Biomedical subjects

J M Boone

Publications and source records attributed to J M Boone.

At least 19 recordsLinked to original sources

PubMed2004

Normal organ volume assessment from abdominal CT.

We determined the normal distribution of abdominal organ volumes measured from abdominal computed tomographic (CT) images. A total of 149 adult abdominal CT studies were selected, and 711 organs (388 from males, 323 from females) were outlined by hand on each CT image by using a computer. More than 18000 organ outlines were traced. The organs studied included left and right kidneys, left and right adrenals, spleen, pancreas, and liver, and the first lumbar vertebrae was also evaluated. Using the known pixel size and section thickness, organ volumes were computed. Organ volumes were corrected for height and weight for each sex. The normal and cumulative normal distributions for each organ studied were computed, demonstrating the range of organ volumes for each sex that exist in the normal adult population. Organ volumes ranged from a mean of 4.4 mL (female left adrenal) to 1710 mL (male liver). Mean organ volumes were 64.4, 156.5, 179.8, and 1411 mL for the female pancreas, kidneys, spleen, and liver, respectively. Corresponding male volumes were 87.4, 193.1, 238.4, and 1710 mL, respectively. Tabular data are provided that indicate the relative size for each organ volume in terms of the cumulative probability distribution. Normative data are provided to allow physicians to estimate where in the normal range a particular organ volume lays. Organ volumes may be useful as quantitative indices of pathologic conditions.

Abdomen↗

PubMed2004

A comprehensive analysis of DgN(CT) coefficients for pendant-geometry cone-beam breast computed tomography.

The use of a computed tomography (CT) scanner specifically designed for breast imaging has been proposed by several investigators. In this study, the radiation dose due to breast CT was evaluated using Monte Carlo techniques over a range of parameters pertinent to the cone-beam pendant geometry thought to be most appropriate. Monte Carlo dose computations were validated by comparison with physical measurements made on a prototype breast CT scanner under development in our laboratory. The Monte Carlo results were then used to study the influence of cone angle, the use of a beam flattening ("bow-tie") filter, glandular fraction, breast length and source-to-isocenter distance. These parameters were studied over a range of breast diameters from 10 to 18 cm, and for both monoenergetic (8-140 keV by 1 keV intervals) and polyenergetic x-ray beams (30-100 kVp by 5 kVp intervals. Half value layer at 80 kVp = 5.3 mm Al). A parameter referring to the normalized glandular dose in CT (DgN(CT)) was defined which is the ratio of the glandular dose in the breast to the air kerma at isocenter. There was no significant difference (p = 0.743) between physically measured and Monte Carlo derived results. Fan angle, source-to-isocenter distance, and breast length have relatively small influences on the radiation dose in breast CT. Glandular fraction (0% versus 100%) for 10 cm breasts at 80 kVp had approximately a 10% effect on DgN(CT), and a 20% effect was observed for an 18 cm breast diameter. The use of a bow-tie filter had the potential to reduce breast dose by approximately 40%. X-ray beam energy and breast diameter had significant influence on the DgN(CT) parameters, with higher DgN(CT) values for higher energy beams and smaller breast diameters. DgN(CT) values (mGy/mGy) at 80 kVp ranged from 0.95 for an 8 cm diam 50% glandular breast to 0.78 for an 18 cm 50% glandular breast. The results of this investigation should be useful for those interested computing the glandular breast dose for geometries relevant to dedicated breast CT.

Breast↗

PubMed2004

Cassette-based digital mammography.

Over the past several years, digital mammography systems have been installed clinically across North America in small but growing numbers. A photostimulable phosphor-based full-field digital mammography image was evaluated in this investigation. Commonly known as computed radiography (CR), its use closely mimics the screen-film mammography paradigm. System performance using modulation transfer function (MTF) and detective quantum efficiency (DQE) metrics show MTF(2.5 mm(-1)) = 0.5, DQE(2.5 mm(-1)) = 0.3, and MTF(5.0 mm(-1)) = 0.2, DQE(5.0 mm(-1)) = 0.05, for a 26 kVp beam, 0.03 mm molybdenum tube filtration, 4.5 cm tissue attenuation, and 15 mR incident exposure to the detector. Slightly higher DQE values were measured at 32 kVp with 0.025 mm rhodium tube filtration. CR mammography advantages include the ability to use existing mammography machines, where multiple rooms can be converted to "digital" operation, which allows overall cost savings compared to integrated digital mammography systems. Chief disadvantages include the labor-intensive handling of the cassettes prior to and after the imaging exam, lack of a direct interface to the x-ray system for recording technique parameters, and relatively slow processing time. Clinical experience in an IRB-approved research trial has suggested that digital mammography with photostimulable storage phosphors and a dedicated CR reader is a viable alternative to conventional screen-film mammography.

Breast Neoplasms↗

PubMed2001

Determination of the presampled MTF in computed tomography.

A technique for measuring the presampled MTF in CT scanners is described. The technique uses a simple phantom consisting of approximately 0.050 mm aluminum foil sandwiched by flat plastic or tissue-equivalent slabs. The aluminum foil is slightly angled with respect to the reconstruction matrix, and CT images are acquired. The acquired CT image yields an angled slit image that can be used to synthesize the presampled line spread function (LSF). The presampled MTF is calculated from the presampled LSF. The technique is a direct extension of that proposed by Fujita et al. [IEEE Trans. Med. Imaging 11, 34-39 (1992)] for MTF calculation on digital radiography images. While the MTF in clinical CT scanners often reaches negligible amplitude below the Nyquist frequency, the technique is easy to implement, requires inexpensive materials, is robust to aliasing, and is more resilient to noise due to greater data averaging than conventional PSF-integration techniques. Use of the proposed technique is illustrated on a clinical multiple detector array scanner, and MTFs are shown for several common reconstruction kernels. It is likely that the proposed technique would be useful for all tomographic imaging systems, including single photon emission computed tomography, positron emission tomography, magnetic resonance imaging and ultrasound scanners.

Models, Statistical↗

PubMed2001

Dedicated breast CT: radiation dose and image quality evaluation.

PURPOSE: To evaluate the feasibility of breast computed tomography (CT) in terms of radiation dose and image quality. MATERIALS AND METHODS: Validated Monte Carlo simulation techniques were used to estimate the average glandular dose (AGD). The calculated photon fluence at the detector for high-quality abdominal CT (120 kVp, 300 mAs, 5-mm section thickness) was the benchmark for assessing the milliampere seconds and corresponding radiation dose necessary for breast CT. Image noise was measured by using a 10-cm-diameter cylinder imaged with a clinical CT scanner at 10-300 mAs for 80, 100, and 120 kVp. A cadaveric breast was imaged in the coronal plane to approximate the acquisition geometry of a proposed breast CT scanner. RESULTS: The AGD for 80-kVp breast CT was comparable to that for two-view mammography of 5-cm breasts (compressed breast thickness). For thicker breasts, the breast CT dose was about one-third less than that for two-view mammography. The maximum dose at mammography assessed in 1-mm(3) voxels was far higher (20.0 mGy) than that at breast CT (5.4 mGy) for a typical 5-cm 50% glandular breast. CT images of an 8-cm cadaveric breast (AGD, 6.3 mGy) were subjectively superior to digital mammograms (AGD, 10.1 mGy) of the same specimen. CONCLUSION: The potential of high signal-to-noise ratio images with low anatomic noise, which are obtainable at dose levels comparable to those for mammography, suggests that dedicated breast CT should be studied further for its potential in breast cancer screening and diagnosis.

Breast↗

PubMed2000

The role of percutaneous biopsy in detection of pancreatic transplant rejection.

The purpose of this study was to investigate the effectiveness and safety of percutaneous pancreatic transplant biopsy guided by ultrasound alone or with a combination of computerized tomography (CT) for pancreas localization and ultrasound for needle placement. We also compare our finding on the use of 18-gauge and 20-gauge needles for percutaneous pancreatic transplant biopsy. In 42 attempted biopsies performed on 21 patients, two different imaging modalities were used. Twenty-seven attempted biopsies were performed under the guidance of ultrasound alone, and 15 used a combination of ultrasound and CT. Of the 27 ultrasound-guided biopsies. 24 produced at least one sample adequate for histopathological analysis for an 89% biopsy success rate. Of the 15 biopsies guided by combined ultrasound and CT, 11 produced adequate samples for a 73% success rate. For all biopsies, an 83% success rate was found. In assessing the use of 18-gauge versus 20-gauge needles, 86 out of 110 tissue cores were adequate for histopathological analysis for a 78% yield. In 27 biopsy attempts using the 18-gauge needle, 75 tissue cores were obtained, for an average of 2.8 cores per biopsy. Fifty-seven pancreas samples collected using the 18-gauge needle were adequate for pathological evaluation for a 76% yield. With 15 biopsy attempts using the 20-gauge needle, 35 tissue cores were collected, for an average of 2.3 cores per biopsy. Twenty-nine pancreas specimens obtained from using the 20-gauge needle were adequate for analysis for an 83% yield. No major complications occurred. Only one incidence of minor complication was reported for a 2% complication rate. The only complication was local, mild bleeding at the biopsy site in one case. Air within the transplant pancreas as revealed by post-biopsy scans and streaky density appearing adjacent to the biopsy site occurred in a total of four cases and were not included. No complications were reported that required any invasive intervention. We conclude that percutaneous biopsy guided by ultrasound is a safe, simple, and effective method to detect pancreatic transplant rejection. Our results for biopsies compare favorably with other reported techniques in terms of effectiveness, complication rates, and ease of use. With its high success rate and low complications, ultrasound-guided percutaneous biopsy is an excellent method to sample pancreatic transplant.

Adult↗

PubMed2000

Scatter/primary in mammography: Monte Carlo validation.

The purpose of this investigation was to compare and validate the performance of the SIERRA Monte Carlo simulation routines for the analysis of the scatter to primary ratio (SPR) in the mammography setting. Two Monte Carlo simulation methods were addressed, the direct method was a straightforward and geometrically accurate simulation procedure, and the convolution method uses idealized geometry (monoenergetic, normally incident delta function input to the scattering medium) to produce scatter point spread functions (PSFs). The PSFs were weighted by the x-ray spectrum of interest and convolved with the field of view to estimate SPR values. The SPR results of both Monte Carlo procedures were extensively compared to five published sources, including Monte-Carlo-derived and physically measured SPR assessments. The direct method demonstrated an overall agreement with the literature of 3.7% accuracy (N=5), and the convolution method demonstrated an average of 7.1% accuracy (N=14). The comparisons were made over a range of parameters which included field of view, phantom thickness, x-ray energy, and phantom composition. Limitations of the beam stop method were also discussed. The results suggest that the SIERRA Monte Carlo routines produce accurate SPR calculations and may be useful for a more comprehensive study of scatter in mammography.

Dose-Response Relationship, Radiation↗

PubMed2000

Monte Carlo assessment of computed tomography dose to tissue adjacent to the scanned volume.

The assessment of the radiation dose to internal organs or to an embryo or fetus is required on occasion for risk assessment or for comparing imaging studies. Limited resources hinder the ability to accurately assess the radiation dose received to locations outside the tissue volume actually scanned during computed tomography (CT). The purpose of this study was to assess peripheral doses and provide tabular data for dose evaluation. Validated Monte Carlo simulation techniques were used to compute the dose distribution along the length of water-equivalent cylindrical phantoms, 16 and 32 cm in diameter. For further validation, comparisons between physically measured and Monte Carlo-derived air kerma profiles were performed and showed excellent (1% to 2%) agreement. Polyenergetic x-ray spectra at 80, 100, 120, and 140 kVp with beam shaping filters were studied. Using 10(8) simulated photons input to the cylinders perpendicular to their long axis, line spread functions (LSF) of the dose distribution were determined at three depths in the cylinders (center, mid-depth, and surface). The LSF data were then used with appropriate mathematics to compute dose distributions along the long axis of the cylinder. The dose distributions resulting from helical (pitch = 1.0) scans and axial scans were approximately equivalent. Beyond about 3 cm from the edge of the CT scanned tissue volume, the fall-off of radiation dose was exponential. A series of tables normalized at 100 milliampere seconds (mAs) were produced which allow the straight-forward assessment of dose within and peripheral to the CT scanned volume. The tables should be useful for medical physicists and radiologists in the estimation of dose to sites beyond the edge of the CT scanned volume.

Computer Simulation↗

PubMed2000

Scatter/primary in mammography: comprehensive results.

Monte Carlo procedures using the SIERRA code (validated in a companion article) were used to investigate the scatter properties in mammography. The scatter to primary ratio (SPR) was used for quantifying scatter levels as a function of beam spectrum, position in the field, air gap, breast thickness, tissue composition, and the area of the field of view (FOV). The geometry of slot scan mammography was also simulated, and SPR values were calculated as a function of slot width. The influence of large air gaps (to 30 cm) was also studied in the context of magnification mammography. X-ray energy and tissue composition from 100% adipose to 100% glandular demonstrated little effect on the SPR. Air gaps over a range from 0 to 30 mm showed only slight effects. The SPR increased with increased breast thickness and with larger fields of view. Measurements from 82 mammograms provided estimates of the range of compressed breast thickness (median: 5.2 cm, 95% range: 2.4 cm to 7.9 cm) and projected breast area onto the film (left craniocaudal view, median: 146 cm2, 95% range: 58 cm2 to 298 cm2). SPR values for semicircular breast shapes, Mo/Mo spectra, and a 15 mm air gap were parametrized as a function of breast thickness and (semicircular) breast diameter. With the coefficients a = - 2.35452817439093, b = 22.3960980055927, and c = 8.85064260299289, the equation SPR= [a + b x (diameter in cm)--(-1.5) + c x (thickness in cm) --(-0.5)]-- -1 produces SPR data from 2 to 8 cm and from 3 to 30 cm breast diameters with an average error of about 1%.

Air↗

PubMed2000

A lesion detectability simulation method for digital x-ray imaging.

A simulation method is described in this work that aids in quantifying the upper limits of lesion detectability as a function of lesion size, lesion contrast, pixel size, and x-ray exposure for digital x-ray imaging systems. The method entails random lesion placement with subsequent simulated imaging on idealized x-ray detectors with no additive noise and 100% quantum detective efficiency. Lesions of different size and thickness were simulated. Mean (expectation) lesion signal-to-noise ratios (LSNRs) were calculated and receiver operating characteristic (ROC) curves were constructed based on LSNR ensembles. Mean (expectation) values of the areas under the ROC curves were calculated for lesions of varying size on pixel arrays of varying size at different exposures. Analyses were performed across several parameters, including lesion size, pixel size, and exposure levels representative of various areas of radiography. As expected, lesion detectability increased with lesion size, contrast, pixel size, and exposure. The model suggests that lesion detectability is strongly dependent on the relative alignment (phase) of the lesion with the pixel matrix for lesions on the order of the pixel size.

Biophysical Phenomena↗

PubMed2000

An edge spread technique for measurement of the scatter-to-primary ratio in mammography.

An experimental measurement technique that directly measures the magnitude and spatial distribution of scatter in relation to primary radiation is presented in this work. The technique involves the acquisition of magnified edge spread function (ESF) images with and without scattering material present. The ESFs are normalized and subtracted to yield scatter-to-primary ratios (SPRs), along with the spatial distributions of scatter and primary radiation. Mammography is used as the modality to demonstrate the ESF method, which is applicable to all radiographic environments. Sets of three images were acquired with a modified clinical mammography system employing a flat panel detector for 2, 4, 6, and 8 cm thick breast tissue equivalent material phantoms composed of 0%, 43%, and 100% glandular tissue at four different kV settings. Beam stop measurements of scatter were used to validate the ESF methodology. There was good agreement of the mean SPRs between the beam stop and ESF methods. There was good precision in the ESF-determined SPRs with a coefficient of variation on the order of 5%. SPRs ranged from 0.2 to 2.0 and were effectively independent of energy for clinically realistic kVps. The measured SPRs for 2, 4, and 6 cm 0% glandular phantoms imaged at 28 kV were 0.21+/-0.01, 0.39+/-0.01, and 0.57+/-0.02, respectively. The measured SPRs for 2, 4, and 6 cm 43% glandular phantoms imaged at 28 kV were 0.20+/-0.01, 0.35+/-0.02, and 0.53+/-0.02, respectively. The measured SPRs for 2, 4, and 6 cm 100% glandular phantoms imaged at 28 kV were 0.22+/-0.02, 0.42+/-0.03, and 0.88+/-0.08, respectively.

Biophysical Phenomena↗

PubMed2000

Monte Carlo validation in diagnostic radiological imaging.

Monte Carlo analysis in the radiological sciences has been used for several decades, however with the ever-increasing power of desktop computers, the utility of Monte Carlo simulation is increasing. A Monte Carlo code called the Simple Investigative Environment for Radiological Research Applications (SIERRA) is described mathematically, and is then compared against an array of published and unpublished results determined by other means. A series of 32 comparisons between data sets, 22 from independent Monte Carlo simulations and 10 from physically measured data, were assessed. The compared parameters included depth dose curves, lateral energy scattering profiles, scatter to primary ratios, normalized glandular doses, angular scattering distributions, and computed tomography dose index (CTDI) values. Three of the 32 comparison data sets were excluded as they were identified as outliers. Of the remaining 29 data sets compared, the mean differences ranged from -14.8% to +17.2%, and the average of the mean differences was 0.12% (sigma = 1.64%), and the median difference was 1.57%. Fifty percent of the comparisons showed mean differences of approximately 5% or less, and 93% of the comparisons showed mean differences of 12% or less. We conclude that for research applications in diagnostic radiology, the SIERRA Monte Carlo code demonstrates accuracy and precision to well within acceptable levels.

Biophysical Phenomena↗

PubMed1999

A Monte Carlo study of x-ray fluorescence in x-ray detectors.

Advances in digital x-ray detector systems have led to a renewed interest in the performance of x-ray phosphors and other detector materials. Indirect flat panel x-ray detector and charged coupled device (CCD) systems require a more technologically challenging geometry, whereby the x-ray beam is incident on the front side of the scintillator, and the light produced must diffuse to the back surface of the screen to reach the photoreceptor. Direct detector systems based on selenium have also enjoyed a growing interest, both commercially and academically. Monte Carlo simulation techniques were used to study the x-ray scattering (Rayleigh and Compton) and the more prevalent x-ray fluorescence properties of seven different x-ray detector materials, Gd2O2S, CsI, Se, BaFBr, YTaO4, CaWO4, and ThO2. The redistribution of x-ray energy, back towards the x-ray source, in a forward direction through the detector, and lateral reabsorption in the detector was computed under monoenergetic conditions (1 keV to 130 keV by 1 keV intervals) with five detector thicknesses, 30, 60, 90, 120, and 150 mg/cm2 (Se was studied from 30 to 1000 mg/cm2). The radial distribution (related to the point spread function) of reabsorbed x-ray energy was also determined. Representative results are as follows: At 55 keV, more (31.3%) of the incident x-ray energy escaped from a 90 mg/cm2Gd2O2S detector than was absorbed (27.9%). Approximately 1% of the total absorbed energy was reabsorbed greater than 0.5 mm from the primary interaction, for 90 mg/cm2 CsI exposed at 100 kVp. The ratio of reabsorbed secondary (fluorescence + scatter) radiation to the primary radiation absorbed in the detectors (90 mg/cm2) (S/P) was determined as 10%, 16%, 2%, 12%, 3%, 3%, and 0.3% for a 100 kVp tungsten anode x-ray spectrum, for the Gd2O2S, CsI, Se, BaFBr, YTaO4, CaWO4, and ThO2 detectors, respectively. The results indicate significant x-ray fluorescent escape and reabsorption in common x-ray detectors. These findings suggest that x-ray fluorescent radiation redistribution should be considered in the design of digital x-ray imaging systems.

Biophysical Phenomena↗

PubMed1999

A multiple detector array helical x-ray microtomography system for specimen imaging.

An x-ray computed microtomography system for specimen and small animal imaging was built and tested. The system used seventeen 48-microm-wide detector arrays (a charge coupled device camera) and helical acquisition techniques. Images were acquired using 540 rays/view and 400 views/2pi. The modulation transfer function (MTF) of the computed tomography images demonstrated 50 microm limiting resolution, with MTF > 10% for objects larger than 60 microm (approximately 8.3 cycles/mm). While soft tissue discrimination was compromised by a low signal-to-noise ratio, equine medullary bone core samples and the murine skeleton were well visualized. The incorporation of multiple detector arrays provided a 17-fold improvement in x-ray efficiency, which is a very important step toward improving the potential of microtomography as a scientific tool.

Algorithms↗

PubMed1999

Glandular breast dose for monoenergetic and high-energy X-ray beams: Monte Carlo assessment.

PURPOSE: To extend the utility of normalized glandular dose (DgN) calculations to higher x-ray energies (up to 120 keV) and to provide the tools for investigators to calculate DgN values for arbitrary mammographic and x-ray spectra. MATERIALS AND METHODS: Validated Monte Carlo methods were used to assess DgN values. One million x-ray photons (1-120 keV, in 1-keV increments) were input to a semicircular breast geometry of thicknesses from 2 to 12 cm and breast compositions from 0% to 100% glandular. DgN values for monoenergetic (1-120 keV) x-ray beams, polyenergetic (40-120 kV, tungsten anode) x-ray spectra, and polyenergetic mammographic spectra were computed. Skin thicknesses of 4-5 mm were used. RESULTS: The calculated DgN values were in agreement within approximately 1%-6% with previously published data, depending on breast composition. DgN tables were constructed for a variety of x-ray tube anode-filter combinations, including molybdenum anode-molybdenum filter, molybdenum anode-rhodium filter, rhodium anode-rhodium filter, tungsten anode-rhodium filter, tungsten anode-palladium filter, and tungsten anode-silver filter. DgN values also were graphed for monoenergetic beams to 120 keV and for general diagnostic x-ray beams to 120 kV. CONCLUSION: The tables and graphs may be useful for optimizing mammographic procedures. The higher energy data may be useful for investigations of the potential of dual-energy mammography or for calculation of dose in general diagnostic or computed tomographic procedures.

Breast↗

PubMed1998

A breast density index for digital mammograms based on radiologists' ranking.

The purpose of this study was to develop and evaluate a computerized method of calculating a breast density index (BDI) from digitized mammograms that was designed specifically to model radiologists' perception of breast density. A set of 153 pairs of digitized mammograms (cranio-caudal, CC, and mediolateral oblique, MLO, views) were acquired and preprocessed to reduce detector biases. The sets of mammograms were ordered on an ordinal scale (a scale based only on relative rank-ordering) by two radiologists, and a cardinal (an absolute numerical score) BDI value was calculated from the ordinal ranks. The images were also assigned cardinal BDI values by the radiologists in a subsequent session. Six mathematical features (including fractal dimension and others) were calculated from the digital mammograms, and were used in conjunction with single value decomposition and multiple linear regression to calculate a computerized BDI. The linear correlation coefficient between different ordinal ranking sessions were as follows: intraradiologist intraprojection (CC/CC): r = 0.978; intraradiologist interprojection (CC/MLO): r = 0.960; and interradiologist intraprojection (CC/CC): r = 0.968. A separate breast density index was derived from three separate ordinal rankings by one radiologist (two with CC views, one with the MLO view). The computer derived BDI had a correlation coefficient (r) of 0.907 with the radiologists' ordinal BDI. A comparison between radiologists using a cardinal scoring system (which is closest to how radiologists actually evaluate breast density) showed r = 0.914. A breast density index calculated by a computer but modeled after radiologist perception of breast density may be valuable in objectively measuring breast density. Such a metric may prove valuable in numerous areas, including breast cancer risk assessment and in evaluating screening techniques specifically designed to improve imaging of the dense breast.

Algorithms↗

PubMed1998

Angiographic film subtraction using a laser digitizer and computer processing.

Digital subtraction angiography has been accepted as an invaluable clinical tool over the past decade; however, film-screen-based angiography is still performed routinely when high-resolution or large field-of-view angiograms are needed. A technique is presented whereby two films from an angiographic sequence are digitized using a high-resolution laser digitizer, and the digitized images are aligned, subtracted, and displayed using the computer. To accommodate for some types of patient motion, an image warping algorithm is presented and discussed in detail. The warping algorithm is piecewise linear, using triangular regions for warping, resulting in a global nonlinear transform across triangle elements. An algorithm describing optimal triangle selection also is discussed. The results show that subtraction images of excellent quality can be produced by the proposed technique, and suggest that, in some settings, digitized subtraction films may be preferred over conventional film subtraction.

Angiography, Digital Subtraction↗

PubMed1998

Mammography spectrum measurement using an x-ray diffraction device.

The use of a diffraction spectrometer developed by Deslattes for the determination of mammographic kV is extended to the measurement of accurate, relative x-ray spectra. Raw x-ray spectra (photon fluence versus energy) are determined by passing an x-ray beam through a bent quartz diffraction crystal, and the diffracted x-rays are detected by an x-ray intensifying screen coupled to a charge coupled device. Two nonlinear correction procedures, one operating on the energy axis and the other operating on the fluence axis, are described and performed on measured x-ray spectra. The corrected x-ray spectra are compared against tabulated x-ray spectra measured under nearly identical conditions. Results indicate that the current device is capable of producing accurate relative x-ray spectral measurements in the energy region from 12 keV to 40 keV, which represents most of the screen-film mammography energy range. Twelve keV is the low-energy cut-off, due to the design geometry of the device. The spectrometer was also used to determine the energy-dependent x-ray mass attenuation coefficients for aluminium, with excellent results in the 12-30 keV range. Additional utility of the device for accurately determining the attenuation characteristics of various normal and abnormal breast tissues and phantom substitutes is anticipated.

Biophysical Phenomena↗