63 research outputs found
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LIQUID XENON MULTIWIRE PROPORTIONAL CHAMBERS FOR NUCLEAR MEDICINEAPPLICATIONS
The need for improved spatial resolution in nuclear medicine has long been recognized. Notable attempts to achieve this goal are the gas-filled wire chambers and solid-state detectors. (1) However, at energies above 100 keV, gas-filled chambers suffer from poor detection efficiency and a long recoil electron range in the gas. While it is advantageous to pressurize these chambers to 10 or more atmospheres, structural design of the thin window presents a formidable task. High-resolution optimal collimators do not appear to have sufficient strength to be used as a pressure support window. Solid-state detectors, while having the potential of a gamma camera with a superb energy resolution, are presently studied on a very small scale due to technological and cost limitations. Aside from the detector, the parallel-hole collimator presents a real limit to the resolution of the camera. A factor of two improvement in the resolution results in a factor of four loss in the collimator's transmission. A careful analysis of optimal collimators and the application of collimators designed for a specific depth range and resoluation are part of our overall program. Our goal has been the development of a liquid-xenon multiwire gamma camera with 2- to 3-mm spatial resolution, high counting-rate performance, high sensitivity, and the potential for scaling-up in size. Important ingredients for successful imaging in the prototype chamber discussed in this paper were the discovery of electron multiplication in liquid xenon, (2) the development of reliable purification techniques, (3) and the ability to extract electrons from the liquid into the gaseous phase. This paper is specifically addressed to the subject of detector development with liquid-xenon totally-filled chambers and recent work with dual-phase chambers in which the {gamma} rays are converted in the liquid phase and are electronically detected in the gaseous phase
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LIQUID XENON FILLED WIRE CHAMBERS FOR MEDICAL IMAGINGAPPLICATIONS
In 1968, Luis Alvarez suggested that a high-resolution multiwire particle detector could be developed using a thin layer of liquified noble gas as the detection medium. After key problems in chamber construction, purification, and readout had been solved, a spatial resolution of 15 {micro} rms was demonstrated. Work is in progress to build high-resolution chambers and measure their properties for particle physics experiments at high-energy accelerators. The liquid xenon multiwire chamber also has potential in nuclear medicine for imaging isotope distributions with an unprecedented combination of gamma-ray detection efficiency and spatial resolution. A preliminary 24-wire chamber has been constructed; this chamber detects 280-keV gamma rays with 65% efficiency and 4-mm FWHM spatial resolution. Initial images of point and distributed sources are very promising, and the liquid purity can be maintained for periods exceeding several days
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ADVANCED INSTRUMENTATION FOR POSITRON EMISSION TOMOGRAPHY
This paper summarizes the physical processes and medical science goals that underly modern instrumentation design for Positron Emission Tomography. The paper discusses design factors such as detector material, crystalphototube coupling, shielding geometry, sampling motion, electronics design, time-of-flight, and the interrelationships with quantitative accuracy, spatial resolution, temporal resolution, maximum data rates, and cost. 71 refs., 3 figs., 3 tabs
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BIOLOGICAL EFFECTS AND PHYSICAL SAFETY ASPECTS OF NMR IMAGING AND IN VIVO SPECTROSCOPY
An assessment is made of the biological effects and physical hazards of static and time-varying fields associated with the NMR devices that are being used for clinical imaging and in vivo spectroscopy. A summary is given of the current state of knowledge concerning the mechanisms of interaction and the bioeffects of these fields. Additional topics that are discussed include: (1) physical effects on pacemakers and metallic implants such as aneurysm clips, (2) human health studies related to the effects of exposure to nonionizing electromagnetic radiation, and (3) extant guidelines for limiting exposure of patients and medical personnel to the fields produced by NMR devices. On the basis of information available at the present time, it is concluded that the fields associated with the current generation of NMR devices do not pose a significant health risk in themselves. However, rigorous guidelines must be followed to avoid the physical interaction of these fields with metallic implants and medical electronic devices. 476 refs., 5 figs., 2 tabs
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Recent developments in positron emission tomography (PET) instrumentation
This paper presents recent detector developments and perspectives for positron emission tomography (PET) instrumentation used for medical research, as well as the physical processes in positron annihilation, photon scattering and detection, tomograph design considerations, and the potentials for new advances in detectors. 117 refs., 4 figs., 4 tabs
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Clamshell tomograph
The invention is a tomograph modified to be in a clamshell configuration so that the ring or rings may be moved to multiple sampling positions. The tomograph includes an array of detectors arranged in successive adjacent relative locations along a closed curve in a first position in a selected plane, and means for securing the detectors in the relative locations in a first sampling position. The securing means is movable in the plane in two sections and pivotable at one point and only one point to enable movement of at least one of the sections to a second sampling position out of the closed curve so that the ends of the section which are opposite the point are moved apart a predetermined space
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