2. Special Imaging Systems
Unit VI
Special Imaging Systems

3. Chapter 40
Fluoroscopy

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Objectives
Differentiate fluoroscopic examinations from static diagnostic radiographic examinations
Describe a typical basic fluoroscopic image chain
Explain difference between fluoroscopic operation and a diagnostic x-ray tube
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Objectives
Describe advantages of image intensified fluoroscopy over conventional screen fluoroscopy
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Objectives
Explain function and operation of:
Image intensification tube input screen
Photocathode
Electrostatic focusing lenses
Anode and output screen
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Objectives
Explain operation of a multifield magnification image intensification tube
Discuss effects of minification and flux gain on total brightness gain
Explain basic function of a fluoroscopic automatic brightness control
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Objectives
Discuss factors affecting:
Fluoroscopic image contrast
Resolution
Distortion
Quantum mottle
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Objectives
Explain operation of:
Optical mirror viewer system
Video camera CCD
Video camera tube
Video monitor
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Objectives
Evaluate three basic types of fluoroscopic viewing systems
Explain uses of dynamic and static fluoroscopic recording systems
Evaluate fluoroscopic recording systems for clinical situations
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Objectives
Explain digital fluoroscopic image acquisition
Relate problems with mobile radiographic equipment to mobile fluoroscopic equipment
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Objectives
Discuss various methods of reducing dose to patient, radiographer, and radiologist during a fluoroscopic examination
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13. Historical Development
Dynamic examination
Active diagnosis
Domain of radiologist
Fluoroscope
Invented by Edison in 1896
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14. Fluoroscopic Imaging Chain
Specialized x-ray tube
Image receptor
Fluoroscopic screen
Mirrors
Image intensification
Video camera and monitor
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Fluoroscopic Uses
Functional studies
GI tract studies
Angiograms
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16. Fluoroscopic Positioning Previewing
Radiographers are trained in positioning
Unnecessary radiation exposure to patient is unethical
Fluoroscopic equipment should not be used to preview patient’s position
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Types of Equipment
C-arm
Under table/over table units
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Types of Equipment
Raise and lower image receptor for accuracy
Can vary beam geometry and image resolution
Full beam intercept
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19. Fluoroscopic X-Ray Tubes
mA range: 0.5 – 5.0 mA
15” minimum SOD in fixed fluoroscopic equipment
Foot switch
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20. Early Fluoroscopic Screens
Very dim
Required dark adapted viewing
Low visual acuity
Uses scotopic vision (rods)
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21. Image Intensification
Introduced in 1948
Higher visual acuity
Uses photopic vision (cones)
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22. Image Intensification Tube Components
Input screen and photocathode
Electrostatic lenses
Magnification tubes
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23. Image Intensification Tube Components
Anode and output screen
Total brightness gain
Minification gain x flux gain
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24. Input Screen and Photocathode
0.1 – 0.2 mm layer of sodium activated CsI
Converts intercepted x-ray beam to light
Photocathode
Emits electrons when struck by light emitted by input screen
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Electrostatic Lenses
Accelerate and focus electron pattern across tube to anode
Primary source of brightness gain
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Magnification Tubes
Greater voltage to electrostatic lenses
Increases acceleration of electrons
Shifts focal point away from anode
Dual focus
23/15
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Magnification Tubes
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Magnification
Input screen diameter
Diameter used during exam
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29. Anode and Output Screen
Positively charged
25 kVp
Hole in center allows electrons to pass through to output screen
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30. Anode and Output Screen
Glass fluorescent screen
Zinc-cadmium sulfide
Emits light when struck by electrons
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Total Brightness Gain
Minification gain x flux gain
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Minification Gain
Minification gain =
Input screen diameter2
output screen diamter2
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Flux Gain
Measurement of conversion efficiency of output screen
1 electron strikes output screen
50 light photons are emitted
Flux gain = 50
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34. Fluoroscopic Generators
Same as those used for static radiography
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Brightness Control
Automatic brightness control
Automatic dose control
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Brightness Control
Automatic brightness stabilization
Automatic adjustments made to exposure factors by equipment
Automatic gain control
Amplifies video signal rather than adjusting exposure factors
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Image Quality
Contrast
Resolution
Distortion
Quantum mottle
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Contrast
Controlled by amplitude of video signal
Affected by:
Scattered ionizing radiation
Penumbral light scatter
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Resolution
Video viewing
Limited by 525 line raster pattern of monitor
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Size Distortion
Affected by same parameters as static radiography
Primarily OID
Can be combated by bringing image intensifier as close to patient as possible
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Shape Distortion
Geometric problems in shape of input screen
Concave shape helps reduce shape distortion, but does not remove it all
Vignetting or pin cushion effect
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Quantum Mottle
Blotchy, grainy appearance
Caused by too little exposure
Most commonly remedied by increasing mA
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Viewing Systems
Video viewing system
Video camera tubes
Cathode
Anode
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Viewing Systems
Video camera charge-coupled device (CCD)
Video monitor
Digital
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Video Viewing System
Closed circuit television
Video camera coupled to output screen and monitor
Video cameras
Vidicon or Plumbicon tube
CCD
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Video Camera Tubes
Plumbicon and vidicon tubes similar
Different target materials
Plumbicon has faster response time than vidicon
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47. Video Camera Tube Components
Cathode
Control grid
Electromagnetic focusing coils
Electrostatic deflecting coils
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48. Video Camera Tube Components
Anode
Face plate
Signal plate
Target
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Cathode
Heating assembly
Electron gun – thermionic emission
Control grid
Shapes electron beam
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Raster Pattern
Electron beam is accelerated across TV camera tube to anode
Slowed at anode by wire mesh in front of target
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Raster Pattern
Electromagnetic focusing coils
Shape electron beam into single point
Deflecting coils
Cause electron stream to scan target in raster pattern
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Anode
Face plate
Signal plate
Positively charged thin film of graphite
Target
Changes light pattern to electronic signal sent to video system
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Target
Thin insulating mica
Matrix of globules of photoconductive material
Vidicon
Antimony trisulfide
Plumbicon
Lead oxide
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54. Video Camera Charged Coupled Devices (CCD)
Semiconducting device
Emits electrons in proportion to amount of light striking photoelectric cathode
Fast discharge eliminates lag
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55. Video Camera Charged Coupled Devices (CCD)
Operate at lower voltages than video tubes
More durable than video tubes
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Video Monitor
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Digital Fluoroscopy
Image intensifier output screen coupled to TFTs
TFT photodiodes are connected to each pixel element
Resolution limited in favor of radiation exposure concerns
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58. Recording the Fluoroscopic Image
Dynamic systems
Cine film systems
Videotape recording
Static spot filming systems
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59. Recording the Fluoroscopic Image
Cassettes
105 mm chip film
Digital fluoroscopy
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Dynamic Systems
Cine film
Videotape
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Cine Film Systems
Movie camera intercepts image
16 mm and 35 mm formats
Record series of static exposures at high speed
30 – 60 frames per second
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Cine Film Systems
Offer increased resolution
At the cost of increased patient dose
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Videotape Recording
VHS
VHS-S
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64. Static Spot Filming Systems
Cassettes
105 mm chip film
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Cassettes
Standard size - 9” x 9”
Stored in lead-lined compartment until ready for exposure
When exposure is made, mA is raised to radiographic level
Multiple image formats
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105 mm Chip Film
12 frames per second
Beam splitting mirror
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Digital Fluoroscopy
Use CCD to generate electronic signal
Signal is sent to ADC
Allows for post processing and electronic storage and distribution
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68. Radiation Protection During Fluoroscopy
The patient
The radiographer and radiologist
Others
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Patient Protection
Tabletop exposure rate
Maximum 10 R/min
Typically 1 – 3 R/min
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Patient Protection
Minimum source-to-skin distance
12” for mobile equipment
15” for stationary systems
Audible alarm at 5 mins.
Same rules for collimation
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Patient Protection
Typical exposure rates
Cinefluorography
7.2 R/min
Cassettes
30 mR/exposure
105 mm film
10 mR/exposure
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72. Protection of Radiographer and Radiologist
Lead apron
0.25 mm Pb/eq
Highest energy scatter
90o angle to the incident beam
Same level as radiographer /radiologist’s gonads
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73. Protection of Radiographer and Radiologist
Single step away from the table decreases exposure exponentially
Bucky slot cover
Lead rubber drape
Radiologist as shielding
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Protection of Others
Radiographer’s responsibility to inform others in the room to wear lead apron
Do not initiate fluoroscopy until all persons have complied
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