Developing Your Own Technique Chart

II. Preparation

A. Set Variables

1. Film Processing

a. Use new chemicals (developer and fixer) and continue using the same type of chemicals

b. Maintain constant chemical temperature

c. Use constant developing time

2. Film-Screen Combination should not vary during chart development

3. Focal- Film Distance (usually 30 or 40'')

B. Derive MAS Chart - using the MA and time stations available on the x-ray machine. MaS=Ma X time in seconds

C. Select an animal to be radiographed

1. Dog weighing approximately 40 pounds

2. No overweight

3. General anesthesia is suggested

III. Trail Exposures

A. With the dog lying in lateral recumbency, make 3 trial exposures centering over the liver. A 14'' x 17'' cassette can be divided into 3 sections to conserve film and to reduce processing variables. Use RE 400 speed screen and do not use a grid

1. Measure the thickness (in centimeters) of the liver area at the highest point. This measurement should be between 10-20cm. This measurement will be used to determine the KVP chart.

2. Set the exposure technique

a. Set the KVP according to the following conversion:
Less then 10 cm = 60 KVP
10-20 cm = 70 KVP
Greater than 20cm = 80 KVP

b. Change only the MAS for the 3 exposure. Use 05 MAS for the first exposure, 1.5 MAS for the second, and 3 MAS for the third. If these exact MAS choices are not available, use numbers that are as close as possible. 

B. Develop the film

C. Choose the technique that allows the greatest visualization of soft tissuestructures. If you are not satisfied with any of the exposure adjust the MAS and try again. Remember it takes at least a 30% change in a MaS to see a change on the radiograph. Change the MaS at least 50% if needed. The chosen technique will be used as the table-top abdomen technique and also as a baseline for the rest of the chart. A radiograph of the entire abdomen is recommended using this technique

IV. Production of the MAS chart: Using your known values as the table-top (T.T.) abdominal chart and using the following conversion factors, derive an MAS chart

Rare Earth Screens (400 Speed)

• TABLE-TOP ABDOMEN Known MAS Value

• GRID ABDOMEN 2 X T.T. Abd.

• TABLE-TOP THORAX 1/2 X T.T. Abd.

• GRID THORAX 2 X T.T Thorax

Slow Speed Screens (detail screens 100 speed)

• TABLE-TOP DETAIL 4 X T.T. Abd

• GRID DETAIL 2 X T.T. Detail

RE 400 Speed to slow (detail 100) speed = 4 X RE 400 speed MAS

V. Preparation of a variable KVP chart: Prepare a variable KVP chart according to the following rules:

• Subtract 2 KVP from the original KVP (70)for each cm decrease from the original measurement

• Add 2 KVP to the original KVP (70) for each cm increase from the original measurement up to 80 KVP

• Add 3 KVP for each cm increase that places the KVP above 80 up to 100

• Add 4 KVP for each cm increase that places the KVP above 100

VI. Try each of the calculated techniques ( TT thorax, Grid, Detail. etc.) using the variable MAS and KVP charts. Make any necessary adjustments. Testing your technique for large dogs, small dogs, and cats is also recommended.

Example of Technique Chart Development

This technique chart was calculated by using an anesthetized 40 pound dog measuring 15cm over the liver area

14'' x 17'' cassette

1.6 MAS @ 70 KVP was chosen as the best technique for T.T., Abd.

MAS Chart

IF THESE EXACT MAS VALUES ARE NOT AVAILABLE ON THE X-RAY UNIT, TRY THE CLOSEST ONES AVAILABLE

KVP CHART FOR MACHINES WITH MAXIMUM CAPACITY OF 100KV

VS, KV and CM chart for regular VS, KV, and CM settings up to and above the 27cm settings at which point use 100KV and add 20% to MAS for each cm increase

The previous technique chart will not work for low output machines with a maximum of KVP of 90. A chart must be developed that does not exceed 90 KVP. Since both MAS and KVP can affect the radiographic density, the MAS can be adjusted to maintain the density while the KVP is lowered.

KVP- Density Relationship
Increase KVP by 20% = Double Radiographic Density or Increase KV by 10
Decrease KVP by 16% = Half Radiographic Density or Decrease KV by 10

MAS - Density Relationship
Double MAS = Double Radiographic Density
Half MAS = Half Radiographic Density

KVP-MAS CHART

* At 24cm. adding 3 KVP tp 89 would be 92. This exceeds the limits of the machine. By subtracting 16% of 92, the KVP is lowered to 77. Consequently this halves the density of the radiograph. To compensate for the loss of density the MAS can be doubled to return the radiograph to its original density.

** Again, adding 3 KVP will exceed the 90kvp maximum. The KVP is decreased by 16% resulting in a 1/2 decrease in radiographic density. To compensate, the MAS was doubled.

NO GRID AVAILABLE AND NO DETAIL CASSETTES
T.T. BONE = T.T. ABDOMEN + .5 MaS
(You may want to vary this MaS factor depending on your individual situation)

NO GRID AVAILABLE - YOU HAVE DETAIL CASSETTES
T.T BONE = 4 X T.T. ABDOMEN
GRID IS AVAILABLE BUT NO DETAIL CASSETTES

T.T. BONE = T.T. ABDOMEN + .5 (SAME AS ABOVE)
GRID BONE = 2 X T.T.BONE
 

IF THE TECHNIQUE CHARTS DO NOT WORK OVER THE ENTIRE KVP RANGE THE UNIT MAY NEED TO BE CALIBRATED

 

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