TYK74
A 6 year old patient with a history of tetralogy of Fallot and MAPCAS with previous coil embolizations of pulmonary collateral vessels needs to undergo a MRI of the heart for further work up. How long after implantation should one wait before this elective procedure be performed?
A. Never
B. 2 weeks
C. 6 weeks
D. 6 months
E. 1 year
Answer
The answer is C.
MRI in itself has been proven safe in pediatric patients. There are no known harmful effects from exposure to the magnetic field. However, implanted devices containing metal can make MRI unsafe. There are several dangers with metal in a magnetic field. These include heating of the metal, movement of the metal, and image artifacts making the test difficult to interpret. Implanted metal devices may move in a magnetic field and cause surrounding tissue damage. This is important in our pediatric population as many patients may have various metal implantations (stents, coils, sternal wires, pacemakers, shunts, etc. ). While the push in medical devices is now to have these materials be MRI safe, there is no strict guideline in place. Pacemakers generally make an MRI contraindicated. Stents, coils, occlusion devices, etc are usually weakly ferromagnetic. This weak attraction results in little heat generation. However, even if the material is weakly ferromagnetic, the material may move in a strong magnetic field. A general guideline from manufacturers is to wait 6 weeks before an MRI after implantation. Fibrosis during this time period is thought to anchor the device more firmly. The 6–week recommendation is arbitrary and not based on a tremendous amount of data. However, the AHA produced a scientific statement in 2007 where they recommended 6 weeks for pretty much everything to minimize movement.
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