IEC 61267-2005 pdf – Medical diagnostic X-ray equipment – Radiation conditions for use in the determination of characteristics.
1 Scope and object This International Standard applies to test procedures which, for the determination of characteristics of systems or components of medical diagnostic X- RAY EQUIPMENT , require well-defined RADIATION CONDITIONS . Except for mammography, this standard does not apply to conditions where discontinuities in radiation absorption of elements are deliberately used to modify properties of the RADIATION BEAM (for example by rare earth filters). R ADIATION CONDITIONS as used for screen-film sensitometry are not covered in this standard. NOTE Screen-film sensitometry is the subject of the ISO 9236 series. This standard deals with methods for generating RADIATION BEAMS with RADIATION CONDITIONS which can be used under test conditions typically found in test laboratories or in manufacturing facilities for the determination of characteristics of medical diagnostic X- RAY EQUIPMENT . Examples of such RADIATION QUALITIES are RADIATION BEAMS emerging through the filtration from the X- RAY SOURCE ASSEMBLY . RADIATION CONDITIONS represent the more general case, where SCATTERED RADIATION emerges from an EXIT SURFACE of a PATIENT or a PHANTOM . This requires a well defined geometrical arrangement. The most complete specification of RADIATION FIELDS is given by the spectral distribution of the photon fluence. Since the measurement of X- RAY SPECTRA is a demanding task, this standard expresses RADIATION QUALITIES in terms of the X- RAY TUBE VOLTAGE , the first and second HALF – VALUE LAYER . In the case of RADIATION CONDITIONS , specifications are performed additionally in terms of PHANTOM properties and geometry.
The attempt to characterize a spectral distribution just by means of the X- RAY TUBE VOLTAGE , the first and possibly the second HALF – VALUE LAYER is thus a compromise between the mutually conflicting requirements of avoiding excessive efforts for establishing a RADIATION QUALITY and of the complete absence of any ambiguity in the definition of a RADIATION QUALITY . Due to differences in the design and the age of X- RAY TUBES in terms of anode angle, anode roughening and INHERENT FILTRATION , two RADIATION QUALITIES produced at a given X- RAY TUBE VOLTAGE having the same first HALF – VALUE LAYER can still have quite different spectral distributions. Given the inherent ambiguity in the characterization of RADIATION QUALITY , it is essential that further tolerances introduced by allowing certain ranges of values, e.g. for X- RAY TUBE VOLTAGE and first HALF – VALUE LAYER , must be sufficiently small not to jeopardise the underlying objective of this standard. This standard is to ensure that measurements of the properties of medical diagnostic equipment should produce consistent results if RADIATION QUALITIES or RADIATION CONDITIONS in compliance with this standard are used.
To achieve this objective, certain degrees of freedom in the way in which a RADIATION CONDITION could be established in the framework of the first edition of this standard have been removed. The essential restriction introduced in this second edition is that the X- RAY TUBE VOLTAGE is measured and set to its ‘correct’ value. The second step is to attempt to establish the prescribed first HALF – VALUE LAYER by adding into the beam the necessary amount of ADDITIONAL FILTRATION . If the INHERENT FILTRATION provided by the X- RAY TUBE alone is so strong that the HALF – VALUE LAYER of the RADIATION BEAM emerging from the X- RAY TUBE ASSEMBLY as such is larger than that to be established, the X- RAY TUBE ASSEMBLY used is not suited for producing the desired RADIATION CONDITION . This may occur if the anode angle of the X- RAY TUBE ASSEMBLY is too small and/or in the case of excessive anode roughening due to tube ageing. In the approach outlined in the two preceding paragraphs the X- RAY TUBE VOLTAGE plays a decisive role. It is therefore essential that the ‘correct’ X-ray tube voltage is chosen irrespective of the type of high voltage generator connected to the X- RAY TUBE . The way in which this is realized in this standard is by measuring the X- RAY TUBE VOLTAGE in terms of the PRACTICAL PEAK VOLTAGE . This quantity is a weighted mean of all values of the X- RAY TUBE VOLTAGE occurring during an exposure. The weighting is done in such a way that identical values of the PRACTICAL PEAK VOLTAGE give identical values of the low level contrast on a radiograph irrespective of the waveform supplied by the generator. Although the PRACTICAL PEAK VOLTAGE can be measured non-invasively, the level of uncertainty required in this standard demands the use of invasive techniques. The design and age of the X- RAY TUBE ASSEMBLY influence the result of non-invasive measurements. When PRACTICAL PEAK VOLTAGE is measured invasively, tube design and age have no influence on the result of such a measurement.