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Diagnostic M.'s Sara Peer mentor > CT Imaging for the PA > Flashcards

CT Imaging for the PA Flashcards

1
Q

What is a CT?

A

Computed Tomography

Used gantry with rotating xray beam and multiple detectors in various arrays along with sophisticated computer algorithms to process the data

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2
Q

What does a CT scan produce?

A

large number of 2D, slicelike images each of which are millimeters in diameter

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3
Q

What are the two major types of CT?

A

Helical

Conventional, Axial, Step and Shoot CT

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4
Q

What is a conventional, axial, Step and shoot CT used for?

A

high-resolution scanning of lungs, coronary artery calcium scoring, and prospective ECG-triggered coronary CT angiography

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5
Q

What are the principal components of a CT machine?

A

xray tube

diametrically opposed array of detectors

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6
Q

What does collimation determine?

A

thickness of a section

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7
Q

What is the standard chest collimation for mediastinum?

A

2.5 mm

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8
Q

What is the standard chest collimation for lung parenchyma?

A

1.25 mm

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9
Q

What is narrow collimation?

A

1 to 1.25 mm

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10
Q

What is narrow collimation used for?

A

CT pulmonary angiography
high resolution CT scanning of the lung parenchyma
imaging of small pulmonary nodules

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11
Q

What is wide collimation?

A

2.5 mm

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12
Q

What is wide collimation used for?

A

heavy patients to decrease the quantum noise at the cost of decreased spatial resolution

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13
Q

What is a CT image composed of?

A

matrix of thousands of tiny squares called pixels which are computer assigned a Hounsfield Number

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14
Q

What is the Hounsfield number?

A

a measure of how much of the xray beam is absorbed by the tissues at each point in the scan

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15
Q

What is the Hounsfield number of air?

A

-1000HU

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16
Q

What is the Hounsfield number of fat?

A

-40 to -100 HU

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17
Q

What is the Hounsfield number of water?

A

0 HU

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18
Q

What is the Hounsfield number of soft tissue?

A

20 to 100 HU

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19
Q

What is the Hounsfield number of bone?

A

400-600 HU

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20
Q

What is the Hounsfield number of metal?

A

> 1000 HU

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21
Q

What are the characteristics of Denser substances on a CT?

A

absorb more xrays
have high CT numbers
demonstrate increased attenuation
displayed as whiter densities on CT scans

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22
Q

What are the characteristics of less dense substances?

A

absorb fewer xrays
have low CT numbers
said to demonstrate decreased attenuation
displayed as blacker densities on CT scans

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23
Q

What is attenuation?

A

the chemical make up of the material; determined by how many xrays make it through the patient to hit the detector and what the image looks like

stopping of xrays

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24
Q

What can a CT image do after it has been taken?

A

the image can be post processed to optimize visibility

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25
Q

What type of imaging is a CT image?

A

structural; represents a moment in time

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26
Q

What is a CT used to rule out?

A

Tumors
Trauma
Infections
bleeding

27
Q

What are the limitations of a CT?

A 
Size of patient - 500 lb max
Girth
Claustrophobia
Hold still for extended period of time
hold breath for extended period of time
Contrast usually needed
28
Q

What is girth?

A

camera cannot touch patients arms or sides

29
Q

What are the risks of using contrast?

A

acute adverse reaction

contrast-induced nephropathy (CIN)

30
Q

What are the methods for contrast administration?

A

IV
Enteric = PO or rectal
Intraarticular

31
Q

What is the base for all modern CT contrast?

A

iodine

32
Q

What are the types of CT contrast?

A

Low osmolality contrast media (LOCM)
Iso-osmolarity contrast media (IOCM)
High osmolarity contrast media (HOCM)

33
Q

What is positive enteric contrast?

A

High attenuation on CT
Consists of dilute suspension of Barium sulfate or dilute solution of an iodinated agent
Used for most indications

34
Q

What is negative enteric contrast?

A

water attenuation on CT
used to delineate the bowel mucosa
used to improve detection of active inflammation or active GI bleeding

35
Q

What can be used a negative contrast?

A

plain water

36
Q

What resource is available to determine what type of contrast administration to use?

A

The American College of Radiology’s Appropriateness Criteria

37
Q

When would you use IV contrast for Head CT?

A 
neoplasm
meningitis
encephalitis
focal neurologic deficit
orbital/vision disorders
pituitary imaging
complicated sinonasal disease
seizures
Ct angiography
38
Q

When would you NOT used IV contrast for Head CT?

A

head trauma
acute stroke
Intracranial hemorrhage

39
Q

When would you use IV contrast for Cervical Spine CT?

A

cervical mass/lymphadenopathy
suspected tumor or infection
abnormalities of cranial nn. X, XI, and XII
brachial plexopathy

40
Q

When would you NOT use IV contrast for Cervical Spine CT?

A

Trauma; unless possible arterial injury or mechanism of injury is penetrating

41
Q

When would you use IV contrast for Cardiothoracic CT?

A

evaluating heart and thoracic vessels
trauma
for staging primary thoracic neoplasms

42
Q

When would you NOT use IV contrast for Cardiothoracic CT?

A

coronary calcium scoring
pulmonary parenchymal evaluation
Lymph node evaluation

43
Q

When would you use IV contrast for Abdominopelvic CT?

A

Gi
Hepatopancreaticobiliary
GU
GYN

44
Q

When would you NOT use IV contrast for Abdominopelvic CT

A

CT colonography
renal stone evaluation
extraparenchymal lymphoma

45
Q

When would you use IV contrast for musculoskeletal CT?

A

evaluation of soft tissue masses
evaluation of suspected septic arthritis
evaluation of infected prostheses

46
Q

When would you NOT use IV contrast for musculoskeletal CT?

A

for most CT exams:
extremities
spine

47
Q

When would you use IV contrast for angiography CT?

A

evaluating lumen of an artery, vein, or a pseudoaneurysm
assess for end-organ ischemia outside brain or lung
to eval for PE
to detect active bleeding

48
Q

When would you NOT use contrast for angiography CT?

A

monitoring a known aneurysm for growth

for detection of a hematoma

49
Q

When would you use Oral contrast for CT?

A

Eval gastric/small bowel perforation following trauma or surgery

Helps separate bowel loops in thin patients with minimal visceral fat

Improve delineation of bowel from mesentery and other peritoneal content

50
Q

When would you NOT use oral contrast for CT?

A 
accurate diagnosis of appendicitis and diverticulitis
Eval of:
liver
kidneys
collecting systems
bladder
spleen
adrenal glands
retroperitoneum
bones
vasculature
51
Q

When is negative enteric contrast helpful?

A

detecting occult GI bleeding when paired with multiphasic CT angiography

52
Q

When would you use rectal contrast for CT?

A

detection of rectal or distal colonic leak

53
Q

When would you NOT use rectal contrast for CT?

A

basically never

54
Q

What are the contraindications for enteric contrast?

A

in patients at risk of aspiration
eval patients with suspected high grade bowel obstruction
avoid barium based in patients who have/at risk for bowel perforations or leak from surgical anastomosis

55
Q

What are not cross reactive?

A

Gadolinium for MRI and CT contrast

56
Q

When will Adverse reactions to CT contrast occur?

A

after enteric, intracavitary or intravascular administration

57
Q

When is the incidence of acute adverse reaction greatest?

A

when IV administration of HOCM

58
Q

What is a mild reaction to CT contrast?

A

self limited
does not progress
rarely requires treatment

59
Q

What is a moderate reaction to CT contrast?

A

requires treatment

may progress to a severe reaction if untreated

60
Q

What is a severe reaction to CT contrast?

A

life threatening

can cause significant morbidity

61
Q

What are allergic like reactions to CT contrast?

A

idiosyncratic- not related to dose
may occur in patient w/o history of prior exposure
do not predictably recur after each antigen exposure

62
Q

What are the signs and symptoms of an allergic like reaction to CT contrast?

A 
itching
urticaria
Erythema
Stridor
Hoarseness
Bronchospasm
Anaphylactoid shock
63
Q

What are physiologic reactions to CT contrast?

A

dose dependent

not mitigated by corticosteroid prophylaxis

64
Q

What are the signs and symptoms of physiologic reaction to CT contrast?

A 
transient warmth or chills
nausea
vomiting
metallic taste
arrhythmia
hypertension
vasovagal reaction

Diagnostic M.'s Sara Peer mentor (27 decks)

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