Formulating Technique Charts

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.

2
Formulating Technique Charts

• Used equipment generally do not come with
  technique charts.
• If you buy someones 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!!!

3
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.

4
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.

5
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 manufacturers best interest
  that your films are of consistently high quality.

6
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.

7
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.

8
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?

9
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?

10
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.

11
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 !

12
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.

13
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.

14
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.

15
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.

16
Supertech Technique Calculator

• The correction factor is used to adjust the
  calculator for the equipment type, calibration
  and film speed.

17
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.

18
Supertech Technique Calculator

• Addition correction factors are provided for
  patient body habitus and changes in SID or film
  speed.
• The Supertech Technique Calculator works !!

19
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

21
The Calculator
22
Houston, we have a problem

• FDA CRCPD
• NEXT studies
• Missouri MORSELS study

23
The body parts
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Choose a body part
25
Enter the appropriate TCF
26
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, 81, 101, 121
• Focal film distance changes
• 40 or 72
• Processing variables
• Temperature, chemical concentration

27
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

31
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

32
Making changes

• Focal film distance
• Grid ratio
• Body habitus
• Casts

33
Changing Focal Film Distance
34
Changing Grid Ratio
35
Calculate TCF _at_ 72, nongrid

• TCF _at_ 40 was calculated as 4
• From 40 to 72 add 3 ½
• Going from 101 grid to nongrid subtract 3 ½
• The new TCF is 4
• The inverse square law change is balanced by
  removing the 101 grid from the beam

36
Adjusting technique for body habitus
37
Adjusting technique for casts
38
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

39
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

40
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

41
Exposure through casts

• For plaster casts
• If still wet, add 3
• If dry, add 2
• For fiberglass casts no adjustment is required

42
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

43
Other help

• More contrast
• Less contrast

44
Other help

• Positioning aids

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Relationships
47
Penetrometer
48
Use the penetrometer

• Expose the penetrometer to 60 kVp and 3.3 mAs at
  each mA station for high frequency generators
• 100 mA _at_ 0.033 seconds
• 200 mA _at_ 0.015 seconds
• 300 mA _at_ 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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