This document describes how to construct an x-ray exposure technique chart. It involves measuring the thickness of the body part to be imaged, the focal film distance, and grid ratio. The initial kVp is calculated using Sante's rule. The initial mAs is based on screen speed. Test exposures are taken and adjusted as needed until the perfect exposure is achieved. The values are then extrapolated to complete the technique chart, adding or subtracting kVp based on increases or decreases in thickness. The chart can then be modified to allow for higher kVp settings by adding 10 kVp and halving the mAs.

2. Identifies reliable exposure factors (mA,
kVp and exposure time) for a known tissue
thicknesses
► A radiograph exposure chart can be
constructed to suit any X-ray machine.
►
► Exposure charts may be kVp-variable or
mAs-variable

3. ► A kVp-variable chart uses constant settings
for mA and exposure time (seconds) and
indicates the appropriate kVp for specific
tissue thicknesses and types
► An mAs-variable chart, recommends
various mAs settings for specific tissue
thicknesses and types, allowing the
operator to keep the kVp constant for all
exposures.

4. ► Two basic charts –
one to list exposures to use in conjunction with a
grid
►
the other to indicate the settings for gridless
radiography.
►
►
A grid is recommended for radiographing
thoraxes deeper than 14cm and any other
body part thicker than 10cm.

5. Construction
technique
of

6. Selecting Patient:
► Average
size animal (say 40-50 lbs dog)
with clean coat, either anesthetized or a
cooperative patient.
► The initial technique chart is constructed for
abdominal settings.
► Other anatomical regions can be
extrapolated from this chart.

7. To Begin
With patient in lateral recumbency, measure
the thickness of the desired part (abdomen at
approximatety twelth rib)
► If the measurement is an intermediate value
(such as 13.4cm=14) record the next highest
whole number.
► Measure FFD( generally 40“ for large stationary
systems)
► Measure Grid ratio (8:1)
►

8. lnitial kVp setting:
►Sante's rule:
(2x measured thickness) + FFD+ (grid factor if > 10 cm) =initial kVp
► Grid Factor Ratio
5:1
8:1
12.1
16:1
Added kVp to sum of Sante's Ru
6-8
8-10
10-15
15-20

9. lnitial mAs setting:
►
Screen Type
Fast (High Speed)
Medium( Par Speed)
Slow (Ultra Detail)
►
Recommended mAs based on a par (medium) speed screen
►
►




►
►
►
mAs
2.5 - 10
5 -12.5
30-40
Table top (no grid) extremity: 2.5mAs
Thorax: 5mAs
Abdomen: 7.5mAs
Spine: 10mAs
. Cats- halve the mAs from dog
High kVp for soft tissue exams( longer gray scale)
Lower kVP for bone studies( shorter gray scale)

10. Evaluate the exposure
technique
► by
the following parameters :

Density - the degree of blackness

Contrast- density difference between two
areas of a finished radiograph.
 Goal = radiograph with a "perfect" exposure
Perfect exposure means:
► For abdominal imaging a longer gray scale preferred
to differentiate between soft tissue structures.
► Bone
studies shorter gray scale

11. Technique modification if required
►Film
too Dark
too Light contrast
Sufficient
between bone and soft
tissue
YES
NO
mAs 30-50%
kVp10-15%
Film
Outline of abdominal
structures visible
mAs 30-50%
kVp10-15%

12. Retake radiograph until a perfect film exposure
is obtained.
► Extrapolate values from "perfect exposure” film
for abdominal technique chart as follows:
►
 Add 2 kVp for each cm increase from the original
measurement upto 80 kVp.
 Add 3 kVp for each cm increase between 80-100
kVp
 Add 4 kVp for each cm increase that places the kVp
above 100
 Subtract 2kVp for each cm decrease from the
original measurement

13. Example
Dog
Thickness at 12 th rib=12”
FFD = 32
Grid ratio=6:1
kVP (2xmeasured thickness) + ffd+ (grid factor if > 10 cm) = kVp
► (2x12) +32+8=64 kVP
► A good starting point for mAs setting for our
medium sized dog for abd. is 7.5 mAs.

14. ABDOMEN
THICKNESS
(cm)
8
9
10
11
12
13
14
Grid Ratio 6 :1
kV
p
56
58
60
62
64
66
68
mAs
7.5
7.5
7.5
7.5
7.5
7.5
7.5
16
72 7.5
17
74 7.5
18
76 7.5
20
78 7.5
21
80 7.5
22
83 7.5
23
86 7.5
24
89 7.5

15. "Tweaking" the technique chart
►It is preferable to use high kVp for soft
tissue exams due to the longer scale of
contrast
►To modify the extrapolated techniques
to allow for higher kVp settings use the
following rule:
 Add 10 kVp then halve the mAs

16. ABDOMEN
THICKNESS kvp
(cm)
8
66
9
68
10
70
11
72
12
74
13
66
Grid Ratio 6:1
mAs 14
15
16
3.75
17
3.75
18
3.75 19
3.75 20
3.75 21
22
7.5
23
68
70
72
74
76
78
80
83
86
89
7.5
7.5
7.5
7.5
7.5
7.5
7.5
7.5
7.5
7.5