► Identifies reliable exposure factors Identifies reliable exposure factors

(mA, kVp and exposure time) for a (mA, kVp and exposure time) for a known tissue thicknesses known tissue 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 Exposure charts may be kVp-variable or mAs-variable or mAs-variable

►A kVp-variable chart uses constant A kVp-variable chart uses constant settings for mA and exposure time settings for mA and exposure time (seconds) and indicates the appropriate (seconds) and indicates the appropriate kVp for specific tissue thicknesses and kVp for specific tissue thicknesses and types 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.

►Two basic charts –Two basic charts –► one to list exposures to use in conjunction one to list exposures to use in conjunction

with a gridwith a grid

► the other to indicate the settings for gridless the other to indicate the settings for gridless radiography.radiography.

► A grid is recommended for A grid is recommended for radiographing thoraxes deeper than radiographing thoraxes deeper than 14cm and any other body part thicker 14cm and any other body part thicker than 10cm.than 10cm.

Construction Construction of of technique charttechnique chart

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.

To BeginTo Begin► With patient in lateral recumbency, With patient in lateral recumbency,

measure the thickness of the desired part measure the thickness of the desired part (abdomen at approximatety twelth rib)(abdomen at approximatety twelth rib)

► If the measurement is an intermediate If the measurement is an intermediate value (such as 13.4cm=14) record the value (such as 13.4cm=14) record the next highest whole number. next highest whole number.

►Measure FFD( generally 40“ for large Measure FFD( generally 40“ for large stationary systems)stationary systems)

►Measure Grid ratio (8:1)Measure Grid ratio (8:1)

lnitial kVp settinglnitial kVp setting::

►Sante's ruleSante's rule::

(2x measured thickness) + FFD+ (grid factor if > 10 cm) (2x measured thickness) + FFD+ (grid factor if > 10 cm) =initial kVp=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

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 Recommended mAs based on a par (medium) speed screenscreen 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)

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 density difference between two areas of a finished radiograph.two 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 For abdominal imaging a longer gray scale

preferred to differentiate between soft tissue preferred to differentiate between soft tissue structures.structures.

►Bone studies shorter gray scale

Technique modification if Technique modification if requiredrequired

►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%

► Retake radiograph until a perfect film Retake radiograph until a perfect film exposure is obtained.exposure is obtained.

►Extrapolate values from "Extrapolate values from "perfect perfect exposureexposure” film for abdominal technique ” film for abdominal technique chart as follows:chart as follows: Add 2 kVp for each cm increase from the Add 2 kVp for each cm increase from the

original measurement upto 80 kVp.original measurement upto 80 kVp. Add 3 kVp for each cm increase between 80-Add 3 kVp for each cm increase between 80-

100 100

kVpkVp Add 4 kVp for each cm increase that places Add 4 kVp for each cm increase that places

the kVp above 100the kVp above 100 Subtract 2kVp for each cm decrease from Subtract 2kVp for each cm decrease from

the original measurementthe original measurement

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 kVP (2xmeasured thickness) + ffd+ (grid factor if > 10 cm) = kVpfactor if > 10 cm) = kVp

►(2x12) +32+8=64 kV(2x12) +32+8=64 kVPP

►A good starting point for mAs setting for A good starting point for mAs setting for our medium sized dog for abd. is 7.5 mAs.our medium sized dog for abd. is 7.5 mAs.

ABDOMEN Grid Ratio 6 :1ABDOMEN Grid Ratio 6 :1

THICKNESS THICKNESS (cm)(cm)

kVkVpp

mAsmAs

88 5656 7.57.5

99 5858 7.57.5

1010 6060 7.57.5

1111 6262 7.57.5

1212 6464 7.57.5

1313 6666 7.57.5

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

2020 7878 7.57.5

2121 8080 7.57.5

2222 8383 7.57.5

2323 8686 7.57.5

2424 8989 7.57.5

""TweakingTweaking"" the technique the technique chartchart

►It is preferable to use high kVp for It is preferable to use high kVp for soft tissue exams due to the longer soft tissue exams due to the longer scale of contrast scale of contrast

►To modify the extrapolated To modify the extrapolated techniques to allow for higher kVp techniques to allow for higher kVp settings use the following rule:settings use the following rule:

Add 10 kVp then halve the mAsAdd 10 kVp then halve the mAs

ABDOMEN Grid Ratio 6:1ABDOMEN Grid Ratio 6:1THICKNESSTHICKNESS

(cm)(cm)kvpkvp mAmA

ss

88 6666 3.73.755

99 6868 3.73.755

1010 7070 3.73.755

1111 7272 3.73.755

1212 7474 3.73.755

1313 6666 7.57.5

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 7.57.52121 8383 7.57.5

2222 8686 7.57.5

2323 8989 7.57.5