scope:

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).

RADIATION 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.

In the framework of what is physically feasible, differences in tube design and ageing are taken into account by adding the appropriate amount of ADDITIONAL FILTRATION.

In Annex C further explanations with regard to the PRACTICAL PEAK VOLTAGE are given.

This standard describes both primary RADIATION QUALITIES, which to a good approximation are free of SCATTERED RADIATION (RQR, RQA, RQC, RQT, RQR-M and RQA-M) and, for PATIENT simulation, RADIATION CONDITIONS containing SCATTERED RADIATION (RQN, RQB, RQN-M and RQB-M).

It is crucial to be aware that in the presence of SCATTERED RADIATION the characteristics of X-radiation in terms of fractions of AIR KERMA associated with the PRIMARY RADIATION and the SCATTERED RADIATION depend on the position and nature of any ADDED FILTER or PHANTOM. It is therefore obvious that AIR KERMA measurements in such RADIATION BEAMS need careful consideration.

Clauses 5 to 9 deal with RADIATION CONDITIONS which are essentially free of SCATTERED RADIATION. Due to the spatial homogeneity of these RADIATION CONDITIONS, the APPLICATION DISTANCE does not influence the RADIATION CONDITIONS to a significant extent. These RADIATION CONDITIONS are called RADIATION QUALITIES.

• Clause 5 deals with RADIATION QUALITIES of the RADIATION BEAM emerging from the X-RAY SOURCE ASSEMBLY. Such RADIATION QUALITIES can be used for determining ATTENUATION properties of ASSOCIATED EQUIPMENT.

• Clause 6 deals with RADIATION QUALITIES of the RADIATION BEAM emerging from an irradiated object, that simulates a PATIENT under the conditions that:

- the contribution of SCATTERED RADIATION in the RADIATION BEAM is not significant;

- exact simulation of the spectral distribution of the RADIATION BEAM emerging from the PATIENT is not a prerequisite

• Clauses 7 and 8 deal with RADIATION QUALITIES derived from those dealt with in Clause 6 in view of special applications like automatic exposure and automatic brightness control systems and computed tomographs. The radiation transmitted through the irradiated object has properties similar to those of the radiation transmitted through a PATIENT under the conditions that:

- the contribution of SCATTERED RADIATION in the RADIATION BEAM is not significant;

- exact simulation of the spectral distribution of the RADIATION BEAM emerging from the PATIENT is not a prerequisite.

• Clauses 9 and 10 deal with RADIATION CONDITIONS where SCATTERED RADIATION is taken into account. This is done either by limiting the amount of SCATTERED RADIATION by appropriate means and/or providing specific additional information.

• Clause 9 deals with measuring arrangements primarily intended in combination with RADIATION CONDITIONS RQB of Clause 10 to be used for those measurements where the contribution of SCATTERED RADIATION to the detected signal is minimal and is known as NARROW BEAM CONDITION.

• Clause 10 deals with RADIATION CONDITIONS to be used for measurements where the contribution of SCATTERED RADIATION to the detected signal is significant and is known as BROAD BEAM CONDITION.

For the RADIATION QUALITIES specified in Clauses 5 to 10 it is assumed that an X-RAY TUBE is available with an anode angle of not less than about 9 degrees. For x-ray tubes with smaller anode angles it may not be possible to realize some or all RADIATION QUALITIES of Clause 5. If some or all RADIATION QUALITIES of the RQR series cannot be realized with a given X-RAY TUBE due to a too strong INHERENT FILTRATION, some special provisions have been made to establish nevertheless the more heavily filtered RADIATION QUALITIES in Clauses 6 to 10 which are in principle based on the RADIATION QUALITIES of the RQR series.

In order to make allowance for the use of X-RAY TUBES with ANODE ANGLES down to 9°, the HALF-VALUE LAYERS of RADIATION QUALITIES RQR 4 to RQR 10 have been increased with respect to the values specified in the first edition of this standard (1994).

Clauses 11 to 14 deal with RADIATION CONDITIONS applicable to mammography.

• Clause 11 deals with RADIATION QUALITIES of the RADIATION BEAM emerging from the X-RAY SOURCE ASSEMBLY. Such RADIATION QUALITIES can be used for determining ATTENUATION properties of ASSOCIATED EQUIPMENT.

• Clause 12 deals with RADIATION QUALITIES transmitted through an irradiated object, that simulates a PATIENT under the conditions that:

- the contribution of SCATTERED RADIATION in the RADIATION BEAM is not significant;

- exact simulation of the spectral distribution of the RADIATION BEAM emerging from the PATIENT is not a prerequisite.

• CLAUSE 13 deals with RADIATION CONDITIONS to be used for studies in mammography under NARROW BEAM CONDITION. These RADIATION CONDITIONS are achieved by applying a special tissue-equivalent PHANTOM.

• CLAUSE 14 deals with RADIATION CONDITIONS to be used for studies in mammography under BROAD BEAM CONDITION. These RADIATION CONDITIONS are achieved by applying a special tissue-equivalent PHANTOM.

The test instrumentation as required in this standard partly comprises SPECIFIC components or a series of equivalent components out of which the most suitable should be chosen in order to provide test conditions required to achieve prescribed test parameters. However, these provisions in terms of hardware may not be available at USER facilities. As an example, clinical mammography units are not suited for producing the RADIATION QUALITIES in Clauses 11 to 14 without modification. In order to adapt them the PATIENT SUPPORT needs to be removed.