AAPM Banner
  • Volume/Page
  • Keyword
  • DOI
  • Citation
  • Advanced
   
 
 
 
Search Issue | RSS Feeds RSS
Previous Issue Next Issue

May 1978

Volume 5, Issue 3, pp. 181-239

Page 1 of 3 Pages Next Page | Jump to Page

Holographically stored x‐ray images: Gray‐tone reproduction

C. Clausen and U. Killat

Med. Phys. 5, 181 (1978); http://dx.doi.org/10.1118/1.594425 (7 pages)

Full Text: | Download PDF

Show Abstract
Storage of radiographs by holographic means is analyzed with emphasis on its gray‐tone reproduction characteristics. The density range and number of gray‐tone levels is found to be limited by random scattering in the holographic medium. The behavior is described quantitatively and is in satisfactory agreement with experimental data. Gray‐tone resolution is shown to be reduced by speckle noise. It is shown that there exists a trade‐off between speckle reduction and reproduced density range.
Show PACS
87.85.-d Biomedical engineering
42.40.Kw Holographic interferometry; other holographic techniques

Establishment of a beam line at the Fermi National Accelerator Laboratory for proton radiography

J. Curry and V. W. Steward

Med. Phys. 5, 188 (1978); http://dx.doi.org/10.1118/1.594426 (7 pages)

Full Text: | Download PDF

Show Abstract
A proton beam is extracted from the 200‐MeV linear accelerator at the Fermi National Accelerator Laboratory to investigate the efficacy of proton radiography in medical diagnosis. Fluence rates from 2×103 to 2×105 protons/cm2 s over a 28‐cm diameter field are obtained with a full width at half‐maximum beam‐energy spread of less than 3.61 MeV. The system is designed to radiograph most parts of the human body, including the head, with high‐speed screen–film as the imaging medium. Beam extraction and test results along with the medical implications of the beam quality are reported.
Show PACS
87.50.C- Static and low-frequency electric and magnetic fields effects
87.57.-s Medical imaging
87.63.-d Non-ionizing radiation equipment and techniques
87.85.Pq Biomedical imaging
29.20.-c Accelerators

Plastic scintillation filament detector system for 14CO2 breath‐analysis tests

Erhard Lorenz, Valerie A. Brookeman, and Walter Mauderli

Med. Phys. 5, 195 (1978); http://dx.doi.org/10.1118/1.594427 (4 pages)

Full Text: | Download PDF

Show Abstract
A 14CO2‐measuring system for breath‐analysis tests is described which utilizes plastic‐scintillator filaments as radiation‐detector elements. The 14C radioactivity in expired breath is measured directly, thus eliminating the need for trapping and counting of liquid scintillation‐counting solutions. Total CO2 concentration in expired breath is measured by an infrared detector, making no assumption of endogenous CO2 output and enabling results to be expressed as either a concentration (percentage of administered dose per unit of CO2) or total expired 14CO2. Advantages of this system over an ionization chamber are: significantly lower background variation and shorter breathing time to fill completely the detecting chamber with expired air. The system is easy to operate, transportable on a small cart to the patient’s bed if necessary, and applicable for continuous monitoring of 14CO2 in experimental animal studies.
Show PACS
29.40.Mc Scintillation detectors
87.50.C- Static and low-frequency electric and magnetic fields effects
87.57.-s Medical imaging
87.63.-d Non-ionizing radiation equipment and techniques
87.85.Pq Biomedical imaging

An empirical equation for screen MTFs

A. E. Burgess

Med. Phys. 5, 199 (1978); http://dx.doi.org/10.1118/1.594473 (6 pages) | Cited 7 times

Full Text: | Download PDF

Show Abstract
An empirical equation is described which accurately fits intensifying‐screen MTF data within the accuracy of the MTF measurements. The equation is S (u) =0.5 erfc[α ln(u/u0)]. The equation was fitted to data for 27 intensifying screens. Graphical and numerical results are presented. The maximum standard error was 0.02 and typical standard error was 0.01. Comparisons between results for three experimenters are also presented.
Show PACS
07.85.-m X- and γ-ray instruments
42.30.Lr Modulation and optical transfer functions

The relationship between resolution and speed of x‐ray intensifying screens

Gopala U. V. Rao and Panos Fatouros

Med. Phys. 5, 205 (1978); http://dx.doi.org/10.1118/1.594428 (4 pages) | Cited 4 times

Full Text: | Download PDF

Show Abstract
Two important physical characteristics of x‐ray intensifying screens, speed and resolution, are inversely related. However, the exact mathematical relationship, if any, between them is not known. To investigate this matter, a simple model is considered, which predicts that the product of the equivalent passband Ne and the square root of the speed is constant for a given phosphor material and given film. This relationship is found to be in excellent agreement with experimental data. The paper concludes with a discussion of the generalized validity of this relationship.
Show PACS
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

Correction for beam hardening in computed tomography

Peter K. Kijewski and Bengt E. Bjärngard

Med. Phys. 5, 209 (1978); http://dx.doi.org/10.1118/1.594429 (6 pages) | Cited 12 times

Full Text: | Download PDF

Show Abstract
Corrections for beam‐hardening artifacts in computed tomography can be made by using a model which assumes that water and bone mineral are the only constituents of tissue. With this model, a correction factor for the measured transmission values can be calculated such that the reconstructed attenuation coefficients have values corresponding to a monoenergetic source of known energy. Systematic errors in the uncorrected attenuation coefficients, which may be 5%, can be reduced to less than 1% if corrected transmission values are used.
Show PACS
87.57.-s Medical imaging
87.63.-d Non-ionizing radiation equipment and techniques
87.85.Pq Biomedical imaging
87.50.C- Static and low-frequency electric and magnetic fields effects

Calculations for beam‐flattening filters for high‐energy x‐ray machines

Ronald D. Larsen, Lisa Hartnagel Brown, and Bengt E. Bjärngard

Med. Phys. 5, 215 (1978); http://dx.doi.org/10.1118/1.594430 (6 pages) | Cited 4 times

Full Text: | Download PDF

Show Abstract
A flattening filter is an important component in a medical accelerator to modify the photon‐beam properties. To simplify the calculations of the flattening‐filter profile, we have developed a computer program which sums primary and scatter and then makes iterations in the primary component to produce a desired total‐dose profile. The program can account, to first order, for radial spectral changes by using an effective primary attenuation coefficient which varies with radius. Calculations made to model the Clinac‐4 dose profiles using the measured variation of half‐value layer with radius show good agreement with the measured data. It is shown that the variation of quality within the beam impairs the flatness that can be achieved over a range of depths. Since perfect flatness cannot be achieved for small and large fields with one flattening filter, one may choose a primary profile which is a compromise over a range of field sizes and depths. A compromise profile for a 4‐MV beam is discussed.
Show PACS
87.53.Bn Dosimetry/exposure assessment
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

Fast and slow neutrons in an 18‐MV photon beam from a Philips SL/75‐20 linear accelerator

D. Gur, J. C. Rosen, A. G. Bukovitz, and A. W. Gill

Med. Phys. 5, 221 (1978); http://dx.doi.org/10.1118/1.594431 (2 pages) | Cited 2 times

Full Text: | Download PDF

Show Abstract
Fast‐ and slow‐neutron contamination in an 18‐MV photon beam from a Philips SL/75‐20 linear accelerator has been measured. Aluminum and indium foils were activated to determine fast‐ and slow‐neutron fluence, which were largely independent of field sizes. Measured fast‐neutron fluences were typically 13.9×104 and 4.4×104 neutrons/cm2/rad of x ray inside and 5 cm outside the field, respectively. Slow‐neutron fluences, 1.3×104 neutrons/cm2/rad of x ray, remained relatively constant inside and outside the field. The reported results are about three times higher than neutron fluences recently reported with a betatron operated at the same energy.
Show PACS
87.50.C- Static and low-frequency electric and magnetic fields effects
87.85.-d Biomedical engineering
29.20.Ej Linear accelerators

Hazards to the eye lens and gonads from hard beta rays

S. M. Rao and S. J. Supe

Med. Phys. 5, 223 (1978); http://dx.doi.org/10.1118/1.594478 (3 pages)

Full Text: | Download PDF

Show Abstract
Considerable attention has been paid to the protection against x and γ radiation but comparatively less stress has been given to the possible hazard due to external radiation from high‐energy beta rays. In order to evaluate the magnitude of this hazard, central‐axis depth doses at different source‐to‐skin distances for 90Sr‐90Y and 32P sources were measured. Isodose curves in a testicular phantom for a 90Sr‐90Y source were measured. The data of Haybittle for 144Ce for 10 cm SSD has been included. From the measured data, the eye‐lens epithelium dose may be as high as 51%, 21.5%, and 82%, respectively, for the three sources instead of 15% as has been conventionally assumed. The isodose curves obtained in the testicular phantom indicate that an appreciable amount of testicular tissue can be subjected to radiation exposures. The radiation hazards due to high‐energy beta rays are not negligible and considerable care should be exercised while using these sources.
Show PACS
87.53.-j Effects of ionizing radiation on biological systems

Modification of electron‐beam dose distributions by transverse magnetic fields

Ravinder Nath and R. J. Schulz

Med. Phys. 5, 226 (1978); http://dx.doi.org/10.1118/1.594420 (5 pages) | Cited 9 times

Full Text: | Download PDF

Show Abstract
By applying a transverse magnetic field to a dosimetry phantom, an incident high‐energy electron beam is made to follow a spiral path in the course of slowing down. Certain levels, determined by the electron energy and the magnetic field strength, will be traversed several times by the same electrons. The net result of this process is an enhancement of the depth dose in relation to the entrance dose, and a more sharply defined depth of penetration. Experiments with 50‐ and 55‐MeV electrons traversing a 20.5‐kG field are shown to support the predictions of a detailed Monte Carlo calculation.
Show PACS
87.53.Bn Dosimetry/exposure assessment
87.50.C- Static and low-frequency electric and magnetic fields effects
Page 1 of 3 Pages Next Page | Jump to Page
Close

Medical Physics is an official science journal of the AAPM and of the COMP/CCPM/IOMP
William R. Hendee, Editor
Departments of Radiology, Radiation Oncology, Biophysics, Community and Public Health, Medical College of Wisconsin
One Physics Ellipse
College Park, Maryland 20740
301-209-3352

© 2013, American Association of Physicists in Medicine. Individual readers of this journal, and nonprofit libraries acting for them, are freely permited to make fair use of the material in it, such as to copy an article for use in teaching or research. (For other kinds of copying see "Copying Fees.") Permission is granted to quote from this journal in scientific works with the customary acknowledgment of the source. To reprint a figure, table, or other excerpt requires, in addition, AAPM may require that permission also be obtained from one of the authors. Address inquiries and notices to Penny Slattery, Journal Manager, Medical Physics Journal, AAPM, One Physics Ellipse, College Park, MD 20740-3846; email: journal@aapm.org.

close