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H H Barrett

Publications and source records attributed to H H Barrett.

45 records · Page 3Linked to original sources
PubMed1981

A low-cost computed tomographic scanner.

The authors describe a film-recorded computed tomographic (CT) scanner that uses optical processing methods for reconstruction of a sectional image. Results are comparable to commercial CT methods using the same patient dose. Consequently, clinically satisfactory CT imaging can be performed at a substantially reduced cost.

Animals↗
PubMedDate not supplied

High-resolution computed tomography of the normal rat nephrogram.

This study describes a unique, film-recorded computed tomography (CT) system and its use in studying contrast flow between anatomic compartments of the rat kidney. The CT apparatus, composed of a microfocal spot tube, rotating animal carrier, film-cassette translator, and control electronics, was used to expose "sinograms" of 3:1 magnification through the kidneys of normal rats prior to and 2, 15, 30, 60, and 120 minutes after intravenous contrast injection. Microdensitometry and computer reconstruction resulted in CT images representing 1-mm thick coronal sections with lateral resolution of 150 micron. With this novel technique of ultrahigh-resolution CT, temporal alterations in absorption coefficient of cortical and medullary nephrographic components were depicted for contrast flow study in our small animal model.

Animals↗
PubMedDate not supplied

Imaging with rotating slit apertures and rotating collimators.

The statistical quality of conventional nuclear medical imagery is limited by the small signal collected through low-efficiency conventional apertures. Coded-aperture imaging overcomes this by employing a two-step process in which the object is first efficiently detected as an "encoded" form which does not resemble the object, and then filtered (or "decoded") to form an image. We present here the imaging properties of a class of time-modulated coded apertures which, unlike most coded apertures, encode projections of the object rather than the object itself. These coded apertures can reconstruct a volume object nontomographically, tomographically (one plane focused), or three-dimensionally. We describe a new decoding algorithm that reconstructs the object from its planar projections. Results of noise calculations are given, and the noise performance of these coded-aperture systems is compared to that of conventional counterparts. A hybrid slit-pinhole system which combines the imaging advantages of a rotating slit and a pinhole is described. A new scintillation detector which accurately measures the position of an event in one dimension only is presented, and its use in our coded-aperture system is outlined. Finally, results of imaging test objects and animals are given.

Animals↗
PubMedDate not supplied

Comparison of NaI(T1), CdTe, and HgI2 surgical probes: effect of scatter compensation on probe performance.

Spatial variation in the background source distribution makes tumor detection difficult for single-detector probes. Using a single energy window that brackets the photopeak helps discriminate against background events dominated by Compton scattering. Another approach is to use the information provided by an additional window in the Compton region. The performances of NaI(T1), CdTe, and HgI2 surgical probes have been compared under realistic simulations of a tumor-staging procedure using optimal single-sided energy windows and a two-window scatter-subtraction technique. Results showed that despite the differences in energy resolution of the detectors, the performances of the probes in a variable background were similar when optimal single energy windows were used. When the background variations were large, using information provided by a second window improved probe performance.

Cadmium↗
PubMedDate not supplied

Comparison of NaI(Tl), CdTe, and HgI2 surgical probes: physical characterization.

The physical properties of three surgical probes containing different radiation detectors are compared: a NaI(Tl) scintillator with a flexible, fiber-optic light guide, and two semiconductor detectors that operate at room temperature, CdTe and HgI2. Also compared are spectra, energy resolutions, and counting efficiencies measured at a variety of gamma-ray energies between 30 and 1000 keV. The energy resolution of the NaI probe is substantially poorer than that of either semiconductor probe due in part to light losses in coupling the scintillator to the fiber optics. The semiconductor probes have complex spectral response due to charge-carrier trapping and K x-ray escape, and not all photoelectric interactions in these detectors contribute to the useful part of the photopeak. Above 120 keV the counting efficiency for the NaI probe is an order of magnitude higher than for the CdTe and HgI2 probes. Both energy resolution and counting efficiency are slightly better for the HgI2 probe than for the CdTe probe.

Cadmium↗