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

Health Physics, West House, Gartnavel Royal Hospital, Glasgow G12 0XH, UK

	Abstract

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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.

	Introduction

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It is more important now than at any stage in the past to ensure the risks that radiation incidents might occur are minimized. The expansion in the range of radiation related examinations and treatments, and the rising complexity of equipment used in carrying out the exposures, have increased the variety of things that can go wrong. It is important that lessons are learned when any failure does occur in order to reduce the risks. The importance of reporting and investigating radiation incidents has been reinforced in recent ionizing radiation legislation and guidance [1–3]. This paper contains a review of the incidents that have occurred over a period of 10 years, during which a central system of incident reporting has been in place for hospitals throughout the West of Scotland. Examples of the different types of incident that can occur are given. The paper looks at the causes of incidents, the doses received in patient overexposures and analyses trends in incident reporting over that time. Consideration is also given to lessons that can be learned.

	Methods

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The Health Physics Service in Glasgow provides radiation protection services for 20 large hospitals and numerous smaller hospitals and health centres within seven Health Board areas serving a population of 2.8 million within the West and Borders of Scotland. A system for the reporting of incidents to the Health Physics Service has been in place for over 10 years and is included in the local rules for individual hospital departments. Departments were asked to report incidents in which a patient or member of staff was exposed to an unintended excess radiation dose or any incident involving a significant spill of radioactive material or spread of contamination. No guidance was given on a lower level to be exempt from reporting, but near misses were not reported through this system, although they are followed up internally in many departments.

A form with a relatively simple set of readily understandable questions geared to radiation has been in use throughout the period of the study. The form asked a series of questions in order that an understanding of what had happened could be obtained. These were:

• What happened?
  
• When did it occur?
  
• Who was involved?
  
• Was anyone exposed or injured?
  
• Was any radioactive contamination produced?
  
• If Yes, what monitoring and decontamination was carried out?
  
• Who was notified?
  
• What action was taken?
  
• Is any further action required?
  

The incidents reported were discussed with radiation protection supervisors (RPSs) who carried out investigations into their causes. The level of investigation and the degree of involvement of the radiation protection adviser (RPA) depended on the severity of the consequences and the likelihood of similar incidents occurring in the future. Evidence about what happened was obtained by interviewing those present and viewing the facilities with the aim of determining the critical factors that led to the incident. Assessments of effective dose were made for patient overexposure incidents, other than those involving the extremities. These used the X-ray exposure parameters or radionuclide activities employed for the exposure and appropriate conversion factors and dose information [4–7]. Assessments of overexposures in radiology were based on dose–area product (DAP) wherever possible. When this was not available, other factors were used including exposure parameters registered by the equipment, film densities, settings of back-up timers from failures of automatic exposure control (AEC) devices and experimental simulations of incidents based on descriptions given by the staff involved. Organ dose calculation software was employed to evaluate doses from CT examinations [8]. A report was then prepared which would include an analysis of the factors contributing to the incident and recommendations made about action that should be taken to minimize the risks of similar incidents occurring in the future, if this was considered appropriate. Implementation of recommendations was the responsibility of individual departments, but there might be further follow up at radiation protection reviews to ensure that procedures, training and other systems to deal with incidents had been put in place.

This paper contains a review of 606 incidents in diagnostic imaging departments reported over the last 10 years. All radiology incidents were placed in three broad categories related to the person receiving the excess exposure and the source of the error. These were: (1) patient overexposure due to human error; (2) patient overexposure due to an equipment fault; and (3) exposure of a member of staff. Unintended doses to fetuses from exposure of pregnant patients were included in category 1, but were analysed separately. Two additional categories were used in nuclear medicine; (4) contamination incidents, which may involve contamination of a person; and (5) failures in management or disposal of radioactive material. In order to aid analysis, each incident had been allocated an abbreviation at the time it was reported, relating to the radiation source, the person affected and the type of incident. However, for the analysis contained in this paper, more detailed re-examination of each incident report was undertaken to categorise reasons for the incidents occurring, to identify the most common causes and to tabulate the effective doses from patient exposure incidents. The categories used in the final analysis of the incidents are given in Table 1. Incidents, which included the exposure of a number of patients due to a single cause, such as a loss of digital image data during archiving, were recorded as a single incident. However, in the dose analysis, values of the effective dose for each patient were noted separately.

	Results

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View larger version (26K): [in this window] [in a new window]   Figure 1. Pie charts showing proportions of different types of incident in imaging departments in the West of Scotland reported over a 10 year period. (a) 417 incidents in radiology departments and (b) 189 in nuclear medicine.

View larger version (28K): [in this window] [in a new window]   Figure 2. Pie charts showing proportions of different types of patient exposure incidents in imaging departments in (a) radiology (352 incidents) and (b) nuclear medicine (71 incidents).

Wrong examination performed
This could occur for a variety of reasons. The wrong examination may have been requested, the handwriting may be misinterpreted by the radiographer, the request may be marked for the wrong limb or the wrong side of the body, or occasionally the radiographer may look at the wrong request.

Repeat exposures for duplicate requests
Duplicate requests can be made for various reasons resulting in a procedure being repeated unnecessarily. Separate requests may be issued by two clinicians from the same ward, or a request may be sent by fax to speed up the referral process, while the original request is sent through the mail. These duplicate requests should normally be identified by the Radiology Information System (RIS), but may not be picked up if the patient has two entries with different unit numbers.

Pregnant patient
Patients who find out that they are pregnant after having a radiation examination form a group for which special precautions should have been taken. If the operator failed to confirm at the time of the examination that there was no chance that a patient might be pregnant, or if the patient gave an inaccurate response to the question or the wrong date for their last menstrual period, this can result in an unintended radiation dose to the fetus. This is particularly important for patients undergoing ¹³¹I therapy, where the dose to the fetal thyroid can be substantial.

Mistakes in performance of examinations
These types of mistake, which result in failure of a procedure and necessitate the repeat of an examination, vary with the imaging equipment. In radiography, commonly occurring errors involved use of the automatic exposure control (AEC), such as failure to align the AEC device with the X-ray tube or selection of the AEC for the wrong tube. Other errors included use of a cassette with an exposed film, no film at all or without erasing an earlier image in computed radiography (CR). In CT scanning, several incidents occurred where the CT scanner position was inadvertently re-set after the scout view. This resulted in the wrong part of the patient being scanned, because the CT scanner executed the movements required for a different position on the patient axis.

A few incidents with fluoroscopic units occurred where the exposure button was depressed by movement of the table, resulting in exposure of patients and staff. In one incident, a fluoroscopy unit was put back rapidly into clinical use by the X-ray engineer in order to allow a procedure to be carried out, but a switch inside the unit was left "on", permanently enabling a low level fluoroscopy exposure for test purposes. This was only identified when the procedure was complete, through the continued illumination of the exposure light on the unit and the warning signs at the room entrance. However, the additional doses, received by both the patient and the staff, were very low.

In nuclear medicine, errors leading to use of the wrong radiopharmaceutical, or incorrect activity, or administration of radiopharmaceutical to the wrong patient are called mal-administrations. This also covers failures in the preparation of the radiopharmaceutical, such as when no pharmaceutical is added to the radionuclide component, or an error in preparation leads to poorer uptake so that the image quality is inadequate for a diagnosis to be made. Errors in preparation could lead to overexposures of a number of patients. In one case a batch of 10 vials were prepared in a central radiopharmacy using the wrong pharmaceutical and then despatched to several nuclear medicine departments. Imaging of the early patients revealed uptake in the wrong organs and prompt action by the nuclear medicine departments and radiopharmacy restricted the overexposure to five patients. The error was triggered as a pharmaceutical agent with a similar name was placed in the area of the fridge normally reserved for the radiopharmaceutical to be administered. Other causes of failure in an examination due to human error involved setting the wrong energy window for an ¹²³I scan, and loss of image data following a scan because the operator had not been adequately trained in the use of newly installed software. Another type of incident called a mis-administration occurred on a few occasions where the radiopharmaceutical was injected into the tissue rather than a vein. This type of incident can give a significant dose to the tissue around the injection site if the radiopharmaceutical does not disperse relatively quickly [9].

The relative proportion of patient exposure incidents originating from failures of different types are shown in Figure 3. Although errors by the staff within the imaging department made up the largest component, errors in the request by the referrer made up 23% of the total and 32% of incidents resulting from human error. There was a small number of incidents in nuclear medicine where patients failed to follow instructions, such as when a patient undergoing a nuclear cardiology examination left after the stress test before being imaged, a refusal to have an examination by a child after injection with radiopharmaceutical, the failure of a patient to give contraindications relating to the test, and failure to make the required urine collection. Although these incidents are attributed to failure of the patients to comply, the adequacy of the instructions given is also a factor.

View larger version (29K): [in this window] [in a new window]   Figure 3. Pie charts showing distributions of sources of error causing patient exposure incidents in (a) radiology and (b) nuclear medicine.

Doses for patient exposure incidents
The distribution of excess doses of 0.1 mSv and above received by patients during radiation incidents are shown in Figure 4 for the different imaging modalities. 154 radiology patients received doses below 0.1 mSv, which made up 49% of all the patients involved in incidents in radiology, but only three nuclear medicine patients received doses less than 0.1 mSv, making up 5% of the total. The distribution of excess doses is similar to that for the range of diagnostic procedures. The large number of low dose incidents mostly involved radiographs of the chest or extremities, which were the examinations carried out most frequently. Almost all the CT exposures had effective doses of 1 mSv and above, whereas the majority of other X-ray exposures were less than 2 mSv. The nuclear medicine exposures were distributed across the whole dose range. In Figure 5 the distributions of doses from incidents involving human error and equipment faults are compared and doses from unintended fetal exposures are also shown. Distributions of doses for the different categories were similar, each covering the full dose range. There were a few fetal exposures at the upper end of the dose range. The highest was from a ¹³¹I therapy and those between 20 mGy and 30 mGy were from two CT examinations and one barium enema. There were 10 fetal exposures under 0.1 mSv, which made up 24% of the total.

View larger version (32K): [in this window] [in a new window]   Figure 4. Distribution of effective doses for unintended patient exposures for nuclear medicine (NM), CT and other radiology techniques (X-ray), where the dose is 0.1 mSv or above. These exclude unintended fetal exposures.

View larger version (35K): [in this window] [in a new window]   Figure 5. Distribution of effective doses of 0.1 mSv and above from patient overexposures due to human error and equipment faults. Fetal doses from exposure incidents are also shown.

• irradiation by scatter when a CT examination was initiated while a staff member was in the room;
  
• irradiation when the exposure button of a fluoroscopy unit became jammed under the X-ray couch;
  
• inadvertent exposure of a staff member when the wrong X-ray tube was selected.
  

In all these cases the doses received were less than 1 mSv. Higher doses were recorded unexpectedly from time-to-time on personal dosemeters. The reasons for these were various and included dosemeters being left in controlled radiation areas or stored adjacent to objects which turned out to be radioactive.

Incidents involving radioactive material
Almost half of the incidents reported in nuclear medicine involved contamination, and in 46% of these the skin or clothing of a person handling the radiopharmaceutical became contaminated (Figure 1b). Spills commonly occurred when vials of radiopharmaceutical were dropped or lids removed and personnel were often splashed while withdrawing radiopharmaceutical into a syringe or while giving injections. Liquid could be sprayed over the operator or patient if a blockage occurred and the person injecting continued to press the plunger beyond the point at which the pressure started to increase. This type of incident occurred more frequently when a venflon or butterfly needle was used, as there was a greater risk of a connection not being made properly, although the reduction in radiation dose and simplification of the procedure when these devices are employed more than compensate for the additional risk of contamination. Contamination incidents also occurred as a result of damage to ¹³¹I therapy capsules. 31% of the contamination incidents involved radioactive body fluids from a patient, usually either urine or vomit. The time after administration for which the risk remains high depends on the physical half-life of the radionuclide and the biological half-life of the pharmaceutical involved. A number of incidents involving leakage of urine occurred with patients who were catheterized. Leakages occurred from around the catheters, from split urine bags or from the tap on the bag when it was opened unintentionally. Extra care is needed in protecting urinary bags when nuclear medicine patients are moved. Other incidents involved patients who vomited or were incontinent following oral administration of ¹³¹I therapy. In all cases staff and the patient were aware of the nature of the hazard and took appropriate action to minimize spread.

Failures in management of radioactive material fell into four categories: loss of a source or a vial of radiopharmaceutical, disposal of radioactive waste through the clinical waste stream, leakage of radioactive material from a drainage pipe and temporary loss of control through transport accidents. Two incidents of loss of radiopharmaceutical occurred; both involved Schilling tests, one administered at a health clinic and the other at a smaller hospital where other radionuclides were not used and responsibilities relating to delivery and storage were not set down clearly. Temporary loss of a ¹⁵³Gd source, used for gamma camera attenuation correction, occurred when there was a change of management in a company to whom a decayed source was returned. No record of receipt for the source was sent and the whereabouts of the source were unknown for a period of time, although it was eventually found some months later. Another type of incident that occurred on a number of occasions was where domestic staff in nuclear medicine placed bags of radioactive waste in the clinical waste stream having forgotten about special arrangements for disposal of radioactive material. Incidents also occurred involving the leakage of drainage pipes from sinks used for disposal of liquid radioactive waste. One such sink was used for disposal of a longer half-life radionuclide and the problems resulting from disposal of contaminated building material from this incident were considerable. Transport incidents that occurred were temporary misplacement of radioactive packages sent by train and involvement of vans transporting radioactive materials in road traffic accidents.

Incident reporting
The number of nuclear medicine incidents in different categories reported to Health Physics each year is shown in Figure 6. The total number of incidents reported has remained fairly constant, although the proportion of patient exposure incidents due to both mal-administrations and equipment faults has increased over the last 3–4 years. In contrast, the number of incidents reported by X-ray departments has changed dramatically with a four-fold increase since the 1990s (Figure 7). The categories that have increased significantly are those involving patient overexposure due to human error, with small increases in the reporting for exposures of pregnant patients and overexposure due to equipment faults. The numbers of incidents reported in which a staff member was exposed remained fairly static over the 10 year period.

View larger version (32K): [in this window] [in a new window]   Figure 6. Numbers of different categories of incident occurring each year in nuclear medicine departments in the West of Scotland.

View larger version (38K): [in this window] [in a new window]   Figure 7. Numbers of main types of incident occurring each year in X-ray departments in the West of Scotland, showing increases in reporting of patient overexposures in recent years.

View larger version (43K): [in this window] [in a new window]   Figure 8. Numbers of incidents occurring each year in X-ray and nuclear medicine (NM) departments in the West of Scotland that were reported to the regulatory authorities Scottish Environment Protection Agency (SEPA), Scottish Executive Health Department (SEHD) and Health and Safety Executive (HSE).

	Discussion

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• Failure in management systems and breakdown of procedures.
  
• Errors by staff due to poor training.
  
• Errors by staff due to pressure of time constraints resulting from poor staffing levels.
  
• Accidental errors by staff, which are unlikely to be repeated.
  
• Performance of new procedures without adequate risk assessment.
  
• Equipment faults.
  

The potential causes, the defences that are in place to pick up such errors when they do occur and the background factors, which can affect the likelihood of an incident occurring, are summarized in Figure 9. Systems for authorizing medical exposures have been tightened up under recent legislation [2], so that radiographers and radiologists may question referrers about dubious requests and will refuse to perform examinations when insufficient clinical or demographic information is supplied [13]. Despite this, the proportion of incidents caused by errors in requests by referrers was significant (Figure 3) and made up 32% of the patient exposure incidents due to human error. It is often more difficult for departmental defences to pick up cases where the wrong demographic details are entered on a request by the referrer, although more comprehensive information technology systems should facilitate identification of such errors. This type of incident commonly occurred when the wrong patient ID label was attached to a request form. Referral of the wrong patient made up 47% of the referral errors. Another common mistake in referrals was specification of the wrong side of the body. Simple confirmatory checks for this type of mistake are made when patients attend for examination in radiology departments. Diligence on the part of the referring clinician, together with correct use of the RIS are important in order to minimize both erroneous referrals and repeat exposures due to duplicate requests.

View larger version (32K): [in this window] [in a new window]   Figure 9. Framework illustrating sources of errors resulting in patient overexposures and defences to prevent them. The upper line of boxes represent the mistakes in various departments that might lead to an incident, while the second line shows the defences that should be in place to identify errors before they develop into incidents. Background influences that may affect the probability of an incident occurring are also shown. RIS, radiology information system; NM, nuclear medicine.

20% of the patient exposure incidents involved equipment faults. When such an error was identified, the equipment was immediately removed from service and a maintenance engineer called in. Frequency of incidents is a factor that should be taken into account when considering the need for equipment replacement. Radiation doses received from some types of incident depend on how the equipment operates. Radiographic overexposures due to the failure of an AEC device or human error, such as misalignment of the AEC device with the X-ray tube, will deliver a dose to the patient that will depend on the setting of the back-up timer. In more modern systems, the dose at the radiation detector may be monitored and the exposure terminated after a shorter time, if no signal is observed, thus minimizing the overexposure [14]. Occasional errors did occur following equipment maintenance. A formal handover system, to promote checks by the service engineer and radiographer have been introduced to reduce the likelihood of errors resulting from test facilities being left in the enabled position or equipment being left with unusual settings.

The numbers of patient overexposure incidents reported has increased in recent years, particularly in X-ray departments (Figure 7). It is possible that a change to a more open culture, which recognizes the need to report and investigate patient overexposures, partly accounts for this increase. Presentations were given on reporting of radiation incidents at local RPS courses in 2001 and 2002, and differences between reporting patterns in different departments were highlighted. It is thought that the risks of clinical incidents may have actually been reduced through the establishment of more robust procedures to prevent errors being made [2] and through formalizing the safety net of checks to pick up mistakes before they had the chance to develop into an incident. The change in the pattern of reporting for patient exposure incidents is less pronounced in nuclear medicine (Figure 6). This may be partly because there had always been a strong reporting culture among the physicists involved and partly because most errors which did occur clearly represented procedural failures. The number of incidents reported over the last few years is considered to be closer to the true situation in radiology.

The average number of patient overexposure incidents reported in radiology departments over the last 3 years was 91 per year, and of these four were reported to the SEHD. The average number of medical X-ray examinations performed in NHS hospitals in the UK is 450 per 1000 population per year [15], so if the frequency in the West of Scotland is assumed to be similar to the UK average, 1.3 million procedures would be performed each year and the frequency of incidents will be about 7 per 100 000 procedures. Although the register of incidents applied to dental as well as medical X-rays, only one of the incidents involved a dental examination and this was a cephalometric radiograph for which the wrong exposure factors were set. The reasons for the low number of reported incidents are likely to be multifarious. They include the simple nature of the equipment; the fact that dental X-rays are frequently taken at the same time as the physical examination, with the dentists or their assistants operating the equipment; and the comparatively low dose associated with most dental X-rays. The average number of patient overexposure incidents in nuclear medicine was seven per year, of which one was reported to the SEHD. Estimates based on extrapolation of UK data [16] indicate that the number of nuclear medicine procedures carried out in the West of Scotland is about 23 000 per year. This would suggest that there are about 30 incidents per 100 000 procedures of which 4 would be reported to the SEHD. Part of the difference in the number of incidents reported in nuclear medicine and radiology departments is likely to result from the application of more robust reporting procedures. The only other data on the rate of reporting to statutory authorities found by the author was 2.5–4 radionuclide incidents per 100 000 procedures reported to the Texas Department of Health Bureau of Radiation Control [17]. However, this study concerned both diagnostic and therapeutic procedures using unsealed and sealed sources and so the comparison is tenuous.

Incidents involving radioactivity
The incidents involving management of radioactive materials highlight the importance of having well defined workable systems in place, which clearly identify a person who takes responsibility for all aspects of radionuclide accounting and trained deputies. The incidents concerned with loss of Schilling tests demonstrated the importance of this even in a smaller unit where few radionuclides are used. Loss of the ¹⁵³Gd source highlighted the importance of ensuring that receipt of sources despatched to other sites is acknowledged. Radioactive material should be transferred to secure storage on entering the department and not left unattended. Clear labelling and identification of agreed locations for storage of radioactive materials and pharmaceuticals is important at all times, as was highlighted by the error in radiopharmaceutical preparation which resulted in overexposure of several patients. Radioactive waste containers must always be labelled and procedures for dealing with the waste set out clearly. Incidents involving disposal of solid radioactive waste through the wrong route emphasise the need for training in the storage and disposal arrangements for all staff who have any duties in a radionuclide department. Training should be given at induction and updated for all staff from time to time.

Although steps can be taken to reduce the risk of incidents involving contamination, it is not possible to eliminate them. Prior risk assessments should be undertaken for areas where radionuclides are handled and appropriate precautions implemented to reduce the risk when a spillage occurs and ensure that staff are aware of the steps they need to take to avoid spread of contamination. Risks of incidents, where patients vomited or there were spills of urine, were kept to a minimum through awareness and prompt action by staff. Special consideration needs to be given to risks of contamination from patients following ¹³¹I and other therapies. The prior risk assessment may identify the need for patients to stay in the department for a period after administration and is likely to require special precautions, if treatment of an incontinent patient is undertaken. However, patients and circumstances vary in different departments and arrangements must reflect local needs and facilities.

The incident involving leakage of radioactive liquid from a drainage pipe highlighted both the need to arrange for checks of routes used for liquid waste disposal and the importance of prior risk assessments before longer half-life radionuclides are disposed of. Checks for leakage may not be easy if access to the pipes is not considered at the time of installation. Resulting doses to personnel, problems from disposal of contaminated building material and financial implications can be considerable if any leakage of longer half-life material does occur.

	Conclusions

Top Abstract Introduction Methods Results Discussion Conclusions References

 
There is a wide range of types of radiation incident that can occur in hospitals. 85% of incidents in radiology departments were overexposures of patients, while in nuclear medicine this was only 37%, as there were also significant numbers resulting from failure in management of radioactive materials and contamination. Doses for patient overexposures were distributed across a range similar to that for diagnostic procedures with higher doses being made up predominantly of CT and nuclear medicine examinations. The numbers of incidents reported were 91 per year in radiology and 12 per year in nuclear medicine for a population of 2.8 million. It is estimated that this represents 7 per 100 000 procedures in radiology and 30 incidents per 100 000 in nuclear medicine. 80% of the patient exposure incidents were due to human error or procedural failure and 32% of these resulted from mistakes in the request made by the referrer. This was despite systems being in place for checking requests for patient examinations. 49% of incidents in nuclear medicine involved contamination, but prompt action by staff in dealing with these avoided any serious spread of contamination or exposure. 10% of the incidents concerned failure of management of radioactive material and emphasised the need for robust procedures and training for all staff working in departments where radioactive material is handled. The operation of a local incident reporting and investigation system has raised staff awareness of the potential for things to go wrong and promoted the review and improvement of systems based on experience.

	Acknowledgments

 
The author wishes to acknowledge the work of Mr A G Brennan, Dr D Gentle, Dr J Robertson, Mr J Kennedy and Mr R Corrigall in investigating and preparing reports on the incidents in the study. He would also like to thank staff in the Radiology and Nuclear Medicine Departments throughout the region for their co-operation in reporting incidents and implementing recommendations to reduce risks of incidents in the future.

Received for publication February 1, 2005. Revision received April 29, 2005. Accepted for publication May 4, 2005.

	References

Top Abstract Introduction Methods Results Discussion Conclusions References

 

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This Article Abstract Figures Only Full Text (PDF) Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Martin, C J Search for Related Content PubMed PubMed Citation Articles by Martin, C J