MRI contrast agents

Question 1

what is a contrast agent and why do we need them

Answer 1

alters image contrast

• aids in visualisation and diagnosis

Question 2

what is întra-articular administration

Answer 2

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

• can be cortecosteroids or pain relief

Question 3

what is the main contrast agent used in MRI

Answer 3

gadolinium

Question 4

what is the general theory behind MRI

Answer 4

• abundance of water in our body is used to produce MRI images

Question 5

what are the 3 types of MRI contrast agents

Answer 5

• extracellular fluid
• blood pool
• tumour specific

Question 6

what is extracellular fluid contrast

Answer 6

• distributed in intravascular compartment initially
• rapidly diffuses through extravascular space

Question 7

what is blood pooling contrast / intravascular contrast

Answer 7

• 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

Question 8

what is a tumour specific contrast agent

Answer 8

pharmaceuticals targeted to tumoura

Question 9

what type of magnetisation do majority contrast agents have?

Answer 9

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

Question 10

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

Answer 10

• these elements shorten the T1/2 relaxation time
• causing increased signal intensity on T1 weighted images OR reduced signal intensity on T2 weighted images

Question 11

why are most contrast elements positive agents

Answer 11

• postive agents shorten T1, so enhanced parts appear bright on T1 weighted images

Question 12

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

Answer 12

• as they are negative contrast agents, the enhanced parts appear darker on T2 weighted images

Question 13

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

Question 14

what is gadolinium (what type of agent is it

Answer 14

• paramagnetic agent
• has large magnetic moment

Question 15

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)

Question 16

why is gadolinium good for being used as contrast

Answer 16

• it is paramagnetic at body temperature

Question 17

what is an isotonic solution

Answer 17

• isotonic solution is at the same concentration as the solution to which is it being compared to

Question 18

how does osmolarity affect torleration

Answer 18

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

Question 19

osmolarity is directly responsible for sensations of heat

Question 20

what is the blood brain barrier

Answer 20

• protects the central neural tissue

Question 21

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

Answer 21

x4

5.5 times more likely to cause a severe reaction

Question 22

what is a monomer and dimer

Answer 22

monomer =
- single molecule of contrast agent

dimer =
- 2 molecules of contrast agent joined together

Question 23

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

Answer 23

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

Question 24

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

Answer 24

• severe asthma
• prior reaction to Gd

Question 25

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

Answer 25

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

Question 26

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

Answer 26

gadovist

Question 27

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

Answer 27

50% in 2 hrs 90% in 12 hrs

Question 28

how fast will the liver excrete the contrast into bile

Answer 28

50% in 56-96 mins

Question 29

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

Question 30

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

Question 31

what age group is most at risk of nephrotic systemic fibrosis

Answer 31

over 65's

Question 32

Gd-cm designated low, medium or high risk GFR <30 high risk GFR <60 low risk

Question 33

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

Question 34

what is negative contrast agents used to see

Answer 34

visualise mucosal enhancement

Question 35

what is mannitol (additive)

Answer 35

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

Question 36

USPIO is a new developed contrast, what is its benefit

Answer 36

has longer plasma half life - biodegradable

Question 37

what is fMRI

Answer 37

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

Question 38

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

Answer 38

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

Question 39

what are the most common contrast reactions

Answer 39

- 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.)

Question 40

give examples of minor adverse reaction

Answer 40

mild rash vomiting nausea flushing

Question 41

give examples of moderate adverse reactions

Answer 41

facial oedema hypotension bronchospasm severe urticarial (rash)

Question 42

give examples of severe reactions

Answer 42

hypotensive shock laryngeal oedema convulsion respiratory/cardiac arrrest

Question 43

how do you treat mild reachtions

Answer 43

- monitor - o2 - anaphylactic drugs e.g antihistamine -

Question 44

how do you treat moderate reactions

Answer 44

- MET - o2 - anaphylactic drugs

Question 45

how do you treat severe reaction

Answer 45

- MET and crash trolley

Question 46

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

Answer 46

30 mins after administration

Question 47

how do you deal with reactions to contrast in MRI room

Answer 47

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

Question 48

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

Answer 48

CRIS - alarm on CRIS - fill out yellow card