MR-Conditional Pacemaker and a 3 T-Only Scanner
Mr. T is a 63-year-old man who presents at 15:00 with two days of progressive bilateral leg weakness, saddle anaesthesia and urinary retention. The emergency physician requests an urgent MRI lumbar spine to exclude cauda equina syndrome. Mr. T has a pacemaker implanted 8 months ago; he produces a wallet card stating it is MR-conditional for 1.5 T only, with stated SAR, gradient and scan-time limits. Your site's only scanner is a 3 T. The sister hospital with a 1.5 T is 45 minutes away by ambulance, its department closes in 3 hours, and the device clinic nurse is not answering her pager. The patient is stable, in sinus rhythm at 72 bpm, and asks you to "just get it done."
1. Can this patient be scanned on the 3 T unit this afternoon? Walk through your reasoning and your immediate actions.
Read the worked answer
No - not on the 3 T, and not by improvisation.
- Conditional status is not transferable between field strengths. The labelling that makes this device "MR safe enough" specifies 1.5 T, a whole-body SAR ceiling, gradient slew limits and a maximum scan duration. At 3 T the lead-tip heating and induced-current behaviour of this system has not been characterised, so scanning would make it a non-conditional implant.
- Non-conditional pacemaker scanning is a risk-benefit decision made by a radiologist and cardiology/EP, not a technologist's judgement call, and there is a safer route to the answer here.
- Cauda equina is time-critical, so the answer is not "come back next week." My actions in order: stop the patient at the console, page the radiologist and speak to the ED physician directly, state the urgency, and lay out the options - transfer to the 1.5 T site, or CT myelography as an alternative that answers the same question tonight, or wait for device verification.
- I do not let the patient's "just get it done" or the ED's time pressure move the decision into the magnet room.
2. Assume the patient is transferred to the 1.5 T site. What must be true before he enters the magnet room (Zone IV)?
Read the worked answer
Zone IV entry requires a completed chain, not a single check:
- Device identity confirmed against a written source - exact generator and lead models, with the conditional status and its conditions verified from the manufacturer's labelling, not from the patient's memory of what he was told.
- No disqualifying hardware - no abandoned leads, no adapters, no other implants that fall outside their own conditions.
- Device interrogated and reprogrammed to an asynchronous/appropriate mode with rate-response disabled, and a plan for post-scan interrogation before he leaves.
- Monitoring and rescue in place - continuous ECG and SpO2, voice contact throughout, a person who can see the patient, an ACLS-trained staff member present, external defibrillator pads and a crash cart immediately available.
- The scanner configured to the label - 1.5 T, implant/conditional mode selected, whole-body SAR and gradient limits entered, receive-only coils only, no transmit coil over the thorax, total scan time within the stated limit.
- Consent and documentation - informed consent covering the specific risks, and a written record of every parameter used.
Any item missing means the scan does not proceed.
3. He arrives at the 1.5 T, but says the generator was replaced two months ago, he has no new card, and the device clinic line goes to voicemail. Now what?
Read the worked answer
Unknown device = non-conditional device. A wallet card describing the old generator tells me nothing about the current one, and a verbal description ("it's the same model") is not verification. I do not scan.
I would:
- Tell the radiologist and the referring team immediately that the conditional status cannot be established tonight.
- Push for an alternative that answers the clinical question: CT myelography is the obvious one for suspected cauda equina and needs no device enquiry of this kind.
- If MRI is genuinely the only acceptable test, arrange device identification through the implanting hospital's records or an on-call EP, and reschedule - with the patient and the ED told explicitly why and what happens next.
- Document the time of the query, who was contacted, what was and was not verified, and who made the decision. A photograph of an old card or a manufacturer name alone is not documentation of the current system.