MRI

Question 1

What is the function of magnetic field gradient

Answer 1

Magnetic field gradients are needed to encode the signal spatially. They produce a linear variation in magnetic field intensity in a direction in space.

Question 2

How is an image produced in MRI very simply

Answer 2

Patient placed in a magnet
Radio wave is sent in
Radio wave is turned off
Patient emits a signal
Image is reconstructed

Question 3

How is an MRI image produced?

Answer 3

Protons have a spin, which creates an electrical current, so has its own magnetic field
When external magnetic field is applied, protons align of either axis (which is longitudinal patient to machine)
External wave is sent (RF) which causes longitudinal marganilisatiom to decrease and creates new transverse marganilisation
Then pulse is switch off and longitudinal marganilisation increases and transverse marganilisation decreases

Question 4

What is the role of the magnetic field

Answer 4

Causes protons to spin and align

Question 5

What are some risks to patients with MRI?

Answer 5

Animals need to go under general anaesthesia
Sensitive to risks of metal,

Question 6

What are the three planes that MRI uses?

Answer 6

Sagittal
Dorsal
Transverse

Question 7

In T1 images what would the following structures look like?

Cortical bone
Fat
Water/ fluid (static)
Soft tissue
Pathology

Answer 7

Black
White
Black
Grey
Grey

Question 8

In T2 images what would the following structures look like?

Cortical bone
Fat
Water/ fluid (static)
Soft tissue
Pathology

Answer 8

Black
White
White
Grey
White

Question 9

How to tell the difference between T1 and T2 images?

Answer 9

CSF is darker in T1 and T2

Question 10

What are STOR sequences and when are they most useful

Answer 10

Fat suppression images
T2 images where signal from fat has been removed
useful when examining structures which contain or are surrounded by fat such as the brachial plexus

Question 11

What are FLAIR images and when are they useful

Answer 11

T2 images with signal from CSF removed
Useful for assessing structures adjacent to the ventricles to the brain

Question 12

What sequence does T1 have

Answer 12

A short TR and short TE

Question 13

What sequence do T2 weighted images have

Answer 13

Long TR and long TE

Question 14

What sequence does a proton dense image have

Answer 14

Long TR and short TE

Question 15

What is a magnetic gradient

Answer 15

An additional magnetic field that may be added manually to the MRI device’s magnetic field. This creates an additional subdivision in the ‘total’ magnetic field. Gradient coils are used among other things to determine the location of the protons in the X, Y and Z axis.

Question 16

What is a proton dense image

Answer 16

Related to the number of nuclei in the image rather than the magnetic characteristics of the nuclei

Question 17

What is the main contrast used for MRIs

Answer 17

Gadolium

Question 18

What happens when radio frequency is turned off in terms of producing an image?

Answer 18

When the radiofrequency field is turned off, the MRI sensors are able to detect the energy released as the protons realign with the magnetic field. The time it takes for the protons to realign with the magnetic field, as well as the amount of energy released, changes depending on the environment and the chemical nature of the molecules.

Question 19

What can gadolinium detect

Answer 19

Inflammation
Increased blood flow

Question 20

What is TR

Answer 20

Repetition Time (TR) is the amount of time between successive pulse sequences applied to the same slice.

Question 21

What is TE

Answer 21

Time to Echo (TE) is the time between the delivery of the RF pulse and the receipt of the echo signal.