1. Creating a Technique Chart
The Cheat Sheet of Radiology!

2. What is a Technique Chart?
Provides suggested technical factors for each type of anatomy.
Unique to each x-ray unit
Unique to each anatomical part
Requires:
Medium sized dog with ideal body condition
One perfectly exposed radiograph
Screens of the same speed and manufacturer
Machine to be serviced/calibrated before beginning

3. Why is it Important? A quick reference for machine settings
Without it:
New calculations would have to be taken before every radiograph.
Increased number of retakes = increased exposure to radiation.

5. Creating a Technique Chart
Step 1: Prepare
Service your processor and ensure screens and film match.
Select a medium-sized dog of average weight.
Step 2: Select your mAs
Use the following for an average speed intensifying screen:
Extremity 2.5 mAs
Thorax 5 mAs
Abdomen 7.5 mAs
Spine 10 mAs
Remember: mA x secs = mAs

6. Creating a Technique Chart
Step 2: Select your mAs (cont.)
To achieve this mAs, the mA and time need to be set separately, and the machine will calculate the mAs for you.
Use these as standard mA settings:
Extremity mA
Other mA
Calculate the time as follows:
Extremity: 150mA X 1/60 secs= 2.5 mAs
Thorax: 300 mA X 1/60 secs = 5 mAs
Abdomen: 300 mA X 1/40 secs = 7.5 mAs
Spine: 300 mA X 1/30 secs = 10 mAs

7. Creating a Technique Chart
Step 3: Select your initial kVp
Calculate initial kVp using Sante’s Rule
Formula: 2 x thickness grid factor
*If a grid is used, add 10 to total
Using a grid means to place the cassette in the tray under the radiology table
Grid is usually indicated for measurements greater than or equal to 10 cms
Example: Extremity = 7 cm
(2 X 7) + 40 = 54 kVp
No grid necessary since < 10 cms
Book states >12 cm
Article states >10
** Note: At VTI, we always use a grid for cats, and sometimes will use a grid as a way to achieve a clearer image, even if the animal is small **

8. Creating a Technique Chart
Step 4: Expose the perfect film
Use the exposure factors calculated above as a starting point
If you can’t see details of internal structures because the image is too dark, the radiograph has been over-penetrated (too much contrast), so decrease kVp by 15%
If you can’t see details of internal structures because the image is too light, the radiograph has been under-penetrated, so increase kVp by 15%
Once the radiograph is close to perfect, reduce the changes to 5% increments until you’re satisfied with the result.
mAs can be adjusted up or down 50% as needed to alter density
This may require a lot of exposures!

9. Creating a Technique Chart
Step 5: Make the technique chart
Complete kVp’s above and below the “perfect entry” as follows:
Subtract 2 kVp from the original kVp for each cm decrease from the original
Add 2 kVp to the original kVp for each cm increase from the original kVp up to 80 kVp.
Add 3 kVp for each cm increase that places the kVp above 80 and up to 100
Add 4 kVp for each cm increase that places the kVp above 100
Step 6: Create a Technique Chart for each different study (abdomen, thorax, extremity, and spine)
Create an additional chart for body parts that may need to be radiographed using a grid (all but extremities)

10. For example…
Cm.
kVp
mAs 7 64
7.5 8 66 9 68 10 70 11 72 12 74 13 76 14 78 15 80 16 83 17 86 18 89 19 92
In this example, the perfect combination of kVp and mAs for a sample 15 cm abdomen is shown in blue…The entries above and below are filled in based on the previous rules.