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Biomedical subjects

L K Wagner

Publications and source records attributed to L K Wagner.

At least 55 records · Page 3Linked to original sources
PubMed1979

Digital radiography using a computed tomographic instrument.

A prototype computed radiography (CR) system was evaluated for its efficacy as an independent diagnostic modality. Preliminary measurements of high contrast resolution, low contrast perceptibility, and dose were obtained. Clinical examinations including skull, abdomen, liver, gallbladder, biliary system, spine, and extremities were performed as an adjunct to either computed tomography or CR. The data suggest that CR can be an effective diagnostic imaging modality by itself. Advantages over conventional radiography include high scatter rejection, low patient dose, wide dynamic range, and good low contrast sensitivity for large objects; disadvantages, its long exposure time and relatively poor high contrast spatial resolution.

Biliary Tract↗
PubMedDate not supplied

Potential biological effects following high X-ray dose interventional procedures.

Some interventional procedures can result in very high x-ray doses. Potential biological effects of high x-ray doses are reviewed. Deterministic and stochastic effects in skin, bone, parotid glands, and lung are discussed. Threshold doses for the effects and relevant dosimetric principles are addressed. General principles for minimizing the potential for these effects are presented. Knowledge about these effects and the means to minimize radiation dose can assist the physician in the care of patients undergoing lengthy invasive radiologic procedures.

Bone and Bones↗
PubMedDate not supplied

Dose efficiency and the effects of resolution and noise on detail perceptibility in radiographic magnification.

The detail signal-to-noise ratio model of radiographic imaging is quantitatively analyzed in terms of its accuracy in describing observer threshold perceptibility of radiographic detail. The model is found to adequately describe the effects of magnification, scatter radiation, and system resolution on observer threshold perceptibility. However, it is shown that the model does not apply in screen/film radiography for very low contrasts and high scatter conditions due to insufficient optical density contrast. The dose-to-information conversion efficiency of a radiographic imaging system is defined and the effects of magnification, scatter, resolution, image processing, detector efficiency, grids, patient table support, field size, and geometry on the dose efficiency of the imaging system are investigated.

Models, Theoretical↗
PubMedDate not supplied

Contrast-detail-dose and dose efficiency analysis of a scanning digital and a screen-film-grid radiographic system.

The purpose of this study is to examine the diagnostic potential of a scanning digital radiography (SDR) system currently used clinically as a CT localization device. The technique of contrast-detail-dose analysis is used to compare the low-contrast sensitivity and dose efficiency of an SDR unit with standard radiography (SR). The theory of threshold perceptibility in both digital radiography and SR is described, including the effects of scattered radiation and antiscatter devices, object attenuation, geometry, system image processing, and recorder quantum efficiency. The concept of dose efficiency is defined and derived from the contrast-detail-dose data. The SDR system is shown to operate with a threshold signal-to-noise ratio of 7.3 +/- 1.2 for large area detection (d greater than or equal to 2 mm); to be relatively scatter-free; and to be as much a 100x more dose efficient than SR for visualization of large low contrast objects (C less than or equal to 0.04, d greater than or equal to 2 mm).

Contrast Media↗
PubMedDate not supplied

Resolution in radiographic magnification.

Radiographic resolution and image sharpness are analyzed as a function of magnification for a few screen/film systems and a microfocal spot x-ray tube. Resolution and sharpness are described in terms of both MTF and effective aperture. The analysis demonstrates advantages of magnification for any combination of radiographic screen/film system and x-ray focal spot, and, in addition, allows one to compare different screen/film systems each used at different magnifications. Such an analysis is applicable to any radiographic system and may serve as a guide in selecting screen/film systems for use in magnification procedures.

Radiographic Magnification↗
PubMedDate not supplied

A Laplace transform pair model for spectral reconstruction.

A four-parameter Laplace transform pair model, which accurately reconstructs an experimental bremsstrahlung spectrum from attenuation data, is presented. Computed spectral values with both aluminum and copper attenuators generally agree with experimental 70-kVp data to better than 2%. Reconstructed spectra at other kVp's also show good agreement with published data.

Mathematics↗
PubMedDate not supplied

Scatter in 240-kVp mobile chest radiography.

The effects of scatter radiation on signal-to-noise ratio and optical density contrast are quantitatively compared for three tissue interfaces at 85, 110, and 240 kVp in mobile chest techniques. It is shown that scatter in the mediastinal portion of the radiograph is virtually independent of energy, while it substantially increases with energy in the lung fields.

Humans↗
PubMedDate not supplied

An examination of errors in characteristic curve measurements of radiographic screen/film systems.

The precision and accuracy achieved in the measurement of characteristic curves for radiographic screen/film systems is quantitatively investigated for three techniques: inverse square, kVp bootstrap, and step-wedge bootstrap. Precision of all techniques is generally better than +/- 1.5% while the agreement among all intensity-scale techniques is better than 2% over the useful exposure latitude. However, the accuracy of the sensitometry will depend on several factors, including linearity and energy dependence of the calibration instrument, that may introduce larger errors. Comparisons of time-scale and intensity-scale methods are made and a means of measuring reciprocity law failure is demonstrated.

Radiographic Image Enhancement↗
PubMedDate not supplied

Relative dose efficiencies of antiscatter grids and air gaps in pediatric radiography.

The relative dose efficiencies (RDE) of various antiscatter grids and air gaps were determined for conditions simulating those found in pediatric radiography, using phantoms representing a newborn child, a 5-yr-old and a 10-yr-old child. Our data indicate than an air gap is best for the newborn, due to the low levels of scatter. The 8:1 fiber grid or 15.2-cm air gap without a grid can improve dose efficiency (DE) for the 5-yr-old child by 20%-25% relative to the 3.3-cm air gap and no-grid technique, while for the 10-yr-old child, DE can be improved by 40% with an 8:1 fiber grid.

Child↗
PubMedDate not supplied

Analysis of variations in contrast-detail experiments.

Three sources of variability in a contrast-detail (CD) experiment have been quantitated: within-observer variance, between-observer variance, and sample variance. It is concluded that (1) it is more efficient to increase the numbers of replicated images and observers than to increase the number of readings; (2) sampling and between-observer variations are approximately equal; (3) one can expect approximately 10% standard errors in the measured value of threshold detail or threshold contrast in a CD experiment which employs four observers, four replicate image samples, and one reading per observer.

Models, Structural↗
PubMedDate not supplied

Application of a Laplace transform pair model for high-energy x-ray spectral reconstruction.

A Laplace transform pair model, previously shown to accurately reconstruct x-ray spectra at diagnostic energies, has been applied to megavoltage energy beams. The inverse Laplace transforms of 2-, 6-, and 25-MV attenuation curves were evaluated to determine the energy spectra of these beams. The 2-MV data indicate that the model can reliably reconstruct spectra in the low megavoltage range. Experimental limitations in acquiring the 6-MV transmission data demonstrate the sensitivity of the model to systematic experimental error. The 25-MV data result in a physically realistic approximation of the present spectrum.

Humans↗
PubMedDate not supplied

Energy and rate dependence of diagnostic x-ray exposure meters.

Variations in x-ray exposure measurements among a variety of contemporary diagnostic exposure meters are investigated. Variations may result from systematic errors due to calibration, beam-quality dependence and exposure-rate dependence. It is concluded that the majority of general purpose diagnostic meters will agree to within 10% of each other if exposure rates are below 1.3 mC kg-1S-1 of air (5 R s-1) and beam qualities are typical for general purpose radiology, excluding mammography. For exposure rates comparable to those in barium enema radiography the variations can range up to 25% or more. Variations up to 40% were observed among general purpose exposure meters at mammographic beam qualities. In the mammographic range, mammographic (thin window) exposure meters varied by no more than 2%.

Biophysical Phenomena↗
PubMedDate not supplied

Laplace reconstruction of experimental diagnostic x-ray spectra.

This paper displays the results of a blind study used to determine the capability of a Laplace transform pair model to accurately reconstruct diagnostic x-ray spectra from experimental attenuation data. Spectra reconstructed from attenuation measurements are compared to experimental spectra obtained on the same unit using an intrinsic germanium spectrometer system. The results show that when pure attenuation materials are used, good agreement is obtained between the experimental and computed spectra. If an alloy attenuator like 1100 aluminum is used, the proportion of contaminants must be included in the Laplace formulation for accurate reconstruction.

Alloys↗
PubMedDate not supplied

Determination of diagnostic x-ray spectra with characteristic radiation using attenuation analysis.

An analytical method to compute x-ray spectra from attenuation data utilizing the Laplace transformation has been extended to include characteristic radiation. It is based on an a priori technique of determining the ratio of characteristic radiation exposure to the total radiation exposure in diagnostic spectra. The technique is shown to produce characteristic intensities in good agreement with experimentally determined values.

Humans↗
PubMedDate not supplied

Probability of causation for cancers potentially induced by ionizing radiation.

Prompted by increasing litigation claiming cancer induction from exposure to radiation from nuclear weapons tests, the United States Congress enacted an amendment to the Orphan Drug Act (Public Law 97-414, January 4, 1983), through which the National Institutes of Health was directed to and did produce Probability of Causation (PC) Tables. This review defines PC and discusses the data, limitations, and uses of the concept.

Breast Neoplasms↗
PubMedDate not supplied

On the measurement of half-value layer in film-screen mammography.

Sources of variations in the measurement of half-value layer (HVL) in film-screen mammography are evaluated. Two principal sources are the energy responses of ionization chambers and the elemental compositions of the 1100 aluminum-alloy attenuation materials. Methods in measuring the thickness of attenuation materials are also an important potential source of error. These factors as well as the influence of geometry of measurement, position of measurement in the field, and precision of radiation output are examined. Recommendations for consistency in measurement are provided.

Biophysical Phenomena↗