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Flashcards in Week 8 Readings Deck (62)
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1

List a place in the body where subject contrast is inherently high

The chest -the pulmonary vessels and ribs have significantly different densities from the aerated lung, which allows for easy identification on the image

2

Two main methods of contrast administration in CT are

Intravascular and gastrointestinal

3

In the case of most agents that contain barium and iodine, the material is of a higher density than the structure. These are typically referred to as ______ agents

Positive

4

Low-density contrast agents are called _____ agents. Ex air or carbon dioxide

Negative agents

5

Certain gastrointestinal agents posses a density similar to water and are referred to as _____ contrast agents

Neutral

6

Iodinated agents properties

-water soluble -easy to administer intravascularly -high safety index

7

Two tissues must differ by at least ____ HU to be visibly different on a CT scan

10

8

Osmolarity

- a property of intravascular contrast media that refers to the number of particles in solution, per unit liquid, as compared with blood -high osmolarity contrast media may have as much as seven times the osmolarity of blood -low osmolarity contrast media has roughly twice the osmolarity of blood -contrast media that is isosmolar has the same osmolarity as blood

9

Hyperosmolar aka hypertonic

When the iodinated contrast medium have a greater osmolarity than blood plasma

10

Viscosity

-a physical property of intravascular contrast media -can be described as the thickness or friction of the fluid as it flows -the brand, temperature and concentration of contrast affect its viscosity

11

⬆️ temperature of iodinated contrast ____ viscosity

⬇️ viscosity

12

⬆️ the concentration of iodine, ___ the viscosity

⬆️ viscosity of the solution

13

For intravascular contrast agents: ionic contrast agents will

-in solution, ionic contrast agents contain molecules that will form ions -composed of molecules that will dissociate into ions when in solution -low osmolarity

14

For intravascular contrast agents: nonionic contrast media

-molecules do not dissociate -most also have low osmolarity

15

Intravascular contrast agent clearance time

-once injected, all types of iodinated contrast media under go very rapid distribution throughout the entire extracellular space -they are not metabolized -excreted by the body nearly exclusively by the kidney via glomerular filtration -in pts with normal renal function the half life (time it takes for half of the dose to be eliminated from the body) is approx 2 hrs

16

Intravascular dose

To accurately assess the dose of inordinate contrast agent to be delivered, both the iodine concentration and volume must be considered -the beam attenuation abilities of a given amount of contrast media are directly related to the concentration of iodine

17

LOCM are measured in

mgI/mL

18

HOCM are measured in

mg/mL

19

The adverse effects of overdosage on iodinated contrast media affect mainly

The pulmonary and cardiovascular systems

20

Regardless of the type of iodinated contrast agent, the ____ dose necessary to obtain adequate visualization should be used

Lowest

21

The combination of volume and concentration to be used for intravascular should be individualized account for what factors?

-age -body weight -size of vessel into which it will be injected -anticipated pathology -degree and extend of opacification required -structure (s) or area to be examined -disease processes affecting the patient -specific equipment available

22

In most clinical practices, the dose used to perform CT exams on paediatric patients is calculated by ____. (For intravascular contrast admin)

Weight -most common formula used is 2 mL/kg

23

Iodinated contrast media during pregnancy

-CT exams are seldom done during pregnancy -occasionally such exams may be vital for the mothers health -iodinated contrast media have been shown to cross the human placenta and enter the fetus "There is no proof that contrast media agents present a risk to the fetus. However, there is not enough evidence to be certain they pose no risk"

24

Iodinated contrast media and lactation

-contrast enhanced CT is sometimes performed on a woman who is breastfeeding -less than 1% of the dose of contrast agent given to the mother is excreted into the breast milk -less than 1% of contrast medium ingested by the infant is absorbed from the GI tract -therefore the expected dose of contrast medium absorbed by an infant from ingested breast milk is extremely low "A very small percentage of the inordinate contrast medium given to a mother will be excreted into breast milk and absorbed by the infant. Therefore it is believed to be safe for the mother and infant to continue breastfeeding after receiving contrast agent"

25

True/false: it is impossible to predict which patients will have an adverse reaction to intravenously administered contrast medium. Therefore CT staff must be trained to respond quickly

True

26

Contrast media reactions can be broadly categorized as either ____ or ____ in nature

Chemotoxic or idiosyncratic in nature

27

true/false: children have a lower frequency of contrast reactions than adults

true

and when they do occur they tend to be idosyncratic in nature

28

side effects of intravascular contrast media administration that are common and can be expected are

  • nausea
  • vomitting
  • altered taste (often described as metallic)
  • perspiration
  • warmth
  • flushing
  • anxiety

these side effects are much less common when LOCM is used

29

classifications of idiosyncratic reactions

  • mild: usually short duration and self limiting. Does not require treatment, the pt should be carefully monitored for at least 20-30 min, as symptoms of a mild reaction may become more severe. Ex cough, rash (hives), itching, nasal stuffiness
  • moderate: not immediately life threatening, although they may progress to be so. Ex bronchospasm, dyspnea, wheezing etc
  • severe: potentially or immediately life threatening. Symptoms include: subtantial respiratory distress, unresponsiveness, convulsions etc
  • most severe reactions occur soon after administration and can begin with any number of signs and symptoms, ranging from anxiety to diffuse erythema to cardiac arrest

30

true/false: although a first time exposure may only produce a mild reaction, repeated exposures may lead to more serious reactions. Once a person is sensitized (has had a previous reaction), even a very limited exposure to a very small amount of allergen can trigger a severe reaction

true

  • the recommendation is that individuals avoid medications that have caused an allergic reaction, even a mild one, in the past
  • the reaction rate is higher among individuals who have had a previous reaction to contrast medium compared with those who have no history of a reaction