Contrast agents Flashcards
what 3 things does the attenuation of the xray depend on
- atomic number of tissue/organ
- density of tissue/organ
- thickness of tissue/organ
what is contrast media
substance added to assist with imaging procedure
what is contrast agent
has different atomic number/density to the surrounding tissue
why is a contrast agent needed
if adjacent structures have similar densities and atomic number they can be hard to distinguish on radiograph
what are 5 essential properties of contrast agents
- tolerable for patient
- stable
- significantly different density
- cost effective
- minimal toxic effects
what are 2 types of contrast agents and give exampples
positive:
- barium sulphate
- iodine
negative:
- air
- co2
- water
when is barium sulphate used as a contrast agent
imaging the GI tract
what format is barium sulphate in
suspension (as it cant dissolve in water)
why is barium sulphate ideal for absorption of xrays
it has a similar k-shell binding energy to rays of 37.4keV and high atomic number of 56
how can barium sulphate be administered
orally, rectally or instilled in enterostomy tube/catheter
how can barium sulphate be used to see oral function after a stoke for exampple
liquid barium or barium coated bread given to patient
function of swallow is monitored on screen
what are adv and dis of using barium sulphate as a contrast agent
ADV:
- relatively cheap
- good opacification
- stable
- high patient acceptability
- homogenous density
DIS:
- fatal if in peritoneal cavity (potential space defined by the diaphragm, walls of the abdominal and pelvic cavities, and abdominal organs)
- high aspiration risks
why might barium sulphate not be a good to use
- suspected perforation
- bowel obstruction
- gi disorders e.g toxic megacolon
- risk of stroke
what is carbex
brand name for granules which fizz to produce gas within GI system (put in barium suspension)
what are the adv of using air, water or co2 as contrast agent
- cheap
- good negative opafication
- stable
- high patient adaptability
- homogenous density
- can be used as alternative in IR to iodinated contrast
what 4 things can iodinated contrast agent be used for
urinary tract, binary and GI tract, spine canal and brain, cardiovascular system
what are the 4 stages of contrast excretion
- body cavity
- absorbed by blood
- filtered by kidney
- excreted by urine
what is the intravenous pathway that a contrast agent follows (9 in total)
peripheral vein
deep vein
right heart
pulmonary arterial tree
left heart
systemic arterial vessel
visceral enhancement
venous drainage
excretion and recirculation
what are 3 characteristics of iodinated contrast agents
- viscosity
- osmolarity
- low toxicity
how does viscosity affect the administration of contrast agent
thickness of agent affects ease in which its injected in and rate of drip infusion
how does osmolarity affect the toxic factor
number of particles dissolved in solution is chief factor of toxicity
what happens when iodinated contrast agents are injected
the molecule begins to dissociate releasing ionic particles (cations and anions)
what is hypervolemia
too much fluid volume in the body
what is vasodilation
when you blood vessels open wider to allow more blood flow and lowers your bp
explain the osmotic effect when contrast is injected
- contrast injected, osmolarity increases
- blood entering capillary bed is hypertonic to fluid in surrounding tissue
- extravascular fluid crosses semi-permeable membrane of capillary to achieve isotonicity causing hypervolemia
- epithelial cells lining intimal wall are similarly effect and can lead to inflammation and thrombophlebitis (swelling of vein)
- flexibility of vessels allow vasolodiation to accommodate hypervolemia
define homeostasis
maintenance of steady state in body despite external environment
what 3 things is viscosity dependant on
concentration
size of molecules
temperature
how does ionic/non-ionic agents affect electrolyte balance
ionic = disrupts electrolyte balance (dissociates into =/- ions)
non-ion = doesnt disrupt electrolyte balance
why is non-ionic contrast agent more costly
higher viscosity
what are some contrast agent considerations
- utilise most suitable agent
- consider patient history and condraictions
- identify suitable conc of contrast
- identify volume of contrast needed
what is the purpose of oral contrast agent that pass through the GI tract
to differentiate GI anatomy from adjacent structures or abnormalities
identify contrast leaks
compare the 2 oral contrast agents of barium, gastrografin and gastromiro
barium= radio dense, cheaper, avoid aspiration
gastrografin = avoid aspiration
gastromiro = safe but more expensive
when is rectal contrast agent used
in enema type examinations (detect leaks)
when is a urethral contrast agent used
to check integrity of uretha (urine tube) or bladder wall
what is angiography
xray for blood vessels
define bolus
single, large dose of medicine
what 4 things need to be controlled when contrast agent is being injected
- temperature/ viscosity
- volume
- flow rate
- rise time (time to full pressure)
why is the tip of a catheter pig tail shaped during contrast insersion
to avoid the spinning of the catheter
what must you do before administering contrast agent
- check documentation
- check correct strength
- check its in date
- visually check bottle and syringe
what are some risks that come along with patients who have a history suggesting lowered kidney function
diabetes
gout
oedema
hypertension
why is it important to ask if a patient is diabetic before administering contrast
metformin, a diabetic drug has been associated with several cases of renal failure and lactic acidosis (build up of lactic acid in blood)
what action must you take when administering contrast to a type 2 diabetic patient
stop metformin 48 hours after examination
give minimal dose of contrast agent
hydration therapy post examination
what are some things you can do to reduce risk from contrast agents
- fluide volume loading
- avoid repeated high dose studies in short intervals
- use low-osmolar non-ionic contrast media
- use diluted contrast media at lowest volume practicable
- avoid concurrent use of drugs that can cause renal vasoconstriction
what are mild reactions of contrast media
flushing
arm pain
pruitis (scratching)
nausea
what are moderate reactions of CM
urticaria (hives)
facial oedema (build up of fluid causing swelling)
hypotension
bronchospasm (constriction of bronchioles)
what are severe reactions of CM
hypotensive shock
laryngeal oedema
convulsions
respiratory/cardiac arrest
what are the 4 h’s in patient care
hisotry
hydration
have equipment and expertise available
heads up (to change in patient condition)ha
what is contrast extravasation
contrast agent leaks into tissue around vein where cannula was placed
how do you treat contrast extravasation
elevate and ice for 2 hrs
consult plastic team if blistering etc
