In the case of x-ray imaging systems, in particular in computed tomography systems, a diaphragm, which initially determines the opening angle of an x-ray beam bundle and the shape of a surface illuminated by the x-ray radiation, is usually attached between an x-ray source and the examination object. A radiation form filter is frequently arranged downstream of this diaphragm in the radiation path of the x-ray radiation, the radiation form filter also being able to change the intensity of the x-ray radiation both spatially or also spectrally. These are essentially planar filters, which are irradiated by the entire x-ray beam (typically delimited by the diaphragm), without the filter having in this way to comprise openings through which the x-ray radiation is able to pass unchanged. These filters are typically made of aluminum or Teflon.
In order to manipulate and further change the spectral or also spatial intensity distribution of the x-ray radiation, different types of radiation form filters, such as for instance bowtie filters (i.e. filters, which in addition focus or expand the x-ray radiation with convex or concave surfaces, typically similar to the shape of a bowtie) or also wedge-shaped filters, known as wedge filters, which can be introduced into the radiation path of the x-ray radiation between an x-ray source of the imaging system and an examination object individually or in combination with a number of radiation form filters. At least local extremes of the x-ray radiation intensity can be defined within the x-ray radiation bundle for instance with the aid of a bowtie filter. The intensity of x-ray radiation can be reduced by a continual attenuation value for instance with the aid of a wedge filter at right angles to the propagation direction of the x-ray radiation. The intensity minimum is usually at the periphery of a used x-ray radiation bundle (delimited by the diaphragm).
There is in particular the possibility of defining the size and/or extent of the irradiated region or regions of one or more radiation extremes. I.e. aside from different types of radiation form filters, there is also still the possibility of selecting between different radiation form filters of the same type. For instance, in the case of filters of the same type, it is possible to select between “narrow filters”, which reduce the irradiated region spatially, or “wide filters” and “very wide” filters, which, if necessary, extend the irradiated region or the region of an intensity extreme.
Furthermore, it is likewise conceivable for the radiation form filter to spatially influence the spectrum of the used x-ray radiation in particular (i.e. when the filter is irradiated, the spectral intensity distribution of the x-ray radiation changes). For instance, in a spatial region determined by the filter, the spectrum of the x-ray radiation can be hardened, i.e. an intensity maximum of the x-ray radiation is changed to smaller wavelengths. Similarly, if necessary, the spectrum of the x-ray radiation can be adjusted more softly in the predetermined spatial region with the aid of the filter (i.e. an intensity maximum is changed to larger wavelengths).
The operator of an x-ray imaging system undertaking an x-ray recording thus has the choice between a plurality of filters, in order to optimize an x-ray recording. The optimization can on the one hand consist in ensuring the image quality of a provided recording and on the other hand also in keeping the radiation exposure of an examination object, on account of image acquisition, as low as possible. A corresponding optimization is based here largely on the experience of the operator.
Ideally, a suitable scan or examination protocol (i.e. a sequence of control steps) is stored for each application of the imaging system with respect to these optimization objectives, on the basis of which scan or examination protocol the image acquisition is controlled in the imaging system and which if necessary prespecifies a radiation form filter to be used. If there is no scan protocol available for a relevant application, this must firstly be generated based on the specialist knowledge of the operator. An optimal selection of the radiation form filters is in this case possibly not always ensured. Furthermore, the assignment of radiation form filters to specific protocols is complicated and stands in the way of a simplification of the operation of an x-ray imaging system.
In the case of an examination protocol for children, a radiation form filter is usually used. The radiation form filter could however also be used for adults as a function of the constitution of the patient and the scanning area, in order to reduce the x-ray dose. On the other hand, it may also be useful in certain instances, in the case of children, to omit the radiation form filter so as to achieve an improved image quality.
Radiation form filters were previously only used in protocols for children. Particularly narrow radiation form filters are usually used for children. In the case of adults, no radiation form filters are by contrast usually used. If a tall child now has the dimensions of an adult for instance, it may be meaningful to omit the radiation form filter or to use a wider radiation form filter, i.e. a radiation form filter with a wider irradiation range, for which no special protocol for children is provided. Nevertheless, in the case of the conventional method, in which special protocols, for instance for children, are assigned to the individual filters, the specific parameters specified in the protocols for children also got lost here. For instance, if instead for instance the radiation filter was omitted in the case of a child and a protocol for adults, in which a higher radiation dose is allowed, were accordingly to be used, a child could as a result be exposed to an excessively high radiation dose. Conversely, it may be meaningful for instance in the case of a small adult to use a radiation form filter. Nevertheless, no adult protocols are suited to the radiation form filters. If a special protocol for children, which is assigned to the radiation form filter used, is now used for adults, the result is not optimal. For instance, on account of an excessively low x-ray dose, the contrast is not as good as it could be in the best case, if an x-ray dose which is still acceptable for adults were to be used. There is therefore the problem that the protocols assigned to the filters or the protocols assigned to the recordings without filters are specified for specific age groups. If the filters or no filter were also to be used in the case of people in other age groups however, there is the problem of not being able to easily transfer the protocols for application on other age groups.