Abstract
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 particular, the method requires that the centre of the slit diaphragm and its axis of symmetry are aligned with the reference axis, which is defined as the line through the centre of the radiation source and parallel to the reference direction or that specified direction to which the characteristics such as target angle are referenced. The manufacturer should specify the reference axis when providing data on anode target angle and size of focal spot.
Published Version
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