MRI

Question 1

2 main advantages of MRI scans

Answer 1

• Excellent soft tissue contrast
• Non-ionising radiation

(Provides - functional and anatomical information)

Question 2

What does the Hydrogen nucleus consist of?

Answer 2

A single proton (no neutrons)

Question 3

What do T1 and T2 stand for

Answer 3

T1 Longitudinal recovery (relaxation in the longitudinal axis)

T2 Transverse relaxation

Question 4

Which plane can the signal be detected in?

Answer 4

The transverse plane only

Question 5

What does TR stand for in MRIs?

Answer 5

repetition time. The time between each of the 90 degree excitations from the longitudinal to the transverse plane.

the amount of time between successive pulse sequences applied to the same slice

Question 6

What does CSF stand for?

Answer 6

Cerebral Spinal Fluid

Question 7

Name 3 characteristic MRI artefacts

Answer 7

1. Aliasing/wrap (when field of view too small)
2. Patient motion
3. Zipper/RF noise (If RF signals get into the room)

Question 8

What does the liquid helium in an MRI machine bathe?

Answer 8

Bathes the super conducting magnet/coil

Question 9

What is the purpose of the shim coil in an MRI?

Answer 9

ensures a homogenous magnetic field inside the scanner – prevent distortions in the magnetic field

Question 10

Another name for ‘Body coil’, and its purpose in an MRI machine?

Answer 10

Body RF transmit receive coil

sends in radio waves into patient and then can detect the transverse oscillating current which can be induced in this coil and converted to a signal

Question 11

What is the size of the magnetic field created by a clinical MRI?

Answer 11

1.5 - 3 Tesla

Question 12

The 2 main hazards of MRIs?

Answer 12

1. Projectile effect (magnetic materials attracted to magnet)
2. Implantable medical device safety and compatibility (e.g. pacemakers)

Question 13

Which is true?

T1(Fat) > T1(water)
T2(Fat) > T2(water)

T1(water) > T1(Fat)
T2(water) > T2(Fat)

Answer 13

T1(water) > T1(Fat)
T2(water) > T2(Fat)

T1: Fat is brighter than water

T2: Water is brighter than fat

Question 14

What is Fluid-attenuated inversion recovery (FLAIR) ?

Answer 14

A T2 weighted MRI image, without the signal from the cerebral spinal fluid (CSF)

Question 15

What causes the magnetic dipole moment in a hydrogen atom?

Answer 15

Hydrogen nucleus consists of single proton which has nuclear spin

‘Spinning’ charge produces magnetic field

Question 16

Why can a signal be detected in the transverse plane

Answer 16

• Net magnetisation is spinning around in the transverse plane as it returns to equilibrium.
• Generates a current

Question 17

What do functional MRIs detect?

Answer 17

‘Active parts’ of the brain that use more oxygen.

Question 18

What contrast agents are used in Contrast Enhanced MRI?

Answer 18

gadolinium-based contrast agents

Question 19

What does B0 represent?

Answer 19

The magnetic field

Question 20

Fill in the blanks:

The ___ net magnetisation reaches equilibrium faster than ___

Answer 20

fat

water

Question 21

Why can tumours be detected by contrast-enhanced MRIs?

Answer 21

Because the (blood) vessels in tumours are very leaky, they release the contrast agent into the interstitial space around the vessels, and stays there for a bit before being reabsorbed into the blood.

Question 22

Another term for functional MRIs?

Answer 22

BOLD MRI

Where BOLD stands for Blood oxygen level dependent