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202 MEDIMAGE > 17. Fluoroscopy and dynamic imaging > Flashcards

17. Fluoroscopy and dynamic imaging Flashcards

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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
what is the equation for the brightness (overall) gain
brightness gain = minification gain x flux gain
26
what is magnification
voltage to focusing electrodes is increased only e- from the central area of the input phosphor reaches the output
27
what is the equation for magnification factor
mag factor = full input diameter/selected input diameter
28
for a larger FOV describe the minification gain spatial resolution image distortion dose
larger FOV higher minification gain lower spatial disortion decreased dose
29
for a smaller FOV describe the minification gain spatial resolution image distortion dose
smaller FOV lower minification gain decreased spatial disortion increased dose
30
what is pincushion distortion
result of curved photocathode and inaccurate focusing of e- from the periphery
31
what is vignetting
loss in intensity between the centre of the image and the edge fewer light photons are collected at the edge
32
what is the cause of pincushion distortion
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
what is the cause of vignetting what consideration must be made in terms of vignetting
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
what is S distortion
distortions arising from external electromagnetic sources
35
what is the cause of S distortion
e- follow fields and results in curved path
36
what is veiling glare and what causes it
scattering of light and defocusing of e- around the image intensifier
37
what component of the machine is the digital detector similar to
image intensifier
38
what is an advantage of using digital flat detectors instead of image intensifiers
Single flat detector so can keep these much more compact rather than bulky IIs
39
what are the 5 advantages of flat panel detector in terms of image quality
improved detection efficiency (except at low exposure) improved uniformity no veiling glare no vignetting no image distortion
40
what are the 2 advantages of flat panel detector in terms of the detectors physical characteristics
physically smaller and lighter improved patient accessibility
41
what are the 2 types of fluoroscopy in terms of the frames
pulsed and continuous
42
how is dose reduced in fluoroscopy
lower frame rate frame averaging
43
what can frame averaging result in
temporal blurring
44
what is image hold and what does it do to the exposure
reduce exposure by displaying the last image
45
what is continuous fluoroscopy
x-ray exposure continues without interruption while the exposure is activated
46
how many frames of images are taken each second in continuous fluoroscopy
30fps
47
what happens to patient dose in continuous fluoroscopy
high dose recieved
48
what is pulse fluoroscopy
x-ray exposure isnt continuous and has gaps of no exposure between each image frame
49
what does pulse fluoroscopy do in terms of patient dose and patient motion
decreases dose reduce visibility of patient motion
50
for graphing the fps what is on the x and y axis in terms of pulsed/continuous fluoroscopy
mA on y axis and time on x axis
51
what is the time and mAs like for pulsed fluro
Higher mA and shorter time = pulsed can pick which images we want
52
is the area between pulsed and continuous fluro the same
Area between pulsed and continuous are the same
53
what happens to the dose if you reduce the number of frames per sec
reduces dose
54
what is digital subtraction angiography in terms of what it does
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
what are the 3 components involved in digital subtraction angiography
mask image post contrast image subtraction image
56
what is road mapping in DSA
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
what is pixel shifted in DSA
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
what is the cumulative air kerma measured in and the units
mGy
59
what is the cumulative air kerma what is it analogous to what effects does it involve
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
what is the kerma area product (dose area product) what is it proportional to
AK x Area proportional to stochastic (long term) risk
61
what is the unit of the kerma area product (dose area product)
mGy.cm^2 mGy.m^2
62
what is the cumulative fluoro time in terms of its unit and what its an indicator of
min very poor indicator of dose
63
what are 8 ways to effectively manage dose in fluor examinations
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
how does using automatic brightness control manage dose in fluro exams what is ABC
automatic adjustment of kV and mAs to maintain image brightness can be controlled to prioritise higher contrast or lower dose
65
time is controlled by what in fluoroscopy
pulse rate
66
mAs is controlled by what in fluoroscopy
AERC
67
how does minimising the use of magnification modes manage dose in fluro exams
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
how does collimating to the region of interest manage dose in fluro exams
minimises scatter to the tissues of interest decreases dose
69
how does minimising the use of spot fluorographs manage dose in fluro exams
acquiring the same pulse rates then get lots of dose to that particular tissue
70
how does spreading out the dose to skin manage dose in fluro exams
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
how does using the lowest appropriate frame rate manage dose in fluro exams
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
how does using lowest appropriate frame rate manage dose in fluro exams what is the one downside that might be present
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
how does using exploiting system geometry manage dose in fluro exams
keep detector close to patient, keep tube away operator needs to stand beside the detector, not by the x-ray tube
74
how does using reducing the dose to personnel manage dose in fluro exams
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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