Magnetic resonance imaging or MRI has become a very common investigation.It provides unsurpassed soft-tissue contrast and multiplanar capability with spatial resolution that approaches that of CT.
It is a powerful diagnostic tool and helps to evaluate structures that are otherwise use to require invasive investigations.
Generally, MRI is a very safe investigation but there are conditions where it should not be done at all and conditions where it should be used with caution.
Safety and Contraindications to MRI
Though MRI has no radiation hazards, due to magnetic fields it generate it can pose dangers to some people and thus there are contraindications to MRI. Risks associated with MRI may be attributed to one or to a combination of the three main mechanisms of the system:
- Strong static magnetic fields may cause an object or device may be moved, rotated, dislodged, or accelerated toward the magnet. Articles such as metallic splinters, vascular clips, and cochlear implants may be dislodged.
- Pulsed gradient magnetic fields are repeatedly and rapidly turned on and off. The rapid changing magnetic fields can induce electrical currents in electrically conductive devices and may directly cause neuromuscular stimulation.
- Pulsed radiofrequency fields- Some of the applied energy will be absorbed by the body and converted into heat. Metallic devices can concentrate radiofrequency energy which leads to local heating. Radiofrequency energy can also induce electrical currents in wires and leads which might induce arrhythmias.
Absolute Contraindications to MRI
These are the conditions where MRI Should Not Be Used At All
- Patients where intracerebral aneurysm clips have been placed
- Patients in whom cardiac pacemakers are installed
- In case of automatic defibrillators
- In presence of biostimulators like Vagus nerve stimulators, loop recorders, insulin pumps, cochlear implants, deep brain stimulators etc
- In cases of implanted infusion devices
- When patient has got internal hearing aids
- If there are metallic foreign bodies in orbit. If there is a doubt, an xray prior to MRI would reveal the foriegn body
- Mri should be used with prudence in first-trimester pregnancy
- If there are middle ear prostheses
- In cases of penile prostheses.
Generally, internal orthopaedic hardware and orthopaedic prostheses are safe and pose no contraindications to MRI study.
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