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RTE1457 Rad Tech 2 > Unit 4: Image Brightness/ABC/Mag. and Fluoro + Pt Exposure and AEC > Flashcards

Unit 4: Image Brightness/ABC/Mag. and Fluoro + Pt Exposure and AEC Flashcards

1
Q

what is flux gain?

A

a ratio of the number of light photons produced at the OP screen to the number of x-rays absorbed by the IP screen

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2
Q

what is the formula for flux gain?

A

numberof output light photons/number of input x-ray photons

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3
Q

what is minification gain?

A

the ratio of the square of the IP screen diameter to the square of the OP screen diameter

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4
Q

What is the formula for minification gain?

A

(Di/Do)^2

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5
Q

OP screen diameter is usually:

IP screen diameter varies from:

A

1 inch (2.5 cm)

9-25 or 30 cm

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6
Q

what determines how much brighter an image will be at the OP screen?

A

minification gain

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7
Q

what is brightness gain?

A

the ability of an II tube to increase the illumination of an image

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8
Q

brightness gain =

A

minification gain x flux gain

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9
Q

the brightness gain of most II tubes is:

A

5000 - 30,000

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10
Q

brightness gain is now called _________________ and is measured in _______________.

A

Conversion Factor

candela per squared meter (cd/m^2)

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11
Q

What is Automatic Brightness Control (ABC)?

A

brightness controlled by and altered by the machine varying the kVp, mA, or both

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12
Q

ABC is designed to compensate for changes in what?

A

tissue density

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13
Q

what is the purpose of ABC?

A

to maintain image brightness on the display monitor

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14
Q

For a fluoro system equipped with ABC mechanism and where the x-ray tube is fixes below the table, moving the image intensifier away from the pt will:

A

increase pt dose

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15
Q

The function of an ABC mechanism of an image intensified fluoro system is to:

A

maintain a fixed dose rate to the image intensifier

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16
Q

the greater the voltage supplied to the electrostatic lenses, the greater the ____________ and closer the ______ ______ moves toward the IP screen. This causes ______________.

A

acceleration; focal point; magnification

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17
Q

image magnification during fluoro is controlled by:

A

varying the voltage on the electrostatic lenses

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18
Q

Which of the following will occur if voltage to the electrostatic lenses increase?

A

magnification

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19
Q

viewing the fluoroscopic image in magnification mode increases:

A

mA
spatial resolution
pt dose

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20
Q

what determines the location of the focal point and the FOV?

A

IP screen diameter

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21
Q

what are advantages of fluoro mag mode?

A

better spatial resolution
less image noise
less vignetting

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22
Q

what are disadvantages of fluoro mag mode?

A

increased pt dose
reduced FOV

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23
Q

what is the weakest link in the fluoro imaging chain?

A

monitor

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24
Q

what increases during mag?

A

MTF

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25
Q

image blur caused by moving the tube rapidly during a fluoro exam is due to:

A

camera tube lag

26
Q

collimation, intermittent exposure, removal of grid, LIH, dose spreading, beam hardening, pulsed exposure, and cumulative timer are all:

A

dose reduction techniques in fluoro

27
Q

last image hold is a:

A

dose-saving feature

28
Q

what is dose spread?

A

method that spreads the max dose over a broader area of the pt’s skin

29
Q

some reduction of max skin dose can be achieved by rotating the fluoroscope about a ____________ within the anatomy of interest.

A

centimeter

30
Q

during dose spread, the angle is changed to:

A

expose different tissue

31
Q

increasing kVp will create a:

A

harder beam

32
Q

maintaining the highest kVp that will provide acceptable image contrast leads to:

A

lower skin dose

33
Q

beam energy primarily depends on the _____ selected and the amount of _________ in the beam

A

kVp; filtration

34
Q

for beam hardening, you need to:

A

increase kVp and lower mA

35
Q

filtration reduces:

A

skin dose

36
Q

how much did an addition of 0.1-0.3 mm of copper reduce skin dose?

A

30-50%

37
Q

size distortion is primarily caused by _____ during fluoro.

A

OID

38
Q

to have the lowest dose to the pt, have the IR:

A

right on top of the pt

39
Q

What is a consequence of using “low dose” during fluoroscopy?

A

quantum mottle

40
Q

during fluoro, which will produce the greatest amount of scatter?

A

patient

41
Q

in the non-mobile fluoro unit, the x-ray tube moves with the:

A

image intensifier

42
Q

The back-up timer is typically set at

A

5 mins

43
Q

before continuation of fluoro what should be done if the timer goes off?

A

timer should be reset

44
Q

AEC stands for:

A

automatic exposure control

45
Q

modern equipment uses ionization chambers introduced by _________________ in _____

A

Russell H. Morgan; 1942

46
Q

Where are AEC detectors located?

A

in between the pt and IR

47
Q

what is crucial when it comes to AECs and ionization chambers?

A

positioning

48
Q

plastic inserts for collimators are only accurate at:

A

the intended SID

49
Q

collimation should be avoided when located:

A

close to activated chambers

50
Q

Collimating within the field of an AEC receptor will result in?

A

overexposure

51
Q

inadequate collimation may result in:

A

light image

52
Q

what is the max exposure per US Public Law?

A

mAs

53
Q

modern minimum reaction time to terminate exposure in AEC:

A

.001 seconds

54
Q

for density controls:
0 =
-1 =
-2 =
+1 =
+2 =

A

normal
25% decrease in exposure
50% decrease in exposure
25% increase in exposure
50% increase in exposure

55
Q

poor positioning skills result in increased ___________ when using AEC?

A

repeat rate

56
Q

What does “APR” stand for?

A

anatomically programmed radiography

57
Q

What is “APR”?

A

system that allows radiographer to select a button that represents anatomic area with exposure factors for that area

58
Q

Having the outer cells on during a lateral chest will result in?

A

underexposure

59
Q

Having only the center cell of the AEC activated for a PA chest will result in?

A

overexposure

60
Q

the safety features of a fluoro unit do not include what?

A

high grid ratio

RTE1457 Rad Tech 2 (5 decks)

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