Image Quality

1. Image Quality Part I

2. Image Quality • Photographic Quality • Geometric Quality Image Quality

3. Photographic Quality • Geometric Quality Image Quality

4. Contrast • Density • Geometric • Detail • Distortion • Radiolucent • Radio-opaque • Tissue density • Optical density • Radiographic contrast • Subject contrast • mAs reciprocity rule • mAs doubling rule • 15% kVp rule • Long scale contrast • Short scale contrast • High/low contrast • Absorption • Differential absorption • Step wedge • Grid • Beam filtration • Anatomic density • Over-exposed • Under-exposed • Over penetrated • Under penetrated • saturation Terminology

5. The films or images have different levels of density – different shades of gray X-rays show different features of the body in various shades of gray. The gray is darkest in those areas that do not absorb X-rays well – and allow it to pass through The images are lighter in dense areas (like bones) that absorb more of the X-rays. Why you see what you see…

6. The radiograph is formed by x-ray photons reaching the image receptor . Primary exposure factors: kV, mAs, SID

7. Image quality

8. density The overall darkening of the image

9. 2 4 3 1

10. 4 5 3 2 1

12. Anatomic Density • Body part/object being x-rayed • Atomic # • Thickness of part • Optical Density • Amount of x-ray photons reaching the image receptor • The mA applied • The time applied • Also referred to as x-ray output DENSITY

14. mA One milli-ampere is equal to one thousandth of an ampere. The amount of current supplied to the x-ray tube Range 10 to 1200 mA Milliamperage

15. In seconds How long x-rays will be produced 0.001 to 6 seconds Time

16. mAs mA X s = mAs

17. 10 mA 1000 mA

18. What do you do in order to double density on an image?

19. 100 mAs + 25%mAS = 25% increase in density DENSITY directly proportional to mAs +50% mAs = 50% increase in density

20. Density is like toast…too much and the toast is burned, too little and it is underdone. • The images differ in density only. Which one looks optimal to you? Density

21. This image was taken at 60 mAs. This Image is overall too dark. What would you do to fix this image? This image was taken at 300 mA. What was the time of the exposure? What would you do? If we wanted to change the mA but keep the mAs the same, what would we do?

22. Density Math Work

23. When mA is unknown… The image was shot at 45mAs using a .75second exposure. What is the mA? When s is unknown…. The image was shot at 80mAs using the 400mA station. What was the time of exposure? Sample problems

25. What changes to mAs are needed for human eye to detect?

26. Prime Controlling Factor Influencing Factors kVp SID Beam Filtration Beam restriction Body part thickness grids • mAs Density(optical density, image density)

27. 15% kVp = doubling of exposure to the film  15% kVp = halving of exposure to the film 15% rule will also change the contrast of the image because kV is the primary method of changing image contrast. Remember : 15% change ( ) KVP has the same effect as doubling or ½ the MAS on density  kVpmore energy = more photons passing though tissue & striking the image

28. This is an actual arm tatoo. Now that’s dedication ! Inverse square law Inverse square law Inverse square law

29. Beam Filtration

30. Always collimate smaller than the image receptor collimators

31. 3 Different Body HabitusHypersthenic Sthenic Hyposthenic

32. A device with lead strips that is placed between the patient and the cassette Used on larger body parts to reduce the number of scattering photons from reaching the image Grids

33. GRIDS

34. Grids absorb scatter –prevents it from reaching the image

35. GRID NO GRIDControls contrast

36. Goal: Producing optimal radiographsDENSITY Too dark Too light

37. review

38. Contrast The difference between the darks and light areas

39. Now what changed?....very subtle, often subjective

40. 2 4 3 1

41. Scale of Contrast? Which one is “better” How does the kVp affect these images?

42. Not very many differences • Between grays • Also known as high contrast Short scale of contrast

43. Patient Interactions Photoelectric effect CASCADE

44. High kVp Penetrates more easily Causes more grays Low contrast Low kVp Decreases penetration Causes more black-white High contrast • Different parts of body attenuate differently • The difference in attenuation is the basis for contrast Beam Attenuation AKA absorption

46. Primary controlling factor Influencing Factors Subject contrast mAs SID Filtration Beam restriction grids • kVp Radiographic contrast

47. Inverse Square Law

48. The exposure from an x-ray tube operated at 70kVp, 200mAs is 400mR at 36 inches. What will the exposure be at 72 inches? 100mR The x-ray intensity at 40 inches is 450mR. What is the intensity at the edge of the control booth which is 10 feet away?......think carefully…  50mR A temporary Chest Unit is set up in an outdoor area. The technique used results in an exposure intensity of 25mR at 72 inches. The area behind the chest stand in which the exposure intensity exceeds 1 mR. How far away from the x-ray tube will this area extend? 30 feet

49. Use Inverse Square Law The first exposure value is 400mR. The first distance is 36 inches. The second intensity is what we are looking for. The second distance is 72” Square both 72 and 36. The exposure from an x-ray tube operated at 70kVp, 200mAs is 400mR at 36 inches. What will the exposure be at 72 inches?100mR Cross multiply Cancel out “inches2”, multiply, divide ?mR= 100mR

50. So 10 feet is equivalent to 120 inches. Short cut method Cross multiply Cancel units The x-ray intensity at 40 inches is 450mR. What is the intensity at the edge of the control booth which is 10 feet away?......think carefully… Use the Inverse Square Law. The first intensity is 450mR, the Second intensity is unknown. The first distance is 40 inches. The Second distance is 10 feet…..Convert feet to inches.