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RAD 412 > Contrast agents > Flashcards

Contrast agents Flashcards

1
Q

what 3 things does the attenuation of the xray depend on

A
  • atomic number of tissue/organ
  • density of tissue/organ
  • thickness of tissue/organ
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2
Q

what is contrast media

A

substance added to assist with imaging procedure

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3
Q

what is contrast agent

A

has different atomic number/density to the surrounding tissue

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4
Q

why is a contrast agent needed

A

if adjacent structures have similar densities and atomic number they can be hard to distinguish on radiograph

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5
Q

what are 5 essential properties of contrast agents

A
  • tolerable for patient
  • stable
  • significantly different density
  • cost effective
  • minimal toxic effects
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6
Q

what are 2 types of contrast agents and give exampples

A

positive:
- barium sulphate
- iodine

negative:
- air
- co2
- water

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7
Q

when is barium sulphate used as a contrast agent

A

imaging the GI tract

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8
Q

what format is barium sulphate in

A

suspension (as it cant dissolve in water)

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9
Q

why is barium sulphate ideal for absorption of xrays

A

it has a similar k-shell binding energy to rays of 37.4keV and high atomic number of 56

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10
Q

how can barium sulphate be administered

A

orally, rectally or instilled in enterostomy tube/catheter

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11
Q

how can barium sulphate be used to see oral function after a stoke for exampple

A

liquid barium or barium coated bread given to patient

function of swallow is monitored on screen

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12
Q

what are adv and dis of using barium sulphate as a contrast agent

A

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

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13
Q

why might barium sulphate not be a good to use

A
  • suspected perforation
  • bowel obstruction
  • gi disorders e.g toxic megacolon
  • risk of stroke
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14
Q

what is carbex

A

brand name for granules which fizz to produce gas within GI system (put in barium suspension)

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15
Q

what are the adv of using air, water or co2 as contrast agent

A
  • cheap
  • good negative opafication
  • stable
  • high patient adaptability
  • homogenous density
  • can be used as alternative in IR to iodinated contrast
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16
Q
A
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17
Q

what 4 things can iodinated contrast agent be used for

A

urinary tract, binary and GI tract, spine canal and brain, cardiovascular system

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18
Q

what are the 4 stages of contrast excretion

A
  1. body cavity
  2. absorbed by blood
  3. filtered by kidney
  4. excreted by urine
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19
Q

what is the intravenous pathway that a contrast agent follows (9 in total)

A

peripheral vein
deep vein
right heart
pulmonary arterial tree
left heart
systemic arterial vessel
visceral enhancement
venous drainage
excretion and recirculation

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20
Q

what are 3 characteristics of iodinated contrast agents

A
  • viscosity
  • osmolarity
  • low toxicity
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21
Q

how does viscosity affect the administration of contrast agent

A

thickness of agent affects ease in which its injected in and rate of drip infusion

22
Q

how does osmolarity affect the toxic factor

A

number of particles dissolved in solution is chief factor of toxicity

23
Q

what happens when iodinated contrast agents are injected

A

the molecule begins to dissociate releasing ionic particles (cations and anions)

24
Q

what is hypervolemia

A

too much fluid volume in the body

25
Q

what is vasodilation

A

when you blood vessels open wider to allow more blood flow and lowers your bp

26
Q

explain the osmotic effect when contrast is injected

A
  1. contrast injected, osmolarity increases
  2. blood entering capillary bed is hypertonic to fluid in surrounding tissue
  3. extravascular fluid crosses semi-permeable membrane of capillary to achieve isotonicity causing hypervolemia
  4. epithelial cells lining intimal wall are similarly effect and can lead to inflammation and thrombophlebitis (swelling of vein)
  5. flexibility of vessels allow vasolodiation to accommodate hypervolemia
27
Q

define homeostasis

A

maintenance of steady state in body despite external environment

28
Q

what 3 things is viscosity dependant on

A

concentration
size of molecules
temperature

29
Q

how does ionic/non-ionic agents affect electrolyte balance

A

ionic = disrupts electrolyte balance (dissociates into =/- ions)

non-ion = doesnt disrupt electrolyte balance

30
Q

why is non-ionic contrast agent more costly

A

higher viscosity

31
Q

what are some contrast agent considerations

A
  • utilise most suitable agent
  • consider patient history and condraictions
  • identify suitable conc of contrast
  • identify volume of contrast needed
32
Q

what is the purpose of oral contrast agent that pass through the GI tract

A

to differentiate GI anatomy from adjacent structures or abnormalities

identify contrast leaks

33
Q

compare the 2 oral contrast agents of barium, gastrografin and gastromiro

A

barium= radio dense, cheaper, avoid aspiration

gastrografin = avoid aspiration

gastromiro = safe but more expensive

34
Q

when is rectal contrast agent used

A

in enema type examinations (detect leaks)

35
Q

when is a urethral contrast agent used

A

to check integrity of uretha (urine tube) or bladder wall

36
Q

what is angiography

A

xray for blood vessels

37
Q

define bolus

A

single, large dose of medicine

38
Q

what 4 things need to be controlled when contrast agent is being injected

A
  • temperature/ viscosity
  • volume
  • flow rate
  • rise time (time to full pressure)
39
Q

why is the tip of a catheter pig tail shaped during contrast insersion

A

to avoid the spinning of the catheter

40
Q

what must you do before administering contrast agent

A
  • check documentation
  • check correct strength
  • check its in date
  • visually check bottle and syringe
41
Q

what are some risks that come along with patients who have a history suggesting lowered kidney function

A

diabetes
gout
oedema
hypertension

42
Q

why is it important to ask if a patient is diabetic before administering contrast

A

metformin, a diabetic drug has been associated with several cases of renal failure and lactic acidosis (build up of lactic acid in blood)

43
Q

what action must you take when administering contrast to a type 2 diabetic patient

A

stop metformin 48 hours after examination

give minimal dose of contrast agent

hydration therapy post examination

44
Q

what are some things you can do to reduce risk from contrast agents

A
  • 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
45
Q

what are mild reactions of contrast media

A

flushing
arm pain
pruitis (scratching)
nausea

46
Q

what are moderate reactions of CM

A

urticaria (hives)
facial oedema (build up of fluid causing swelling)
hypotension
bronchospasm (constriction of bronchioles)

47
Q

what are severe reactions of CM

A

hypotensive shock
laryngeal oedema
convulsions
respiratory/cardiac arrest

48
Q

what are the 4 h’s in patient care

A

hisotry
hydration
have equipment and expertise available
heads up (to change in patient condition)ha

49
Q

what is contrast extravasation

A

contrast agent leaks into tissue around vein where cannula was placed

50
Q

how do you treat contrast extravasation

A

elevate and ice for 2 hrs

consult plastic team if blistering etc

51
Q
A

RAD 412 (20 decks)

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