An alignment test jig for measuring the effective focal-spot size of mammographic X-ray tubes

Following publication of the Forrest Report (Department of Health and Social Security (DHSS), 1986) and with the implementation of a breast cancer screening programme in the UK, there is considerable interest in the technical aspects of mammographic systems. The equipment requirements for mammographic X-ray screening units have been identified (DHSS, 1987) and guidance on the commissioning and routine testing of mammographic X-ray equipment is also expected (Institute of Physical Sciences in Medicine (IPSM), 1989). These documents relate to all aspects of the mammographic X-ray set including the specification and measurement of the size of the X-ray tube focal spot. It is recommended (DHSS, 1987) that effective focalspot sizes are measured using a pair of slit radiograms in the manner described in BS 6530 (British Standards Institution (BSI), 1985). This standard provides details on the construction of the slit diaphragm and the geometry to be employed when performing focal-spot measurements. In particula...