MRI contrast agents Flashcards

1
Q

what is a contrast agent and why do we need them

A

alters image contrast

  • aids in visualisation and diagnosis
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what is întra-articular administration

A

a type of shot that’s placed directly into a joint to relieve pain.

  • can be cortecosteroids or pain relief
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

what is the main contrast agent used in MRI

A

gadolinium

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

what is the general theory behind MRI

A
  • abundance of water in our body is used to produce MRI images
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

what are the 3 types of MRI contrast agents

A
  • extracellular fluid
  • blood pool
  • tumour specific
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

what is extracellular fluid contrast

A
  • distributed in intravascular compartment initially
  • rapidly diffuses through extravascular space
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

what is blood pooling contrast / intravascular contrast

A
  • intravascular contrast agent that lasts in the blood for up to an hour rather than leaving the system in a few mins like others
  • differentiated from other contrast agents due to their high molecular weight and higher relativities
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

what is a tumour specific contrast agent

A

pharmaceuticals targeted to tumoura

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

what type of magnetisation do majority contrast agents have?

A

paramagnetic ion complexes (with applied magnetic field, they are partially / weakly aligned)

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

most contrast agents in MRI contain a lanthanide element such as Gd3+, how does this affect the T1/2 relaxation time and what happens to the image

A
  • these elements shorten the T1/2 relaxation time
  • causing increased signal intensity on T1 weighted images OR reduced signal intensity on T2 weighted images
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

why are most contrast elements positive agents

A
  • postive agents shorten T1, so enhanced parts appear bright on T1 weighted images
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

ferromagnetic agents and super paramagnetic agents are negative contrast agents/ how does this show on T2 weighted images

A
  • as they are negative contrast agents, the enhanced parts appear darker on T2 weighted images
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

reminder :
paramagnetic = weak attraction
ferromagnetic = strongly attracted
diamagnetic = weakly repelled

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

what is gadolinium (what type of agent is it

A
  • paramagnetic agent
  • has large magnetic moment
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

MRI contrast agents

  • increase T1 singnals by rapidly returning protons to their baseline
  • allowing quicker regrowth of longitudinal magnetisation
  • which produces a brighter t1 signal

(commonly gadolinium used)

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

why is gadolinium good for being used as contrast

A
  • it is paramagnetic at body temperature
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

what is an isotonic solution

A
  • isotonic solution is at the same concentration as the solution to which is it being compared to
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

how does osmolarity affect torleration

A

the more isotonic a contrast agent is, the better it is tolerated

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

osmolarity is directly responsible for sensations of heat

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

what is the blood brain barrier

A
  • protects the central neural tissue
21
Q

how many more times likely is an ionic contrast to cause a reaction compared to a non-ionic contrast

A

x4

5.5 times more likely to cause a severe reaction

22
Q

what is a monomer and dimer

A

monomer =
- single molecule of contrast agent

dimer =
- 2 molecules of contrast agent joined together

23
Q

what is the difference in the way linear agents work with gadolinium and how macrocyclic agents work with gadolinium

A
  • linear agents dont fully surround the gadolinium ion
  • macrocyclic molecules fully enclose gadolinium with nitrogen
24
Q

gadolinium has a excellent safety profile but what are some screening criteria relating to reaction

A
  • severe asthma
  • prior reaction to Gd
25
Q

be aware that gadolinium does have risk of nephrogenic systemic fibrosis, what is this

A

a progressive multiorgan fibrosing condition mainly caused by patients’ exposure to gadolinium-based contrast agents (GBCAs) used for magnetic resonance imaging (MRI)

26
Q

what is the name of the commonly used contrast agent in MRI containing macrocyclic galdinium

A

gadovist

27
Q

how fast will excretion of contrast be in kidneys (glomerular filtration)

A

50% in 2 hrs
90% in 12 hrs

28
Q

how fast will the liver excrete the contrast into bile

A

50% in 56-96 mins

29
Q

Gd-cm is only used during pregnancy if very necessary but it has no known effect on lactation (going into breast milk)

A
30
Q

if lactating woman is given gadolinium, they are advised to excite enough breast milk for 24 hours post injection (only for high risk agents)

low risk agents do not require woman to pre make breast milk

A
31
Q

what age group is most at risk of nephrotic systemic fibrosis

A

over 65’s

32
Q

Gd-cm designated low, medium or high risk

GFR <30 high risk
GFR <60 low risk

A
33
Q

know that linear gadolinium can have a large proportion retained in the brain

  • macrocyclic not as much and studies show it can be washed out over time
A
34
Q

what is negative contrast agents used to see

A

visualise mucosal enhancement

35
Q

what is mannitol (additive)

A

used to decrease pressure in the eyes, as in glaucoma, and to lower increased intracranial pressure.

36
Q

USPIO is a new developed contrast, what is its benefit

A

has longer plasma half life

  • biodegradable
37
Q

what is fMRI

A

Functional magnetic resonance imaging or functional MRI measures brain activity by detecting changes associated with blood flow

38
Q

what is the difference between dose-dependent and dose-independent adverse events with contrast

A

dose-dependant (caused directly by contrast) =
e.g due to osmolatiry
- pain
- heat

dosé-indépendant (as a result of contrast/ not directly caused by agent) =
- allergic or sensitivity reactions

39
Q

what are the most common contrast reactions

A
  • anaphylactic (allergic) severe (immune triggered)
  • anaphylactoid (allergic) minor (no immune trigger)
  • hyperosmolar (a condition in which the blood has a high concentration of salt (sodium), glucose, and other substances.)
40
Q

give examples of minor adverse reaction

A

mild rash
vomiting
nausea
flushing

41
Q

give examples of moderate adverse reactions

A

facial oedema
hypotension
bronchospasm
severe urticarial (rash)

42
Q

give examples of severe reactions

A

hypotensive shock
laryngeal oedema
convulsion
respiratory/cardiac arrrest

43
Q

how do you treat mild reachtions

A
  • monitor
  • o2
  • ## anaphylactic drugs e.g antihistamine
44
Q

how do you treat moderate reactions

A
  • MET
  • o2
  • anaphylactic drugs
45
Q

how do you treat severe reaction

A
  • MET and crash trolley
46
Q

how long does it take for a delayed adverse reaction to take pplace

A

30 mins after administration

47
Q

how do you deal with reactions to contrast in MRI room

A

remove patient from room to be treated due to continuous magnet in the rooma

48
Q

all actions from patient reaction case must be documented and uploaded to where

A

CRIS
- alarm on CRIS
- fill out yellow card

49
Q
A