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22.1 Radiographic Quality Control Variables in Radiographic Equipment

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22.1 Radiographic Quality Control Variables in Radiographic Equipment kVp Calibration mA Calibration Timer accuracy Collimator accuracy Beam Alignment – PowerPoint PPT presentation

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Title: 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 _at_ 40 to Bucky
  • Place 8X10 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 14x17x2
  • 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.

56
End of Lecture
  • Return to Lecture Index
  • Return to Rad Tech 2 Home Page
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