22.1 Radiographic Quality Control Variables in Radiographic Equipment

1. 22.1 Radiographic Quality ControlVariables in Radiographic Equipment kVp Calibration mA Calibration Timer accuracy Collimator accuracy Beam Alignment Grid Centering Focal Spot Impacts technique Impacts technique Impacts Technique Impacts Collimation Impacts Grid Cut off Impacts Grid Cut Off Impacts Resolution

2. Radiographic Quality Assurance Begins with the Acceptance Tests to set baseline values and assure proper operation. Periodic monitoring to assure continued compliance. Annual or Semiannual After major component repair or replacement

3. Radiographic Performance Standards kVp Accuracy mA, Timer, mAs Collimator Beam Alignment Grid Centering Exposure Reproducibility ± 5%; ± 2 between 60 and 100 kVp ± 5% ±2% of SID ± 2º ± 2º ± 5%

4. 22.2 Collimator Accuracy and Beam Alignment Tools needed: 9 pennies or Collimator alignment tool Beam perpendicularity test tool Standard: Must be within 2% of SID or 0.8” at 40” SID

5. Collimator Accuracy and Beam Alignment Procedure: Set SID @ 40” to Bucky Place 8”X10 Cassette in Bucky Center beam to film center Collimate to 5” square Mark borders with pennies taped to Bucky Make exposure and process film.

6. Collimator Accuracy and Beam Alignment Procedure: mark center and horizontal and vertical axis of beam The exposure should be to the outer edges of the pennies. Must be within the diameter of the pennies to pass the test.

7. Collimator Accuracy and Beam Alignment Procedure: mark center and horizontal and vertical axis of beam The exposure should be to the outer edges of the pennies. Must be within the diameter of the pennies to pass the test.

8. Collimator Accuracy and Beam Alignment Frequency: semiannual or after replacement of collimator light bulb or tube replacement. You should hold the x-ray machine supplier to a much higher standard. The beam and light fields should match!

9. Collimator Accuracy and Beam Alignment Procedure with beam alignment test tool: Set SID to 40” to Bucky Center 8” x 10” film to Beam Tape collimator test tool to Bucky centered to light field. Collimate to marked borders on tool (5” x 7”)

10. Collimator Accuracy and Beam Alignment Procedure with beam alignment test tool: Tape the beam perpendicularity test tool to the collimation tool with the metal ball centered to center of tool. Make exposure and process the film

11. Collimator Accuracy and Beam Alignment Viewing of test film The both small balls must be within the first circle to be in proper alignment. Collimation should match borders of test tool. Frequency : semiannual or after tube or Bucky replacement or repair

12. 22.3 Grid Cut Off and Perpendicularity Testing If the tube is not perpendicular to the Bucky, Grid Cut-Off will result. If the grid focus is not correct, grid cut off will also result. The left knee is under exposed compared to the right. This is grid cut off.

13. Grid Cut Off and Perpendicularity Testing Tools Needed: A homogenous phantom that will produce some density on the film. This cane be : A lead apron or piece of Lucite 14”x17”x2” Densitometer 14” x 17” Cassette

14. Grid Cut Off and Perpendicularity Testing Procedure: Set the SID at 40” Bucky Drape Apron over Bucky or Place Lucite in stool in front of Bucky Place cassette in Bucky Tray and center tube to film.

15. Grid Cut Off and Perpendicularity Testing Procedure: Collimate to film size and make exposure. Process film Repeat test at 72” SID. Process Film

16. Grid Cut Off and Perpendicularity Testing Standard: There should be not more than ± 0.10 OD change from center of image to sides of image. If 40” or 72” test passes and the other fails, the focal range of the grid may be wrong. If both fail, the grid is misaligned.

17. Grid Cut Off and Perpendicularity Testing Grid misalignment can be common with new installations. If the Bucky crashes to the floor, the grid can be knocked out of alignment. Frequency of test: Semiannual

18. 22.4 Linearity Of Exposure “The same mAs should produce the same exposure each time.” This will be true if the mA and Timer are accurately calibrated. The kVp must be the same.

19. Linearity Of Exposure Tools needed: Aluminum Step wedge Lead Blockers 14” x17” Cassette Densitometer Standard: Exposure should be within ± 5% across the mA, Time and mAs settings

20. 22.4 Linearity Of Exposure Procedure: Set SID to 40” table top Place cassette on table Step wedge is placed on cassette. Collimation set to size of step wedge. Lead blockers cover the area around exposure.

21. Linearity Of Exposure Procedure: Set a baseline technique and initiate first exposure Cover exposed section of film and prepare for second exposure. Change control setting and the put back to original setting. Make exposure.

22. Linearity Of Exposure Procedure: Continue process with changes in power level or mA setting, Focal Spot settings and time settings. Make sure that the exposed areas of the cassette are covered by the lead blockers. Process the film.

23. Linearity Of Exposure This is an example of poor calibration of the x-ray generator. The small and large focal spot mA setting are not calibrated. This was a new unit that the service engineer failed to calibrate.

24. Linearity Of Exposure This is an example of proper calibration of the machine. Each exposure is virtually identical. If you need to adjust a technique on this machine, you can do it reliably.

25. 22.5 Focal Spot Testing Test Tools: RMI Focal Spot Test Tool or Pin Hole Camera or NEMA Star Pattern Test Tool Extremity Cassette Lead Blocker

26. Focal Spot Testing Procedure: Place Extremity Cassette or Card Board Film Holder on Table. Cover half of cassette with Lead Blocker Set SID to 40” Table Top Place test tool on cassette with rivets aligned with the anode and cathode.

27. Focal Spot Testing Procedure: Collimate to size of test tool. Set technique and make exposure on small focal spot. Cover exposed section of cassette. Set tool on unexposed section of cassette.

28. Focal Spot Testing Procedure: Place “L” on film and make exposure with large focal spot. Process the film.

29. Focal Spot Testing Interpretation of film: Compare vertical and horizontal three bars. 1.0mm Focal spot will resolve 11 line pairs/mm. 2.0mm focal spot will resolve 5 to 6 line pairs/mm. If you cannot see this far, the tube may be bad.

30. Focal Spot Test Film Passed

31. Focal Spot Testing While the focal spot passes the test, the exposure is different between the large and small focal spots. This was the first clue that the calibration of the machine was wrong.

32. Focal Spot Test Film Both exposures are at the same mAs and kVp Resolution: Passed Exposure: Fail

33. Accessory Testing Accessories include the cassettes, grids outside the Bucky, Lead Aprons and gonadal protection. The cassettes and screens are the primary concern. Screens should be cleaned monthly with screen cleaner. Keeping the darkroom clean is also important for screen cleanliness.

34. 23.4 Screen Contact Testing Procedure: Clean screens and let them dry. Use screen cleaner design for the screen used. With a felt tip pen, write an identification number on the screen next to the I.D. and on the back of the cassette. Load cassettes.

35. Screen Contact Testing Procedure: Set SID to 40” Table Top Place cassette on table. Place wire mesh tool on cassette. Set collimation to film size. Make exposure and process film.

36. Screen Contact Testing Procedure: Hang film on view box. Step back 72” from view box and view film. Areas of increased density or loss of resolution indicates poor contact or stained screens.

37. Screen Contact Testing Procedure: The I.D. # will help you find a cassette that needs to be cleaned or taken from service. Frequency of tests: semiannual

38. Poor Screen Contact There is a loss of detail in the thoracic and lumbar spine due to poor screen contact. This was a new cassette.

39. Poor Screen Contact Note the blurry image in the spine but sharp image of the ribs. The screens were not in proper contact in the middle of the cassette due to a bow in the cassette back.

40. Screen Cleaning Materials needed: Screen Cleaner designed for type of screens used. 4 x 4 gauze or cotton balls Tape & Pen

41. Screen Cleaning Procedure: Unload cassette if contact is not being tested. Apply cleaner with gauze. Wipe excess off with dry gauze.

42. Screen Cleaning Leave open to air dry. Make sure cassette # is still legible. After dry, reload cassette.

43. Screen Cleaning Record date on tape and place on back of cassette. By having each cassette identified, selected cassette can be cleaned as needed.

44. Screen Cleaning California Department of Radiologic Health recommends cleaning screens monthly. Should definitely be done quarterly and sooner as needed when artifacts are identified on films. Never use alcohol or detergents not designed for cleaning screens.

45. Cassette Care Methods to get the maximum life from cassettes: Avoid dropping the cassettes Open only far enough the change films Keep outside of cassette clean and dry. Keep screens clean Store on end.

46. Dirty or Damaged Screens Dirty or damaged screen will cause white spots on the image.

47. Dirty & Damaged Screens The white spots on this film are the result of damaged or worn out screens. Never use alcohol or detergents to clean screens.

48. Speed Matching After looking for screen contact problems: Measure speed of cassettes by reading density with the Densitometer. The density of the exposed area should not vary more than ± 0.05 OD. As screen age, they loose speed. Always make sure the light spectrum of the screens and film are matched.

49. 23.5 Apron and Gonad Shield Testing Lead aprons and shields should be tested semiannually for defects Aprons with defective lead provide little protection for the patient.

50. Apron and Gonad Shield Testing Tools needed: 14” x 17” cassette View Box Coat Apron Procedure: Drape apron over Bucky Place cassette in Bucky make exposures in upper and lower Bucky slots.

51. Apron and Gonad Shield Testing Coat Apron Procedure: Note that this is the same test as used for grid alignment. Process films View films on view box:

52. Apron and Gonad Shield Testing Half Apron and Small Shield Procedure: Place cassette on table Set SID at 40” Place apron or shields on cassette. Make exposure and process the film.

53. Apron and Gonad Shield Testing Viewing the test films: Note creases in the lead. Full holes will produce a black area on the film. If cracks or defects are in the area that should cover the gonads, replace apron.

54. Care of Aprons Never fold aprons Store flat or hung on apron rack Use only aprons with the lead equivalency of 0.5mm for patient and staff protection. Do not use as lead blockers for extremity films. Protect from heat and direct sun light.

55. Grid Uniformity Testing Procedure is the same as testing the Bucky Grid. Place homogenous phantom or lead apron over grid that is taped to the top of the cassette. Make exposure and look for density changes and grid damage.

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