Transcript Fluoroscopy Intro to EQUIPMENT

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
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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.
5
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.
6
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

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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.
8
Fluoro objectives


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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.
9
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.
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Fluoro & Rad Protection
objectives




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
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
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Basic “Imaging Chain”
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Basic Componets of “old”
Fluoroscopy “Imaging Chain”
Fluoro
TUBE
Primary
EXIT
Radiation
PATIENT
Radiation
Cassette
105
Photospot
Image
Intensifier
Fiber Optics
OR
ABC
LENS
SPLIT
Image
Recording
Devices
CINE
VIDICON
CONTROL
Camera Tube
UNIT
TV
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Basic Componets of “NEW
DIGITAL” Fluoro“Imaging Chain”
Fluoro
TUBE
Primary
Radiation
EXIT
Radiation
PATIENT
Analog to
Image
Intensifier
ABC
CCD
Digital
Converter
ADC
TV
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Fluoroscopy: a “see-through”
operation with motion

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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
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Fluoroscopy


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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
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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
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Direct Fluoroscopy: obsolete
In older fluoroscopic examinations radiologist stands
behind screen and view the picture
Radiologist 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
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CONVENTIONAL FLUOROSCOPY
INVENTED BY THOMAS EDISON
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Conventional Fluoroscopic Unit
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Conventional fluoroscopy
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User viewed faint image on screen
User in direct path of beam
Very high dose to user and patient
Excellent resolution
No longer used
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Older Fluoroscopy
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Older Fluoroscopic Equipment
(still in use in some countries)
Staff in DIRECT beam
Even no protection
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Red goggles for dark
adaptation
More about the eye and vision later in unit………….
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Conventional older
Fluoroscopy systems
30 min for dark adaptation
RODS or CONES VISION?
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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
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The main components of the
fluoroscopy imaging chain
Image
Intensifier
Associated
image
TV system
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Basic Componets of “old”
Fluoroscopy “Imaging Chain”
Primary
Fluoro
TUBE
EXIT
Radiation
PATIENT
Radiation
Cassette
105
Photospot
Image
Intensifier
ABC
Fiber Optics
OR
Image
Recording
Devices
CINE
VIDICON
CONTROL
Camera Tube
UNIT
TV
35
NEWER SYSTEMS –
DIGITAL FLUORO
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Basic Componets of “NEW
DIGITAL” Fluoro“Imaging Chain”
Fluoro
TUBE
Primary
Radiation
EXIT
Radiation
PATIENT
Analog to
Image
Intensifier
ABC
CCD
Digital
Converter
ADC
TV
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IMAGE INTENSIFICAITON

IMAGES ARE VIEWED ON A TV SCREEN/MONITOR
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FLUOROSCOPY
IMAGES 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
Photons used: Fluoro vs
Radiography
kVp:
mA:
Time (sec):
mAs:
Ratio:
Spotfilm
Fluoroscopy
85
200
0.3
60
100
85
3
0.2*
0.6
1
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Modern Image Intensifier based
fluoroscopy system
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Modern Fluoroscopic Unit
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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
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Remote control systems
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Not requiring the presence
of
medical
specialists
inside the X Ray room
Mobile C-arms

Mostly used in surgical
theatres.
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C-ARM UNIT -STATIONARY
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MOBILE C-ARM UNIT
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Mini c-arm
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Basic Componets of “old”
Fluoroscopy “Imaging Chain”
Fluoro
TUBE
Primary
EXIT
Radiation
PATIENT
Radiation
Cassette
105
Photospot
Image
Intensifier
Fiber Optics
OR
ABC
LENS
SPLIT
Image
Recording
Devices
CINE
VIDICON
CONTROL
Camera Tube
UNIT
TV
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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

II
IMAGE INTENSIFIER
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Basic Componets of “old”
Fluoroscopy “Imaging Chain”
Fluoro
TUBE
Primary
EXIT
Radiation
PATIENT
Radiation
Cassette
105
Photospot
Image
Intensifier
Fiber Optics
OR
ABC
LENS
SPLIT
Image
Recording
Devices
CINE
VIDICON
CONTROL
Camera Tube
UNIT
TV
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Image Intensifier

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VACUUM TUBE
ENCASED IN A LEAD
HOUSING
= 2MM PB
(PRIMARY BARRIER)
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Image intensifier systems
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Image Intensification Tube
Components

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
Input screen and
photocathode
Electrostatic lenses
Magnification tubes
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Image Intensification Tube
Components
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Anode and output
screen
Total brightness gain

Minification gain x flux
gain
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INPUT PHOSPHOR
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Functioning of Image
Intensifier
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IMAGE INTENSIFIER
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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
65 YOU WILL HAVE TO DRAW THIS
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IMAGE INTENSIFIER
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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
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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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Cesium Iodide (CsI) Phosphor
on 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
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Image 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
Electrode E1
Electrode E2
Electrode E3
I.I.Output Screen
Photocathode
+
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Image Intensifier Tube

Vacuum diode tube
1. Input phosphor (CsI)

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X-rays  light
2. Photocathode
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Photoemission
Light  electron beam
3. Electrostatic lenses
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4. Anode
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Attracts e- in beam
5. Output phosphor (ZnS-CdS)

4
Maintain & minify e-
e-  light
1
2
3
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Magnification
Input screen diameter
 Diameter used
during exam

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Multi-field II Units
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II that allows selection of
input phosphor size
2 or 3 size selections

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25 cm vs. 17 cm
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
larger
mag 
smaller
larger 2
dose  
smaller 2
STOPPING PLACE
FOR DAY 1 - 2010
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Magnification Tubes

Greater voltage to electrostatic lenses
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Dual focus
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Increases acceleration of electrons
Shifts focal point away from anode
23/15 cm
Tri focus

12/9/6 inches
9/6 inches
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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
IP NEW SIZE
2
2
dose
= ↑ pt
84
Fluoroscopic Dose Rates
may show as “boost” button
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Intensifier Format and Mag
Modes
86
Image Intensifier Performance

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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
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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
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BRIGHTNESS GAIN
can be expressed as:

conversion factor
= intensity of OP
Ø
mR/sec

conversion factor =
Output phosphor illumination
(candelas/m2 )
Input exposure rate (mR/sec)
89
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
90
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
OP SIZE
2
2
93
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
94
Intensifier Flux Gain
95
FLUX GAIN






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
96
BG = MG X FG

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
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
97
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:
98
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
99
Image Intensifier FORMULAS

Brightness Gain

Ability of II to increase illumination
BG  minificati on gain  flux gain
2

input phosphor 
MG 
output phosphor 2

Minification Gain

Flux Gain (usually stated rather than calculated)
FG 
MAGNIFICATION?????
# light photons output
# xrays photons input
10
0
MAG MODE FORMULA
IP OLD SIZE
IP NEW SIZE = %mag
10
1
PT dose in MAG MODE
IP OLD SIZE
IP NEW SIZE
2
2
dose
= ↑ pt