Search PubMed⌕ Search

Biomedical subjects

R G Waggener

Publications and source records attributed to R G Waggener.

At least 19 recordsLinked to original sources
PubMed2001

Comparison of five methods for the derivation of spectra for a constant potential dental X-ray unit.

OBJECTIVES: To compare the diagnostic X-ray spectra derived by different methods for a constant potential dental X-ray unit. MATERIALS AND METHODS: Five methods of deriving X-ray spectra for a constant potential dental X-ray unit were compared: measurement by spectrometer using cadmium-zinc-telluride (CZT) detector, calculation by Monte Carlo simulation, calculation by two different, semi-empirical methods and estimation from transmission data. The dental X-ray set was a Heliodent MD unit (Sirona, Charlotte, NC, USA) operable at 60 or 70 kV. A semiconductor detector was used in the spectrometer measurements and an ionization chamber dosimeter in the transmission measurements. From the five methods, photon-fluence spectra were derived. Based on the photon-fluence spectra, average energies and transmission curves in aluminum were calculated. RESULTS: For all five methods, the average energies were within 2.4% of one another. Comparison of the transmission curves showed an average difference in the range of 1 to 6%. CONCLUSION: All of the five methods of deriving spectra are in extremely good agreement with each other.

Algorithms↗
PubMed1999

Measured water transmission curves and calculated zero field size tumor maximum ratios for 4, 6, and 15 MV x-rays.

A multihole diverging Cerrobend plug for megavoltage energies was used to measure water transmission values at different locations in a 20 x 20 cm field at 100 cm source-to-axis distance (SAD) for 4, 6, and 15 MV therapy photon beams. The transmission curves in water were measured at 25 locations across the 20 x 20 field, and each location was separated by 5 cm at the isocenter. Each transmission value was made using a 0.3175 cm diameter (0.079 cm2 area) hole of 20 cm length at the central axis (CAX). The small field measured transmission curve in water was used to derive the zero field size tumor maximum ratio (TMR) and the primary photon exposure spectrum as a function of energy at depth. The exposure spectrum was used to find an effective photon energy and linear attenuation coefficient at depth and at different locations in the field. These values were found to vary with location in the field.

Biophysical Phenomena↗
PubMed1999

Half-value layer and intensity variations as a function of position in the radiation field for film-screen mammography.

Differences in half-value layer (HVL) and radiation intensity are investigated as a function of position in the mammographic radiation field. Sources of systematic variation include the heel effect, the inverse square law, and differential photon path lengths through thicknesses of inherent and added filtration. The combination of these effects can increase the HVL by as much as 9% and reduce intensity by as much as 40% along the cathode-anode axis. To the left and right of the x-ray field central axis, reductions in radiation intensity of up to 9% and minor increases in HVL are noted as well. Optical density variations as a function of position in the field correlate well with the measured radiation intensity changes.

Electrodes↗
PubMed1999

X-ray spectra estimation using attenuation measurements from 25 kVp to 18 MV.

Attenuation measurements for primary x-ray spectra from 25 kVp to 18 MV were made using aluminum filters for all energies except for orthovoltage where copper filters were used. An iterative perturbation method, which utilized these measurements, was employed to derive the apparent x-ray spectrum. An initial spectrum or pre-spectrum was used to start the process. Each energy value of the pre-spectrum was perturbed positively and negatively, and an attenuation curve was calculated using the perturbed values. The value of x-rays in the given energy bin was chosen to minimize the difference between the measured and calculated transmission curves. The goal was to derive the minimum difference between the measured transmission curve and the calculated transmission curve using the derived x-ray spectrum. The method was found to yield useful information concerning the lower photon energy and the actual operating potential versus the nominal potential. Mammographic, diagnostic, orthovoltage, and megavoltage x-ray spectra up to 18 MV nominal were derived using this method. The method was validated using attenuation curves from published literature. The method was also validated using attenuation curves calculated from published spectra. The attenuation curves were then used to derive the x-ray spectra.

Aluminum↗
PubMed1998

Calculated mammographic spectra confirmed with attenuation curves for molybdenum, rhodium, and tungsten targets.

A model for calculating mammographic spectra independent of measured data and fitting parameters is presented. This model is based on first principles. Spectra were calculated using various target and filter combinations such as molybdenum/molybdenum, molybdenum/rhodium, rhodium/rhodium, and tungsten/aluminum. Once the spectra were calculated, attenuation curves were calculated and compared to measured attenuation curves. The attenuation curves were calculated and measured using aluminum alloy 1100 or high purity aluminum filtration. Percent differences were computed between the measured and calculated attenuation curves resulting in an average of 5.21% difference for tungsten/aluminum, 2.26% for molybdenum/molybdenum, 3.35% for rhodium/rhodium, and 3.18% for molybdenum/rhodium. Calculated spectra were also compared to measured spectra from the Food and Drug Administration [Fewell and Shuping, Handbook of Mammographic X-ray Spectra (U.S. Government Printing Office, Washington, D.C., 1979)] and a comparison will also be presented.

Biophysical Phenomena↗
PubMed1992

CT reconstruction algorithm for a dental panoramic x-ray unit.

A variable Jacobian and weighted backprojection algorithm, used for medical CT, was adapted to perform CT reconstructions on data obtained with a dental panoramic x-ray unit. A detector array, fitted to the unit for the purpose of acquiring digital panoramic radiographs, was used to collect the data. Compensations were made for the incomplete (230 degrees) rotation of the panoramic x-ray unit, the non-fixed centre of rotation, the irregular rotation of the x-ray target and detector, and the resulting variances in magnification. The algorithm was tested on mathematically simulated phantoms and on acquired data. Reconstruction of simulated data proved the success of the algorithm. Real data reconstructions showed some defects as a result of inaccuracies in quantifying the experimental panoramic device.

Algorithms↗
PubMed1989

Spatial resolution requirements for digitizing dental radiographs.

A study was performed to determine the appropriate spatial resolution for digitizing and transmitting dental radiographs with the KODAK EKTASCAN, a computer-based digital enhancement and transmission system. Periapical, bitewing, and panoramic radiographs were digitized in three formats representing varying spatial resolution parameters. Eight viewers used a 5-point rating scale to evaluate the detectability of periapical pathosis on the periapical images, of proximal surface caries on the bitewing images, and of various bony abnormalities on the panoramic images. Receiver operating characteristic curves were generated, and the results of the periapical, bitewing and panoramic experiments were presented as trapezoidal and maximum likelihood receiver operating characteristic curve areas. The results of this study indicate that digital images of dental radiographs provide adequate diagnostic accuracy for evaluating the presence of periapical pathosis, proximal surface caries, and specified bony abnormalities. The digitization parameters established for the KODAK EKTASCAN provide a guide for digitizing dental radiographs on other commercially available digital image-processing systems.

Computers↗
PubMed1978

A method for rapid determination of the energy of electron beams from medical linear accelerators.

A method has been developed using a Varian Clinac-18 LINAC for the rapid determination of electron beam energy for clinically used linear accelerators. The method involves measuring the ionization values in a water or polystyrene phantom with an ion chamber at two predetermined depths. Then with predetermined Bremsstrahlung "tail" values which are presented here or which can be developed by the user, the practical range, Rp can be measured. With the Rp, the effective surface energy Eo of the electron beam can be determined by the Markus range-energy formula. Thus, by measuring just two depth ionization values, one is quickly able to determine the Eo of an electron beam without plotting a full depth ionization curve.

Electrons↗