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Diagnostic methods > CT Imaging > Flashcards

CT Imaging Flashcards

1
Q

what size should you take the slices on CT?

A

always less than 3-5mm or you’ll miss things

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2
Q
  1. ) What is a CT image composed of ?
  2. )CT # will vary according to?
  3. ) What CT # is assigned to air and what CT # is assigned to water?
A
  1. )tiny squares called pixels- will be assigned a number from -1000 to +1000 measured in Hounsfield units (HU’s)
  2. )-CT number will vary according to density of tissue scanned and is a measure of how much of the x-ray beam is absorbed by the tissue at each point in the scan
  3. )air: -1000 Hu
    water: 0 Hu
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3
Q

what is the order of the densities detected in CT in Hounsfield units?

A

air: -1000
fat: -40 → -100
water: 0
soft tissue: 20-100
bone: 400-600
metal >1000

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4
Q

what are 2 characteristics of denser substances in CT?

A

absorb more xrays
↑ attenuation (brighter)
whiter on CT

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5
Q

what is attenuation?

A

stopping of xrays

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6
Q

After CT scans are obtained they can be?

A

windowed to optimize visibility of different types of pathology (enhance different structures)

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7
Q

CT can be ordered to evaluate which 4 conditions?

A

tumors
trauma
infection
bleeding

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8
Q

CT is structural imaging not? Because it represents?

A

Not functional imaging because it represents a moment in time

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9
Q

What are the CT limitations?

A
  • Size of patient (<500lbs)
  • Claustrophobia
  • Can they hold still?
  • Can they hold their breath?→ issues with elderly patients
  • Use water-soluble oral contrast if perforation is suspected or aspiration concern
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10
Q

Axial plane

A

cut body in half like magician would

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11
Q

Coronal plane

A

think of a tiara like cut through the body→ anterior and posterior sections

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12
Q

Sagittal plane

A

think about the lab where we split the gonads in half or when we wanted to view the sinuses

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13
Q

which 3 ways can contrast be administered?

A

IV
enteric (oral or rectal)
intrarticular

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14
Q

what are the risks of omitting contrast when it is indicated?

A

diagnostic/treatment errors

unnecessary morbidity & costs

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15
Q

what are 2 ADRs of contrast?

A

acute adverse reactions

contrast induced nephropathy (CIN)

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16
Q

all modern contrast is made of what substance?

A

iodine base

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17
Q

what are the 3 classifications of IC contrast? which causes the most allergic reactions? what is most common?

A
  • High-osmolarity contrast media (HOCM)**allergic reactions, not used
  • Low-osmolarity contrast media (LOCM)→ most common
  • Iso-osmolariry contrast media (IOCM)
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18
Q

what is enteric contrast made of and how likely are they to cause allergic reaction?

A

some is iodine based

all have small potential to cause acute reaction

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19
Q

What is the most important thing when it comes to giving contrast?

A

timing

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20
Q

what are the uses for positive and negative enteric contrasts? what are they made of?

A

positive:
- high attenuation in CT
- dilute suspension of barium or iodinated agent

negative:
- water attenuation on CT, distends belly to delineate bowel mucosa, detect active inflammation or active GI bleeding
- plain water for stomach and duodenum but absorbed after that

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21
Q

where can you find recommendations for CT indication?

A

ACR appropriateness criteria

22
Q

in what 3 scenarios should you not use contrast in a head CT? why?

A

trauma, stroke, intracranial hemorrhage

-blood will provide enough contrast

23
Q

when should you not use contrast for cervical spine CT?

A

trauma unless arterial injury possibility or penetrating MOI

→ MOI: mechanism of injury

24
Q

when SHOULD you use contrast for cardiothoracic CT?

A

evaluating heart and thoracic vessels
trauma
staging of primary thoracic neoplasms

25
Q

when should you not use contrast for an abdominopelvic CT?

When should you use it?

A

CT colonography
renal stone eval (stone will show)
extraparenchymal lymphoma

SHOULD USE: for virtually all other indications
-→ GI
→ hepatopancreaticobiliary
→ GU
→ GYN
26
Q

when should you not use contrast in a MSK (orthopedic) CT?

When should you use it?

A

extremities
spine

SHOULD USE IT: evaluation of soft tissue masses

27
Q

when should you not use contrast in CT angiography?

A
  • monitoring a known aneurysm for growth

- detection of a hematoma

28
Q

when should you use enteric contrast?

A
  • gastric/small bowel perf post surgery
  • separate bowel loops in pts with minimal visceral fat
  • neg contrast for GI bleed
29
Q

when should you not use enteric contrast?

A

-diagnosis of appendicitis and diverticulitis

-eval of: Kardashians BALS Bones Very Retro
liver, 
kidney,
bladder, 
spleen, 
adrenal glands, 
retroperitoneum, 
bones,
vasculature
30
Q

what are 2 contraindications for enteric contrast?

A
  • aspiration risk (?mental status)

- high grade bowel obstruction

31
Q

Avoid barium based oral contrast in patients who have?

A

-Pts that are at risk for bowel perf because it can lead to ↑ risk for mediastinitis & peritonitis

32
Q

What patients are at low risk of complications when using barium based contrast? Why?

A

-patients with chronic leaks/fistulae because these cavities are already experience chronic exposure to bowel content

33
Q

can you use LOCM/IOCM with previous allergic reaction to HOMC?

A

yes, much less likely to occur

34
Q

what should you ask about if someone reports a previous allergic reaction to contrast dye?

A

iodinated or not (not iodinated ex: gadolinium for MRI)

35
Q

what are 6 symptoms of anaphylaxis?

A

I See U Eating Hot Ass Brownies

itching 
urticaria (hives)
erythema
stridor→ high pitch wheezing
hoarseness
bronchospasm
anaphylactic shock (hypotension, bradycardia)
36
Q

Signs and symptoms of physiologic symptoms of IV contrast are?

These are directly related to ?

A
  • transient warmth or chills
  • nausea
  • vomiting
  • metallic taste

the dose
→ dose-dependent rxn’s

37
Q

what regimen should you give to a patent with a previous allergic reaction to contrast requiring contrast presently?

A

corticosteroid (solo-medrol) +/- antihistamine
PO over 12-13 hrs or
IV over 5hrs

38
Q

If patient the patient comes to the ER needing an emergent and necessary CT scan requiring contrast but had a prior rxn to iodine contrast (mild) should you give it to them

A

yes

39
Q

will someone with a previous history of iodine based contrast react to gadolinium?

A

no not molecularly similar and not cross-reactive

40
Q

when should you check renal function prior to IV contrast admin?

A
  • pt >60yrs old, but healthy

- younger with DM

41
Q

what should you coadminister with contrast?

A

bolus IV fluids to protect the kidneys

42
Q

what medication needs to be held for 1-2days before contrast admin?

A

metformin

43
Q

what food allergy predisposes to IV contrast allergy?

A

true seafood allergy (can be premedicated outpatient with Benadryl and solumedrol

44
Q

what scan should you do for trauma?

A

non-contrast CT

45
Q

what’s the next step if a CXR shows a nodule?

A

contrast CT

46
Q

what scan should you do for ?PE?

A

CT angiogram (contrast)

47
Q

should you use contrast for renal CT?

A

no, don’t need it

48
Q

what are the differences with abdominal CT in thin and BMI >25 in terms of contrast?

A

BMI>25 IV contrast

thin: need to give oral contrast which takes some time to get into abdomen

49
Q

when should you do an abdominal CT for abdominal pain?

A

no evidence of gall bladder, ovarian cyst, and can’t convince them they’re fine

50
Q

a thin teen patient with a ?appendicitis should have which test first?

A

ultrasound

51
Q

which 2 tests should you preform for a patient with previous kidney stones with abdominal pain?

A

ultrasound and KUB

→ KUB= kidney ureter bladder x-rays

Diagnostic methods (11 decks)

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