bluuebunny/crossref_metadata_2025 huggingface dataset:
Increased neutron penetration in partially deuterated water: Application to neutron capture therapy
Authors: Kiszenick W. , Fairchild R. G. , Slatkin D. N. , Zubal G.
Published: August 2003

Theoretically, partial deuteration of body water should allow significantly increased neutron penetration in tissue. To evaluate the possible usefulness of partially deuterated water in neutron capture therapy (NCT), neutron flux density distributions were measured in a 23×16.5 cm (length×diameter) cylinder for incident thermal and epithermal neutron beams, at 20 and 40 at. % deuteration of water. Relative to neutron flux densities in nondeuterated water, flux densities increased significantly with increasing depth and increasing levels of deuteration. For example, at a depth of 6 cm, flux density was increased ∼20% to 50% for 20 to 40 at. % deuteration. In a clinical situation, this would increase tumor dose by ∼30%. Further benefits include the reduced hydrogen neutron capture and the chemical radioprotective effects of partial deuteration for photon radiation
The effect of the momentum transfer on the sensitivity of a photon scattering method for the characterization of tissues
Authors: Leichter I. , Karellas A. , Craven J. D. , Greenfield M. A.
Published: August 2003

The ratio of coherent to Compton photons scattered by a tissuelike material depends on its effective atomic number. This ratio can, therefore, be used for the in vivo characterization of tissues. The intrinsic sensitivity of this measurement is defined as the change in the coherent‐to‐Compton ratio for a given change in the atomic number. The effect of the scatter angle on the sensitivity has already been described by us in a paper recently submitted to this journal. In this study, the dependence of the sensitivity on the energy of the incident photons is investigated in two ways. The first approach is quasitheoretical and is based on computations of the cross sections of the coherent and Compton scattering for various energies. The second approach is experimental and it involves the measurement of the scatter ratio from a series of K2HPO4 solutions for three primary photon energies: 60, 81, and 140 keV. The combined effect of both the photon energy and the scatter angle on the sensitivity can be described by a single parameter which is the momentum transfer. It is concluded that for the limited range of the atomic numbers which apply to trabecular bone (8≤Z̄≤11) the momentum transfer reflects completely the effect of the scatter angle and photon energy on the sensitivity.
Studies of x‐ray energy absorption and quantum noise properties of x‐ray screens by use of Monte Carlo simulation
Authors: Chan Heang‐Ping , Doi Kunio
Published: August 2003

The imaging properties of the phosphor layer in fluorescent screens or image intensifiers are related to its x‐ray absorption characteristics. In this study, we applied Monte Carlo methods for the simulation of x‐ray photon diffusion in a phosphor layer. The K‐reabsorption factor, absorbed x‐ray energy, quantum absorption efficiency, statistical factor, and noise‐equivalent absorption were determined as a function of the incident energy and angle of the x rays for eight commonly used phosphor layers. These basic physical quantities will be useful for the prediction of the information transfer properties of a phosphor layer.
Radiographic image subtraction in gas ionography
Authors: Fallone B. G. , Podgorsak E. B.
Published: August 2003

The feasibility of radiographic image subtraction based on electrostatic imaging techniques is demonstrated. Ionographic latent images are essentially foil electrets with surface charge densities modulated by x‐ray transmission through the object. Latent image charging at one polarity corresponding to the production of the primary image, and latent image discharging with the opposite polarity, are used to create the final latent image representing the region of interest. The technique is simple and could be in its present form applied to industrial radiography. Using high‐pressure xenon ionographic chambers, the technique could be developed into a clinical tool as an inexpensive alternative to conventional digital radiography.
A simple model combining quantum noise and anatomical variation in radiographs
Authors: Ruttimann Urs E. , Webber Richard L.
Published: August 2003

A model is presented for the detection of uniform focal lesions by means of an ideal photon detector. The difference of observed photons between an area overlaying the embedded lesion and an adjacent reference area of equal size constitutes the signal to be detected. Application of ROC analysis reveals that the exact probability distribution of this photon count difference can be approximated well by a Gaussian, on condition that modulation <0.1 and signal‐to‐noise ratio (SNR)>1. Moreover, within these constraints, SNR emerged as the more salient parameter characterizing detection performance. It is shown that in the absence of anatomical variation, lesions of arbitrarily small size may be detected at any prescribed level of confidence, provided one is willing to accept the required high photon exposure. The effect of anatomical variation on detection performance is conveniently demonstrated in a graph of SNR versus exposure. There, two global regions are identified, each characterized by an asymptote, corresponding to either photon‐limited or photon‐saturated imaging. Under the first condition, quantum fluctuations are dominating the noise, and thus, detection performance is influenced by the photon exposure. Under the second, anatomical variations limit the SNR to an upper value, irrespective of exposure magnitude. Data obtained from dental radiographs demonstrate that anatomical variation is amenable to experimental measurement, and that it sets the upper limit for the SNR achievable in the diagnostic task of detecting incipient carious lesions.
The effect of counting system deadtime on thyroid uptake measurements
Authors: Simpkin Douglas J.
Published: August 2003

Equations are derived and the results of numerical calculations shown that illustrate the effect of counting system deadtime on measured thyroid uptake of radioiodine. It is predicted that the observed uptake is higher than the true uptake due to system deadtime. This is shown for both paralyzing and nonparalyzing deadtime. The effect of increasing the administered activity is shown to increase the measured uptake, in a manner predicted by the paralyzable and nonparalyzable deadtime models.
Neutrons from high‐energy x‐ray medical accelerators: An estimate of risk to the radiotherapy patient
Authors: Nath Ravinder , Epp Edward R. , Laughlin John S. , Swanson William P. , Bond Victor P.
Published: August 2003

The problem of neutrons produced by many of the high‐energy x‐ray therapy machines (10 MV and above) is reviewed, and the possible risk their presence poses to radiotherapy patients is estimated. A review of the regulatory background containing a summary of the recommendations of the U. S. Council of State Governments (USCSG), and of the International Electro‐Technical Commission (IEC), as well as an indication that recommendations will be forthcoming from the National Council on Radiation Protection (NCRP) and the International Commission of Radiological Protection (ICRP) is presented. The neutrons in question are produced by high‐energy photons (x rays) incident on the various materials of the target, flattening filter, collimators, and other essential components of the equipment. The neutron yield (per treatment dose) increases rapidly as the megavoltage is increased from 10 to 20 MV, but remains approximately constant above this. Measurements and calculations of the quantity, quality, and spatial distribution of these neutrons and their concomitant dose are summarized. Values of the neutron dose are presented as entrance dose, midline dose (10‐cm depth), and integral dose, both within and outside of the treatment volume. These values are much less than the unavoidable photon doses which are largely responsible for treatment side effects. For typical equipment, the average neutron integral dose from accelerator‐produced neutrons is about 4–7 g cGy (per treatment cGy), depending on the treatment plan. This translates into an average dose of neutrons [averaged over the body of a typical 70‐kg (154 1b) patient] of 0.06–0.10 cGy for a treatment of 1000 cGy. Using these neutron doses and the best available neutron risk coefficients, it is estimated that 50×10−6 fatal malignancies per year due to the neutrons may follow a typical treatment course of 5000 rads of 25‐MV x rays. This is only about 1/60th of the average incidence of malignancies for the general population. Thus, the cancer risk to the radiotherapy patient from accelerator‐produced neutrons poses an additional risk to the patient that is negligible in comparison.
Analytic calculation of electron beam isodose distributions
Authors: Nelson C. E. , Haneman W. , Young K. , O'Foghludha F.
Published: August 2003

Analytical techniques have been developed to generate electron beam isodose distributions from a modest set of experimental data. These techniques include (1) development of a compact yet powerful linear least‐squares optimization program with a graphic display of the results, (2) coordinate transformations to allow straightforward fitting of the isodose distributions with simple polynomial functions, and (3) accurate interpolation methods to allow production of treatment planning dose matrices. The program, written in fortran, has been implemented on a minicomputer and uses the standard peripherals of a commercially available treatment planning system (AECL TP‐11). The computer‐generated isodose and central‐axis distributions correspond very closely with the data for electron energies from 5 to 20 MeV and for all field sizes.
Microdosimetry of 10–15 MeV bremsstrahlung x rays
Authors: Amols H. I. , Zellmer D. L.
Published: August 2003

Experimental techniques have been developed for obtaining microdosimetric spectra on a hospital‐based linear accelerator. Teletherapy beams of 10 and 15 MeV bremsstrahlung x rays from a Varian Clinac‐18 and Clinac‐20, respectively, have been produced at ultralow dose rates (50–200 μGy/h) which enables direct measurements of lineal energy distributions with a conventional Rossi‐type gas proportional counter. Extensive measurements have been made to insure that the dosimetric properties of these low dose rate beams are nearly identical to those produced under high dose rate clinical conditions. Analytical procedures have been developed to correct measured lineal energy spectra for pileup caused by the low duty factor of the linear accelerator. The lineal energy spectra of these megavoltage beams differ significantly from Co‐60, with dose averaged lineal energies (ȳD) being 20%–30% lower than for Co‐60. Although such differences may not be important at clinical doses, the theory of dual radiation action does predict a lower biological effectiveness for these beams at very low dose levels.
Noise reduction methods for hybrid subtraction
Authors: Nishimura Dwight G. , Macovski Albert , Brody William R.
Published: August 2003

In digital subtraction angiography, hybrid subtraction provides selective vessel images free of soft‐tissue motion artifacts but with a lower signal‐to‐noise ratio (SNR) than temporal subtraction images. An image processing method called measurement‐dependent filtering has been developed to enhance the SNR of hybrid images without losing resolution or selectivity. Linear combinations of four images consisting of a pre‐ and postcontrast dual‐energy measurement pair form both the hybrid image and a lower noise but less selective vessel image. The noise‐reduced image is derived by combining the low‐frequency components of the hybrid image with the high‐frequency components of the lower noise image in a variety of ways. The results of the filtering method, when tested on both phantom and clinical data, display images with about the same degree of conspicuity as the hybrid image and a SNR approaching that of the temporal image.
Image quality and dose in computerized tomography: Evaluation of four CT scanners
Authors: Borasi G. , Castellani G. , Domenichini R. , Franchini M. , Granata M. , Torresin A. , Tosi G.
Published: August 2003

Spatial resolution, statistical noise, and patient dose are important parameters for the evaluation of the performances of computerized tomography (CT) scanners. These parameters are combined to develop some “synthetic indices,” and to be able to describe intrinsic properties of a CT scanner (the maximum obtainable spatial resolution and dose efficiency). This type of analysis has been applied to the evaluation of four CT scanners, three of third, and one of fourth generation.
Measurement of dose distribution around Fletcher–Suit–Delcos colpostats using a Therados radiation field analyzer (RFA‐3)
Authors: Ling C. Clifton , Spiro Ira J. , Kubiatowicz David O. , Gergen James , Peksens Richard K. , Bennett J. Douglas , Gagnon William F.
Published: August 2003

Using a small silicon diode and the Therados RFA‐3 automated dosimetry system, the relative dose distribution around Fletcher–Suit–Delcos colpostats was measured. Thermoluminescent dosimeters (LiF) were used for absorbed dose measurements. These data provide the basis for computerized dose calculations which will account for the attenuation effects of the rectal and bladder shieldings. The stainless‐steel housing attenuated the radiation of a Cs‐137 source by 6%. The tungsten shields caused a further dose reduction of 15%–25%.
Image quality of an analog radiation therapy simulator‐based tomographic scanner
Authors: Kijewski Marie Foley , Judy Philip F. , Svensson Goran K.
Published: August 2003

The spatial resolution and noise level of images produced by a commercial analog tomographic scanner have been measured and compared to those of images reconstructed digitally from projections from the same detector. The full width at half maximum of the line spread function was 3.6 mm for images from the analog scanner and 1.1 mm for the digitally reconstructed images. The standard deviation of the CT numbers over a 10‐cm2 circular area at the center of a large water phantom, calculated as a percentage of the linear attenuation coefficient of water, was 3.5% for the analog images, 15.4% for high‐resolution digital images, and 3.2% for digital images reconstructed using a convolution filter which reduced the resolution to that of the analog images. The data contributing to each digital image were fewer than those contributing to each analog image by a factor of 10. The noise level did not depend on tube current in either the analog or the digital images. The utility of this analog device in radiation therapy planning will depend upon whether errors in contour localization resulting from transferring data from diagnostic CT scanners exceed the errors due to its poorer image quality.
Calculation of surface dose in rotational total skin electron irradiation
Authors: Pla C. , Heese R. , Pla M. , Podgorsak E. B.
Published: August 2003

A single‐field rotational total skin electron irradiation technique has recently been developed at the McGill University for treatment of skin malignancies. The dose received by a given surface point during rotation in a uniform large electron field depends on the radius of rotation of the surface point, on the local radius of curvature of the contour in the vicinity of the point of interest, and on the shadows cast by limbs (arms upon trunk or head and neck, and legs upon each other). A method for calculating the surface dose distribution on a patient is presented accounting for the various parameters affecting the dose. A series of measurements were performed with polystyrene and a humanoid phantom, and an excellent agreement between measured and calculated dose distributions was obtained.
A review of normal tissue hydrogen NMR relaxation times and relaxation mechanisms from 1–100 MHz: Dependence on tissue type, NMR frequency, temperature, species, excision, and age
Authors: Bottomley Paul A. , Foster Thomas H. , Argersinger Raymond E. , Pfeifer Leah M.
Published: August 2003

The longitudinal (T1) and transverse (T2) hydrogen (1H) nuclear magnetic resonance (NMR) relaxation times of normal human and animal tissue in the frequency range 1–100 MHz are compiled and reviewed as a function of tissue type, NMR frequency, temperature, species, in vivo versus in vitro status, time after excision, and age. The dominant observed factors affecting T1 are tissue type and NMR frequency (ν). All tissue frequency dispersions can be fitted to the simple expression T1=AνB in the range 1–100 MHz, with A and B tissue‐dependent constants. This equation provides as good or better fit to the data as previous more complex formulas. T2 is found to be multicomponent, essentially independent of NMR frequency, and dependent mainly on tissue type. Mean and raw values of T1 and T2 for each tissue are tabulated and/or plotted versus frequency and the fitting parameters A, B and the standard deviations determined to establish the normal range of relaxation times applicable to NMR imaging. The mechanisms for tissue NMR relaxation are reviewed with reference to the fast exchange two state (FETS) model of water in biological systems, and an overview of the dynamic state of water and macromolecular hydrogen compatible with the frequency, temperature, and multicomponent data is postulated. This suggests that 1H tissue T1 is determined predominantly by intermolecular (possibly rotational) interactions between macromolecules and a single bound hydration layer, and the T2 is governed mainly by exchange diffusion of water between the bound layer and a free water phase. Deficiencies in measurement techniques are identified as major sources of data irreproducibility.
Performance characteristics of A150 plastic‐equivalent gases in A150 plastic proportional counters for 14.8‐MeV neutrons
Authors: DeLuca Paul M. , Schell M. C. , Pearson D. W. , Higgins P. D. , Attix F. H.
Published: August 2003

Two recently developed A150 plastic‐equivalent gas mixtures have been tested for suitability in proportional counter applications. Methane‐ and propane‐based “tissue‐equivalent” gases were also included for comparison purposes. Event‐size weighted dose distributions were measured in a 14.8‐MeV neutron beam. Resolution was found to be independent of gas mixture. Moreover the gains of the two A150 mixtures were the same, and comparable to that of the methane‐based gas mixture. The ionization yield per event size was also independent of the hydrogenous gas mixture employed. Neutron doses determined with the proportional counter were in reasonable agreement with those obtained from an ionization chamber.
Photonuclear activation ratios in fluorine compounds; an index of bremsstrahlung quality
Authors: Prado K. L. , Anderson D. W.
Published: August 2003

Samples of potassium hexafluorosilicate (K2SiF6) and polytetrafluoroethylene (C2F4)n were irradiated in the bremsstrahlung beam from a clinical linear electron accelerator at integral values of endpoint energy between 13 and 32 MeV. Sample positron activities produced by the reactions 39K(γ, n) 38K, 19F(γ, n) 18F, and 12C(γ, n)11C, were determined by counting the gamma radiation. Saturation activities per target nucleus were calculated from these data. For the K2SiF6 samples, the photonuclear activation ratio (PAR) of the 7.6 min 39K saturation activity per nucleus divided by the 18F result increased by more than 20% per MeV between 15 and 21 MeV. For the (C2F4)n samples the ratio (PAR) of the 11C saturation activity per nucleus to that for 18F increased by more than 24% per MeV between 22 and 26 MeV. Quality changes caused by the lead flattening filter were easily detectable using the PAR technique. Because of the high sensitivity to bremsstrahlung spectrum changes these PAR values can serve as sensitive indices of quality for high‐energy beams.
Radiation dose in diagnostic radiology: Monte Carlo simulation studies
Authors: Chan Heang‐Ping , Doi Kunio
Published: August 2003

We applied Monte Carlo calculations to determine the radiation dose absorbed in water phantoms. Monoenergetic incident x‐ray beams with energies from 15 to 100 keV and phantom thicknesses from 5 to 20 cm were considered in this study. We calculated the spatial distributions of energy absorption in the phantom, the rad/R conversion factors, the average rad/R conversion factors, and the scatter‐to‐primary ratios of absorbed dose. We also compared the relative absorbed doses under various imaging conditions when the transmitted radiation produced a given optical density on radiographic film. The information provided will be useful for the estimation of radiation doses in various radiographic procedures.
Analysis of physical parameters associated with the measurement of high‐energy x‐ray penumbra
Authors: Dawson D. J. , Harper J. M. , Akinradewo A. C.
Published: August 2003

The effect of dosemeter type and configuration on the measured penumbral distribution for Co‐60, 6‐MV, and 31‐MV x rays has been determined in air using equilibrium buildup caps for three commercial detection systems including a silicon diode and two ionization chambers. The diode is shown to be measuring a different parameter in the penumbral region than the ionization chambers. This fact in combination with the lateral spread of the secondary electrons and the difference in the inside diameters of the ionization chambers results in significant differences between the measured beam penumbra. The latter effect is studied in more detail with a series of specially designed ionization chambers of varying inside diameter from 0.3 to 1.4 cm. A theoretical model is described which resolves these differences, indicates a method to determine the true penumbral primary‐dose distribution and introduces the concept of an effective diameter for the ionometric measurement of high‐energy x‐ray penumbra. Recommendations are made concerning the dosemeters of choice for penumbral measurements over this range of photon energies.
Neutron leakage measurements from a medical linear accelerator
Authors: Palta Jatinder R. , Hogstrom Kenneth R. , Tannanonta Chirapha
Published: August 2003

The McCall method has been used to measure neutron leakage from the Mevatron 77, 18‐ and 15‐MV photon beams. Gold foil activation has been used employing a beta counting technique for the 18‐MV beam and a gamma counting technique for both the 18‐ and 15‐MV beam. The two counting techniques were used to evaluate their relative merit. The measurements were made at various locations in the patient‐treatment plane for different field sizes. The results show that the thermal‐neutron dose equivalent contributes only about 1%–2% of the total neutron dose equivalent. At 100 cm, the neutron dose equivalent for the 18‐MV beam is approximately six times that of the 15‐MV beam, slightly exceeding the 0.1% of the useful beam criteria used by some of the regulatory agencies. In light of the uncertainty in fluence to dose equivalent conversion factors, the increased dose equivalent above 0.1% is insignificant.
Image noise reduction on the EMI 7070 CT scanner by the reduction of the noise resident in the CT wedge profiles
Authors: Mott David J.
Published: August 2003

On the EMI 7070 CT scanner the data contained in the wedge files has been averaged resulting in a 6% reduction in the noise content of images. This noise reduction can either be used to improve image quality or can be offset by reducing the x‐ray tube current by 12%. The averaging method will be outlined and its rationale discussed.
Demonstration of relatively new electron dosimetry measurement techniques on the Mevatron 80
Authors: Meyer Jeffrey A. , Palta Jatinder R. , Hogstrom Kenneth R.
Published: August 2003

A comprehensive set of electron dosimetry measurements at 7, 10, 12, 15, and 18 MeV was made on a Mevatron 80. Dosimetry measurements presented include percentage depth dose, dose in the buildup region, field size dependence of output, output at extended distances, lead transmission measurements, and isodose curves. These beam measurements are presented to document the electron beam characteristics of this linear accelerator. Three relatively new dosimetry techniques, which have not been standardly used in the past, are illustrated. One technique determines the depth dose of fields too small to measure. A second technique accurately converts depth dose measured in polystyrene to depth dose in water. A third technique calculates the output at extended distances.
The density scaling theorem applied to lateral electronic equilibrium
Authors: O'Connor J. E.
Published: August 2003

Some theoretical considerations concerning the application of the density scaling theorem to secondary electrons from high‐energy x‐ray beams are discussed. It is concluded that the theorem is expected to be applicable with acceptable accuracy for 10‐MV x‐ray beams in low‐density materials. Measurements reported by different groups of workers are discussed and shown to be in general agreement with the theorem, with one exception. It is shown that the theorem can be applied in combination with phantom scattering correction factors to calculate the dose in homogeneous bodies which differ from water in their density. The method of calculation is similar to the equivalent tissue–air ratio method, but takes account of the effects of loss of lateral electronic equilibrium.
The effects of CT drift on xenon/CT measurement of regional cerebral blood flow
Authors: Kearfott K. J. , Lu H. C. , Rottenberg D. A. , Deck M. D. F.
Published: August 2003

A systematic increase in computed tomography (CT) number of approximately 0.13 Hounsfield unit per scan (HU/scan) was observed when serial DeltaScan 2020 CT scans of a uniform water phantom were equally spaced at 0.5, 1.0, or 2.0 min and a shaped aluminum beam‐hardening filter was employed. Much smaller drifts (<0.06 HU/scan) were observed with flat aluminum or shaped beryllium oxide filters. This machine drift, which was not associated with a rise in water phantom temperature and did not consistently correlate with estimated x‐ray tube heat, could result in a significant overestimation of regional cerebral blood flow (rCBF) for a xenon/CT rCBF protocol involving 5–7 sequential scans obtained at 1‐min interscan intervals.
Derivation of gamma variate indicator dilution function from simple convective dispersion model of blood flow
Authors: Harpen Michael D. , Lecklitner Myron L.
Published: August 2003

The gamma variate function, commonly used to analyze time–activity curves obtained in nuclear medicine flow studies, is shown to be related to the solution to the differential equation obtained from a one‐dimensional convective dispersive model of blood flow.
A scanning‐slit x‐ray videoabsorptiometric technique for bone mineral measurement
Authors: Dobbins James T. , Pedersen Per L. , Mazess Richard B. , Cameron John R. , Hansen Jorgen L. , Hefner Lance V.
Published: August 2003

An x‐ray videoabsorptiometric technique was developed for measurement of bone mineral content (BMC) in vivo. The principle utility of this technique is the precise measurement of commonly fractured bones, such as the femoral neck, that are difficult to measure by other techniques because of repositioning problems. Scanning slits reduce scattered radiation and improve linearity of measurements. Heavily filtered, high‐kVp beams are used to minimize errors from beam hardening, and data renormalization is employed to compensate for spatial nonuniformities of the beam and detector. Linearity of measured BMC over the range 0.8 to 5 g/cm2 is very good (r=0.998) and compares well to single‐ and dual‐photon absorptiometry. A 1.6% change in measured BMC is observed for a 10% change (∼2 cm) in tissue thickness while a 10% change in marrow type causes a 0.6%–0.8% change in BMC. Manual repositioning of a femur phantom revealed a variation of 0.84% over ten measurements when femur values were referenced to standards. A computer repositioning algorithm provides much easier identification of the region for analysis and yields comparable variation (0.9%).
A simple derivation of Ngas, a correction in Awall, and other comments on the AAPM Task Group 21 protocol
Authors: Attix F. H.
Published: August 2003

The new AAPM Task Group 21 dosimetry protocol is a useful document that will no doubt result in improved accuracy in radiotherapy beam standardization when it is generally understood and widely adopted. It does however, require some “debugging.” The present paper clarifies the derivation of Ngas, points out an error in the Awall data, and discusses the impracticality of applying the gradient approach in correcting for ion chamber perturbation of dose in phantoms irradiated by electron beams.
A xenon ionization detector for scanned projection radiography: Xenon/Freon 13B1 comparison
Authors: Drost D. J. , Mehuys D. , Fenster A.
Published: August 2003

In a companion paper, we reported on the construction and testing of a xenon gas ionization detector for use in line scanned projection radiography. Experimental results indicate that the detector has sufficient resolution for chest radiography, but higher resolution is required for mammography. Theoretical analysis suggested that a detector pressurized with Freon 13B1 would have better resolution and higher x‐ray energy efficiency than a xenon‐filled detector for energies below 60 keV. In this paper we compared, theoretically and experimentally, Freon 13B1 to xenon as the detector gas. For a 120‐kVp x‐ray spectrum, the detector filled with 2.0 MPa of xenon had less channel‐to‐channel crosstalk, a higher quantum efficiency (QE), and twice the output signal than the detector filled with 1.4 MPa of Freon (highest possible pressure at room temperature), while for a 60‐kVp spectrum, crosstalk is the same, but the detector has slightly higher QE and 1.4 times the energy efficiency when filled with Freon instead of xenon. We conclude that xenon is better for high‐kVp imaging, while Freon at a lower pressure is slightly better for low‐kVp imaging.
Investigation of basic imaging properties in digital radiography. I. Modulation transfer function
Authors: Giger Maryellen Lissak , Doi Kunio
Published: August 2003

The effect of various digital parameters, such as the sampling aperture, sampling distance, and display aperture, on the modulation transfer function (MTF) of digital radiographic imaging systems was investigated by means of theoretical simulation studies. The MTFs were also determined experimentally to confirm the relationship used in the simulation studies. The results indicate that the overall MTF of a digital system cannot specify the resolution properties in the same way as can the MTFs of analog systems. The MTF of a digital system may include a “false” response due to aliasing, which could lead to an incorrect interpretation of the resolution properties. The magnitude of aliasing that will occur in a digitized signal depends on the sampling parameters chosen and on the frequency content of the radiologic object being imaged. Thus, the type of object to be detected as well as various digital parameters must be considered in the design and evaluation of digital imaging systems.
A photodiode array x‐ray imaging system for digital angiography
Authors: Cunningham I. A. , Fenster A.
Published: August 2003

A line scanning imaging system that can be used to make low‐noise x‐ray images to detect low‐contrast structure is described. The system makes use of a 1024‐element, self‐scanning, photodiode array (Reticon RL 1024S) optically coupled to an x‐ray image intensifier tube. Low‐noise images are obtained by imaging only small areas of interest at a time to reduce the noise resulting from the detection of scattered radiation, and by making use of the very large dynamic range (8000:1) solid‐state photodetector. Some performance characteristics of the diode array system are discussed. It was found that while sensitivities of individual elements differed by up to ±15% from the average, they could be corrected with a precision of 0.02% to 0.04% of the maximum signal. The limiting spatial resolution of the system in the direction of the diode array was 2.0 cycles/mm, limited by the image intensifier. The system linearity was studied by measuring the attenuation of a monoenergetic x‐ray beam by Plexiglas. The measured attenuation agreed with the expected exponential decrease over a range of approximately 1000 to within experimental error. The imaging capabilities of the system were demonstrated by imaging an angiographic phantom consisting of an iodine‐filled tube with an asymmetric 20% stenosis. The stenosis was oriented on the tube surface furthermost from the detector resulting in an image with a 2% radiographic contrast change but no decrease of the tube width. The stenosis was clearly imaged using a temporal subtraction technique.
Collimator‐produced energy degradation of megavoltage x rays
Authors: Amols H. I. , Rubin A. , Peck R. A.
Published: August 2003

Monte Carlo computer calculations have been made to assess the effects of small collimators (i.e., output field sizes ≤1 cm) on megavoltage x‐ray beams. Such collimators are often used in experiments to measure beam energy, half value layers, and other beam parameters. Our calculations demonstrate, however, that such procedures can introduce significant changes in these same parameters. Under certain conditions, more than 40% of the transmitted photons exiting the collimator do so with degraded energy. Optimum collimator design, however, can greatly reduce these effects. In particular, it is shown that the thickness of material required to effect a good collimator is not only dependent upon the photon energy, but also upon the size of the collimator hole.
Frontotemporal Dementia
Authors: Honig Lawrence S. , Bell Karen , Chin Steven S.
Published: August 2003

In this case study, we describe the symptoms, neuropsychological testing, and brain pathology of a man with frontotemporal dementia (FTD). FTD most often presents with either a change in personality or behavior, such as social withdrawal, increased gregariousness, disinhibition, or obsessive behaviors; or with impairment of language function. Memory difficulties are common, but usually are less prominent than these other symptoms in the early stages of the disease. Frequently, psychiatric diagnoses are initially the primary consideration. Cases may be either familial or sporadic. In this familial case, an autopsy was ultimately performed and revealed findings characteristic of FTD, with grossly evident focal brain degeneration in the frontal and temporal regions, microscopic signs of gliosis, and cellular abnormalities of the intracellular microtubule-associated protein tau.
Evolution as Frozen Music
Authors: Levinton Jeffrey S.
Published: August 2003

Developmental Plasticity and Evolution
. by Mary Jane West-Eberhard. Oxford University Press, New York, 2003. 814 pp. $100, £79.50. ISBN 0-19-512234-8. Paper, $49.95, £31.99. ISBN 0-19-512235-6.

Discussing a wide range of ideas and empirical studies that support them, West-Eberhard focuses on showing what recent findings in development, physiology, and behavior suggest about the origins of evolutionary novelties.
Validity and composition of the Silurian trilobite genera Borealarges and Dicranogmus, with new species from the Canadian Arctic
Authors: Adrain Jonathan M
Published: August 2003

New silicified material from Arctic Canada demonstrates that the lichid trilobite genera Borealarges and Dicranogmus, recently claimed to be synonyms, are independent groups with no close phylogenetic connection to one another. Dicranogmus has been known mainly from cranidia alone; prior association of librigenae and pygidia with the Arctic Canadian species D. skinneri has been queried. This association is correct beyond reasonable doubt, based on description of new material of both D. skinneri and a new species. Three new species of Borealarges are related to B. tuckerae Adrain 1994. Cladistic analysis supports the monophyly of this species group. Pending further new information, however, the group is retained within the genus Borealarges. The stratigraphic range of the species group is extended from the lower Wenlock (Sheinwoodian) to upper Ludlow (Ludfordian) by the discovery of a rare species in the Douro Formation of Cornwallis Island, Arctic Canada. New taxa from the Wenlock of the Cape Phillips Formation, Arctic Canada, include Dicranogmus wynni, Borealarges nicoae, B. warholi, and B. yulei.
Silurian deformation and metamorphism of Ordovician arc rocks of the Casco Bay Group, south-central Maine
Authors: West Jr. David P , Beal Heather M , Grover Timothy W
Published: August 2003

The Casco Bay Group in south-central Maine consists of a sequence of Late Cambrian to Early Ordovician interlayered quartzofeldspathic granofels and pelite (Cape Elizabeth Formation) overlain by Early to Late Ordovician back-arc volcanic (Spring Point Formation) and volcanogenic sedimentary rocks (Diamond Island and Scarboro formations). These rocks were tightly folded and subjected to low-pressure amphibolite-facies metamorphism in the Late Silurian. This phase of deformation and metamorphism was followed by the development of a variety of structures consistent with a period of dextral transpression in Middle Devonian  Early Carboniferous time. Previously dated plutons within the sequence range in age from 422389 Ma and record a period of prolonged intrusive activity in the region. Similarities in age, volcanic rock geochemistry, and lithologic characteristics argue strongly for a correlation between rocks of the Casco Bay Group and those in the Miramichi belt of eastern Maine and northern New Brunswick. The Cape Elizabeth Formation correlates with Late Cambrian to Early Ordovician sediments of the Miramichi Group (Gander Zone) and the Spring Point through Scarboro formations correlate with Early to Late Ordovician back-arc basin volcanics and volcanogenic sediments of the Bathurst Supergroup. The folding and low-pressure metamorphism of the Casco Bay Group is attributed to Late Silurian to Early Devonian terrane convergence and possible lithospheric delamination that would have resulted in a prolonged period of intrusive activity and elevated temperatures at low pressures. Continued convergence and likely plate reconfigurations in the Middle Devonian to Carboniferous led to widespread dextral transpression in the region.
The effects of forest harvesting and best management practices on streamflow and suspended sediment concentrations during snowmelt in headwater streams in sub-boreal forests of British Columbia, Canada
Authors: Macdonald J S , Beaudry P G , MacIsaac E A , Herunter H E
Published: August 2003

This paper examines suspended sediment concentration and stream discharge during freshet in three small sub-boreal forest streams (<1.5 m in width) in the central interior of British Columbia for 1 year prior to (1996) and for 5 years following forest harvesting (19972001). Harvesting prescriptions in a 20-m strip beside one stream required complete removal of merchantable timber (>15 cm diameter at breast height (DBH) for pine and >20 cm for spruce), while all stems <30 cm DBH were retained beside a second stream. A third stream remained unharvested as a control. The two riparian treatments were prescribed to test the efficacy of current British Columbia legislation that allows for varying amounts of riparian retention as best management practices for the management of windthrow. Both treated watersheds were clear-cut harvested (approximately 55% removal) in January 1997, and in the following year, temporary access roads were deactivated, including two stream crossings in the low-retention watershed. An increase in peak snowmelt and total freshet discharge was first noted in the second spring following harvest in both treatments and remained above predicted in all subsequent years. Suspended sediment also increased during freshet following harvest but returned to levels at or below preharvest predictions within 3 years or less in the high-retention watershed.
An Efficient Approach to the Travelling Salesman Problem Using Self-Organizing Maps
Authors: Vieira Frederico Carvalho , Neto Adrião Duarte Dória , Costa José Alfredo Ferreira
Published: August 2003

This paper presents an approach to the well-known Travelling Salesman Problem (TSP) using Self-Organizing Maps (SOM). The SOM algorithm has interesting topological information about its neurons configuration on cartesian space, which can be used to solve optimization problems. Aspects of initialization, parameters adaptation, and complexity analysis of the proposed SOM based algorithm are discussed. The results show an average deviation of 3.7% from the optimal tour length for a set of 12 TSP instances.
Neural Network Training with Global Optimization Techniques
Authors: Yamazaki Akio , Ludermir Teresa B.
Published: August 2003

This paper presents an approach of using Simulated Annealing and Tabu Search for the simultaneous optimization of neural network architectures and weights. The problem considered is the odor recognition in an artificial nose. Both methods have produced networks with high classification performance and low complexity. Generalization has been improved by using the backpropagation algorithm for fine tuning. The combination of simple and traditional search methods has shown to be very suitable for generating compact and efficient networks.
IMAGING PERFORMANCE OF ADVANCED QWIP FOCAL PLANE ARRAYS
Authors: GOLDBERG ARNOLD
Published: August 2003

Since the first demonstration of the quantum well infrared photodetector (QWIP) in the 1980s, there has been much progress in the application of QWIPs to the production infrared (IR) imaging systems. At this time, focal plane arrays (FPAs) made from QWIPs are readily available for insertion in IR cameras with formats as large as 640 × 480 pixels. Several organizations now have commercially available IR camera systems using QWIPs. In spite of the low single-pixel quantum efficiency relative to MCT, excellent IR imagery has been demonstrated with large format (640 × 480 pixels) single-band and moderate format (256 × 256 pixels) dual-band FPAs. With a large-format staring FPA, one can integrate the signal current for a relatively long time to produce images of similar quality to that from a scanned line array run at the same frame rate. In fact, it can be shown that due to the nature of the noise in a QWIP device, the noise performance of a QWIP FPA can be better than that of MCT FPA as long as the conversion efficiency (the product of the quantum efficiency and the photoconductive gain) is high enough for the read-out integrated circuit (ROIC) integration capacitor to be filled in a frame time. In this chapter the results of laboratory and field tests on large-format single-color QWIP FPAs operating in the LWIR band and dual-band FPAs operating in both the MWIR and LWIR bands simultaneously will be shown. Single-color and dual-band arrays will be shown to give excellent imaging performance and that dual-band FPAs offer unique capabilities to investigate the phenomenology of targets and backgrounds. The performance of the FPAs will be presented from a system performance perspective over a wide range of operating conditions (temperature, bias, integration time, etc.). Results of measurements of noise-equivalent temperature difference (NEΔT), minimum resolvable temperature difference (MRTD measured as a function of target spatial frequency), responsivity, and dark current will be reported. Imagery collected in the field will show the utility of large-format LWIR FPAs for increasing the range at which targets can be identified over previous-generation scanning imagers. Dual-band imagery collected using a QWIP FPA will show how such an array as part of a future imaging system may be able to exploit differences in the IR signatures of targets and backgrounds in the MWIR and LWIR bands to enhance the visibility of targets in cluttered environments. We also show how such an array can be used to make accurate remote temperature measurements. Finally, we will compare the performance of state-of-the-art FPAs made from QWIPs and MCT.
GaAs/AlGaAs MULTI-QUANTUM WELL-BASED INFRARED FOCAL PLANE ARRAYS FOR INFRARED IMAGING APPLICATIONS
Authors: GUNAPALA S. D. , BANDARA S. V.
Published: August 2003

New infrared focal plane arrays (FPAs) with multi-spectral coverage, high sensitivity, and lower manufacturing costs are required for many ground-based and space-based infrared imaging applications, One of the most promising FPA technologies is a GaAs/AlGaAs based Quantum Well Infrared Photodetector (QWIP) FPAs. In this paper we discuss the importance of focal plane array non-uniformity on the performance, demonstrations of varies infrared imaging cameras based on narrow-band QWIP FPAs, demonstration of long-wavelength/very long-wavelength dual-band QWIP imaging camera, demonstration of the first broad-band QWIP imaging camera, and a novel multi-quantum-well based infrared detection device structure for low-background and low-temperature operations.
MULTI-COLOR, BROADBAND QUANTUM WELL INFRARED PHOTODETECTORS FOR MID-, LONG-, AND VERY LONG-WAVELENGTH INFRARED APPLICATIONS
Authors: LI SHENG S.
Published: August 2003

Quantum well infrared photodetectors (QWIPs) have been widely investigated for the 3–5 μm mid-wavelength infrared (MWIR) and 8–12 μm long-wavelength infrared (LWIR) atmospheric spectral windows as well as very long wavelength infrared (VLWIR: λc > 14 μm) imaging array applications in the past decade. The mature III-V compound semiconductor growth technology and the design flexibility of device structures have led to the rapid development of various QWIP structures for infrared focal plane arrays (FPAs) applications. In addition to the single-color QWIP with narrow bandwidth, multi-color or broadband QWIPs required for advanced IR sensing and imaging applications have also emerged in recent years. Using band gap engineering approach, the multi-color (2, 3, and 4-color) QWIPs with multi-stack quantum wells and voltage-tunable asymmetrical coupled quantum well structures for detection in the MWIR, LWIR, and VLWIR bands have been demonstrated recently. The triple-coupled (TC-) QWIP employs the quantum confined Stark effect to tune the peak detection wavelength by the applied bias voltage, A typical single-color QWIP exhibits a rather narrow spectral bandwidth of 1 to 2 μm. For certain applications, such as spectroscopy, sensing of a broader range of infrared radiation is highly desirable. Using the stacked quantum wells with different well width and depth, the digital-graded superlattice barrier (DGSLB) or the linear-graded barrier (LGB) structures, broadband (BB-) QWIPs covering the 8–14 μm atmospheric spectral window have been reported recently.

In this chapter, the basic operation principles of a QWIP, and the design, fabrication, and characterization of multi-color and broadband QWIPs based on the GaAs/AlGaAs and InGaAs/AlGaAs material systems for the MW/LW/VLWIR applications are depicted.