Radiographic Quality: Factors Affecting and Measurement Techniques

1. بسم الله الرحمن الرحيم

2. Under supervision of : Prof. Dr . Nader AbdelSalam Alsherbeny

3. RADIOGRAPHIC QUALITY By

4. Radiographic quality : is a term refers to the faithful imaging of an anatomical structure on a radiograph . • A high quality radiograph = film showing sufficient accurate details of the imaged structure . • It is related to many factors many of them are under control , these factors are : -

5. Factors affecting radiographic quality

6. Factors affecting radiographic quality :

7. I- Film factors

8. *I- Film factors* • Sensitometry : it is the study of the relationship between the intensity of exposure & blackening of the film after processing . • This occur by estimating of percentage of light transmitted through processed film . • The relationship between exposure & density is represented by characteristic curve ( H & D curve ).

9. 1- CHARACTERISTIC CURVE • It is the curve representing the relation ship between * NET DENSITY of film & • EXPOSURE Logarithm . c b density a Exposure log

10. * As showen in Diagram , Characteristic curve divided into : A- The Toe portion B- The Linear portion & C- The Shoulder A- In the toe portion : Film response is very slowly . Change in exposure  narrow range of difference in Density . It is valueless in dosimetry .

11. B- In LINEAR portion : • It is the region of Exposure measure . • Change in exposure  very rapid change in Density . • Accuracy in this part is the best . • The extent of this portion = the useful range of the film . • CONTRAST OF THE FILM : it is the slope of this portion, i.e. ability of the film to differentiate between 2 near levels of exposure .

12. C-In SHOULDER portion : • It is the region of saturation. • Large change of exposure  Little density change . • It is the least useful region in measurement of exposure . • IN SOME FILMS : • Increase Exposure  Decrease Density ,due to unexplained cause

13. How to obtain this curve?

14. How to obtain this curve : • Two apparatuses are needed : 1- Penetrometer 2- Densitometer • Penetrometer : it is a wedge shape of aluminum . * It is radigraphed on the examined film gradient of densities on the film related to thickness of different parts of this wedge . * The film is radigraphed at a standard factors ( fixed Kv )

15. Penetrometer

16. 2- Densitometer: * It is a source of light in which light passing through a pin hole opening  passing through film  received on a light sensing receptor . • Radiographic film has a wide range of sensitivity ( 5 mR : more than 1000 mR )

17. Densitometer

18. 1- Density : • it is the degree of blackness in an X ray film. • The numerical value of density ( D ) = Io D = log ------- I t • I 0 = Light incident on a processed film • I t = Light transmitted through this film

19. Film densities range 0 : 4 . * Density 0 = All Photons falling are transmitted eg. High quality glass * Density 4 = only 1 of 10,000 photons pass • Undesirable densities : Are densities already present in each film due to : A- Base density B-Fog density * Base density : it is the density due to tint added to film base to give it bluish pleasant color .

20. Base density = about 0.05 * Fog density : it is density due to film exposure during storage  development of valueless silver grains . Fog density = about 0.05 : 0.15 • Useful range of radiographic densities about 0.5 : 2.5 .

21. 2- Contrast : • It is the difference in densities on radiographic film . • Sharp differences in density = high contrast. • This difference in densities is the responsible to image formation. • Film contrast = the slope of linear portion of characteristic curve . • At slope 45’ , contrast = 1 ( low contrast )

22. Average gradient : • It is the slope of a straight line drawn between 2 points of densities 0.25 & 2 , above combined Base & Fog densities . D2 – D1 • Average gradient = ------------------- LRE 2 – LRE 1 * D = Density *LRE = Logarithm of Relative Exposure

23. Ex. :- *Base D = 0.05 * Fog D = 0.10 .: point of densities : D1 0.25 +( 0.05 + 0.10 ) = 0.40 D2 2 +( 0.05 + 0.10 ) = 2.15 & if logarithms of relative exposures are : * LRE 1 = 0.95 * LRE 2 = 1.75 :. Average gradient =(2.15-0.40)\(1.75-0.95) = 1.75 \ 0.8 = 2.19

25. 3- Speed • It is the ability of a film to respond to a minimum quantity of X ray exposure . film speed = sensitivity of this film • Use intensifying screens  increase its speed . 1 • Speed = ---------------------------------------- Number of roentgens density 1

27. 4- Latitude : • It is range of exposures at which film is respond by useful densities . :. Latitude inversely proportionate with contrast . i.e. High contrast film has narrow latitude . • latitude also = gray scale • eg. Wide latitude = long gray scale .

28. II- Film Processing: • Optimum processing factors are needed for good radiographic quality . • Factors affecting proper development are: 1-Chemicals composition 2-Degreeof Agitation 3-Time of development 4-Temperature of de. • The last 2 factors are under control of technologist .

29. 1- Development Time : • Variation of time  variation of curve shape & position . • Increase time  * increase speed & fog *increase then decrease contrast • The time recommended by the manufacture is the way to maximum contrast .

30. 2- Development Temperature : • Maximum contrast is achieved by using the recommended temperature . • Increase temp.  * increase Fog & Speed • Time & Temperature are related to each others , change of one of them affect the other . i.e. ( time  compensate temperature ) & reverse is true .

31. II- Geometric factors

32. *II- Geometric factors* • These factors are controlling sharpness of shadow image , these are : 1- Magnification 2- Distortion 3- penumbra

33. 1- Magnification : • It means that all images on a radiograph are larger than objects . • Magnification should be as low as possible (except in certain types of examination –Magnification radiography- ) • It is expressed by Magnification Factor (MF) Image size MF = ------------------------ Object size

34. MAGNIFICATION MF = TFD / TOD

35. As determination of object size is not possible ……..so TFD • MF = ------------------ TOD i.e. If film & object are on the same distance  MF = 1 .: No magnification • .: to decrease magnification  decrease Object Film Distance • Famous ex. Of avoiding magnification  heart radiography in postro- Anterior view.

36. P-A view  heart more near to the film ( as it anterior structure )  less magnification .

37. 2- Distortion : • It is the unequal magnification of different parts of the same object . • It cause improper interpretation of the radiograph . • Factors affecting Distortion are : 1- Size & shape of object . 2- Position of object . • Larger size of object  more distortion . • The more simple shape  less distortion .

38. * OBJECT POSITION : The more parallel object & film less distortion . • Foreshortened : it is a type of distortion in which the image is smaller than object due to marked obliqing in position of object . * Amount of foreshortening is increase by increasing of angle .

39. Foreshortened More oblique object = more foreshortened

40. Spatial distortion : IT IS Misinterpretation of relation between objects , due presence at different distances • if two objects having the same size & angle , but present at different distance from film , the nearer to the film will be appear smaller . • Spatial distortion will be more appearing if these 2 objects are displaced laterally to the central beam .

41. SPATIAL DISTORTION More lateral = more distortion

42. 3-Geometric unsharpness (Penumbra ) • It is the unsharpness appear at the edge of the radiograph.

43. III- Subject factors

44. *III- Subject factors* • These are the third group of factors controlling quality . • It related mainly to patient size , shape & composition . 1- SUBJECT CONTRAST : • It the 2nd component of radiographic contrast • Radiographic contrast = subject contrast X Film contrast

45. Subject contrast is difficult to be obtained as a quantity , but many factors affecting it , which are : 1- Patient thickness . 2- Tissue thickness 3- Object shape 4- Effective atomic number 5- Kilovoltage • These factors also called ( Absorption Unsharpness factors )

46. 1- Patient thickness : The more thickness of examined part more X ray attenuation. :. The more thin body = more subject contrast • 2-Tissue density : Many tissues may have the same thicknesses but different densities . :. More dense tissue = Less subject contrast .

47. 3- Shape : • Different shapes of Radiographed part different levels of attenuation . • The wedge shape structure parallel to X ray beams is the best for subject contrast .

48. SHAPE ATTENUATION

49. 4- Effective atomic number : • The atomic number of the examined part variation  variation of level of Compton reaction & interaction with this part . 5- Kilovoltage : • The previous 4 factors are not under control of technologist . • Kv is the only factor under control . • Higher Kv  Less subject contrast • :. Radiograph should be taken at least suitable Kv .

50. BUT …… use of low Kv  More dose , as more beams will be absorbed , as low Kv = low beams energy . • Contrast medias : *using of contrast medias  enhancing subject contrast • This is due to high Z number ( I 53 ) , ( Br 56 )