MR-conditional pacemaker, orbital metal history and an oxygen cylinder in Zone III
A 61-year-old man is referred for an MRI of the lumbar spine for suspected discitis. On his screening form he reports a heart device implanted three years ago, a metallic foreign body in the left eye from grinding twenty years ago with no current symptoms, and a long career as a welder. He brings a manufacturer's card reading 'MR-conditional: 1.5 T only, maximum spatial gradient 720 G/cm, whole-body SAR no more than 2 W/kg, no scanning within six weeks of implant'. The department has both a 1.5 T and a 3 T scanner; the booking clerk scheduled him on the 3 T because the waiting list is shorter. He walks into the screened Zone III with a walking frame, and his relative is pushing an oxygen cylinder alongside him. The radiographer is the only MRI-trained staff member present.
1. What checks must be completed before this patient is scanned, and what is your decision about the 3 T booking and the eye history?
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Device identification comes before scheduling. A referral form and even a patient-held card are starting points, not clearance. The device model and serial number must be matched against the manufacturer's current MR-conditional documentation for that exact device, and against the actual scanner (field strength, gradient system, coil type, software level). If the documentation cannot be obtained, the answer is no.
Field strength. The card specifies 1.5 T only. An MR-conditional label is not transferable: the conditions include field strength, maximum spatial gradient, SAR and coil configuration. Scanning at 3 T breaches the conditions and voids the liability position of both the operator and the hospital. The decision is to rebook on the 1.5 T scanner; the shorter waiting list is irrelevant. All other conditions (six weeks post-implant, SAR limit, gradient limit) then have to be satisfied at 1.5 T, and the radiologist, not the radiographer, authorises the scan in writing, with cardiology informed.
Eye history. A metallic intraocular foreign body is a recognised cause of serious injury in the magnet. Grinding twenty years ago with no symptoms does not exclude it. The patient needs bilateral orbital radiographs or a CT of the orbits read before the scan, and the MRI must not proceed until the result is documented. If metal is present within or near the orbit, MRI is generally contraindicated and the referral returns to the radiologist for an alternative imaging plan. This must not be delegated to the patient to decide.
Sequencing. Screen, verify, image the orbits, obtain written authorisation, plan monitoring, then scan.
2. What must happen immediately regarding the oxygen cylinder, the relative and the zoning of this area?
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The cylinder is the urgent problem. Ferromagnetic gas cylinders are among the best-documented fatal MRI incidents: they can be pulled into the bore with enough force to kill. As soon as the cylinder crosses into the screened Zone III it must be removed by a staff member who has confirmed no one is inside Zone IV, or by the relative under direct instruction, and it must be secured outside the zone boundary. Only MR-safe (typically aluminium) cylinders, checked and labelled, may enter Zone III, and none may enter Zone IV unless the site's policy permits it and the cylinder is verified MR-safe.
Zoning reasoning. The four-zone concept exists so that the risk increases gradually and control is applied at each step. Zone I is freely accessible; Zone II is a transition area under supervision; Zone III is screened and physically locked, accessible only after a person has been screened and changed; Zone IV is the magnet room itself. The failure here is at the Zone II/III boundary: the relative was never screened and was not supervised.
Immediate actions.
- Stop the relative at the line, take the cylinder, and re-screen the relative on the MRI safety questionnaire and with the metal detector.
- Screen the walking frame - most are aluminium, but aluminium is not the same as MR-safe. It must be verified and left outside Zone IV regardless, and the patient must be transferred to a non-ferromagnetic chair or trolley.
- Account for who is inside Zone IV before anyone else enters.
- Re-brief the reception and portering staff, because the booking clerk and the porter both contributed to this near-miss.
- Record it as a safety incident with the MRI safety officer - a near-miss logged honestly is worth more than a quiet correction.
3. If the scan is cleared and proceeds on the 1.5 T system, what monitoring would you require and what would you do if the patient developed symptoms during the scan?
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Before the patient enters. Confirm written radiologist authorisation and cardiology agreement, device programmed to the appropriate MR mode by a competent cardiac physiologist or cardiology nurse present in the department, a full baseline set of observations, and a plan agreed for the duration of the scan and the post-scan device check. Verify the SAR and gradient limits the scanner will use are within the card's conditions, and use a receive-only coil arrangement that does not place conductors across the chest.
Monitoring during the scan. Continuous ECG and pulse oximetry compatible with the magnet, voice contact via intercom, a squeeze bulb in the patient's hand, and direct visualisation through the window. Keep total scan time within the agreed limit and avoid unnecessary sequences.
If symptoms occur - palpitations, chest discomfort, a feeling of heating, pain, or a sensation of device movement - stop the scan immediately, take the patient out of the magnet room by the standard route (do not pull the trolley past the bore), reassess ABC, obtain a 12-lead ECG and inform cardiology at once. Do not re-enter Zone IV with ferromagnetic equipment. If the patient deteriorates after leaving the room, treat it as a medical emergency and run the standard resuscitation protocol at the door to Zone IV, keeping the resuscitation trolley outside the magnet room.
After the scan. Post-procedure device interrogation, documentation of all parameter limits used, and a written record that the conditions were met. If any condition was breached, the MRI safety officer and cardiology must be informed and the patient followed up.