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At least 19 recordsLinked to original sources
PubMed1979

Scattered radiation from beam modifiers used with megavoltage therapy units.

The magnitude and distribution of scattered radiation produced by scatterers inserted into megavoltage therapy beams, including the beams from an 8MV medical linear accelerator and a 60Co teletherapy unit, were investigated. The intensity distribution of scatter depends on the distance from the scatterer to the measurement plane (retraction distance) and also, to a lesser extent, on the atomic number of the scattering material. The effective energy of the scattered radiation was determined by depth dose measurements in tissue equivalent material using thermoluminescent dosimeters and was found to increase with photon beam energy.

Cobalt Radioisotopes↗
PubMed1976

Exposure of radiologists to scattered radiation during radiodiagnostic examinations.

The exposure to scattered radiation was measured on both hands, the forehead and gonads of six radiologists by means of thermoluminescent dosimeters in two fluoroscopy rooms. Exposure of the forehead was found not to exceed approximately 1% of the maximum permissible exposure (MPD) (3% pursuant to NCRP (recommendations). During examinations of the colon, the exposure of the right hand proved to be significantly higher compared to the left. There was only slight exposure to the gonads as measured behind the apron.

Environmental Exposure↗
PubMed1977

Scattered radiation doses to infants and children during EMI head scans.

Scattered radiation doses to the eyes, thyroid and gonads of infants and children undergoing EMI head scans have been measured with thermoluminescent dosimeters. An average skin dose of 1.3 rad per scan was measured. Results are reported relative to incident skin dose and indicate that it is likely that there is no somatic or genetic hazard due to scattered radiation during an EMI head scan.

Body Height↗
PubMed1978

The intensity of scattered radiation in mammography.

The ratio of scattered-to-primary radiation has been measured for a range of x-ray tube voltages, field sizes and phantom thicknesses that typify clinical mammographic situations. The relative intensity of scattered radiation measured was essentially independent of kVp but increased as the phantom thickness and radiation field size increased. For the range of field sizes and phantom thicknesses that typify clinical situations the intensity of scattered radiation varied from about 40 to 85% of the primary beam intensity indicating that only from about 54 to 71% of the primary beam contrast is imaged in mammography.

Mammography↗
PubMed1975

Spectral measurements and Monte Carlo calculations of scattered radiation from therapeutic radiation sources.

Spectral measurements have been made on scattered radiation in a perspex phantom in various depths from a kilocurie 60Co unit and a 6 MeV linear accelerator using a NaI crystal spectrometer. The measurements are compared to Monte Carlo calculations and a good agreement is obtained. The measured total photon distributions make the basis for calculations of absorbed dose and track length distributions in LET and their average values for the different depths and fields.

Cobalt Radioisotopes↗
PubMedDate not supplied

Dynamic radiography. An evaluation of cardiac motion by the analysis of scattered radiation during fluoroscopy.

A non-invasive technique, utilizing scattered radiation, has been developed to monitor and measure the motion of the epicardial surface during fluoroscopy. A number of dogs were studied using a monitoring device which consists of an X-Ray beam collimator, collimated sodium iodide dectetors and their associated electronics. The detector signals are computer processed to obtain frequency fingerprints of epicardial motion that may, in the future, indicate the condition of the myocardium.

Computers↗
PubMed1977

Sensitivity of radiographic screens to scattered radiation and its relationship to image contrast.

For incident X-ray beams of greater than 60 kVp, intensifying screens of rare earth phosphors produced higher radiographic image contrast in the presence of scattered radiation than did screens of calcium tungstate. This was attributed to fundamental energy absorption interaction differences. X-ray absorption is a function of the position of the k-absorption edge of the screen phosphor relative to the X-ray energy spectra of the primary and scattered X-rays. Spectral measurements of X-ray absorption showed that the ratio of primary absorption to scattered absorption is higher for the rare earth screens, causing lower relative sensitivity to the non-information-containing scattered radiation from the radiographic object.

Gadolinium↗
PubMed1977

Radiation scattering and the determination of regional cerebral blood flow by radioisotope clearance.

The sources of error involved in the measurement of regional cerebral blood flow (rCBF) with radioactive tracers in man have been studied. This report shows that one of the main sources is the weakness of the energy emitted by the tracers used. Clearance curves obtained with scalp detectors are subject to interference: the radiation measured originates not only in the region studied but also, by scattering, from the rest of the brain. Because of the weak energy levels involved, the scattered radiation contributes significantly to the total measured radiation, and for the same reason it is impossible to distinguish clearly the scattered radiation from that arriving directly. These systematic errors in rCBF measurements were studied quantitatively by in vitro tests and computer simulation, and limits were established for resulting alterations of all varialbes determined (grey and white matter flow, mean flow, compartment weight). It was concluded that the biologic origin of a modification of rCBF can be affirmed only in the case of changes of at least 10%.

Cerebrovascular Circulation↗
PubMed1975

Exposure of the radiologist to scattered radiation during angiography.

At least 90% of the exposure of a radiologist's crystalline lens and right hand to scattered radiation during angiography, investigated by thermoluminescent dosimetry, proves to be due to radiography during and immediately after manual injection of the contrast medium. Therefore, manual injection should be replaced by remotely controled injection by means of an injector. The exposure of a radiologist's gonads (measured behind a lead apron) proves negligible. At the low exposure rates to be expected, integrating measurements should be made.

Angiography↗
PubMedDate not supplied

Analysis of the significance of scattered radiation in reduced dose mammography, including magnification effects, scatter suppression, and focal spot and detector blurring.

A systems analysis of reduced dose mammography with scatter removal has quantitatively specified the relationships between the several parameters in mammography systems. While the results are only preliminary in the sense that they need to be proven experimentally, they do seem to provide a good feel for the nature of the important trade-offs. The major uncertainties in the analysis probably have to do with the formal equivalence, that is implicit in the aperture theory, between large area and detail contrast, as well as the output versus focal spot relationship that was adopted. Also, there are important questions about specifying motion unsharpness as a function of exposure time in mammography examinations.

Mammography↗
PubMedDate not supplied

Scattered radiation from a neutron collimator.

Fast-neutron beams are being employed in radiotherapy trials and associated radiobiology studies at numerous centers in the U.S., Europe, and Japan. Since collimated beams of various sizes and shapes are employed, it is desirable to know the composition of the scattered radiation component contributed by the collimator. A simple method is shown for deducing the field composition in terms of a three-component model, from measurements made with three ionization chambers (tissue-equivalent, graphite, and magnesium). The dose contributed by the scattered radiation in the present example was found to be predominantly due to fast neutrons indistinguishable from those in the primary spectrum (from 35-MeV D+ on Be). This method may prove useful for measurements in phantoms as well.

Fast Neutrons↗
PubMed1979

Scattered radiation from trimmer bars in the cobalt-60 teletherapy machines.

The amount of scattered radiation resulting from four Cobalt-60 teletherapy units in four different hospitals when trimmer bars were fully extended was studied. Scatter was present for all machines checked at between 10% and 20% of the central axis dose. Clinical significance is also discussed.

Cobalt Radioisotopes↗
PubMed1979

A new technique for the calculation of scattered radiation from 60Co-teletherapy beams.

An alternative to the Clarkson technique for calculating total scattered radiation is presented. Resultant TAR values are compared with those obtained by the Clarkson technique for the same field. The new scatter technique is always more than 2.8 times faster than the Clarkson technique and more than 4 times faster on a large number of fields. The new approach appears to offer a simple and expedient alternative to the more traditional methods for iiregular field dose calculations.

Cobalt Radioisotopes↗
PubMed1976

A method to absorb scattered radiation without attenuation of the primary beam.

A method is presented for improving image quality by decreasing the scattered radiation. Two pairs of lead plates, one above and one below the patient, move in arcs with a common pivot point, the focal spot of the x-ray tube. The lower plates are separated by a 1-cm slot. The upper plates are also separated by a slot, the edges of which lie on common radii from the focal spot. The image is formed by moving the slots so that the X-ray beam emerging from the object sweeps across the film with a uniform speed during the exposure.

Humans↗