1
Q
major types of CT
A
- helical- most common
- conventional, axial, step and shoot (used for high resolution scans of lungs, coronary artery)
2
Q
CT scanner
A
- x-ray tube rotates around pt and generates xray beam
- gantry motion is helical during helical and circular during conventional
- detectors record radiation and rejects scattered radiation from outside tube
3
Q
CT collimation
A
- determines thickness of section
- standard is 2.5 mm for mediastinum and 1.25 for lung parenchyma
- wider than 2.5 used in heavy pts
4
Q
CT image
A
- thousands of tiny pixels
- each pixel is -1000 to 1000 HU
- number will vary based on tissue density
5
Q
what is HU for air
A
-1000 HU
6
Q
what is HU for water
A
0
7
Q
what is HU for fat
A
-400 to -100
8
Q
what is HU for soft tissue
A
20 to 100
9
Q
what is HU for bone
A
400 to 600
10
Q
what is HU for metal
A
> 1000
11
Q
denser substances on CT
A
- absorb more xrays
- have higher CT numbers
- demonstrate increased attenuation
- display as whiter
12
Q
less dense substances on CT
A
- absorb fewer xrays
- low CT number
- demonstrate decreased attenuation
- display as blacker
13
Q
attenuation
A
- chem make up of material determines how many xrays make it through to detector
- is the stopping of xrays
14
Q
cross sectional planes in CT
A
- axial
- coronal
- sagittal
15
Q
CT limitations
A
- size of pt (500 lb max)
- claustrophobia
- pt need to hold still
- pt needs to hold breath
- water soluble contrast used for perforations
16
Q
what are possible adverse reactions to CT contrast
A
- allergy
- contrast induced nephropathy
17
Q
contrast admin for CT
A
- IV
- Enteric (PO or rectal)
- all IV is iodine-based
18
Q
positive enteric contrast for CT
A
- high attenuation
- dilute suspension of barium sulfate solution of iodinated agent
- used for most indications
19
Q
negative enteric contrast for CT
A
- water attenuation
- used to delineate bowel mucosa
- used to improve detection of active inflammation/ GI bleed
- can use plain water but only distends stomach and duodenum due to absorption
20
Q
C/I for enteric contrast
A
- pt at risk of aspiration
- high grade bowel obstructions
- no barium based contrast in pts at risk of bowel perforation
21
Q
adverse/allergic reaction prevention
A
- corticosteriod +/- antihistamine
- usually admin PO over longer duration or IV over shorter duration
- NO cross reaction with gad for MRI
diagnostic methods
flashcards
Decks in class (6)
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