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S J Gibbs

Publications and source records attributed to S J Gibbs.

64 records · Page 4Linked to original sources
PubMedDate not supplied

Volumetric determination of placental and uterine growth relationships from B-mode ultrasound by serial area-volume determinations.

Serial area-volume determinations may be made from B-mode ultrasonography. Multiple sonographic sections are taken through a structure of interest. The area of the structure of interest is determined on each sonographic section by a form of planimetry and multiplied by the step-interval to obtain the volume of the structure of interest between sonographic sections. The total volume of the structure of interest is the sum of the individual volumes. The volume is computed from both transverse and longitudinal images and an average obtained for improved accuracy. Total intrauterine volume and placental volume were determined by the serial area-volume method in 63 normal patients and the results were analyzed. Placental and total intrauterine volumes were also determined for five cases of intrauterine growth retardation. Although there is some error in the serial area-volume method, the initial evaluation of five cases with intrauterine growth retardation suggests a greater precision and accuracy than volume estimates based on prolate ellipsoid geometry. Placental volume may provide an acceptable parameter to screen for intrauterine growth retardation.

Female↗
PubMedDate not supplied

Physical approach to depth dose distributions in a water phantom irradiated by a teleisotope photon beam.

The physical basis of deposition of radiation dose within a homogeneous phantom irradiated by a monoenergetic photon beam has been studied in terms of photon attenuation and energy-absorption properties of the phantom material. A semi-empirical model based on the Klein-Nishina formula for Compton scattering, and the ratio of multiply scattered to singly scattered photon fluences, has been developed for the scatter dose component within a realistic phantom to determine the central-axial percent depth dose (PDD) and off-central-axis ratios (OCR). Differences between the predicted and measured values of PDD and OCR for cobalt-60 and cesium-137 beams are less than 3% for fields of equivalent-square-side less than 20 cm, and less than 5% for larger fields. Beam profiles of all field sizes can be well simulated by this model and reasonable agreement has been found between the predicted and tabulated values of scatter functions and the backsetter factor for cobalt-60 beams. This formulation involves no variable parameters, and is valid for all values of the source-to-surface distance, field length and width, and field shape. However, the algorithm developed is not suitable for routine multiple-field treatment planning because it requires large computer memory size.

Cesium Radioisotopes↗
PubMedDate not supplied

Removing effects of eddy currents in proton MR spectroscopy.

The use of pulsed gradients to define a volume of interest for localized magnetic resonance spectroscopy produces magnetic field perturbations which distort both the free induction decay and the spectrum after Fourier transformation. A technique is presented that removes the artifacts from eddy currents from a sampled free induction decay. To linearize the phase, the nonlinear phase of a reference free induction decay is subtracted from the phase of a sample free induction decay. Next, to move the frequency to resonance and perform a zero-order phase correction, the line fit from a linear regression is subtracted from the phase. After reconstructing the free induction decay, the resulting frequency spectra are sorted into absorption mode and dispersion mode components.

Artifacts↗