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PubMedDate not supplied

[Use of linear proportional chambers for small-angle synchrotron radiation scattering in solutions of biopolymers].

The results of applying linear position sensitive proportional counters to diffuse small-angle synchrotron radiation scattering to biopolymer solutions are presented. Synchrotron radiation of the VEPP-3 storage ring (Institute of Nuclear Physics, Novosibirsk) was used. On the basis of small-angle scattering curve obtained from protein pepsinogen it has been shown that the exposure is about 100 times less than with conventional X-ray technique.

X-Ray Diffraction↗
PubMed2000

Ring filter to locate external boundaries in SPECT using scattered radiation.

A novel form of filter for SPECT is described, in which, after back projection and summation, the reconstructed signal is a measure of the total activity within a ring of specified radius, centre and width. The filter is applied to the problem of using Compton scattered radiation to locate external boundaries. In the simple case of the determination of the radius of a circular scattering body of known centre, the filter output would identify a transition region and define an appropriate threshold as the boundary was crossed. However it can also be applied to locate the boundaries seen in individual SPECT projections and hence trace out the envelope of the scattering body. Monte Carlo simulation based on 99mTc is used to test the performance of the filter in a range of situations, with encouraging results.

Monte Carlo Method↗
PubMed1983

Attenuation of primary and scatter radiation in concrete and steel for 18 MV X-rays from a Clinac-20 linear accelerator.

With the increasing number of high-energy linear accelerators being installed in radiation-therapy facilities, an increasing need exists for carefully measured data concerning the shielding parameters of photon radiation in the energy range above 10 MeV. In this study, the 18 MV X-ray beam from a Varian Clinac 20 linear accelerator was employed. Transmission parameters were measured for the primary X-ray beam in concrete and steel. The tenth value layer for steel was 11.3 +/- 0.6 cm and for concrete 45.0 +/- 2.0 cm. Also measured were the transmission parameters for scattered radiation vs angle in concrete and steel.

Construction Materials↗
PubMed1996

Understanding the relative sensitivity of radiographic screens to scattered radiation.

This study compared the relative response of various screen-film and computed radiography (CR) systems to diagnostic radiation exposure. An analytic model was developed to calculate the total energy deposition within the depth of screen and the readout signal generated from this energy for the x-ray detection system. The model was used to predict the relative sensitivity of several screen-film and CR systems to scattered radiation as a function of various parameters, such as x-ray spectra, phantom thickness, phosphor composition, screen thickness, screen configuration (single front screen, single back screen, screen pair), and readout conditions. In addition, measurements of the scatter degradation factor (SDF) for different screen systems by using the beam stop technique with water phantoms were made to verify the model results. Theoretically calculated values of SDF were in good agreement with experimental data. These results are consistent with the common observation that rare-earth screens generally produce better image quality than calcium tungstate screens and the CR screen.

Humans↗
PubMed2002

An investigation into the source of low energy scattered radiation of significance in film dosimetry.

The nature of the background optical density on films exposed to orthovoltage x-rays and electron beams has been studied for correction purposes. A higher than expected background value can be demonstrated by comparing the film scanned beam profile with water phantom ionisation scans of the same beam. A range of 3-5% increased background in the penumbral tail, with energy dependence, has been shown experimentally. Testing the assumption that this increased background is due to Cerenkov radiation produced in the film, Filmstrips were interleaved in a solid water equivalent phantom and exposed to 300kV orthovoltage x-ray beams and 5MeV to 12MeV electron beams. The film stacks were made up of single or multiple bare filmstrips, multiple filmstrips interleaved with black paper, and multiple filmstrips interleaved with overhead transparency sheet. The experimental result demonstrated that visible light was not significantly responsible for an enhanced film optical density, but rather that this was due to scattered radiation, with a complex low energy spectrum, arising from the film silver halide emulsion or base. An improved background correction technique is developed which incorporates this unexpected background value as an added component in the correction applied to the measured optical density. The resulting profiles exhibit improved agreement between film and ionization chamber measurements in the penumbra and tail regions.

Artifacts↗
PubMed2004

The effect of source to image distance on scattered radiation to the image receptor.

In performing experimental or theoretical studies of the effect of source to image distance on dose to the patient, it is conventional to assume that the dose to the image receptor should remain constant at each SID. However, if the proportion of scattered radiation reaching the image receptor depends on the SID, then this assumption will be invalid. In this paper, the effect of SID on the scatter fraction has been determined using a Monte Carlo simulation, using EGSnrcMP. The Monte Carlo code was first benchmarked against three independent experimental studies, and shown to give excellent agreement. In order to obtain agreement with experiment, it was necessary to include Rayleigh scatter and bound Compton effects and to properly simulate multiple scattering. The scatter fraction was then determined for a range of SIDs from 100 to 300 cm, for a range of conditions, including kVp setting, phantom thickness, field size, object to image distance, collimation to entrance surface, centre of phantom and image receptor, and a range of image receptor materials. The results indicate that the scatter fraction is independent of SID within a few percent, except when there is a large object to image distance.

Algorithms↗
PubMed1991

[Leaded screens for protection of the body against scattered radiation in intraoral radiography].

The use of a protective leaded shield as an alternative to leaded aprons and leaded neck collars for reduction of body doses originating from scattered radiation in intraoral radiography is discussed. The shield is stiff and has a U-shaped form fitting the neck of the patients and is kept in position by the patient himself. During exposure the shield is pressed against the patient's neck and kept in close contact with the inferior border of the mandible in a horizontal position. Three products of shields are described, all having lead equivalents of 0.5 mm. The protection of the thyroid gland is of maximum efficiency. Measurements of absorbed doses have shown the shield to have a protective effect equal to leaded aprons in cranial body regions, while gonadal doses are a little higher. Upper extremities are always protected by a shield, while many patients keep their hands and arms upon and not under an apron. Shields are easy to handle for the staff, hygienic, and cheaper than an apron. They can hardly be damaged and leaks following handling will not occur as for aprons. Leaded shields have recently been accepted as alternative to leaded aprons by the Danish National Institute of Radiation Hygiene.

Adolescent↗
PubMed1996

Scatter radiation intensities about mammography units.

The intensity of scattered x rays about two clinically installed mammographic units was measured at 25, 30, and 35 kVp over a range of scattering angles. The scatter-to-primary ratio for backscattering is measured to be 4 to 7 times greater than that for 90 degrees scattering. The scatter fraction is the ratio of scatter dose at 1 m to primary dose at 1 m per primary x-ray field area. Averaged over various phantom and field sizes, the scatter fraction for mammography ranges from 0.01 x 10(-6) cm-2 to 0.2 x 10(-6) cm-2 at 0 degrees, approximately 0.25 x 10(-6) cm-2 at 90 degrees, to 1.7 x 10(-6) cm-2 at 163 degrees, with not more than 30% difference between the scatter intensity generated at 25 and 35 kVp. The differences in the scatter fraction measured off two mammography units from two manufacturers are less than 10% for scattering angles greater than 45 degrees. However, the intensity of forward scatter depends strongly on the construction of the image receptor assembly and x-ray tube collimator, with a sharp rise in the scatter fraction at approximately 25 degrees for the 18 x 24 cm2 image receptor apparently due to scatter off the collimator. The dose (normalized at 1 m per 100 patients) in directions toward adjacent walls, ceiling, and floor is conservatively calculated, providing a quick method for estimating the unshielded dose to an occupied area.

Female↗