Xeroradiography

Xeroradiography is the production of visible image utilizing the charged surface of a photoconductor (amorphous selenium) as the detecting medium, partially dissipating the charge by exposure to X rays to form a latent image and making the latent image visible by xerographic processing.

1. Xeroradiography Presented by:Dr Alma Swathi Dsouza Moderator: Dr Rithi M Dsilva

2. P roduction of visible image amorphous selenium -detecting medium dissipating charge by X rays Latent image visible by xerographic processing. ‹#›

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5. PHOTOCONDUCTION ‹#›

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7. PHOTOCONDUCTIVE LAYER Three properties required: good insulator material must become electrically conducting mechanical properties of durability & ease of fabrication ‹#›

8. COMPONENTS OF XERORADIOGRAPHY : 1. Xerographic plate 2. Croton 3. Cassette 4. Toner 5. Special paper ‹#›

9. XERORADIOGRAPHIC PLATE ‹#›

10. ALUMINIUM SUBSTRATE meticulously cleaned with exceedingly smooth surface ‹#› INTERFACE LAYER Heat treatment of aluminum substrate thin layer of aluminum oxide insulator SELENIUM COATING amorphous (vitreous form) deposited onto the aluminum substrate

11. PROTECTIVE OVERCOATING Cellulose acetate 0.1µ thick layer bonds well with selenium high resistance prevent lateral conduction of charges It extends the life ‹#›

12. PRINCIPLE xray plate is charged by a corotron Placed in a cassette xray strikes the selenium photoconduction occurs charge image ‹#›

13. Image is visible by adding toner/ developer Resultant powder image is transferred to a paper and fused ‹#›

14. THE FUNCTIONAL STEPS: ‹#›

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18. EXPOSURE OF CHARGED PLATE Exposure to Xray electron- hole pairs electrons migrate to plate surface and discharge the positive charge originally laid down ‹#›

19. +ve holes migrate toward the substrate neutralized by the induced negative charge amt of discharge of +ve charge is ∝ to intensity of Xrays The remaining charge pattern on plate surface is electrostatic latent image ‹#›

20. Photoconductivity induced by Xrays vs light Xray photons can penetrate into selenium Absorption - uniform energy of Xray photon is transferred to a photoelectron or recoil electron ‹#›

21. ‹#› ELECTRIC FIELD DISTRIBUTION ABOVE LATENT IMAGE

22. ‹#› XERORADIOGRAPHIC UNDERCUTTING D/t i onisation of air space btw selenium surface & lid of cassette Caused d/t interaction air molecules or High speed electrons.

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24. ‹#› POWDER DEVELOPMENT

25. POSITIVE DEVELOPMENT NEGA TIVE DEVELOPMENT ‹#›

26. LIQUID DEVELOPMENT Liquid toner particles are black particle size 1.7 µ Smaller particle + less charge on each particle = more toner particles deposited per image ‹#›

27. POSITIVE IMAGE NEGATIVE IMAGE ‹#›

28. ‹#› EDGE ENHANCEMENT

29. I MAGE TRANSFER AND FIXING I mage is transferred to paper & fixed electrostatic transfer process used paper coated with slightly deformable layer of plastic paper Pushed against the powder image under high pressure ‹#›

30. PLATE CLEANING All toner must be removed plate is exposed to a light source corotron exposes the plate to an alternating current cleaning brush then mechanically brushes the residual toner ‹#›

31. RELAXATION If the plate charged for new exposure without rest, ghost image of previous exposure will appear on development( long as several hours) rest period can be reduced to 2-3 min If heated to 140˚F for 150 sec. ‹#›

32. STORAGE The cleaned and relaxed plate is then held in the storage compartment at 89˚ F until needed for another exposure ‹#›

33. ADVANTAGES: High contrast 1/3rd the exposure Easy to use Produces permanent dry images Image is easily reversible Useful in endodontics ‹#›

34. DISADVANTAGES: Edge enhancement artefacts. Processors are expensive. High radiation dose needed for extra oral techniques. 2.4-16.2 times larger than conventional ‹#›

35. USES: Mammography Cephalometry Evaluation of bone lesions- mandible Sialography dental and non-dental structures TM joint tomography ‹#›

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40. CONCLUSION: xeroradiography has peculiar positive properties which enable both detailed bony and soft tissue examination, as well as subtle visualisation of structures. ‹#›

41. THANK YOU ‹#›