Intensifying screens are major component of the image receptor used in conventional radiography.Its function is to convert the X-rays into visible light through the process of fluorescence.

2.  There are three key parts of the Image Receptor for Conventional
Radiography:
 Film to record the image
 Intensifying Screens to
expose the film
 Cassette to protect the
screens and film
 Most conventional radiographic
cassettes have a pair of screens
that sandwich the film. This design
use double emulsion film.
Screens
Film

3.  A part of the cassette used in the conventional X-ray film radiography containing
fluorescent phosphors as active material
 Different types of I.S. emit different intensities & color of light when irradiated by x-
ray.
 Radiographic I.S resemble flexible sheets of plastic or cardboard
 I.S. come in sizes that correspond
to film sizes

4. In early February 1896,

5. Direct film radiography
Screen film radiography Essentials of radiologic S

6.  Contains FOUR distinct layers:
 Protective coating
 Phosphor
 Substratum
 Base

7. Essentials of radiologic Science

8. In 1921, the cleanable fluorescent intensifying screen was
developed by applying a thin protective coating over the
phosphor. This innovation extended screen life and decreased
the high cost of screen replacement
Layer closest to the radiographic film
About 10 to 20 µm thick
Made up of acetate

9.  Protection: It resists surface abrasion & damage caused by handling.
 It also helps to eliminate the buildup of static electricity & provides a
surface for routine cleaning without disturbing active phosphor layer.
 It includes qualities like:-
Thin coating to reduce distance between film & phosphor & minimize
unsharpness.
Transparent to light so that light produced in fluorescent layer will
reach the film.
 Waterproof to protect sensitive phosphor crystals.

10.  This is a bounding layer between the base & phosphor layer.
 It is 25 µm thick.
It is made up of shiny substance & highly reflective white pigment,
magnesium oxide or titanium dioxide.
The function of reflective layer is:
Maximize effect of screen by reflecting light back towards film
emulsion which would otherwise be lost through screen base.

11. It is made by adding a special dye to it.
This dye prevents any light travelling backwards towards the
screen base from being reflected by base & is instead absorbed.
It has less photographic unsharpness.
It reduces screen speed.

13. It is the farthest layer from the film.
It is made from paper, cardboard or more usually a clear plastic
such as polyester.
It is about 1mm thick.
The function of base is to provide a strong, smooth but flexible
support for fluorescent layer.
The base, sometimes contains titanium dioxide (e.g. Kodak
Lanex screens) has same function as the reflective layer.

14.  Chemically inert, not prone to interact with the phosphor layer.
 moisture resistant.
 Resistant to radiation damage & discoloration with age.
 Strong and flexible.
 Lacking impurities that would be imaged by x-rays.
 Uniformly radioparent.

15. Active layer of the I.S.
Layer from which the X-ray photons are converted into visible
light photons
Fluorescent crystals present in this layer is responsible for the
conversion
For each absorption, large number of visible light photons are
emitted
Phosphor layer vary in thickness from 50-300 µm depending on
the type of screen. Individual phosphor crystals are 5-15µm
thick.

16. It refers to the emission of light from a substance due to stimuli
like electric current, stress on the crystals ,biochemical reactions,
electromagnetic radiation
Divided into many types like Chemiluminescence,
Electroluminescence, Mechanoluminescence,
Photoluminescence, etc
Involves excitement of outer shell electrons to different energy
levels emitting light of different wavelength by de-exciting(thus
different colors)
Out of these, we will be discussing only about
Photoluminescence

17. The amazing Northern Lights, officially known in the Northern hemisphere as Aurora Borelias, are
natural phenomena that features amazing colored light displays

18.  It is the process of luminescence due the
absorption of photons i.e. electromagnetic
radiation
 In the case of I.S . the electromagnetic radiation
are the X ray photon emitted from the x ray tube

19. A form of luminescence when light is produced instantaneously,
i.e. it lasts only as long as the radiation exposure is given

20.  The light emission continues for some time even after the radiation
exposure has stopped
 This phenomena is also known as Lag or Afterglow.
An undesirable phenomena in X ray imaging because the delayed emission
of light fogs the film in the cassette before the radiographer can get it to the
processor.

21. Visible Light Photon
striking on the x ray film
Vacancy is created
Electron at the excited state
Fig: An Atom of a fluorescent crystal (Bhor’s Model)
De-excitation of electron emitting visible light
Interaction of X-ray and the Electron
X ray
Photon
Reflective layer

22.  W. C. Roentgen’s interest in studying the glow of various substances led
to his discovery of X rays; in 1895,
 He had darkened his laboratory and
completely enclosed his Crookes tube
with black photographic paper
 A plate coated with barium
platinocyanide, happened to be glowing
several meters from the Crookes tube
 Eventually, because of the luminescent property he discovered X rays,
naming the cause of this glow as X ray

23.  It is a substance that exhibit the phenomenon of luminescence(photoluminescence)
 Phosphor are hygroscopic so, they are suspended in a transparent binder ,polyurethane
 It prevents any moisture penetration to prevent reduced luminescence
 Polyurethane binds or hold the crystals together.
 The binder in high resolution screen may contain carbon or colored granules called
‘acutance dye’.
 Laterally scattered light(irradiation)must be absorbed by the dye to prevent image
unsharpness, but reduces speed of the screen.

24.  At first in 1895, William Conrad Roentgen observed luminescence of
barium platinocyanide & was applied to diagnostic radiography.
 Edison and his associates tested approximately 8500 different materials,
during this work, about 1800 substances were found to be fluorescent.
 Out of these substance calcium tungstate was found to have fluorescence
approximately 6 times more intense and was used in I.S
 Later in 1948, I.S. were introduced that were composed of a barium lead
sulfate phosphor; they were the first commercially successful radiographic
screens not made of calcium tungstate and provided greater speed

25.  in the early 1970s the use of rare-earth screens for medical radiography
was introduced, first brought to market in 1974
 It significantly changed screen-film radiography
 Since then, rare earth series of elements(gadolinium
oxysulphide,lanthanum oxysulphide, lanthnaum oxybromide,yttrium
oxysulphide, yttrium tantalate) are the phosphor material used

26. High atomic number so x-ray absorption will be high. Detective Quantum
Efficiency(DQE)
 Emit a large amount of light per x-ray absorption. Conversion
Efficiency(CE)
 Light must be of proper wavelength to match the sensitivity of the film
Spectral Matching
 Phosphor Afterglow should be minimal.
 Phosphor should not be affected by heat, humidity or other environmental
conditions.

27. Detective Quantum efficiency(DQE):
 The ratio of x-ray absorbed to the amount of incident x-ray photon
 When the x-ray energy equals the K-shell electron binding energy,
absorption is high.
 Rare earth screens exhibit better absorption properties than Ca tungstate in
between the respective K-shell absorption edges.
 DQE mainly depends on the type of phosphor.
 Other factors are thickness of phosphor, coating wt. & photon energy of
incident beam
:Radiologic Science for
Technologist

28. Conversion Efficiency(CE):
 It is the ratio of visible light energy emitted to the x-ray energy absorbed.
 When x-ray interacts photoelectrically, its energy reappears as heat or
light through rearrangement of electrons in crystal lattice of phosphor. If
all energy reappears as heat, the phosphor would be worthless.
 CE of Ca tungstate is 5% & that of rare earth phosphors is about 20%.

29.  Elements(transitional metal) with atomic number between57(lanthanum)
and 71(lutetium)
 Has two important physical attributes which gives them advantage over
conventional phosphors
High DQE
High CE
 Those used in I.S. are principally Gadolinium, Lanthanum, & Yttrium.
 requires low patient dose, low thermal stress on x-ray tube & less lead
shielding for x-ray rooms.
 Rare earth screens are faster as compared to Ca tungstate but no significant
increase in noise.

30. Use of activators
•phosphors are
used invariably in
conjunction with activators
which are small quantities
of some foreign element
added to the phosphor
during manufacture.
•The phosphor-activator
combination not only
determine the intensity of
luminescence obtainable
from the screen but
also the color of the light
emitted. :Radiologic Science for

31.  Low exposure factors can be used as compared to non-screen film thus
Reduced patient dose,
 Fine focal spots can be used
Successful use of low output equipments i.e. no need of powerful generators & high
heat capacity tubes &
Long x-ray tube life
Reduced costs
 Low exposure time & reduce movement unsharpness
 Exposure to personnel from scattered x-rays is reduced
 Lower spatial resolution
Less detail than direct exposure film

33.  IF is defined as the ratio of exposure required to produce the same
optical density without a screen, to exposure required with screen.
 IF= Exposure required without screen
Exposure required with screen
 For e.g.: if exposure required to give density of 2 on a film used
without screen is 150 mAs & 10 mAs when used with screen, then
IF= 150 = 15
10

34. Mainly three types of screen of different speed
SCREEN SPEED
High Resolution Slow
Regular or Standard Medium
Fast Fast

35. It is made by making substratum layer absorptive.
It has slow speed.
It requires greater exposure than regular screens.
It can be used when radiation dose is less important & high tube
loading is not necessary.
Contraindicated when there is risk of patient movement.
It can be used in extremity radiography.

36. It has medium speed.
It provides adequate speed & sharpness.
It can be used for most general radiographic application.
It provides the base from which the speed of I.S. can be
calculated.

37.  It produce greater film blackening
 Sharpness will be decreased
 It can be used in high risk of image blur from movement. (e.g.
paedriatric radiography)
 It use rare earth phosphors.

38. In mammography film single screen cassette is used in
conjunction with single coated emulsion film.
Reduces photographic unsharpness.
The screen is usually placed at back, rather than at the front.
This results in light being produced in those phosphor nearest to
the film
:Radiologic Science for
Technologist

39. Primary characteristics of radiographic I.S. are
 screen speed,
 image noise,
 spatial resolution &
 image unsharpness.

40.  The capability of a screen to produce visible light is called screen speed
 The properties which determine nature & quality of screen in terms of
speed are
Type of phosphor used
Thickness of layer
Density with which the crystals are packed
Coating weight:- It is an expression of quantity of phosphor grain
incorporated with phosphor layer and therefore depends on grain size and
coating thickness

41.  Presence of reflective/absorptive layer
 Dye in the layer
 Crystal size

42.  It occurs as speckled background.
 It occurs mainly when fast screens & high KV techniques are used.
 It increase with higher CE but not with higher DQE.
 Principal component of image noise is quantum mottle.
 Quantum mottle often is a direct result of use of very fast speed
screen-film systems that require very small amounts of exposure &
result in a grainy, mottled or splotchy image.

43. Spatial resolution refers to how small the object can be imaged
whereas contrast resolution refers to the ability to image similar
tissues.
IS lowers spatial resolution compared with direct exposure.
High speed screens have low spatial resolution & fine detail
screens have high spatial resolution

44. :Radiologic Science for

45. The use of I.S. introduces certain degree of unavoidable
unsharpness into image in comparison to non-screen film
material due to light divergence.
The unsharpness produced is considered as intrinsic unsharpness.
It is also caused when cassette becomes damaged & the close
contact between film & screen is lost.

47.  Procedure:
Place cassette on table.
Place wire mesh tool on cassette.
Set collimation to film size.
Make exposure and process film.
View the film in view box
Areas with loss of resolution indicates poor contact or stained screens.

48. :Radiologic Science for
Technologist

49. Unsharpness
Real image

51. Crossover can be decreased by
placing a light-absorbing layer
between the film emulsion and
film base, using a base material
that selectively absorbs the light
wavelengths emitted by the
intensifying screens, and
designing the film emulsion
to increase light absorption.

52. Changing the shape of the crystal improved
light absorption and reduced crossover.

53.  It is vitally important that films are matched to colour of I.S. emission to
obtain maximum film blackening for the least radiographic exposure and
optimum speed.
 It refers to using blue sensitive film with blue light-emitting screens and
likewise with other colours
 Failure to match the screen and film results in inappropriate radiographic
density.
 Luminescence is concentrated in narrow bands of wavelength in rare earth
phosphors unlike the calcium tungstate having continuous spectrum.
 Thus calcium tungstate known as broad-band emitters, while rare earth
phosphors are line emitters. :Radiologic Science for
Technologist

54. Spectral sensitivity of blue sensitive film and spectral emission of
CaWO4 (450nm to 495nm is for the blue color of light)

55.  Screens should be handled only when they are being installed in cassettes
& when they are being cleaned. There should be the record of type of I.S.,
time of install & cleaning
 When the screens are mounted in cassette, manufacturer's instruction must
be followed carefully.
 Finger marks, stains, dust, or foreign fragments affect screen’s fluorescent
emission.
 Small scratch made by fingernail, edge of film, etc can cause artifacts in
radiograph so special care should be taken.

56. The only way screens become useless is through improper
handling & maintenance.
X-ray interaction do not cause the I.S. to wear out i.e. no
radiation fatigue.
While replacing I.S. the only remedy is to replace both screens as
they are sold in pairs correctly matched.

57.  I.S. is provided with adhesive tape on the back of the surface for better
positioning of screen.
 The front screen marked by the manufacturer is mounted first.
 The screen should be handled on the edges.
 The prepared screen is dropped carefully into the well of the cassette.
Active surface of front & back screen should face each other.

58.  We should not leave the cassette open as screen can be damaged by any
chemicals, liquids, dust or other particles that fall on it.
 We should not store the cassettes near the source of heat.
Essentials of radiologic Science

59.  I.S. must be cleaned periodically on the basis of amount of use & level of dust in work
environment.
 Special screen cleaning materials containing antistatic compound or mild soap & water
are used under the guidance of manufacturers.
 CAUTION: NEVER USE ALCOHOL.
 Procedure:
Moisten some cotton wool with solution & gently wipe
the surfaces.
Water must not reach the back or the edge of the
screen.
Wipe the screen with fresh cotton.
Wipe till dry.

60. Worn radiolucent foam
Loose, bent, or broken hinges
Warped screens caused by excessive moisture
Warped cassette front
Sprung or cracked cassette frame
Foreign matter under the screen

61. Features Screen Speed Recorded Detail Patient Dose
Thick phosphor layer ↑ ↓ ↓
Large phosphor crystal ↑ ↓ ↓
High density layer ↑ ↓ ↓
Higher DQE
↑ ↓ ↓
High CE
↑ ↓
↓
Absorbing layer ↓ ↑ ↑
Dye in phosphor layer ↓ ↑ ↑

62.  Today, the film-screen cassette is gradually being replaced by alternative
X-ray detectors such as the photostimulable phosphor plate and selenium
plate.
 Although appearing quite similar to a regular intensifying screen, an
imaging plate(IP) functions quite differently.
 Intensifying screens use fluorescent material; whereas,
 An imaging plate uses a phosphorescence material. By using a europium
activated Barium Fluoro halide Phosphor(BaFX:Eu2+,X=Cl,Br,I), to trap
and hold electrons,
 A latent image is formed directly on the imaging plate itself; therefore, the
term filmless.

63. Like intensifying screens, imaging plates are coated with several different layers to
achieve its optimum luminescent quality.

64.  Chesney's’ Radiographic Imaging, John Ball & Tony Price, 6th edition,
Blackwell Publishing, Oxford, UK.
 Radiologic Science for Technologists
-Stewart Carlyle Bushong
 Essentials of Radiologic Science
-Robert Fosbinder, Denise Orth
 Screen Film Processing Systems for Medical Radiography: A Historical Review
-Arthur G. Haus and John E. Cullinan
 www.e-radiography.net