Presentation on theme: "Formulating Technique Charts"— Presentation 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.
2 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!!!
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 manufacturer’s 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 usedConsistent contrast is maintainedReduced exposure for the patientGreater latitude of exposure.Fixed mAs charts lack these qualities.
7 Getting StartedMake 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 StartedThe 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 ChartUnits 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 FactorsPatient 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 PilotBy entering the machine correction factor, technique charts can be printed.
20 Supertech®: Radiographic Technique Calculator Gary M. Guebert, D.C., DACBR™
26 What is a TCF? It takes into account all of the variables involved: X-ray generating systemSingle phase vs high frequencyFilm/screen speed100, 400/800, 600/1200Grid ratioNon grid, 8:1, 10:1, 12:1Focal film distance changes40” or 72”Processing variablesTemperature, chemical concentration
30 How to establish your TCF Work backwards from an existing good radiographUse the penetrometer
31 Work backwards from an existing good radiograph From the exposure log find the part sizee.g. 21 cm lumbar spine, APYou cannot set the TCF at this pointTurn the Supertech® overFind the time & mA (or mAs used)Line up the kVp next to that mAs valueTurn the Supertech® over again and there is your TCF for THAT EXPOSURE
32 Making changesFocal film distanceGrid ratioBody habitusCasts
35 Calculate TCF @ 72”, nongrid 40 was calculated as –4From 40 to 72 add 3 ½Going from 10:1 grid to nongrid subtract 3 ½The new TCF is –4The inverse square law change is balanced by removing the 10:1 grid from the beam
38 The 15% rule is built inSupertech permits you to use kVp changes other than 15% to change contrastThere is a lower limit to kVpMust 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 adultsUse the red boxesThe 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 +1For patients with a diminished bone density subtract a MINIMUM of -1
41 Exposure through casts For plaster castsIf still wet, add +3If dry, add +2For 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 FFDYou can use the Supertech® to adjust the programmed technique for your circumstance
48 Use the penetrometerExpose the penetrometer to 60 kVp and 3.3 mAs at each mA station for high frequency generatorssecondssecondssecondsProcess the filmUse the master film to determine TCFThe penetrometer image should be virtually identical at each mA station