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Biomedical subjects

R G Waggener

Publications and source records attributed to R G Waggener.

33 records · Page 2Linked to original sources
PubMedDate not supplied

Estimation of chemical composition and density from computed tomography carried out at a number of energies.

A method is presented by whichcomputed tomography scans carried out at a number of energies may be utilized to obtain cross-sectional images of density and atomic number in addition to the conventional array of linear attenuation coefficients. This type of analysis has been carried out for various substances of biological relevance. Computer simulated reconstructions of clinical situations suggest that the method shows promise for providing additional diagnostic information and might dispense to some extent with the necessity of injecting contrast agents into the patient.

Autoanalysis↗
PubMedDate not supplied

Spectral effects on three-dimensional reconstruction from rays.

Continuous bremsstrahlung spectra were calculated for 120 kVp for constant and sinusoidal potentials. Fluorescent radiation for the tungsten target was added to the bremsstrahlung, and the spectra were attenuated through various filter materials. A drawing of an object to be scanned was divided into an array of small squares in which the composition was assumed to be constant. Transmission data for 120 rays at each of 120 angles spanning a range of 180 degrees were calculated. Two algorithms for the reconstruction of attenuation coefficients from projection data, an algebraic reconstruction technique (ART) and the convolution method, were utilized to reconstruct effective coefficients. The effect of spectral filtration on the quality of the reconstruction was evaluated. Lightly filtered x-ray beams give rise to severe distortions in image quality, with values of the reconstructed coefficients rising toward the periphery of the object. Highly filtered beams give rise to images with less pronounced distortion.

Diagnosis, Computer-Assisted↗
PubMedDate not supplied

Measurement of primary bremsstrahlung spectrum from an 8-MeV linear accelerator.

The bremsstrahlung spectrum from an 8-MeV linear accelerator has been measured using a NaI(T1) spectrometer system. The spectrum shows a low-energy cutoff at 0.4 MeV and the maximum photon energy to be approximately 6% greater than the nominal energy. The maximum emission of energy fluence was 1.6 and 1.8 MeV for measured and calculated values, respectively. The fast neutron dose in the photon beam was approximately 0.09% of the x-ray dose. The weighted mean energy was 2.3 MeV, measured value, and 2.4 MeV, calculated value.

Radiometry↗
PubMedDate not supplied

Correction for spectral artifacts in cross-sectional reconstruction from x rays.

A monoenergetic response correction is described which, along with adequate filtration, may be used to remove the spectral shift artifact encountered in three-dimensional reconstruction from x rays. Reconstructions were carried out by means of a convolution algorithm for simulated data using this method. These are compared with reconstructions obtained using fixed-length water-bath scans as a remedy for the special artifact. These studies suggest that the spectral artifact can be successfully eliminated from computerized cross-sectional scans without resorting to the use of the water bath while, at the same time, improving quantum statistics and/or permitting operation at a lower tube current.

Filtration↗
PubMedDate not supplied

Extrapolation of linear attenuation coefficients of biological materials from diagnostic-energy x-ray levels to the megavoltage range.

A dual-energy algorithm is used in determining the effective atomic number, atomic density, and electron density of biological substances. These quantities are then used to calculate linear attenuation coefficients at the megavolttage level. The validity of this method is checked several ways, including a comparison of extrapolated values with experimental data reported by Rao and Gregg where linear attenuation coefficients at 60 and 122 keV are used to extrapolate coefficients at 662 keV. Except for a few instances, the extrapolated values agree quite well with the reported experimental values. This method is also used to calculate coefficients at the 60Co range, and these are compared with experimental values measured in water and various types of tissue-equivalent materials. An additional algorithm is developed to extrapolate coefficients in water and bone up to 10 MeV. These quantities are compared with accepted values previously reported in the literature.

Animals↗
PubMedDate not supplied

Treatment planning in Cobalt-60 radiotherapy using computerized tomography techniques.

Cobalt-60 transmission measurements were made through an Alderson phantom utilizing a transverse axial tomographic device and a NaI (Tl) detector. Measurements were made on different sections of the phantom for as many as 162 angles and 120 linear increments. The attenuation coefficients were reconstructed using both convolution and algebraic reconstruction techniques. Three-dimensional isodose distributions were obtained using the reconstructed attenuation coefficients. Comparison with standard treatment plans and measured isodose distribution using TLD techniques suggest that a more accurate isodose distribution may be obtained using the reconstructed attenuation coefficients, particularly in regions involving tissue heterogeneities.

Cobalt Radioisotopes↗
PubMedDate not supplied

Determination of effective energies in CT calibration.

The effective energy of a polychromatic beam for a Computed Tomography (CT) scanner can be measured directly only with difficulty. However, a linear relationship exists between the measured CT numbers and corresponding attenuation coefficients of known materials at the effective energy of the x-ray beam. The effective energy can then be determined by searching all energies for the best linear correlation between the CT numbers and the attenuation coefficients. This can be performed by two methods: graphically, by means of choosing visually the straightest of the fitted lines or, mathematically, by maximizing the correlation coefficient. The energy corresponding to the optimal fit is therefore selected as the effective energy. The latter method was implemented by computer and demonstrated by scanning the AAPM phantom, which contained known materials, and determining the effective energies and the relationship between the linear attenuation coefficients and CT numbers for three commercial units.

Tomography, X-Ray Computed↗
PubMedDate not supplied

Extraction of information from CT scans at different energies.

The image displayed in computed tomography is a scaled representation of attenuation coefficients within the patient's body. A number of authors have presented methods by which additional information (such as electron density, effective atomic number, and extrapolated attenuation coefficients for therapy applications) can be extracted from CT scans carried out at different energies. In the present paper, the dual-energy method described by Rutherford has been used to produce complete images of effective atomic number and electron density of a known phantom (the AAPM phantom) in order to investigate the usefulness of applying this method to current commercial scanners.

Tomography, X-Ray Computed↗
PubMedDate not supplied

Electron beam depth dose scaling by means of effective atomic number reconstructed from CT scans.

A method is developed by which the computed tomography scans of a medium carried out at a number of diagnostic energies can be utilized to obtain the in situ "Effective Atomic Number" and "Effective Density". The electron depth dose curves in water when scaled by these factors estimate the actual electron depth dose distribution in that medium. It appears that the use of CT scans for electron beam treatment planning, in the management of cancer, is quite promising.

Electrons↗