MRI Revision 1.2.24

Question 1

What does M stand for?

Answer 1

Net magnetisation - generated in the patient

Question 2

What is B created by?

Answer 2

Created by the scanner

Question 3

What does TE stand for?

Answer 3

Time echo

Question 4

What does the Larmor equation give?

Answer 4

Gives the processional frequency of something in a magnetic field

Question 5

Why are Gradients are applied?

Answer 5

To temporarily vary the main magnetic field

Question 6

What happens when the Gradients are off?

Answer 6

All spins have the same frequency
Rf pulse exited all spins
No localisation

Question 7

What happens when theGradients are on?

Answer 7

Frequency depends on position.
RF pulse, only excite spins in a certain slice.
Signal only from that slice.

Question 8

What is the Readout gradient ?

Answer 8

Gradient applied during signal detection

Question 9

What Mega Hertz is a 1.5T scanner?

Answer 9

64 MHz

Question 10

What megahertz is a 3T scanner?

Answer 10

128 MHz

Question 11

What does FID stand for?

Answer 11

Free induction decay

Question 12

What does PNS stand for?

Answer 12

Peripheral nerve stimulation

Question 13

Which direction do gradients point ?

Answer 13

They point in the z direction otherwise the processional frequencies wouldn’t change

Perpendicular to the magnetic field (B0)

Question 14

Which direction is Frequency encoding ?

Answer 14

Side to side

Question 15

Which direction is Phase encoding ?

Answer 15

Up and down

Question 16

What does TR stand for?

Answer 16

Repetition time

Question 17

How does fat, fluid and muscle appear on T1 weighted images?

Answer 17

Fat - bright
Muscle - intermediate
Fluid - dark

Question 18

What TR and TE do T1 weighted sequences have?

Answer 18

Short TR
Short TE

Question 19

How does fat, fluid and muscle appear on T2 / T2* weighted images?

Answer 19

Muscle - dark
Fat - intermediate
Fluid - bright

Question 20

How does Gradient echo work?
What does the signal strength depend on?

Answer 20

1. Initial negative gradient dephases the signal.
2. A positive gradient rephrases to form a complete echo

The signal strength depends of the T2* decay and the TE

Question 21

How does spin echo (SE) work?
What does the signal strength depend on?

Answer 21

1. Combination of the readout gradient and a 180’ RF pulse
2. 180’ pulse reverses the effect of the main magnetic field variations which cause T2* decay

Signal depends on pure T2 decay.
T2 signal is larger than GE, T2* signal

Question 22

SE VS GE

Answer 22

• SE - T2 rather than GE - T2*
• Signal and SNR higher from SE compared to GE
• The 180’ pulse in SE reverses dephasing
• SE less susceptible to artefacts
• GE uses shorter TR values so shorter scan times

Question 23

What do RF pulses do to the Mz ?

Answer 23

The pulses flip Mz into Mxy

Question 24

What is spatial resolution?

Answer 24

The ability of the image receptor to resolve small structures

Question 25

what is temporal resolution?

Answer 25

The ability to display a moving body using a short exposure

Question 26

What is contrast resolution?

Answer 26

The ability of the IR to differentiate between structures of similar densities.

Question 27

What does a Fourier transform do?

Answer 27

It separates the higher, middle and lower frequencies

Question 28

What does FLAIR stand for?

Answer 28

Fluid attenuated Inversion recovery

Question 29

What does STIR stand for?

Answer 29

Short tau/T1 Inversion recovery