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Fluoro Flashcards

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
US Gov Air Kerma rate limit?
**87mGy/min**
26
High Level Control US Gov limit for high limit
**176 mGy/min** **must have audible or visual alarms**
27
Pin cushion due to?
Large FOV
28
S distortion cause make it better?
Large FOV Earth's mag field affecting flow of electrons mu metal
29
Flair or Glare artifact
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
30
Vignetting artifact
**dark periphery, light center** **furthest path to outer phosphor at the edges** ***vignette = short at beginning and end***
31
Saturation artifact
dose cranked up to penetrate a dense object (metal), regions around metal look very bright
32
Flat panel detectors (FPD) more modern system
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
Pitch (in fluoro)? fill factor?
linear dimension of a detector element percentage of each detector element actually sensitive to light Fill factor = sensitive area ------------- Pitch squared
34
Detector element size and fill factor and spatial resolution
**Smaller elements** have **better spacial res** but **worse fill factor** ie **better spatial res but need more radiation**
35
1 detector element = 1 pixel
that is all
36
Pixel, matrix, FOV equation
Pixel = FOV(mm)/matrix 1100 x 1100 matrix 25cm FOV pixel = 250/1100 = 0.23mm
37
Binning quantum mottle
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
Binning and noise spatial resolution
Less mottle, **can reduce radiation and keep same noise** ## Footnote **WORSE spatial res**
39
Frame averaging
image processing, combines images together ## Footnote **better SNR** **more ghosting and motion**
40
FPD artifacts
NO cushion, S distortion, vignette, glare or saturation Bad pixel = white or black spots, fixed by interpolating Lag, Ghosting
41
Spatial resolution in i i limited by?
TV. (scan lines, bandwidth, FOV) not a problem in FPD (displays have same matrix as image receptor)
42
Vertical resolution (on TV or display) formula
Raster lines x Kell Factor -------------------------------------- 2 x FOV so smaller FOV = better spatial resolution
43
Better pure spatial res FPD or ii?
ii, and change with FOV
44
pulsed vs continuous fluoro and mAs when are they equal
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
pulse fluoro good for ?
moving patients (less motion blur)
46
Reduced dose going from 30 to 15 fps?
**30%**
47
Factors affecting spatial res FOV
smaller better
48
Factors affecting spatial res focal spot size
usually doesn't matter unless anatomy further from receptor
49
Factors affecting spatial res binning
worse res, better SNR
50
Fluoro QA spatial res? distortion?
Lead bar pattern for spatial res Mesh screen or plate (looking for straight lines, not pin cush or S distortion)
51
kVp and contrast. Iodine vs Barium
**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
kVp and dose
**higher = less skin dose**, slightly more organ dose ## Footnote **if you drop mA (15% kV up, half mA), dose decreases** **kV always increases dose in CT**
53
Fluoro in IR focal spot? anode angle? FOV and detector size?
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
Fluoro in IR kVp
60-80 Iodine k edge 33
55
Fluoro in IR Filter?
soft filter or equalization filter leg, arm, peds
56
Fluoro in IR Grid?
**not in extremities or peds**
57
DSA
moving parts don't get subtracted image the moving contrast
58
Dose in IR ?pulsed % skin dose? skin dose in a fatty? lateral and oblique views? Run dose per frame? Total dose?
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
SSD in IR
determined by table height ## Footnote **small SSD = high dose**
60
Interventional reference point IRP
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
Dose at 1 meter from patient relative to patient dose?
**1/1000** **with no lead**
62
Regulatory doses HLC during image recording
87mGy/min 10R/min 176 mGy/min 20R/min NO limit during image recording IF PULSED
63
Skin doses Below 2Gy?
Do nothing
64
Skin doses 2-5 Gy?
Advise pt to look for burns (10 days post procedure)
65
Skin doses above 5Gy
**Procedure and dose should be reviewed** by physics
66
Skin doses Early transient erythema?
2Gy
67
Skin doses Temporary epilation?
(hair loss) 3Gy
68
Skin doses Chronic/main erythema
6Gy
69
Skin doses permanent epilation?
(hair loss) 7Gy
70
Skin doses telangiectasia?
10Gy TEn = TElaNgiectasia
71
Skin doses Dry desquamation
13Gy
72
Skin doses Moist desquamation/ulceration
18Gy
73
Skin doses Secondary ulceration
24Gy
74
Operator doses One usually gets in a year?
5mSv
75
Operator doses regulatory limit per year
50mSv
76
Operator doses fetus dose limit
0.5mSv PER MONTH
77

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