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Biomedical subjects

K Faulkner

Publications and source records attributed to K Faulkner.

At least 91 records · Page 5Linked to original sources
PubMed1994

An investigation into the radiation dose associated with different imaging systems for chest radiology.

With the advent of digital imaging there now exists a range of imaging techniques which may be used to acquire chest images. The purpose of this investigation was to determine typical radiation doses associated with the use of a conventional film-screen system, 100 mm film technique, large-field digital image intensifier radiography, computed radiography and a scanning slit system (AMBER, Oldeft, Netherlands). Radiation doses to relevant organs were assessed using direct measurements made with lithium fluoride thermoluminescent dosemeters, together with calculations made using normalized dose data. Typical doses were assessed using anthropomorphic phantoms for both postero-anterior and lateral projections. The risk-related quantities, i.e. effective dose and effective dose equivalent, were then calculated from these organ doses. When compared on the basis of effective dose equivalent, certain imaging techniques were seen to offer the potential for significant dose reduction, possibly at the expense of image quality.

Humans↗
PubMed1994

Energy imparted to neonates during X-ray examinations in a special care baby unit.

Neonates in a special care baby unit may receive a large number of X-rays and their dosimetry is of particular importance. A method of calculating energy imparted to neonates has been developed and a survey carried out in one unit, over a period of 18 months. Entrance dose was calculated from the technique factors used and measurement of tube output. Technique factors were recorded by the radiographer for each exposure taken, and output was measured both with and without an incubator present. Field size was determined by measurements made retrospectively from the radiograph, and a Monte Carlo simulation was used to determine factors for conversion to imparted energy. 119 neonates were included in the survey, and the mean total energy imparted was found to be 0.09 mJ. The maximum value was a factor of nine greater than this. This study also highlighted the potential for dose reduction with regard to better collimation and shielding.

Humans↗
PubMed1994

A comparison of radiation dose in examination of the abdomen using different radiological imaging techniques.

Typical radiation doses for abdominal examinations were determined for field sizes and entrance doses commonly selected on image intensifier based digital radiographic systems. In addition, measurements were also performed using conventional film-screen methods, a 100 mm camera combination and a phosphor storage computed radiography system. Both antero-posterior and postero-anterior projections were assessed. An anthropomorphic phantom loaded with lithium fluoride thermoluminescent dosimeters was used to measure entrance surface doses. Organ equivalent doses, deduced using normalized organ dose data, were used to calculate effective dose and effective dose equivalent. A comparison of the imaging techniques on the basis of effective dose indicated that significant dose reductions (by approximately a factor of 3) may be expected if the abdomen is imaged using a postero-anterior rather than an antero-posterior projection for a given imaging system. If digital imaging systems are used instead of a conventional film-screen technique, patient effective dose for a given projection can be lower by at least a factor of 5.

Abdomen↗
PubMed1994

Measurements of the frequency distribution of optical density in screening mammography.

A method for obtaining histograms of the frequency of occurrence of optical densities in mammograms has been implemented. Averaged optical density distributions were produced for approximately 50 screening mammograms at each of two centres using different film-screen and processing chemistry combinations. Additional measurements were made on films of two commercially available anthropomorphic breast phantoms. The results show that screening mammograms, on average, exhibit a strongly peaked optical density distribution which corresponds closely to the target optical density measured using the current recommended test protocol for automatic exposure control devices.

Breast Neoplasms↗
PubMed1993

Luminol and lucigenin as detectors for O2.-.

Univalent oxidation of luminol and univalent reduction of lucigenin must precede reaction with O2.- if that reaction is to lead to luminescence. The assumption that luminol or lucigenin, per se, reacts with O2.- in a way leading to luminescence is incorrect, and leads to misinterpretation of results. The chemical reactions leading to the O2(.-)-dependent luminescences of luminol and of lucigenin are discussed.

Acridines↗
PubMed1993

Normalized organ dose data measured as a function of field size for abdominal examinations.

Doses to 14 radiosensitive organs were measured as a function of field size for both antero-posterior (AP) and postero-anterior (PA) projections of the abdomen. The organ doses were measured using thermoluminescent dosemeters (TLD) placed within a Rando anthropomorphic phantom. Circular field sizes 14 cm, 26 cm and 36 cm in diameter (measured at the image intensifier input plane) were set for the PA irradiations. For the AP projections, the circular field sizes measured 14 cm, 20 cm, 27 cm and 40 cm in diameter, again specified at the input plane of the image intensifier. Organ doses were also measured for the conventional 35 x 35 cm film/screen technique, for both AP and PA views. The dose measurements were made at a tube potential of 81 kV, which is commonly used in radiological examinations of the abdomen. TLD were also used to measure the entrance surface dose (with backscatter) for each field size and projection. The organ doses are presented normalized to this entrance surface dose. A brief comparison is made between the data measured in the current study and normalized organ dose data published by other authors.

Humans↗
PubMed1993

The relationship of effective dose to personnel and monitor reading for simulated fluoroscopic irradiation conditions.

The exposure of staff during fluoroscopic procedures was simulated for overcouch x-ray tube/undercouch image intensifier and undercouch x-ray tube/overcouch image intensifier geometries. A Rando phantom with film badge dosimeters attached to the skin surface at seven commonly used monitoring sites and loaded with lithium fluoride thermoluminescent dosimeters was irradiated for an extended period in the vicinity of a patient couch. Scattered radiation generated from the irradiation of an anthropomorphic phantom using primary radiation in the range of 70 kVp-110 kVp was used. The radiation dose to organs which were shielded by a lead apron was estimated from the unattenuated organ dose readings by applying an experimentally determined scattered radiation transmission factor. The ratio of effective dose to film badge reading was obtained for a range of irradiation conditions and lead apron thicknesses. For most irradiation conditions studied, a dosimeter worn above the lead apron will significantly overestimate effective dose by a factor of between 2 and 60, depending on the irradiation conditions. A dosimeter worn under the apron at either waist or chest level, will generally yield a closer (although usually an underestimate of) effective dose, typically within a factor of 7 for the most common lead apron thicknesses and irradiation conditions. No single dosimeter can accurately monitor effective dose for all irradiation conditions in fluoroscopy.

Fluoroscopy↗
PubMed1993

Radiation doses to paediatric patients undergoing less common radiological procedures involving fluoroscopy.

A semi-automated dosimetry survey has been undertaken to monitor the radiation doses to patients in a paediatric fluoroscopy room. The doses were assessed using large area Diamentor ionization chambers to measure dose x area product, and by means of thermoluminescent dosemeters attached to the patient's skin in various places. Details of patients and examinations were entered into a computer, all information being stored on a data base. Many radiological examinations have been monitored, including renal and jejunal biopsies, nephrostograms, loopograms, tracheograms and fistulograms. Patients included in the study have been divided into three age bands for dose assessment. Radiation doses for different types of examination have been compared, including more common examinations for which data have been previously presented.

Adolescent↗
PubMed1993

Organ absorbed doses in intraoral dental radiography.

A dental radiography unit operating at 70 kV (nominal) and 20 cm focus-skin distance was used to irradiate an anthropomorphic phantom loaded with lithium fluoride thermoluminescent dosemeters, in order to assess the variation in organ absorbed dose with intraoral periapical radiographic view. 14 views using the bisecting-angle technique and four views using the paralleling technique were studied. The results are presented and the doses and dose distributions examined. Doses for the paralleling and bisecting-angle techniques are compared, and the effects of focus-skin distance and beam collimation upon patient dosimetry discussed. Sources of uncertainty in dental dosimetry studies using phantoms are also considered.

Bicuspid↗
PubMed1993

Dose reduction in panoramic radiography.

A modern programmable panoramic radiography unit was used to irradiate an anthropomorphic phantom in order to assess the variation in organ absorbed dose and calculated effective dose with program selection. The results of the measurements for five of the 12 programs available are presented, together with those obtained from an older, non-programmable unit. The results of dosimetry measurements are compared between units, between programs, and with previous data. Variations in radiation dose and their implications are discussed, and the opportunities for reductions in organ dose and effective dose of up to 85% and 50%, respectively, demonstrated.

Humans↗
PubMed1992

The dependence of the scattered radiation dose to personnel on technique factors in diagnostic radiology.

The measurement and prediction of scattered radiation dose to staff in diagnostic radiology is particularly important, owing to the increased use and complexity of interventional radiology. The air kerma-area product and scattered radiation dose in the vicinity of the patient couch, for both overcouch and undercouch X-ray tube geometries, were simultaneously monitored. The scattered radiation distribution at the couchside was deduced at a range of tube potentials for both overcouch and undercouch X-ray tube geometries. The variation of scattered radiation with field size on both geometries was investigated, as well as the variation with focus-table distance on an overcouch tube geometry. It was discovered that the scattered radiation dose at a point correlated with the air kerma-area product and the result may be used for radiation protection purposes. A method of predicting the scattered radiation dose at a given position is described.

Humans↗
PubMed1992

Results of a survey of doses to paediatric patients undergoing common radiological examinations.

A survey has been performed to investigate typical radiation dose levels for children undergoing a number of common radiological examinations. Doses have been assessed using a Diamentor ionization chamber to measure dose-area product, and by attaching thermoluminescent dosemeters to the patient's skin to determine entrance and organ doses. The survey has been automated by using a personal computer for data collection and storage. Doses have been monitored for a large number of children, primarily in a dedicated paediatric X-ray room, and the results presented can be used as a baseline for making comparative measurements elsewhere. Entrance skin doses were found to range from 0.3 mGy to 5.7 mGy for radiographic examinations, and values of dose-area product from 3 to 225 cGy cm2. The corresponding dose ranges for fluoroscopic examinations are 7.4-26.2 mGy and 130-1241 cGy cm2.

Adolescent↗
PubMed1992

The determination of total filtration on mammographic X-ray sets.

Data produced by a computer model are presented which allow the amount of molybdenum filtration on a molybdenum target mammographic X-ray set to be estimated from the measurement of the half value layer (HVL) in aluminium. Existing data refer either to tungsten target tubes or to molybdenum target tubes for a single anode angle and a constant potential waveform with the compression plate present. In addition to the tube voltage, the present data take account of the waveform of the tube potential and target angle. The results of an experimental verification of the model are presented and the effect of the geometry used in the experimental set-up discussed. Theoretical predictions of the molybdenum filter thickness made using the data from the model are in good agreement with the measured filter thickness, provided that attention is paid to the experimental geometry.

Computer Simulation↗
PubMed1992

An alternative approach to contrast-detail testing of X-ray image intensifier systems.

The difficulties of making the results of threshold contrast-detail diameter tests on X-ray image intensifier systems consistent with published performance standards are discussed. The current approach to contrast-detail testing is described and an alternative method intended to give greater consistency for all image intensifier input field diameters proposed. The current and alternative test conditions are compared on two image intensifier systems. The results obtained show that the contrast-detail curves for image intensifier systems with a wide range of input field diameters can be effectively normalized to be directly comparable to a common reference standard by applying the proposed alternative test conditions. The implications of this result on the interpretation of the contrast-detail test are discussed.

Quality Control↗
PubMed1992

An investigation into the effect of protective devices on the dose to radiosensitive organs in the head and neck.

A series of experiments were performed to determine the dose reduction afforded to radiosensitive organs in the head and neck by various protective devices. These included spectacles with plastic, standard glass, photochromic and lead-glass lenses, a thyroid collar and a lead-acrylic face mask. The measurements were performed using an anthropomorphic phantom loaded with lithium fluoride thermoluminescent dosemeters, in conditions realistic of clinical practice. Irradiations were performed using scattered radiation produced by a pelvic phantom, for X-ray beams generated at 80 kVp and 110 KVp. It was found that the reduction in dose to the lens of the eye ranged between 0% and 97%, whilst the dose to the thyroid and oesophagus was reduced by between 76% and 97%, and was dependent on the protective device and tube potential employed. A reduction in brain dose of up to 81% was also measured, for the lead-acrylic face mask. Also presented is the ratio of organ dose to dose to the bridge of the nose for thyroid, oesophagus, brain and sinuses, as measured for the case of no head or neck protection.

Brain↗