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How It’s Made : The Diagnostic Radiograph

Eastern Veterinary Technician Association meeting 2010

LeeAnn Pack DVM

Diplomate ACVR

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www.upei.ca/~vetrad

www.upei.ca/~vetrad

Exposure settings: 4 components

• kVp

• mAs

• Time

• Focal film distance (FFD)• All can be changed alone or in combination

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Make it just right• Make a film more black

• Increase the kVp, mAs or time• Decrease the FFD

• Make a film less black• Decrease the kVp, mAs or time• Increase the FFD

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Questions to Ponder

• Is there adequate penetration of the part imaged?

• How much contrast is needed on the film (some inherent?)?

• Is motion a strong possibility during the exposure?

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Inverse Square Law

• Decrease distance by ½ intensity is increased by 4 times

• Increase distance by 1 intensity is decreased by 4 times

• Technical applications

• Radiation safety

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Radiographic Density

• Subject density• Additive – thick parts absorb more

• Summation

• Over exposed = film to black

• Under exposed = film not black enough

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Factors that affect film density

• Subject density – we can’t change this

• mAs – biggest factor

• kVp – increases the penetrability

• Distance

• Development time and temp

• Scatter and fog

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Turn that dial: Density

• The 16-20 rule• ↑ kVp by 20% will double film density• ↓ kVp by 16% will half film density• Double mAs double density• Half mAs half density• Combos:

• Inc kVp by 20% and dec mAs by half• Dec kVp by 16% and double mAs

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Magnification

• Enlargement of the image relative to the actual size• Causes loss of detail and blurring

• Subject film distance• Dec SFD decreases magnification

• Focal film distance• Inc FFD decreases magnification

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Distortion

• Image which does not represent the true shape of the object• Unequal projection of an object

• Femurs

• Location of an object within the beam• spine

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Scatter radiation

• What is scatter?• Bounce around undergo numerous

interactions

• Scatter increases with:• Increased thickness of the patient• Increased X ray beam energy• Amount of patient exposed (collimate)

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www.upei.ca/~vetrad

Patient Identification

• Films are legal documents• Must be in the emulsion

• Not written on afterwards

• Hospital or Doctor name• Patient name• Date

• Other info like breed, sex, age, owners name can be added but is not required

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How is this done?

• Lead impregnated tape• Info. written on tape and then placed on cassette

• Lead identification markers• Make up name stick on white tape put on cassette

– lose them they are small

• Photoprinter• Inside cassette, screen missing upper right hand

corner• Info. gets stamped onto the film with little flash of

light into the film emulsion

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www.upei.ca/~vetrad

www.upei.ca/~vetrad

Everyday Radiation Exposure

• Natural • Cosmic rays (altitude, sunlight, plane

flights)• Natural, ingested or inhaled terrestrial radio

nuclides

• Man Made• Medical, nuclear storage facilities• Products (lanterns, fire detectors)

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Personnel Monitoring Devices (PMD)

• Anyone who is likely to receive 25% or more of the MPD should be monitored.

• Film Badges

• Pocket Dosimeter

• Thermoluminescent Dosimeter

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www.upei.ca/~vetrad

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Restraint

• Tape

• Gauze

• Rope

• Positioning trays

• Foam wedges

• Sandbags

• Drugswww.upei.ca/~vetrad

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Thorax - Lateral

• Potential for Movement• Decrease mAs

• High inherent contrast area• High kVp

• Collimation• Centering – caudal

scapula• Thoracic inlet to

diaphragm• Pull forelimbs forward

• Inspirationwww.upei.ca/~vetrad

Inspiratory vs. Expiratory Lateral

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Abdomen

• VD and lateral views• Positioning

• Include from the diaphragm to the pelvic inlet

• Femurs are placed perpendicular to the spine

• Hind legs pulled forward for “butt shot”

• Exposure is made on expiration• Collimate to decrease scatter!www.upei.ca/~vetrad

Is the positioning here good?

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Pelvis - VD

• Extended VD view• Used for OFA• Legs pulled down

and rotated inward• Must include the

entire pelvis and stifles

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www.upei.ca/~vetrad

www.upei.ca/~vetrad

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