LO2 Step 2.1 - MRI

What does MRI use in-place of ionizing radiation?

It uses the properties of hydrogen with a radiofrequency pulse, and magnetic fields

What part of the process in MRI produced a capturable signal?

the relaxation of the hydrogen atoms following the radiofrequency pulse that excites them

What is the awesome benefit of MRI?

great contrast between tissues in images

What are 5 key limitations to MRI?

• inferior to CT in detecting acute hemorrhage

• Inferior to CT for visualization of bony injury

• Very long acquisition time

• More probability to motion artifact

• claustrophobia and small gantry size

What are the 2 most common magnet strengths used in MRI?

1.5T or 3T (T=Tesla)

What are the 3 types of magnets used in MRI?

Superconductive (cryogenic) - cold wire loops with liquid helium - MOST COMMON!

Permanent - just magnets with nothing special

Resistive - electromagnets with coils plus electric current

what do RF coils do?

transmit and receive signal from patient to computer

what do gradient coils do?

read the signal spatially and encode it

What is a faraday cage?

encloses the MRI suite to stop any stray radio-waves from entering the room and screwing up the RF pulse

What is SAR?

specific absorption rate - the rate the the electromagnetic energy from the RF pulse is absorbed by the tissue during image acquisition (Watts/kg)

AKA the energy being absorbed by the patient during the scan

Why are ferromagnetic metals a danger in MRI?

they are attracted to the massive magnet and can seriously injury patients or staff with high force!!! SCARY!!

Iron, Nickle, Cobalt, ect

What are the 3 classifications of medical devices for MRI?

MRI Safe

MRI Unsafe

MRI Conditional - may need to limit time due to SAR or other reasons, or use a lower magnet strength

What are some common medical devices that are risky in MRI?

ECG leads can burn skin

ICD or pacemakers are commonly no-gos

Scissors, Oxygen tankes, stretchers