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202 MEDIMAGE > 17. Fluoroscopy and dynamic imaging > Flashcards

17. Fluoroscopy and dynamic imaging Flashcards

1
Q

in fluoroscopy images the denser tissues appear ___

what kind of image does fluoroscopy produce

A

darker

reverse contrast type image

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2
Q

for radiography how would you describe the xray burst and how many images are taken

when is the image viewed

A

single x-ray burst

single image taken with one exposure

viewed after acquisition

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3
Q

for radiography what is the current and is image intensification required

A

high current (mA)

image intensity sufficient, dont need intensification

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4
Q

for fluoroscopy how would you describe the xray burst and how many images are taken

when is the image viewed

A

continuous x-ray beam

multiple images

real time image viewing

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5
Q

for fluoroscopy what is the current and is image intensification required

A

low current (mA)

image intensification needed

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6
Q

what are the 4 components of the fluoroscopy machine in the arm portion

A

CCD

ABC sensor

Image intensifier

Antiscatter grid

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7
Q

what are the 4 components of the fluoroscopy machine in the portion under the patient

A

KAP meter

collimator

filters

x-ray tube

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8
Q

what does the image intensifier in the fluoroscopy machine do

A

intensifies the exposure and increases the number of photons

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9
Q

what are the 5 components of the image intensifier

A

input phosphor

photocathode

electrostatic focusing lenses (focusing electrodes)

anode

output phosphor

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10
Q

in the image intensifier what interacts with the input phosphor and what occurs

A

exit radiation from the anatomic area of interest interacts with the input phosphor for conversion to visible light

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11
Q

what occurs at the photocathode in the image intensifier

A

light intensities from the input phosphor are equal to the intensities of the exit radiation and are converted to e- by the photocathode

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12
Q

what is the name of the process at the photocathode in the image intensifier

A

photoemission

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13
Q

what happens at the electrostatic focusing lenses in the image intensifier

A

e- are focused and accelerated towards an anode

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14
Q

what occurs at the output phosphor in the image intensifier

A

e- are accelerated towards an anode to strike the output phosphor to create a brighter image

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15
Q

what is the input phosphor made of

A

Cesium iodide

CsI

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16
Q

what is the structure of the materials in the input phosphor

how does the structure relate to its function

A

CsI has column structure and means incoming x-rays are directed towards cathode and produces e- at specific locations minimizing scatter, improves image quality

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17
Q

what is the purpose of optical coupling

A

focuses the light from the output phosphor onto the CCD

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18
Q

what is the CCD

A

charge coupled device camera

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19
Q

what is the purpose of the CCD

A

receives the light photons from the output phosphor

incident light photons cause e- to be released and

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20
Q

the number of e- produced by the CCD is proportional to what

A

the number of e- is proportional to the intensity of light

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21
Q

what is flux gain

A

accelerating e- increases the light intensity at the output

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22
Q

what is the equation for flux gain

A

flux gain = number of output light photons/number of input x-ray photons

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23
Q

what is minification gain

A

e- incident on a smaller area increases light intensity

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24
Q

what is the equation for minification gain

A

area of input phosphor/area of output phosphor = di^2/do^2

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25
Q

what is the equation for the brightness (overall) gain

A

brightness gain = minification gain x flux gain

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26
Q

what is magnification

A

voltage to focusing electrodes is increased

only e- from the central area of the input phosphor reaches the output

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27
Q

what is the equation for magnification factor

A

mag factor = full input diameter/selected input diameter

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28
Q

for a larger FOV describe the

minification gain

spatial resolution

image distortion

dose

A

larger FOV

higher minification gain

lower spatial disortion

decreased dose

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29
Q

for a smaller FOV describe the

minification gain

spatial resolution

image distortion

dose

A

smaller FOV

lower minification gain

decreased spatial disortion

increased dose

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30
Q

what is pincushion distortion

A

result of curved photocathode and inaccurate focusing of e- from the periphery

31
Q

what is vignetting

A

loss in intensity between the centre of the image and the edge

fewer light photons are collected at the edge

32
Q

what is the cause of pincushion distortion

A

Image intensifiers are round

Test phantom with straight gridlines but gets curves towards the edges = pin cushion distortion

Photocathode is curve and reflects on flat output phosphor and gets worse towards the edges

33
Q

what is the cause of vignetting

what consideration must be made in terms of vignetting

A

Result of fact that edges have fewer light photons on the edges

make sure tissues of interest are close to the centre rather than the periphery

34
Q

what is S distortion

A

distortions arising from external electromagnetic sources

35
Q

what is the cause of S distortion

A

e- follow fields and results in curved path

36
Q

what is veiling glare and what causes it

A

scattering of light and defocusing of e- around the image intensifier

37
Q

what component of the machine is the digital detector similar to

A

image intensifier

38
Q

what is an advantage of using digital flat detectors instead of image intensifiers

A

Single flat detector so can keep these much more compact rather than bulky IIs

39
Q

what are the 5 advantages of flat panel detector in terms of image quality

A

improved detection efficiency (except at low exposure)

improved uniformity

no veiling glare

no vignetting

no image distortion

40
Q

what are the 2 advantages of flat panel detector in terms of the detectors physical characteristics

A

physically smaller and lighter

improved patient accessibility

41
Q

what are the 2 types of fluoroscopy in terms of the frames

A

pulsed and continuous

42
Q

how is dose reduced in fluoroscopy

A

lower frame rate

frame averaging

43
Q

what can frame averaging result in

A

temporal blurring

44
Q

what is image hold and what does it do to the exposure

A

reduce exposure by displaying the last image

45
Q

what is continuous fluoroscopy

A

x-ray exposure continues without interruption while the exposure is activated

46
Q

how many frames of images are taken each second in continuous fluoroscopy

A

30fps

47
Q

what happens to patient dose in continuous fluoroscopy

A

high dose recieved

48
Q

what is pulse fluoroscopy

A

x-ray exposure isnt continuous and has gaps of no exposure between each image frame

49
Q

what does pulse fluoroscopy do in terms of patient dose and patient motion

A

decreases dose

reduce visibility of patient motion

50
Q

for graphing the fps what is on the x and y axis in terms of pulsed/continuous fluoroscopy

A

mA on y axis and time on x axis

51
Q

what is the time and mAs like for pulsed fluro

A

Higher mA and shorter time = pulsed

can pick which images we want

52
Q

is the area between pulsed and continuous fluro the same

A

Area between pulsed and continuous are the same

53
Q

what happens to the dose if you reduce the number of frames per sec

A

reduces dose

54
Q

what is digital subtraction angiography in terms of what it does

A

increases visibility of contrast enhanced vessels by removing other anatomy from the image

Take image before contrast agent is applied (mask) just image of anatomy. Inject contrast agent that changes the opacity of vessels. Using baseline mask can subtract away anatomy to just see contrast anatomy

55
Q

what are the 3 components involved in digital subtraction angiography

A

mask image

post contrast image

subtraction image

56
Q

what is road mapping in DSA

A

use the image at peak opacification as the mask for subtraction in subsequent frames

vasculature appears as a map to guide the procedure

Take initial image to take info about vascular anatomy. Inject contrast agent that changes opacity of vessels so end up with bottom right image where vessels are clear. After a while the contrast washes through and wont hold for very long so want to use this as the reference as shows where the vessels are. End up seeing where vasculature is and is useful for guidelines in vessels

Peak opacification = vessels most bright

57
Q

what is pixel shifted in DSA

A

shift an existing mask in post-processing to account for translational movement relative to the acquired mask

minimises the need for an additional exposure to acquire a new mask

Rather than taking map again and giving more dose you could use digital images to shift a few pixels to get better alignment so you can continue w/out another mask exposure

58
Q

what is the cumulative air kerma measured in and the units

A

mGy

59
Q

what is the cumulative air kerma

what is it analogous to

what effects does it involve

A

kinetic energy released in matter/air

like exposure

deterministic effects (skin)

How much energy is transferred to charged particle in tissue, measure of deterministic effect, exposed too long may damage skin

60
Q

what is the kerma area product (dose area product)

what is it proportional to

A

AK x Area

proportional to stochastic (long term) risk

61
Q

what is the unit of the kerma area product (dose area product)

A

mGy.cm^2

mGy.m^2

62
Q

what is the cumulative fluoro time in terms of its unit and what its an indicator of

A

min

very poor indicator of dose

63
Q

what are 8 ways to effectively manage dose in fluor examinations

A

use ABC

minimise use of magnification modes

collimate to region of interest

minimise use of spot flurographs

spread out dose to skin

use lowest appropriate frame rate

use lowest appropriate frame rate

exploit system geometry

reduce dose to personnel

64
Q

how does using automatic brightness control manage dose in fluro exams

what is ABC

A

automatic adjustment of kV and mAs to maintain image brightness

can be controlled to prioritise higher contrast or lower dose

65
Q

time is controlled by what in fluoroscopy

A

pulse rate

66
Q

mAs is controlled by what in fluoroscopy

A

AERC

67
Q

how does minimising the use of magnification modes manage dose in fluro exams

A

avoiding geometric magnification as the dose rate is proportional to (mag factor)^2.

use digital zoom instead

Magnification increases dose and as we change the magnification the patient may get moved closer to the tube to achieve magnification so increases dose

68
Q

how does collimating to the region of interest manage dose in fluro exams

A

minimises scatter to the tissues of interest

decreases dose

69
Q

how does minimising the use of spot fluorographs manage dose in fluro exams

A

acquiring the same pulse rates then get lots of dose to that particular tissue

70
Q

how does spreading out the dose to skin manage dose in fluro exams

A

Xray tube in one location, run risk of deterministic effects

Minimise long exposure to single site, move x ray tube

Changing the tube angle and tube position spreads out dose to skin

71
Q

how does using the lowest appropriate frame rate manage dose in fluro exams

A

minimise the beam-on time

use fluoro only to observe motion or positioning and use shorter pulse lengths to reduce blur

Reduce pulse length either the mAs needs to increase or the image quality per image decreases

72
Q

how does using lowest appropriate frame rate manage dose in fluro exams

what is the one downside that might be present

A

shifting the window of averaged frames reduces noise

Rather than using each single image, combine images together and average them to get higher image quality. Appearance of larger pulse rate image

Improve image quality at expense of lag and temporal resolution

73
Q

how does using exploiting system geometry manage dose in fluro exams

A

keep detector close to patient, keep tube away

operator needs to stand beside the detector, not by the x-ray tube

74
Q

how does using reducing the dose to personnel manage dose in fluro exams

A

wear appropriate protective equipment and clothing and maximise distance from the x-ray source

monitor cumulative radiation dose

202 MEDIMAGE (18 decks)

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