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PubMed2004

Determination of the modulation transfer function using the edge method: influence of scattered radiation.

The edge method for measuring the modulation transfer function (MTF) has recently gained popularity due to its simplicity and appropriateness particularly for digital imaging systems. Often edge test devices made of rather thin metal sheets are used, which are semitransparent to x rays and may generate scattered radiation. The effect of this scattered radiation on the determined MTF was investigated both theoretically (assuming an ideal detector) and experimentally using a CsI-based digital detector. It was found that the MTF increases due to the scattered radiation for all spatial frequencies larger than 0 mm(-1). The theoretical model developed in this study predicts that the maximum error compared to the true detector MTF is given by S/A, where A is the attenuated fraction and S is the scattered fraction reaching the detector, relative to the incident radiation. Theoretical and experimental results are in good agreement for radiation qualities corresponding to general radiography (RQA3, RQA5, and RQA7), whereas for chest beam quality (RQA9) the experimentally observed MTF error is larger than predicted by the simple model, possibly because the energy response of the CsI-based detector differs from that of an ideal one. The theoretical MTF error reaches a value of 18% for a 0.25 mm thick lead edge of RQA9. Since the MTF enters squared into the determination of the detective quantum efficiency (DQE), an error of at least 36% in DQE may result when using this edge test device. In conclusion, the use of fully absorbing edge material is advised for MTF determination with the edge method.

Algorithms↗
PubMed2006

Characterization of scattered radiation in kV CBCT images using Monte Carlo simulations.

Kilovoltage (kV) cone beam computed tomography (CBCT) images suffer from a substantial scatter contribution. In this study, Monte Carlo (MC) simulations are used to evaluate the scattered radiation present in projection images. These predicted scatter distributions are also used as a scatter correction technique. Images were acquired using a kV CBCT bench top system. The EGSnrc MC code was used to model the flat panel imager, the phantoms, and the x-ray source. The x-ray source model was validated using first and second half-value layers (HVL) and profile measurements. The HVLs and the profile were found to agree within 3% and 6%, respectively. MC simulated and measured projection images for a cylindrical water phantom and for an anthropomorphic head phantom agreed within 8% and 10%. A modified version of the DOSXYZnrc MC code was used to score phase space files with identified scattered and primary particles behind the phantoms. The cone angle, the source-to-detector distance, the phantom geometry, and the energy were varied to determine their effect on the scattered radiation distribution. A scatter correction technique was developed in which the MC predicted scatter distribution is subtracted from the projections prior to reconstruction. Preliminary testing of the procedure was done with an anthropomorphic head phantom and a contrast phantom. Contrast and profile measurements were obtained for the scatter corrected and noncorrected images. An improvement of 3% for contrast between solid water and a liver insert and 11% between solid water and a Teflon insert were obtained and a significant reduction in cupping and streaking artifacts was observed.

Algorithms↗
PubMed1993

Scatter radiation in mammography.

Current information pertinent to scatter radiation for mammographic x-ray spectra is limited. Data presented by the National Council on Radiation Protection and Measurements (NCRP), the current shielding authority, are restricted to 50 kVp tungsten target spectra and contain several incompatibilities with the modern mammographic situation. The ratio of scattered to incident exposure was measured for two molybdenum target spectra (36 kVp, 30 microns molybdenum filtration and 49 kVp, 50 microns aluminium filtration). The maximum scatter ratio occurred at 150 degrees to the primary beam direction for both spectra; the values were (1.73 +/- 0.09) x 10(3) and (2.6 +/- 0.1) x 10(3) respectively for a field area of 400 cm2, a scattering distance of 1 m and a primary beam exposure distance of 1 m from the x-ray source. The results obtained differ significantly from NCRP based data presently used for mammographic shielding calculations. The consequences of these differences are discussed.

Female↗
PubMedDate not supplied

Scattered radiation in fan beam imaging systems.

Scatter-to-primary energy fluence ratios (S/P) have been studied for fan x-ray beams as used in CT scanners and slit projection radiography systems. The dependence of S/P on phantom diameter, distance from phantom to image receptor, and kilovoltage is presented. An empirical equation is given that predicts S/P over a wide range of fan beam imaging configurations. For CT body scans on a 4th-generation machine, S/P is approximately 5%. Scattered radiation can produce a significant cupping artefact in CT images which is similar to that due to beam hardening. When multiple slices are used in scanned slit radiography, they can be arranged such that the increase in S/P is negligible. Calculations of scatter-to-primary ratios for first order scattering showed that for fan beams the contribution of coherent scatter is comparable to or greater than that of incoherent first scatter.

Radiography↗
PubMed2002

The hazard of scattered radiation in a trauma intensive care unit.

OBJECTIVE: Patients admitted to the trauma intensive care unit (TICU) often require bedside imaging procedures such as radiographs, fluoroscopic placement of enteral feeding tubes, and insertion of vena cava filters. The potential for scattered radiation exposure is a concern to healthcare workers. Our study's purpose was to measure the level of scattered ionizing radiation present in a TICU. DESIGN AND SETTING: This prospective study was conducted over 3 months in an open-design, ten-bed TICU of a Level I trauma center. INTERVENTIONS AND MEASUREMENTS: Fifteen dosimeters were placed in selected areas of the TICU to measure the amount of scattered radiation present. Standard radiation protection precautions were used throughout the study period. At the end of each month, data from the dosimeters were sent to the manufacturer for analysis. MAIN RESULTS: One thousand seventy-four radiologic studies were performed at the bedside during the study period (803 portable chest radiographs, 103 abdominal radiographs, 303 extremity radiographs, 223 spine radiographs, and 15 fluoroscopic procedures). Dosimetry analysis showed <5 mrem (1/1000 roentgen equivalent in man) scattered radiation per month (<60 mrem/year) in each of the monitored areas. All monitored areas measured <2 mrem per week of scattered radiation when adjusted for occupancy. CONCLUSIONS: The level of scattered radiation in our TICU is less than the recommended allowable exposure of <100 mrem/year, indicating that radiation exposure is not a significant occupational hazard in our TICU, even in the setting of frequent use of bedside imaging studies.

Fluoroscopy↗
PubMed1999

A mobile shield to reduce scatter radiation to the contralateral breast during radiotherapy for breast cancer: preclinical results.

PURPOSE: To design a practical breast shield and to investigate its efficacy in reducing scattered radiation to the contralateral breast of patients undergoing radiation therapy for breast cancer. METHODS AND MATERIALS: We constructed a mobile shield consisting of (a) a mobile base and a counterweight; (b) a vertical column adjustable in height and a diagonal arm adjustable in angle; (c) a curved, 2.5-cm thick lead sheet with a 1-cm thick polystyrene liner for blocking scattered radiation; and (d) diode detectors to verify that the edge of the lead sheet is not in the useful beam in addition to the use of the field light. Measurements were performed with thermoluminescent dosimeters on 10 patients without the shield and on an anthropomorphic phantom with a pair of wax breasts with and without the shield. All of the patients were treated with 6-MV photons (Varian 6/100). The scattered radiation from the medial and lateral fields was measured separately. RESULTS: The contribution of the medial field to the total scattered dose was 70% to 75%, whether a medial wedge was used or not. However, without a medial wedge, the scattered dose was reduced by nearly 33% at 3 to 9 cm away from the medial border. In the anthropomorphic phantom study with wax breast, the mobile shield reduced the medial field contribution to the total scatter dose to less than the contribution from the lateral field without a shield. With a prescribed dose of 50 Gy and a medial wedge, the median scatter dose to the contralateral breast from 6 patients was 5.3 Gy; without a medial wedge, it was 3.8 Gy from 4 patients at 6 cm from the medial border. In the phantom study, with the shield the total dose to the contralateral breast was 1.0 Gy at 6 cm from the medial border with a same prescribed dose. CONCLUSION: The mobile shield reduced the scatter dose to the contralateral breast from the linear accelerator (Varian 6/100, 6-MV photons) by a factor of 3 to 4. The shield greatly reduced the scattered dose in the wax phantom. Equivalent reductions in patients may be clinically significant by reducing the risk of radiation-induced breast cancer in the contralateral breast of woman undergoing radiation therapy for breast cancer. The shield is safe and easy to adjust to each patient.

Breast↗
PubMed2005

Radiation scattering to the primary surgeon during closed locked femoral nailing.

A prospective study of the radiation exposure to the primary surgeon during closed static locked femoral nailing was performed in 50 cases. There were 44 males and 6 females whose ages ranged from 15 to 70 years (average, 32). The degree of fracture comminution was classified by Winquist. The cases included 1 Winquist (WQ)1, 9 WQ2, 27 WQ3 and 13 WQ4. The Grosse-Kempf femoral nail was used in 40 cases and the AO interlocking femoral nail was used in 10 cases. The C-arm image intensifier model Phillip BV212 and BV 300 were used during the present study. The average operation time was 52 minutes (range, 30 to 120). The fluoroscopic time for the entire procedure average 132 seconds (range, 23 to 366). The radiation exposure to the primary surgeon ranged from 2 to 231 micro-Sv with an average of 30 micro-Sv per procedure. From the present study, it was found that radiation scattered to the primary surgeon during current practice for closed static femoral nailing using the recent model of C-arm image intensifier was minimal and far below the permissible dose. It was also found that the group using the C-arm model BV 300 (n = 16) had significant lesser fluoroscopic time and less radiation scattering to the primary surgeon than the group with model BV 212 (n = 34).

Adolescent↗
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↗
PubMed1996

Scattered radiation in portal images: a Monte Carlo simulation and a simple physical model.

The scattered radiation in 6 MV radiotherapy portal images is analyzed. First, a quantity SPR* is studied, by means of Monte Carlo (MC) modeling. SPR* is defined as the ratio, on the central axis, of the signal due to scattered radiation to that due to the primary radiation. The detector model mimics a high-energy photon detector in the context of transit dosimetry. Second, a physical model of SPR* has been developed from first principles. For a cylindrical phantom, placed symmetrically about the isocenter, it predicts that SPR* depends on the area A at the isocenter of the circular field and the phantom thickness d as follows. SPR* = k0Ad(1 + k1d)(1 + k2A), where k0 = 0.0266(L1 + L2)2/(L1L2)2, k2 = - [L1(-2) + L2(-2) + (L1(-1) + L2(-1))2((2/3) + (3 kappa/2))]/2pi, L1 is the source-to-isocenter distance, L2 is the isocenter-to-detector distance, and kappa is the mean energy of the radiation beam (MeV/0.511). Constant k1, for which there is no simple expression, depends on L2. Comparison to the MC data shows that for 60 or= 50 cm. Third, experimental measurements of the scatter-to-primary ratio were obtained using our custom built imaging system mounted on a Philips SL25 linear accelerator. In the first experiment, A was varied from 40 to 400 cm2 with L1 = L2 = 100 cm with d = 20 cm. In the second experiment water depth d was varied from 0 to 28 cm with L1 = L2 = 100 cm and A = 200 cm2. The rms agreements between the MC data and the experiments were 0.0015 and 0.0045, respectively.

Biophysical Phenomena↗
PubMed1987

Scatter radiation exposure during knee arthrography.

Knee arthrography, as performed at the authors' institution, was simulated and scattered radiation exposure to a radiologist's gonads, thyroid, and eye lens was measured with a sensitive ionization chamber. Results show that radiologists who regularly conduct knee arthrography examinations can incur doses to the gonads that are less than 6% of the U.S. limits, and to the thyroid and eye that are approximately 10% of the U.S. limits. Since the scatter radiation from overhead imaging of stress views constituted most (greater than or equal to 60%) of the dose to the lens of the eye and the thyroid, spot imaging was evaluated as a substitute for overhead imaging in the assessment of the anterior cruciate ligament. This substitution resulted in no loss of clinical information and has now completely replaced overhead imaging of stress views at this institution.

Arthrography↗
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↗
PubMed1985

Scattered radiation doses to some critical organs during pediatric radiotherapy.

The levels of scattered radiation doses imparted to the eyes, thyroid and gonads of pediatric patients treated with orthovoltage radiation (300 kVp, 2.0 mmCu HVL) and with a 4-MV linear accelerator, were determined by making thermoluminescent dosimeter (TLD) measurements in three paraffin phantoms of different sizes. These phantoms were made from molds of mannequins used for store display, of approximate heights 30", 40" and 50", representing children of ages 1-2, 4-5 and 8-10 yr, respectively. The sites chosen for irradiation were (1) the whole brain, (2) the chest, (3) the kidney bed, (4) the whole abdomen and (5) the spinal column. These sites are normally treated in such pediatric malignancies as medulloblastoma, neuroblastoma and Wilms' tumor. Some of the doses measured are less than 10 rad for an entire treatment regimen, and would therefore be categorized as low-level doses. Where radiation was the only mode of treatment for long-term survivors of such malignancies, especially those treated 20-30 yr ago with orthovoltage radiation, useful data may be extracted for contributing to our knowledge about the long-term effects of low levels of radiation.

Cerebellar Neoplasms↗
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↗
PubMed1993

Spreading oligemia in the migraine aura--most likely an artifact due to scattered radiation.

The view that "spreading oligemia" reflects spreading depression in the human brain during the migraine aura is based on a defective analysis of CBF data where the most important methodological source of error (scattered radiation) has been ignored. When scattered radiation is taken into account it appears that CBF in the low flow area during the migraine aura is reduced to the ischemic level. There is no reason to believe that "spreading" of the low flow area occurs. Most likely the blood flow decreases in an area of fixed size. All available CBF evidence in fact lends support to "the vascular theory" of migraine pathogenesis.

Animals↗
PubMed1995

The effect of scattered radiation in dual-energy analysis.

Dual-energy techniques can be used to provide additional information during x-ray examinations. A recent development has been in the application of dual-energy analysis to fluoroscopic procedures. In this paper the effects of scattered radiation upon the results obtained with a small area, dual-energy probe used during fluoroscopy has been evaluated. The method employed has been the development and application of a Monte Carlo photon transport computer program. Experimental confirmation of the model has been performed and the model extended to study the effects of scattered radiation upon the chemical sensitivity of the dual-energy probe. These effects have been studied using a simplified phantom geometry to represent a homogeneous patient. The results indicate that for tissue analysis where the effective atomic number (Z) is less than 13 the effects of scattered radiation lead to errors in estimates of Z of +/- 0.25 when the acceptance angle of the detected radiation is below +/- 20 degrees.

Computer Simulation↗