摘要:

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.

ISSN:0269-3127    

DOI:10.1118/1.594414

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

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.

ISSN:0269-3127    

DOI:10.1118/1.594415

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

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.

ISSN:0269-3127    

DOI:10.1118/1.594471

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

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 appropriateCλorCEmultiplied by the60Co 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‐cm3Farmer, 0.5‐cm3Spokas, 3‐cm3Shonka, 1‐cm3PTW, and 1‐cm3Memorial 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.

ISSN:0269-3127    

DOI:10.1118/1.594416

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

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.

ISSN:0269-3127    

DOI:10.1118/1.594417

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

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.

ISSN:0269-3127    

DOI:10.1118/1.594470

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

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.

ISSN:0269-3127    

DOI:10.1118/1.594418

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

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.

ISSN:0269-3127    

DOI:10.1118/1.594419

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

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).

ISSN:0269-3127    

DOI:10.1118/1.594406

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

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.

ISSN:0269-3127    

DOI:10.1118/1.594407

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY