20. MRI basics Flashcards
What does MRI rely on to work?
The magnetic properties of hydrogen ions
How they are different across each tissue
This leads to contrast
What are the components of an MRI?
Magnet- magnetic field
Gradient coil- create secondary field, act of rapidly changing currents (nosiy bit)
RF coil- create radiofrequency pulse
Discuss how hydrogen is exploited in an MRI scanner?
Protons typically spin in a random direction
A magnetic field is passed through them allowing them to line up parallel
Radiofrequency pulse allows the protons to spin in the same direction
What is the difference T1 and T2
T1 relaxation- return to low energy parallel state
T2- protons start to spin out of sync (out of phase)
Different tissues have different T1 and T2 times
Can you have an MRI with a pacemaker?
Most new pacemakers are safe
Need cardiologist pacemaker specialist
Can those with heart valves and coronary stents have an MRI?
Everyone in Europe to get one after 2000 is MRI safe
Are Hip implants safe for MRI?
Low magnetic content
Are cemented into bone so shouldn’t move
How is pregnancy affected by MRI?
No evidence of risks
Safe to continue breast feedings even with gadolinium based contrast
What are the characteristics of a T2 sequence?
Fat and fluid are bright
What contrasts are used in MRI?
Paramagnetic metal ions
Gadolinium
Tissue specific contrast
What are the characteristics of a T1 sequence?
Fat is bright, fluid is dark
What are the different subtypes of T2 sequences?
Fluid sensitive (FLAIR/STIR)-oedema Susceptibility weighted imaging (SWI)- blood
What is the best imaging technique to see the vertebral discs?
MRI
What is the most sensitive imagine to detect early ischaemia?
DWI (diffusion weighted) MRI images
What is meant by post processing?
Can get rid of certain signals e.g. get rid of fat enhancement. Can allow contrast to be given
