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Biomedical subjects

C J Martin

Publications and source records attributed to C J Martin.

At least 19 recordsLinked to original sources
PubMed2006

Calibrating automatic exposure control devices for digital radiography.

The energy responses of digital radiography detectors differ from those of screen-film systems. To provide a consistent level of image quality at different tube potentials automatic exposure control (AEC) devices must be calibrated to suit the energy response of the image receptor with which they are intended for use. AEC calibration for digital radiography systems requires an alternative parameter to optical density, ideally one related to the quality of a digital image. Energy responses of computed radiography (CR) and indirect digital radiography (IDR) image receptors have been calculated, and compared with those for screen-film systems. Practical assessments of the relative sensitivities of a CR detector made using the detector dose indicator (DDI), pixel value and signal-to-noise ratio showed similar variations with tube potential. The DDI has been used to determine the correct kV compensation curve required to calibrate the AECs for the loss in detector sensitivity with tube potential. AECs are set up relative to a predetermined air kerma incident on the detector at 80 kV for CR and IDR systems using this curve and the method used is described. Factors influencing the calibration of AECs for digital radiography including techniques, types of phantom and contributions from scatter are reviewed, and practical methods recommended for use.

Aluminum↗
PubMed2006

Application of contrast-to-noise ratio in optimizing beam quality for digital chest radiography: comparison of experimental measurements and theoretical simulations.

The contrast-to-noise ratio (CNR) has been employed in optimizing beam quality for imaging a chest phantom using digital radiography. The relationship between CNR and tube potential has been studied for regions of different attenuations representing the lung, heart and abdomen, and a figure of merit (FOM) incorporating effective dose has been calculated to enable dose performance to be included. Direct measurements of imaging performance have been compared with simulations based on a model representing object attenuations. The study has shown reasonable agreement between measurements of CNR and calculated values. The CNR values in the lung and heart regions are higher at 60-80 kV, while those for the abdomen are higher at 90-110 kV. Incorporating a 0.2 mm copper filter has minimal effect on image quality and the FOM is higher because of the reduction in dose. For imaging the heart and abdomen, performance was improved through use of a technique to remove scatter, with an air-gap technique giving a higher FOM because of the lower dose. The CNR and FOM can provide useful quantities for evaluating imaging performance to optimize beam quality for different imaging tasks.

Abdomen↗
PubMed2006

Ultraviolet phototherapy: review of options for cabin dosimetry and operation.

Ultraviolet (UV) treatment dose is determined by the length of time that a patient spends in a phototherapy cabin. The output from UV fluorescent lamps declines with use and a method is needed to compensate for the change in irradiance and to identify and replace any lamps that fail. The decline in lamp output with age and the magnitudes of localized areas of low irradiance resulting from failed lamps have been measured and results used to assess different approaches to lamp replacement. In current cabin models, single failed lamps give cold spots with 7%-12% lower irradiances and replacements with new lamps give 3%-6% higher localized irradiances. However, cold spots with 30% lower irradiances may result from lamp failures in some older dual UVA/TL01 lamp cabins. The use of internal cabin detectors that can be employed to compensate for changes in irradiance level is beneficial. Cabins having pairs of internal detectors provide a reasonable reflection of the changes in irradiance that occur and the position of the patient in the cabin should not affect the treatment dose by more than +/-6%. There should be a robust system to identify and replace failed lamps to minimize the risk of erythema.

Humans↗
PubMed2006

Techniques for measurement of dose width product in panoramic dental radiography.

Dose width product (DWP) is the quantity recommended for assessment of patient dose for panoramic dental radiography. It is the product of the absorbed dose in air in the X-ray beam integrated over an exposure cycle and the width of the beam, both measured at the receiving slit. A robust method for measuring the DWP is required in order to facilitate optimization of practices and enable comparison of dose levels at different centres. In this study, three techniques for measuring the DWP have been evaluated through comparison of results from 20 orthopantomographic units. These used a small in-beam semiconductor detector and X-ray film, a pencil ionization chamber and an array of thermoluminescent dosemeters (TLDs). The mean results obtained with the three techniques agreed within +/-6%. The technique employing a pencil ionization chamber of the type used for dose assessment of CT scanners is the simplest and most reliable method. The in-beam detector and film method has larger errors both from positioning the radiation detector and from measurement of X-ray beam width, which should be the full width at half maximum obtained from a scan of the film optical density. The TLD array method was accurate, but more time consuming to carry out. The mean DWP for the units studied was 65 mGy mm and the mean dose-area product was 89 mGy cm2. The DWP for 30% of the units tested exceeded the diagnostic reference dose of 65 mGy mm, recommended by the National Radiological Protection Board.

Humans↗
PubMed2005

Dose-image quality optimisation in digital chest radiography.

A range of techniques has been developed in conventional radiography for the chest, because of technical difficulties in imaging the wide variation of tissue densities. These techniques can differ significantly in tube potential selection, for scatter reduction and in application of manual or automatic exposure control. In this study a geometric chest phantom designed to simulate a chest image, has been used to study image quality on an indirect digital radiography (DR) system. Relative values for the signal-to-noise ratio (SNR), have been derived from analysis of contrast detail objects within the lung, heart and subdiaphragm regions of the phantom. Results showing the variation in SNR and detail perception with tube potential are presented for three radiographic techniques: using a grid, an air gap and no scatter reduction. SNR measurements provided a useful objective measure for assessment of image quality for optimising DR systems.

Artifacts↗
PubMed2005

Optimising automatic exposure control in computed radiography and the impact on patient dose.

Automatic exposure controls (AECs) used with computed radiography (CR) equipment need to be set for a constant signal level in the resultant images. The response varies with the energy of the X-ray beam in a different way from conventional film screen combinations. Dose to the imaging receptor has been employed in adjustment of the AECs for varying exposure conditions for CR systems installed in hospitals in the west of Scotland. However, other parameters could potentially be applied. In this study, three quantities have been investigated for use in setting the AEC function: the exposure indicator defined by the CR manufacturer, dose to the image receptor and image noise. Experiences gained in setting up the systems are described and results of a patient dose survey are reported.

Dose-Response Relationship, Radiation↗
PubMed2005

A study of the distribution of dose across the hands of interventional radiologists and cardiologists.

The magnitude and distribution of doses across the hands of interventional radiologists and cardiologists have been studied. The aims were to determine the region of highest dose, investigate variations in dose distribution, and propose an effective method for dose monitoring. Doses have been measured using sets of up to 18 thermoluminescent dosemeters (TLDs) for 183 single procedures. Important factors influencing the dose to the hand are the type of procedure, particularly the access route, the X-ray equipment used, and the experience of the operator. Radiologists performing percutaneous procedures received the highest doses, because of the proximity of their hands to the X-ray tube. The majority of procedures involve a combination of twisting and prodding actions, and the relative proportions of each determine the parts of the fingers which receive a higher dose. For most interventional radiology and cardiology procedures the bases of the ring and little fingers receive the highest dose. However, during percutaneous procedures the tips of the middle and ring fingers could receive doses which were 20-30% higher than this. For radiologists and cardiologists with a mixed workload, monitoring using TLD rings located at the base of the little or the ring fingers on either hand should provide a reasonable estimate of dose to the most exposed area. Monitoring is recommended for operators who may receive over 50 mSv to their hands per year, and should be considered for operators carrying out therapeutic procedures involving patient dose-area products over 500 Gy cm2 per month.

Cardiology↗
PubMed2005

A survey of incidents in radiology and nuclear medicine in the West of Scotland.

Data on 606 incidents in radiology and nuclear medicine departments reported to a central health physics service have been analysed and causes reviewed. 85% of incidents in radiology departments and 37% in nuclear medicine were overexposures of patients. 80% of these resulted from human error or procedural failure, and of these 32% were mistakes by the referrer. Other incidents in nuclear medicine were contamination events (49%) and failure in management of radioactive materials (10%). Effective doses for patient overexposures covered a broad range with those for CT being 1 mSv and above, while those for other radiology examinations were mostly less than 2 mSv. Reporting of patient overexposure incidents in radiology has increased by four-fold in recent years. The average numbers reported during the last 3 years were 91 per year in radiology and 12 per year in nuclear medicine, for hospitals with a population base of 2.8 million. Incident investigations demonstrated the importance of robust procedures and defences to identify mistakes that could lead to incidents. The central incident reporting and investigation system has raised the awareness of staff about the type of mistakes which could lead to incidents and promoted the introduction of recommended actions to reduce these risks.

Clinical Competence↗
PubMed2004

Organisation of the disposal of radioactive sources from Scottish hospitals.

An amnesty for disposal of sealed radioactive sources from Scottish hospitals has been funded by the Scottish Executive to address problems arising from accumulation of sources. The contract was awarded to a company involved in radioactive source recycling. Coordination of uplifts from several hospitals allowed considerable financial savings to be made, so source amnesties could offer monetary advantages to Health and Education Departments elsewhere in the UK, as well as alleviating the problem from security and storage of sources that are no longer required. The sources originated in 14 hospitals, but were uplifted from five pick-up points. There were a total of 246 sources with 167 of these being caesium-137. The total activity was 16.2 TBq with one large 16.1 TBq blood irradiator source and the activities of all the other sources adding up to 167 GBq. This paper describes organisation of the collection. Options for achieving compliance with the Radioactive Substances Act 1993 are discussed, although in the event, special authorisations were obtained for each hospital. Arrangements for transport of the sources and source security were drawn up including emergency procedures for dealing with foreseeable incidents. The police provided secure overnight storage for the loaded truck and assistance in directing and monitoring progress of the load.

Hospitals↗
PubMed2004

The interpretation of zinc protoporphyrin changes in lead intoxication: a case report and review of the literature.

BACKGROUND: Zinc protoporphyrin (ZPP) has been used both as a screening and diagnostic test for overexposure to lead for nearly 30 years, although limitations for both purposes are recognized. METHODS: We present longitudinal findings for ZPP and whole-blood lead in a man with two episodes of acute lead intoxication and review the literature on the use of ZPP. RESULTS AND CONCLUSIONS: ZPP elevations in both chronic and acute exposure settings lag behind elevations in whole-blood lead by approximately 8-12 weeks. Therefore, ZPP measurement, in conjunction with whole-blood lead determination, has clinical utility in cases of substantial overexposure by providing information on how long an individual may have been overexposed to lead. A guide to the interpretation of various combinations of whole-blood lead and ZPP results is provided. However, while ZPP levels do correlate with whole-blood lead measurements in aggregate, the considerable individual variability of ZPP measurements, poor sensitivity at lower ranges of lead exposure, poor specificity and delayed changes in unstable exposure conditions indicate that this test contributes little to screening programs. Finally, our results confirm that basophilic stippling is seen in acute as well as chronic lead intoxication, and may provide the first indication of lead intoxication.

Acute Disease↗
PubMed2004

A review of factors affecting patient doses for barium enemas and meals.

A study of patient doses for barium enema and meal examinations has been carried out for hospitals in the West of Scotland to assess the impact of dose reduction facilities on new X-ray equipment. Dose-area product (DAP) information has been collected on examinations for groups of patients at 20 hospitals and results reviewed together with data on equipment performance measurements. Median DAPs for barium enemas and meals were 15.7 Gy cm(2) and 4.8 Gy cm(2), respectively, and effective doses estimated from the results are 3.5+/-0.7 mSv and 1.5+/-0.5 mSv, respectively. These doses are lower than those reported in earlier studies and in previous surveys in the West of Scotland. The reduction in dose is linked primarily to the low dose facilities available on newer X-ray equipment, such as low dose pulsed fluoroscopy, digital imaging facilities and use of copper filtration. Use of the image intensifier for decubitus images on C-arm units employed for barium enemas also gives a significantly lower dose. Equipment with copper filtration had the lowest doses. The reduction in effective dose will be significantly less than the reduction in DAP for units in which a copper filter is included and the adoption of lower diagnostic reference levels is proposed for units with this facility. It is important that the operators are aware of the low dose imaging options on their equipment in order that techniques can be fully optimized.

Barium Sulfate↗
PubMed2003

Investigation using an advanced extremity gamma instrumentation system of options for shielding the hand during the preparation and injection of radiopharmaceuticals.

Staff preparing and injecting radiopharmaceuticals in hospitals may receive significant radiation doses to their hands. These doses may be high enough to warrant that they be classified as radiation workers. The influence of local shielding on finger doses has been investigated. Staff preparing radioactive liquids in a radionuclide dispensary and drawing up and injecting radiopharmaceuticals in a nuclear medicine department have been studied. Measurements have been recorded with an electronic extremity dose monitor, an advanced extremity gamma instrumentation system (AEGIS), worn near to the finger tip. The electronic dosimeter allows the pattern of doses received during different procedures to be determined. Doses received for individual manipulations during many routine sessions have been recorded for different staff members. Dose distributions around shielded vials and syringes have also been measured using AEGIS. In the radionuclide dispensary the vials from which radioactive liquids are dispensed are held in tungsten shields, whereas in nuclear medicine simple lead pots are used. Syringe shields are employed for some parts of dispensing and patient injections. Data on dose distributions have been used in interpretation of results from monitoring. Use of syringe shields during dispensing reduced the finger dose by 75-85%. The peaks in dose rate were 60% lower, and periods of exposure to high dose rates were reduced in length by a third because of the restriction in the region of high dose rate. The extremity doses to staff dispensing and injecting radiopharmaceuticals in nuclear medicine were of similar magnitude. Doses received during dispensing varied from 10 to 555 microGy depending upon whether the vial containing the radiopharmaceutical was directly handled or not. Dose received from individual injections varied from 1 to 150 microGy depending on the degree of difficulty experienced during the injection.

Drug Compounding↗
PubMed2003

Application of ALARP to extremity doses for hospital workers.

The implementation of ALARP for hospital workers is considered in relation to extremity doses. Criteria are proposed which could provide guidance in determining strategies for both implementing radiation protection measures and dose monitoring for the extremities. Two groups of hospital workers have been studied, namely interventional radiologists/cardiologists, and radionuclide staff preparing and administering radiopharmaceuticals. The radiology procedures can give high doses to both the hands and legs. Those to the legs can be reduced by the use of lead rubber shields. Study of the distribution of dose across radiologists' hands has identified the ring position on the little finger as the appropriate position for dose monitoring. The variations in dose across the hands of radionuclide workers are greater, with the tip likely to receive the highest dose. The protection strategy will need to be determined for each department, because of the wide range in techniques used in handling radiopharmaceuticals. It is hoped that the criteria could aid balanced decision-making about the appropriate protection strategy and ensure that protection measures are in place where they are required, but avoid their introduction where they are unnecessary.

Extremities↗
PubMed2003

A study of the correction factor for ultraviolet phototherapy dose measurements made by the indirect method.

BACKGROUND: Optimization of ultraviolet (UV) phototherapy for treatment of psoriasis and other skin conditions requires accurate dosimetry. One factor involved in whole body treatments is the correction that needs to be applied to radiometer measurements of irradiance made remotely without a person in the phototherapy cabin. OBJECTIVES: To evaluate the correction factor for cabins of different design and to consider whether different factors should be used for different phototherapy cabins and radiometers. METHODS: An automated UV dosimetry system capable of recording irradiances at positions around the circumference of a circle equating to a human trunk has been developed. The system has been combined with a phantom to derive values for the ratio between irradiance measurements made by the direct method with a person in a cabin, and indirect measurements recorded remotely. In addition, values for the ratio in UVA cabins have been derived from comparisons between measurements made directly by persons in a cabin and indirect measurements. RESULTS: Variations in direct to indirect ratio (DIR) with cabin type were less than between individual sets of measurements. The mean DIR obtained for cabins with TL01 lamps was 0.85 +/- 0.02, while that for UVA cabins was 0.80 +/- 0.05. The DIR for dual lamp (TL01/UVA) cabins, when TL01 lamps were illuminated, was higher (0.92). CONCLUSIONS: The DIR should be applied to any measurements made using radiometers without a person or equivalent phantom in a cabin. It is proposed that standard values are appropriate for groups of cabins with a single type of lamp and similar reflectors.

Electronic Data Processing↗
PubMed2003

Radiation doses to the legs of radiologists performing interventional procedures: are they a cause for concern?

The purpose of this study was to ascertain the magnitude and distribution of doses to the legs of radiologists when performing interventional procedures. LiF:Mg,Ti TLD100 chips were used to measure simultaneously doses to the lower limbs and, for comparison, the hands during 100 interventional procedures. Results show leg dose was dependent upon type and complexity of procedure, equipment used and whether lead protection was available. Where no lead protection was used, the doses to the lower limbs were frequently similar to or higher than those received by the hands. The mean dose to the legs ranged from 0.19 mSv to 2.61 mSv per procedure, compared with 0.04 mSv to 1.25 mSv to the hands. During transjugular intrahepatic portosystemic shunt and embolisation procedures the leg dose could be as much as 2-3 times greater than that to the hands. When lead protection was used, the dose to the legs was reduced significantly to 0.02 mSv to 0.5 mSv per procedure. A clear linear relationship was shown between the dose-area product (DAP) reading and the dose to the feet of the radiologist. As a "rule of thumb", a DAP reading of 100 Gy cm(2) will give a dose of 1 mSv to the legs, if no lead protection was used, dropping to approximately 0.02 mSv if lead protection was present. This study demonstrates that the dose to the legs of radiologists can be higher than that to the hands when no lead protection is used. The inclusion of a lead screen to protect the legs is an effective method of dose reduction when performing interventional procedures.

Embolization, Therapeutic↗
PubMed2002

Guidelines for dosimetry and calibration in ultraviolet radiation therapy: a report of a British Photodermatology Group workshop.

This report examines the dosimetry of ultraviolet (UV) radiation applied to dermatological treatments, and considers the definition of the radiation quantities and their measurement. Guidelines are offered for preferred measurement techniques and standard methods of dosimetry. The recommendations have been graded according to the American Joint Committee on Cancer classification of strength of recommendation and quality of evidence (summarized in Appendix 5).

Humans↗