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Instrumentation 2 > Fluoro 1 + 2 > Flashcards

Fluoro 1 + 2 Flashcards

1
Q

Purpose of input layer

A

Convert x-rays to e-

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2
Q

Purpose of electron lenses

A

focuses e-

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3
Q

Purpose of anode

A

to accelerate e-

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4
Q

Purpose of output layer

A

e- to visible light

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5
Q

How many light photons are given off per x ray in input phospher

A

2000-3000:1

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6
Q

Is the input phospher curved or flat?

A

curved

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7
Q

What is important about the scintillating phospher layers structure?

A

Thin spaces to channel light (improved spatial resolution)

and thick , dense material to absorb light.

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8
Q

What element is contained in the photocathode?

A

Antimony cesium oxide (Sb-CsO)

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9
Q

What is the conversion efficiency of Sb-CsO?

A

15-20% ( so 15 to 20 electrons are ejected from photocathode for every 100 light photons.)

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10
Q

What does the black paint on Output window stop?

A

veiling glare …. this is when light photons bounce around the output window , off axis and reduce image contrast.

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11
Q

Ration of e- to light photons at output window?

A

1:1000

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12
Q

What is an optical distributor?

A

acts to convert the small image on the output image to a video image.

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13
Q

What is CCD and CMOS?

A

Optical distributors that give a continuous readout of fluoroscopic images at 30 FPS

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14
Q

minification gain

A

: in which a given number of light photons

emanates from a smaller area

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15
Q

flux gain

A

where electrons accelerated by high voltages produce

more light as they strike a fluorescent screen.

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16
Q

brightness gain

A

ratio of brightness between output screen of II and brightness of the standard screen.

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17
Q

What is the overall brightness gain range?

A

2500 - 7000

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18
Q

What creaates the gain in brightness

A

flux x minification

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19
Q

The number of light photons created in the output is dependent on?

A

The energy of the e- .

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20
Q

What is a typical flux gain value?

A

at least 50

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21
Q

Minification gain equation

A

(di/do) squared

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22
Q

What should the constant tube potential be when measuring conversion factor?

A

85 kvp

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23
Q

What are the 4 main artefacts in the Image intesifier?

A

Veiling glare

Pincushioning

vignetting

S distortion

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24
Q

What causes pin cushioning?

A

Curved input screen , curving the image on the output due to bending of electrons

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25
Q

What causes vignetting?

A

Brighter centre and dimmer periphery

occurs due to reduced exposure at periphery of input and reduced precision of e- hitting periphery at output.

26
Q

What is S distortion?

A

SPATIAL WARPING OF IMAGE and caused by STRAY MAGNETIC FIELDS

27
Q

What does a flat panel detecor have over a II?

A

TFT

28
Q

when is the Ma and the Kv able to be changed by the AERC

A

Continuous mode

29
Q

What is the purpose of the AERC?

A

To keep the SNR constant

30
Q

Is it better to have a wider or narrow dynamic range?

A

Wider such as when using a flat panel detector.

31
Q

What is typical spatial resolution capabilities of the fluoro system is in the range of?

A

4-6 Lp/mm

32
Q

Why doesnt the rad change exposure settings when in magnification mode?

A

The AERC does it itself.

33
Q

What is Interrogation time?

A

is the time required for the tube to be

switched on and reach the required kVp and mA

34
Q

What is the exctinction time?

A

is the time required for the tube to be switch

off

35
Q

What is. the interrogation and extinction times of digital fluoro

A

less than 1ms

36
Q

What inch II is used for cardiac imaging?

A

typically, 9 inch.

37
Q

What adjusts in magnification mode?

A

collimater to make a smaller FOV on the input … less divergence. .. more focusing

38
Q

Why is the AERC important for magnifcation mode?

A

as FOV on input decreases (increased mag) the brightness gain also decreases.. meaning we need to compensate by increasing exposure.

39
Q

Purpose of frame averaging

A

To lower temporal resolution (fluoro has this in abundance) to decrease noise….

Will create a less noisy image but MORE LAG.

40
Q

Can frame averaging lower dose?

A

Yes.

41
Q

What will a decrease in temporal resolution cause?

A

increased lag

42
Q

What is road-mapping?

A

Software enhanced last frame hold.

can be done on dual monitor.. one with the still and one with the live feed.

or

overlay

43
Q

what is roadmapping good for?

A

catheter implantations

44
Q

Typical fluoro spatial res?

A

3-5 cycles/mm … 4-6 lp/mm

45
Q

what limits spatial res in fluoro?

A

Video camera

matrix sampling size across FOV

inability to focus elctrodes

res of input and output fluoro screens

46
Q

What lowers spatial res outside the II

A

Scattered x-rays

Patient movement

potential fluctuations

47
Q

is contrast better or worse in fluoro when compared to general xray?

A

worse.

It has a LOW SNR

48
Q

how can you increase contrast res in fluoro?

A

increase Mas

49
Q

What causes blurring in temporal resolution

A

movement in time domain

50
Q

Why are video cameras the weakest area of fluoro unit

A

they have high lag. and create the most lag in the entire fluro unit

51
Q

what time does human eye create lag at

A

0.2 seconds

52
Q

The radiation dose depends on the:

A

 type of examination,
 patient size,
 equipment, the technique,

53
Q

 The performance of the fluoroscopy system with respect

to radiation dose is best characterized by:

A

 Receptor entrance exposure

 Skin entrance exposure rates.

54
Q

The receptor entrance exposure rate is:

A

 the most important dose performance parameter.
 measures the effective “speed” of the imaging system, that is, the
amount of radiation used in image formation.
 critical because
 skin dose is dependent on and increases with increasing receptor entrance exposure
 because the level of image noise, and thus the perceptibility of lowcontrast detail, is also dependent on it.
 normally specified as the entrance exposure at the surface of the image receptor (with the grid removed) required to produce a
single image for a given x-ray spectrum.

55
Q

Skin Dose

A

This measurement, quantifies the dose at the beam
entrance surface to a patient-simulating medium on a
fluoroscopy system.

56
Q

TO get a realistic measurement of patient dose that is it importnant to meausre?

A

average skin entrance exposure

57
Q

What is the DAP

A

Dose area product meter

Indirect and widely used method of monitoring dose.

58
Q

Skin doses may be reduced by using:

A 
intermittent exposures,
 grid removal,
 last image hold,
 dose spreading,
 beam filtration,
 pulsed fluoroscopy,
59
Q

Why can a higher quality beam reduce dose in fluoro

A

more chance of transmission over absorption

60
Q

 There are two basic ways to magnify the image in

fluoroscopy:

A

 Geometric: Using divering beam by changing FFD or OID… can lead to higher dose if patient is moved closer to tube… closer to tube = more mag bbut more dose.
 Electronic:

61
Q

What are dose level settings?

A

Built in exposures that give differnt doses.. low, med and high.

low dose = lower SNR. (more noise)

High dose = Increased SNR

Instrumentation 2 (4 decks)

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