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QUESTIONS
» MRI Safety

Exposures, limits, safe systems of work. This section explores safety issues in magnetic resonance imaging.

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Sheet Metal Worker

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What would you advise about scannning a sheet-metal worker?

Don't scan without taking an x-ray of the patient's eyes first. Movement of metal splinters in the eye poses a risk of retinal detachment.

Intra-ocular ferrous foreign bodies, bullets and shrapnel are hazards in MRI. It is not uncommon for patients who have worked with sheet metal to have fragments of metal in the eye, and this should be ruled out by analysis of a plain film x-ray. This mode of imaging is sufficient to detect any metal fragments large enough to cause discernible clinical damage. It has been shown that some ammunition has traces of ferromagnetic alloys, and the location of any bullets or shrapnel in the patient should be taken into account before imaging.

Particular attention should be paid to a relatively new development with respect to MR-and-implants safety. This is the inclusion of a silicon chip as part of a transponder device embedded in any implant. It is typically a 2x11 mm capsule consisting of an RF tuned circuit and an antenna. It is a tagging device for making easy the future non-invasive determination of the type/model/age and origin of the implant. It will emit, when properly prompted, a signal with this information encoded. Unfortunately the RF circuit will respond to the RF pulses and may cause localised heating effects. It is not difficult to see these devices becoming more widespread in many applications—they are difficult to steal and so make ideal tools for use in money transfers, medical records, even passports.

Further reading on this topic:
Books: Q&A in MRI p293-294, 298-299, MHRA Guidelines p57-58
Online: MRIsafety.com, Kanal 1, 2

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