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Biomedical subjects

B R Archer

Publications and source records attributed to B R Archer.

At least 19 recordsLinked to original sources
PubMed2005

Radiation protection standards: their evolution from science to philosophy.

The concept of applying constraints on individual sources to a small fraction of the public dose limit has been deemed inappropriate when shielding the medical X-ray sources. This represents a broad-based consensus of medical physics and radiological societies in the United States, and the report series on the shielding design for medical X-ray sources (including dental, X-ray imaging and therapeutic X ray) from the National Council on Radiation Protection and Measurements (NCRP) utilises 1 mSv y(-1) as a source control limit. In the present study, the rationale for such a conclusion is discussed, and a somewhat critical look at the current model of radiation protection of the public is made.

Environmental Exposure↗
PubMed2000

Management of patient skin dose in fluoroscopically guided interventional procedures.

PURPOSE: To simulate dose to the skin of a large patient for various operational fluoroscopic conditions and to delineate how to adjust operational conditions to maintain skin dose at acceptable levels. MATERIALS AND METHODS: Patient entrance skin dose was estimated from measurement of entrance air kerma (dose to air) to a 280-mm water phantom for two angiographic fluoroscopes. Effects on dose for changes in machine floor kVp, source-to-skin distance, air gap, electronic magnification, fluoroscopic dose rate control settings, and fluorographic dose control settings were examined. RESULTS: Incremental changes in operational parameters are multiplicative and markedly affect total dose delivered to a patient's skin. For long procedures, differences in doses of 8 Gy or more are possible for some combinations of operational techniques. CONCLUSIONS: Effects on skin dose from changes in operational parameters are multiplicative, not additive. Doses in excess of known thresholds for injury can be exceeded under some operating conditions. Adjusting operational parameters appropriately will markedly reduce dose to a patient's skin. Above all other operational factors, variable pulsed fluoroscopy has the greatest potential for maintaining radiation exposure at low levels.

Angiography↗
PubMed2000

Protecting patients by training physicians in fluoroscopic radiation management.

During the past 15 years, developments in x-ray technologies have substantially enhanced the ability of practitioners to treat patients using fluoroscopically guided interventional techniques. However, many of these procedures require a greater use of fluoroscopy and serial imaging (cine). This has increased the potential for radiation-induced dermatitis, epilation, and severe radiation-induced burns to patients. It has also increased the potential for radiation injury and radiation-induced cancer in personnel. This work will describe a number of the cases that have appeared in the literature and current recommendations and credentialing requirements of various organizations whose members use fluoroscopy. Finally, a program for implementing training of physicians in radiation management as a means of reducing the risk of injury to patients and personnel is recommended.

Burns↗
PubMed1995

History of the shielding of diagnostic x-ray facilities.

The results of inadequate protection of radiation workers against the harmful effects of diagnostic x-rays became appallingly apparent shortly after the turn of this century. After these effects (which included erythema, malignancy, and even death) became widely known, efforts were begun to implement recommendations to reduce the hazards to radiologic workers and members of the general public. This work will trace the development of diagnostic radiation shielding standards from the earliest days to the present time.

History, 19th Century↗
PubMed1994

Attenuation properties of diagnostic x-ray shielding materials.

Single- and three-phase broad-beam x-ray attenuation data have been obtained using lead, steel, plate glass, gypsum wallboard, lead acrylic, and wood. Tube voltages of 50, 70, 100, 125, and 150 kVp were employed and the resulting curves were compared to transmission data found in the literature. To simplify computation of barrier requirements, all data sets were parametrized by nonlinear least-squares fit to a previously described mathematical model. High attenuation half value layers and the lead equivalence of the alternate materials were also determined.

Acrylic Resins↗
PubMed1994

Exposure rates during special procedures with C-arm type fluoroscopic systems.

PURPOSE: To test for regulatory compliance of free-in-air entrance air kerma rates (EAKR) in C-arm type fluoroscopic equipment, measurements are frequently made under minimum source-to-image receptor distance (SID) and at 300 mm from the image intensifier. However, this is not representative of normal patient geometry, and the automatic brightness controls on these units frequently increase tube output as SID increases. This study investigated effects of these circumstances on actual EAKRs. MATERIALS AND METHODS: Typical patient geometries were observed and recorded for 23 consecutive body vascular procedures. EAKRs were measured under compliance and normal patient geometries with use of five modern C-arm type systems for special procedures. RESULTS: SIDs of 1 m were typical when rapid film changers were employed and the patient's entrance skin surface was typically 500 mm from the image receptor. Actual EAKRs were found to be up to 2.5 times those measured under compliance geometry. CONCLUSION: Actual patient geometries should be used to ensure correct estimates of EAKRs.

Fluoroscopy↗
PubMed1988

A modified x-ray spectra reconstruction technique.

We have previously reported on a four-parameter Laplace transform pair model that accurately reconstructs x-ray spectra from attenuation data. However, for some spectra, the model exhibits non-physical characteristics at the higher x-ray energies. This results when one of the fitted parameters, v, is less than or equal to 0.6. Simply limiting the parameter to values greater than 0.6 produces an unsatisfactory result. It is shown that improved accuracy is obtained when the model is applied to a more filtered segment of the attenuation curve. The resulting spectrum is satisfactory for the more filtered beam. One can then reliably construct the original spectrum by mathematically correcting for the additional filtration.

Models, Theoretical↗
PubMed1986

Conceptus dose from two state-of-the-art CT scanners.

Two phantoms, constructed from plastic and water and appropriately proportioned to simulate the female pelvis, were used in the evaluation of the dose delivered to a conceptus from two widely used computed tomographic (CT) scanners. Doses were measured along the central axis and surface of each phantom while scanning 25 contiguous 1-cm sections. Ionization chambers were used for data acquisition. Methods for correcting for partial volume effects inside the chambers are examined. Formulas for calculating the dose to the conceptus in a wide variety of possible situations are presented. These data may be used to guide management of pregnant patients who require or have had CT examinations.

Fetus↗
PubMed1983

Diagnostic X-ray shielding design based on an empirical model of photon attenuation.

A series of nomograms that simplify determination of diagnostic X-ray shielding requirements with lead are presented. All recommendations of the NCRP, except that to "add one half value layer" in determining secondary barriers, were followed in the production of these curves. For secondary barriers, the shielding required to reduce the weekly exposure to the applicable MPD has been determined. This eliminates the over-shielding inherent in the "add one HVL" approximation and allows a variety of more cost effective materials to be considered for secondary barriers.

Hospital Departments↗
PubMed1979

Bone marrow dose in chest radiography: the posteroanterior vs. anteroposterior projection.

The dose to active bone marrow resulting from anteroposterior (AP) and posteroanterior (PA) chest examinations was estimated using an Alderson Rando phantom and extruded lithium fluoride dosimeters. The AP projections resulted in a mean marrow dose range of 1.9-2.6 mrad (0.019-0.026 mGy) as compared to doses for PA projections of 3.4-3.8 mrad (0.034-0.038 mGy) for optimally diagnostic exposure taken at 70, 90, and 120 kVp.

Bone Marrow↗
PubMedDate not supplied

Dosimeter placement in the Rando phantom.

Each section of the Alderson Rando phantom contains a tissue-equivalent plastic coating layer approximately 2 mm thick, applied to both faces. This compensates for material removed in the sawing process. Conventional use of thermoluminescent dosimeters positions them totally or partially within the coating layer. Analysis shows that, in the lung region, dosimeters placed in this layer received a dose averaging 39% lower than those placed at midsection. Where bony structures interfere, some dosimeters in the coating layer received an 18% higher dose than those at midsection. Therefore, positioning dosimeters at the center of a section is recommended.

Models, Structural↗
PubMedDate not supplied

Multivariate analysis of TLD orientation effects.

The effect of orientation on extruded thermoluminescent dosimeters has been investigated. TLD's placed on the surface and within a phantom were exposed separately to five diagnostic beam qualities and to 60Co gamma rays. The resulting data were subjected to analysis of variance and examined for significant correlations. The response of dosimeters on the phantom surface varied with orientation and was energy dependent. In the phantom and with 60Co, no orientation effects were observed.

Analysis of Variance↗
PubMedDate not supplied

A Laplace transform pair model for spectral reconstruction.

A four-parameter Laplace transform pair model, which accurately reconstructs an experimental bremsstrahlung spectrum from attenuation data, is presented. Computed spectral values with both aluminum and copper attenuators generally agree with experimental 70-kVp data to better than 2%. Reconstructed spectra at other kVp's also show good agreement with published data.

Mathematics↗
PubMedDate not supplied

Application of a Laplace transform pair model for high-energy x-ray spectral reconstruction.

A Laplace transform pair model, previously shown to accurately reconstruct x-ray spectra at diagnostic energies, has been applied to megavoltage energy beams. The inverse Laplace transforms of 2-, 6-, and 25-MV attenuation curves were evaluated to determine the energy spectra of these beams. The 2-MV data indicate that the model can reliably reconstruct spectra in the low megavoltage range. Experimental limitations in acquiring the 6-MV transmission data demonstrate the sensitivity of the model to systematic experimental error. The 25-MV data result in a physically realistic approximation of the present spectrum.

Humans↗