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Biomedical subjects

R E Shuping

Publications and source records attributed to R E Shuping.

8 recordsLinked to original sources
PubMed1998

Report of the ad hoc committee of the AAPM radiation therapy committee on 125I sealed source dosimetry.

PURPOSE: Two developments in 125I-sealed source dosimetry have necessitated swift and accurate implementation of TG43 dosimetry in clinic: (a) the dosimetry constants of 125I endorsed by the AAPM Task Group 43 Report result in calculated dose rate that deviates by as much as 15% from currently accepted dose-rate distributions, and (b) The National Institute of Standards and Technology (NIST) has proposed modifying the 125I air-kerma strength standard by approximately 10%. METHODS AND MATERIALS: The ad hoc committee of AAPM Radiation Therapy Committee describes specific procedures to implement these two developments without causing confusion and mistakes. CONCLUSIONS: Confusion and mistakes may be avoided when the following two general steps are taken: 1) STEP I, TG-43 implementation, and 2) STEP II, new air-kerma strength standard implementation when available from NIST.

Brachytherapy↗
PubMed1984

Investigation of energy responses of germanium detectors and correction of measured spectra by means of Monte Carlo simulation.

A Monte Carlo program was developed which determines the energy response of X-ray detectors of various "nested" sizes simultaneously. Twenty-one planar germanium detectors with cylindrical crystals were chosen, which are commercially available for X-ray spectrometry. The photopeak efficiency, K alpha and K beta escape fractions. Compton fraction, elastic fraction, penetration fraction, and the Compton continuum were tabulated as a function of incident X-ray energies from 12 to 300 keV in 2-keV increments. Coefficients of polynomials fitted to the Compton continua were also calculated to facilitate computer implementation of spectrum corrections. Spectrum correction methods which use the Compton continua determined by Monte Carlo calculation were compared with those approximated by rectangles. Comparison of the residual root-mean-square (RRMS) values between the incident and corrected spectra showed that the former method yielded lower RRMS values. However, the differences in these values are small, indicating that the simple rectangular approximation may be adequate for most spectral measurements.

Germanium↗
PubMed1978

A comparison of mammographic x-ray spectra.

X-ray spectra produced by mammographic systems are compared to spectra from conventional diagnostic x-ray systems. Some systems use special anode materials and beam filters to produce x-ray spectra more suitable for mammography. The data show that the spectra produced by some systems are unique; in fact, one using molybdenum for both an anode and beam filtering element can produce an x-ray spectrum having more than 80% of the photons below 20 KeV. Using some typical breast phantom materials as attenuators, the primary x-ray spectra incident upon the imaging system were simulated and displayed. Implications of spectral shaping to image quality and patient dose are discussed.

Humans↗
PubMedDate not supplied

Photon energy distribution of some typical diagnostic x-ray beams.

A high-purity germanium spectrometer system was used to determine primary x-ray spectra over the 45--90-kVp region. Methods were devised for producing and examining spectra stimulating diagnostic conditions without operating the x-ray generator at high current levels. The techniques used to correct the experimental data and produce a photon fluence spectrum are discussed. The results, presented graphically and in tables, have been normalized to yield the relative number of photons per 2-keV interval. Methods for converting a normalized spectrum into a photon fluence spectrum that will produce an exposure of 1 R are presented. The analytical model and procedures used to calculate the K-escape fraction are discussed.

Technology, Radiologic↗
PubMedDate not supplied

Energy absorbed in calcium tungstate x-ray screens.

The energy which must be absorbed in a CaWO4 x-ray intensifying screen to produce unit net opetical density on a film has been evaluated by measurement and calculation for a screen-film system over a range of beam qualities (1.4--7.4 mm A1 HVL) spanning the diagnostic x-ray region. It was found to be constant within experimental error. The absorbed-energy constant for three additional CaWO4 screens is presented for a single beam quality. To correct the estimation of absorbed energy, the fractional escape of tungsten K x rays has been evaluated and the results are presented as a function of phosphor loading. The absorbed-energy constant is useful for predicting optical density for variable beam conditions; a family of characteristic curves based on exposure is reduced to one curve for a particular film-screen system, expressed as optical density as a function of absorbed energy.

Calcium↗
PubMedDate not supplied

Resolution and contrast reduction.

Lack of resolution (unsharpness) can reduce contrast in diagnostic radiography if the proper conditions of magnification and unsharpness are met. To describe this phenomenon, a modification of the contrast reduction factor (CRF) was introduced which used the response function of a semi-opaque edge to predict contrast reduction for small bar-shaped objects. To predict CRF, unsharpness is employed as a single-term description of resolution and is obtained experimentally from the edge response function. The unsharpness term is defined as the distance over which the response goes from 16.5% to 83.5% of the maximum. Measured and predicted CRFs were compared and the CRF concept was found to be an excellent predictor of contrast reduction. The individual components of unsharpness were determined experimentally and the sum-of-squares rule predicted adequately their combination. Three methods to measure unsharpness were compared: (a) the ICRU prescription using pinhole radiographs of the focal spot, (b) one-dimensional integration of the focal-spot pinhole radiograph, and (c) the unsharpness term produced by a semi-opaque edge. The latter two were measured using a microdensitometer.

Mathematics↗