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303 MEDIMAGE > 7. Contrast media II: MRI & Tutorial > Flashcards

7. Contrast media II: MRI & Tutorial Flashcards

1
Q

how are MRI contrast agents detected

A

indirectly through changing the magnetic properties of nearby water molecules

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2
Q

what are paramagnetic contrast agents

A

contain metal ions that have unpaired e-

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3
Q

what are the 2 types of paramagnetic contrast agents

A

gadolinium based

non gadolinium

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4
Q

what are the 2 paramagnetic metal ions

A

gadolinium and manganese

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5
Q

what do paramagnetic metal ions do to the T1 and T2 proton relaxation times

A

efficiently reduce both

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6
Q

what is relaxation times

A

relaxation time is the time taken for protons in water molecules to go back to a relaxed state from excited state

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7
Q

what aspect of proton relaxation time does T1 agents reduce

A

longitudinal

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8
Q

what aspect of proton relaxation time does T2 agents reduce

A

transverse

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9
Q

why cant the paramagnetic metal ions be used as contrast agents in their ionic from

as a result what must be done to them

A

toxic and undesirable distribution and accumulation in the body

must be chelated into a complex

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10
Q

what does it mean when an ion is chelated

A

bonds formed around metal ion stabilise it and prevents large amount from accumulating in body

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11
Q

what is the relationship between T1 and T2 reduction

A

Any contrast that reduces T1 will also reduce T2 but contrast that is T2 reducing wont necessarily decrease T1

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12
Q

classificaiton of T1 or 2 depends on what

A

on the relative relaxation time is greater for T1/2

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13
Q

how many unpaired e- does gadolinium have

A

7

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14
Q

what does it mean when we say that gadolinium ions are cytotoxic

A

blocks voltage gated calcium channels at very low conc and inhibits certain enzymes

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15
Q

gadolinium ions are hydrolysed at what pH and what does it produce

A

hydrolysed at physiological pH to produce insoluble Gd(OH)3

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16
Q

what does chelation do to renal elimination and distribution

A

enhances renal elimination and limits distribution in the extravascular space

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17
Q

what are the 4 aspect in the classification of GBCAs

A

shape
ionicity
biodistribution
risk of nephrogenic systemic fibrosis

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18
Q

is PK affected by the chemical structure of GBCAs

A

no

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19
Q

what does tight chelation prevent

A

prevents cellular uptake of gadolinium ion

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20
Q

what are the 2 shapes of GBCA

A

macrocyclic and linear

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21
Q

what is the characteristics of macrocyclic shaped GBCA in terms of rigidity, stability, binding to Gd and protection

A

rigid
more stable
stronger binding to gadolinium
better protection

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22
Q

what is the characteristics of linear shaped GBCA in terms of rigidity, stability and protection

A

flexible
open chains
fold and unfold easily

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23
Q

what are the 2 forms of biodistribution for GBCA

A

nonspecific agents

specific agents

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24
Q

what are non specific agents

A

no specific interaction with a particular cell type

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25
Q

what are specific agents

A

targeted agents

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26
Q

what are the 2 types of non specific agents

A

extracellular fluid agents

blood pool agents or intravascular agents

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27
Q

what is the ECF agents characteristics in terms of MW, movement from intravascular space and excretion route

A

low MW complexes

equilibrate rapidly between intravascular and interstitial space

excreted renally

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28
Q

what is the blood pool agents characteristics in terms of MW, movement from intravascular space and excretion route

A

high MW complexes

stays within the intravascular space

slowly excreted via the kidneys and or the liver

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29
Q

ECF agents diffuse from blood to where and what effect does this have on acquisition time

A

rapidly from blood to Extracellular space, limits acquisition time to 1-3mins

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30
Q

how is ECF agents excreted

A

renally

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31
Q

what is the elimination half life for ECF agents in normal renal function

A

1.5 hrs

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32
Q

what is the elimination half life for renally impaired people

A

up to 34hrs

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33
Q

in patients with normal BBB does accumulation occur

A

limited permeation

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34
Q

in patients with diseased BBB does accumulation occur

A

accumulation may appear

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35
Q

what are the 2 types of ECF agents

A

ionic and non ionic

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36
Q

wjat is the size of blood pool agents in comparison to ECF agents

A

larger in size

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37
Q

what does blood pool agents do to the diffusion between fluid compartments

A

prevents diffusion from blood to interstitial fluid

remains in intravascular space

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38
Q

does blood pool agents need metabolism and if yes what for

A

yes requires metabolism of the macromolecules for renal excretion

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39
Q

the fact that blood pool agents need metabolism for renal excretion has what effect on the plasma conc and image acquisition time

A

maintains conc in plasma stable over 1h

image acquisition time increased to 1hr in comparison to ECF

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40
Q

what does blood pool agents do in terms of time it remains and where it remains

A

remains for longer time in intravascular space

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41
Q

why is blood pool agents advantageous over ECF agents

A

longer image acquisition time that allows higher resolution and better quality angiograms

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42
Q

what does blood pool agents allow in terms of measurement

A

allows tissue blood volume and perfusion to be measured

43
Q

what does blood pool agents allow in terms of enhancement

A

allows enhancement in both arteries and veins

44
Q

what are the 2 further categorisations for blood pool agents

A

albumin binding gadolinium complexes

polymeric gadolinium complexes

45
Q

what is the binding like for albumin binding complexes and is the reversible

A

extensive binding to plasma proteins like albumin

reversible

46
Q

where is albumin binding complexes confied

A

intravascularly

47
Q

what is the relative retention time of albumin binding complexes

A

longer retention within the blood

48
Q

how much of the albumin binding complexes reach the ECF

A

only a small amount

49
Q

can albumin binding complexes be used interchangeably with ECF agents

A

no

50
Q

what are the 2 phases of tissue specific liver agents

A

extracellular phase and delayed hepatocyte uptake and biliary excretion

51
Q

what does the extracellular phase of tissue specific liver agents allow

A

imaging of vasculature

52
Q

what does the delayed hepatocyte uptake phase of tissue specific liver agents allow

A

evaluation of hepatic tissues with altered functions

53
Q

what are the 2 elimination pathways for tissue specific agents

A

hepatobiliary

renal

54
Q

what are 2 examples of tissue specific agents

A

multihance and eovist/primovist

55
Q

what is the protein binding, metabolism and elimination of multihance like

A

no significant protein binding and metabolism

elimination via kidneys

56
Q

what is multohance a substrate for - 2 transporters

A

OATP1 and cMOAT

57
Q

renal impairment does what to multihance

A

prolongs elimination of multihance

58
Q

what effect does hepatic impairment have on the PK of multihance

A

little impact

59
Q

what is multihance in terms of cMOAT drugs

A

competitive inhibitors of cMOAT drugs

60
Q

what is multihance in terms of heart electrical activity

A

QT prolongation, distorts the hearts electrical activity

61
Q

what are the 3 aspects that multihance and primovist differ in

A

uptake by hepatocytes
acquisition times for hepatobiliary phase
compensatory elimination

62
Q

how does multihance and primovist differ in terms of uptake by hepatocytes

A

multihance has 97% renal elimination

primovist has 50/50 biliary and renal excretion

63
Q

how does multihance and primovist differ in terms of acquisition time for the hepatobiliary phase

A 
multihance = 1-3 hrs after administration (~2hrs)
primovist = 10-120min after administration (~20min)
64
Q

compared to ICM what is gadoliniums rate of adverse reactions

A

lower rate

65
Q

what is the osmolality of MRI contrast agents in relation to plasma

A

hyperosmolar

66
Q

what is the viscosity of MRI CM compared to ICM

A

lower

67
Q

what is the injection volume like for MRI CM compared to ICM

A

lower injection volumes to decrease osmotic load

68
Q

does osmolality, ionicity and viscosity of GBCAs play significant role in tolerability and safety

in what scenario does this answer apply

A

no if at standard dose and volume

69
Q

what variable indicates how tightly the gadolinium is bound/chelated

A

equilibrium constant

70
Q

what is the equilibrium constant of gadolinium presented on in terms of scale and what does larger values mean for the binding

what are lower values associated with

A

log scale

larger values = tighter binding

lower values associated with higher rate of NSF due to accumulation of Gd in tissues

71
Q

what are the acute adverse reactions to GBCAs

A

similar to ICM

72
Q

what are the renal adverse effects for GBCAs in terms of the CI-AKI at usual MRI doses compared to ICM

A

very low risk

73
Q

what are the 4 reasons for thinking that GBCAs are associated with lower renal toxicity

A

low doses, volumes, viscosity and injection rates

74
Q

GBCAs were thought to be less renal toxic until what was reported

A

Once thought GBCA associated with less renal toxicity until NSF was reported

75
Q

what is nephrogenic systemic fibrosis

A

fibrosing disorder

76
Q

what are the 4 most common manifestations of nephrogenic systemic fibrosis

A

thickening and hardening of skin
muscle weakness
bone pain
joint contractures

77
Q

is nephrogenic systemic fibrosis reversible and can it be treated

A

irreversible and no treatment available

78
Q

in what patients has nephrogenic systemic fibrosis be reported

A

patients with impaired renal function

79
Q

what is nephrogenic systemic fibrosis believed to begin with

A

displacement of Gd ions from its chelate by another metallic ion

80
Q

what is transmetallation reaction and what is the chemical equation

A

displacement of Gd ions from its chelate by another metallic ion

metal ion + Gd chelate metal chelate + Gd3+

81
Q

why is incidence of NSF difficult to define

A

NSF symptoms can develop many years after exposure

82
Q

what are 2 high NSF risk contrasts

A

omniscan

magnevist

83
Q

what are 2 medium NSF risk contrasts

A

primovist

multihance

84
Q

what are 2 low NSF risk contrasts

A

dotarem

gadovist

85
Q

what are the patient related risk factors for NSF

A

severe renal dysfunction

86
Q

what are 2 contrast related risk factors for NSF

A

type - linear agents

repeated injections

87
Q

what is the importance of renal functions in terms of GBCA dissociation and accumulation

A

patients with poor renal function have reduced GBCA excretion so GBCA remain in the body for a longer time which increases the risk of gadolinium dissociating and accumulating in body

88
Q

gadolinium deposition occurs in certain brain regions and are dependent on what and independent of what 2 factors

A

dose dependent

independent of renal function and BBB integrity

89
Q

what are the EMA recommendations for GBCAs in terms of shape

A

linear gadolinium agents release Gd to greater extent than macrocyclic

90
Q

what are the 3 medsafe GBCAs reccomendations in terms of usage, dose and shape

A

limit use of GBCAs where possible
use the approved dose where possible
macrocyclic agents preferred over linear agents

91
Q

what gadolinium agents can prolong coagulation time

A

ionic and non ionic

92
Q

ionic and non ionic Gd agents can potentiate effects of what 2 medicines

A

anticoagulant
antiplatelet
fibrinolytic

93
Q

what lab test can GBCA interfere with

A

calcium level test

94
Q

can GBCA cross the placenta and if needed to be used what type should be used

A

yes

macrocyclic

95
Q

half life of GBCA can be what in paeds

A

can be prolonged

96
Q

why is half life of GBCA prolonged in premature infants

A

lower GFR and renal clearance rate than older children and adults

97
Q

what is the increased risk of GBCA for paeds

A

may have increased risk of increased exposure to free Gd

98
Q

what are the 4 recommendations for paeds in terms of GBCAs

A

Gd based CM should not be first choice
macrocyclic agents should be used
renal function must be assessed
multiple dose should be avoided

99
Q

GFR < what means GBCA shouldnt be used

A

if its <30mL/min/1.73.^2

100
Q

what are manganese based contrast agents

A

paramagnetic

101
Q

how many unpaired e- does manganese based CM have

A

5

102
Q

what are natural oral contrast agents and why are they CM

A

fruit juice - blueberry and pineapple as they contain high level of manganese

103
Q

what is US contrast

A

gas containing microbubbles or microspheres for injection

303 MEDIMAGE (14 decks)

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