PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Scattering, Radiation”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 145 records · Page 8Linked to original sources
PubMedDate not supplied

Scatter radiation.

Explore the source record for details and available documents.

Absorption↗
PubMed2000

Measurements of the average thickness of material using scattered radiation

A method for determination of the average thickness of material placed between a gamma-ray source and a detector is presented. The method requires the measurement of the ratio between the number of gamma-rays scattered at small angles in the material and registered in the spectrum and the number of gamma-rays penetrating the material without interacting with it and registering in the full-energy peak. The relation describing that ratio in terms of the average gamma-ray path length in the sample, the energy interval where the scattered radiation is measured and the detector response to unscattered gamma-rays was verified by measurements of gamma-ray path lengths in material with known thicknesses at energies of 662 and 1115 keV. Differences between the measured and known thicknesses were less than 15% for thicknesses of copper between 2.5 and 17 g/cm2.

Journal Article↗
PubMedDate not supplied

Characterization of the point spread function and modulation transfer function of scattered radiation using a digital imaging system.

A digital radiographic system was used to measure the distribution of scattered x radiation from uniform slabs of Lucite at various thicknesses. Using collimation and air gap techniques, [primary + scatter] images and primary images were digitally acquired, and subtracted to obtain scatter images. The scatter distributions measured using small circular apertures were computer fit to an analytical function, representing the circular aperture function convolved with a modified Gaussian point spread function (PSF). On the basis of goodness of fit criterion, the proposed Gaussian function is a very good model for the scatter PSF. The measured scatter PSF's are reported for various Lucite thicknesses. Using the PSF's, the modulation transfer functions are calculated, and this spatial frequency information may have value in analytical scatter removal techniques, grid design, and air gap optimization.

Computers↗
PubMedDate not supplied

Experimental verification of a technique for predicting scattered radiation transfer: application to low photon energies.

It is shown that predictions can be made of scatter-to-primary ratios for a variety of mammographic configurations. The different configurations can be produced by changes in source-detector distance; source-phantom distance; air gap; photon energy; phantom composition, thickness, and cross-sectional area. A detailed analysis of the effect of a grid is also considered. The predictions are not computationally intensive. Experimental verifications of the predictions for varying phantom cross-sectional dimensions, source-detector distance, and air gaps with and without a grid have been carried out. Variations with phantom thickness were not considered in this paper. Detailed comparisons between experiment and theory indicate that scatter-to-primary ratios were predicted within one standard deviation and the coefficient of variation is within 3% for most of the data points with the worst case coefficient of variation about 6%. Measurements of grid secondary transmission have also been compared to theoretical predictions and agreement is within the coefficient of variation of about +/- 15%.

Humans↗
PubMed2006

CT fluoroscopy shielding: decreases in scattered radiation for the patient and operator.

PURPOSE: High-radiation exposure occurs during computed tomographic (CT) fluoroscopy. Patient and operator doses during thoracic and abdominal interventional procedures were studied in the present experiment, and a novel shielding device to reduce exposure to the patient and operator was evaluated. MATERIALS AND METHODS: With a 16-slice CT scanner in CT fluoroscopy mode (120 kVp, 30 mA), surface dosimetry was performed on adult and pediatric phantoms. The shielding was composed of tungsten antimony in the form of a lightweight polymer sheet. Doses to the patient were measured with and without shielding for thoracic and abdominal procedures. Doses to the operator were recorded with and without phantom, gantry, and table shielding in place. Double-layer lead-free gloves were used by the operator during the procedures. RESULTS: Tungsten antimony shielding adjacent to the scan plane resulted in a maximum dose reduction of 92.3% to the patient. Maximum 85.6%, 93.3%, and 85.1% dose reductions were observed for the operator's torso, gonads, and hands, respectively. The use of double-layer lead-free gloves resulted in a maximum radiation dose reduction of 97%. CONCLUSIONS: Methods to reduce exposure during CT fluoroscopy are effective and should be searched for. Significant reduction in radiation doses to the patient and operator can be accomplished with tungsten antimony shielding.

Antimony↗
PubMed1994

Method for reducing scatter radiation dose to the contralateral breast during tangential breast irradiation therapy.

PURPOSE: To reduce scatter dose to the contralateral breast during tangential breast irradiation therapy. MATERIALS AND METHODS: The authors used a 4-mm-thick commercially available vinyl-coated flexible lead shield that contains a compound of vinyl resin and lead powder of 1-mm-equivalent lead density. Contralateral scatter dose was measured at 5 cm outside the geometric field edge and along the field axis, with and without use of block trays and different wedges. RESULTS: On the skin, contralateral scatter dose from the medial tangential beam was reduced from about 15% to about 5% of the therapeutic dose delivered to the treated breast. The bulk of scatter dose was absorbed within the first 2 cm of breast tissue. CONCLUSION: Reduction in unwanted scatter dose to the contralateral breast is in accord with the philosophy of keeping radiation exposure as low as reasonably achievable and might be of most benefit for young patients.

Breast↗