1 fluoroscopy intro to equipment rt 244 fall 2008/9/10 rev week 1 mon – day 1 ref: fluoroscopy –...
TRANSCRIPT
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Fluoroscopy Intro to EQUIPMENT
RT 244
FALL 2008/9/10 rev
Week 1
Mon – day 1
Ref: Fluoroscopy – Bushong’s Ch. 24
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Topics for WEEK 1 RT 244
Example of fluoroscopy systems Components of the Imaging Chain Image intensifier, Camera tubes TV & viewing system……..etc Recording systems Digital Fluoroscopy (?)
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Fluoro objectives
Draw a cross sectional view and identify the components of an image intensifier tube.
Describe the operation of an image intensifier tube, including the different image carriers (photons and electrons) that are utilized in the tube.
Describe the concepts of brightness gain, minification gain, and flux (electronic) gain as applied to an image intensifier.
Show how the total gain is computed from the minification gain and the flux (electronic) gain.
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Fluoro objectives
Define conversion factor for an image intensifier.
A fluoroscopic system is switched to the enlargement mode so that the center 6 inches of the input screen is visualized in place of the entire 9 inch diameter screen. If the brightness of the output screen remains constant, estimate the relative increase in exposure rate that has occurred.
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Fluoro objectives
Sketch and explain the function of the typical optical beam-splitter used to permit televised fluoroscopy and spot filming or cine-radiography.
Describe briefly the video process whereby an image on the output screen of an image intensifier is transferred to the screen of a television monitor.
Explain the process of video line interlacing and why it is used.
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Fluoro objectives Describe video image fields and frames and the times associated with
each. Describe the factors that influence the horizontal detail (blur) and the
vertical detail (blur) of a fluoroscopic image and how you can change detail during a procedure.
Describe the principles of operation of an automatic brightness control unit used with fluoroscopy.
Describe the principle factor that affects quantum noise in fluoroscopy. Describe the process of evaluating a fluoroscopic system for quantum
noise . Explain how the quantum noise level can be changed. State typical and regulatory maximum exposure rates to patients with
normal fluoroscopy. Identify the major factor that produces high patient and staff exposures
during fluoroscopy. Explain the purpose of the High Level Control (HLC) fluoroscopic mode,
when is it used, and potential hazards.
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Fluoro objectives
Describe video image fields and frames and the times associated with each.
Describe the factors that influence the horizontal detail (blur) and the vertical detail (blur) of a fluoroscopic image and how you can change detail during a procedure.
Describe the principles of operation of an automatic brightness control unit used with fluoroscopy.
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Fluoro objectives
Describe the principle factor that affects quantum noise in fluoroscopy.
Describe the process of evaluating a fluoroscopic system for quantum noise .
Explain how the quantum noise level can be changed.
10 Fluoro & Rad Protectionobjectives
State typical and regulatory maximum exposure rates to patients with normal fluoroscopy.
Identify the major factor that produces high patient and staff exposures during fluoroscopy.
Explain the purpose of the High Level Control (HLC) fluoroscopic mode, when is it used, and potential hazards.
Review the State Syllabus on Fluoroscopy and Radiation Protection with Title 17
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SO, LET’S GET STARTED!
Are you ready?
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FLUOROSCOPY Primary function – dynamic motion studies Motion of internal structures in real time
CONVENTIONAL FLUORO HAS BEEN REPLACED BY IMAGE INTENSIFICAITON
Conv Fluoro – Rad directly observing images on a fluoroscopic screen
13 Basic “Imaging Chain”
14 Basic Componets of “old” Fluoroscopy “Imaging Chain”
Fluoro TUBE
Primary
Radiation PATIENT
EXIT Radiation
Image Intensifier
ABC Image Recording Devices
Fiber Optics OR
105 Photospot
CINE
Cas
sett
e
VIDICON
Camera Tube
CONTROL
UNITTV
LENS
SPLIT
15 Basic Componets of “NEW DIGITAL” Fluoro“Imaging Chain”
Fluoro TUBE
Primary
Radiation PATIENT
EXIT Radiation
Image Intensifier
ABC CCD
Analog to
Digital
Converter
ADC
TV
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Used to visualize motion of internal fluid, structures
Operator controls activation of tube and position over patient
Early fluoroscopy gave dim image on fluorescent screen
Physician seared in dark room Modern systems include image
intensifier with television screen display and choice of recording devices
Fluoroscopy: a “see-through” operation with motion
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X-ray transmitted trough patient The photographic plate replaced by fluorescent screen Screen fluoresces under irradiation and gives a life picture Older systems direct viewing of screen Nowadays screen part of an Image Intensifier system Coupled to a television camera Radiologist can watch the images “live” on TV-monitor;
images can be recorded Fluoroscopy often used to observe digestive tract
Upper GI series, Barium Swallow Lower GI series Barium Enema
Fluoroscopy
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Early Fluoroscopy
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DIRECT FLUOROSCOPY
Early fluoroscopy = the image was viewed directly – the xray photons struck the fluoroscopic screen – emitting light.
The Higher KVP – brighter the light DISADVANTAGES:
ONLY ONE PERSON CAN VIEW IMAGE ROOM NEED COMPLETE DARKNESS PATIENT DOSE (& RADIOLOGIST) WAS VERY
HIGH
20 Direct Fluoroscopy: obsolete
In older fluoroscopic examinations radiologist stands behind screen and view the pictureRadiologist receives high exposure; despite protective glass, lead shielding in stand, apron and perhaps goggles
Main source staff exposure is NOT the patient but direct beam
21 CONVENTIONAL FLUOROSCOPYINVENTED BY THOMAS EDISON
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Conventional Fluoroscopic Unit
Conventional fluoroscopy User viewed faint image on screen User in direct path of beam Very high dose to user and patient Excellent resolution No longer used
24 Older Fluoroscopy
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Older Fluoroscopic Equipment(still in use in some countries)
Staff in DIRECT beamEven no protection
26 Red goggles for dark adaptation
More about the eye and vision later in unit………….
27 Conventional older
Fluoroscopy systems
30 min for dark adaptation
RODS or CONES VISION?
28 Light Levels and Fluoroscopy
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Early Image Intensified FLUORO
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Conventional I I system
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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
33 The main components of the fluoroscopy imaging chain
Image Intensifier
Associated image
TV system
34 Basic Componets of “old” Fluoroscopy “Imaging Chain”
Fluoro TUBE
Primary
Radiation PATIENT
EXIT Radiation
Image Intensifier
ABC Image Recording Devices
Fiber Optics OR
105 Photospot
CINE
Cas
sett
e
VIDICON
Camera Tube
CONTROL
UNITTV
35 NEWER SYSTEMS –DIGITAL FLUORO
36 Basic Componets of “NEW DIGITAL” Fluoro“Imaging Chain”
Fluoro TUBE
Primary
Radiation PATIENT
EXIT Radiation
Image Intensifier
ABC CCD
Analog to
Digital
Converter
ADC
TV
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IMAGE INTENSIFICAITON IMAGES ARE VIEWED ON A TV SCREEN/MONITOR
38 FLUOROSCOPYIMAGES IN MOTION
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THE IMAGING CHAIN
Historical maybe–
but you have to know this………
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Image Intensified Fluoroscopy
Electronic conversion of screen image to light image that can be viewed on a monitor
resolution dose
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Photons used: Fluoro vs Photons used: Fluoro vs RadiographyRadiography
Spotfilm Fluoroscopy
kVp: 85 85mA: 200 3Time (sec): 0.3 0.2*mAs: 60 0.6Ratio: 100 1
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Modern Image Modern Image Intensifier based Intensifier based
fluoroscopy systemfluoroscopy system
44 Modern Fluoroscopic Unit
45 Modern fluoroscopic system components
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FLUORO TUBES
CAN BE LOCATED UNDER OR OVER THE TABLE…..
FIRST COVERED – UNDER THE TABLE
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Remote – over the table tube
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Different fluoroscopy systems
Remote control systems Not requiring the presence
of medical specialists inside the X Ray room
Mobile C-arms Mostly used in surgical
theatres.
51C-ARM UNIT -STATIONARY
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MOBILE C-ARM UNIT
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Mini c-arm
54 Basic Componets of “old” Fluoroscopy “Imaging Chain”
Fluoro TUBE
Primary
Radiation PATIENT
EXIT Radiation
Image Intensifier
ABC Image Recording Devices
Fiber Optics OR
105 Photospot
CINE
Cas
sett
e
VIDICON
Camera Tube
CONTROL
UNITTV
LENS
SPLIT
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Fluoroscopy mA
Low, continuous exposures .05 – 5 ma (usually ave 1 – 2 ma)
Radiographic Exposure (for cassette spot films)
mA increased to 100 – 200 mA
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I IIMAGE INTENSIFIER
57 Basic Componets of “old” Fluoroscopy “Imaging Chain”
Fluoro TUBE
Primary
Radiation PATIENT
EXIT Radiation
Image Intensifier
ABC Image Recording Devices
Fiber Optics OR
105 Photospot
CINE
Cas
sett
e
VIDICON
Camera Tube
CONTROL
UNITTV
LENS
SPLIT
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Image Intensifier
VACUUM TUBE ENCASED IN A LEAD
HOUSING = 2MM PB (PRIMARY BARRIER)
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Image intensifier systems
60 Image Intensification Tube Components
Input screen and photocathode
Electrostatic lenses Magnification tubes
61 Image Intensification Tube Components
Anode and output screen
Total brightness gain Minification gain x flux
gain
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INPUT PHOSPHOR
63 Functioning of Image
Intensifier
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IMAGE INTENSIFIER INPUT PHOSPHOR – CESIUM IODIDE PHOTOCATHODE (LIGHT TO E’S) ELECTOSTATIC LENSES – FOCUSES AND ACCELERATES THE E INTENSIFIES LIGHT = BRIGHTNESS GAIN
(BG) BG = MG X FG
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YOU WILL HAVE TO DRAW THIS
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IMAGE INTENSIFIER
CESIUM IODIDE – Input Phosphor ZINC CADMIUM SULFIDE – Output
phosphor
ELECTRON FOCUSING LENS + CURRENT ATTRACTS e TO ANODE 25 – 35 KVP POTIENTIAL ACROSS TUBE Output phosphor contains a thin al plate to
prevent light returning to the photocathode
67 Input Screen and Photocathode
Input screen 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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69 Cesium Iodide (CsI) Phosphoron Input Phosphor
CsI crystals grown linear and packed closely together
The column shaped “pipes” helps to direct the Light with less blurring
Converts x-ray photons to visible light
SIDE VIEW
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II Image Intensifier
The input phosphor converts x-ray to light* Light from the input phosphor is sent to the
photocathode made of cesium and antimony compounds*
Photocathode turns light into electrons (called photoemission)*
Now we have electrons that need to get to the anode……….. this is done by the electrostatic lenses
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Electrostatic Lenses
Accelerate and focus electron pattern across tube to anode
Primary source of brightness gain
72Image intensifier component
Input screen: conversion of incident X Rays into light photons (CsI)
1 X Ray photon creates 3,000 light photons Photocathode: conversion of light photons into electrons
only 10 to 20% of light photons are converted into photoelectrons
Electrodes (lenses): focalization of electrons onto the output screen
electrodes provide the electronic magnification Output screen: conversion of accelerated electrons into light
photons
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The image intensifier (I.I.)
+
I.I. Input Screen
I.I.Output Screen
Photocathode
Electrode E1
Electrode E3
Electrode E2
Electrons Path
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Image Intensifier Tube
Vacuum diode tube1. Input phosphor (CsI)
X-rays light2. Photocathode
Photoemission Light electron beam
3. Electrostatic lenses Maintain & minify e-
4. Anode Attracts e- in beam
5. Output phosphor (ZnS-CdS) e- light
1
5
2 3
4
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Magnification
Input screen diameter Diameter used
during exam
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Multi-field II Units
II that allows selection of input phosphor size
2 or 3 size selections 25/17 cm 25/17/12 or 23/15/10
Smaller input magnifies output by moving focal point away from output
Requires more x-rays to maintain brightness
25 cm vs. 17 cm
smaller
largermag
2
2
smaller
largerdose
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STOPPING PLACE FOR DAY 1 - 2010
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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 cm 9/6 inches
Tri focus 12/9/6 inches
79 Intensifier Format and Modes
Note focal point moves farther from output in mag mode
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MAG MODE VS PT DOSE
MAG USED TO ENLARGE SMALL STRUCTURE OR TO PENETRATE THROUGH LARGER PARTS
FORMULA:
PATIENT DOSE IS INCREASED IN THE MAG MODE –
DEPENDANT ON SIZE OF INPUT PHOSPHOR
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MAG MODE FORMULA
IP OLD SIZE
IP NEW SIZE = %mag
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PT dose in MAG MODE
IP OLD SIZE 2
IP NEW SIZE 2 = ↑ pt dose
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Fluoroscopic Dose Ratesmay show as “boost” button
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Intensifier Format and Mag Modes
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Image Intensifier Performance Conversion factor is the ratio of output phosphor
image luminance (candelas/m2) to x-ray exposure rate entering the image intensifier (mR/second).
Very difficult to measure: no access to output phosphor
No absolute performance criteria
Bushong pg 362 – 0.01 x brigtness gain Usually 50-300 (BG= 5000 to 30000
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BG = MG X FG
Brightness gain BG = MINIFICATION GAIN X FLUX GAIN Brightness gain is a measure of the
conversion factor that is the ratio of the intensity of the output phosphor to the input phosphor
conversion factor = intensity of OP Ø
mR/sec
88BRIGHTNESS GAINcan be expressed as:
conversion factor = intensity of OP Ø
mR/sec
conversion factor =
Output phosphor illumination (candelas/m2 )
Input exposure rate (mR/sec)
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Brightness gain
The II makes the image brighter because it minified it and more light photons.
Multiply the flux gain times the minification gain.
BG = MG X FG
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Intensifier Brightness Gain (BG)
BG = MG x FG
Minification Gain x Flux Gain
Minification gain (MG): The ratio of the squares of the input and output phosphor diameters. This corresponds to “concentrating” the light into a smaller area, thus increasing brightness
MG = (Input Diameter )2
(Output Diameter)2
91 Minification
(↑ BRIGHTNESS OF LIGHT)
Electrons had to be focused down to fit through the hole at the anode Input phosphor is much bigger than the anode opening
Input phosphors are 10-35 cm in diameter* (6, 9 , 12 inches)Output phosphors are 2.5 to 5 cm (1 in) in
diameter*Most fluoro tubes have the ability to operate in 2
sizes (just like small and large focal spot sizes)Bi focus - M=Newer units - tri focus
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Minification gain - again
BG = MINIFICATION GAIN X FLUX GAIN MINIFICATION GAIN – same # e at input
condensed to output phosphor – ratio of surface area on input screen over surface area of output screen
IP SIZE 2
OP SIZE 2
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Flux gain
The ratio of the number of light photons striking the output screen to the ratio of the number of x-ray photons striking the input screen is called fluxgain
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Intensifier Flux Gain
95 1000 light photons at
the photocathode from 1 x-ray photon photocathode
decreased the # of ë’s so that they could fit through the anode
Output phosphor = 3000 light photons (3 X
more than at the input phosphor!)
This increase is called the flux gain
FLUX GAIN
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BG = MG X FG
FLUX GAIN – increase of light brightness due to the conversion efficiency of the output screen
1 electron = 50 light photons is 50 FG Can decrease as II ages Output phosphor almost always 1 inch Zinc cadnium phosphot Flux gain is almost always 50
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Intensifier Brightness Gain
Flux Gain (FG): Produced by accelerating the photoelectrons across a high voltage (>20 keV), thus allowing each electron to produce many more light photons in the output phosphor than was required to eject them from the photcathode.
Summary: Combining minification and flux gains:
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Intensifier Brightness Gain
Example:
Input Phosphor Diameter = 9”
Output Phosphor Diameter = 1”
Flux Gain = 75 (usually 50)
BG = FG x MG = 75 x (9/1)2 = 6075
Typical values: a few thousand to >10,000 for modern image intensifiers
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Image Intensifier FORMULAS
Flux Gain (usually stated rather than calculated)
input
output
photonsraysx#
photonslight#FG
Brightness Gain Ability of II to increase illumination
gainfluxgainonminificatiBG Minification Gain
2
2
phosphoroutput
phosphorinputMG
MAGNIFICATION?????
100MAG MODE FORMULA
IP OLD SIZE
IP NEW SIZE = %mag
101PT dose in MAG MODE
IP OLD SIZE 2
IP NEW SIZE 2 = ↑ pt dose