1 formulating technique charts accurate measurements and the used of technique charts will have the...
TRANSCRIPT
1
Formulating Technique Charts
• Accurate measurements and the used of technique charts will have the greatest impact on image quality and minimizing radiation exposure to the patient.
• Remember that over half of the repeated films are due to errors in the technical factors resulting in under or over exposed films.
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Formulating Technique Charts
• Used equipment generally do not come with technique charts.
• If you buy someone’s practice, you may not get accurate charts.
• The complete x-ray chain must be in proper working order in order to establish accurate charts. Acceptance testing is a must!!!
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Sources of Technique Charts
• If you have high frequency equipment, the Nolan Filter System and the screen speed matches those described in the text, baseline charts can be used based upon those in the text book.
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Sources of Technique Charts
• Major x-ray equipment manufacturers may provide help with making technique charts for their equipment.– Anatomically programmed generators have
charts built into the unit. Make sure that they can be easily modified.
– Smaller dealer sold companies may not have the resources to provide much help.
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Sources of Technique Charts
• Major film and screen manufacturers can be a source for help producing technique charts.– The screens and film must match in order to
get consistent results. The manufacturer can be a great help in this area.
– It is in the film manufacturer’s best interest that your films are of consistently high quality.
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Types of Charts
• Fixed kVp charts are recommended because:– Optimum kVp for the body part is used– Consistent contrast is maintained– Reduced exposure for the patient– Greater latitude of exposure.
• Fixed mAs charts lack these qualities.
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Getting Started
• Make sure that the x-ray machine is properly calibrated across all mA stations.
• Make sure the processor is working properly and has fresh chemistry.
• The x-ray machine type (single phase, three phase or high frequency) will have a significant impact on the charts.
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Getting Started
• The method for entering factors will affect the appearance of the chart.– Do you enter mAs or mA and time?– What focal spot and mA selections are
available?– Do you have power selection capabilities?– Does the unit have line voltage adjustment?
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Getting Started
– Do you have a non-Bucky film holder?– What is the grid ratio of the Bucky?– What is the Relative Speed Value of the
cassettes and film used?– What additional information do you want on
the charts?• SID, Tube Angles, Film Size or I.D. Location?
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mAs Chart
• Units where the mA and time are set independently need a mAs Chart.
• You can change the mA stations and time to help control motion and get the same mAs.
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Hand Written Charts
• This beats nothing.• If may be all you get
with a used unit.• It is a good starting
point.• This is all we had at
Palmer when I arrived and there were no extremity charts !
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Complete Technique Charts
• Chart should be located in the control booth and easy to read.
• This will help avoid technique errors.
• They will work fine for 85% of the patients.
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Adjustment of Factors
• Patient body habitus will greatly impact the technical factors.– Fit muscular patient will require higher kVp
and sometime increased mAs also.– Fatty tissue will need an increase in mAs and
no increase in kVp.– Frail or elderly patients need a reduction in
kVp.
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Supertech Technique Calculator
• The Supertech Technique Calculator can be used to compute the technical factors.
• It consists of the slide rule, a penetrometer and calibration film.
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Supertech Technique Calculator
• An exposure is made of the penetrometer for each mA station and cassette speed used.
• This can be used to check mA calibration and different factor established for each mA station.
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Supertech Technique Calculator
• The correction factor is used to adjust the calculator for the equipment type, calibration and film speed.
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Supertech Technique Calculator
• With the correction factors are set, just enter the patient measurements on one side.
• Turn it over and read the combinations of mAs and kVp that will produce a satisfactory image.
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Supertech Technique Calculator
• Addition correction factors are provided for patient body habitus and changes in SID or film speed.
• The Supertech Technique Calculator works !!
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Supertech Technique Program
• A computer program is also available. Supertech is now available for the Palm Pilot
• By entering the machine correction factor, technique charts can be printed.
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Supertech®: RadiographicTechnique Calculator
Gary M. Guebert, D.C., DACBR™
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The Calculator
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“Houston, we have a problem”
• FDA – CRCPD– NEXT studies
• Missouri MORSELS study
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The body parts
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Choose a body part
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Enter the appropriate TCF
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What is a TCF?
• It takes into account all of the variables involved:– X-ray generating system
• Single phase vs high frequency
– Film/screen speed• 100, 400/800, 600/1200
– Grid ratio• Non grid, 8:1, 10:1, 12:1
– Focal film distance changes• 40” or 72”
– Processing variables• Temperature, chemical concentration
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Turn the Supertech® over
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Select kVp, mA, time
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mA stations
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How to establish your TCF
• Work backwards from an existing good radiograph
• Use the penetrometer
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Work backwards from an existing good radiograph
• From the exposure log find the part size– e.g. 21 cm lumbar spine, AP
• You cannot set the TCF at this point• Turn the Supertech® over• Find the time & mA (or mAs used)• Line up the kVp next to that mAs value• Turn the Supertech® over again and there
is your TCF for THAT EXPOSURE
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Making changes
• Focal film distance
• Grid ratio
• Body habitus
• Casts
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Changing Focal Film Distance
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Changing Grid Ratio
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Calculate TCF @ 72”, nongrid
• TCF @ 40 was calculated as –4
• From 40 to 72 add 3 ½
• Going from 10:1 grid to nongrid subtract 3 ½
• The new TCF is –4– The inverse square law change is balanced
by removing the 10:1 grid from the beam
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Adjusting technique for body habitus
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Adjusting technique for casts
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The 15% rule is built in
• Supertech permits you to use kVp changes other than 15% to change contrast– There is a lower limit to kVp– Must be enough to penetrate the body part
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How to account for children
• Children under the age of 12 have less calcium in their bones, compared to adults
• Use the red boxes– The difference in the position of the red/black
boxes constitutes a 30% decrease in mAs for children
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Change TCF for non normal patient
• For patients with a muscular body habitus add a MINIMUM of +1
• For patients with a diminished bone density subtract a MINIMUM of -1
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Exposure through casts
• For plaster casts– If still wet, add +3– If dry, add +2
• For fiberglass casts no adjustment is required
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But I have a new x-ray machine with programmed techniques…
• These programs often only anticipate one film/screen combination at a fixed FFD
• You can use the Supertech® to adjust the programmed technique for your circumstance
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Other help
• More contrast• Less contrast
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Other help• Positioning aids
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Relationships
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Penetrometer
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Use the penetrometer
• Expose the penetrometer to 60 kVp and 3.3 mAs at each mA station for high frequency generators– 100 mA @ 0.033 seconds– 200 mA @ 0.015 seconds– 300 mA @ 0.01 seconds
• Process the film• Use the master film to determine TCF
– The penetrometer image should be virtually identical at each mA station
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TCF test
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TCF test
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TCF test
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TCF test
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Bad test, 200 mA out of calibration
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TCF test film
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Master film
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Using Master Film
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The End
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Nolan Accu-rad Calipers
• Along with the filter system, Dr. Nolan designed the Accu-Rad Calipers.
• Once set up by setting film speed, grid ratio and machine type, the calipers will:
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Nolan Accu-rad Calipers
– Provide the technical factors
– CM thickness– Points for additional
filters needed for the view.
• The caliper system uses high kVp to reduce patient exposure.
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End of Lecture
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