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Radiology > CT > Flashcards

CT Flashcards

1
Q

what is the scientific unit of measurement for radiation (effective dose - refers to radiation risk averaged over entire body)?

A

mSv (millisievert)

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2
Q

what is the effective radiation dose in the ankle CT?

A

0.07 mSv

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3
Q

effective dose of radiation ina dults for extremity x rayu

A

o0.0001 mSv

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4
Q

digital image consists of a square matrix of

A

pixels, each a voxel of tissue

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5
Q

CT image is

A

map of measured average linear voxels of a section of teh body

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6
Q

how many hounsfield units is air?

A

-1000

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7
Q

fat?

A

-60 to -120

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8
Q

water

A

0

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9
Q

compact bon

A

+1000

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10
Q

what is the tissue density calculated from, uses transmission to calculate?

A

attenuation coefficient

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11
Q

what method is used to calculate attenuation coefficient of each pixel?

A

filtered back projection

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12
Q

what is term for midpoint of CT number range?

A

window level WL

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13
Q

Attenuation of each voxel is represented by CT number or ___________ number, which is a linear transformation of the original linear attenuation coefficients, represented by a shade of grey determined by window level and width controls, and actual number by defining a ROI (region of interest)?

A

hounsfield

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14
Q

what is term for band of CT numbers centered about WL (window level)?

A

WW, window woidth

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15
Q

if WW (window width) is large, will contrast be more or less?

A

less

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16
Q

if WW (window width) is small, will contrast be more or less?

A

more

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17
Q

Which of the following would have the greatest Hounsfield units?

Air
Fat
Water
Compact bone

A

compact bone

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18
Q

what determines image quality in CT?

Bone: high frequency “edge-enhanced”
ST: low frequency “smoothing”
Trade-off between spatial resolution and noise
slice thickness

A

reconstruction kernel

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19
Q

2nd generation: Helical, spiral
3rd generation: Multidetector (MDCT)

type of scanning methid?

A

volumetric

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20
Q

what scanning method?

Scout topogram
Scanogram (e.g. leg length)

A

digital projection

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21
Q

what generation CT scanner has single detector, pencil-like X-ray beam, 25-30 min scan?

A

1st gen

22
Q

what generation CT scanner has up to 30 detectors, fan shape, >90 sec scan?

A

2nd gen

23
Q

what generation CT scanner 700->2000 detectors, fan-shaped beam, <5 sec scan?

A

3rd/4th

24
Q

what kind of CT uses Shorter time-less motion, Reconstruction in different slice widths, Increasing slices increases efficiency of X-ray beam use (4-slice-80%, 64 slice-97%), Reduced radiation dose, Tube current is automatically adjusted to patient size, Improved spatial resolution, Isotropic imaging, Better multiplanar recon and 3D?

A

MDCT

25
Q

what tissue type uses high frequency, endge enhanced?

A

Bone

26
Q

what tissue type uses low frequency, smoothing?

A

soft tissue

27
Q

what type of CT do Substances have different attenuation coefficients at different energies (K-edge)
New CT systems can acquire images at 2 different energies near simultaneously
Typically 80kVp and 140 kVp
Can distinguish iodine, Ca++ and UA crystals from ST?

A

dual energy CT

28
Q

what type of CT allows for 3-D weightbearing CT, uses cone-shaped X-ray beam
Reduced radiation dose
Standing or sitting
48 seconds for bilateral scan
Used in biomechanical evaluation, pre-op planning and post-op evaluation?

A

WB pedCT

29
Q

what type of CT is Fusion of CT and PET (positron emission tomography) using radioactive isotope of FDG (fluorodeoxyglucose)
PET provides tumor specificity
CT provides anatomic localization?

A

PET CT

30
Q

what CT artifact is inconsistency in a single measurement?

A

streaking

31
Q

what CT artifact is groups of views deviating gradually from true measurement?

A

shading

32
Q

what CT artifact are errors in individual detector calibration?

A

rings

33
Q

what CT artifacts are due to helical reconstruction?

A

distortion

34
Q

what origin of CT artifact are the following?

Beam hardening: Beam becomes “harder” (i.e. its mean energy increases) as it passes through the object because lower energy photons are absorbed more rapidly than high energy photons
Produces streaks and dark bands
Manufacturer correction: filtration, calibration, special software
Operator: tilt gantry, filter selection
Partial volume: off-center dense object protrudes into the beam path
Use thin acquisition width
Photon starvation
Undersampling

A

physics based

35
Q

what origin of CT artifact are the following?

Metallic materials: Severe streaking due to high density of metal
Manufacturers: interpolation techniques
Operator: remove jewelry etc.
Motion: misregistration artifact
Incomplete projection: parts of patient outside FOV degrade the image
Operator: patient positioning inside scanner
Manufacturers: large bore scanner (up to 70 cm)

A

patient based

36
Q

what type of artifact is More common in the skull due to thickness of calvarium?

A

Beam-hardening artifact

37
Q

what type of CT is used for Gout?

A

Dual energy

38
Q

what type of fracture?

A

Pylon

39
Q

?

A

OCD lesion

40
Q

PED CAT

A

3D weightbearing CT, for biomechanical,

41
Q

PED shows utility in

A

staging and classifying PT dysfunction and pes planus

42
Q

PET CT

A

tumor imaging, pet amd ct in one using FDG isotope

43
Q

Infications for foot ankle CT

A

Fx
surgical planning
Post op, healing comps or non unions
tarsal soalitions
cortical tumors
gout

44
Q

fx?

A

calc

45
Q

fx?

A

talar fx

46
Q
A

lisfranc

47
Q

??

A

tarsal coalition

48
Q
A

trauma with ST entrapment

49
Q
A

ST infection

50
Q
A

healing related complications

51
Q

wat is gantry

A

donut looking thing

Radiology (10 decks)

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