Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

CT Theory > Week 8 Readings > Flashcards

Week 8 Readings Flashcards

1
Q

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

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Two main methods of contrast administration in CT are

A

Intravascular and gastrointestinal

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

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

A

Positive

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

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

A

Negative agents

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

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

A

Neutral

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Iodinated agents properties

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

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

A

10

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Osmolarity

A
  • 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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Hyperosmolar aka hypertonic

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Viscosity

A

-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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

⬆️ temperature of iodinated contrast ____ viscosity

A

⬇️ viscosity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

⬆️ the concentration of iodine, ___ the viscosity

A

⬆️ viscosity of the solution

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

For intravascular contrast agents: ionic contrast agents will

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

For intravascular contrast agents: nonionic contrast media

A

-molecules do not dissociate -most also have low osmolarity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Intravascular contrast agent clearance time

A

-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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Intravascular dose

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

LOCM are measured in

A

mgI/mL

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

HOCM are measured in

A

mg/mL

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

The adverse effects of overdosage on iodinated contrast media affect mainly

A

The pulmonary and cardiovascular systems

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

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

A

Lowest

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

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

A

-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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

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

A

Weight -most common formula used is 2 mL/kg

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Iodinated contrast media during pregnancy

A

-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”

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Iodinated contrast media and lactation

A

-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”

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

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

A

True

26
Q

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

A

Chemotoxic or idiosyncratic in nature

27
Q

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

A

true

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

28
Q

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

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

these side effects are much less common when LOCM is used

29
Q

classifications of idiosyncratic reactions

A
  • 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
Q

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

A

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
31
Q

Asthma and contrast media reactions

A
  • asthma is a risk factor
  • pts with asthma had approximately 8x the risk with HOCM and about 5x the risk with LOCM compared to pts without asthma
32
Q

True/false: pts with a history of allergy to foods that contain iodine ex seafood often cause particular concern in the CT department

A

false

  • an allergy to seafood (or other iodine-containing foods) is no more significant than an allergy to other foods. Also, an allergy to topical iodine skin preparation does not indicate an allergy to iodinated contrast media
33
Q

pts identified as being at increased risk of an adverse reaction to contrast medium

A
  • should be brought to the attention of the radiologist
  • is contrast media is deemed essential the pt should be monitored in the radiology department for 1 hour and should recieve LOCM
34
Q

what is the most important method of reducing the risk of an idiosyncratic reaction?

A

the use of LOCM

  • the risk associated with using these agents is 4-5 times lower than that of HOCM
35
Q

steroid pre treatment in reducing rate of idiosyncratic reactions

A
  • steroid pre treatment is effective in reducing the rate of idiosyncratic adverse effects when HOCM is used
  • however, data are unclear regarding the effectiveness of steroid pre treatment in conjunction with LOCM
  • some radiologists believe it is only effective in preventing minor reactions; others conclude it also reduces moderate and severe reactions
36
Q

documentation for an adverse reaction to contrast medium administration

A
  1. amount and type of contrast injected
  2. signs and symptoms of the reaction
  3. interventions or medications given during the reaction and the pts response to treatment
  4. final outcome (ex was the pt sent home or admitted to the hospital)
37
Q

chemotoxic reactions

A

contrast reactions that stem from the contrast agents pharmacologic properties are reffered to as chemotoxic

38
Q

intravascular contrast agents and kidney function

A

intravascular contrast agents affect kidney function. in most cases the effects are confined to a short period of kidney dysfunction that does not produce symtoms. However, in some instances iodinated agents can result in significant nephrotoxic effects, particularly in patients who are considered to be at high risk for nephropathy

39
Q

serum creatinine as an index of GFR

A

Creatinine is a by product of muscle protein metabolism generated by the body at a fairly steady rate and excreted entirely in the urine

  • measuring serum creatinine (SeCr or SCr) is a fast and inexpensive way to assess renal function, although it does have significant limitations
40
Q

factors affecting serum creatinine concentration: kidney disease

A

effect on SeCr:

increase

Mechanism:

decreased GFR (although the increase in SeCr is blunted by increased tubular secretion of creatinine, and reduced creatinine generation

41
Q

factors affecting serum creatinine concentration: reduced muscle mass

A

effect on SeCr:

decrease

mechanism:

reduced creatinine generation: common in children, women, and older and malnourished pts

42
Q

factors affecting serum creatinine concentration: ingestion of cooked meat

A

effect on SeCr:

increase

mechanism:

transient increase in creatinine generation, although the increase may be blunted by a transient increase in GFR

43
Q

factors affecting serum creatinine concentration: malnutrition

A

effect on SeCr:

decrease

mechanism:

reduced creatinine generation caused by reduced muscle mass and reduced meat intake

44
Q

factors affecting serum creatinine concentration: use of cimetidine (Tagament)

A

effect on SeCr:

increase

Mechanism:

inhibition of tubular creatinine secretion

45
Q

factors affecting serum creatinine concentration: use of flucytosine (an anti fungal), some cephalosporins (group of antibiotics)

A

effect on SeCr:

increase

Mechanism:

positive interference with iminohydrolase and picric acid assays for creatinine

46
Q

factors affecting serum creatinine concentration: ketoacidosis (high level of ketones in blood, most commonly as a result of hyperglycemina)

A

effect on SeCr:

increase

Mechanism:

positive interference with picric acid assay for creatinine

47
Q

several studies have show a ____ correlation between the volume of contrast administered and the risk of CIN (contrast media induced nephropathy)

A

direct

48
Q

renal failure

A

The inability of the kidney to filter waste from the blood. Renal insufficiency is used when renal function is abnormal but capable of sustaining essential body function.

Technically, nephropathy denotes any condition or disease affecting the kidney; however it is sometimes used synonymously with renal impairment

49
Q

contrast induced nephropathy (CIN)

A

an acute impairment of renal function that occurs after the intravascular administration of contrast material (for which alternate causes have been excluded)

50
Q

methods of preventing CIN

A
  • identify pts at high risk. patients with diabetes mellitus or other risk factors scheduled for any procedure including IV contrast should have SeCr measured
  • use LOCM or IOCM
  • ensure adequate pt hydration
  • minimize contrast material volume
  • allow at least 48 hours between procedures requiring contrast material
  • discontinue other nephrotoxic medications before the procedure (ex NSAIDs and the antiplatelet agent dipyridamole)
51
Q

metformin

A

should be temporarily discontinued after any examination involving iodinated contrast; it can be resumed after 2 days, assuming kidney function is normal

  • because iodinated contrast agents have been associated with renal dysfunction, the administration of iodinated contrast media to pts taking metformin is a clinical concern. If CIN were to occur, it could indirectly lead to lactic acidosis (most often fatal) by causing an accumulation of metformin in the body
52
Q

the half-life of iodinated contrast media in pts with normal renal function is approx __ hours. In pts with severe renal dysfunction it can be extended to more than __ hours depending on the extent of renal impairment

A

2, 30

53
Q

iodinated contrast media in pts with a history of hyperthyroidism

A

in pts with a history of hyperthyroidism, iodinated contrast media can intensify thyroid toxicosis, and in rare cases it can precipitate a thyroid storm, which is a severe, life-threatening condition

54
Q

delyaed reactions to intravsacular iodinated contrast media

A

are defined as reactions occuring between 1 hour and 1 week after contrast media injection

55
Q

true/false: iodinated contrast agents will not cross an intact BBB

A

true

56
Q

gastrointestinal contrast medium

A

in the GI tract, contrast medium is essential to distinguish loops of bowel from a cyst or absess or neoplasm. For this reason, oral contrast material is used in most CT scans of the abdomen and pelvis. For some indications, the rectal administration of contrast material is useful

57
Q

in general, contrast media is classified as positive if it appears ___ on the image, and negative if it appears ___ on the image

A

bright, dark

58
Q

Barium sulfate query perf

A

barium sulfate should NOT be given if perforation of the GI tract is suspected. Barium leaking into the peritoneal cavity is referred to as barium peritonitis and is associated with a significant mortality rate. It can be prevented by substituting a water-soluable iodinated oral contrast agent whenever perforation is suspected

59
Q

true/false: barium sulfate and water-soluable contrast material cause comparable bowel opacification. Because of low concentrations used, neither coats the mucosa signifcantly

A

true

60
Q

air vs carbon dioxide

A

carbon dioxide has some advantages over room air in that it is:

  • readily absorbed by the body and is eliminated by respiration
  • induces less spastic response of the bowel wall and is therefore better tolerated by pts
  • requires relatively little pt education to achieve similar results

Room air can result in significant post procedure cramping and discomfort for the pt

61
Q

for post myelogram (while the contrast is in the intrathecal space)

A

to reduce the incidence of headache, keep the pts head elevated approx 30 degrees. Rolling the pt once or twice before scanning is recommended to mix the contrast material that may have settled since the myelogram

62
Q

intraarticular contrast

A

CT arthrography has the advantage of allowing simultaneous evaluation of bone and soft tissue

CT Theory (11 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions