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Original Research |
1 Department of Diagnostic Radiology, Peter MacCallum Cancer Centre, St. Andrews
Pl., East Melbourne, Victoria 3002, Australia.
2 Department of Radiology, Western Hospital, Footscray, Victoria 3011,
Australia.
3 Department of Radiology, The Alfred Hospital, Melbourne, Victoria,
Australia.
4 Department of Radiology, Princess Alexandra Hospital, Woolloongabba,
Queensland, Australia.
Received July 12, 2006;
accepted after revision October 11, 2006.
Address correspondence to N. J. Ferris
(njferris{at}internode.on.net).
Abstract
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MATERIALS AND METHODS. A questionnaire was distributed to more than 100 MRI facilities in Australia.
RESULTS. Ninety-two responses, representing 102 MRI systems, were received. Respondents from approximately one in 15 sites were aware they had inadvertently imaged a patient who had a permanent pacemaker (eight patients). One of these episodes led to a death. Use of modified request forms, on which referring physicians are asked for MRI safety information, was incomplete (48/90 facilities). Four facilities deliberately imaged pacemaker patients. Seventy-seven of 89 facilities responded that they do not image patients with temporary pacing wires. Aneurysm clips were accepted by most sites (71/91), and only one site associated with a neurosurgical service refused such patients. Seventy of 71 facilities required written identification of the clip type. Most (77/90) of the sites reported delays due to the unknown MRI safety status of implants. Only four of 92 sites reported routine use of a metal detector. The guidelines of the American College of Radiology and of the Royal Australian and New Zealand College of Radiologists were equally influential (38% each). Only 10 of 90 respondents reported use of external audits of safety processes.
CONCLUSION. Ongoing vigilance is required for avoiding MRI of patients with pacemakers, particularly when information from the patient is unreliable or unobtainable. Requiring referring physicians to provide MRI safety information may help to minimize risk.
Keywords: MRI • safety
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APPENDIX 1 : MRI Safety Screening Survey
The survey sought basic information about MRI equipment (field strength, gradient performance), the relationship of the service to a neurosurgical service, and safety policy (19 yes-or-no questions). Respondents were given the option of an anonymous response. They also had the opportunity to provide detailed comments.
Positive responses to each dichotomous (yes or no) question were totalled and expressed as percentages of the total number (n) of responses to that question. The margin of error for these percentages was estimated to be 1 divided by the square root of n, expressed as a percentage. Stated margins were adjusted to avoid implication of negative percentages when the margin of error was larger than the estimated proportion of positive responses.
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90%, total number of systems not precisely
known) in the state of Victoria, which contains one fourth of the Australian
population, than in other states (70-80%). This difference in response rate
may have been caused by greater awareness of MRI safety issues after the
death, which occurred in Victoria, or better recognition of the survey team,
which was based in Victoria. Most of the participating facilities had
high-field systems with gradient slew rates greater than 50 T/m/s. Only four
facilities had MRI systems with field strength less than 0.5 T.
Inadvertent Imaging of Patients with Permanent Pacemakers
Seven responses showed that a total of at least eight patients with
pacemakers had been inadvertently imaged, including the patient who died. No
adverse event was identified in relation to the other seven inadvertent
exposures. Therefore, at least one in 15 sites (7%; range, 0-18%) was aware
that it had inadvertently imaged a patient who had a cardiac pacemaker.
In the case of the death, the presence of a pacemaker was known to two of the treating clinicians but was not communicated to the MRI staff. The patient denied having a pacemaker. The Victoria coroner recommended that referring physicians be required to complete safety questions on MRI referral forms (Appendix 2). Overall, 48 (53% ± 11%) of 90 facilities responded that they required referring physicians to provide safety screening information. In Victoria, where the death occurred, the proportion was 81% ± 20% (21/26); the proportion was 42% ± 13% among respondents outside Victoria. Only a minority of sites (22/53, 42% ± 14%) formally audited the completeness and accuracy of the safety information on the referral forms.
APPENDIX 2 : Sample Information Sheet Used by Referring Physicians
Deliberate Imaging of Patients with Permanent Pacemakers
Eight responses indicated a willingness to image a patient with a pacemaker
with appropriate (unspecified) precautions. Four of these facilities had
actually imaged such a patient.
Temporary Pacing Wires
Seventy-seven (87% ± 11%) of 89 responses indicated that patients
who had remnants of temporary pacing wires would not be accepted for imaging,
but this percentage might have been an underestimate of the number of
facilities that image these patients in practice. Temporary pacing wires and
fragments of wires often are left in situ after cardiac surgery, and they may
not be recognized before imaging. Of the sites accepting such patients, only
four placed restrictions on the MRI sequences used.
Intracranial Aneurysm Clips
Twenty (22% ± 10%) of 91 responses stated that no patient with an
intracranial aneurysm clip would be accepted for imaging, but only one of the
40 facilities associated with a neurosurgical service responded that they
would refuse all such patients. Nearly all (70/71, 99%; range, 87-100%)
facilities relied on written identification of the clip type. Only 10 (18%
± 13%) of 57 facilities required that the clip be in its original
packaging at the time of surgery, and only four of 61 (7%; range, 0-20%)
facilities tested clips on site. Similar proportions of facilities relied on
clip manufacturer (43/66, 65% ± 12%) and third-party (47/65, 72%
± 12%) data on implant safety.
Other Implants
Most (77/90, 86% ± 11%) of the facilities reported delays due to
difficulties in establishing the MRI safety and compatibility of implants. The
frequency of these delays ranged from daily (three facilities) through weekly
(27 facilities) to monthly (47 facilities).
Metal Detector Use
Only four (4%; range, 0-15%) of 92 responses indicated that a metal
detector was used in routine screening. Anecdotal evidence from one of these
sites showed that no significant implant had been identified with use of the
metal detector alone. A ferromagnetic detection system (entry and prescreen
system, Ferralert, Kopp Development) that has received publicity in North
America is not available in Australia.
Use of Guidelines
Many sites reported changes in practice based on information in published
materials. The American College of Radiology
[1] (32/85, 38% ± 11%)
and Royal Australian and New Zealand College of Radiologists
[2] (34/89, 38% ± 11%)
guidelines were similarly influential in affecting local practices.
Use of an External Audit Process
Ten (11% ± 11%) of 90 facilities responded that they had engaged an
external consultant to review their safety procedures.
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The pacemaker incident also illustrated the dependence of MRI safety screening on accurate information from patients and their associates. The occurrence, acknowledged in our survey results, of at least seven (nonfatal) inadvertent exposures of pacemaker patients to MRI further emphasizes the potential for disaster.
This survey was addressed to the radiologist supervising each MRI facility. This person may not always have been the one who completed the questionnaire. We were not able to ensure that every member of an MRI staff was consulted, and it is possible that additional safety incidents involving pacemakers and other devices occurred but were not reported. Our survey results therefore represent only the lower limit of the frequency of such incidents.
Notwithstanding that a number of patients with pacemakers have safely undergone imaging with appropriate precautions, a large number of patients with potentially unsafe devices continue to undergo imaging [3]. Unremitting vigilance is required, and any suspicion that a patient may not be an accurate informant (e.g., because of dementia or an acute confusional state) should prompt further assessment by clinical examination, consultation with caregivers and referring physicians, review of previous images, and, if necessary, acquisition of appropriate conventional radiographs.
In response to the fatal incident, the Victoria coroner, who is empowered to investigate and make recommendations about unexpected deaths, recommended that referring physicians be required to complete safety screening information as part of the MRI referral process. This recommendation was prompted in part by the peculiar feature of the case in question, that the treating physicians were aware of the presence of the pacemaker, but did not realize that MRI would be hazardous to such a patient and did not communicate their knowledge to the MRI staff. The survey results show that this recommendation has been widely but not universally influential in Victoria, but is followed less than 50% of the time in other states. Even in Victoria, it is well recognized that some referring physicians will not complete the screening information accurately or at all and that the information cannot and should not be relied on. Ongoing audit of the completeness of such information apparently is uncommon. For there to be any chance of accurate referral information, such audits are clearly needed.
Referral safety questionnaires produce an additional layer of precautionary screening and raise the awareness of referring physicians about the issue. They have not, however, been shown to reduce the number of MRI safety incidents or to save lives. Evidence supporting such an outcome would be difficult to obtain.
We found that most Australian sites require written evidence of the type of aneurysm clip known to have been inserted in a patient and require third-party information on the MRI compatibility of the clip type in assessing the safety of MRI of patients with such clips. Variations in practice with regard to aneurysm clips have prompted discussions with the Neurosurgical Society of Australia that are aimed at standardizing clip handling and documentation in operating suites. Documentation of the MRI safety of other implants continues to be difficult, particularly because most of these devices are manufactured outside Australia. This issue is being discussed with the Therapeutic Goods Administration, the Australian organization responsible for the regulation of such devices.
Stage 3 of the Royal Australian and New Zealand College of Radiologists accreditation program for radiology practices includes onsite inspection of MRI systems, including safety procedures, but this inspection is not as comprehensive as a dedicated external safety audit. There may be greater scope for the use of MRI safety advisors, as recommended by the UK Medicines and Healthcare Products Regulatory Agency [4].
In conclusion, ongoing vigilance is required to minimize pacemaker-related MRI incidents. At least one in 15 Australian MRI facilities is aware that it has inadvertently performed imaging on a patient with a pacemaker. Particular care is needed when the patient may not be able to respond accurately to MRI safety questions. Consideration should be given to requiring referring physicians to supply safety information at the time of referral to give an additional level of hazard recognition.
Acknowledgments
We thank Professor Ken Thomson for allowing us to work with his research
team.
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