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Week 1 Flashcards

(84 cards)

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1
Q

Primary functions of fluoroscopy

A
  • live display of anatomy
  • dynamic motion / process
  • interventional procedures
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2
Q

Differences between plain radiography & fluoroscopy

A

SNR: good in radiography but poor in fluoroscopy

Temporal resolution: poor in radiography but good in fluoroscopy

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3
Q

Although fluoroscopy provides excellent temporal resolution, images are ___

A

Noisy

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4
Q

How does one compromise temporal resolution to lower image noise?

A
  • real time averaging in computer memory for display
  • noticeable image lag but can reduce noise
  • reduce dose in some cases
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5
Q

LIH

A

Last image hold

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6
Q

Where is the II when in AP position

A

II directly over patient

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7
Q

Where is II in RAO / LAO

A

RAO: right side of patient
LAO: left side of patient

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8
Q

Which systems are used for DSA

A
  • floor mounted
  • ceiling mounted
  • biplane
  • robotic C-arm
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9
Q

What are the major components of conventional fluoroscopy equipment

A
  • high voltage generator
  • x-ray tub
  • II
  • viewing system
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10
Q

Fundamental components of II includes:

A
  • vacuum enclosure
  • input phosphor layer
  • photocathode
  • series of electronic electrodes
  • output phosphor
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11
Q

Purpose of output phosphor

A

Converts accelerated e- back to visible light

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12
Q

Input phosphor is usually made of __ crystals which are grown in ___ to prevent ___

A

Cesium Iodide; dense needle like structure; lateral light spread

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13
Q

Purpose of photocathode is __

A

To convert light photons to e- with 10-20% efficiency

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14
Q

Anode is a very thin coating of ___ on ___ which is electrically conducive to___ once they deposit energy into phosphor

A

Aluminium; vacuum side of output phosphor; carry away e-

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15
Q

Output phosphor is made of __

A

Thin powdered phosphor (zinc cadmium sulphide)

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16
Q

Thin layer of Al backing is used to __

A

Prevent light from output phosphor travelling backwards to photocathode

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17
Q

Minification gain formula

A

Input diameter^2 / output diameter^2

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18
Q

Brightness gain formula

A

BG = electronic gain x minification gain

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19
Q

Brightness gain ranges from ____ in real clinical practice

A

2500 - 7000

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20
Q

Geometric magnification is achieved by ____

A

Selecting smaller central portion of input phosphor to project onto output phosphor

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21
Q

Magnified images results in more ___ & reduced ___ but these an be corrected by ___

A

noise; SNR; increasing IAKR

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22
Q

IAKR

A

Incident air karma rate

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23
Q

FOV specifies the size of ___ of II

A

Input phosphor

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24
Q

When image is more magnified, brightness gain __

A

Decreases & x-ray exposure rate must increase to compensate

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25
Disadvantages of magnification technique
- decreased minification gain means higher mAs must be used to maintain image brightness = higher dose - lower FOV
26
What happens when a larger FOV is utilized?
- minification gain increases - lower output spatial res - more image distortion - lower radiation dose
27
What happens when a larger FOV is utilized?
- lower minification gain - higher output spatial res - lower image distortions - higher dose
28
In FPDs, magnification is done by __
Digitally enlarging the display which causes slight loss of resolution since smaller number of pixels used in smaller FOV
29
In FPDs, since magnification by enlargement does not result in more dose, what can the radiographer do to reduce dose
Cone down
30
Automatic brightness control is used to prevent __
Fluctuations in image brightness & SNR
31
What are the major parts in optical systems
Collimating lens, aperture, focusing lens
32
What is collimating lens used for
Shapes divergent light from output phosphor
33
What is aperture used for
Limits amount of light reaching video camera
34
What are the focusing lens used for
Focuses image onto video & cine camera
35
What does the optics camera system do
Captures & converts light photons into analogue electrical signals
36
Video cameras conform to __
TV / Monitor display requirement
37
Cine camera conforms to __
Recognised video format
38
Which old TV camera was best for cardiology
PLUMBICON TV camera which has lower image lag but higher quantum noise
39
CCD
Charged coupled device
40
CCDs function
Photosensitive silicon chips that convert light into digital video image
41
Advantages of CCDs
- no artifacts, image lag, maintenance, warm up - lower dose - linear response for DSA - greater sensitivity to light & higher DQE - lower electric noise = higher SNR & contrast
42
How does II digital fluoro work
Analogue signal > ADC > microprocessor circuit > image Feed image from TV camera to monitor for immediate viewing
43
How does FPD digital fluoro work
Feed images directly into image processor Pixel rows in AMA switched continuously to allow continuous updating of image to obtain live images
44
Difference between monochrome grey scale images & bi-stable images
Monochrome = each pixel produces varying degree of grey tones Bi-stable = either black or white
45
Monitor scan display modes
- continuous fluoro - pulsed interlaced - pulsed progressive scan - slow scan
46
How is continuous fluoroscopy mode shown
Continuous fluoro at low mA value (< 5mA) 20 - 30 fps but quantum mottle & noise present
47
How is Pulsed Interlaced Scan mode shown
Short high intensity x-rays at 1/s which reduces quantum mottle, noise & dose
48
How is pulsed progressive scan mode shown
Pulsed x-ray but monitor scans lines in natural order instead of interlaced which reduces image flicker & improves resolution but needs 1023 line monitor
49
How is slow scan mode shown
Doubled image resolution since 7.5, 1050 line frames scanned per second
50
Advantages of digital fluoro
- LIH - Road Mapping - Digital temporal filtering - image enhancement - image restoration
51
How does image restoration work
Corrects distortion & vignetting in II
52
How does image enhancement work
Manipulates contrast (WW) & brightness (WL)
53
How does LIH work
Allows last image in com memory to be displayed on the monitor even when X-ray is off
54
How does road mapping work
Allows an image to be captured & displayed, and live image to be shown simultaneously. Also allows overlapping of image with contrast onto live image
55
How does digital temporal filtering work
Add different pixel values & averages them to reduce quantum noise but increases image lag due to lower fps
56
Read-out rate
Rate at which entire flat panel array is sampled & displayed
57
Pixel element size
Smaller pixels = higher spatial resolution
58
Pixel fill factor
% of any area in pixel that is involved in converting x-ray to image
59
Pros of II
Lower noise / IAKR = higher SNR
60
Cons of II
Bulky & risk of image distortions
61
Pros of FPD
- less bulky - no image distortions - CBCT applications
62
Cons of FPDs
High electronic noise at low noise level range compared to II
63
Difference between fluoro & angio
Fluoro is live video image of organs but angio is static image of insides of blood vessels
64
5 factors that affect image quality
Contrast, noise, sharpness, distortion, temporal resolution
65
How can contrast be improved in fluoro
- radiopaque markers - exogenous contrast agents - higher exposure
66
What is used to maintain patient dose at acceptable level
Low incident air Kerma rate
67
II noise is characterized by __
Additive electronic noise which are fluctuations in external electric sources
68
CCD type FPD noise is characterized by
Readnoise which is all the noise generated by system components
69
Sharpness in II is influenced by
- display matrix (CRT) - FSS - noise - motion - FOV
70
Sharpness in FPD is influenced by __
- display matrix - FSS - image noise - motion - pixel size
71
What are the different artifacts encountered when using CRT TV monitors
- veiling glare - vignetting - blooming - pincushion distortion - S distortion
72
What is veiling glare
Stray light that fogs images & reduces image contrast
73
What are sources of stray light in II that causes veiling glare
Light photons within glass output window & electrons within electron optical system
74
What are the solutions to veiling glare artifacts
- thick II output window which has dopants to absorb scattered light & sides coated with light absorbing material - optical coupling system replaced by direct fiber optic linkage
75
What is vignetting
Image brightness reduces towards peripheral compared to Center
76
Causes of vignetting are ___
TV camera deterioration
77
What are the short term solutions to vignetting
Restrict aperture size of video camera as larger = blurrier
78
What are blooming artifacts
Signal input exceeds dynamic range resulting in diffused image & intense signals causes lateral charge spread within camera target
79
What are pincushion distortions
In II, electrons exist form photocathode is focused by electronic lens which requires input screen to be curved surface and results in unavoidable artifact
80
What is S distortion
Straight line appears curved on CRT monitor
81
What causes S distortion
Presence of external magnetic filed such as nearby MRI & earth
82
What is the solution to S distortion
Proper site planning & encasing II in highly magnetic susceptibility metal casing
83
Blurring in time domain is called __
Image lag
84
What are the solutions to lag
- disable frame averaging but causes lower contrast - replace vidicon TV camera with ones with low lag performance

Fluoro (5 decks)

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