Focal Spot Test Tool
The measurement of focal spot dimensions is of great importance in checking the performance of
mammographic screening units. Measurements can be made from radiographs of a slit or a starpattern
test object, but these must be positioned on the central axis of the X-ray beam.
Since the Xray tube is angled with respect to the imaging plane, a special jig is needed which will hold a film cassette at the same angle, and will also hold the slit or start pattern in alignment with, and perpendicular to, the central axis.
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