed. Depth of missing tissue contours are produced by the camera over the treatment field, accurately registered to the patient's simulated treatment position. An optical enlargement technique is used to transfer the depth of missing tissue contours in the photograph to a lead sheet compensating filter.
Calculation of the average energy absorbed in photon interactions
Authors: Cunningham J. R. , Johns H. E.
Published: August 2003

High energy electrons set into motion by photon interactions with matter lose some of their energy by bremsstrahlung. This loss must be evaluated before energy absorption coefficients may be calculated. Recent extensive tables of data published by Plechaty et al. contain an appreciable error in this quantity. The error results from two simplifying assumptions and for the case of very high photon energies interacting with high atomic number materials can be as much as a factor of two. This has important implications for the evaluation of quantities used in radiation dosimetry.
Physical factors determining the utility of radiation safety glasses
Authors: Moore W. E. , Ferguson G. , Rohrmann C.
Published: August 2003

Ten types of lenses were tested for their radiation protection properties in three experimental circumstances: (a) Their good geometry (scatter free) attenuation was determined as a function of HVL in a direct x‐ray beam. (b) Their dose reducing properties were determined under simulated clinical fluoroscopic conditions, using both ion chambers and thermoluminescent dosimeters (TLD's) while the lenses, mounted in frames, were worn by a head phantom. The head was oriented in four different directions to simulate clinical conditions in a fluoroscopic room. (c) Their dose reducing properties were measured with TLD's while the glasses were worn by radiologists during clinical fluoroscopic procedures. Although several of the lenses could attenuate a direct x‐ray beam several thousand times, none of the glasses offer more than a factor of 8 reduction in eye exposure when the glasses are worn during fluoroscopy. This is attributed to backscatter from the fluoroscopist's head and deficient lateral shielding. Some of the glasses may even be causing an increase in eye exposure when the TV monitor is located 90° or more from the patient.
Calculative technique to correct for the change in linear accelerator beam energy at off‐axis points
Authors: Hanson W. F. , Berkley L. W. , Peterson M.
Published: August 2003

The change in energy of linear accelerator x‐ray beams from the central ray to off‐axis points causes errors in the dose calculated by conventional techniques for large, irregularly shaped fields. A modification of conventional calculative methods to correct for the change in beam energy is presented. The results of measurements in irregular fields on a Clinac‐4 are reported which verify the validity of the calculative method. A discussion of the clinical significance will point out errors of 3% to 4% in conventional dose calculations.
Absorbed dose water calorimeter
Authors: Domen Steve R.
Published: August 2003

Advantage was taken of the low thermal diffusivity of water and the imperviousness of polyethylene film to water to construct a calorimeter for directly measuring absorbed dose in that medium. An ultrasmall bead thermistor was sandwiched between two thin films stretched on polystyrene rings and immersed in an unregulated water bath. Ten cobalt‐60 irradiation runs were made with a precision of 0.5% mean error of the mean at a dose rate of 66 mGy/s. Further development is directed toward a standard instrument that can be used in a medical therapy beam.
Thin‐walled parallel plate ionization chamber for use with photon and electron beam dosimetry
Authors: Keys David J. , Purdy James A. , Israel Martin H. , Velkley Donald E.
Published: August 2003

The design and construction of a thin‐walled parallel plate ionization chamber is described. The chamber makes use of a sputtered collecting electrode. The characteristics of this chamber include low leakage (less than 10−13 A), no stem effect, and reproducibility within 1%. No polarization effects have been seen for electron beams over an energy range 7–25 MeV while for cobalt 60–25 MV photon beams, it is only 10%–15%.
Coincidence sum peak assay of 125I activity using solid state detectors
Authors: Ling Ching Clifton , Biggs Peter J.
Published: August 2003

The use of solid state detectors in the coincidence sum peak technique of 125I activity assay has been studied. The improved energy resolution of these detectors allows distinct resolution of the Kα, Kβ, and γ peaks, and four sum peaks resulting from the coincident detection of the different X and γ photons. Theoretical considerations yield three separate equations, each of which can be used, in conjunction with the experimental sum peak spectrum, to give the activity of the 125I sample in question. This method is suitable for calibration of 125I activities in the range of 0.01–0.5 μCi with precisions of 2%–3%.
Determination of red cell survival in rabbits by fluorescent excitation analysis of stable rubidium
Authors: Cesareo Roberto , Ciancarelli Maria Giuliana , Scarnati Eugenio
Published: August 2003

Nonradioactive rubidium was used to label red cell in rabbits and its concentration was determined by employing a simple version of radioisotope‐induced x‐ray fluorescence analysis. About 10 ml of red cells were labeled in vitro with 0.5–1 mg of RbCl and subsequently reinjected, resulting in a Rb concentration of about 50 ppm by the red cells. Four milliliters of blood were collected about every week, the concentrated erythrocytes deposited on filter paper disks, and the Rb content analyzed. Except for the first four to seven days, a function of the type N=N0e−kt fitted very well the experimental Rb disappearance curve data. The mean half‐time value deduced from the experimental data was 310±15 days, which should be compared with the values of T1/2=260±20 h and T1/2=206±30 h obtained, respectively, by these authors and by Price et al., employing radioactive 51Cr‐labeled red cells. The possibility of labeling human red cells with stable Rb is discussed.
Experimental dual xenon detectors for quantitative CT and spectral artifact correction
Authors: Drost D. J. , Fenster A.
Published: August 2003

A 41‐channel xenon detector array has been built in our laboratory to be used in a fan‐beam CT scanner. Each channel is split into a front and rear detector producing two signals for each ray through the patient. Since the front and rear detectors measure different photon energies of the x‐ray spectra, dual energy information is obtained from a single CT scan. This information can be used to determine electron density and effective atomic number images of the patient and correct spectral artefacts. A 7.7‐cm‐diam plexiglas cylinder, filled with water and various plastics, was scanned. With this phantom, electron density was determined to an accuracy of 2% and effective atomic number to 4%. Details of the detector design and calibration are discussed and electron density, effective atomic number, and spectral artifact corrected images are presented.
Physical approach to depth dose distributions in a water phantom irradiated by a teleisotope photon beam
Authors: Ahuja Sain D. , Stroup Steven L. , Bolin Marion G. , Gibbs S. Julian
Published: August 2003

The physical basis of deposition of radiation dose within a homogeneous phantom irradiated by a monoenergetic photon beam has been studied in terms of photon attenuation and energy‐absorption properties of the phantom material. A semi‐empirical model based on the Klein–Nishina formula for Compton scattering, and the ratio of multiply scattered to singly scattered photon fluences, has been developed for the scatter dose component within a realistic phantom to determine the central‐axial percent depth dose (PDD) and off‐central‐axis ratios (OCR). Differences between the predicted and measured values of PDD and OCR for cobalt‐60 and cesium‐137 beams are less than 3% for fields of equivalent‐square‐side less than 20 cm, and less than 5% for larger fields. Beam profiles of all field sizes can be well simulated by this model and reasonable agreement has been found between the predicted and tabulated values of scatter functions and the backscatter factor for cobalt‐60 beams. This formulation involves no variable parameters, and is valid for all values of the source‐to‐surface distance, field length and width, and field shape. However, the algorithm developed is not suitable for routine multiple‐field treatment planning because it requires large computer memory size.
Investigation of cables for ionization chambers
Authors: Spokas John J. , Meeker Ralph D.
Published: August 2003

Seven coaxial cables which are in use for carrying currents generated in ionization chambers have been critically studied with reference to their suitability to this application. Included in this study are four low‐noise triaxial cables and three low‐noise two‐conductor cables. For each cable the following characteristics were considered: inherent noise currents, currents produced by cable movements, polarization currents, the degree of electrostatic shielding of the central signal‐carrying conductor, and radiation‐induced cable currents. The study indicated that of the seven cables, two low‐noise triaxial cables, both employing solid Teflon dielectric surrounding the central conductor, appear to offer the best overall performance for use with ionization chambers.
Off‐axis beam quality change in linear accelerator x‐ray beams
Authors: Hanson W. F. , Berkley L. W. , Peterson M.
Published: August 2003

The effective energy of the x‐ray beam from linear accelerators changes as a function of the position in the beam due to nonuniform filtration by the flattening filter. In this work, the transmittance through a water column was measured in good geometry and the beam quality characterized in units of HVL in water. Measurements were made on a variety of linear accelerators from 4 to 10 MV. The beam energy decreased with increasing distance from the central ray for all accelerators measured.
Nonlinear partial volume artifacts in x‐ray computed tomography
Authors: Glover G. H. , Pelc N. J.
Published: August 2003

Dark streaks connecting the petrous bones are often observed in cranial transverse section CT reconstructions. These artifacts are usually only slightly diminished by two‐pass beam hardening corrections. However, it is found that by narrowing the slice thickness the artifacts are substantially reduced. In this paper, it is shown that axial partial volume effects can account for the presence of the artifacts. These axial partial volume effects occur when, at any point in the slice, the object has axial variations in attenuation. In such cases the logarithm of the integrated intensity measured by the detector is not a linear function of the integrated attenuation (even for monochromatic beams). This nonlinearity causes inconsistencies in the data set which in turn can cause streaks in the image. We have studied the partial volume effect using computer simulation. Algorithms are presented whose purpose is to correct for these effects by estimating the axial variation using neighboring slices. These correction algorithms are successful in computer simulation cases but failed with clinical data. It is concluded that no practical correction method is viable unless overlap scanning is employed. However, thin‐slice scanning for sections where these artifacts are common is perhaps a more preferable solution.
Calculation of 131I‐ortho‐iodohippurate absorbed kidney dose: A literature review
Authors: Flannery Ann , Veber Jill , Greenfield Moses A. , McIntyre Arthur B. , Hamilton Donald R.
Published: August 2003

Extensive information has been made available relative to the physical aspects necessary for calculation of radiation absorbed dose from radiopharmaceuticals. A similar data base for the biological factors involved in these calculations has not been documented as thoroughly. The authors present an extensive literature review for the radiation absorbed dose of 131I‐ortho‐iodohippurate and discuss the rationale for adjusting previously accepted values with new biodistribution information.
Microwave leakage during patient treatment
Authors: Kopecky Walter J.
Published: August 2003

In light of the BRH proposed draft standard for microwave leakage of 10 mW/cm2, microwave leakage measurements were taken under two conditions. The first used a microwave tissue equivalent phantom in which leakage data was accumulated as a function of net forward power and aperture‐to‐skin distance (SSD). This is similar to the BRH setup. In the second condition, during actual microwave hyperthermia treatments data was accumulated on several patients at different anatomical sites. The results of these experiments show a marked increase of microwave leakage occurring during patient treatment than that which can be predicted from static phantom results.
Graphite calorimeter in water phantom and calibration of ionization chambers in dose to water for 60Co gamma radiation
Authors: Rao I. S. Sundara , Naik S. B.
Published: August 2003

A graphite calorimeter similar in size and shape to a Farmer type 0.6‐cm3 ionization chamber was developed for direct measurement of absorbed dose at a specified depth in a water phantom irradiated by a beam of 60Co gamma radiation. The accuracy of the absorbed dose determined was estimated to be ±1.1% at a dose level of 4 rad/s (4×10−2Gy s−1). The absorbed dose to water at the calibration depth of 5 cm was standardized for our 60Co gamma beam, for a 60‐cm SSD and 10×10 cm2 field. Farmer type ionization chambers were calibrated against the standardized absorbed dose. The overall accuracy in calibrating the ionization chambers was ± 1.2%.
Cadmium telluride matrix gamma camera
Authors: Allison Jerry D.
Published: August 2003

An experimental gamma camera that has significant performance has been designed, constructed, and tested. The new camera has a matrix of cadmium telluride semiconductors as the detecting medium. The detectors are located within the collimating holes (rather than behind them). Coincident outputs from each row and column are used to digitally identify the individual detector in which the energy deposition occurred. Direct digital localization of detected events and the attenuation of scatter radiation between matrix elements by the collimator septa that separate detectors, contribute to reasonable resolution and imaging time. The superior radiation detection characteristics of cadmium telluride (in comparison to sodium iodide) could provide superior discrimination against scattered radiation that contributes only spurious information to the image. Detector reliability and uniformity limit the camera's performance; however, the availability of large numbers of small cadmium telluride detectors that have uniform radiation detection properties would make a clinical camera viable.
Xeromammographic image quality
Authors: Fatouros Panos P. , Rao Gopala U. V. , Kao Cheng C.
Published: August 2003

Xeroradiography is a diagnostic modality whose image‐forming properties are fundamentally different from those of the conventional silver halide process. In this work, the xeromammographic process, representing the low‐contrast limit of xeroradiography, is analyzed in detail. A step by step approach is taken, whereby the limiting factors in the exposure and development stages are identified and quantified. The sensitivity of the Se layer is also computed and the concept of optimal exposure introduced. The paper concludes by considering a simple model for xeroradiographic noise.
Free‐focus radiography using conventional films—Radiation exposures in a simulated clinical study
Authors: Jensen Th. Warnich , Randall G. J. , Goldberg A. J.
Published: August 2003

This study compared air exposures during conventional dental and maxillofacial radiography and similar views using free‐focus radiography with conventional image receptors. The results show that periapical type surveys on nonscreen film placed extraorally or in the buccal fold may be carried out with an exposure to the surface tissues, which is similar to or less than conventional dental radiography. Extraoral survey type radiographs of the jaws may be carried out with significantly less surface exposure than lateral oblique views of the jaws. The least exposure was required, when the film was placed in the buccla fold instead of against the face during free‐focus radiography. The exposures with film screen combinations were reduced by an order of magnitude when compared to the nonscreen techniques. Proper filtration of the beam of the miniaturized x‐ray machines radiography in dentistry may thus be desirable and applications in other parts of the body encouraged.
Determination of the exposure rate constant for 125I using a scintillation detector
Authors: Schulz R. J. , Chandra Premala , Nath Ravinder
Published: August 2003

A scintillation spectrometer was employed to determine the exposure rate constant for an 125I seed of the type used in therapeutic radiology. The method consisted of converting counting rate to photon fluence incident upon the detector, and then calculating the exposure rate from the photon fluence. Corrections are required for absorption of the 125I photons in the air path, in the aluminum window of the NaI crystal, and in the aluminum–oxide reflector. Corrections are also required for the escape of iodine K–characteristic radiation, and the intrinsic peak efficiency of the crystal. The experimentally determined exposure rate constant in a direction perpendicular to the long axis of the seed is 1.309 R cm2 mCi−1 h−1±5.8%, and this compares favorably with a calculated value of 1.284 R cm2 mCi−1 h−1. The photon fluence as a function of angle of rotation about an axis perpendicular to the seed's long axis was also measured. These data were used to estimate an average exposure rate constant for 125I seeds of 1.089 R cm2 mCi−1 h−1.
A temperature regulating circuit for experimental localized current field hyperthermia systems
Authors: Astrahan Melvin A. , George F. W.
Published: August 2003

Interest in localized current field (LCF) hyperthermia tumor therapy is rapidly increasing. As yet, however, there is no integral LCF system commercially available. An experimental LCF system may be readily assembled from discrete, general purpose components, except for the tumor temperature regulating circuitry. In this article we present an LCF system designed around general purpose components and a simple circuit for temperature regulation. Comments on system safety, calibration, and performance are also included.
Spot scanning system for proton radiotherapy
Authors: Kanai Tatsuaki , Kawachi Kiyomitsu , Kumamoto Yoshikazu , Ogawa Hirotsugu , Yamada Takanobu , Matsuzawa Hideo , Inada Tetsuo
Published: August 2003

In order to provide a uniform and desirable dose distribution over a large radiation field, spot beam scanning is one of the most useful methods. A new spot beam scanning system was constructed for a 70 MeV proton beam. The lateral dose distribution was uniform with ±2.5% for an 18 cm square field. It was possible to control the dose at each point in the radiation field by this spot scanning method. This system has been confirmed to be satisfactory for delivering a proton beam in the desired field shape and dose level.
An evaluation of HgI2 detectors for x‐ray computed tomography
Authors: Beinglass I. , Kaufman L. , Hoisier K. , Hoenninger J.
Published: August 2003

Mercuric iodide (HgI2) presents a set of attractive features as a semiconductor x‐ray detector for computed tomography (CT). Its response is stable, it operates at room temperature, and thin detectors have a high detection efficiency. The properties of HgI2 permit the assembly of high spatial resolution detectors in a compact configuration. On the other hand, HgI2 exhibits a long memory, and some detectors also exhibit polarization effects, both of which are detrimental in CT. A pulse‐shaping technique has been used to overcome these effects, thus demonstrating the suitability of HgI2 for use in CT.
Computer‐assisted quality assurance for radiographic equipment
Authors: Glaze Sharon , Schneiders Nicholas , Archer Benjamin , Bushong Stewart
Published: August 2003

A quality assurance procedure which includes a computer program has been implemented to facilitate measurement of some of the parameters normally tested on diagnostic radiographic equipment. These include: reproducibility of output, linearity of mA settings, filtration, kVp calibration, timer error, SID indication, light field—x‐ray field coincidence and effective focal spot size. The user may omit those sections which are not applicable to his needs. Full use is made of the data reducing the number of field measurements needed.
Monte Carlo simulation studies of detectors used in the measurement of diagnostic x‐ray spectra
Authors: Chen Cecilia S. , Doi Kunio , Vyborny Carl , Chan Heang‐Ping , Holje Gunnila
Published: August 2003

Accurate determination of diagnostic x‐ray spectra requires, among many other technical considerations, correction of the experimental data for the energy‐dependent response of the x‐ray detector. In this study, we investigated the energy response of three types of detectors (intrinsic germanium, lithium‐drifted silicon, and sodium iodide) commonly used in the diagnostic energy range. We used a Monte Carlo simulation technique to compute photopeak efficiencies, escape peak losses, and Compton fractions as a function of incident x‐ray energy for a variety of detector thicknesses and diameters. Calculated responses were compared with experimental results obtained for the Ge and Si(Li) detectors. The measurements, in which we used fluorescent x ray to simulate the monoenergetic beams assumed for the calculations, indicate good agreement between theoretical and experimental approaches. Techniques for correction of measured spectra for the known response of the detector were also evaluated.
Early two‐dimensional reconstruction and recent topics stemming from it
Authors: Cormack A. M.
Published: August 2003

Early developments of computed tomography are traced. (AIP)
Noninvasive magnetic detection of cardiac mechanical activity: Theory
Authors: Wikswo John P.
Published: August 2003

Because the magnetic susceptibility of the heart and the intracardiac blood is substantially greater than that of the surrounding lung tissue, the periodic redistribution of blood and tissue during the cardiac cycle will alter an externally applied magnetic field. These magnetic field changes can be detected by a magnetometer outside the body and have been termed magnetic susceptibility plethysmography (MSPG) signals. This paper presents a theoretical analysis of the MSPG technique. A single moving sphere model is used to explain the susceptibility induced field changes and the detection of the MSPG signals. The susceptibility distribution within the thorax and a more detailed model of the heart are then used to predict the MSPG waveform. Several other contributions to the MSPG signal are analyzed. This model has demonstrated that the time dependence of certain MSPG components closely resembles that of the total heart volume while other components have waveforms similar to the displacement of the cardiac center of mass. The magnitude and direction of the MSPG field has been shown to depend on the location of the field point, the volume change of the heart, and the motion of the heart's center of mass. It has also been shown that 90% or more of the MSPG signal recorded near the heart but outside the body will be produced by cardiac volume changes. For these reasons, the MSPG technique may provide a noninvasive method of measuring changes both in total cardiac volume and in the position of the cardiac center of mass throughout the cardiac cycle.
Measurement of the velocity of ultrasound in the human femur in vivo
Authors: André Michael P. , Craven J. Duncan , Greenfield Moses A. , Stern Richard
Published: August 2003

A pulse‐echo technique for measuring the velocity of ultrasound in the cortex of the femur in vivo is presented. The average result for 27 asymptomatic volunteers is 3250±190 m/s. The results show no significant differences between proximal and distal femoral sites, right and left femora, males and females. There is also no significant difference between the velocity of sound in the femur and in the radius in normal volunteers. The reproducibility of the time of flight measurement for three volunteers is found to be about 2%, and the total uncertainty of the femoral velocity of ultrasound measurement is determined to be 4% for proximal sites and 7% for distal sites. As the femur is a load‐bearing bone, the site of frequent fracture both in the elderly and in the osteoporotic, the measurement of the velocity of sound at this new site may of great value in investigating these conditions and may ultimately be helpful in assessing ’'quality” of the femoral cortex in those patients undergoing total hip or knee replacement.
An intercomparison of neutron measurements for a 25 MV x‐ray radiotherapy accelerator
Authors: Nath Ravinder , Price K. W. , Holeman G. R.
Published: August 2003

High‐energy x‐ray radiotherapy machines produce neutrons by photonuclear reactions which present a potential radiation hazard to the personnel and patient. A series of measurements of the neutron flux from a 25 MV x‐ray linear accelerator, inside and outside the treatment room, have been performed using a multisphere spectrometer, Nemo dosimeter, and activation detectors. These results are compared with other mixed photon–neutron field measurements for the same machine performed using an argon/propane ionization chamber, silicon diode, track‐etching detectors, and Monte Carlo calculations. It is found that these measurements agree with each other within a factor of two except for silicon diode measurements in the photon beam. Measured neutron spectra at various locations in the treatment room are also compared with the results of Monte Carlo transport calculations.
A method for calculating megavoltage x‐ray dose and dose parameters
Authors: Bagne Farideh
Published: August 2003

Limitations of the most commonly used dose calculation methodologies as apply to medium and high‐energy x rays are discussed. A method is presented whereby the dose to a point in medium is divided into several components with expressions given for various components. The depth of transient‐charged particle equilibrium is chosen as the reference point. Equations are derived for calculating and relating the dose parameters including the percent depth dose, the tissue‐reference ratio, and the scatter‐reference ratio. Particular emphasis is placed on the accuracy and adequacy of the technique in the region of buildup. The applicability of the present method to megavoltage photons is established for a number of x‐ray beams in the range 4–45 MeV maximum energy.
Calculation of pion dose distributions in water
Authors: Hogstrom Kenneth R. , Rosen Isaac I. , Gelfand Eric , Paciotti Michael A. , Amols Howard I. , Luckstead Steve
Published: August 2003

Techniques for calculating negative pion beam depth and off‐axis dose distributions in a water phantom have been developed at the Clinton P. Anderson Meson Physics Facility in Los Alamos. The superposition of the unmodulated depth‐dose curve produced modulated depth‐dose curves. The addition of the collimator neutron dose, which has been shown to depend on field size, to the modulated depth‐dose curve yields the collimated depth‐dose distributions. Off‐axis dose distributions under a collimator are produced by calculating the distortion of the uncollimated beam caused by multiple Coulomb scattering and beam phase space. Several comparisons of calculated and measured distributions are shown with agreement of nominally ±3% of peak dose or ±3 mm for a particular dose contour. These distributions are then modified by computerized tomographic data to give patient isodose distributions.
In vivo activation analysis of spinal calcium using 25 keV neutrons
Authors: Cousins T. , Kennett T. J. , Prestwich W. V. , Webber C. E.
Published: August 2003

The applicability of 25 keV neutrons to the in vivo activation analysis of spinal calcium is examined both theoretically and experimentally. It is shown that the use of this energy results in an increase in sensitivity over higher energy neutrons so that patient dose may be significantly reduced.