Sat27November0445PM 22

Are the following true or false with regard to anaesthesia for magnetic resonance imaging (MRI) scanners?

True / False

An emergency stop of the scanner may release a hazardous gas Correct

Items marked as 'MR safe' are known not to adversely affect the scanner, but their function and operation may be affected Correct

Presence of a permanent pacemaker means that a MRI scan should never be performed Correct

Infusion pumps cannot be reliably used as the magnetic field affects the rate of infusion Incorrect answer selected

MR contrast contains a high osmolar concentration of iodine Incorrect answer selected

Explanation

Anaesthesia for MR scanning is a core part of paediatric anaesthetic practice.

MR scanning works by aligning hydrogen atoms with a strong magnetic field and then allowing them to return to normal, in the process emitting radio waves. These radio signals are converted into an image. This technology relies upon superconduction which occurs only at extremely low temperatures. These temperatures are achieved with liquid helium. Stopping the scanner rapidly leads to release of helium gas which can act as a suffocant.

The nature of a MR scanner poses challenges for the anaesthetist. Monitoring is usually remote and some pieces of equipment cannot be used normally or at all.

Devices can be classified into:

MR safe - generally work well and do not affect the scanner

MR conditional - will work well when certain conditions are met (for example, maximum magnetic field strength)

MR unsafe - should not be used for MR scanners.

The term 'MR compatible' is now obsolete due to confusion. However, it must be noted that 'MR safe' items are merely designated as such provided that they present no safety hazard to patients or personnel and that instructions for use are followed. It does not guarantee that the device will function normally.

The MR scanner poses a risk to the patient. The contrast is gadolinium-based, and a lot safer on the whole than the hyperosomolar iodine-based contrast used in radiographic imaging. However, there is still a small risk of anaphylaxis and a rare condition of systemic fibrosis when used in renal failure. Indwelling devices such as pacemakers pose a risk. However, modern devices are safer, and cases have been described of planned MR with a pacemaker in situ in certain controlled conditions.

Reference:

Association of Anaesthetists of Great Britain and Ireland, et al. Safety in magnetic resonance units: an update. Anaesthesia. 2010;65:766-70.

Answer Statistics

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Average score: 69.06%

Times answered: 256