Creating a Technique Chart The Cheat Sheet of Radiology!

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

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.

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

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 150 mA Other 300 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

Creating a Technique Chart Step 3: Select your initial kVp Calculate initial kVp using Sante’s Rule Formula: 2 x thickness + 40 + 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 **

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!

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)

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.