MRI Sequences

Question 1

What does T2 contrast depend on?

Answer 1

TE and tissue T2

Question 2

What does T1 contrast depend on?

Answer 2

TR and tissue T1

Question 3

What makes good MRI sequence?

Answer 3

Acceptable to patient (time, noise)
Good contrast
Good anatomical resolution
Information on structure, blood supply, function
Reproducible

Question 4

Properties of T2 weighted scan

Answer 4

Spin echo (so not T2*)
Long TE (100ms), long TR (3000ms) - so not T1 weighted
Fluid decays slowly, solid decays quickly so fluid is bright. Good for edema.

Question 5

Properties of T1 weighted scan

Answer 5

Spin echo or gradient echo
Short TE (10ms) - so not T2 weighted, short TR (450ms)
Fluid has long T1 so dark, fluid is dark. Good grey-white matter contrast.

Question 6

Properties of proton density scan

Answer 6

TR long (3000ms), TE short (10ms)

Question 7

Grey matter T1 and T2

Answer 7

T1 1.1s
T2 90ms

Question 8

White matter T1 and T2

Answer 8

T1 0.56s
T2 80ms

Question 9

CSF T1 and T2

Answer 9

T1 2.1s
T2 600ms

Question 10

Liver T1 and T2

Answer 10

T1 0.8s
T2 26ms

Question 11

Muscle T1 and T2

Answer 11

T1 0.9s
T2 33ms

Question 12

What causes contrast in MRI?

Answer 12

Differences in:
T1
T2
Water content (proton density)
Blood flow
Water diffusion properties

Question 13

Why are there large differences between T1 and T2 in tissues with similar water contents?

Answer 13

Different chemical compositions and physical properties

Question 14

What can we change to change contast?

Answer 14

Echo time TE (to centre of ACQ) for T2
Repetition time TR for T1

Question 15

Spin echo vs gradient echo for T2

Answer 15

Spin echo refocuses spatial field variations, relaxation mechanism is T2 not T2*
Spin echo therefore has more signal but takes longer than gradient echo

Question 16

Fat saturation

Answer 16

Remove lipid signals from an image
Use fatsat prepulse - narrow RF pulse exciting only lipid protons, then have crusher gradients and then begin imaging

Question 17

Inversion recovery

Answer 17

Inversion prepulse - 180 degree pulse and delay prior to imaging, inverts magnetisation and wait for recovery.
Short T1 tissues have significant recovery, long T1 has little relaxation

Question 18

Example of inversion recovery

Answer 18

FLAIR imaging - fluid attenuated inversion recovery
Brain images with good contrast between grey and white matter and suppression of signal from CSF - inversion time chosen for zero signal from CSF.

Question 19

Faster imaging

Answer 19

All of k-space in one acquisition
Echo planar imaging, move through k-space by increasing slice select gradient a bit each time and varying readout gradient positive and negative.

Question 20

T1w and T2w in brain

Answer 20

T2w good for pathology - eg oedema, fluid is bright
T1w good for anatomy - good WM/GM contrast, fluid is dark

Question 21

Prepulses

Answer 21

Additional RF and gradient pulses prior to imaging sequence, aim is to alter contrast by modulating magnetisation
Examples: fat-saturation, inversion recovery and perfusion imaging