Prepared by:- KAMARUL AMIN BIN ABDULLAH @ ABU BAKAR · Spot film or direct optical viewing depend on geometrical factors, includes minification gain, electrostatic focal point, input

LECTURE 7

Prepared by:-

KAMARUL AMIN BIN ABDULLAH @ ABU BAKAR

UiTM Faculty of Health SciencesMedical Imaging Department

LESSON OBJECTIVESAt the end of the session, the students should be able to: Briefly explain the purpose, construction

and principles of fluoroscopy. Briefly explain the image intensifier, the

principles and its construction. List the components in II and explain the

function of each components. Briefly explain its viewing and recording

system.

10/18/2012 2Kamarul Amin (c)

INTRODUCTION Fluoro: is dynamic radiographic

examination. Fluoroscopy is primarily domain of the

radiologist. However, the role of radiographer to

assist and routine post-fluoroscopic radiography.

Fluoroscopy was discover 1896.





Fluoroscopic Equipment

1. X-ray Tube.

2. Image Receptor (Image Intensification).

3. Viewing Systems

4. Recording Systems

Kamarul Amin (c) 710/18/2012

Cont’d..

X-ray Tube and Image Intensification

are mounted to a C-arm to maintain their

alignment at all times.

C-arm permits the image receptor to be

raised and lower to vary the beam

geometry for maximum resolution while x-

ray tube remains in position.


Cont’d..

C-arm can move all direction.

2 types of C-arm:

under couch, and

over couch


Cont’d..

Carriage is the arm supports the equipment

suspended over the table include I.I., x-ray

tube, control power drive, spot film selection,

tube shutters, spot filming, cine camera,

video input tube etc.

Exposure cannot commence until the carriage

is return to a full beam intercept position.

10/18/2012 Kamarul Amin (c) 10

1) X-ray Tube

Similar to General X-ray Tubes except:

Designed to operate for longer periods of time at

much lower mA i.e. fluoroscopic range 0.5-5 mA

Tube target must be fixed to prevent an SOD of

less than 15 inch (~ 40 cm).

Fluoroscopic tube can operate by Foot Switch

Equipped with electrically controlled shutter.


2) Image Intensification

(II)

Was developed 1948.

Is designed to amplify the brightness of

an image.

New II are capable of increasing image

brightness 500-8000 times.


Cont’d..

Major components of an

II are:-

i. Input Window

ii. Input Phosphor

iii. Electrostatic Lenses

iv. Output Phosphor

v. Output Window

vi. Envelope





Principle Operation

The primary x-ray beam exits the patient and

strikes the input screen of the II, which is a

vacuum tube with a cathode and an anode.

Fluorescent screen is built into the image

intensifier as input screen, which absorbs the

x-ray photons and emits light photons.


Cont’d..

Photocathode is 2nd layer which prevent

divergence of the light.

The photocathode absorb the light and

emits electrons.


Cont’d..

Then electrons accelerated from the

cathode toward the anode and the output

screen by 25 kV potential difference.

Electrostatic lenses is used to accelerate

and focus the electron beam.

The output screen absorbs the electrons

and emits light photons.


Cont’d..

II is encased in a lead lined housing that

effectively absorbs the primary beam.

A getter is ion pump is used to remove

ions during operation and maintain the

vacuum within the tube.


i) Input Window

Older IIs used glass ==> x-ray scattering and absorption effects in this material.

Now use thin sheet ( 0.25 - 0.5 mm) of aluminium or titanium==> strength to sustain vacuum & minimal x-ray attenuation.


ii) Input Phosphor Uses CsI doped with Na, deposited on aluminium

substrate. CsI:Na is grown in a structure of monocrystalline needles, each ~ 0.005 mm in diameter < 0.5 mm long. ==>Uses total internal reflexionto transmit as much light as poss'.

The aluminium substrate ~ 0.5 mm thick The input phosphor is typically 15 to 40 cm in

diameter.



Cont’d.. Cs and I are good absorbers of x-photons at

diagnostic energies: K-edges at 36 and 33 keV,respectively. The CsI:Na phosphor gives emittedblue visible light, directed to photocathode.

Intermediate layer (e.g. indium oxide) ==>highoptical transmission. Also chemically isolates thephosphor and photocathode.

The photocathode usually an alloy of antimonyand caesium SbCs3.

Photons interact mainly via photoelectric events==> they disappear and produce recoilelectrons.



CUT OFF VIEW OF II

iii) Electrostatic Lenses A vacuum enables the electrons to travel

without interacting with anything A voltage ~ 25 to 35 kV accelerates the

electrons. Electrodes are used in places (electron

optics) to guide ( focus) the electrons onto the output phosphor.


Cont’d.. Electron current of ~10-8 to 10-7 A is

produced. Both (i) acceleration and (ii) focusing

of the electrons enables imageintensification.


Cont’d.. The image at the output phosphor is

inverted relative to the input image at theinput phosphor (see the focal point due tothe e-optics).

Input phosphor and photocathode are intruth curved This means the electron pathlengths are equalized and reduces imagedistortion.


iv) Output Phosphor ZnCdS: Ag is deposited on the ouput

window ~ 0.005 mm thick and 25 to 35mm in diameter.

Emits a green light upon absorption ofthe photo-electrons from thephotocathode.


Cont’d.. A thin aluminium film on the inner surface

of the phosphor (i) electrical connection for ANODE (ii) to reflect light back towards the output window – attempts to maximize the output luminance and to prevent these light photons from `going back' into the II and interacting with the photocathode.



v) Output Window Various designs exist and have intention of

enhancing the 'straight thru' transmission ofphotons and preventing back reflections intothe II.

Examples are: (i) a glass window (e.g. 15mm thick) with external anti-reflection layers,(ii) tinted glass window and (ii) fibre-opticwindow

The output window image is transmitted toan optical system to be viewed by a cine-camera, photographic camera, video cameraor combinations of these.



vi) II Envelope II envelope is made from glass or non-

magnetic stainless steel Input window is welded to the envelope. Entire assembly is housed inside a metal

container which contains lead, forradiation shielding, and mu-metal, toshield the electron optics from externalmagnetic fields.


Cont’d.. The input window is typically protected by

an aluminium faceplate (e.g. 0.5 mmthick) and is also a safety device in caseof implosion of the II.

Some IIs also have an anti-scatter gridmounted at the faceplate.


Fluoroscopic Generators

Same as those used for

static/conventional radiography.


Brightness Control

Automatic Brightness Control

Automatic adjustments made to exposure factors by

equipment.

Automatic Gain Control

Amplifies video signal rather than adjusting exposure

factors.


Image Quality

Contrast

Resolution

Distortion

Quantum Mottle


Contrast Controlled by amplitude of the video signal.

It is effected by penumbral light scatter in the

input and output screens.

Affected by scatter radiation.

Back scatter effect from the output to the input

screen→ background fog.

Edge of the image decreases image contrast.


Resolution The primary limitation is 525-line raster pattern of the video

camera monitor.

Spot film or direct optical viewing depend on geometrical

factors, includes minification gain, electrostatic focal point,

input and output screen diameter, viewing system resolution

i.e. TV, OID, phosphor size and thickness.

CsI II capable of 4 lp/mm, magnification or multifield image

intensifiers capable of up to 6 lp/mm.


Distortion

Size distortion is caused the same factors affect by

static radiographic e.g. OID.

Shape distortion is caused by geometric problems.

Edge distortion problem (vignetting).


Quantum Mottle Insufficient radiation which cause grainy appearance.

Should be control by high mA and time setting.

Can be also from video noise.

Factors influence mottle are, total no. of photons

arriving retina which include radiation output, beam

attenuation, conversion efficiency, minification gain, flux

gain, total brightness gain, viewing system, distance of

the eye from the viewing system.


Viewing Systems• Older fluoroscopy equipment will have a

television system using a camera tube.

• The camera tube has a glass envelope containing a thin conductive layer coated onto the inside surface of the glass envelope.

• In a PLUMBICON tube, this material is made out of lead oxide, whereas antimony trisulphide is used in a VIDICON tube.




• The surface of the photoconductor isscanned with an electron beam and theamount of current flowing is related to theamount of light falling on the televisioncamera input surface.


The scanning electron beam is producedby a heated photocathode. Electrons areemitted into the vacuum and acceleratedacross the television camera tube byapplying a voltage. The electron beam isfocussed by a set of focussing coils.


Viewing Systems

1. Video Viewing System

2. Video Camera Tubes

A. Cathode

B. Anode

3. Video camera charge-coupled device (CCD)

4. Video monitor

5. Digital


1. Video Viewing

Systems

Closed circuit television

Video camera coupled to output screen and monitor

Video cameras

Vidicon or Plumbicon tube

CCD


2. Video Camera Tubes

Plumbicon and vidicon tubes similar

Different target materials.

Plumbicon has faster response time than vidicon.


Cont’d.. Components of Video Camera Tubes:-

1. Cathode

Control grid

2. Electromagnetic focusing coils

3. Electrostatic deflecting coils

4. Anode

Face plate

Signal plate

Target


Cont’d..

1) Cathode

Heating assembly

Electron gun

thermionic emission

Control grid

Shapes electron beam


Cont’d..

2) Electromagnetic Focusing

coils

Shape electron beam into

single point

3) Deflecting coils

Cause electron stream to

scan target in raster pattern


Cont’d..4) Anode

Face plate

Signal plate

Positively charged thin film of

graphite.

Target

Changes light pattern to

electronic signal sent to

video system.


Video Camera Charged Coupled

Devices (CCD)

Semiconducting device.

Emits electrons in proportion to amount of light

striking photoelectric cathode.

Fast discharge eliminates lag.


3. Video Camera Charged

Coupled Devices (CCD)

Operate at lower voltages than video tubes.

More durable than video tubes.


4. Video Monitor


5. 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.


Recording the Fluoroscopic

Image

1. Dynamic Systems

Cine Film Systems

Videotape Recording

2. Static Spot Filming Systems

Cassettes

105 mm Chip Film

3. Digital Fluoroscopy


Dynamic Systems

1. Cine Film System

2. Videotape Recording


1. Cine Film Systems Consist of cine camera positioned behind output screen.

Required 90% of image intensity for proper exposure.

16 mm and 35 mm formats are currently use.

More pt dose.

Record series of static image at high speed.

Shutter and pulses of radiation should synchronize for the

exposure.

Generator and fluoro x-ray tube must able to handle large heat

loads.


2. Videotape Recording

VHS-S system required.

High resolution camera.

Recorders tape and monitors.

Operate same as home video systems.


Static Spot Filming

Systems

1. Cassettes

2. 105 mm Chip Film


1. 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.


2. 105 mm Chip Film

12 frames per second.

Beam splitting mirror.


Digital Fluoroscopy

Use CCD to generate electronic signal.

Signal is sent to ADC.

Allows for post processing and electronic storage

and distribution.


Documents

Prepared by:- KAMARUL AMIN BIN ABDULLAH @ ABU BAKAR · Spot film or direct optical viewing depend on geometrical factors, includes minification gain, electrostatic focal point, input