Technique chart construction

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

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

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

5. Construction Construction
of of

technique technique
chartchart

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

8. lnitial kVp settinglnitial kVp setting::
►Sante's ruleSante's rule::

(2x measured thickness) + FFD+ (grid factor if > 10 cm) =initial kVp(2x measured thickness) + FFD+ (grid factor if > 10 cm) =initial kVp
►Grid Factor RatioGrid Factor Ratio Added kVp to sum ofAdded kVp to sum of
5:1 6-85:1 6-8
8:1 8-108:1 8-10
12.1 10-1512.1 10-15
16:1 15-2016:1 15-20
Sante's RuleSante's Rule

9. lnitial mAs setting:lnitial mAs setting:
Screen Type mAsScreen Type mAs
►Fast (High Speed) 2.5 - 10Fast (High Speed) 2.5 - 10
►Medium( Par Speed) 5 -12.5Medium( Par Speed) 5 -12.5
►Slow (Ultra Detail) 30-40Slow (Ultra Detail) 30-40
►Recommended mAs based on a par (medium) speed screenRecommended mAs based on a par (medium) speed screen
Table top (no grid) extremity: 2.5mAs Table top (no grid) extremity: 2.5mAs
Thorax: 5mAs Thorax: 5mAs
Abdomen: 7.5mAs Abdomen: 7.5mAs
Spine: 10mAsSpine: 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 Evaluate the exposure
techniquetechnique
►by the following parametersby the following parameters::
 DensityDensity - the degree of blackness - the degree of blackness
 Contrast-Contrast- density difference between two density difference between two
areas of a finished radiograph.areas of a finished radiograph.
Goal = radiograph with a "perfect" exposureGoal = radiograph with a "perfect" exposure
Perfect exposure means:Perfect exposure means:
►For abdominal imaging a longer gray scale preferred For abdominal imaging a longer gray scale preferred
to differentiate between soft tissue structures.to differentiate between soft tissue structures.
►Bone studies shorter gray scale

11. Technique modification if requiredTechnique modification if required
►Film too DarkFilm too Dark Film Film
too Lighttoo Light

Sufficient contrast
between bone and soft
tissue
Outline of abdominal
structures visible
YES
NO
mAs 30-50%
mAs 30-50%
kVp10-15%
kVp10-15%

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

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

14. ABDOMEN Grid Ratio 6 :1ABDOMEN Grid Ratio 6 :1
THICKNESS THICKNESS
(cm)(cm)


kVkV
pp

mAsmAs
88 56567.57.5
99 58587.57.5
1010 60607.57.5
1111 62627.57.5
1212 64647.57.5
1313 66667.57.5
1414 68687.57.5
1515 70707.57.5
1616 72727.57.5
1717 74747.57.5
1818 76767.57.5
2020 78787.57.5
2121 80807.57.5
2222 83837.57.5
2323 86867.57.5
2424 89897.57.5

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

16. ABDOMEN Grid Ratio 6:1ABDOMEN Grid Ratio 6:1
THICKNESSTHICKNESS
(cm)(cm)
kvpkvpmAsmAs
88 66663.753.75
99 68683.753.75
1010 70703.753.75
1111 72723.753.75
1212 74743.753.75
1313 66667.57.5
1414 6868 7.57.5
1515 7070 7.57.5
1616 7272 7.57.5
1717 7474 7.57.5
1818 7676 7.57.5
1919 7878 7.57.5
2020 8080 7.57.5
2121 8383 7.57.5
2222 8686 7.57.5
2323 8989 7.57.5