6. Contrast media I: general imaging and CT Flashcards
(154 cards)
1
Q
what does the contrast media do
A
changes density of structures in the body and improves visualisation
2
Q
what will an ideal contrast agent do
A
provide opacification without altering physiology
3
Q
what is the atomic number level of positive contrast media
A
high atomic number
4
Q
what is the atomic number level of negative contrast media
A
low atomic number
5
Q
what does positive contrast media do to the opacity
A
increases opacity
6
Q
what does negative contrast media do to the opacity
A
decreases opacity
7
Q
what are 2 examples of positive contrast media
A
iodine and barium
8
Q
what are 2 examples of negative contrast media
A
air or CO2
9
Q
what are the soluble and insoluble positive contrast media
A
iodinated CM = soluble
barium sulphate = insoluble
10
Q
what is the functional group of all iodinated contrast media - ie what are they all derived from
A
derived from tri-iodinated benzene rings
11
Q
what are 3 reasons that iodine is used
A
high atomic number for radiopacity
can form soluble compound with low toxicity
suitable for injection into human body
12
Q
what are the 5 key properties of iodinated CM
A
iodine conc osmolality ionicity chemical structure viscosity
13
Q
what does iodine concentration affect for iodinated CM
A
affects the degree of contrast
14
Q
the higher the conc of iodine what effect does this have for iodinated CM
what is the pro and con
A
pro = better opacification con = higher risk of adverse reactions
15
Q
higher conc of iodine means what for the osmolality and viscosity
A
higher for both
16
Q
what does the choice of iodine conc depend on - 2 things
A
patient and type of exam
17
Q
can ionic agents contain different ratio of iodinated compounds
A
yes
18
Q
what is osmolality
A
measure of solute particles
19
Q
what is osmolality expressed as
A
milliosmoles per Kg of water
osm/kg or mOsm/kg
20
Q
in normal water how does water diffuse
A
in both directions so 0 net movement and volume remains constant
21
Q
what will a CM administration to water do
A
create a conc difference
22
Q
what is responsible for the flow of fluids to maintain balance
A
osmotic pressure
23
Q
what are osmolality and osmolarity measures of
A
solute particles
24
Q
what is the osmolarity
A
osmalal conc expressed as milliosmoles per L of soln
Osm/L or mOsm/L
25
what is osmolality based on
number of solutes based on weight
26
what is osmolarity based on
number of solutes based on volume
27
osmolarity is dependent on what
why
temperature as body volume is dependent temp
28
is osmolality dependent on temperature
why
no as it is based on mass
29
what is a osmole
one osmole is one gram of molecular weight of osmotically active solute
30
what is the tonicity related to
the impact of the osmolality of a soln on the surrounding cells
31
what is the osmolality of a isotonic soln relative to blood
what impact does this have on surrounding cells
similar
no impact on surrounding cells
32
what is the osmolality of a hypertonic soln relative to blood
what impact does this have on surrounding cells
higher than blood
water is drawn out of the cells
33
what is the osmolality of a hypotonic soln relative to blood
what impact does this have on surrounding cells
lower than blood
water is taken into cells
34
what are the 3 groups of osmolality CM can be classified into
high, low and iso-osmolar
35
what is the mOsm/kg of high osmolar CM
>1400mOsm/kg
36
what is the mOsm/kg of low osmolar CM
780-800mOsm/kg
37
what is the mOsm/kg of iso-osmolar CM
290mOsm/kg
similar to plasma
38
most ICM are what osmolar
hyperosmolar
39
high osmolality have what effects on reactions
high reactions
40
what kind of osmolality of CM has better tolerance
closer the osmolality of CM to body fluid
41
tolerability and safety improves with ___/___-osmolar agents
low/iso-osmolar
42
what will hyperosmolar iodinated CM do to the water movement in the body
Iodinated CM are hyperosmolar in relation to blood so administration will cause movement of water into vascular compartment so water is pulled from tissues into vasculature leading to expansion of blood volume
43
what are the vascular effects of injection of hyperosmolar ICM in terms of plasma osmolality and water movement
increases plasma osmolality and water moves out from cells and extracellular spaces
fluid from cells in interstitial space to move into vascular lumen and dilutes the osmotically active particles
44
what are the vascular effects of injection of hyperosmolar ICM in terms of haematocrit and plasma volume
decrease in both
45
why does the plasma volume decrease after injection of hyperosmolar ICM
due to rapid clearance of ICM and diuretic effect of hyperosmolality on the kidney
Urine becomes hyperosmolar when CM is excreted into it so Promote production of urine = diuretic effect
46
what does hemodilution do to blood electrolytes
transient decrease in blood electrolytes
47
what are the 4 vascular effects of ICM
haemodilution
increase in blood viscosity
peripheral arterial vasodilation
vasodilation
48
what does peripheral arterial vasodilation from ICM lead to
transient hypotension
49
what does vasodilation from ICM lead to in terms of intravascular volume and CO
increase in both
50
how can IV injection of hyperosmolar fluids temp disrupt the BBB
impair the BBB impermeability
transient reversible opening of intracellular junctions
51
how much damage to the endothelial cells does low osmolality CM cause compared to HOCM
less damage
52
how does HOCM damage endothelial cells
water loss = shrinkage and damage
53
what aspect of ICM interaction with BBB can explain some adverse clinical symptoms
direct contact with CM and areas that lack BBB
54
what are 6 effects of hyperosmolality
```
sensation of heat/discomfort
endothelium damage
BBB damage
renal damage
thrombosis and thrombophlebitis
disturbance of electrolyte balance in small children
```
55
how does hypo osmolality lead to thrombosis and thrombophlebitis
Hypoosmolality CM can lead to hypo tension and hyper viscosity of blood which can predispose patients to thrombosis and thrombophlebitis
56
how does hypo osmolality lead to renal damage
Osmotic shift between intra and extravascular compartments can lead to renal damage
57
how does hypo osmolality lead to vasovagal reaction
If the hypo osmolar CM is injected into carotid arteries can result in intra arterial osmotic pressure changes that can stimulate receptors involved in vascular homeostasis such as baroreceptors and chemoreceptors and these can lead to a vasovagal reaction resulting in hypotension and bradycardia
58
what is ionicity about
molecules break up or dissociate into positive cations and negative anions (charged)
59
what osmolality are ionic CM
higher osmolality
60
what osmolality are non ionic CM
lower osmolality
61
do ionic or non ionic CM dissociate
ionic = yes dissociate in soln
| non ionic = no its soluble but remain as one particle in soln
62
what is the pro and con of meglumine salts compared to sodium salts
meglumine has better solubility but has higher viscosity
63
what is the difference between a monomer and a dimer
monomer is one benzene ring
dimer is 2 benzene rings
64
what is the ratio equation for iodinated CM
ratio = number of iodine atoms/number of particles
65
what is ratio 1.5 media like in terms of structure and dissociation
ionic monomer dissociates to form cation and anion
66
what is ratio 3 media like in terms of structure and dissociation
2 options
ionic dimer dissociates to form cation and anion
non ionic monomer
67
what is ratio 6 media like in terms of structure and dissociation
non ionic dimer
68
what is viscosity
measure of fluidity of a soln
69
what is the unit for viscosity
milipascal second (mPa.s)
70
what does high viscosity mean in terms of contrast
thicker contrast
71
what can thicker high viscosity contrast do to the body and what does it mean for the delivery of the CM (3 things)
cause friction and resistance when it travels through the body
more pressure needed to deliver CM
injection can cause discomfort
lower rate of flow so needs longer infusion times
72
what viscosity allows the use of rapid bolus
low viscosity
73
how does increasing iodine conc influence the viscosity
increases viscosity
74
how does the size of the molecule influence the viscosity
larger molecules have higher viscosity
75
how does the temperature influence the viscosity
increase temp means lower viscosity
76
what are 2 advantages of using intra arterial CM delivery for digital subtraction angiography
allows a lower total dose of CM = less haemodilation
advantageous for patients with poor CO
77
why does using intra arterial CM delivery for digital subtraction angiography allow for lwoer total dose
due to difference of distribution of CM when injected into arteries and veins
78
what does the amount of CM depend on for enteral administration
size of patient and site of examination
79
what is an advantage of using enteral administration
poor absorption in GI tract so less toxic effects
80
what is intra thecal CM delivery used for
looking at spinal canal - myelographic exam
81
what type of contrast media can result in serious adverse reactions if given intra thecally for a myelographic exam
hyperosmolar ionic contrast
82
why does patient movement need to be limited in intra thecal myelographic exam
to prevent mixing of CM with CSF
83
intrathecal injections are absorbed from where to where
how does this impact the way its excreted
from CSF to blood stream
excreted in same way as IV CM
84
why is active manipulation required for direct CM injections in arthrography
to disperse the CM throughout the joint space
85
how is contrast injection different from IV injection
contrast is not rapidly cleared by kidneys as it is absorbed slowly back by kidneys
86
what is the difference between hepatobiliary CM and ECF CM
low water solubility than ECf CM and higher plasma protein binding
87
where does the hepatobiliary CM distribute to in hepatocytes
ECF and intracellularly
88
what is the 2 ways of excreting hepatobiliary CM and which is the main method
biliary = main
| renal
89
how does the hepatobiliary CM differ from ECF CM in terms of PK variability
what are the 2 reasons for this
PK varies more for hepatobiliary CM
plasma protein binding and hepatobiliary CM is cleared by biliary system so is dependent on liver blood flow
90
what is the PK of ICM distribution in terms of plasma protein binding level and what kind of ICM they are
are ECF ICM and is very low in PPbinding
91
what does poor lipid solubility for ICM mean for its distribution
limited distribution to intracellular compartments
92
why does ICM's poor lipid solubility cause it to have limited distribution to intracellular compartments
3 things
poor permeability across all membranes
BBB tight endothelial junctions prevent distribution into normal CNS
pathological tissues may be more permeable
93
what 2 factors influence the intensity and timing of the contrast enhancement
rate and extent of the distribution of CM
94
ICM is primarily eliminated by what
the kidneys
95
does ICM undergo metabolism
not really, its negligible
96
with normal renal function how fast is ICM excreted
all of ICM dose is excreted within 24hrs
97
what is the elimination half life in normal renal function for ICM
what about renal impairment
1.5-2h
renal impairment = prolonged and can take up to several days
98
what might be observed in renal impairment for the routes of elimination
increased elimination via hepatic biliary duct
99
in renal impairment excretion of ICM what might you see in the image that is different from normal renal function excretion
Much lower opacification in kidney as more will be eliminated by biliary and Gi tract so those areas are more
100
what is the 2 compartment model of ICM excretion
IV injection into vascular compartment/plasma has quick exchange with extravascular compartment
it also has slow excretion into urine
see 2 distinct phases in conc time profile
101
what is the eGFR
used to identify severely impaired renal function
102
what are the 3 categories of ICM adverse reactions
acute vs delayed
idiosyncratic vs chemotoxic
renal vs non renal
103
when do ICM acute adverse reactions occur
<1hr of contrast media administration
104
what is idiosyncratic adverse reactions
method not well understood but its not dose related so increasing conc will not affect it
105
what is chemo toxic adverse reaction
related to CM dose and result from CM disrupting homeostasis
106
what are 3 patient related risk factors for acute reactions
hx of reaction to ICM
asthma
hypersensitivity
107
what are 2 contrast medium related risk factors for acute reactions
osmolality and iconicity
108
which types of CM increase risk of acute adverse reactions in terms of osmolality and iconicity
HOCM>LOCM & IOCM
ionic > non ionic CM
109
when do delayed adverse reactions occur
1h to 1wk after contrast media administration
110
what are 2 risk factors for delayed adverse reactions
previous late reaction to CM
IL2 treatment
111
what is contrast induced encephalopathy
acute and reversible neurological deficit
112
what are 3 symptoms of CIE
transient cortical blindness
transient global amnesia
epilepsy
113
what kinds of CM have higher incidence of CIE
high osmolality > LOCM
114
what is the pathogenesis of CIE
BBB suspected involved
high conc of CM can increase BBB permeability causing osmotic pressure changes leading to cerebral edema
115
how do HOCM affect CIE
hyperosmolality can cause hemodynamic changes which can aggravate cerebral vasospasm
116
what is contrast induced acute kidney injury
abrupt decline in renal function
117
what is the serum creatine level change associated with CI-AKI
relative increase of serum creatinine >25% from baseline or rise in serum creatinine within 3 days of exposure to CM
118
what are the 4 things that ICM can affect that lead to adverse reactions
cytotoxicity and oxidative stress
hyperosmolality
viscosity
RBC deformity
119
how does ICM induced cytotoxicity and oxidative stress cause injury
2 ways
tubular epithelial cells undergo tubular dysfunction
endothelial cells can undergo dysfunction and vasoconstriction
120
how does ICM induced hyperosmolality cause injury
intra renal hemodynamic changes
121
how does ICM induced viscosity cause injury
intra renal hemodynamic changes
122
what is the final result of all factors of ICM induced acute kidney injury
hypoxia, ischemia, tubular necrosis
123
what are 5 CI-AKI risk factors related to patients
```
preexisting renal dysfunction
increased age
diabetes mellitus
dehydration
poor renal perfusion
```
124
is metformin nephrotoxic
no
125
are there direct drug drug interactions between metformin and ICM
no
126
what % of metformin is excreted unchanged in 24hrs and in form are they excreted
90% excreted renally and unchanged form
127
what 3 factors increasing and decreasing can increase the risk of lactic acidosis
factors that decrease metformin excretion
factors decreasing metabolism of lactate
factors increasing blood lactate levels
128
what should patients with low eGFR or with AKI do with metformin before procedure
and when should metformin be restarted
stop taking metformin for 48hrs
restarted if renal function has returned to normal
129
what are 4 CI-AKI CM related risk factors
high osmolality
high viscosity
high injection volume
multiple injections within 3 days
130
what can ICM do to clotting time
prolong clotting time
131
does ionic or non ionic agents interact with drugs and can precipitate
ionic agent can precipitate but not an issue with non ionic
132
what is extravasation
accidental release of injected soln from vein into surrounding tissues
133
what is air embolism
blood vessel blockage due to air bubbles in the circulatory system
134
what are 3 patient related risk factors for extravasation
inability to communicate
fragile or damage veins
obesity
135
what are 3 CM related risk factors for extravasation
high osmolar contrast media
high viscosity contrast media
injecting large volume
136
what are technique related risk factors for extravasation
power injector
| lower limbs and small distal veins
137
what can IV administration of CM do in pregnancy
ICM can cross the placenta and enter foetal circulation
138
why is osmolality of CM in pediatrics important
as they are more susceptible to fluid shift
lower tolerance for intravascular osmotic loads
injection of hyperosmolar agents can lead to blood volume expansion and there if there is a large fluid shift then it may lead to cardiac fail and pulmonary edema
139
why is viscosity of CM in pediatrics important
small gauge angiocatheters in very small blood vessels and there is risk of blood vessel injry
140
what are 3 things that we need to keep in mind when using CM for the pediatric population
small volumes of CM used
injection site monitored for extravasation
slower injection rate to prolong intravascular acquisition
141
what are 4 medical considerations for ICM
thyroid disease
myasthenia gravis
phaeochromocytoma
sickle cells disease
142
why is thyroid disease a medical considerations for ICM
increases risk of developing thyrotoxicosis
143
why is myasthenia gravis a medical considerations for ICM
breathing difficulty may worsen with ICM
144
why is phaeochromocytoma a medical considerations for ICM
injection of ICM into adrenal or renal arteries/veins may precipitate a hypertensive crisis
145
why is sickle cell disease a medical considerations for ICM
high osmolality may induce osmotic shrinkage of RBC and may exacerbate sickle cells
146
what is the use of barium sulfate
imaging procedures of the GI tract
147
what is a non iodinated CM
barium sulfate
148
what is the route of administration for barium sulfate
only oral or rectal routes
149
what is oral admin of barium sulfate used to visualise
oesophagus and stomach or small intestine
150
what is rectal admin of barium sulfate used to visualise
rectum and colon
151
is bariums sulfate absorbed in the normal GI tract
not absorbed
152
is bariums sulfate distributed widely in the body or is it limited to one area
limited to GI lumen
153
is bariums sulfate metabolised
no
154
how is bariums sulfate excreted
excreted unchanged in faeces
