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AJT Physics > PHYSICS - Fluoro > Flashcards

PHYSICS - Fluoro Flashcards

1
Q

Typical grid ratio (fluoro)

A

10:1 (same as general radiography)

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2
Q

Grid indicated when tissue thickness is…

A

> 12 cm (e.g. not an extremity or peds)

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3
Q

ABC monitors…

A

light eminating from output phosphor (I.I. systems)

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4
Q

ADC monitors…

A

electronic signal detected by FPD

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5
Q

Conversion gain

A

decreases with increasing image intensifier age

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6
Q

Solutions for decreased conversion gain

A

use larger aperture, allow ABC to use more radiation, replace system

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7
Q

Large F#

A

smaller aperture (and vice-versa for small F#)

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8
Q

Effect of a larger F# on dose and noise

A

larger F# => less noise, more dose

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9
Q

Effect of binning on SNR and spatial resolution

A

increased SNR, decreased spatial resolution

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10
Q

Effect of binning on dose

A

can decrease dose while maintaining SNR, at the cost of spatial resolution

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11
Q

Combining 4 DELs reduces dose by…

A

50%

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12
Q

Pitch (fluoro)

A

size of a DEL; measured from center to center

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13
Q

Effect of geometric mag on AK and KAP

A

increased AK and KAP (from ABC via inverse square law)

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14
Q

Effect of electronic mag (I.I.) on AK and KAP

A

increased AK (from ABC), same KAP (smaller area exposed)

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15
Q

Effect of electronic mag (FPD) on AK and KAP

A

slightly increased AK, same KAP (smaller area exposed)

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16
Q

Each electronic magnification setting increases dose by…

A

1.4 to 2 times

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17
Q

Which increases dose more, geometric or electronic mag?

A

geometric magnification

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18
Q

Do I.I. or FPD systems have better dynamic range?

A

FPD systems

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19
Q

Effect of electronic mag (I.I.) on resolution

A

increased spatial resolution (because less minification)

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20
Q

Effect of electronic mag (FPD) on resolution

A

no change in spatial resolution (just zooming in)

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21
Q

Resolution-limiting component for I.I. systems

A

quality of display TV

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22
Q

Resolution-limiting component for FPD systems

A

DEL size

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23
Q

More or less scatter with a large FOV (less collimation)?

A

more scatter with larger FOVs (relative to smaller FOVs)

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24
Q

Dose reduction techniques

A

position patient away from source, use smallest possible FOV (collimation), avoid magnification (either kind), pulsed fluoro

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25
Q

Effect of collimation

A

smaller FOV => less scatter, less dose

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26
Q

Optimal position of source and detector relative to patient

A

maximize SOD and minimize SID; taking advantage of inverse square law to decrease patient dose while maximizing x-rays reaching detector

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27
Q

Pulsed fluoro

A

can maintain image quality at decreased dose or improve image quality at same dose; less susceptible to motion

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28
Q

Ideal kVp for DSA

A

70 kVp (take advantage of k-edge of iodine)

29
Q

Digital spot modifications (relative to regular fluoro)

A

increased mA, larger focal spot; also no binning => higher resolution

30
Q

Focal spot in fluoro (relative to general radiography)

A

smaller focal spot utilized to limit geometric blurring; 0.3-0.6 mm

31
Q

Effect of frame averaging

A

decreased quantum mottle => increased SNR; risk of lag/ghosting/persistence

32
Q

Vertical resolution of FPD display is determined by…

A

number of raster lines; line pair = 2 raster lines

33
Q

Horizontal resolution of FPD display is determind by…

A

number of dots per raster line; line pair = 2 dots

34
Q

Ideal place for operator to stand

A

same side of patient as detector

35
Q

Lateral and oblique views require higher or lower dose?

A

higher dose

36
Q

50% of beam is attenuated in what distance

A

initial 3-5 cm of tissue

37
Q

Effect of lead apron

A

0.5 mm Pb stops 95% of radiation (or 99% per Ram)

38
Q

Lead should be worn if within…

A

6 feet of patient/source

39
Q

Federal regulation for entrance dose rate (fluoro)

A

cannot exceed 88 mGy/min (measured at 30 cm from detector surface)

40
Q

Federal regulation for high level control entrance dose rate (fluoro)

A

cannot exceed 176 mGy/min (measured at 30 cm from detector surface); must have a visual or audible alarm

41
Q

Personnel dose standing 1 meter from patient

A

1/1000 of patient dose

42
Q

Most influential factor on patient dose in fluoro

A

fluoro time

43
Q

Joint commission sentinel event

A

cumulative dose of 15 Gy or more to a single field; requires root-cause analysis and visit by JC inspector

44
Q

Entrance air kerma limit for DSA

A

no limit for DSA

45
Q

Absorbed dose

A

energy deposited per unit mass; expressed in Gy (J/kg)

46
Q

Equivalent dose

A

absorbed dose times a radiation weighting factor; expressed in Sv

47
Q

Effective dose

A

equivalent dose times a tissue weighting factor; expressed in Sv

48
Q

Air kerma relates to which risk type?

A

deterministic risk (CAK does too)

49
Q

Kerma area product relates to which risk type?

A

stochastic risk

50
Q

Lower pulse rate (or fps)

A

decreased dose (despite an increase in mA to maintain perceived image quality), decreased temporal resolution

51
Q

Replace I.I. when conversion gain falls to…

A

50% or less

52
Q

KERMA (meaning)

A

Kinetic Energy Release per unit MAss

53
Q

Effect of collimation on dose (fluoro)

A

unchanged AK, decreased KAP; ABC is turned of with collimation (per Huda)

54
Q

Artifact: periphery is dark than center (I.I.)

A

vignetting artifact; shorter path to center of detector than to edge of detector

55
Q

Geometric magnification in fluoro is typically performed by…

A

increasing SID (unchanged SOD); result is increased dose by ABC => increased AK and KAP

56
Q

Binning is useful with…

A

large FOVs; usually turned off for electronic magnification and digital spot => higher resolution

57
Q

Artifacts that FPD systems do not get

A

pincushion, S-distortion, vignetting, glare, saturation

58
Q

Artifacts that FPD systems do get

A

bad pixel, lag/ghosting

59
Q

50% reduction in frame rate (pulsed fluoro) reduces dose by…

A

30% (don’t worry about why, just memorize 30%)

60
Q

Spatial resolution is tested for with…

A

lead bar pattern

61
Q

Image distortion is tested for with…

A

mesh screen or plate

62
Q

Typical entrance dose rate

A

30 mGy/min

63
Q

Road map

A

similar idea to DSA (subtraction of normal anatomy); uses lower dose => more noise; vessels appear white

64
Q

DSA

A

higher dose with a lower frame rate; less noise

65
Q

Benefits of minimizing ODD

A

decreased dose (inverse square law), decreased geometric blurring, detector blocks scatter to personnel

66
Q

AK measurement

A

ionization tube at the international reference point (15 cm toward x-ray tube from machine’s isocenter)

67
Q

Relationship of AK and peak skin dose (PSD)

A

AK is an appromixation of the PSD; PSD is not easily measured

68
Q

Effect of mag 1, mag 2, and mag 3 on AK

A

2x, 4x, and 8x, respectively

AJT Physics (7 decks)

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