Basics and Introduction of Fluoroscopy (with dose reduction) for Radiology Residents

1. !1
Dr.Girendra Shankar
JR-1, KIMS BBSR
FLUOROSCOPY

2. !2
Fluoroscopy
• Invented by Thomas A. Edison in 1896
• Real-time radiographic imaging (30fps)
• Used for positioning (not necessarily recorded):
– Positioning catheters/biopsies/needles (e.g. angio) – tracking contrast
media (HSG, ERCP, sinogram)
– positioning prior to radiography/spot/cine (e.g. Ba)
• Long exposure
– need to keep radiation dose low
– Need VERY sensitive detector (200-600x film-screen)
• Most systems are digital (or soon will be) – but physics of conventional
fluoroscopy with image intensifier still needed for ABC

3. !3
Direct Fluoroscopy

4. !4
30 min for dark adaptation
Direct Fluoroscopy systems

5. !5
Copper - activated zinc cadmium
GREEN SCREEN FLUOROSCOPY

6. !6
Direct Fluoroscopy
DISADVANTAGES:
– Room needs complete
darkness
– Patient (& Radiologist)
Dose Was Very High
– Only One Person Could
View Image

7. !7
Fluoroscopy
• C-arm &Under table/over table units
• Conventional & Digital Units

8. !8
Fluoroscopic imaging chain
-More sensitive
detector system than
film screen
-Same basic
arrangement
-Tube capable of
prolonged current

9. !9

10. Energy conversion at input phosphor
1 x-ray photon
~60keV
~1,600 e-

11. !11
Electrostatic Focussing Lens
Photoelectrons are accelerated by the anode
Positively charged electrodes inside the glass envelope.
Lenses prevent diverging of the x-ray beams
Electron focussing inverts and reverse the image → point
inversion → because common focal point .

12. !12

13. !13
Accelerating Anode
• In neck of the I.I. tube
• The potential applied at the anode is +25 to +35
kv more than cathode.
• gain of kinetic energy by the electrons

14. Energy conversion at output phosphor
~2,000 visible
photons ~530nm
1 accelerated e-

15. !15
• ZnS:CdS: Ag activated
• electrons → visible light
• smaller than the input phosphors (to 1 inch)
• Crystal size and layer thickness are reduced
to maintain resolution in minified image.
• photo e- have much higher energies from
input screen
• more light photons (increase approx. 50
folds)
• Anode is a very thin coating of aluminum on
the vacuum side of the phosphor

16. !16Image Intensifiers
( 23-, 30-, 35, 40-cm diameter )
(9,12,14,16”)
• Large – GI/GU
• Small – Cardiac/
arthroscopy

17. !17
• Conversion Factor (= “gain”) [Cd s / mR m2]
= light out (Cd/m2) /X-rays in (mR/sec)
• Typically 100-200
• Brightness gain/ Intensification factor
– Electronic gain (~50x) x Minification gain
(Minification gain = input:output area ~(input FOV)2 in inches)
• Flux gain (Electronic gain)-Number of light photons
striking the output screen : Number of x- ray photons
striking the input screen.
IMAGE INTENSIFIER PERFORMANCE

18. !18
Contrast
the brightness ratio of the periphery to the center
of the output window when the center portion of
an image intensifier entrance is totally blocked by
a lead disk.
IMAGING CHARACTERISTICS

19. !19
Sideways Light Scattering
Unsharpness due to the lateral diffusion of light after
being produced by the input phosphor before reaching
the photo cathode.
Geometric Unsharpness
Can be avoided by placing the image intensifier as close
to the patient body as possible.

20. !20
Lag
• Persistence of luminescence
after x-ray stimulation has been
terminated.
• Lag degrades the temporal
resolution of the dynamic
image.
• Usually of short duration- older
tubes(30-40 ms) with CsI
tubes-1ms.

21. !21
Magnification
• ↓input FOV , magnification
• Reduces ↓ pincushion - But ↓ brightness gain
»

22. !22
Pincushion distortion
Distortion
Different path-length of
electron beam
- Longer path at
periphery (more
distortion)
Spiral warp due to
electron path in
stray magnetic
field
“S-distortion” (spiral)

23. !23
A fall-off in brightness at the
periphery of an image is
called vignetting.
As a result, the center of an
image intensifier has better
resolution, increased
brightness, and less
distortion.
Vignetting

24. !24
Veiling Glare
• Scattering of light and the defocusing of
photoelectrons within the image intensifier are
called veiling glare.
• Veiling glare degrades object contrast at the output
phosphor of the image intensifier.
• X-ray, electron, and light scatter all contribute to
veiling glare.

25. !25
Optical system
Camera (100mm film or CCD digital) - 75-100 µR/image
Cine (35mm or digital) - 10-15 µR/image

26. !26
MULTI FIELD IMAGE INTENSIFIERS
In this type either the
central part of the
image can be viewed
or the whole image.
This can be brought
about by increasing the
charge of the focusing
lens

27. !27
Magnification Tubes
Greater voltage to electrostatic lenses
– Increases acceleration of electrons
– Shifts focal point away from anode
– Used to enlarge small structure or to penetration
through larger parts
• Dual focus
– 9/6 inches
• Tri focus
– 12/9/6 inches

28. !28
Viewing the Fluoroscopic Image

29. !29 Fluoroscopic Image monitoring
Optical Coupling
Lens coupling
Fibre optic coupling

30. !30
Uses fibre optic cables thus reducing light loss from the
II to video camera
• Prevents any additional accessories being used.
• Preserves better spatial resolution
Fibre optic coupling

31. !31
Viewing system
It is development of the image from output
screen to the viewer these include video, cine
and spot film systems
Most commonly used is video as closed circuit
through cables to avoid broadcast interference

32. !32
TV Image
• Composed of discrete horizontal scan lines
• No of lines independent of monitor size
• broadcast TV standard
– 525lines
• High definition
– 1025lines
– more popular ,more expensive

33. !33
Converts light to coded electrical signal
Camera Tube –
• Vidicon - cheapest / compact / laggy
• Plumbicon - enhanced vidicon / less lag
• CCD -Semiconductor, not a tube
TV Camera

34. !34
Vidicon tubes use antimony trisulfide (Sb2S3)
(photo-conductive) while Plumbicon use lead oxide
(PbO) in mica matrix

35. !35
CCD REPLACED THE CAMERA IN VIDEO SYSTEM

36. !36 Semiconductor Video Cameras
• based on the charged coupled
device (CCD) technology
• CCD - semiconductor chip which
is sensitive to light – not vacuum
tubes
• many thousands of e- electronic
sensors
• Light photon strikes the
photoelectric cathode of CCD
and electrons released

37. !37
Basic Components of old fluoroscopic “Imaging Chain”

38. !38
Basic components of Digital Fluoro Imaging Chain

39. Image intensifier vs. Array detector
IMAGE INTENSIFIER
• Circular FOV
• Pincushion distortion
• Nonuniform
• <3 lp/mm
• 12” FOV
FLAT PANEL
• Rectangular FOV
• No distortion
• High uniformity
• >4 lp/mm
• Up to 19” FOV

40. !40
Solid state flat panel
• Flat panel have
replaced image
intensifier & video
system.
• High quality flat
panels OK for
radiography too
(~100µm)

41. !41
DEL - a
scintillation
layer, thallium-
activated CsI
FPD arrays - indirect
solid-state systems,
X-ray energy →
light → electronic
signal.

42. Musculoskeletal and Orthopaedics
Arthrogram
Nerve root injection
Joint injection
Head & Neck
Video fluoroscopy swallow
Sialogram
Gastrointestinal
Barium swallow
Barium Meal
Barium Enema
Small bowel follow-through
Fistulogram
Stomogram
Proctogram

43. !43
Neurology
Myelogram
Gynaecology
Hysterosalpingogram
Urology
Cystogram
Nephrostogram
Urethrogram
Urodynamics

44. !44
Dose reduction
Balance of dose vs. noise
Higher dose = lower noise (+ better delectability) and
vice versa
1 mR 0.1 mR 0.01 mR
• Balance of dose vs. mortality/morbidity
• Reducing patient dose reduces YOUR dose

45. !45
Dose Metrics• Cumulative Air Kerma (mGy)
• Kinetic energy released in matter (air)
• Analogous to “Exposure in mR”
• Deterministic effects (skin)
• Kerma Area Product (also Dose Area Product)
• Unit: mGycm2 (also mGym2)
• AK x Area
• Proportional to Stochastic Risk
• Cumulative Fluoro time (min)
• Very poor indicator of dose
• May be only available on units pre-2006
• Peak skin dose* • Skin dose maps*
*Desired but not readily available

46. !46
1.Automatic Brightness Control
Adjust radiation exposure (mA, kV, pulse width, pulse
height) to keep output phosphor brightness constant.
Higher mA → higher dose
Higher kVp → lower dose since ABC reduces mA
Small body parts: 70 kVp
Large body parts: 100-120 kVp
Iodine contrast: >66 kVp (Iodine K-edge)

47. !47
2.Minimize use of Magnification Modes
• Avoid geometric magnification, electronic MAG •
Dose rate depends on the area of FOV
• Dose rate proportional (mag factor)2
• Use digital zoom instead
2. Minimize use of Magnification Modes
• Avoid geometric magnification, electronic MAG
• Dose rate depends on the area of FOV
• Dose rate proportional (mag factor)2
• Use digital zoom instead
12 in 6 in
MAG II (1/4 area) ≈ 4X Dose
12” 6”

48. !48
3.Collimate to region of interest
• Adjust collimator without fluoroscopy turned on
• Improves image contrast by reducing scatter
• Use spacer cones if applicable
• Collimating reduces dose, improves image contrast
3. Collimate to region of interest
• Adjust collimator without fluoroscopy turned on
• Improves image contrast by reducing scatter
• Use spacer cones if applicable
• Collimating reduces dose, improves image contrast

49. !49
4.Minimize use of spot fluorographs (digital spot
films, DSA, cine)
• Spot images and series require higher doses than
fluoroscopic viewing
• Use “Tap Fluoro” and Last-Image-Hold (LIH)
• Save LIH in lieu of spot where possible
4. Minimize use of spot fluorographs
(digital spot films, DSA, cine)
• Spot images and series require higher doses than
fluoroscopic viewing
• Use “Tap Fluoro” and Last-Image-Hold (LIH)
• Save LIH in lieu of spot where possible
Fluoroscopy
1 nGy
Fluorography
10-60 nGy

50. !505. Spread dose to skin by changing tube angle and
position
• Often recommended when Cumulative AK Alert Level is
reached (2000 mGy) but do so carefully
• Tricky issue: angulation can increase dose if patient
thickness is increased
• Most prevalent skin injury factor is long exposure to
single site
• 83% of injuries with beam
in steeply angled orientation
• Avoid lateral projections

51. !51

52. !52
6. Lowest appropriate fluoro frame rate
• Minimize beam-on time
• Use fluoro only to observe motion or positioning
• Use intermittent “tap fluoro” method
• Most IR procedures: 2-7.5 fps
• Cardiology/EP: 7.5-15 fps
• Arthrograms or needle guidance: 1-2 fps
• Use shorter pulse lengths to reduce blur (2-20 msec)

53. !53 7. Use system geometry to reduce pt dose and
personnel scatter radiation exposure
• Keep detector close to patient, keep tube away
• Scatter radiation originates in patient
• Operator always stands by detector, not by x-ray tube
• Use under-table tube systems whenever possible
7. Use system geometry to reduce pt dose
and personnel scatter radiation exposure
• Keep detector close to patient, keep tube away
• Scatter radiation originates in patient
• Operator always stands by detector, not by x-ray tube
• Use under-table tube systems whenever possible
– Operator not shielded from scatter with over-table units
– Drapes not feasible with over-table units
Higher due to backscatter and
attenuation in patient. Not a
good place to stand.
Preferred
Use system geometry to reduce pt dose
nd personnel scatter radiation exposure
ep detector close to patient, keep tube away
atter radiation originates in patient
erator always stands by detector, not by x-ray tube
e under-table tube systems whenever possible
Operator not shielded from scatter with over-table units
Drapes not feasible with over-table units
Higher due to backscatter and

54. !54
• The patient
• The radiographer and radiologist
• Others

55. !55
The Patient & Scatter

56. !56
• Primary barrier – protection from Primary
radiation (for the Patient & Radiologist) - The I.I.
is a 2.0 mm pb eq barrier
• Secondary barrier - protection from Secondary
radiation (from the patient)
- Protection for the technologists, etc

57. !578. Use personnel and patient protective devices
correctly
• dosimeters
• Recommend apparel with 0.5 mm Pb (≈ 95% scatter
reduction)
• Use gonadal shields and blockers when in primary
beam
• Thyroid shields, especially for younger staff
• Aprons, goggles must fit
• Passive shields under and over table

58. !58

59. !59
9.Record+Review Dose Report in PACS and Chart
Record following data (ACR Guidelines)
– Operator (MD)
– Air Kerma
– Kerma Area Product
– Fluoro Time
– Skin location for higher
dose component

60. !60
10. Observe notification and sentinel event levels
• First Notification Level 3000 mGy AK
• Announce AK to team every 1000 mGy thereafter
• For cumulative AK >3000 mGy
• self-exam for erythema for 2-3weeks
• If reddening does not fade after 4w/painful ,
patient should return for examination

61. !61
• For cumulative AK >5000 mGy
• Dermatology consult 4-8w after
• Avoid skin punch biopsies(non-healing ulcer)
• Report AK >5000 mGy to Radiation Safety Officer
– Review case with RSO
– Estimate skin dose to a single port

62. !62Mean effective doses and DAP values from contrast
procedures involving fluoroscopy
Mean effective doses and DAP values from
contrast procedures involving fluoroscopy
Radiography / Fluoroscopy
procedures
Mean Effective Dose
(mSv)
Mean DAP
(mGy.cm2)
Equivalent number of PA chest
radiographs (each 0.02 mSv)
Orthopaedic pinning (hip) 0.7 35
Pelvimetry 0.8 40
Micturating Cystourethrogram
(MCU)
1.2 6400 60
Hysterosalpingogram (HSG) 1.2 4000 60
Discography 1.3 65
Barium Swallow 1.5 75
Fistulogram 1.7 6400 85
Cystography 1.8 1000 90
Myelography 2.46 12,300 123
Barium meal 2.6 130
Barium meal follow through 3 150
Sinography 4.2 16,000 210
Barium enema 7.2 28,000 360
Coronary angiography 2-15 (12.7) 49,000 635
IAEA Radiation Protection of Patients, rpop.iaea.org

63. !63Dose Rate to radiologist
• Fluoroscopy is a significant source of
occupational exposure
• Everything that reduces patient dose also
reduces your dose!
• 1m away at 90° you get 0.1% of the patient dose
• Remember 1/R2

64. !64

65. !65
THANK YOU