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PubMedDate not supplied

Monte Carlo simulation of the scattered radiation distribution in diagnostic radiology.

Monte Carlo techniques were employed to evaluate the point spread function (PSF) of scattered radiation in diagnostic radiology. The Monte Carlo procedure is described and shown to compare well with Monte Carlo scatter analysis of other authors. The intensity and distribution of the PSF are described independently. The effects of object thickness, air gap, and beam spectra are examined. An analytic derivation of the scatter PSF is presented in a companion article, and the Monte Carlo results discussed herein are used for comparison.

Biophysical Phenomena↗
PubMedDate not supplied

[The measurement of scattering radiation in the radiation control of x-ray offices].

A procedure for measuring the power of an ambient and goal-oriented equivalent scattered radiation dose in the radiation control of X-ray rooms. The procedure is based on the concept of the effective solid angle of a dosimeter directivity diagram. The plots of the angular response of a S2010 selective X-ray dosimeter for studying the radionuclides 119Sn, 241Am, 57Co are exemplified. The scaling factors for dosimetric reading for isotropic and nonuniform fields of radiation were calculated from the obtained values of effective angular solid angles (0.7, 0.8, 1.2 pi).

Humans↗
PubMed1983

The validity of Monte Carlo simulation in studies of scattered radiation in diagnostic radiology.

A computer program using Monte Carlo methods has been developed for the simulation of photon scattering in tissue-equivalent phantoms for incident x-rays in the diagnostic energy range. The study verified that the sampling schemes used in the program can produce random samples according to the theoretical probability distribution functions which describe the photon-scattering process. The Monte Carlo program was applied to determinations of the scatter fractions and edge responses for various phantom sizes, X-ray energies, and recording systems. These quantities were also measured experimentally under comparable imaging conditions. Excellent agreement was obtained between the predicted and experimental results. This investigation established the validity of our Monte Carlo calculations for studies of the physical characteristics of scattered radiation in diagnostic radiology.

Computers↗
PubMed1984

Effect of scatter radiation on the planar source sensitivity of a collimated detector.

A theoretical model is proposed to describe the effect of a scattering medium on the plane-source sensitivity of a collimated detector. According to this model the scatter fraction fs(z) of the system is a linear function of the thickness z of the scattering medium and for any collimator geometry depends on the photopeak energy and the window settings as well as on the geometrical and physical characteristics of the scintillation detector. To calculate the parameters of the linear function fs(z), physical constants from the literature were used. The validity of the model was verified by experimental data. The computed parameters were found to differ slightly from the experimental ones and the differences were attributed to several approximations made during the theoretical analysis. The approach used for the determination of these parameters has contributed to a better understanding of the physical meaning of the factors affecting the generation of the scattered radiation and its detection by scintigraphic imaging systems.

Mathematics↗
PubMed1994

Incorporation of scattered radiation into dual-energy radiologic theory and application to mammography.

A previous analysis of dual-energy imaging is extended to incorporate scattered radiation. The analysis is general and can include polyenergetic beams and nonideal detectors. In the dual-material basis plane, scatter generates a displacement of the vectors representing the imaged materials. This changes the target versus background signal difference and the projection angle for cancellation of background contrast due to varying amounts of two materials. Complete cancellation is not possible, because vectors representing various mixtures of the two background constituents are displaced differently and thus no longer lie on a straight line in the dual-material plane. The effect can be minimized by allowing a typical amount of scatter to reach the image receptor when determining the parameters of the transformation from log attenuation to equivalent materials thicknesses. The analysis has been applied to dual-energy mammography. The presence of scatter has minimal effect on the optimum beam energies with an ideal detector, which are about 20 and 70 keV.

Female↗
PubMedDate not supplied

Dual-energy x-ray projection imaging: two sampling schemes for the correction of scattered radiation.

In addition to the familiar problems of reduced contrast and signal-to-noise ratio (SNR) in the single energy case, dual-energy subtractions in the presence of scattered radiation suffer further degradations from: (1) artifacts due to nonuniform subtraction of scatter, and (2) a serious deterioration of the signal of interest. To determine the expected performance of scatter correcting schemes, we simulated energy subtractions performed in the presence of scatter. We discuss scatter's detrimental effects on contrast and SNR in these simulations and the expected improvements from scatter corrections to within 5% to 10%. We introduce two sampling schemes for the correction of scatter. Each scheme requires two measurements, and each involves placing an x-ray opaque sampling grid between the source and the object. In the first method, the grid is an array of lead disks present only during one measurement. Using these samples we generate an estimate of the scatter field and then subtract it from the second measurement yielding a scatter corrected image. In the second method, the grid is an array of lead strips present during both measurements but displaced between measurements by one-half of a strip spacing to completely sample the image. From the two measurements we generate an image to be corrected, an estimate of the scatter field, and a scatter corrected image. In phantom studies implemented on a digital fluoroscopy system, we observed for single energy images of blood vessel phantoms improved contrast and field uniformity. For scatter corrected selective material cancellations in human phantoms we observed improved contrast and significant reduction in artifacts. In both cases we observed no significant loss in SNR. These results facilitate the implementation of efficient large area detectors for dual-energy imaging.

Algorithms↗
PubMed1980

A comparative study of scattered radiation levels from 80-kVp and 240-kVp x rays in the surgical intensive care unit.

The levels of scattered radiation from 80-kVp and 240-kVp mobile x-ray units were measured in the surgical intensive care unit (ICU). The intensity of scatter of the 240-kVp x rays does not decrease with distance as rapidly as with the 80-kVp beam. In an ICU with four beds, the weekly radiation exposure at the nurses' station approximated 0.05 mR (0.13 X 10(-7) C/kg) for the 80-kVp beam and 0.2 mR (0.52 X 10(-7) C/kg) for the 240-kVp beam. Thus, the annual exposure from either unit would be well below the Maximum Permissible Exposure for nonoccupational workers.

Intensive Care Units↗
PubMed1983

The influence of scattered radiation on the CT numbers of bone on a scanner with a fixed detector array.

A dependence of the CT number upon radial position of a bone plug in a unit density phantom is observed with a scanner employing a fixed detector array. The effect of the signal produced by scattered radiation from the phantom is analysed. A scatter correction consisting of a fixed fraction of the incident x-ray intensity is considered. The resultant error from such a correction is found to depend upon the ratio of the scatter to the primary detected intensities and is shown to be consistent with the observed results.

Bone and Bones↗
PubMedDate not supplied

Correction for scattered radiation and other background signals in dual-energy computed tomography material thickness measurements.

Both beam hardening and the detection of scattered radiation cause nonlinearity errors in x-ray computed tomography (CT), leading to artifacts and CT number inaccuracies. Dual-energy measurements can be used to correct beam hardening effects to a high degree of accuracy. However, in the imaging of thick body sections the transmitted intensity of the primary beam is low, making scatter the most significant cause of CT number inaccuracy. Furthermore, the scatter-to-primary ratio is energy dependent, causing a shift in the apparent effective atomic number of the absorbing material. We have measured scatter under a variety of conditions on a third generation CT scanner with dual-energy capability in order to determine its effect on the accuracy of quantitative measurements. The effects of off focus radiation, detector cross-talk, and detector dark current were also accounted for in the analysis of the measured scatter data. Our results indicate that on this well collimated system, an accurate correction for scatter can be made based on the detected intensity in projections.

Biophysical Phenomena↗