Questions and Answers
What is the line focus principle?
By angling the face of the anode target, a large actual focal spot size can be maintained, and a small focal spot can be created.
What is a focal spot?
The area of the target where X-rays are emitted.
What defines the actual focal spot?
The area of the target that is actually bombarded with filament electrons.
What is the effective focal spot?
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What controls the actual focal spot?
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What is the purpose of the line focus principle?
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The smaller the actual focal spot, the smaller the effective focal spot size.
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A large actual focal spot generates more heat than a small one.
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What is the target angle generally used for X-ray rooms?
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What is a limitation factor on the target angle?
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What is a bi-angle target?
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What are the limitations to the line focus principle?
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What is the advantage of the line focus principle?
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What causes the anode heel effect?
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How does the anode heel effect occur?
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What are the radiation intensity levels due to the anode heel effect?
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What is the central ray?
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What is the purpose of the anode heel effect?
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When is the anode heel effect most apparent?
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Study Notes
Line Focus Principle
- Angling the anode target face maintains a large actual focal spot while creating a small effective focal spot.
- The principle enhances heat distribution while improving image quality.
Focal Spot
- The focal spot is the area from which X-rays are emitted, serving as the actual x-ray source.
Actual Focal Spot
- Represents the area bombarded by filament electrons; larger size enhances heat distribution.
- Smaller electron streams generate more concentrated heat, necessitating better heat spread over a larger area.
Effective Focal Spot
- Acts as the origin of the X-ray beam, influencing image quality.
- Visualized from the patient's perspective; defined by the controlled actual focal spot size.
- Smaller effective focal spots yield sharper images.
Controls of Actual Focal Spot
- Influenced by various factors: filament length, target angle, charge on the focusing cup, filament depth, and focusing cup dimensions.
Purpose of Line Focus Principle
- Allows for a larger heating area on the anode while retaining a smaller effective focal spot for better image clarity.
Direct Relationship
- Smaller actual focal spots correlate directly with smaller effective focal spots, and vice versa.
Large Actual Focal Spot
- Distributes heat more effectively than smaller focal spots due to the larger area over which X-rays are emitted.
Target Angle
- Optimal between 5-20 degrees for general X-ray use; affects effective focal spot size.
- Smaller angles result in improved heat dissipation and enhanced image quality.
Limitation Factor on Target Angle
- Ensures adequate X-ray coverage of the largest field size used, typically 35cm x 43cm image receptor.
Bi-angle Target
- Features two target angles, requiring two vertically-aligned filaments; adjusting the angle alters effective focal spot size.
Limitations to Line Focus Principle
- Extremely small target angles may result in inadequate X-ray beam area, limiting anatomy coverage and producing a narrower beam.
Advantage of Line Focus Principle
- Enhances both spatial resolution and the heat capacity of the X-ray system.
Anode Heel Effect
- Results from the line focus principle, reducing X-ray intensity on the anode side due to a longer travel path and increased absorption.
- Cathode side emits greater intensity compared to the anode side; effect magnifies with smaller anode angles.
How Anode Heel Effect Happens
- X-ray production involves electron bombardment leading to emission at angles between 45-90 degrees.
- Electrons on the anode side encounter more material before leaving the tube, causing absorption and energy loss.
Radiation Intensity
- Central ray intensity is at 100%, while the anode side may decrease to 75%, and the cathode side can reach up to 120%.
Central Ray
- Represents an imaginary line that defines the useful beam's center; it is marked by 100% intensity output.
Purpose of Anode Heel Effect
- Positioning the cathode side over denser anatomy ensures uniform radiation exposure across the image receptor.
Anode Heel Effect is Most Apparent
- This effect is pronounced with larger image receptor sizes and shorter source-to-image distances (SID).
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Description
Explore the concepts of the line focus principle and the anode heel effect through these flashcards. Understand the relationship between actual and effective focal spots, and learn about the significance of the focal spot in x-ray imaging. Ideal for students of radiography and medical imaging.
