bluuebunny/crossref_metadata_2025 huggingface dataset:
An evaluation of four methods of 111In planar image quantification
Authors: van Rensburg Ado J. , Lötter Mattheus G. , Heyns Anthon du P. , Minnaar Philip C.
Published: March 2003

The accurate quantification of the in vivo distribution of 111In labeled platelets, other cells, and proteins with a scintillation camera is important in clinical and experimental medicine. Planar techniques of image quantification were therefore evaluated with the aim of improving on the accuracy, and simplifying the techniques currently in use. The attenuation of the 172‐ and 247‐keV photons of 111In, singly and in combination, was determined for varying diameter flat sources (3.4 to 16.9 cm). The influence of region of interest (ROI) selection on the shape of the attenuation curves was also determined for five different ROI's. Defining the attenuation curves mathematically generated parameters of fit for three approaches to in vivo quantification, namely: a single exponential geometric mean approach that takes into account source size, depth‐dependent, and depth‐independent buildup factor approaches to account for the contribution of scatter. The accuracy of these techniques was ascertained and compared to the classical geometric mean method. This was done in a waxen phantom of a human thorax with a hollow liver and spleen. The results indicated that the depth‐independent buildup factor is the best method; the error for quantification in the spleen was 0.8%±2.2%. The classical geometric mean approach gave a corresponding error of 43.3%±3.4%. Since the attenuation of the two energies of 111In differ, their ratio changes with depth. This phenomenon was investigated with the goal of determining whether the depth of an object can be estimated from one set of planar images. This was not successful. Based on these results, we recommend that quantification of organ radioactivity is best done by using both energy peaks of 111In, acquiring parallel opposing images and correcting for attenuation and scatter with the depth‐independent buildup factor.
Bulk flow model for multislice magnetic resonance imaging sequences with phantom validation
Authors: Meyer Charles R. , Williams David M.
Published: March 2003

A simple conceptual model for describing the effects of one‐dimensional bulk flow on image intensities is presented and validated using a multislice imaging sequence specific to one vendor. The model allows quantitative estimates of echo amplitudes versus velocity by using the equation of motion to follow the pulse history of fluid volumes influenced by the readout pulse for any slice of interest. Each affected volume is divided into equal elemental components and the state of each component is computed at discrete times in a pulse position‐timing diagram until readout occurs. The final amplitude for the composite volume is determined by the signed summation of each of the elemental components. Validation of the quantitative model was performed by imaging a rotating bulk flow phantom centered at each of the slices of a multislice, partial saturation, spin‐echo sequence. Effects due to rf field inhomogeneities were normalized by dividing the results of the dynamic scans by the corresponding static one. The results presented here are relatively insensitive to odd‐echo dephasing (even echo rephasing).
Problems with organic materials for magnetic resonance imaging phantoms
Authors: Hinks R. Scott , Henkelman R. Mark
Published: March 2003

Organic liquids are frequently used as magnetic resonance (MR) phantom materials. It is often not appreciated that indirect spin–spin coupling can dramatically affect signal amplitudes in spin‐echo experiments. These effects are evidenced in three ways: (1) modulation of spin‐echo amplitudes; (2) decrease in measured T2 relaxation times; and (3) dependence of spin‐echo modulation and measured T2 values on the echo time (TE) in multiecho Carr–Purcell–Meibroom–Gill experiments. This paper illustrates these effects and warns against the inappropriate use of organic liquids as MR phantoms.
Therapy imaging: Source sizes of radiotherapy beams
Authors: Munro P. , Rawlinson J. A. , Fenster A.
Published: March 2003

We have developed a novel method, which employs large lead collimators and computed tomography reconstruction techniques, to measure the intensity distributions of x‐ray sources of radiotherapy devices. Using this method, we have measured the intensity distributions of x‐ray sources from 60 Co, 6‐, 18‐, and 25‐MV radiotherapy devices. The x‐ray sources of the accelerators were all elliptical in shape, but varied in eccentricity, and the sizes of the accelerator sources varied from 0.7 to 3.3 mm full width at half‐maximum. The 60 Co source was circular in shape and 20 mm in diameter, however, the output from this source was not uniform across its face. The modulation transfer functions (MTF's) (at the image plane) calculated for the accelerator sources, assuming an image magnification of 1.2, had similar magnitudes at low spatial frequencies as the MTF's of the metal plate/film detectors commonly used for therapy imaging. However, the source MTF's declined much more rapidly at high spatial frequencies. Therefore, for geometries commonly found in radiotherapy, the loss in spatial resolution due to the x‐ray source was at least equal to that caused by electron and photon scatter within the metal plate/film detectors.
Output factor constituents of a high‐energy photon beam
Authors: Luxton Gary , Astrahan Melvin A.
Published: March 2003

Measurements designed to separate primary and various scatter components of central axis dose of the highest energy photon beam of the CGR Saturne 25 linear accelerator are described. This beam has an unusually large output variation with field size. The measurements are performed both in air and in a water phantom, with and without an aperture external to the collimator system. Results are presented in the form of relative output factors for different field sizes due to (i) flattening filter scatter, (ii) water phantom scatter, (iii) collimator backscatter into the monitor chamber, and (iv) collimator forward scatter onto the central axis. It is found that the flattening filter is the single largest scatter component, but that each of the other factors is significant in determining the output dose per monitor unit as a function of field size.
Bootstrap sensitometry for nuclear medicine
Authors: Mumma Cynthia Goodman , Prince John R.
Published: March 2003

A full radioscintigraphic monitor/film system sensitometric curve has been obtained utilizing a bootstrap technique in which individual characteristic curve segments, obtained from stepwedge‐graded exposures, are tied together at the point of overlap. Curve segments were first smoothed by employing the linearized form of the logistic distribution function. This function allows calculation of gradient‐exposure and gradient‐density relations for the full characteristic curve.
Real‐time distortionless high‐factor compression scheme
Authors: Liénard Jean
Published: March 2003

Nowadays, digital subtraction angiography systems must be able to sustain real‐time acquisition (30 frames per second) of 512×512×8 bit images and store several sequences of such images on low cost and general‐purpose mass memories. Concretely, that means a 7.8 Mbytes per second rate and about 780 Mbytes disk space to hold a 100‐s cardiac examination. To fulfill these requirements at competitive cost, a distortionless compressor/decompressor system can be designed: during acquisition, the real‐time compressor transforms the input images into a lower quantity of coded information through a predictive coder and a variable‐length Huffman code. The process is fully reversible because during review, the real‐time decompressor exactly recovers the acquired images from the stored compressed data. Test results on many raw images demonstrate that real‐time compression is feasible and takes place with absolutely no loss of information. The designed system indifferently works on 512 or 1024 formats, and 256 or 1024 gray levels.
Performance characteristics of a real‐time digital x‐ray fluoroscopic system using an intensified charge injection device camera and CsI:Na crystal
Authors: Atari Nader A.
Published: March 2003

A digital x‐ray photoelectronic imaging system has been constructed using an optically flat 152‐mm‐diam, 2.5‐mm‐thick CsI:Na scintillating crystal. X‐ray images formed by the scintillator are viewed by a single microchannel plate intensified charge injection device (ICID) camera and digitized at a real‐time rate by a computerized frame‐grabbing system. Video images are recorded and selected image frames are subjected to image processing and analysis schemes. Parameters governing the performance characteristics of the system are determined accordingly. For a 152‐mm field size at the crystal plane, a spatial resolution limit of 1.50±0.10 1p/mm (1σ) measured at the 4% level of the modulation transfer function of the system has been obtained. This result is consistent with the measurements of the full width at half‐maximum of the line spread function which is found to be 645±35 μm (1σ). Similarly, the intrinsic resolution of the CsI:Na scintillator only was found to be 6.5±0.5 1p/mm (1σ). Contrast ratio measurements, which are mainly determined by the quality of phosphor, have indicated a value of 12.1±0.6, whereas minimum visible details are observed at radiation exposure rates of 100 μR/s. This limit has been reduced to 10 μR/s using the single‐scan integrating option provided by the ICID camera. A maximum contrast resolution of 1% corresponding to 100 statistically significant meaningful gray levels is achieved at a maximum exposure rate of 1000 μR/s. Consequently, although the imaging capability of the present system compares favorably with that of conventional x‐ray video‐fluoroscopic systems, a better performance may be achieved by using a higher resolution cooled dual‐microchannel intensified CID camera in conjunction with a thinner CsI:Na crystal and a real‐time digital image processing subsystem.
Convective–dispersive characteristics of tracer transport calculated from transfer function analysis of biological indicator‐dilution curves
Authors: Palmer Bradley M. , McInerney Joseph J.
Published: March 2003

A solution to the convection–dispersion model of tracer transport in biological systems is presented. This solution provides for the characterization of tracer transport through a network of blood vessels based on the tracer transients recorded at the inlet and outlet points of the circulation under investigation. Fourier transformations of the transients are used to produce a transfer function from which the mean transit time as well as other transport characteristics can be calculated. The practical aspects of applying transfer function analysis to retrieve transport characteristics under experimental conditions are also presented. The application demonstrates the efficacy of the transfer function analysis method independent of tracer recirculation effects and a priori knowledge of actual tracer concentrations.
Optimization of parameters for fitting linear accelerator photon beams using a modified CBEAM model
Authors: Ayyangar Komanduri , Daftari Inder , Palta Jatinder , Suntharalingam Nagalingam
Published: March 2003

Measured beam profiles and central‐axis depth‐dose data for 6‐ and 25‐MV photon beams are used to generate a dose matrix which represents the full beam. A corresponding dose matrix is also calculated using the modified CBEAM model. The calculational model uses the usual set of three parameters to define the intensity at beam edges and the parameter that accounts for collimator transmission. An additional set of three parameters is used for the primary profile factor, expressed as a function of distance from the central axis. An optimization program has been adapted to automatically adjust these parameters to minimize the χ2 between the measured and calculated data. The average values of the parameters for small (6×6 cm2), medium (10×10 cm2), and large (20×20 cm2) field sizes are found to represent the beam adequately for all field sizes. The calculated and the measured doses at any point agree to within 2% for any field size in the range 4×4 to 40×40 cm2.
The use of carbon−loaded thermoluminescent dosimeters for the measurement of surface doses in megavoltage x‐ray beams
Authors: Thomas S. J. , Palmer N.
Published: March 2003

To determine the absorbed dose to the skin of patients undergoing radiotherapy with megavoltage radiations, it is necessary for the dose to be measured at shallow depths. This report assesses the suitability of carbon‐loaded thermoluminescent dosimetry (manufactured by Vinten Instruments Limited) for this purpose. Measurements have been made of the effective measurement depth of the dosimeters, the linearity with dose, and the variation of sensitivity within a batch. The variation of surface dose with incident angle of radiation for 5‐MV x rays has been measured using these disks; the results are compared with results obtained using a thin‐windowed ionization chamber.
An isodose shift technique for obliquely incident electron beams
Authors: Ulin Kenneth , Sternick Edward S.
Published: March 2003

It is well known that when an electron beam is incident obliquely on the surface of a phantom, the depth dose curve measured normal to the surface is shifted toward the surface. Based on geometrical arguments alone, the depth of the nth isodose line for an electron beam incident at an angle θ should be equal to the product of cos θ and the depth of the nth isodose line at normal incidence. This method, however, ignores the effects of scatter and can lead to significant errors in isodose placement for beams at large angles of incidence. A semi‐empirical functional relationship and a table of isodose shift factors have been developed with which one may easily calculate the depth of any isodose line for beams at incident angles of 0° to 60°. The isodose shift factors are tabulated in terms of beam energy (6–22 MeV) and isodose line (10%–90%) and are shown to be relatively independent of beam size and incident angle for angles <60°. Extensive measurements have been made on a Varian Clinac 2500 linear accelerator with a parallel‐plate chamber and polystyrene phantom. The dependence of the chamber response on beam angulation has been checked, and the scaling factor of the polystyrene phantom has been determined to be equal to 1.00.
Installation of an ambient‐temperature control system in a 1.5‐tesla whole body system to facilitate animal studies
Authors: Madden A. , Leach M. O.
Published: March 2003

An ambient‐temperature control system, designed to maintain small, anaesthetized animals at physiological temperatures during long examination times, is described. The system is suitable for installation in large bore, whole‐body magnets and can be positioned close to the animal under study. Design details and a description of the equipment used is given. The system proved to be satisfactory in maintaining mice at physiological temperatures.
Dose parameters of 125I and 192Ir seed sources
Authors: Weaver Keith A. , Smith Vernon , Huang David , Barnett Colleen , Schell Michael C. , Ling Clifton
Published: March 2003

As mandated by an NCI brachytherapy contract, we measured dosimetric parameters for 192Ir seeds and two models of 125I seeds. Measurements were with LiF powder in a water‐equivalent phantom. Data were corrected for background, sample mass, and finite detector volume. Selected parameters were also investigated through Monte Carlo calculations. Results are presented in terms of a dose parametrization that is described in detail, and are compared to published data. Our results agreed well with published data for relative quantities such as radial and angular dose dependence. Our measured value for the 192Ir dose factor was 4.55 cGy(H2O) cm2 mCi−1 h−1, also in good agreement with commonly used values. However, the measured dose factors for 125I seed models 6702 and 6711 were 1.18 and 1.06 cGy(H2O) cm2 mCi−1 h−1, values well below those in general use.
Design of apparatus for precise x‐ray dose chamber calibrations
Authors: Zeitz Louis , Schwar Robert , Miodownik Saul
Published: March 2003

An apparatus for precision calibration of ion chambers in the x‐ray region from 16 to 320 kV is described. The development of a fast‐acting shutter with “opening” and “closing” times of less than 3‐ms eliminates the requirement for operating time corrections. Controls from outside the radiation room permit changing x‐ray filters and alternately positioning both test and standard ion chambers in the x‐ray beam. Thus, the remote controls eliminate the need to enter the x‐ray room in the course of a series of calibrations. The potential advantages resulting from the capabilities of this apparatus are described in this Technical Report.
Radiation therapy and clinical physics practices in the midwest (1982–1986)
Authors: DeWerd Larry A. , Light Mary C. , Liss Margaret M. , Mesina Carmen F.
Published: March 2003

As a part of an on‐site physics review procedure, the Midwest Center for Radiological Physics (MWCRP) interviewed midwest clinical radiotherapy physicists and radiation therapists in institutions that participated in federally funded Cancer Control Programs. Information from 77 institutions was compiled regarding types of megavoltage units, daily patient load, radiotherapy personnel, treatment planning responsibilities, dosimetric practices, and treatment planning computers. Even though some practices, such as frequency of patient charge checks, were consistent throughout the midwest, other practices varied considerably such as patient load with the number of megavoltage units. This information may be useful either for planning a new facility, considering the needs for staff, or for comparing existing practices and responsibilities.
Electron dose calculation using multiple‐scattering theory: Thin planar inhomogeneities
Authors: Jette David , Lanzl Lawrence H. , Pagnamenta Antonio , Rozenfeld Martin , Bernard Damian , Kao Mark , Sabbas Albert M.
Published: March 2003

In this article in our series on electron dose calculation using multiple‐scattering theory, we apply the Fermi–Eyges theory to the problem of a thin planar inhomogeneity present in an otherwise‐layered medium. We derive expressions for the distribution function P and the location distribution L (which multiplied by the restricted mass collision stopping power is the dose directly deposited by the primary electrons) for various types of incident beams: a completely arbitrary distribution, a Gaussian point source, a pencil beam, an isotropic point source, and a broad parallel beam. We show how divergent‐beam dose distributions can be determined from parallel‐beam calculations, through use of equivalent configurations dependent upon the depth of dose calculation. Also, we indicate how this work can be applied to the design of wedges (or “compensators”) for beam shaping to provide desired dose distributions or to match juxtaposed radiation fields. Explicit formulas for thin plates are then worked out, and we examine the appearance of hot and cold spots distal to the edge of a localized inhomogeneity, for thin half‐slabs and for narrow strips. Finally, considering the case of a thin straight wedge‐shaped inhomogeneity, we theoretically discover the phenomenon of a “focused hot spot” without an accompanying cold spot, and suggest the design of a “multiple‐scattering lens”.
Tissue doses from radiotherapy of cancer of the uterine cervix
Authors: Stovall Marilyn , Smith Susan A. , Rosenstein Marvin
Published: March 2003

For use in an epidemiologic study of subsequent tumors, absorbed doses from brachytherapy and external beam radiotherapy were measured and calculated for various tissues of patients treated for cancer of the uterine cervix. External beams included orthovoltage x rays (1.9 and 3.0 mm Cu half‐value layer), cobalt‐60 gamma rays, 2 MV x rays, and 25 MV x rays. The brachytherapy sources were encapsulated radium. Measurements were made in an Alderson anthropomorphic phantom and a water phantom; calculations were made using a Monte Carlo technique or standard radiotherapy methods. Depending upon stage of disease and radiation energy, the absorbed doses (cGy) from typical treatment regimes to tissues of interest were: ovaries, 1400–5200; stomach, 130–320; kidneys, 120–310; pancreas, 100–260; lungs, 22–48; breasts, 19–52; thyroid, 6–17; salivary glands, 4–11; brain, 2–7, and total active bone marrow, 320–1100. The lower values of each range were for stage I of the disease.
Two interpolating filters for scatter estimation
Authors: Wagner Frederick C. , Macovski Albert , Nishimura Dwight G.
Published: March 2003

We have previously reported on a dual‐measurement sample‐and‐estimate technique for scatter correction. In this paper, we present a scatter‐correction technique that uses the previous sampling scheme but a different method of estimation. To provide samples of the scatter directly, an array of small, uniformly spaced lead disks is placed immediately before the object during only the first measurement. Interpolating from these samples we form an estimate of the scatter. We subtract this estimate from the second measurement to form a scatter‐corrected image. Previously, we used least‐squares interpolation to estimate the scatter. Because the samples are uniformly spaced, classical sampling theory motivated the investigation of interpolating filters for scatter estimation. To form the scatter image, we convolved the sample set with two different interpolating filters—a sinc function from classical sampling theory and a jinc function because the scatter function is radially symmetric. Using phantoms as objects, we applied both filters for scatter correction in vessel imaging and energy‐subtraction imaging. Initial corrected images contained an artifact attributed to aliasing. We modified the filter widths to reduce the aliasing. Although improvements in image quality were measured and the artifact was less pronounced, the artifact was still present. We present the phantom results obtained with this class of filters and discuss methods for its improved performance.
A review of mammography test objects for the calibration of resolution, contrast, and exposure
Authors: Kimme‐Smith Carolyn , Bassett Lawrence W. , Gold Richard H.
Published: March 2003

Mandated and voluntary accreditation and quality control programs for mammography require the use of standardized mammography test objects. We evaluated eleven commercially available test objects and three prototype test objects, comparing them with respect to their resolution targets, contrast targets, and the dose they required when imaged by the same automatic exposure meter. Ion chamber and/or thermoluminescent dosimeter measurements of exposure were made with each test object, while attenuation was measured for seven. Measurements of dosage using acrylic (5 test objects) and tissue equivalent epoxy (9 test objects) showed as much as a 400% variation in the radiation supplied by the same automatic exposure device when differences in thicknesses of test objects were normalized. Speck visibility was as dependent on the composition of the specks and of the surrounding material as on the size of the specks. Contrast targets were adequate in only three test objects. Optical density differences between images of a 4‐cm‐thick breast and of different test object materials, also 4 cm in thickness, exposed to the same radiation, imply that untested acrylic or epoxy resin materials should not used in the calibration of automatic exposure controls.
Effect of finite phosphor thickness on detective quantum efficiency
Authors: Nishikawa Robert M. , Yaffe Martin J. , Holmes R. B.
Published: March 2003

In this paper we describe theoretically the relationship between the finite thickness of a phosphor screen and its spatial‐frequency‐dependent detective quantum efficiency DQE(f). The finite thickness of the screen causes a variation in both the total number of light quanta emitted from the screen in a burst from a given x‐ray interaction and in the spatial distribution of the quanta within the light burst [i.e., shape or point spread function (PSF) of the light burst]. The variation in magnitude of the burst gives rise to a spatial‐frequency‐independent reduction in DQE, characterized by the scintillation efficiency AS. The variation in PSF causes a roll off in DQE with increasing spatial frequency which we have characterized by the function RC (f). Both AS and RC (f) can be determined from the moments of the distribution of the spatial Fourier spectrum of light bursts emitted from the phosphor and thus they are related: AS is a scaling factor for RC (f). Our theory predicts that it is necessary for all light bursts which appear at the output to have the same magnitude to maximize AS and the same shape to maximize RC (f). These requirements can lead to the result that the fluorescent screen with the highest modulation transfer function will not necessarily have the highest DQE(f) even at high spatial frequencies.
Measurement of replacement factors for a parallel‐plate chamber
Authors: Goswami Ganesh C. , Kase Kenneth R.
Published: March 2003

We have measured the replacement correction factors (Prepl) for a PTW/Markus parallel plate chamber at mean incident electron energies of 3.1, 4.4, 8.9, 13.0, 16.3, and 18.8 MeV. The factors are significantly different from unity at low energies.
The dosimetric properties of an intraoperative radiation therapy applicator system for a Mevatron‐80
Authors: Nelson Charles E. , Cook Richard , Rakfal Susan
Published: March 2003

An applicator system for intraoperative radiation therapy has been fabricated which does not require physical docking with the accelerator. A dosimetric study has been completed which documents the properties of this system for a variety of electron beam energies, applicator sizes, collimator settings, both primary and secondary, and source–surface distance (SSD) settings. Sensitivity of the system to common misalignment errors was also determined. Results indicate (a) applicator leakage of less than 5%, (b) beam flatness to within plus or minus 5% at the dMAX with a single primary collimator setting, (c) smooth changes in output with cone size, beam energy and SSD, and (d) negligible changes in dose distributions within alignment errors permitted by the system.
Scatter factor corrections for elongated fields
Authors: Higgins P. D. , Sohn W. H. , Sibata C. H. , McCarthy W. A.
Published: March 2003

Measurements have been made to determine scatter factor corrections for elongated fields of Cobalt‐60 and for nominal linear accelerator energies of 6 MV (Siemens Mevatron 67) and 18 MV (AECL Therac 20). It was found that for every energy the collimator scatter factor varies by 2% or more as the field length‐to‐width ratio increases beyond 3:1. The phantom scatter factor is independent of which collimator pair is elongated at these energies. For 18 MV photons it was found that the collimator scatter factor is complicated by field‐size‐dependent backscatter into the beam monitor.
Optimization of the wedge filter parameters for a radiotherapy treatment planning system
Authors: Willemse C. A. , Duvenage J. , Lötter M. G. , Minnaar P. C. , Goedhals L.
Published: March 2003

When a treatment planning system uses an empirical or semianalytical approach to describe the influence of a wedge filter on a photon beam, a number of experimentally determined parameters are required. These may be found from direct measurement. However, if the beam model is sensitive to the parameters, it will be necessary to optimize the parameter values to obtain better correspondence between dose profiles calculated by the model and actual measured profiles. The procedure is time consuming if optimization is done manually. We have developed an optimization scheme, using a personal computer, to find the set of wedge parameters which will result in the best fit of calculated wedge profiles (using the beam model of the treatment planning system) to measured wedge profiles. The procedure is efficient and calculated profiles were found to match measured profiles to within 2% of the central axis value.
An optimal synthetic aperture for circular tomosynthesis
Authors: Ruttimann Urs E. , Qi Xiang‐lin , Webber Richard L.
Published: March 2003

In circular tomosynthesis obtained from a sufficient number of radiographs with projection directions forming a single cone, object detail at a distance from the plane of interest is blurred according to the zero order Bessel function. The main lobe of this window function defines slice thickness, while its ringing side lobes are undesirable because they permit further outlying structures to “leak” through. Using the orthogonality of Bessel functions, a sampling scheme consisting of multiple, concentric projection cones was designed to synthesize by a finite Fourier‐Bessel series a slice window with superior side lobe suppression. The window that concentrates the most “energy” within a finite slice, and can be realized by a limited number of sampling cones, is the zero order circular prolate spheroidal function. Its application to tomosynthesis of 3 mm thick slices with a characteristic detail size of 0.5 mm, concentrated 95% of the total series expansion to only 3 concentric circular scans, yielding a theoretical suppression of the first side lobe of −38 dB, to be compared to −8 dB achieved with the Bessel function. Experimental implementation of this optimal sampling scheme using 3, 8, and 14 projection views, distributed over cones with opening half‐anges of 1.92, 4.39, and 6.88°, respectively, resulted in a side‐lobe attenuation of at least −20 dB. This attenuation reduced significantly artifacts arising from out‐of‐plane detail of high spatial frequency (e.g., edges) in tomosynthetic images of clinical interest in dentistry.
A video‐based patient contour acquisition system for the design of radiotherapy compensators
Authors: Andrew J. W. , Aldrich J. E. , Hale M. E. , Berry J. A.
Published: March 2003

Recent advances in computer and video technology have enabled significant advances in the field of surface topography measurement. This paper will describe a digital video patient contour acquisition system for the design of radiotherapy beam compensators. The system is mounted on a tray which slides into the collimator of a radiotherapy simulator. The tray holds a source which projects a 1‐mm wide fan beam of light along the simulator beam axis onto the patient. The tray also holds a small solid state video camera which views the projected line of light on the patient surface. Video images are digitized and processed on an 80386 based IBM PC‐compatible computer. Transverse contours are obtained from one digitized video image or, in case of opposed fields, from two or more image frames taken at different gantry angles. Entire surfaces are measured by scanning the bed longitudinally and acquiring a number of transverse contours. Posterior surfaces are obtained by scanning a mold. A printer produces a template for making the compensator from sheet lead.
In vivo measurement of cortical bone lead using polarized x rays
Authors: Wielopolski L. , Rosen J. F. , Slatkin D. N. , Zhang R. , Kalef‐Ezra J. A. , Rothman J. C. , Maryanski M. , Jenks S. T.
Published: March 2003

An x‐ray fluorescence system which utilizes polarized radiation to measure lead in vivo in human subjects is described. The minimum detection limit is approximately 6.4 ppm wet weight lead in the cortex of the tibia with 4 mm of overlying soft tissue. This appears to be adequate for assessing lead stores in lead‐toxic preschool children. The measurement requires 16.5 min and is associated with an effective equivalent whole body dose to the subject of 2.5 μSv. The system, its calibration and its validation are described herein.
Radionuclide synthetic Fourier images of cardiac wall motion abnormalities
Authors: Sychra Jerry J. , Pavel Dan G. , Olea Enrique
Published: March 2003

At present, the phase images together with amplitude images are used in nuclear medicine to aid the diagnosis of cardiac regional wall motion abnormalities (RWMA). The phase images represent the spatial distribution of the relative phase of the first harmonic fit of pixel time activity curves, and the amplitude images represent the distribution of the amplitude of the fit. These images contain only part of the information present in the original radionuclide images, and have to be mentally integrated with other known information to obtain a diagnosis. The proposed synthetic Fourier images overcome these deficiencies as their pixel intensity is a function of additional Fourier parameters of pixel time activity curves and of pixel location and are not limited to the first harmonic. But most importantly, their computation is based on “teaching” the computer by examples of previously diagnosed cases. The images offer direct and robust diagnosis which is superior to that derived from separate phase and amplitude images, especially for the detection of mild RWMA.
The effect of breast composition on absorbed dose and image contrast
Authors: Skubic Stanley E. , Fatouros Panos P.
Published: March 2003

We have studied the effect of breast composition on the average whole breast dose, average glandular dose, and image contrast in mammography, using both computational and experimental methods. Three glandular/adipose compositions were considered: 30/70, 50/50, and 70/30 by weight, for both 3‐ and 5‐cm breast thickness. Absorbed dose was found to increase with greater glandular content and this increase is more pronounced for thick breasts and softer beams. For typical screen–film x‐ray beams, the average dose to a highly glandular breast is nearly twice the dose to a highly adipose breast and the average glandular dose about 40% higher. Dose was reduced when higher energy beams were employed. The use of a grid increased the dose by a factor of 2.0 to 2.6. Finally, the measured image contrast decreases with increasing breast glandularity, to a greater extent in small breasts and when low energy beams were employed.
System for digital acquisition of gastrointestinal images
Authors: Rowlands J. A. , Hynes D. M. , Edmonds E. W.
Published: March 2003

Previous theoretical work and clinical experience with digital acquisition of fluoroscopic images have identified several problems which needed to be solved. These are: image resolution; blurring due to patient motion, combined with long exposure times; and excessive x‐ray quantum mottle levels. We will show that application of pulsed progressive readout (PPR) methods to the TV camera solves these problems. By permitting a high‐intensity x‐ray pulse to be delivered, all motion is stopped and quantum mottle is reduced to acceptable levels. It will be shown that 1024×1024 digital matrices provide adequate resolution and 8‐bit digitization is sufficient to permit the same quality as is used in conventional 100‐mm photofluorography. User acceptance can be made easier by incorporation of existing photofluorographic controls (with which the radiologist is already familiar) to acquire the digital images. It is possible to interface PPR video systems using existing 100‐mm exposure circuits without much modification and the resulting system can be regarded as a digital 100‐mm camera.
A study of motion in gastrointestinal x‐ray fluoroscopy
Authors: Nguyen T. C. , Rowlands J. A.
Published: March 2003

Studying motion in the gastrointestinal (G.I.) tract is the first step towards our goal of designing a digital algorithm for real‐time noise and motion blurring reduction by temporal and spatial averaging in x‐ray fluoroscopy. The present work concerns the types of motion relevant to G.I. fluoroscopy (e.g., motion of the walls of the oesophagus, the stomach, the small intestine, and the colon), and measurement of the range of velocities in different parts of the G.I. tract from tape recorded fluoroscopic sequences. The relationship between image contrast and velocity, the effects of motion on system response, and in particular the influence of these parameters on the evaluation of velocities will also be discussed.
Collapsed cone convolution of radiant energy for photon dose calculation in heterogeneous media
Authors: Ahnesjö Anders
Published: March 2003

A method for photon beam dose calculations is described. The primary photon beam is raytraced through the patient, and the distribution of total radiant energy released into the patient is calculated. Polyenergetic energy deposition kernels are calculated from the spectrum of the beam, using a database of monoenergetic kernels. It is shown that the polyenergetic kernels can be analytically described with high precision by {A exp(−ar)+B exp(−br)}/r2, where A, a, B, and b depend on the angle with respect to the impinging photons and the accelerating potential, and r is the radial distance. Numerical values of A, a, B, and b are derived and used to convolve energy deposition kernels with the total energy released per unit mass (TERMA) to yield dose distributions. The convolution is facilitated by the introduction of the collapsed cone approximation. In this approximation, all energy released into coaxial cones of equal solid angle, from volume elements on the cone axis, is rectilinearly transported, attenuated, and deposited in elements on the axis. Scaling of the kernels is implicitly done during the convolution procedure to fully account for inhomogeneities present in the irradiated volume. The number of computational operations needed to compute the dose with the method is proportional to the number of calculation points. The method is tested for five accelerating potentials; 4, 6, 10, 15, and 24 MV, and applied to two geometries; one is a stack of slabs of tissue media, and the other is a mediastinum‐like phantom of cork and water. In these geometries, the EGS4 Monte Carlo system has been used to generate reference dose distributions with which the dose computed with the collapsed cone convolution method is compared. Generally, the agreement between the methods is excellent. Deviations are observed in situations of lateral charged particle disequilibrium in low density media, however, but the result is superior compared to that of the generalized Batho method.
Temperature measurements during ultrasound hyperthermia
Authors: Hynynen K. , Edwards D. K.
Published: March 2003

In this study the ultrasonic field distortions and the temperature measurement errors caused by temperature sensing probes were investigated. It was found that probes with diameters equal to or greater than 1/2 of the square root of the wavelength (λ) scatter and reflect the waves, and thus distort the field significantly. Smaller probes down to λ1/2/5 in diameter had a detectable effect which was very local and, therefore, will probably not have a significant effect on the overall temperature distribution. When the temperature measurement errors were studied, even the smallest probes showed some self‐heating artifact and its magnitude depended on the probe size, material, structure, orientation, and the operating frequency. This error was small with most of the nonultrasound absorbing probes (such as bare wires or stainless steel needle probes), but significant with plastic shielded thermocouples. The energy absorption associated with plastic coated probes can be reduced by orienting the probe parallel to the beam, by scanning the focus in such a manner that the focus is not passing on the sensor, and by inserting the probe in a stainless steel catheter. The temperature measurement error can also be reduced by covering the plastic probe with a high‐ (or low‐) acoustical impedance material around the sensor. This would scatter the sound around the probe, thus preventing energy absorption in the plastic. This arrangement can preserve the desirable properties of plastic probes (mainly flexibility, strength, and electrical isolation from the patient) while at the same time allowing fairly absorption artifact free measurements.
Contrast enhancement of noisy images by windowing: Limitations due to the finite dynamic range of the display system
Authors: Metz Charles E. , Chan Heang‐Ping , Doi Kunio , Shen Jong‐Her
Published: March 2003

A theoretical model has been developed to explain the effects of simple linear windowing on the apparent contrasts of signals in displayed digital images. The model predicts, and experimental results demonstrate, that the effective displayed contrast of a digital radiographic signal depends in a complex way upon interactions among the endpoints of the display scale, the signal contrast and noise level of the original data, the window center and display center selected, and the contrast enhancement factor applied. The results obtained from this work apply quantitatively to the highly idealized situation in which (i) a uniform signal is superimposed on a uniform background containing Gaussian pixel‐value noise, and (ii) a linear (or exponential) relationship exists between the optical density of a film display (or the light intensity of a luminous display) and pixel value in some finite range. However, the qualitative effects demonstrated here may be expected to arise in a broad variety of situations involving strong digital contrast enhancement.
Hybrid reconstruction algorithm for x‐ray computed tomography
Authors: Waggener R. , Lee M. , Mickish D. , Lange J. , Feldmeier J.
Published: March 2003

A hybrid reconstruction algorithm (HRA) is derived for fan beam geometry for use with systems utilizing a linear array of detectors. The algorithm uses fan beam geometry with a modified parallel beam reconstruction formula. The parallel beam algorithm is used with fan beam geometry by a simple geometric conversion and a different back projection formula. Correction for center of rotation shift is done during the back projection. Computer simulations are shown, both with the center of rotation shift uncorrected and corrected.
Accuracy and reproducibility of image derived relaxation times on a clinical 1.5 T magnetic resonance scanner
Authors: Masterson M. E. , McGary R. , Schmitt K. , Koutcher J. A.
Published: March 2003

A methodology for evaluating the accuracy and reproducibility of calculated T1's and T2's has been developed and applied to a General Electric 1.5 T Signa System. Specifically studied were absolute accuracy and temporal stability of image derived T1's and T2's as well as the dependence of calculated relaxation times on position in the scan plane, position along the axis of the magnet bore, the scan plane orientation (axial, sagittal, coronal), and the center frequency. The results of this study of the accuracy and reproducibility of image relaxation times have direct bearing on the design of clinical investigations assessing the diagnostic usefulness of these values.
Fast Fourier transform convolution calculations of x‐ray isodose distributions in homogeneous media
Authors: Boyer Arthur L. , Zhu Yunping , Wang Lisa , Francois Pascal
Published: March 2003

Convolution concepts were implemented using the discrete fast Fourier transform (FFT) to model the three‐dimensional dose distribution due to x‐rays produced by a medical linear accelerator. Convolution kernels were employed that had been calculated by Mackie using the EGS4 Monte Carlo code. The EGS4 code was also used to estimate initially the spectrum by simulating the production, filtering, and flattening of the beam in the collimator of the linear accelerator. The continuous bremsstrahlung spectrum was modeled using five discrete energies. The more subtle field‐size effects of collimator scattering on the spectrum were obtained by calculating corrections to the spectral components using a least‐squares search technique. Dose distributions were obtained using FFT convolutions of the kernels for each energy with the spectrally weighted fluence distributions for that energy. The dose distributions were compared with isodose distributions measured in a water phantom. The agreement was generally found to be better than 1% on the central axis. The calculation time for a single three‐dimensional beam was ∼20 min using a VAX/750 without an array processor. Methods were explored to reduce the calculation time using similar hardware, and estimates were made of how to reduce the calculation time using a more sophisticated computer system.
Application of the dyadic Green's function method to calculate the heat generated by a direct contact applicator
Authors: Kassaee A. , Pandey L. N. , Rustgi M. L.
Published: March 2003

A rigorous formalism using the dyadic Green's function to determine the relative heating pattern in a two‐layer fat–muscle medium of a dipole‐corner reflector applicator in direct contact with the finite fat layer is described. The results are compared with the earlier approximate calculations of Guy and Lehmann. Though the two theories give identical results for the relative heat produced in the muscle layer, the relative heating patterns predicted by the present theory in the fat layer are different.
A slice geometry phantom for cross sectional tomographic imagers
Authors: Coffey C. W. , Taylor R. , Umstead G.
Published: March 2003

This investigation presents the design and fabrication of a magnetic resonance imaging (MRI) test phantom for determining slice thickness, slice adjacency, slice offset, and slice angulation. This test phantom is a three‐dimensional conic section of MRI image producing material; proper orientation allows analysis in each of the major imaging planes. The phantom design (geometrical configuration) incorporates both theoretical and quantitative methodologies. The necessary mathematical analyses are both simple and rapid. In addition, this phantom has been successfully used to assess the image slice parameters for computed tomography (CT) scanners and single photon emission computed tomography (SPECT) imaging systems. Slice profile parameter results, full width at half maximum (FWHM), from this phantom design are compared with conventional methods.
Correction of phase wrapping in magnetic resonance imaging
Authors: Axel Leon , Morton Daniel
Published: March 2003

In phase reconstruction MR imaging, e.g., for velocity measurement, phase shifts beyond ±π radians will “wrap around” to smaller apparent phases. Such large phase shifts could arise either due to large background (non‐flow‐related) phase variations or due to large velocity‐induced phase shifts. For sufficiently smooth phase variation, such discontinuities can be automatically recognized and corrected, thus restoring the correct phase values and extending the effective dynamic range of such phase imaging techniques.
Measurement of the restricted linear energy transfer of stray radiation close to the treatment volume of 12 and 18 MeV clinical photon beams
Authors: Makrigiorgos G. , Antonadou D. , Proukakis C. , Throuvalas N.
Published: March 2003

The restricted dose mean linear energy transfer (LET) (L̄500,D) of the stray radiation field a few centimeters outside the treatment volume has been measured for 12 and 18 MV photons produced by a clinical Therac‐20 (AECL) accelerator. The measurements were performed as a function of field size and distance from the edge of the treatment volume, using the method of the high‐pressure ionization chamber. Contrary to what was found in a previous investigation for a clinical Co‐60 unit and despite the presence of photoneutrons (in the case of 18 MV photons), the L̄500,D outside the beam does not increase significantly relative to the L̄500,D of the primary beam.
Input of treatment planning data via a video frame grabber
Authors: Amols Howard I.
Published: March 2003

Video frame grabbers are powerful devices which perform rapid conversion of video images into digital format for subsequent computer processing. Recently, the cost of these devices has become competitive with sonic and magnetic digitizing tablets commonly used in radiation therapy treatment planning. Frame grabbers, plus all associated hardware/software can be interfaced to a variety of personal or microcomputers, and allow input of irregular treatment field and patient contour data into standard treatment planning systems. Such a system is described, which offers advantages of speed, accuracy, and resolution as compared to more conventional digitizing systems.