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Imaging > Fundamentals of CT-Midterm > Flashcards

Fundamentals of CT-Midterm Flashcards

1
Q

what is the axial CT

A

it is feet up so looking through the body in circular slices

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2
Q

what is a coronal CT

A

it is one where you see the outline of the front of the body and pass through it

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3
Q

what is a saggital CT

A

it is from the side and seeing through that direction

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4
Q

name the CT planes

A

sagital, coronal, axial

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5
Q

what plane is a chest Xray

A

coronnal

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6
Q

is CT spatial resolution better or worse than xray

A

CT has a ten times reduction in spatial resolution

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7
Q

is CT contrast resolution better or worse than xray

A

CT has increased contrast resolution

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8
Q

why does CT have increased contrast resolution

A

decreased scatter because of scatter rejection, detectors have higher signal to noise ratios and linear response over wide dynamic range. \
CT does not have overlapping anatomy as well

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9
Q

what is radon transform

A

it is mathmatical reconstruction of internal structure from multiple external projections.

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10
Q

what is Cormack contribution to CT

A

created a calculation from radiation transmission

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11
Q

where was the first CT scanner

A

London

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12
Q

what is the EMI mark 1 scanner

A

it is the first CT scanner at Mayupo. It rotated around the patient and the x-ray tube would go across one degree at a time which created six images

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13
Q

as CT improves, what is the general thing that is changing

A

it is getting more contrast and it is faster so better resolution and better contrast

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14
Q

what are the basics of CT

A

x-ray tubes comes out in thin spaces then absorbs the dose by detector and spins so lots of x-rays at different angles

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15
Q

what is the width of a CT detector in real life

A

it is everything with magnification and focal spot stays the same

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16
Q

what is a voxel

A

it is a pixel with volume

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17
Q

which is the pair of materials with constant CT number values for different X-ray tube voltages

A

air and water

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18
Q

what is CT number and the formula

A

CT (u-uwater)/uwater x1000»»> it is hounsfeld units. Normalize for water so that it is equal to zero. Scale it to make it more readable. EMI=500 sealing, but 1000 now.

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19
Q

what is the CT number for air

A

-1000

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20
Q

what is the CT number range

A

tissue/material is the basis

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21
Q

if the CT number is negative what does it mean

A

its probably fat

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22
Q

what is a CT number for bone

A

1000

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23
Q

what would be a good estimate for liver

A

142

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24
Q

what is window width

A

of CT number mapped to total number of shades of grey which are 64 overall.

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25
Q

display window level

A

CT number in the center of the window

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26
Q

Display window what do you do to optimize it

A

wide window, so full range (all numbers) but if want more detail, map narrower range (whatever is too high to get the most ranges)

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27
Q

what is the interaction in CT for bone and oter

A

it is photoelectric effect and compton scattering

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28
Q

What does Compton do during CT

A

:it is based on density effect: electrons/volume

29
Q

what does photoelectric effect do for CT

A

strong Z and E effects formula is Z3/E3

30
Q

draw an x-ray spectra for CT

A

draw it

31
Q

what filter is used for CT

A

titanium and aluminum filter so it absorbs lower energy x-rays

32
Q

what anode is used for CT

A

tungsten

33
Q

CT signal reflects differences in rho, rho e, and Z

A

chart off page 11

34
Q

which generation of CT has made it

A

Generation III

35
Q

what does the electron beam CT do

A

electron beam swept around tungsten ring so super fast

36
Q

what is fifth generation used for

A

built for cardiac imaging. Could get through jore area faster. Fundamental dose is insufficient it is fifth generation CT

37
Q

what is the single slice axial scan

A

the table moves, it is step and shoot, it spins around the patient then moves and then does it again. The cables were the limitation at this point. Volume coverage was very slow

38
Q

what is a helical scan

A

it added the slippage technique where the signal could hop across the tube so it can move around the patient better. It is continuous spin while there is the patient moving. Uniform longitudinal sampling density, arbitrary slice thickness for reconstruction

39
Q

what is the difference between single slice and multi slice

A

single slice is the patient moving through the plane spiral path. and multislice is more coverage per rotation so thinner slices and shorter scan times. More detectors and less gaps between the data points

40
Q

what is dual source CT

A

it has double sources so that you dont have to make a wider beam

41
Q

cone beam CT is

A

it is more for ENT and dental and innervention. It is slower rotation time and inferior image quality as compared to diagnositic CT.

42
Q

what are the components of a CT scanner

A

tube, generator, collimators, filters, detectors, data aquisition system, gantry and slip ring, p[atient table and alignment lights operator console, image reconstruction system

43
Q

what is differnt about the x0-ray tube

A

it is higher generator power, higher anode heat capacity, faster spin so makes more electrons overall, the anode and cathode are parallel to xz-axis to prevent heal effect. Nomal focal spot, and the tube has a life of 200,000 exoisure

44
Q

what is the collimation for the CT

A

there are pre-patient collimator- so there is beam shaping and reduces dose, adn there is post patient colimators for the scatter rejection

45
Q

what is a bowtie filter

A

it is shaped to get less patient dose on teh sides, but it can crack leading to artifact

46
Q

what type of detector is used in CT

A

it is a scintillator with titanium scintilates light and light stays and localits hit in between reflextors. Light hits the phtoelectrode to create electrons for the electronic signal

47
Q

what is the energy integrating detector

A

higher energy of phton leaves a higher enery of signal. Iodine is used a lot but it can swamp lowe energy leading to missed information

48
Q

what is the effect of detector apperature

A

digital detector has width of a and under sample necause it is not sampling two its a width so it roolls it off to prevent aliasing?

49
Q

flying focxal spot and how it is used

A

it has lots of asliasing so it wobbles so the flying focal spot helps to fit it into the Nyquist criteia

50
Q

what does flying focal spot do

A

it increases sampling

51
Q

what effects data aquisition system performance

A

it is influence by dark current. signal cross talk, linearity, electronic noise, dynamic range, thermal stability, and quantization accuracy

52
Q

what is dark current

A

it is signal residue when there’s no light so interferes with low current

53
Q

slip ing is what

A

eliminates need to rewind the gantry. Mandatory for helial aquisition of data. Passes detector data to the computer

54
Q

gantry is what

A

it is the spinner. It spinds fast and one rotation in a quarter of a second. Acquires quickly

55
Q

patient table weight limit

A

400-600 pound weight limit

56
Q

image reconstruction what is it

A

it is a parallel processing sys

57
Q

what are the functions of image reconstruction

A

it is pre-processing (calibration, data correction), image reconstruction, and some post processing. THere is parallel computing, iterative reconstruction requires more computational power

58
Q

what are the things in a CT scanner that can both improve image quality adn reduce dose

A

bow tie filter and Al/Cu filter

59
Q

what is topogram or scout image

A

tube stays and point moves so that can figure out where to go

60
Q

scan more that is axial

A

it is sequential and step and shoot

61
Q

what is cine scanning is

A

continuous scanning that is axial with no table movement

62
Q

can you choose different slice widths for this

A

yes

63
Q

what is the formula for pitch

A

it is pitch=table translation per rotation/deterction colimation

64
Q

what is pitch

A

space between slices

65
Q

effetve mAs

A

mAs/pitch

66
Q

image thickness is

A

nominal width o fimage secotion sensitivit yprofile: line spread function

67
Q

patial volume

A

get by with no increase dose but better images is that softness of edge is ebcause image changes slightly in the z diretion

68
Q

what happens with slimmer slices

A

more noisey but better resolution

69
Q

what happens with thicker slices

A

it is less noisey- it is for general imaging better.

Imaging (19 decks)

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