Title: 22.1 Radiographic Quality Control Variables in Radiographic Equipment
122.1 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
2Radiographic 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
3Radiographic 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
422.2 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
5Collimator 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.
6Collimator 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.
7Collimator 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.
8Collimator 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!
9Collimator 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)
10Collimator 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
11Collimator 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
1222.3 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.
13Grid 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
14Grid 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.
15Grid Cut Off and Perpendicularity Testing
- Procedure
- Collimate to film size and make exposure.
- Process film
- Repeat test at 72 SID.
- Process Film
16Grid 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.
17Grid 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
1822.4 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.
19Linearity 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
2022.4 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.
21Linearity 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.
22Linearity 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.
23Linearity 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.
24Linearity 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.
2522.5 Focal Spot Testing
- Test Tools
- RMI Focal Spot Test Tool or
- Pin Hole Camera or
- NEMA Star Pattern Test Tool
- Extremity Cassette
- Lead Blocker
26Focal 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.
27Focal 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.
28Focal Spot Testing
- Procedure
- Place L on film and make exposure with large
focal spot. - Process the film.
29Focal 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.
30Focal Spot Test Film Passed
31Focal 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.
32Focal Spot Test Film
- Both exposures are at the same mAs and kVp
- Resolution Passed
- Exposure Fail
33Accessory 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.
3423.4 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.
35Screen 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.
36Screen 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.
37Screen 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
38Poor Screen Contact
- There is a loss of detail in the thoracic and
lumbar spine due to poor screen contact. - This was a new cassette.
39Poor 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.
40Screen Cleaning
- Materials needed
- Screen Cleaner designed for type of screens used.
- 4 x 4 gauze or cotton balls
- Tape Pen
41Screen Cleaning
- Procedure
- Unload cassette if contact is not being tested.
- Apply cleaner with gauze.
- Wipe excess off with dry gauze.
42Screen Cleaning
- Leave open to air dry.
- Make sure cassette is still legible.
- After dry, reload cassette.
43Screen Cleaning
- Record date on tape and place on back of
cassette. - By having each cassette identified, selected
cassette can be cleaned as needed.
44Screen 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.
45Cassette 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.
46Dirty or Damaged Screens
- Dirty or damaged screen will cause white spots on
the image.
47Dirty 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.
48Speed 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.
4923.5 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.
50Apron 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.
51Apron 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
52Apron 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.
53Apron 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.
54Care 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.
55Grid 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.
56End of Lecture
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