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Fluoro Flashcards

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1
Q

Fluro vs conventional xray

mA

kVp

exposure time

focal spot

A

Way less mA (0-5 vs 200-800)

Same 50-120

Longer exposure times

Smaller focal spot (0.3-0.6mm) Xray = 1mm

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2
Q

How many ‘spots’ = 1 minute of fluoro

A

5-10 spots = 1 minute of fluoro

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3
Q

i i setup

A

ii

———-grid

O patient

collimated beam

Tube

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4
Q

Parts of i i

A

input phosophor - CsI, Xrays to light

photo cathode - light to electrons

voltage diff

output phosphor - electrons to light

PCP Phosphor Cathode Phosphor

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5
Q

Flux gain

A

increased magnitiude of light between input and output phosphors 2/2 voltage (25-35 kV) accelerating electrons

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6
Q

Minification gain

A

output phosphor smaller than input

more electrons/energy per unit area

“Mag” = less minification

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7
Q

Brightness gain

A

old term due to combined effects of minification gain and flux gain

BG = flux gain x minification gain

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8
Q

Conversion gain

old machines

A

efficiency

how good i i is at turning electrons back into light

brightness gain and conversion gain both get worse with age of machine = more dose

older machine = more dose

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9
Q

conversion gain level to just replace i i at?

A

replaced when conversion gain falls to 50%

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10
Q

electronic mag (zoom)

A

decrease input field of view

smaller input, same output

1.4-2x dose per setting increase in dose (AEC kicks in)

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11
Q

Fluoro abc vs xray

A

xray abc ups the mA

fluoro abc adjusts mA, kVp or both

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12
Q

Fluoro and spatial res

what improves it?

main limiter?

A

Improved with magnification (less minification)

limited by resolution of display TV

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13
Q

Dose and…

field of view

A

Dose increases with decreased field of view in both

i i and FPD systems

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14
Q

Order of mA and kVp increase effect on dose

A

mA increased before kVp, dose gets higher

kVp increased first, dose GOES UP LESS

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15
Q

Dose and…

filtration

A

more filtration = fewer low energy Xrays = less dose

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16
Q

Dose and…

adding an aperture

A

Smaller hole, larger focal length (F#), blocks more light from hitting output phosphor

Greater Dose

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17
Q

Dose and…

kVp

A

Higher kVp = more penetrating xrays

Lower *skin dose

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18
Q

% blocked by Pb

when to wear

A

1mm of Pb stops 90%

Wear within 6 feet

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19
Q

Steps to reduce patient dose

A

Position away from the source

collimating, small FOV (also improves resolution)

Avoiding mag

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20
Q

KERMA

A

Kinetic Energy Release per unit MAss

TOTAL amount of energy deposited from ionizing radiation divided by a unit of mass (more quantifiable)

TOTAL because kinetic energy of particle movement but also HEAT

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21
Q

AIR KERMA

A

best way to measure heat and kinetic is to measure it just prior to transfer

AIR KERMA = estimation of how many photons are in a unit of air prior to energy striking skin

estimating peak skin dose based on potential transfer of energy

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22
Q

Kerma Air (area) Product

KAP

A

Amount of kerma (potential dose) multiplied by cross-sectional area of the xray beam

Total radiation potentially incident on patient/ total radiation used in exam moreso than actual dose to patient

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23
Q

more juice used in a smaller area, change in KAP?

A

potentially none

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24
Q

Electronic mag, air kerma and KAP

A

Electronic mag increases Air Kerma and therefore skin dose

DOES NOT increase KAP (decreased cross sectional area)

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25
Q

US Gov Air Kerma rate limit?

A

87mGy/min

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26
Q

High Level Control

US Gov limit for high limit

A

176 mGy/min

must have audible or visual alarms

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27
Q

Pin cushion due to?

A

Large FOV

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28
Q

S distortion

cause

make it better?

A

Large FOV

Earth’s mag field affecting flow of electrons

mu metal

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29
Q

Flair or Glare artifact

A

Transition from heavy to minimal attenuation

glare at periphery near decreased attenuation

overproduction of xrays in this area to compensate for nearby high attenuation area

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30
Q

Vignetting artifact

A

dark periphery, light center

furthest path to outer phosphor at the edges

vignette = short at beginning and end

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31
Q

Saturation artifact

A

dose cranked up to penetrate a dense object (metal), regions around metal look very bright

32
Q

Flat panel detectors (FPD) more modern system

A

Xrays

—————-Grid

——————–carbon fiber protects components

——————-CsI needles (phosphor) xray photons to light

photodiode array———————- light to electrons

read out element, transistors and gates (constructs image from charges in photodiode array

33
Q

Pitch (in fluoro)?

fill factor?

A

linear dimension of a detector element

percentage of each detector element actually sensitive to light

Fill factor = sensitive area

Pitch squared

34
Q

Detector element size and fill factor and spatial resolution

A

Smaller elements have better spacial res but worse fill factor

ie better spatial res but need more radiation

35
Q

1 detector element = 1 pixel

A

that is all

36
Q

Pixel, matrix, FOV equation

A

Pixel = FOV(mm)/matrix

1100 x 1100 matrix

25cm FOV

pixel = 250/1100 = 0.23mm

37
Q

Binning

quantum mottle

A

several detector elements made into a large detector element

Reduced amount of data (less mottle) less variation in xray photons from pixel to pixel

38
Q

Binning and

noise

spatial resolution

A

Less mottle, can reduce radiation and keep same noise

WORSE spatial res

39
Q

Frame averaging

A

image processing, combines images together

better SNR

more ghosting and motion

40
Q

FPD artifacts

A

NO cushion, S distortion, vignette, glare or saturation

Bad pixel = white or black spots, fixed by interpolating

Lag, Ghosting

41
Q

Spatial resolution

in i i limited by?

A

TV. (scan lines, bandwidth, FOV)

not a problem in FPD (displays have same matrix as image receptor)

42
Q

Vertical resolution (on TV or display) formula

A

Raster lines x Kell Factor

2 x FOV

so smaller FOV = better spatial resolution

43
Q

Better pure spatial res FPD or ii?

A

ii, and change with FOV

44
Q

pulsed vs continuous fluoro and mAs

when are they equal

A

pulsed = periodic higher mA

continuous = always on low mA

30 pulses/second dose is unchanged/equal

lower fps has higher mA per pulse, but overall decreased mAs

45
Q

pulse fluoro good for ?

A

moving patients (less motion blur)

46
Q

Reduced dose going from 30 to 15 fps?

A

30%

47
Q

Factors affecting spatial res

FOV

A

smaller better

48
Q

Factors affecting spatial res

focal spot size

A

usually doesn’t matter unless anatomy further from receptor

49
Q

Factors affecting spatial res

binning

A

worse res, better SNR

50
Q

Fluoro QA

spatial res?

distortion?

A

Lead bar pattern for spatial res

Mesh screen or plate (looking for straight lines, not pin cush or S distortion)

51
Q

kVp and contrast. Iodine vs Barium

A

Iodine - 70 kV to max out k edge (33keV for I)

Barium 100 kV - use more barium than I, need higher kV to PENETRATE

52
Q

kVp and dose

A

higher = less skin dose, slightly more organ dose

if you drop mA (15% kV up, half mA), dose decreases

kV always increases dose in CT

53
Q

Fluoro in IR

focal spot?

anode angle?

FOV and detector size?

A

ALL SMALL

small focal spot- looking at small things

smaller anode angle- increased heel effect but doesn’t matter because…

SMALL FOV and detector size (only imaging central portion of beam)

54
Q

Fluoro in IR

kVp

A

60-80

Iodine k edge 33

55
Q

Fluoro in IR

Filter?

A

soft filter or equalization filter

leg, arm, peds

56
Q

Fluoro in IR

Grid?

A

not in extremities or peds

57
Q

DSA

A

moving parts don’t get subtracted

image the moving contrast

58
Q

Dose in IR

?pulsed

% skin dose?

skin dose in a fatty?

lateral and oblique views?

Run dose per frame?

Total dose?

A

Most IR pulsed

50% of dose delivered to 3-5cm most superficial

Higher in fatties 2/2 abc

more with lat and oblique

0.5 mGy per frame at entrance skin position (10-20x more than fluoro per image)

dose per frame x frame rate x duration of run

59
Q

SSD in IR

A

determined by table height

small SSD = high dose

60
Q

Interventional reference point IRP

A

ionization chamber with a set ref point, to measure radiation emitted from source

ignores geometry, table attenuation, and back scatter

over or underestimates skin dose but best measure?

61
Q

Dose at 1 meter from patient relative to patient dose?

A

1/1000

with no lead

62
Q

Regulatory doses

HLC

during image recording

A

87mGy/min 10R/min

176 mGy/min 20R/min

NO limit during image recording IF PULSED

63
Q

Skin doses

Below 2Gy?

A

Do nothing

64
Q

Skin doses

2-5 Gy?

A

Advise pt to look for burns (10 days post procedure)

65
Q

Skin doses

above 5Gy

A

Procedure and dose should be reviewed by physics

66
Q

Skin doses

Early transient erythema?

A

2Gy

67
Q

Skin doses

Temporary epilation?

A

(hair loss)

3Gy

68
Q

Skin doses

Chronic/main erythema

A

6Gy

69
Q

Skin doses

permanent epilation?

A

(hair loss)

7Gy

70
Q

Skin doses

telangiectasia?

A

10Gy

TEn = TElaNgiectasia

71
Q

Skin doses

Dry desquamation

A

13Gy

72
Q

Skin doses

Moist desquamation/ulceration

A

18Gy

73
Q

Skin doses

Secondary ulceration

A

24Gy

74
Q

Operator doses

One usually gets in a year?

A

5mSv

75
Q

Operator doses

regulatory limit per year

A

50mSv

76
Q

Operator doses

fetus dose limit

A

0.5mSv PER MONTH

77
Q
A

physics factoids (8 decks)

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