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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
Effect of collimation
smaller FOV => less scatter, less dose
26
Optimal position of source and detector relative to patient
maximize SOD and minimize SID; taking advantage of inverse square law to decrease patient dose while maximizing x-rays reaching detector
27
Pulsed fluoro
can maintain image quality at decreased dose or improve image quality at same dose; less susceptible to motion
28
Ideal kVp for DSA
70 kVp (take advantage of k-edge of iodine)
29
Digital spot modifications (relative to regular fluoro)
increased mA, larger focal spot; also no binning => higher resolution
30
Focal spot in fluoro (relative to general radiography)
smaller focal spot utilized to limit geometric blurring; 0.3-0.6 mm
31
Effect of frame averaging
decreased quantum mottle => increased SNR; risk of lag/ghosting/persistence
32
Vertical resolution of FPD display is determined by...
number of raster lines; line pair = 2 raster lines
33
Horizontal resolution of FPD display is determind by...
number of dots per raster line; line pair = 2 dots
34
Ideal place for operator to stand
same side of patient as detector
35
Lateral and oblique views require higher or lower dose?
higher dose
36
50% of beam is attenuated in what distance
initial 3-5 cm of tissue
37
Effect of lead apron
0.5 mm Pb stops 95% of radiation (or 99% per Ram)
38
Lead should be worn if within...
6 feet of patient/source
39
Federal regulation for entrance dose rate (fluoro)
cannot exceed 88 mGy/min (measured at 30 cm from detector surface)
40
Federal regulation for high level control entrance dose rate (fluoro)
cannot exceed 176 mGy/min (measured at 30 cm from detector surface); must have a visual or audible alarm
41
Personnel dose standing 1 meter from patient
1/1000 of patient dose
42
Most influential factor on patient dose in fluoro
fluoro time
43
Joint commission sentinel event
cumulative dose of 15 Gy or more to a single field; requires root-cause analysis and visit by JC inspector
44
Entrance air kerma limit for DSA
no limit for DSA
45
Absorbed dose
energy deposited per unit mass; expressed in Gy (J/kg)
46
Equivalent dose
absorbed dose times a radiation weighting factor; expressed in Sv
47
Effective dose
equivalent dose times a tissue weighting factor; expressed in Sv
48
Air kerma relates to which risk type?
deterministic risk (CAK does too)
49
Kerma area product relates to which risk type?
stochastic risk
50
Lower pulse rate (or fps)
decreased dose (despite an increase in mA to maintain perceived image quality), decreased temporal resolution
51
Replace I.I. when conversion gain falls to...
50% or less
52
KERMA (meaning)
Kinetic Energy Release per unit MAss
53
Effect of collimation on dose (fluoro)
unchanged AK, decreased KAP; ABC is turned of with collimation (per Huda)
54
Artifact: periphery is dark than center (I.I.)
vignetting artifact; shorter path to center of detector than to edge of detector
55
Geometric magnification in fluoro is typically performed by...
increasing SID (unchanged SOD); result is increased dose by ABC => increased AK and KAP
56
Binning is useful with...
large FOVs; usually turned off for electronic magnification and digital spot => higher resolution
57
Artifacts that FPD systems do not get
pincushion, S-distortion, vignetting, glare, saturation
58
Artifacts that FPD systems do get
bad pixel, lag/ghosting
59
50% reduction in frame rate (pulsed fluoro) reduces dose by...
30% (don't worry about why, just memorize 30%)
60
Spatial resolution is tested for with...
lead bar pattern
61
Image distortion is tested for with...
mesh screen or plate
62
Typical entrance dose rate
30 mGy/min
63
Road map
similar idea to DSA (subtraction of normal anatomy); uses lower dose => more noise; vessels appear white
64
DSA
higher dose with a lower frame rate; less noise
65
Benefits of minimizing ODD
decreased dose (inverse square law), decreased geometric blurring, detector blocks scatter to personnel
66
AK measurement
ionization tube at the international reference point (15 cm toward x-ray tube from machine's isocenter)
67
Relationship of AK and peak skin dose (PSD)
AK is an appromixation of the PSD; PSD is not easily measured
68
Effect of mag 1, mag 2, and mag 3 on AK
2x, 4x, and 8x, respectively

AJT Physics (7 decks)

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