Lab Test 3

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Images and concepts from the labs on density, contrast, detail, and distortion. Includes relationship charts of these variables

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Lab Test 3

  1. 1. Density, Contrast, Distortion & Detail Lab Test #3
  2. 2. Contrast and the 15% Rule Objective: To  demonstrate the influence of the 15% rule on contrast 1st exposure at  recommended technique Used as control 
  3. 3. Contrast and the 15% rule Apply the 15% rule  twice and ↑ kVp ↓ mAs accordingly All other factors stay the  same The math doesn’t quite  add up on this one, so I think the images are from 2 different groups
  4. 4. Contrast and the 15% rule Again, this image doesn’t  match my lab sheet, I believe we lowered the kVp 15% and shot another on just for S&G At this point, we should  compare the 2 images to determine which has the longest scale of contrast See next slide 
  5. 5. Contrast and the 15% rule Low kVp=High Contrast= Short scale High kVp=Low Contrast= Long scale More B&W More Shades of Gray
  6. 6. Density- Control Image Objective: To  demonstrate the effect of select factors on density Control image of knee  phantom taken @ 5mAs, 60kVp, & 40” SID.
  7. 7. Density- Filter With no change in tech  factors, a copper sheet is taped to the face of the collimator Filters have an inverse  relationship on density thus: ↑ Filtration ↓ Density 
  8. 8. Density- Grid Copper filter removed  No change in technical  factors Grid is introduced to IR  Result: Adding a grid  decreases density this is an inverse relationship (+) ↑ Grid ↓Density 
  9. 9. Density- SID Grid removed  No change in technical  factors SID increased from 40”  to 60”
  10. 10. Density-Tissue Thickness Grid is removed and hand  phantom is substituted for knee No change in technical  factors Overall, the hand the tissue  thickness of the hand is much less than that of the knee ↑ tissue thickness ↓density 
  11. 11. Density- Collimation-Control Torso phantom is  substituted for hand 14x17 collimation  Use technique  recommended by console + 20 mAs This image will be  compared with the highly collimated image.
  12. 12. Density- Collimation Collimation is  increased to a 4x4 square. Repeat exposure of  torso with no change in technical factors ↑collimation ↓density 
  13. 13. Density- Anode Heel Effect Use a foot phantom  and a 14x17 cassette 2 mAs, 60 kVp, 40” SID  Leave collimation open  lengthwise to 17” Orient toes over the  anode side
  14. 14. Density- Anode Heel Effect All technical factors remain the  same Foot is moved to opposite end of  cassette to place toes on cathode side In practice, the thickest tissue  should be placed at the cathode end of tube In theory, placed thicker tissue at  anode end would effect density A visible change in density would  only be appreciated with film/screen
  15. 15. Size Distortion: Control Objective: To  demonstrate the various types of distortion Control image of hand  shot at 40” SID Technique: Pre-  programmed
  16. 16. Size Distortion: 6” OID 2nd image  6” OID is created with  sponges All other factors remain  the same Compare with control  image to note distortion (magnification)
  17. 17. Size Distortion: 12” OID Image #3  OID is ↑ to 12”  Collimation is exactly the  same No other factors have  been changed Note magnified  appearance of hand Such distortion can mask  pathology
  18. 18. Distortion: OID + SID OID is ↓ to 6”  SID is ↓ to 20”  All remaining tech factors  are unchanged Result: Size distortion  (magnification in this case) can be caused by OID, SID or both
  19. 19. Shape Distortion: Control Control exposure of  knee phantom w/recommended tech factors This image will be used  for comparison with others
  20. 20. Shape Distortion: Angled Tube 2nd image of knee  phantom Tube is angled  All tech factors remain  the same
  21. 21. Shape Distortion: Angled IR 3rd exposure of knee  phantom IR is angled  All tech factors are  unchanged from control Note closed joint  spaces
  22. 22. Shape Distortion: Angled Anatomy 4th exposure of knee  phantom All tech factors remain  constant except… Phantom is angled  Result: Shape distortion  can be caused by the angulation of tube, IR or anatomy being imaged.
  23. 23. Density & mAs Objective is to  demonstrate the effects of overexposure & underexposure on CR images First image is made @  60kVp, 10mAs w/40” SID
  24. 24. Density & mAs 2 mAs is ↑ 50  All other technical factors  remain the same LGM#’s of all images will be  compared with control LGM represents the # of  photons reaching IR to form the latent image LGM is proportional to mAs 
  25. 25. Density & mAs 3 ↑ to 100 mAs  No other technical  factors are changed At this stage, LGM#’s  appear to be ↑ as mAs is ↑ (a direct relationship).
  26. 26. Density & mAs 4 ↑ to 200 mAs  Remaining tech factors  unchanged LGM#’s increase with  each increase in mAs mAs is THE controlling  factor of density
  27. 27. Detail and Distortion: Motion Objective: To demonstrate  the effect of motion on detail Technical factors: The  programmed technique for a foot but ↓ mA Decrease in mA is necessary  to ↑ exposure time (applicable in next image) 1st image of top taken on  10x12 w/no motion
  28. 28. Detail and Distortion: Motion 2nd image- top is  spinning while exposure is taken Technical factors are  unchanged The lower mA ↑  exposure time, allowing the motion to be caught on film
  29. 29. Detail and Distortion: Motion Additional image of this  experiment Compared to the 1st image  (stationary), the lead letter attached to top is blurred. Result: Increased motion  decreases detail Motion↑↓ Detail  Although motion is generally a  detriment to good films, it can be used to the RT’s advantage Ex: Using breathing technique to  blur ribs
  30. 30. Quantum Mottle Definition: a lack of  sufficient incoming data to process an image; AKA quantum noise No idea what this  image has to do with anything, but that’s how it was labeled That would be a cool  name for a band though
  31. 31. Contrast- Control Image Objective: To  demonstrate how selected factors effect contrast 66kVp, 10 mAs, 40”  SID on table top
  32. 32. Contrast 66kv Skull phantom is  replaced w/step wedge Exposure taken with no  changes in technical factors Compare this image  w/second exposure using a higher technique
  33. 33. Contrast: ↑kVp ↓mAs ↑ to 86kVp  Compensate by ↓mAs to  ¼ of its original value All other factors remain  the same
  34. 34. Contrast- 86kv Again, step wedge  takes the place of skull phantom No change in technical  factors Compare shades of  gray in adjacent densities
  35. 35. Comparison of Contrast Low kVp High kVp
  36. 36. Contrast: +Grid 3rd image of skull  Grid is introduced  mAs ↑ 4x to  compensate All remaining factors  unchanged
  37. 37. Contrast: Scatter 4th image of skull  Collimation open wide  to expose IR to scatter All remaining factors  unchanged Compare this series of  images to note differences in adjacent densities
  38. 38. Contrast Collimation Skull is now positioned  laterally This exposure will use  bucky instead of table top 100 kVp @ 20mAs 
  39. 39. Contrast: Collimation Repeat exposure of  lateral skull Collimated to 3”x3”  area All remaining factors  are unchanged
  40. 40. Short vs Long Scale Contrast: kVp Objective: To  demonstrate short & long scale contrast Elbow phantom @  46kVp & 5mAs
  41. 41. Stepwedge 2 Contrast ???? I think this is supposed  to be part of a contrast lab but I couldn’t match it up with anything Also, it was posted  twice in the images file…so there’s nothing to compare it to as far as I can tell
  42. 42. Short vs Long Scale Contrast; kVp 2nd image of elbow  phantom ↑ to 70kVp  ↓to 3mAs 
  43. 43. Density Chart Variables Effects Density Relationship ↑↓ ↓↑ Filtration Inverse ↑↓ ↓↑ Grid Inverse ↑↓ ↓↑ Tissue Thickness Inverse ↑↓ ↓↑ SID Inverse ↑↓ ↓↑ Collimation Inverse Cathode: ↑ Anode Heel Effect *In theory the N/A unless film Anode: ↓ anode heel effect screen technology does cause a is involved change in density but this is not evident in digital imaging
  44. 44. Contrast Chart Variable Effect Contrast Relationship ↑↓ ↓↑ kVp inverse Ø Ø mAs none Ø Ø SID none ↑↓ ↑↓ OID direct ↑↓ ↓↑ Filtration inverse ↑↓ ↑↓ Collimation direct ↑↓ ↓↑ Tissue Thickness inverse ↑ Contrast Media + direct ↑↓ ↑↓ Grid ratio direct Ø Ø Focal spot size none ↓ Always ↓ contrast Film Processing *+/- developing time and temp beyond optimal
  45. 45. Detail Chart Variable Effect Detail Relationship ↑↓ ↑↓ SID direct ↑↓ ↓↑ OID inverse ↑↓ ↓↑ Tissue Thickness inverse ↑↓ ↓↑ Focal Spot Size inverse ↑↓ ↓↑ Motion inverse

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