THE INTENSIFYING SCREENS Under supervision of Prof Dr

THE INTENSIFYING SCREENS Under supervision of : Prof. Dr. /NADER A. AL SHERBENY By : Ahmad Mokhtar Abodahab 10/18/2021 3

INTRODUCTION : X-ray is not visible , To be visualized, following methods do this : 1 - Direct X ray exposure of sensitive Emulsion. 2 - Converting it into visible light by INTENSIFYING SCREENS. 10/18/2021 4

* INTENSIFYING SCREEN : Is the device that convert X ray energy into visible light , to which film is more sensitive. n It INTENSIFY ( Amplify ) the radiation reaching the film. n It used in the cassette , on both sides of the film. n 10/18/2021 5

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The action of INTENSIFYING SCREEN depend on FLOURESCENCE Phenomenon. n X ray SCREEN == FLOURSCENCE Light act on emulsion. n What is the value of converting X ray into light ? n The emulsion is sensitive to light several times than to X ray. n About 95 % of the formed image is due to light n 10/18/2021 7

Immersed from INTENS. SCREENS & only 5 % of image is due to direct exposure to X ray 10/18/2021 8

. • As it magnify the effect of X ray on the film , • Thus by using it , less dose of X ray is needed to obtain satisfactory image. • Decreasing X ray dose have the following advantages : 10/18/2021 9

1 - Decrease patient exposure less harming. n 2 - “ “ exposure time less bluring of image caused by patient movement. n 3 - Increase life of X ray tube. n 4 - Giving ability to use of low power X ray unit i. e. Portable apparatuses. n All these factors improving the quality of the image. n 10/18/2021 10

N. B. n Radiography without using of screens more sharp image , so it is not used in BONE radiography. 10/18/2021 11

SCREEN • CONSTRUCTION : 10/18/2021 12

The structure of Screens as follow : * Shape : seems like a fixable sheet of plastic. * Size : correspond to the size of films , the film is sandwiched between 2 screens. * Structure : It is composed of 4 layers 1 - Base 2 - Reflecting layer 3 - Phosphor layer 4 - Protective plastic layer 10/18/2021 13

STRUCTURE OF SCREEN : 10/18/2021 14

* 1 - THE BASE : * Structure : white sheet of polyester or cardboard * Thickness : About 1 mm *Function : Mechanical support to the phosphor layer. *Properties : Screen base should have the following properties : 10/18/2021 • • 15

1 - Inert : Not interacting with phosphor layer. 2 - Insensitive to Radiation : not damaged or discolored by Radiation. 3 - Moisture resistant. 3 - Radio transparent , & free from any immpurites. 4 - Flexible & Flat 10/18/2021 16

2 -THE REFLECTING LAYER : Very thin layer , shiny white substance. • * Structure : Magnesium oxide or Titanium dioxide. * Function : Reflecting of light photons again toward the film save these photons to be lost more action on sensitive emulsion better image. (Increase the efficiency of screen) 10/18/2021 17

* Screen Efficiency : * It is the quantity of light emitted by the screen & expose the film. * For Typical Screens : about 50 % of light reach the film , & the other part wasted & absorbed in the screen. 10/18/2021 18

Diagram of action of reflecting layer: n 10/18/2021 19

* When X ray falling on Ant. Screen light photons falling on Ant. Layer of emulsion penetrating it. * If there is no Post. Screen , this photons will be lost. * The reflecting layer in Screen prevent losing of these photons by reflecting it the film again , & so the film is double coated by emulsion. 10/18/2021 20

3 -THE PHOSPHOR LAYER : * It is the active layer in the Screen. * It converting the energy of X ray to visible light. * Structure : 3 materials have been used 1 - Calcium tungstate. 2 - Barium lead sulphate. 3 - Zinc sulphide. 10/18/2021 21

1 -Ca Tungstate 2 -Barium lead 3 -Zinc sulphide sulphate *Most common * 3500: 5200 • * 3000: 4700 A * 3900: 5500 A A • i. e. v. b. &green i. e. ultraviolet, • * violet & blue (to intensifying>Ca *were used e which film is most Tungstate. low kv sensitive) SO • * IT IS Ideal • 10/18/2021 * afterglow *large grains so Not used 22

4 - PROTECTIVE LAYER : * Structure : Plastic layer, surrounding sides & edges of screen. *Thickness : Extremely thin. *Properties : * waterproof • * Transparent • *Function : Protection from • abrasions. Cleaning without damage • 10/18/2021 23

* SCREEN SPEED * * It is relative number used to quantitate The efficiency of the screen. *This is as follow : Slow speed Medium speed High speed 0. 5 1(it is the base of comparison Smallest crystals Thinnest 10/18/2021 Average ) 2 : 2. 5 Largest crystals Thickest 24

*The amount of emitted light is depends on : 1 - Size of crystals (of phosphor layer ) 2 - Thickness of phosphor layer. 3 - Prescience of light absorbing dyes. 10/18/2021 25

*INTENSIFICATION FACTOR* *It is the ratio of 2 exposures required at a specific KV , one e using of INT Screen & other with out. *Exposure =(m. As at ‘x’ KV) *I. F. = EXPOSURE without EXPOSURE with 10/18/2021 26

THANK YOU 10/18/2021 27