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Mar 1978

Volume 5, Issue 2, pp. 79-171

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Thermometry considerations in localized hyperthermia

T. C. Cetas and W. G. Connor

Med. Phys. 5, 79 (1978); http://dx.doi.org/10.1118/1.594414 (13 pages) | Cited 10 times

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The introduction of local hyperthermia as a method of cancer therapy implies the necessity of quantitative measurements of the thermal dose. Our intention is to describe the nature of the problem, both physically and physiologically, with illustrations drawn from thermographic measurements in phantoms and in animals. The characteristics of a thermometry calibration facility are described. Some measurement problems associated with conventional thermometer probes are mentioned and several new thermometers which were developed for use in the electromagnetic fields are reviewed. We present some of the concepts that will guide the development of noninvasive thermometry. Systemic hyperthermia is not considered. We recommend that other reviews specifically directed toward localized hyperthermia be prepared on the methods of heating and on thermal physiological problems.
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87.55.-x Treatment strategy
87.50.S- Radiofrequency/microwave fields effects
87.50.W- Optical/infrared radiation effects

Theoretical approach to laser trabeculotomy

Chmouel R. Goldschmidt and Uriel Ticho

Med. Phys. 5, 92 (1978); http://dx.doi.org/10.1118/1.594415 (8 pages) | Cited 3 times

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Theoretical aspects of laser characteristics as well as the physics parameters involved in laser trabeculotomy in open‐angle glaucoma are put forward. Outflow hydrodynamics and perforation mechanism as well as the required optical matching system are evaluated in detail.
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87.50.S- Radiofrequency/microwave fields effects
87.50.W- Optical/infrared radiation effects
42.66.-p Physiological optics

Electron paramagnetic resonance investigation of high‐spin iron (III) in cancer

F. W. Warner, R. Stjernholm, and I. Cohn

Med. Phys. 5, 100 (1978); http://dx.doi.org/10.1118/1.594471 (7 pages) | Cited 2 times

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The concentration of iron (III)–transferrin (IT) in whole blood and serum, along with another high‐spin (five unpaired electrons) iron complex (probably IT) accumulated by tumor tissue, was investigated by electron paramagnetic resonance (EPR) spectroscopy during the development of Murphy–Sturm rat lymphosarcoma. The observed changes in concentration (μg/ml) of IT in sera/blood were generally complementary to those from tissue and the character of the modifications suggested the existence of three distinct phases of systemic response to the implantation: (1) an initial response, evidenced by a sharp reduction in serum IT and somewhat high tissue‐IT concentration (μg/g); (2) a period in which the tumor is becoming established, indicated by relatively constant tissue IT levels and near normal serum IT; and (3) the onset of rapid cell multiplication, characterized by increased total tissue‐IT accumulation that rises to above 200% of normal available serum iron, increasing tissue‐IT concentration, and rapidly declining serum‐IT concentration. The results suggest that, in the face of an implanted tumor there are two detectable abnormal serum‐IT responses: (1) an initial change, probably due to systemic blockage of iron reutilization; and (2) extraction of IT from serum by multiplying tumor cells, which is probably a major contributor to reduced serum‐IT levels and ultimately anemia.
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33.35.+r Electron resonance and relaxation
87.57.-s Medical imaging
87.63.-d Non-ionizing radiation equipment and techniques
87.85.Pq Biomedical imaging

Ionization collection efficiencies of some ionization chambers in pulsed and continuous radiation beams

J. G. Holt, R. E. Stanton, and R. E. Sell

Med. Phys. 5, 107 (1978); http://dx.doi.org/10.1118/1.594416 (4 pages) | Cited 2 times

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The most commonly used method of calibrating high‐energy photon or electron beams consists in converting cavity ionization to dose by the application of the appropriate Cλ or CE multiplied by the 60Co correction factor. The correct interpretation of calibration data for pulsed photon or electron beams requires a knowledge of the charge collection efficiencies of the ionization chambers used. The results are presented of efficiency measurements for both pulsed and continuous beams made with these chambers: 0.6‐cm3 Farmer, 0.5‐cm3 Spokas, 3‐cm3 Shonka, 1‐cm3 PTW, and 1‐cm3 Memorial pancake. The dependence of collection efficiency on collection voltage, dose rate, and dose per pulse is demonstrated. These results are shown to agree with Boag’s formulas for collection efficiency. Attention is drawn to the fact that several kinds of dosimeters provide only minimal collection voltages for efficient collection of charge at high dose rates, especially in Linac electron beams. It is recommended to check the collection efficiency of chambers which are to be used at high dose rates, and a simple method for this purpose is described.
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87.55.-x Treatment strategy
87.50.C- Static and low-frequency electric and magnetic fields effects

Development of Bragg diffraction imaging for medical use

D. Frieda, P. Spiegler, F. Kearly, M. Greenfield, and R. Stern

Med. Phys. 5, 111 (1978); http://dx.doi.org/10.1118/1.594417 (4 pages)

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Experience gained in developing a real‐time acoustical imaging system using Bragg diffraction is presented. Particular emphasis has been placed on medical applications. We have studied the difficulties in assembling a system capable of producing high‐quality images. Engineering data on the optical mounting and on the design of the transducer along with representative images are presented and discussed.
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87.57.-s Medical imaging
87.63.-d Non-ionizing radiation equipment and techniques
87.85.Pq Biomedical imaging
43.80.-n Bioacoustics
87.50.Y- Biological effects of acoustic and ultrasonic energy

Noise characteristics of a microchannel plate x‐ray image intensifier

Robert G. Gould, Philip F. Judy, and Bengt E. Bjärngard

Med. Phys. 5, 115 (1978); http://dx.doi.org/10.1118/1.594470 (5 pages)

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The noise performance of an experimental microchannel plate x‐ray image intensifier has been evaluated. The intensifier, constructed for use with photons of energies between 20 and 150 keV, uses an MCP as the photon‐to‐electron converter. The influence of noise was determined by analysis of the optical‐density fluctuations of a photograph of the viewing screen of the intensifier when the conversion layer was exposed to between 1 and 60 mR. Additionally, the contrast‐detail performance of the experimental device was determined. The influence of both stochastic noise, due to quantum mottle and pulse‐height variations, and structural noise, due to fluctuations in inherent gain from point to point, have been considered by using a model that adds these components.
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87.57.-s Medical imaging
87.63.-d Non-ionizing radiation equipment and techniques
87.85.Pq Biomedical imaging
07.85.-m X- and γ-ray instruments

An automated dosimetry data‐acquisition and analysis system at the LAMPF pion therapy facility

I. Rosen, A. Smith, R. Lane, C. Kelsey, D. Lake, K. Hogstrom, J. Somers, J. Helland, R. Kittell, H. Amols, J. Bradbury, and C. Richman

Med. Phys. 5, 120 (1978); http://dx.doi.org/10.1118/1.594418 (4 pages)

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An automated data‐acquisition and analysis system has been developed for dosimetry measurements on the pion therapy beam at the Clinton P. Anderson Meson Physics Facility Biomedical Channel in Los Alamos using a PDP‐11/45 computer and CAMAC interface. Initialization, test, and monitor programs allow the user to set the physical limits of scanner travel, test the data lines, calibrate the analog signals for the scanner position, and monitor the analog versus digital values of the scanner position during operation. Data‐acquisition programs scan beams in one, two, and three dimensions. Many options are available to the user in selecting the scan parameters and in changing some of these parameters during scanning. Data‐analysis programs provide reproduction of stored data, comparison of linear scans, beam profiles along any line of a planar or volume scan, and isodose distributions from any planar scan or from any plane of a volume scan. Other programs summarize stored data files and search for specific data according to the user’s instruments.
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87.80.-y Biophysical techniques (research methods)
87.50.C- Static and low-frequency electric and magnetic fields effects

An evaluation of the performance characteristics of different types of collimators used with the EMI brain scanner (MKI) and their significance in specific clinical applications

Stephen R. Thomas, Andrew J. Schneider, James G. Kereiakes, Robert R. Lukin, A. Alan Chambers, and Thomas A. Tomsick

Med. Phys. 5, 124 (1978); http://dx.doi.org/10.1118/1.594419 (9 pages) | Cited 2 times

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The characteristics of various types of collimators have been studied systematically for the EMI Mark I brain scanner. The degree of collimation ranged from the 13‐mm adjacent A and B slices to 3‐mm separated slices. Multiple phantom studies (including variable density immiscible liquid interfaces) have been performed to evaluate the effect of collimation on (a) the line‐spread function, (b) the change in effective absorption number, and (c) volume averaging. Effects associated with the technique settings involving the kVp, the mA, and the scan time were also investigated. The results of TLD dose measurements as a function of collimation are presented. The significance of collimation in specific clinical studies involving small, fairly well‐circumscribed lesions is discussed.
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87.85.-d Biomedical engineering
87.80.-y Biophysical techniques (research methods)
07.85.-m X- and γ-ray instruments

New method for the experimental evaluation of x‐ray grids

C. E. Dick and J. W. Motz

Med. Phys. 5, 133 (1978); http://dx.doi.org/10.1118/1.594406 (8 pages) | Cited 3 times

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This work describes a new method for the experimental evaluation of antiscatter x‐ray grids in radiography. Five commercial grids are evaluated in terms of two parameters which are determined only by the construction of the grid and the x‐ray energy. A comparison of the grid performances was made for the x‐ray energies and scatter conditions that usually apply to chest radiography and mammography. The results show that for maximum scatter conditions the grid enhances the subject contrast by factors of approximately 6 and 2 in chest radiography and mammography, respectively, and that the contrast increases as the grid ratio increases. Also, in these examinations, the results show that, with improved grids, it is possible to reduce the patient exposures required for the no‐grid case by approximately one‐half without loss of the image‐information content (signal‐to‐noise ratio).
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87.57.-s Medical imaging
87.63.-d Non-ionizing radiation equipment and techniques
87.85.Pq Biomedical imaging
07.85.-m X- and γ-ray instruments

An instrument with digital readout for indirect determination of kVp

Edward L. Chaney and William R. Hendee

Med. Phys. 5, 141 (1978); http://dx.doi.org/10.1118/1.594407 (5 pages) | Cited 4 times

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An electronic instrument with digital readout has been designed and constructed for indirect determination of the kVp applied to diagnostic x‐ray tubes. The signals from two detectors exposed simultaneously to a differentially filtered x‐ray beam are processed by analog computing circuitry to yield an output signal directly proportional to the applied peak kilovoltage. Theory and preliminary results are presented and discussed.
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07.85.-m X- and γ-ray instruments
87.57.-s Medical imaging
87.63.-d Non-ionizing radiation equipment and techniques
87.85.Pq Biomedical imaging
87.50.S- Radiofrequency/microwave fields effects
87.50.W- Optical/infrared radiation effects
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Medical Physics is an official science journal of the AAPM and of the COMP/CCPM/IOMP
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Departments of Radiology, Radiation Oncology, Biophysics, Community and Public Health, Medical College of Wisconsin
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301-209-3352

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