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Huda > Chapter 10 Interventional Radiology > Flashcards

Chapter 10 Interventional Radiology Flashcards

1
Q

examples of IR procedures

A

stenting, vertebroplasty, angioplasty, chemoembolization

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2
Q

what does IR do

A

use images to direct needles and catheters, avoiding large incisions

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3
Q

flat panel detectors in IR

A

-similar to digital radiography
-if fluoro, must minimize electronic noise because detected signals are a hundred times lower than in radiography

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4
Q

flat panel detector material

A

CsI

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5
Q

flat panel detector FOV

A

smaller FOV = increase in Kair at image receptor to reduce image mottle (no ABC, this is just done to reduce perceived mottle)
-increases in Kair are programmed by vendor

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6
Q

flat panel detector pixel size

A

170 um

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7
Q

is a TV or CCD required to read out the flat panel detector?

A

No, they are read out electronically

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8
Q

response of flat panel detectors

A

linear response over wide dynamic range

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9
Q

flat panel detector vs II FOV adjustements

A

-halving FOV would quadruple Kair for II but only fouble Kair for FPD
-FPD fluoro performed with larger FOV would likely add four pixels together (binninb) to reduce mottle
-binning also halves resolution

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10
Q

FPD vs II image detectors

A

both are 400 um CsI
FPDs have carbon cover which transmits slightly more x-rays than the 1.5 mm Al used in II
-ie. FPD detects 90% vs 75%

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11
Q

fluoro of II vs FPD

A

FPD: 3 lp/mm
II: 1 lp/mm using 500 line TV

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12
Q

distortions for FPD vs II

A

II have pin cushion, S, vignetting, glare, saturation
-FPD is excellent
-FPDs have linear response that is superior to sigmoidal response of II

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13
Q

what are equalization filters

A

use Pb/plastic mixtures to reduce transmission of x-rays to peripheral regions used as anatomical landmarks

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14
Q

digital subtraction angiography

A

-mask image without contrast is subtracted from corresponding image with contrast to show the vasculature
-removes anatomical background

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15
Q

road mapping

A

permits an image to be captured and displayed on a monitor while a second monitor shows live images
-can also be used to capture images with contrast material and overlay it onto a live fluoro image

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16
Q

tube voltage in angiography and dsa

A

70 kV, to match k-edge of iodine

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17
Q

tube current, exposure time of angriography and DSA

A

400 mA
50 ms
200 mAs

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18
Q

Kair at image receptor in angiography and DSA

A

3 uGy/image, similar to radiographic imaging

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19
Q

frame rates in angiography/DSA

A

4 frames/s

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20
Q

source to image distance in IR

A

100 cm
-shorter SIDs increase skin dose and image distortion from variable magnification
-longer SIDs require increased x-ray tube output (IS law)

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21
Q

what does geometric magnification introduce?

A

focal spot blurring
increased skin doses
air gap (scatter exiting patient irradiates techs)

-minimize by reducing gap between patient and image receptor

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22
Q

minimum focus to skin distance

A

38 cm for fixed systems
30 cm for mobile units

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23
Q

where are grids optional?

A

-IR in infants and knees
-removing grids (with AEC) will halve Kair

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24
Q

entrance Kair of lateral vs AP projections

A

lateral is double

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25
Q

entrance Kair for normal sized patient in angiography and DSA

A

1-3 mGy/image

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26
Q

what is interventional reference point

A

imaginary point, 15 cm closer to focal spot than system isocenter
-IR gantries rotate around the isocenter

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27
Q

IRP Kair

A

measured by vendors in air
-excludes patient backscatter
-NOT patient skin dose, conservative estimate of patient skin dose

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28
Q

how to convert IRP Kair into peak skin dose

A

-have to account for physical differences between air/tissue, backscatter radiation, x-ray attenuation by the table
-also account for differences in IRP location relative to patient skin and overlap from multiple projections

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29
Q

what is dose index

A

peak skin dose/ IRP Kair
-usually 0.5-0.8

30
Q

typical peak skin dose

A

2 Gy

31
Q

what procedures have highest peak skin doses

A

TIPS and embolization procedures
could be > 5 Gy

32
Q

how to reduce chance of skin overlap?

A

use collimation to reduce overlap of beams from opposite obliquities

33
Q

skin exposure policy in IR

A

< 2 Gy: radiation burns not ecpected
2-5 Gy: inform patient of possible burn
>5 Gy: MP should evaluate assumption of IRP Kair as peak skin dose

34
Q

unintended skin dose of what Gy is a sentinel event?

A

15 Gy
-requires root cause analysis and visit from joint commission inspector

35
Q

how many IR procedures result in serious radiation burn requiring major clinical intervention?

A

1/10,000

36
Q

kerma area product values in IR vs radiography, fluoro

A

mean of 200 Gycm^2
10X higher than fluoro
100X higher than radiography

37
Q

IR procedures with high KAP

A

spine arteriovenous malformation eolization > 500 mGycm^2

38
Q

KAP for nephrostromy obstruction

A

25 Gycm^2

39
Q

patient effective dose/ KAP factors for infants vs adults

A

10X higher in infants

40
Q

typical patient effectrive doses for IR procedures

A

10-50 mSv
30 mSv mean

41
Q

E/KAP for head

A

0.03 mSv/Gycm^2

42
Q

E/KAP for body

A

0.1- 0.25 mSv/Gycm^2

43
Q

operator dose 1 m from patient

A

0.1 % of patient dose

44
Q

principle source of scatter in IR

A

where x-ray beams enter patient
radiation entering is 100X more intense than radiation entering
operators should stand away from entry points

45
Q

typical IR operator effective dose

A

5 uSv for IR procedure with KAP of 200 Gycm^2

annual effective doses ~ 5 mSv for IR fellow, 1-5 mSv for tech

larger patients require more radiation therefore staff get more radiation

46
Q

effective dose for spine embolization

A

90 mSv

47
Q

effective dose for nephrsostomy

A

6 mSv

48
Q

effective dose for pulmonary angiography

A

15 mSv

49
Q

how are eye lens doses monitored?

A

place dosimeter close to eye

50
Q

IR operator eye doses

A

< 150 mSv/year, but likely more than 20 mSv/year as recommended by ICRP 2011

51
Q

effect to patient and operator dose if FOV area is halved

A

patient skin dose + 50 %
patient effective dose - 25 %
operator effective dose - 25%

52
Q

effect to patient and operator dose if 0.2 mm Cu added

A

patient skin dose halved
patient effective dose halved
operator effective dose halved

53
Q

effect to patient and operator dose if switch from AP to lateral projection

A

patient skin dose doubles
patient effective dose doubles
operator effective dose doubles

54
Q

double badge dosimeters

A

-one dosimeter outside lead apron and one inside

55
Q

fetal dose for pregnant workers

A

0.5 mSv/month

56
Q

collimating beam to reduce area by 25 % will reduce patient and operator dose by what amount?

A

25 %

57
Q

how does increasing distance from patient reduce dose to operator?

A

by IS law

58
Q

how much does 0.5 mm Pb shielding transmit

A

< 10 %

59
Q

shielding clothing for body

A

wrap-around aprons
skirt and vest
thyroid collars
lead impregnated sterile gloves- attenuate 50% of incident radiation
-90% reduction

60
Q

eye lens protection

A

glasses with lateral shields (oeprators usually looking at monitors not at patient)

61
Q

why don’t leaded glasses reduce dose as much as predicted given the low transmission of leaded glass?

A

x-rays can be backscattered into the lens from areas exposed beyond the leaded glass
-only 65% reduction

62
Q

what is best way to reduce eye lens dose

A

“hang down” transparent lead barrier between patient and operator

63
Q

how much do regular plastic or glass glasses attenuate the radiation?

A

< 5 %

takes 30 mm of glass or tissue to attenuate beam by 50 %

64
Q

how much Pb in walls do IR rooms have?

A

2 mm

65
Q

ancilliary shielding

A

lead draoes attached to table to reduce scatter from x-ray tube and patient
leaded plastic transparent drapes between patient and operator
lead barriers in room where staff can stand behind

66
Q

what % of IR patients are likely to have cumulative IRP Kair > 2 Gy?

A

30%

1 Gy- 50%
2 Gy- 30%
3 Gy - 20 %
5 Gy - 5%

67
Q

what % of IR patients would received a peak skin dose > 5 Gy?

A

2 %

1 Gy- 40 %
2 Gy - 25%
3 Gy- 10%
5 Gy- 2%

68
Q

why use flat panel detectors instead of image intensifiers?

A

less artifacts

69
Q

average kerma area product for IR procedures

A

200 Gy-cm2

70
Q

patient scatter radiation results in doses at 1 m that are what % of radiation intensity incident on the patient?

A

0.1%

71
Q

by how much do the Pb impregnated gloves reduce extremity dose by?

A

50%

Huda (20 decks)

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