Formulating Technique Charts by ghsi90336

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									 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.

                                               1
 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!!!
                                               2
  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.




                                              3
  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.


                                                      4
  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.


                                                        5
           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.


                                            6
            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.


                                                7
            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?



                                                  8
           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?




                                                    9
                 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.

                             10
         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 !

                               11
   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.


                               12
       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.


                                                13
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.


                             14
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.



                             15
Supertech Technique Calculator

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




                             16
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.


                             17
Supertech Technique Calculator

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

                             18
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.
                              19
Supertech®: Radiographic
  Technique Calculator
      Gary M. Guebert,
      D.C., DACBR™



                           20
The Calculator




                 21
 “Houston, we have a problem”
• FDA – CRCPD
  – NEXT studies
• Missouri MORSELS study




                                22
The body parts




                 23
Choose a body part




                     24
Enter the appropriate TCF




                            25
                  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


                                                     26
Turn the Supertech® over




                           27
Select kVp, mA, time




                       28
mA stations




              29
   How to establish your TCF
• Work backwards from an existing good
  radiograph
• Use the penetrometer




                                         30
       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

                                             31
             Making changes
•   Focal film distance
•   Grid ratio
•   Body habitus
•   Casts




                              32
Changing Focal Film Distance




                               33
Changing Grid Ratio




                      34
 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


                                                35
Adjusting technique for body
           habitus




                               36
Adjusting technique for casts




                                37
      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




                                                38
   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




                                                  39
  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




                                              40
      Exposure through casts
• For plaster casts
  – If still wet, add +3
  – If dry, add +2
• For fiberglass casts no adjustment is
  required




                                          41
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




                                         42
             Other help
• More
  contrast
• Less
  contrast




                          43
        Other help
• Positioning
  aids




                     44
45
Relationships




                46
Penetrometer




               47
        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

                                                           48
TCF test




           49
TCF test




           50
TCF test




           51
TCF test




           52
53
Bad test, 200 mA out of
      calibration




                          54
TCF test film




                55
Master film




              56
Using Master Film




                    57
The End




          58
      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:

                                59
      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.

                                60
    End of Lecture

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   Return to Radiologic
Technology Two Home Page

                             61

								
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