Magnification(macro and micro radiography), distortion

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1. MAGNIFICATION (MACRORADIOGRAPHY/ MICRORADIOGRAPHY) DISTORTION PARTHA JYOTI DAS MSc MIT

2. Contents Macroradiography Principles Magnification with fixed FFD Magnification with fixed FOD Unsharpness with macroradiography Applications Microradiography Mass miniature radiography Distortion References

3. The technique of producing an image by direct magnification is called macroradiography . Enables fine anatomical details than the original and accurate diagnosis. Macroradiography

4. Principles Magnified image can be produced by increasing the object to film distance in which the x rays diverging from the point source will produce a directly magnified image.

5. Relation: The relationship between size of object and it’s image. FFD FOD OFD Image Size X-ray Focus Film Plane Object Plane

6. Principles Magnification (M) can be calculated by the following formula: focus to film distance (FFD) focus to object distance(FOD) . The focus to object distance (or object to film distance) is taken from the mid level or part. M =

7. MAGNIFICATION WITH FIXED FFD Magnification is increased by bringing the object nearer to the x ray tube FOD = FFD/Magnification. For eg : With a fixed FFD of 100cm, if a magnification factor of 1.6 is required then; FOD = 100/1.6 = 62.5 cm

8. MAGNIFICATION WITH FIXED FOD The required magnification is obtained by moving the film away from the object. The required OFD for a given magnification is then calculated from OFD = FOD(M – 1) Eg . FOD is fixed at 100cm , given magnification factor 1.6 OFD = 100(1.6 – 1) = 60cm

9. UNSHARPNESS WITH MACRORADIOGRAPHY

10. MOVEMENT UNSHARPNESS Direct magnification by increased object to film distance can be carried out if there is complete immobilization of the patient Any movement due to lack of immobilization or involuntary movement will be magnified on the radiograph due to increased OFD

11. Movement unsharpness

12. Some steps Use of immobilization devices, e.g. supports, binders,sandbags and pads. Instructions should be given to the patient to remain still.

13. GEOMETRIC UNSHARPNESS Occurs because the source of x rays is not a point source and any distance between the object and film will cause an image penumbra in addition to magnifying the image

14. The geometrical unsharpness for given focal spot size calculated by Focal Spot Size x Object-Film Distance Ug = Focus-Object Distance

15. Geometric unsharpness

16. How to minimize Ug :- Focal Spot size:- By reducing Focal Spot Size. Object image Distance:- By reducing object image distence . Focus object Distance:-By increasing the Focus object distence .

17. Relationship between focal spot size and magnification For a given focal spot size there is a limit to magnify the image without significant loss of details.

18. APPLICATIONS Limited use of macroradiography Dacrocystography of Skull ( Lacrimal ducts after injection of contrast) Imaging the carpal bones in cases of suspected fracture of scaphoid Localised areas of the lung Localised areas during angiography eg : cerebral angiography

19. Macroradiograph of wrist with a magnification factor of 2

20. Microradiography An imaging technique used to examine very small objects or minute details, often with the use of high-voltages, very small focal spot size, and an ultrafine film emulsion.

21. Ultrafine Emulsion film Photo print made by these films performs rich sharpness, high definition, strong scratch resistance, as well as long lasting by pigment 

22. Microradiography It is also called as chest fluoroscopy. The image on a fluorescent screen is photographed on a small film. Screen and film are separated and the image is focused on the film by a camera lens  Miniature radiographs ( 70mmx70mm or 100mmx100mm roll or cut films were used ). A permanent record is possible. 

23. Mass Miniature Radiography(MMR) In order to control tuberculosis, medical research council, London appointed their Committee on Tuberculosis in 1941. The detection of symptomless or latent pulmonary tuberculosis by mass radiography had been the subject of much careful investigation. An excellent instrument was designed by the council for this purpose and in 1943 the Ministry of Health announced that a limited number of mobile miniature radiography sets.

24. The equipment consist of Fluorescent screen(emits blue or green light) A mirror optics system on recording exposure on film

25. Survey in progress Control Panel

26. Apparatus for MMR 1.Power unit :- High tension unit Four valve rectification An output of from 100 to 400mA A maximum kilovoltage of 100 kVp and 91 kVp respectively

27. 2. X-ray Tube The rotating anode X-ray tube Dual focus, Focal-spot sizes are 1mm and 2mm square. An optical centring device. Adjustable diaphragm

28. 3.Fluorescent Screen and Grid: 16 by 16 inches fluorescent screen Covered by a sheet of protective lead glass.  Yellow-blue or green type of screen A stationary grid is also present which reduces scatter 4.The Camera .: An electrically operated camera is linked with the X-ray exposure switch. Lead glass protection is present on the camera side of screen 5.The lens : a number of different lenses

29. Developing MMR films Special tanks meant for roll films on a spiral frame Development time was 7min at 68 degree F

30. Viewing of MMR FILMS Projector for viewing miniature radiographs Magnifying glasses

31. DISTORTION

32. DISTORTION Misrepresentation of the true size and shape of an object is called distortion. Distortion results from unequal magnification of different parts of the same object.

33. Focal Spot Film The object AB is tilted with respect to the plane of the film. The size and shape of image vary with the amount of tilting. Distortion A B A B

34. Distortion of the image of an object will be different in different parts of the x-ray beam.

35. Distortion of thick object occurs if they are not directly in the central part of the x-ray beam.

36. When the part to be imaged does not lay parallel with the IR (cassette). If the Central Ray is not perpendicular to the part.

37. Caused by improper alignment object with relation to tube focus and film . Distortion of an object will be different in different part of the x-ray beam.

38. Elongated Foreshortened Normal

39. GOOD RADIOGRAPHS MAKES EVERYONE HAPPY

40. REFERENCES CHESNEY’S RADIOGRAPHIC IMAGING, 6 TH EDITION JOHN BALL, TONY PRICE HDCR CLARK’S POSITIONING IN RADIOGRAPHY, 12 TH EDITION A. Stewart Whitley Charles Sloane Graham Hoadley Adrian D. Moore Chrissie W. Alsop .

41. Thank You