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W M Oswald

Publications and source records attributed to W M Oswald.

5 recordsLinked to original sources
PubMed1988

Use of profile analysis for the measurement of organ dimensions.

We have developed a method for measurement of organ dimension based on the use of the full width half maximum (FWHM) of profiles taken through an organ. In vitro studies were performed using a large rectangular lucite box filled with water. Five circular lucite phantoms with internal diameters of 1.4-10.2 cm and 1 elliptical phantom with dimensions 9.6 x 4.0 cm were filled with 99mTc-pertechnetate at various concentrations. Phantoms were imaged on a gamma camera at a depth of 5-25 cm in water and the FWHM calculated from horizontal profiles taken across the cylinders. The FWHM showed no variation with 99mTc concentration in the same cylinder. Phantom profiles were deconvolved with a system line spread function measured under similar conditions of scatter and depth. The correction factor to convert the deconvolved profile FWHM to true diameter was independent of cylinder depth and diameter over a range of FWHM 3-10 cm and depth 5-25 cm. The mean value for the correction factor was 1.23 +/- 0.04 for circular phantoms and 1.14 +/- 0.02 for the elliptical phantom. This technique should allow an objective and reproducible estimate of organ dimensions from planar images that is relatively independent of the depth and size of an organ.

Anatomy↗
PubMed1988

The line resolution pattern: a new intrinsic resolution test pattern for nuclear medicine.

Routine measurement of spatial resolution of a gamma camera is normally performed through the use of a four-quadrant bar phantom or one of several commercially available resolution phantoms. These phantoms all provide a qualitative index of system resolution with the inherent assumption that any change in intrinsic resolution would be apparent in the bar/hole pattern image. However on nine gamma cameras, comparison of intrinsic resolution determined from the line spread function by NEMA standards and from visual estimation of a four-quadrant bar phantom image showed poor correlation. The purpose of this study was to design and evaluate a new test pattern which would provide a more accurate estimate of resolution. We developed a line resolution phantom (LRP) which consisted of a 16-cm-diameter lead disk with a series of horizontal and vertical slits. This phantom permits a quantitative estimate of intrinsic resolution (to within 0.5 mm) from a visual examination of the LRP image. Evaluation on nine gamma cameras showed good agreement between results obtained with the LRP and measurement of resolution from the line spread function. The LRP is a simple and inexpensive test phantom which should find applications in quality control and acceptance testing.

Models, Structural↗
PubMed1985

Performance evaluation of xenon-133 inhalation rebreathing systems for regional blood flow measurements.

A quality-control phantom is described which is capable of testing the performance of inhalation rebreathing systems for measurements of regional cerebral blood flow (rCBF). The phantom is designed so that data similar to those from a patient study are obtained. The standard rCBF data-processing algorithm is used for the calculation of phantom study results. Malfunctions were induced to simulate instrument malfunction, and their effects on detector and air curves were evaluated. The use of this phantom is recommended prior to a patient study if the rCBF instrument is used infrequently or after service for routine maintenance or malfunction.

Cerebrovascular Circulation↗