Image quality and artifacts

1. Image quality and artifacts

2. Why you see what you see… • 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.

3. Image Production • Primary Beam– The beam of photons, B4 it interacts with the pt’s body. • Remnant (exit) Beam-The resulting beam that is able to exit from the patient. • Scatter Radiation– Radiation that interacts with matter & only continues in a different direction – not useful for image production. • Attenuated Beam– Primary radiation that is changed (partially absorbed) as it travels through the pt.

4. Image quality and artifacts

5. Image quality and artifacts Photographic Quality

6. Image quality and artifacts Geometric Quality

7. density The overall darkening of the image

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

9. 10 mA 1000 mA

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

12.  kVpmore energy = more photons passing though tissue & striking the image • 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

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

14. collimators Always collimate smaller than the image receptor

15. 3 Different Body HabitusHypersthenic Sthenic Hyposthenic

16. Goal: Producing optimal radiographsDENSITY Too dark Too light

17. contrast The range of dark, lights, grays in the image

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

19. Patient Interactions Photoelectric effect CASCADE

20. Patient Interactions Compton scattering • COMPTON SCATTERING • Outer shell electron in body • Interacts with x-ray photon from the tube • 3. Moderate energy electron

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

22. Radiographic contrast • Subject Contrast • Tissue thickness • Tissue density • Tissue type (atomic #) • Contrast agents • Scatter radiation

23. 10 mA 1000 mA

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

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

26. Effects of collimation (beam restriction) on scatter

27. Grids • 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

28. GRIDS

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

30. GRID NO GRIDControls contrast

31. detail Resolution, ability to distinguish shapes

32. detail • Image sharpness • Spatial resolution • Smallest separation of two lines or edges • Measured by lp/mm • Motion • SID • Focal spot size • OID • Image receptor type Factors that affect detail

33. RECORDED DETAIL • The degree of sharpness in an object’s borders and structural details. • How “clear” the object looks on the radiograph

34. RESOLUTION TEST TOOLS LINE PAIRS/ MM Depicts how well you can see the differences in structures More lines=more detail

36. Motion • Can be voluntary or involuntary • Best controlled by short exposure times • Use of careful instructions to the pt. • Suspension of pt. respiration • Immobilization devices

37. Blurring of image due to patient movement during exposure.

39. SID • Shine a flashlight on a 3-D object, shadow borders will appear “fuzzy” -On a radiograph called penumbra • Penumbra (fuzziness) obscures true border • Farther the flashlight from object = sharper borders. Same with radiography.

41. OIDObject to Image Distance • The closer the object to the film, the sharper the detail. • OID , penumbra , sharpness  • OID , penumbra , sharpness  • Structures located deep in the body, radiographer must know how to position to get the object closest to the film.

43. The position of the structure in the body will influence how magnified it will be seen on the image The farther away – the more magnified

44. distortion The imaging of the true shape and size of the object

45. distortion FACTOR INFLUENCING DISTORTION SID OID Beam Angulation Body Part-Beam alignment • Misrepresentation of the size or shape of an object • Two types: • Size Distortion • magnification • Shape distortion • Foreshortening • elongation

47. 40” SID VS 72” SID Which one is which?

48. Which one was taken at 72”?

49. Minimal magnification small OID