CT Application 1 CM Flashcards
Role of contrast media
- improve sensitivity & specificity
- differentiation
- evaluate vascular structures
- assess abdominopelvic region
high contrast CT exams usually require ____ to differentiate structures of different densities
no contrast media
low contrast CT exams usually require ____
contrast media to improve tissue contrast
what type of contrast are CO2 and Air
negative contrast
what type of contrast are water & volumen
neutral contrast
how does the diff contrast appear as
positive contrast - white
neutral “ - grey
negative “ - black
what type of contrast are barium & iodinated
positive contrast
example of barium contrast
barium sulphate
example of iodinated contrast
iodine based IV contrast gastrografin
limits of using plain water
- transits rapidly & absorbed distally
- suboptimal distension which mimics / masks lesions
pros of using plain water
AVA
- administered orally
- assess luminal pathology & bowel wall
- very good for upper GIT if scanned at appropriate timing
what does VoLumen contain
- diluted barium sulfate suspension
- sorbitol
what effect does sorbitol have
laxative effect
how many bottles does a patient drink
2-3 bottles of VoLumen
how can barium contrast be administered
oral & rectal
what is barium contrast commonly used in
esophagus, intestine, very intense intestinal contrast
contra-indications of barium
- intestinal perforation
- intestinal obstruction
- swallowing difficulties
K-edge of iodine
33.2 keV
what is a function indicator of x-ray energy
probability of photoelectric absorption since it corresponds to binding energy of iodine
higher kVp leads to ___ compton effect & ___ photoelectric effect
higher; lower
properties of iodinated contrast
- oligomerization
- iodine concentration
- osmolarity
- viscosity
what are the 2 main groups and subgroups of water soluble iodinated contrast
ionic
- monomer + dimer
non-ionic
- monomer + dimer
currently available contrast media are either __
monomer (1 benzene ring) + dimer (2 benzene ring)
examples of ionic iodinated contrast media
- hypaque
- isopaque coronar
- hexabrix
what is gastrografin
diatrizoate
what is hypaque AKA
diatrizoate
what is isopaque coronar AKA
metrizoate
what is hexabrix AKA
ioxaglate
examples of non-ionic iodinated contrast
- ultravist
- visipaque
what is ultravist AKA
iopromide
what is visipaque AKA
iodixanol
although overdose is unlikely but possible, ___ needs to be defined
upper limits
what factors influence iodine concentration/dose
protocol, injection rate, delay imaging
how is iodine concentration standardized for pediatric patients
weight
drink ___ of water to minimize iodine side effects
1L
what is osmolarity
measurement assessing number of particles dissolved in 1kg of water
Osmolality of iodinated contrast media is compared to the osmolality of ___
human plasma (300mOsm/kg H2O)
iodinated contrast is either ___ or __ tonic
hyper-; iso-
what does osmolarity contribute to
- non-allergic adverse reactions
- injection pain
- endothelial damage
- RBC deformation
what is the osmolarity of ionic CM
very high
what is the osmolarity of non-ionic CM
moderate to high
cP
centipoise
what is viscosity of IV CM
measure of liquid resistance / friction to flow
what does viscosity of IV CM influence
- IV injectability
- cannula gauge
- contrast induced kidney injury risk
high viscosity leads to ___ infusion times
longer
how much iodine containing CM is removed 24hr after IV administration
90% mostly eliminated by kidneys
in the event of renal failure / insufficiency, how can CM be extracted
dialysis
iodine containing CM can/cannot cross cell membranes or Blood brain barrier
cannot
CM firstly transits through the vessel system (“Vascular compartment”) and secondly enters the space between vessels and cells (“interstitial compartment”) by ____
free diffusion
what are the 3 main groups of IV contrast enhancement
- patient
- CT scanning parameters
- contrast media
what are the scan delays possible
fixed, test-bolus, bolus-tracking
what are the injection patterns available
uniphase, biphase, exponentially decay
iodine dose formula
(concentration x vol of contrast) / 1000
why should the CM administered be greater in larger patients compared to smaller patients?
larger patients = larger blood volume = more diluted CM
what are the diff cannula available
18G, 20G, 22G, 24G
what is the flow rate of 18G
4 - 6 ml/s
what is the flow rate of 20G
3 - 4 ml/s
what is the flow rate of 22G
2 - 3 ml/s
what is the flow rate of 24G
1 - 1.5 ml/s
which cannula for pediatrics
24G
which cannula for difficult veins esp post chemotherapy
24G
which cannula for arterial & venous phase of CT scan
22G
which cannula for most phases
20G
which cannula for fast CT contrast flowing studies
18G
saline chaser allows for the reduction of ___
contrast volume & increases peak attenuation
saline chaser reduces ___ artifacts from vein & right heart
streak
adverse reactions of IV iodinated contrast
- CI-AKI
- adverse reaction post administration
- extravasation
- air embolism
CI-AKI means?
contrast induced - acute kidney injury
which patients are prone to CI-AKI
patients with compromised kidney function such as diabetes and chronic kidney disease
what indicators suggest patient is at higher risk of AKI
- eGFR (mL/min): 30 - 0
- elevated serum creatinine (mg/dL): 2 - 4.5
- Moderate reduced kidney function
how to reduce chance of CI-AKI
- screen for patient risk
- administer periprocedural hydration
- lower osmolar iodinated contrast media
- stop metformin
NSAIDs
Non-Steroidal Anti-Inflammatory Drugs
how to minimize reactions
- hydration
- stop NSAIDs
- use other modalities / non-contrast
eGFR is calculated using ___
diet modification in renal disease formula
what do you need for diet modification in renal disease formula
- serum creatinine
- age
- gender
serum creatinine is ___ indicator of kidney function
insensitive
what is the best overall indicator of kidney function
GFR
eGFR
estimated glomerular filtration rate
if eGFR > 90, should you continue with IV iodinated CM
yes since excretion half time is 1-2 hrs
if eGFR > 60, should you continue with IV iodinated CM
- weight benefits & risks with radiologist
- consider other modalities / non-contrast
- recheck serum creatinine and eGFR 48 hrs after scan
if eGFR < 30, should you continue with IV iodinated CM
if on dialysis, use non-contrast/other modalities
if not on dialysis, recheck serum creatinine and eGFR 48 hrs after scan
____ are well established methods to prevent CI-AKI
volume expansion & hydration treatment
IV saline hydration reduces risk of CI-AKI by ___
almost 50%
lactic acidosis
when lactate production exceeds its metabolism in your body
what is the main factor for metformin related lactic acidosis
diabetes
how to minimize reactions involving metformin
- discontinue 48 hrs after contrast
- check creatine before resuming
what causes 50% mortality for adverse reactions
metformin + chronic renal insufficiency + IV contrast = lactic acidosis
when to resume metformin
eGFR > 30mL/min/1.73m^2
protocol for eGFR < 30mL/min/1.,73m^2
stop metformin 48hrs before and after CM injection
which pathway involves IgE allergic reaction
anaphylactic true allergy
what are the IV contrast reaction pathways
- anaphylactic true allergy
- anaphylactoid “allergy-like”
what do IV contrast reactions activate
mast cells
strategies to avoid adverse reactions
- evaluate risk and benefit
- use other modalities / non-contrast
- diff CMs
- guidelines if contrast must be used
what causes extravasation
failed IV injection leading to compartment syndrome
what is compartment syndrome
increased pressure within confined space
management strategies for extravasation
MISE
- elevate limbs
- ice pack
- monitoring
- surgery if severe
clinical feature of air embolism
- dyspnoea
- cough
- chest pain
treatment for air embolism
- 100% oxygen
- hyperbaric oxygen tank
- patient in left lateral decubitus
