Artifacts and the Machine- Anode Heel Effect and the Inverse Square Law

Anode Heel Effect: Definition

Variation in x-ray intensity across the primary beam as x-rays diverge from origin.

Anode Heel Effect: Patient Positioning

X-ray intensity is greatest closest to the cathode side.

Anode Heel Effect: SID Relationship

Shorter SID increases the anode heel effect.

Anode Heel Effect: Field Size Relationship

Larger x-ray field size increases the anode heel effect.

Anode Heel Effect: Anode Angle Relationship

Smaller anode angle increases the anode heel effect.

Inverse Square Law: Definition

X-ray field intensity is inversely proportionate to the square of the distance from the source.

Inverse Square Law: Doubling Distance (80 SID)

Doubling distance from 40 to 80 inches reduces intensity to 1/4 (4x less).

Inverse Square Law: Tripling Distance (120 SID)

Tripling distance from 40 to 120 inches reduces intensity to 1/9 (9x less).

Inverse Square Law: Halving Distance (20 SID)

Halving distance from 40 to 20 inches increases intensity by 4x.

Inverse Square Law: 1/3 Distance (13 SID)

Decreasing distance to 1/3 (13 inches) increases intensity by 9x.

Geometric Distortion: Magnification

Occurs when anatomy is far from the image receptor, making it appear larger.

Geometric Distortion: Foreshortening

Occurs when anatomy is far from and not parallel to the image receptor.

Artifacts: Most Common Small Animal Technical Error

Patient motion.

Artifacts: Patient Motion Prevention

Use the shortest exposure time possible and sedation or anesthesia when appropriate.

Artifacts: Technical Errors Examples

Human anatomy present on film, collars, leashes, and tags.

Artifacts: Intentional Artifacts Examples

External fixators, splints, casts, microchips, and buckshot/gunshot.

Radiographic Landmarks: Purpose

Used for proper centering, collimation, and measurement to prevent structure obscuration or distortion.

Quality Assurance: SID Standard Check

Verifies that the distance from the x-ray tube to the cassette is 40 inches.

Quality Assurance: Inspection Frequency

Perform quick checks monthly; thorough evaluations annually and after new equipment installation.

Nine Penny Test: Purpose & Layout

8 pennies mark collimated light edges; 1 penny in lower left corner provides film orientation.

Marker Placement: Primary Functions

Indicates patient side, limb aspect, field orientation, and ensures proper interpretation.

Naming Radiographic Views: Essential Components

Field orientation, anatomy of interest, and front or hind designation for limbs.

Naming Radiographic Views: Beam Direction Rule

Described according to the direction x-rays pass through the anatomy.

Viewing Radiographs: Lateral View Head Position

Point patient's head toward the viewer's left.

Viewing Radiographs: Lateral View Dorsal Aspect

Point patient's dorsal aspect toward the top of the view box.

Viewing Radiographs: Lateral View Marker Placement

Place dorsal or ventral to anatomy indicating side closest to image receptor.

Viewing Radiographs: VD/DV View Head Position

Point patient's head toward the top of the view box.

Viewing Radiographs: VD/DV View Left/Right Orientation

The patient's left side should be on the viewer's right.

Viewing Radiographs: Lateral Limb Marker Placement

Place marker on the cranial/dorsal aspect of the limb.

Viewing Radiographs: Limb Radiograph Toe Orientation

Point toes toward the bottom of the viewbox for forelimb and hindlimb images.

Viewing Radiographs: General Limb Marker Placement

Place marker on the lateral aspect of the limb indicating right or left.