Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

RD2032 > introduction to MRI > Flashcards

introduction to MRI Flashcards

1
Q

basic hardware of MRI machine

A
  • primary magnet
  • gradient coils
  • radiofrequency RF coils
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what are the 3 magnet types

A
  • permanent
  • resistive
  • superconductive
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

list features of a permanent magnet

A
  • limited field strength
  • 20-30 tonnes
  • iron, cobalt, nickel used
  • low power consumption
  • they generate a magnetic field without an external power source
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

list features of a resistive magnet

A
  • require stable supply to create B0
  • water cooling required
  • field strength = 0.3T
  • uses electric current flowing through coil of wire to generate magnetic field
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

what does current produce in resistive magnet

A
  • produces heat through resistive turns
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

can strength of resistive magnet be managed

A

yes, can be adjusted by changing the current

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

list features of superconductive magnets

A
  • use a coil that when cooled to low temperatures, loses all electrical resistance
  • allows persistent strong magnetic field to be maintained with minimal energy loss
  • can generate strong and stable magnetic fields = ideal for high field applications
  • always ON
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

materials of superconducting magnet

A

niobium/ titanium alloy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

what are gradient coils used for

A

used to spatially encode MR signals produced by photons in the body, allowing creation of 2D and 3D images

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

gradient coils role

A
  • used to introduce small, controlled magnetic field gradients in addition to main magnetic field
  • provide slops within field, 3 orthogonal X Y Z
  • noisy
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

what are radiofrequency RF coils

A

responsible for sending RF pulses into patient’s body during MRI scans
- these pulses are used to excite protons in body causing them to emit MR signals

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what is passive shielding

A

involves the use of materials and physical barriers to block/ absorb electromagnetic interference without requiring external power source

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

what is active shielding

A

employs active electronic components such as amplifiers and feedback control systems to actively counteract and cancel out unwanted electromagnetic interference

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

what are faraday cages designed to do

A

designed to block electromagnetic fields
- conducted from electrically conductive materials such as copper, aluminium/ steel

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

basic principles of MRI

A
  • hydrogen nuclei protons are MR active
  • behave like random mini bar magnets (N + S pole)
  • protons aligned in same direction as magnetic field
  • creates net magnetisation in direction of magnetic field
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

what is spin?

A

refers to the intrinsic property of certain atomic nuclei, particularly hydrogen nuclei, that makes them suitable for detection in MRI

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

what is the principle element that detects signals

A

protons
- tissues with more water will give higher signal

18
Q

two possible orientations of spin

A
  • parallel
  • anti-parallel
19
Q

what is the energy difference between parallel and anti-parallel

A

directly proportional to the strength of B0 (magnetic susceptibility)

20
Q

how can an MRI scanner be made - superconducting?

A
  • selection of superconducting material
  • formation of superconducting wire coils
  • cooling system
  • integration into magnet structure
21
Q

3 advantages of the superconducting MRI scanner

A
  • higher magnetic field strength
  • stability and persistent current mode
  • energy efficiency
22
Q

3 disadvantages of superconducting MRI scanners

A
  • high initial cost
  • high maintenance
  • long ramp-up time to reach optional magnetic field strength
23
Q

what are RF pulses used to do

A

manipulate the magnetic properties of (hydrogen) nuclei within body

24
Q

what is B0

A

the main magnetic field

25
Q

what happens before RF pulse applied

A

protons within the body are randomly orientated with respect to main magnetic field (B0)
- this is the resting state

26
Q

RF pulse application

A
  • RF pulse is short burst of radiofrequency energy applied perpendicular to B0
  • frequency of RF pulse matches resonant frequency of protons
27
Q

what is resonance and tipping

A

when RF pulse matches frequency of protons it causes them to absorb energy and enter higher energy state (known as resonance)
- RF pulse tips magnetic moments of protons away from direction of main magnetic field

28
Q

flip angle

A

the angle at which the magnetic field is tipped is called the flip angle
- the flip angle is a critical parameter that determines amount of magnetization tipped into transverse plane

29
Q

what happens when the RF pulse is turned off

A

the tipped magnetic moments begin to rotate back towards B0
- while they are precessing they emit radiofrequency signals known as free induction decay (FID)

30
Q

what does free induction decay contain

A

these signals contain information about local tissue characteristics

31
Q

signal detection

A

these emitted signals are detected by the coils in MRI system and are used to create detailed images of internal structure

32
Q

what are relaxation times

A

it describes how long the magnetisation takes to get back to equilibrium after an RF pulse

33
Q

what are the two types of relaxations

A
  • T1 recovery
  • T2 relation
34
Q

what is T1 recovery

A
  • refers to recovery process in MRI that is associated in T1W images
  • process where energy absorbed by the excited protons/ spins are released back into surrounding lattice re-establishing thermal equilibrium
35
Q

what type of magnetisation does T1 recovery refer to

A
  • longitudinal magnetisation is returned to its equilibrium
36
Q

what is T2 relaxation also known as

A

spin-spin relaxation

37
Q

what is T2 relaxation

A
  • whenever spin comes close to each other, an interaction takes place which affects their individual magnetic moment and relative phase angle (phase scrambling)
  • with time phase scrambling increases until it reaches a point where spins run out of phase thus reaching ZERO magnetisation
38
Q

what does ‘phase’ refer to

A

represents position/ location of signal in space

39
Q

what does ‘magnitude’ refer to

A

represents the amplitude/ strength of signal

40
Q

what is T2 star

A

when T2 relaxation time is influenced by both magnetic field inhomogeneities and other effects (like susceptibility effects) the resulting decay is referred to as T2 star

41
Q

what is T2 star sensitive to

A
  • certain substances such as deoxy blood, iron, air
  • substances that can cause magnetic field variations

RD2032 (18 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions