MRI safety

How is heat generated in a superconducting magnet?

Higher the current passed through the wire, the more resistance the coil experiences, increasing the temperature

How is wire in MRI adapted to reduce heat generation?

Made of a superconducting alloy to avoid resistance and must be cooled to -269 to operate

How does the MRI cooling system work?

Cryogens such as liquid helium are circulated around the magnet by a compressor

What are gradient coils?

Three individual electromagnets used to alter the magnetic field strength by switching them on and off rapidly during acquisition

What are radiofrequency transmitter coils?

Coils in the MRI magnet which administer a radiofrequency pulse to produce an image

What is the function of receiver coils?

Receive the MRI coil

What is the faraday cage?

Structure of conductive material producing shielding against radiofrequency waves and preventing interference

What are the three environments in an MRI room?

MR environment of magnetic field

Projectile zome

MR controlled access area

What are the three sensory effects of magnetic field strength?

Dissiness

Nausea

Metallic taste

What is torque?

Where metal implants try to align with the magnetic field

What is quench?

Demagnetisation of the magnetic field strength by evaporating liquid helium raising the mri temperature

What is spontaneous quench?

Helium escaping through the quench pipe causing loss in magnetisation

Why is oxygen monitoring necessary in MRI rooms?

Lighter helium forces oxygen downwards creating an oxygen deficient environment

What are three main patient contraindications for MRI scans?

Implantable devices e.g. hip implant

Electronic implants e.g. pacemaker

Seizures

What are four consequence when placing feromagentic implants in the MRI machine?

Become magnetised by the magnetic field

Strongly attracted to the magnet

Aligns with the magnetic field

Heat up and move causing tissue damage

What are the four classifications of implantable devices?

MR safe

MR conditional

MR unsafe

MR non conditional

What implantable devices are allowed in the MR environment?

Compatible implants that have been in place for more than 6 weeks where scar tissue has been allowed to form

What areas of the body where implants are located are always contraindicated and why?

Eyes, brain, ears

Scar tissue cannot form

What actions should be taken with electronic implants?

Removed if possible

Programmed to MR safe mode and monitored

Why is epilepsy contraindicated?

Scanner can alter the magnetic field causing biological effects which produce currents

Can interfere with muscle fibre and nerve cell function

What actions should be taken if there is a history of seizures?

Ask if well controlled and perform the scan

If not well controlled consult radiologist

What are the biological effects of the static magnetic field and gradient magnetic field?

Dizziness and vertigo

Peripheral nerve stimulation

What are the biological effects of the radiofrequency field?

Tissue heating

Radiofrequency burns

What are the psychological effects of the MR scanner?

Claustrophobia

Why are gadolinium based contrast agents avoided during pregnancy?

Some studies suggest potential risks like stillbirth and rheumatological conditions

Why are transdermal patches a contraindication of MR scanning?

Patches with metallic backs will heat and can cause burns

Accelerated drug release