Focal Spot (Actual & Effective), Field Size and Line Focus Principle | Radiology Physics Course #12
Introduction to X-ray Beam Geometry
In this section, the speaker delves into the geometry of the X-ray beam, focusing on how changing parameters can impact the effective focal spot and field size.
Understanding X-ray Beam Geometry
- The actual focal spot is where x-rays are produced, while the effective focal spot represents the x-ray beam heading towards the patient.
- The Line Focus principle involves calculating the relationship between anode angle and focal spots using trigonometry.
- Narrowing the effective focal spot can be achieved by reducing the anode angle or selecting a smaller filament on the cathode.
- An increase in anode angle leads to a wider effective focal spot and larger field size, impacting image sharpness and geometric blurring.
Effective Focal Spot Size and Anode Hill Effect
The discussion delves into the effective focal spot size variations, particularly in relation to the anode Hill effect, highlighting changes in field size and geometry.
Effective Focal Spot Size Variations
- The effective focal spot size varies depending on the position within the x-ray beam, changing as one moves from the anode side to the cathode side.
- As we move towards the anode side of the field, the effective focal spot narrows, reducing geometric blurring in images. Conversely, moving towards the cathode side results in a larger effective focal spot.
- Not only does changing the anode angle affect effective focal spot size, but there is also variation throughout the field. Closer to the anode, the effective focal spot becomes smaller.