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Fluoroscopy Equipment Operation

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Fluoroscopy Equipment Operation Rad T 290 * * Explanation or/and additional information Instructions for the lecturer/trainer * * * * * * * * * * * * DDR ... – PowerPoint PPT presentation

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Title: Fluoroscopy Equipment Operation


1
Fluoroscopy Equipment Operation
  • Rad T 290

2
Topics for WEEK 2
  • Describe the components of an image intensifier.
  • Describe the components of flat panel digital
    fluoroscopy.
  • TV viewing system..etc

3
II Fluoroscopy
  • The II was developed to replace the conventional
    fluorescent screen.
  • The II raised illumination into the cone vision
    region, where visual acuity is greatest.
  • Technical factors is similar to radiographic
    image quality. Generally, high kVp and low mA are
    preferred.

4
Image Intensifier
  • VACUUM TUBE
  • ENCASED IN A LEAD HOUSING
  • 2MM PB
  • (PRIMARY BARRIER)

5
Image intensifier systems
6
Image Intensification Tube Components
  • Input screen and photocathode
  • Electrostatic lenses
  • Anode and output screen

7
Steps to image intensification
  • Object of the II is to convert remnant radiation
    into an amplified light image
  • 5 basic parts
  • Input phosphor
  • Photocathode
  • Electrostatic lenses
  • Accelerating anode
  • Output phosphor

8
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

9
II Fluoroscopy
  • During image-intensified fluoroscopy, the
    radiologic image is displayed on a television
    monitor or flat panel monitor.
  • X-ray tube is operated at less
  • than 5 mA. Radiographic exams the x-ray
  • tube current is measured in hundreds of mA.
  • Despite this fluoro dose tends to
  • be much higher?

10
kVp
  • KVp depends entirely on the anatomy being
    examined. Fluoroscopic equipment operates by
    selecting an image brightness. The automatic
    brightness control (ABC)
  • The ABC maintaines image brighness automatically
    by varying the kVp, the mA, or sometimes both.
  • Generally kVp is maintained by adjust the mA
    depending on part/patient thickness

11
IMAGE INTENSIFIER
12
Image-intensifier
  • Remnant photons enter the image-intensifier tube
    transmitted through the glass envelope and
    interact with the input phosphor, which is cesium
    iodide (CsI). When an x-ray interacts with the
    input phosphor, its energy is converted into
    visible light.
  • Where else does this occur in radiography?

13
INPUT PHOSPHOR
14
Cesium Iodide microlight pipes
  • CsI crystals are grown as tiny needles and
  • are tightly packed in a
  • layer of approximately
  • 300 µm

15
Input phosphor
  • Is a round tube that can
  • A diameter of 6, 9,
  • 12 or 16 inches

16
Photocathode
  • The next active element of the image-intensifier
    tube is the photocathode.
  • Bonded directly to the input phosphor with a
    thin, transparent adhesive layer. The
    photocathode is a thin metal layer composed of
    cesium and antimony compounds that respond to
    stimulation of input phosphor light by the
    emission of electrons.
  • The photocathode emits e- when illuminated by the
    input phosphor

17
Photoemission
  • This process is known as photoemission.
  • Photoemission is electron emission that follows
    light stimulation.
  • The number of electrons emitted by the
    photocathode is directly proportional to the
    intensity of light that reaches it.

18
Electrostatic Focusing Lenses
  • A series of metal rings which have varying
    positive voltage.
  • They pull the e- from the input side toward the
    put out phosphor.
  • This process is called
  • minification.

19
The image intensifier (I.I.)
I.I. Input Screen
Electrode E1
Electrode E2
Electrode E3
Electrons Path
I.I.Output Screen
Photocathode

20
The anode of the II
  • The anode is a circular plate about 20 away
    from the photocathode. It has a hole in the
    middle of it allowing electrons to pass through
    and hit the output phosphor made of zinc cadmium
    sulfide.
  • Electrostatic lenses have a negative charge to
    repel the negative electrons and push them to the
    anode and focus them to a narrow beam.
  • The electrons are carrying the latent image and
    when they hit the output phosphor they are turned
    into light again.

21
Accelerating Anode
  • II tube is
  • approximately
  • 50 cm long
  • Potential difference
  • between photocathode
  • and anode of 25,000
  • - 30, 000 V

22
Flux gain (flow)
  • 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

23
Intensifier Flux Gain
24
FLUX GAIN
  • 1000 light photons at the photocathode
  • from 1 x-ray photon
  • Output phosphor
  • 3000 light photons (3 X more than at the input
    phosphor!)
  • This increase is called the flux gain

25
Output Phosphor
  • a 1 circular plate with a hole in the middle
    through which electrons pass.
  • Made of zinc cadmium sulfide that produces light
    by interacting with e-.
  • Output phosphor is always 1.
  • Very concentrated bright light is direct to a TV
    camera tub or CCD.

26
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 or newer units - tri focus

27
Total brightness gain (BG)
  • The II makes the image brighter because it is
    minified and amplified (more light photons).
  • BG MG X FG
  • Multiply the minification gain times the flux
    gain.

28
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

29
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

30
BG MG X FG
  • FLUX GAIN increase of light brightness due to
    the conversion efficiency of the output screen
    (estimation)
  • 1 electron 50 light photons is 50 FG
  • Can decrease as II ages
  • Flux gain is almost always 50

31
Intensifier Brightness Gain
  • Example
  • Input Phosphor Diameter 9
  • Output Phosphor Diameter 1
  • Flux Gain 50
  • BG FG x MG 50 x (9/1)2 4,050
  • Typical values a few thousand to gt10,000 for
    modern image intensifiers

32
Intensifier Brightness Gain
  • Flux Gain (FG) Produced by accelerating the
    photoelectrons across a high voltage (gt20 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

33
Image Intensifier FORMULAS
  • Brightness Gain
  • Ability of II to increase illumination
  • Minification Gain
  • Flux Gain (usually stated rather than calculated)

34
Conversion Factor
  • International Commission of Radiologic Units and
    Measurements (ICRU) recommends evaluating the
    brightness gain of the II based upon the
    conversion factor.

35
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).
  • II has conversion factors between 50 - 300
  • Usually 5000 to 30,000 brightness gains

36
Image Intensifier Tube
  • Vacuum diode tube
  • 1. Input phosphor (CsI)
  • X-rays ? light
  • 2. Photocathode
  • Photoemission
  • Light ? electron beam
  • 3. Electrostatic lenses
  • Maintain minify e-
  • 4. Anode
  • Attracts e- in beam
  • 5. Output phosphor (ZnS-CdS)
  • e- ? light

37
Multifield Image Intensification
  • FOV selection gives you the active diameter of
    the input phosphor. 6, 9, 12 or 16
  • In 16 mode photoelectrons from the entire input
    phosphor are accelerated to the output phosphor.
  • 12 mode, the voltage on the electrostatic
    focusing lenses increase causing the electron
    focal point to move farther from the output
    phosphor. Only 12 of input phosphor are on the
    output phosphor.

38
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

39
Intensifier Format and Modes
Note focal point moves farther from output in mag
mode
40
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41
FOV
  • This change in focal point will reduce the FOV
    and the image appears magnified.
  • Using the smaller dimension of a multifield
    image-intensifier tube always results in a
    magnified image, with a magnification factor in
    direct proportion to the ratio of the diameters.

42
Magnification Factor FORMULA
  • IP OLD SIZE
  • IP NEW SIZE mag

43
Intensifier Format and Mag Modes
44
Whats the catch?
  • Image will be much dimmer, less light entering II
    less light per output pixel. Minification gain
    is reduced.
  • Reduced signal-to-noise ratio (SNR). Noise will
    become more visible in the image.
  • ABC will compensate, how?

45
Image Quality in Mag Mode
  • Improved spatial resolution

46
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

47
Basic Componets of NEW DIGITAL FluoroImaging
Chain
Primary Radiation
EXIT Radiation
Fluoro TUBE
PATIENT
Analog to Digital Converter ADC
Image Intensifier
ABC
CCD
TV
48
Dynamic Flat-Panel Digital Fluoroscopy
49
Flat-Panel Detectors (FPD)
  • II tubes are being replaced by Flat-panel
    detectors.

50
Coating for DR
  • AMORPHOUS SILICON (indirect)
  • X-ray photon to light photon
  • AMORPHOUS SELENIUM (direct trapped e-)
  • No light

51
Flat-Panel Detectors (FPD)
  • Two types of dynamic FPDs
  • Indirect using cesium iodide (CsI) phosphors
    coupled to an active matrix array of amorphous
    silicon (a-Si), which holds a charge on its
    surface that can then be read out by a TFT.

52
Active Matrix Array (AMA) Pixels are read
sequentially, one at a time
  • Each TFT or CCD detector represents a pixel
  • DEL charge collecting detector element

53
Flat-Panel Detectors (FPD)
  • Direct capture detector using an AMA of Amorphous
    selenium (a-Se) TFTs
  • Direct e- capture

54
Capture Element
  • Where the remnant photons are captured.
  • DR Cesium iodide (CsI), Gadolium oxysulfide
    (GdOS), or Amorphous selenium (a-Se).

55
Collection element
  • Collects converted x-ray signal.
  • Types Photodiode, A charge-coupled device (CCD),
    or A thin-film transistor (TFT).
  • Photodiode CCD collect light. TFT is charge
    sensitive and collects E-.

56
Charge-Coupled Device
  • CCD, which is the light-sensing element.
  • The CCD is a silicon-based semiconductor
  • has three principal advantageous imaging
    characteristics sensitivity, dynamic range, and
    size.

57
Sensitivity
  • is the ability of the CCD to detect and respond
    to very low levels of visible light
  • This sensitivity is important for low patient
    radiation dose in digital imaging.

58
Direct vs Indirect Conversion
  • In direct conversion, x-ray photons are absorbed
    by the coating material and immediately converted
    into an electrical signal. The DR plate has a
    radiation-conversion material or scintillator,
    typically made of a-Se. This material absorbs
    x-rays and converts them to electrons, which are
    stored in the TFT detectors.

59
Indirect Conversion
  • Indirect conversion is a two-step process x-ray
    photons are converted to light, and then the
    light photons are converted to an electrical
    signal.
  • A scintillator converts x-rays into visible
    light. The light is then converted into an
    electric charge by photodetectors such as
    amorphous silicon photodiode arrays or
    charge-coupled devices (CCDs).

60
Scintillation DR
61
CCD Array with a scintillation phosphor
62
TFT
  • The thin-film transistor (TFT) is a
    photosensitive array made up of small (about 100
    to 200µm) pixels. Each pixel contains a
    photodiode that absorbs the electrons and
    generates electrical charges.

63
DR
  • A field-effect transistor (FET) or silicon TFT
    isolates each pixel element and reacts like a
    switch to send the electrical charges to the
    image processor.

64
Amorphous Selenium
  • No scintillation phosphor is involved
  • The image-forming x-ray beam interacts directly
    with amorphous selenium (a-Se),
  • producing a
  • charged pair.

65
Amorphous Selenium
  • The a-Se is both the capture element and the
    converting element.
  • a-Se is a direct DR process by which x-rays are
    converted
  • to electric signal

66
DDR only using amorphous selenium (a-Se)
  • The exit x-ray photon interact with the a-Si
    (detector element/DEL). Photon energy is trapped
    on detector (signal)
  • The TFT stores the signal until readout, one
    pixel at a time

67
Direct vs Indirect DR
68
FPD vs. dynamic FPD
  • Fluoroscopy FPD are larger and have larger matrix
    sizes. Pixel sizes?

69
Digital Fluoroscopy (DF)
  • DF, the under-table x-ray tube operates in the
    radiographic mode. Tube current is measured in
    hundreds of mA instead of less than 5 mA, as in
    image-intensifying fluoroscopy.
  • Pulse-progressive fluoroscopy

70
Pulsed Fluoroscopy
71
Fluoroscopic Image Display
72
Image Display
  • 2 Methods
  • Thermionic television camera tube
  • Solid state charge-coupled device (CCD)
  • Coupling I.I. to TV or CCD
  • Fiber optics
  • Lens system

73
Viewing
  • The output phosphor of the II is connected by
    fiber optic cables directly to a TV camera tube
    when the viewing is done through a television
    monitor.
  • The most commonly used camera tube - vidicon
  • Inside the glass envelope that surrounds the TV
    camera tube is a cathode, an electron gun, grids
    and a target.
  • Past the target is a signal plate that sends the
    signal from the camera tube to the external video
    device

74
Type of TV camera
  • VIDICON TV camera
  • improvement of contrast
  • improvement of signal to noise ratio
  • high image lag
  • PLUMBICON TV camera (suitable for cardiology)
  • lower image lag (follow up of organ motions)
  • higher quantum noise level
  • CCD TV camera (digital fluoroscopy)
  • digital fluoroscopy spot films are limited in
    resolution, since they depend on the TV camera
    (no better than about 2 lp/mm) for a 1000 line TV
    system

75
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76
Vidicon (tube) TV Camera
77
Bandpass/Horizantal Resolution
  • Horizontal resolution is determined by the
    bandpass.
  • Bandpass is expressed in frequency (Hz) and
    describes the number of times per second the
    electron beam can be modulated.
  • The higher the bandpass, the better the resolution

78
TV RESOLUTION-Horizontal
  • Along a TV line, resolution is limited by how
    fast the camera electronic signal and monitors
    electron beam intensity can change from minimum
    to maximum.
  • This is bandwidth. For similar horiz and vertical
    resolution, need 525 changes (262 full cycles)
    per line. Example (at 30 frames/second)
  • 262 cycles/line x 525 lines/frame x 30
    frames/second
  • 4.2 million cycles/second or 4.2 Megahertz (MHz)

79
Video Camera Charged Coupled Devices (CCD)
  • Operate at lower voltages than video tubes
  • More durable than video tubes
  • Semiconducting device
  • Emits electrons in proportion to amount of light
    striking photoelectric cathode
  • Fast discharge eliminates lag

80
CCDs
81
Digital Uses Progressive Scan
  • 1024 x 1024
  • Higher spatial resolution
  • As compared to 525
  • 8 images/sec
  • (compared to 30 in 525 system)

82
Monitors
  • Cathode ray tube (CRT)
  • Liquid crystal display (LCD)
  • Plasma screen

83
Soft copy viewing digital cathode ray tube (CRT)
84
active matrix liquid crystal display (AMLCD)
85
Active matrix liquid crystal displays are
superior to cathode ray tube displays.
  • LCD design gives out more light,
  • reduces ambient light
  • Better contrast resolution
  • Less noise
  • Less maintenance

86
Crystals can be aligned by an external electric
field
87
Plasma Display
  • The plasma displays are made up of many small
    fluorescent lights that are illuminated to form
    the color of the image.

88
Questions?
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