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Components of Image Quality & Radiographic Artifacts

Components of Image Quality & Radiographic Artifacts. Radiologic Technology A SPRING 2012. X-ray Exposure Factors Radiographic Density & Contrast Components of Image Quality Radiographic Artifacts. Review. Primary radiation exits the tube Interacts with various densities in the body

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Components of Image Quality & Radiographic Artifacts

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  1. Components of Image Quality & Radiographic Artifacts Radiologic Technology A SPRING 2012

  2. X-ray Exposure Factors • Radiographic Density & Contrast • Components of Image Quality • Radiographic Artifacts

  3. Review • Primary radiation exits the tube • Interacts with various densities in the body • Photons may be absorbed • Scattered • Passed through without any interference to the cassette or image receptor (IR)

  4. How well we can see something on the image

  5. Image detail is affected by:Photographic propertiesand Geometric properties

  6. Photographic Properties • Contrast • Density

  7. Factors Affecting Density • Primary control factor • mA • Time (seconds) • Influencing factors • kVp • Grids • Beam restriction • Body structures (size of pt, pathology • Processing • SID & OID • Film Screen combinations

  8. Primary Controlling Factor of Density • mAs • mA = AMOUNT of electrons sent across the tube combined with TIME (S) = mAs • mAs controls DENSITY on radiograph • primary function of mAs is DENSITY

  9. Imagine this… • If the mA station is changed from 200 to 400 mA, twice as many electrons will flow from the cathode to the anode. • From 10 mA to 1000 mA = 100 x more • mA controls how many electrons are coming at the target • mAs is a combination of how many and for how long(seconds)

  10. 10 mA 1000 mA

  11. Changing Mas – Changes Density+ 25 % + 50 % mas

  12. Influencing Factor on Density:kVp

  13. Change in kVp • kVp controls the energy level of the electrons and subsequently the energy of the x-ray photons. • A change from 72 kVp will produce x-rays with a lower energy than at 82 kVp • Difference between a ball traveling 72 mph and 82 mph (how much energy did it take to throw the ball at the rates?)

  14. + 15% kvp - 15% kvp This will also influence the density on the image Increasing kVp = increase energy reaching the IR

  15. Radiolucent vs. Radiopaque • Radiolucent materials allow x-ray photons to pass through easily (soft tissue). • Radiopaquematerials are not easily penetrated by x-rays (bones)

  16. Transmission no interaction Responsible for dark areas Scatter (grays) – produces no diagnostic info Absorption (photoelectric effect) Responsible for light areas Creating the Image

  17. Images • DENSITY = THE AMOUNT OF BLACKENING “DARKNESS” ON THE RADIOGRAPH (mAs) • CONTRAST – THE DIFFERENCES BETWEEN THE BLACKS TO THE WHITES (kVp)

  18. 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.

  19. Patient Body Size and Pathology

  20. 3 Different Body HabitusHypersthenic Sthenic Hyposthenic Dr. Charman, Eric Guzman, Adam Guzman Thank you to the 3 men in my life !  DCharman

  21. PATHOLOGY • Pleural • Effusion • Excessive fluid in lung • More dense than air

  22. Pneumonia

  23. The right lung is almost completely collapsed; vascular shadows can not be seen in this area (arrow). Lung collapses No tissue in space Easy to penetrate with x-ray photons Pneumothorax

  24. LungCancer

  25. LUNG CANCER

  26. Density and Images

  27. Goal: Producing optimal radiographsDENSITY Too dark Too light

  28. Controlling Factor ofContrast

  29. Controlling Factor of Contrast • Kilovolts to anode side – kVp • Kilovolts controls how fast the electrons are sent across the tube • kVp – controls CONTRAST on images

  30. Producing optimal radiographsContrast Scale Long scale short scale

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

  32. Beam Restriction and Grids

  33. Creates fog Lowers contrast (more grays) Increases as kV increases Field size increases Thickness of part increases Scatter

  34. Effects of collimation (beam restriction) on scatter

  35. Collimate to area of interest -reduces scatter and radiation dose to the patient

  36. 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

  37. Basic Grid Construction • Radiopaque lead strips • Separated by radiolucent interspace material - Typically aluminum • Allow primary radiation to reach the image receptor (IR) • Absorb most scattered radiation • Primary disadvantage of grid use • Grid lines on film

  38. GRIDS

  39. Grid is placedbetween patient (behind table or upright bucky) & cassette

  40. Grids absorb scatter –prevents it from reaching the image GRID STOPS SCATTER

  41. Contrast changes with the use of a grid Less scatter radiation – shorter scale = “better contrast” With Grid No Grid

  42. GRIDS CAN LEAVE LINES ON THE IMAGE

  43. GEOMETRIC Properties • Recorded Detail • DISTORTION • Size distortion • Magnification • Shape distortion • Elongation • Foreshortening

  44. RECORDED DETAIL

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

  46. Recorded Detail • The degree of sharpness in an object’s borders and structural details. • Other names: -sharpness of detail -definition -resolution -degree of noise

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