RT

1. Line-Focus Principle & Anode
Heel Effect
Cline Reeve Venci L. Argallon

2. - The focal spot is the area of target from which
x-rays are produced.

3. Radiology requires small focal spots because
smaller focal spots improves spatial resolution
and improves image quality.

4. Large filament – produce large focal spot
Small filament – produce small focal spot

5. In general, large body parts will
require the selection of the
large focal spot setting and
small parts, require the small
focal spot.

6. • 300 mA and above uses large focal spot
• 300 mA and below small and large focal spot

8. Automatic Exposure Control

11. Line-focus principle
- Results in an effective focal spot much less
than the actual focal spot size.

12. Line-focus principle
Effective focal spot must always be smaller than
the actual focal spot.
Actual focal spot must be large enough to
accommodate more heat dissipation.

13. Line-focus principle
- By angling the target (decreasing angle), one
makes the effective focal spot much smaller
than the actual focal spot.

14. As target angle decreases, so
does the effective focal spot.
Diagnostic x-ray tube has 5-20
degrees target angle.

16. The smaller the anode angle, the greater the
anode heel effect.

18. X-ray tube must have a small
effective focal spot and target
angle but minimal anode heel
effect.