4. X-Ray Tube Focal Spot Measurements
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Purpose
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RTI Slit Camera User’s Manual
4.
X-Ray Tube Focal Spot Measurements
4.1.
Purpose
To assure that the tube and x-ray tube focal spot size is within acceptable limits.
4.1.1.
Equipment Recommended for Focal Spot Measurements
1. Slit assembly
2. A Focal Spot Test Stand (See Figure 4-1)
3. Alignment Tools
4. Metric ruler
5. Reading tools
- Image analyzing software for digital images
- Magnifier (>6X) with 0.1 mm scale for film analysis
Figure 4-1. Focal Spot Test Stand
4.2.
Focal Spot Test Stand Alignment
1. Remove all objects between the focal spot and table, e.g., compression
device, diaphragms, cones, etc., which can be removed easily.
2. Place the focal spot test stand on the imaging table, with the slit direction
perpendicular to the direction you intend to measure the focal spot dimension.
3. Adjust to maximize the slit to image receptor distance and adjust the focal
spot-to-film distance to obtain the correct magnification factors (Table 4-1).
4. Use the light field (if available) to position the slit and slit holder where you
intend to perform the measurement.
5. Make an exposure and verify that the image of the slit holder is centered over
the position you intended to evaluate the focal spot at.
Table 4-1 Minimum Magnification for Slit Measurement Technique
