Retrieving patient orientation from previous images
FIELD OF THE INVENTION
The present invention relates to re-positioning a patient, and relates in particular to a medical X-ray imaging system, to a method for re-positioning of a patient in relation to an X-ray image acquisition device, as well as to a computer program element and to a computer readable medium.
BACKGROUND OF THE INVENTION
In clinical procedures it may be desired or even become necessary to position a patient in an orientation in relation to the X-ray imaging system that matches a previously existing orientation. As an example, for the examination of blood flow in a vessel, two image sequences from different points in time are compared. As a further example, for examining tissue perfusion during endovascular procedures, pre- and post-procedural images are compared to identify perfusion differences to verify the level of perfusion achieved by the procedure. As a still further example, for bringing pre-interventional 3D data in the same frame of reference with a 2D live X-ray, steps to compensate for patient movement between the two acquisitions may become necessary. For example, WO 2011/042832 Al describes a patient table comprising a positioning system. For automatically positioning the patient table, position data of movable joints with sensor arrangements is acquired, and, upon further moving of the table, a difference between the position data can be determined. However, this requires additional data processing and storage.
SUMMARY OF THE INVENTION
Thus, there may be a need to facilitate the re-positioning of a patient in relation to an X-ray imaging system.
The object of the present invention is solved by the subject-matter of the independent claims, wherein further embodiments are incorporated in the dependent claims. It should be noted that the following described aspects of the invention apply also for the medical X-ray imaging system and the method for re-positioning of a patient in relation to an X-ray image acquisition device, as well as for the computer program element and the computer readable medium.
According to the present invention, a medical X-ray imaging system is provided that comprises an X-ray image acquisition device, a patient support device, an interface device, a processing device, and a positioning device. The interface device is configured to provide previously acquired first image data of a patient in a first spatial position in relation to the X-ray image acquisition device. The X-ray image acquisition device is configured to acquire current second image data with the X-ray image acquisition device of the patient in a second spatial position in relation to the X-ray image acquisition device. One of the first or second image data is a 3D volume data of the patient, and the other one of the second or first image data is 2D image data of the patient. The processing device is configured to register the first image data and the second image data, and to determine a relative movement between the first and the second spatial position. The X-ray image acquisition device and the patient support device are movable in relation to each other. The positioning device is configured to adjust a relative position between the X-ray image acquisition device and the patient support device. The positioning device is further configured to re-position the patient in relation to the X-ray image acquisition device in a repositioned spatial position based on the determined relative movement for movement compensation to achieve a predetermined matching degree with the first spatial position. The X-ray image acquisition device is configured to acquire further image data of the patient in the re-positioned spatial position.
This provides the advantage that the re-positioning is based on the image data, and no further data processing, such as determining positioning data of positioning measurement arrangements, is necessary. Rather, the positioning, i.e. the re-positioning, is achieved by using image data, in particular image data that is available due to being acquired previously.
The interface provides the image data, for example stored in data storage. According to an example, the X-ray image acquisition device is a movable C- arm system.
According to the present invention, also a method for re-positioning of a patient in relation to an X-ray image acquisition device is provided. The method comprises the following steps:
a) providing previously acquired first image data of a patient in a first spatial position in relation to an X-ray image acquisition device; b) acquiring current second image data with the X-ray image acquisition device of the patient in a second spatial position in relation to the X-ray image acquisition device;
wherein one of the first or second image data is a 3D volume data of the patient, and the other one of the second or first image data is 2D or 3D image data of the patient;
c) registering the first image data and the second image data;
d) determining a relative movement factor between the first and the second spatial position; and
e) re-positioning the patient and the X-ray image acquisition device in relation to each other in a re-positioned relative spatial position based on the determined relative movement factor for movement compensation to achieve a predetermined matching degree of the re-positioned spatial position with the first spatial position for acquisition of further image data.
The patient motion is assumed to be rigid.
The term "current" relates to an actual, i.e. present situation.
The term "spatial position" relates to an arrangement of the patient in relation to the imaging apparatus, i.e. the image acquisition device, in respect of translational and rotational movement possibilities. The "spatial position" refers to the arrangement of the patient in the X-ray beam.
The term "predetermined matching degree" relates to a matching of the repositioned spatial position and the first spatial position with a deviation of maximum +/- 15 %, e.g. +/- 10 % or +/- 5 %. In an example, an exact matching is achieved, i. e. a matching with a deviation of approximately 0 %, i.e. +/- 2 % or even of exactly 0 %.
According to an example, it is further provided a step of:
f) acquiring further image data of the patient in the re-positioned spatial position.
In step f), the further images are acquired in the same spatial position as the first image data.
In one example, the spatial positions are provided in relation to a global frame of reference that connects a frame of reference of the patient support with a frame of reference of the image acquisition device.
The re-positioning is based exclusively on image registration. The repositioning is based on the capability of the X-ray system to precisely position the system to programmed angles. This can be achieved by an X-ray system that is fixedly installed in an examination room. A movable X-ray system could also be used that is temporarily locked in its position in the room to allow precise adjustment of the imaging system. Adjustability between patient support and X-ray imaging system is required to re-position the patient to the desired position.
The re-positioning of the patient in relation to the X-ray image acquisition device can be provided by actually re-positioning the patient in relation to the X-ray image acquisition device or by re-positioning the X-ray image acquisition device in relation to the patient in a re-positioned spatial position. Re-positioning can also be provided by repositioning both the patient and the X-ray image acquisition device.
The "relative spatial position" can be provided as a particular spatial positioning of the patient or a particular spatial positioning of the X-ray image acquisition device, or both. The "first image data" in the "first spatial position" can also be referred to as "original image data" in the "original spatial position".
The "current second image data" in the "second spatial position" can also be referred to as "current image data", i.e. actual image data, in the "current spatial position", i.e. actual spatial position.
The "further image data" in the re-positioned spatial position can also be referred to as "re-positioned image data" or "follow-up image data" in the re-positioned spatial position.
In an example, "original image data" is provided in step a), and "re- positioning image data" is acquired in step b), and "follow-up image data" is acquired in step f) after re-positioning to match with the spatial position of the original image data.
According to an example, in step a), the first image data is a 2D X-ray image sequence. In step b), the second image data is a rotational scan of X-ray images, and a 3D volume is reconstructed to capture the current orientation and position of the patient. In step c), the 3D volume is registered with the 2D image sequence, and in step d), the orientation and position of the current spatial patient position relative to the first spatial position is determined for determining the movement factor. Further, before step e), a compensation movement factor is calculated to obtain the first spatial position of the patient and the X-ray image acquisition device relative to each other.
According to a further example it is provided the steps of:
g) acquiring current third image data with the X-ray image acquisition device of the patient in a third spatial position in relation to the X-ray image acquisition device;
h) registering the second image data and the third image data;
i) determining a first relative movement factor portion between the second and the third spatial position, and, based on step c), determining a second relative movement factor portion between the first and the third spatial position, and determining a further relative movement factor based on the first and the second movement factor portion; and j) re-positioning the patient in relation to the X-ray image acquisition device based on the determined further relative movement factor for further movement
compensation to achieve a predetermined matching degree of the re-positioned spatial position with the first spatial position for acquisition of further image data.
Relating to this example, the "current third image data" in the "third spatial position" can also be referred to as "current (i.e. actual) image data" in the "current (i.e. actual) spatial position", whereas the "current second image data" in the "second spatial position" (of step b)), would then be referred to as "intermediate image data" in the
"intermediate spatial position".
The "further image data" in the "re-positioned spatial position" can also be referred to as "further re-positioned image data" or "further follow-up image data" in the "further re-positioned spatial position".
In case the second image data of step b) is "first follow-up image data", then the further image data of step k) is "second follow-up image data". The first follow-up image data is nevertheless used for re-positioning for further, second follow-up image data.
According to an example, it is further provided the step of:
k) acquiring further image data of the patient in the re-positioned spatial position.
In an example, "original image data" is provided in step a), and "first repositioning image data" is acquired in step b), and "first follow-up image data" is acquired in step f), and "second re-positioning image data" is acquired in step g), the first re-positioning image data acting as intermediate image data, and "second follow-up image data" is acquired in step k) after re-positioning to match with the spatial position of the original image data.
In a further example, further re-positioning loops for further follow-up image data are provided.
The re-positioning may also be provided in a repeated manner in case no further follow-up images are acquired after re-positioning, but in cases where the patient moves after re-positioning.
In an example, for subsequent movement, in the first position, 2D X-ray image data is provided, and in the second position, a 3D volume is provided, and in the third position, second 2D X-ray image data is provided. According to an aspect of the present invention, the patient and the X-ray imaging system are re-positioned in the same position and orientation in relation to each other compared to a previously acquired image sequence. Thus, patient movement (that may be rather large), which itself would make it difficult to obtain images in the same position and orientation, and thus would make the comparison of images difficult and inaccurate, can be compensated so that a new X-ray image, or a new X-ray image sequence can be obtained from the same position and orientation as a previously acquired image sequence, in relation to the patient. For example, when using a fixed X-ray system, a rotational scan can be acquired, from which a 3D volume is reconstructed. The 3D volume captures the current orientation and position of the patient. This volume is registered using 2D-3D registration with a previously acquired 2D image sequence. The registration yields the position and orientation of the previously acquired image sequence relative to the current position and orientation of the patient. The relative position and orientation encodes how much the system should be moved to obtain the position and orientation of the previously acquired image sequence. The patient motion, at least the relevant region of interest, is assumed to be rigid in this context. Thus, according to the present invention, the re-positioning of patient and X-ray image acquisition in relation to each other is provided in an image based manner. An existing difference between an actual position and a previously position is detected by registering the respective image data and by determining a relative movement factor that is then used for the re-positioning.
These and other aspects of the present invention will become apparent from and be elucidated with reference to the embodiments described hereinafter.
BRIEF DESCRIPTION OF THE DRAWINGS
Exemplary embodiments of the invention will be described in the following with reference to the following drawings:
Fig. 1 shows a schematic setup of an example of a medical X-ray imaging system;
Fig. 2 shows basic steps of an example of a method for re-positioning a patient in relation to an X-ray image acquisition device;
Fig. 3 shows a further example of a method for re-positioning; and Fig. 4 shows a still further example of a method for re-positioning. DETAILED DESCRIPTION OF EMBODIMENTS
Fig. 1 shows a medical X-ray imaging system 100 comprising an X-ray image acquisition device 102 and a patient support device 104, for example a patient table. Further, an interface device 106, a processing device 108, and a positioning device 110 is provided.
The X-ray image acquisition device may be provided as a C-arm structure 112 with a detector 114 and an X-ray source 116 arranged on opposing ends of a C-arm 118. The C-arm can be movably mounted by a support structure 120, for example allowing a first rotational movement 122 around a first rotation axis, and a second rotational movement 124 around a second rotational axis. Further, also a so-called rolling movement 126 may be provided, and in addition, as an option, a further rotational movement 128 of the detector 114 may be provided.
Further, also the support structure 120 can be movably mounted to a second support structure, thus forming a support arrangement (not shown), for example allowing translational movement in a first horizontal direction, and in a second horizontal direction. Also movement in a vertical direction may be provided by the support arrangement.
However, it must be noted that also further X-ray image acquisition device types can be used, for example systems with robot arms supporting detector and X-ray source, respectively. Still further, also a fixed X-ray image acquisition device can be provided, i.e. a system with non-movable X-ray source and X-ray detector, but a movable patient support. Still further, also a limited movable system can be provided, for example allowing only limited movement.
Further, the patient support device 104 may be provided as a patient table with an adaptable support stand 130 allowing translational movement in a first horizontal direction 132, a second horizontal direction 134, and a vertical direction 136.
Further, the adaptable stand 130 could allow a first rotational movement around a first rotational axis, and a second rotational movement around a second rotational axis, and a third rotational movement around a third rotational axis. The respective
movements are also referred to as pivot, tilt and cradle movements.
In a further example, the patient support is a support structure for a patient to lean against in a standing position. In a still further example, the patient support is a support structure for body parts of the patient, e.g. an arm, leg or head support, or a breast support for mammography. It must be noted that the positioning device 110 is indicated with simplified frames only, since the respective movement components for allowing the positioning are not further shown in detail.
The interface device 106 is configured to provide previously acquired first image data 138 of a patient in a first spatial position in relation to the X-ray image acquisition device. The X-ray image acquisition device 102 is configured to acquire current second image data, indicated with an arrow 140 with the X-ray image acquisition device 102, wherein the patient is in a second spatial position in relation to the X-ray image acquisition device 102. One of the first or second image data 138, 140 is a 3D volume data of the patient, and the other one of the second or first image data 140, 138 is 2D image data of the patient. The processing device 108 is configured to register the first image data and the second image data 138, 140, and to determine a relative movement between the first and the second spatial position. A detailed description of registration methods is provided for in "A review of 3D/2D registration methods for image-guided interventions" by P. Markelj et al, as published in Medical Image Analysis 16 (2012) 642-661. The X-ray image acquisition device 102 and the patient support device 104 are movable in relation to each other.
The positioning device 110 is configured to adjust a relative position between the X-ray image acquisition device and the patient support device, and to re-position the patient in relation to the X-ray image acquisition device in a re-positioned spatial position based on the determined relative movement for movement compensation to achieve a predetermined matching degree with the first spatial position.
The X-ray image acquisition device 102 is further configured to acquire further image data of the patient in the re-positioned spatial position.
In a further example, not further shown in detail, the X-ray image acquisition device 102 is further configured to acquire current third image data with the X-ray image acquisition device 102 of the patient in a third spatial position in relation to the X-ray image acquisition device. The processing device 108 is configured to register the second image data and the third image data, and to determine a first relative movement factor portion between the second and the third spatial position, and to determine a second relative movement factor portion between the first and the third spatial position, and to determine a further relative movement factor based on the first and the second movement factor portion. The positioning device 110 is configured to re-position the patient in relation to the X-ray image acquisition device based on the determined further relative movement factor for further movement compensation to achieve a predetermined matching degree of the re-positioned spatial position with the first spatial position for acquisition of further image data. The X-ray image acquisition device 102 is configured to acquire further image data of the patient in the repositioned spatial position.
It must be noted that the above-mentioned examples are also further explained in relation with the respectively used method for re-positioning of a patient in relation to an X-ray image acquisition device described below.
Fig. 2 shows a method 10 for re-positioning of a patient in relation to an X-ray image acquisition device. The method 10 comprises the following steps:
In a first step 12, previously acquired first image data 14 is provided of a patient in a first spatial position in relation to an X-ray image acquisition device.
In a second step 16, current second image data 18 is acquired with the X-ray image acquisition device of the patient in a second spatial position in relation to the X-ray image acquisition device. One of the first or second image data is a 3D volume data of the patient, and the other one of the second or first image data is 2D or 3D image data of the patient.
In a third step 20, the first image data 14 and the second image data 18 are registered.
In a fourth step 22, a relative movement factor 24 between the first and the second spatial position is determined.
- In a fifth step 26, the patient and the X-ray image acquisition device are repositioned in relation to each other in a re-positioned relative spatial position based on the determined relative movement factor 24 for movement compensation to achieve a
predetermined matching degree of the re-positioned spatial position with the first spatial position for acquisition of further image data.
The first step 12 may also be referred to as step a), the second step 16 as step b), the third step 20 as step c), the fourth step 22 as step d), and the fifth step 26 as step e).
In an example, shown as option in Fig. 2, a sixth step 28 is provided, in which further image data 30 of the patient in the re-positioned spatial position is acquired. However, a dotted connection line 32 indicates this as an option.
The further shown sixth step 28 may also be referred to as step f).
According to an example, the spatial position relates to an arrangement of the patient in relation to the imaging apparatus in respect of translational and rotational movement possibilities referring to an arrangement of the patient in the X-ray beam. According to an example, not further shown in detail, the first image data are primary X-ray images that are acquired in the first spatial position at a first point in time. The second image data are secondary X-ray images that are acquired in the second spatial position at a second point in time. Further X-ray images are acquired in the re-positioned spatial position at a further point in time.
In one example, the primary X-ray images are the first image data.
According to an example, in step a), the first image data is a 2D X-ray image sequence. In step b), the second image data is a rotational scan of X-ray images, and a 3D volume is reconstructed to capture the current orientation and position of the patient. In step c), the 3D volume is registered with the 2D image sequence. In step d), the orientation and position of the current spatial patient position relative to the first spatial position is determined for determining the movement factor. Before step e), a compensation movement factor is calculated to obtain the first spatial position of the patient and the X-ray image acquisition device relative to each other.
In an example, the first image data is a 2D X-ray image. In step b), the second image data is a 3D rotational reconstruction based on a plurality of second 2D X-ray images taken from different angles.
According to an example (not further shown), the first image data is a 3D X- ray image, and in step b), the second image data is a 2D X-ray image, or a plurality of 2D X- ray images taken from different angles forming at least a part of a 3D X-ray image.
The 3D X-ray image may be a 3D image generated from a plurality of 2D X- ray image slices.
As indicated above, in step e) the re-positioning is achieved by either moving a patient support, or by moving the X-ray image acquisition device. In a further example, both moving the patient support and moving the X-ray image acquisition device, are provided in a combined manner.
For example, the patient support is a motorized patient table. In a further example, the X-ray image acquisition device is, as mentioned above, a movable C-arm structure. For step e), movement instructions are provided for user-activated relative movement in a further example.
Fig. 3 shows a further example where the following further steps are provided:
Following the fifth step 26 (step e)), or the sixth step 28 (step f)), a further acquisition step 34 is provided, in which current third image data 36 is acquired with the X- ray image acquisition device of the patient in a third spatial position in relation to the X-ray image acquisition device.
A further registration step 38 is provided, in which the second image data, indicated with a first arrow 40, is registered with the third image data 36.
In a further determining step 42, a first relative movement factor portion 44 between the second and the third spatial position is provided.
Further, based on step c), a further determination step 46 is provided, in which a second relative movement factor portion 48 between the first spatial position, indicated with a second arrow 50, and the third spatial position is determined.
A still further determination step 50 is provided, in which a further relative movement factor 52 is determined based on the first and the second movement factor portions 44, 48.
Still further, a further re-positioning step 54 is provided, in which the patient is re-positioned in relation to the X-ray image acquisition device based on the determined further relative movement factor 52 for further movement compensation to achieve a predetermined matching degree of the re-positioned spatial position with the first spatial position for acquisition of further image data.
The further acquisition step 34 is also referred to as step g), the further registration step 38 as step h), the further determination step 42, the still further determination step 46 and the still further determination step 50 as step i), and the re-positioning step 54 as step j).
In a further example, shown as an option in Fig. 3, it is further provided a further acquisition step 56, in which further image data 58 of the patient in the re-positioned spatial position is acquired. The further acquisition step 56 is also referred to as step k).
In a further example, step g) is referred to as step b2), step h) as step c2), step i) as step d2), step j) as step e2), and step k) as step f2).
Fig. 4 shows a further example of a method, in which in step a), a 2D X-ray sequence 60 is provided of a patient in a first previous spatial position. Between step a) and step b), it is further provided the following steps: In a further provision step 62, also referred to as step ai), previously acquired second image data 64 of the patient in a second previous spatial position is provided, wherein the previously acquired second image data is previously acquired 3D volume. In step c), it is provided the following two-step registration: in a first registration step 66, also referred to as step Ci), the previously acquired first image data and the previously acquired second image data are registered. In a second registration step 68, also referred to as step c2), the previously acquired second image data 64 and the second image data 18 are registered. In step d) it is provided a two-step determination with a first determination step 70, also referred to as step di), in which a first relative movement factor 72 between the first previous spatial position and the second previous spatial position is determined. In a second determination step 74, also referred to as step d2), a second relative movement factor 76 between the second previous spatial position and the second spatial position is determined. In a still further determination step 78, a continued relative movement factor 80 based on the first and second relative movement factor is determined. The third determination step 78 is also referred to as step d3).
Further, the re-positioning in step e) is provided based on the continued relative movement factor 80.
Of course, still further image acquisition steps may be provided, as indicated with dotted arrow 82.
In an example, in step a), the first image data is a 3D rotational reconstruction based on a plurality of first 2D X-ray images taken from different angles. In step b), the second image data is a 2D X-ray image, and in step c), the 2D X-ray image is registered with the 3D rotational reconstruction. In step d), the orientation and position of the current spatial position relative to the first spatial position is determined, and before step e), a compensation movement is calculated to obtain the first spatial position of the patient and the X-ray image acquisition device relative to each other.
In another example, the first image data is a 3D dataset, e.g. a CT dataset. In still another example, the first image data is an MRI dataset.
In a further example, not further shown in detail, but with reference to Fig. 1, a 2D-3D registration is used. As an example, the six parameters are provided: three
translational components and three rotational components. The relative position (translational components) requires three parameters storing the relative height, relative lateral and relative longitudinal position. The relative orientation (rotational components) can be stored as Euler angles representing three composed rotations around the z-, y-, and x-axes, for example the vertical axis 136, the first horizontal axis 132 and the second horizontal axis 134. For example, the new orientation can be obtained by a motorized X-ray system with a rotating C- arm structure, for example by rotation an upper L-arm 142, or by propeller and role movement, i.e. the first rotational movement 122 and the rolling movement 126. Since the volume is reconstructed at the center of rotation of the system, the center of rotation of the registration matches with the center of rotation of the system, in one example. For example, two rotations are required to obtain any position of the detector 114, whereas the third determines the rotation of the detector in the image plane, for example provided as the extra rotation 128. Thus, the image can also be rotated by opposed processing operation.
Alternatively, the user could choose a fixed L-arm position, and move only the propeller and role, and finally rotate the image by post processing. Alternatively, instead of post processing the image, the detector could be rotated.
The new position is obtained by either moving a motorized table to the new position, or alternatively to move the C-arm to the new position. Further, a combination of both is provided.
The distance between the source and the detector determines the amount of magnification. Since patient movement has no influence on this parameter, there is no need in an example to solve this parameter using 2D-3D registration.
In a further example, subsequent movement is provided. In case of the volume being acquired after previously acquired images, the volume captures the current position and orientation of the patient. However, it is provided in an example to avoid obtaining a new volume every time the patient moves. Hence, instead of acquiring a new volume, it is proposed to acquire a single X-ray image and to register this image with the volume acquired before. The new image encodes the new current position and orientation of the patient. By registering the new image with the volume, it is possible to achieve relative movement since the time the volume was acquired. By subsequently registering the volume with the previously acquired image, the relative movement between the new image and the volume is obtained. The two registrations are then combined to yield the relative position and orientation of the previously acquired image with the current image, i.e. the new image.
In an example, the computed relative orientation between the old and the new image may not match with the system center of rotation. By the second registration, it is possible to compute the relative position between the volume and the new image, and hence the translation of the center of rotation. Knowing this translation of the center of rotation and the relative orientation, the system angles and translations, e.g. by table movement, are calculated.
In a further solution, as an alternative of the option of acquiring a volume and an X-ray image to compute the position, it is provided to reuse a volume of the same patient that was acquired some other time, for example in the same examination as the previously acquired image, and only acquire one new X-ray image. In such case, the conversion between patient orientation and system angles and translation is computed using the system angles, at which the new image is recorded. The registration between the volume and the image can hence not be used to calculate the system parameters, because the volumes frame of reference might not match the systems frame of reference. However, the latter is the case when the volume is acquired on another X-ray system, or when the system has been recalibrated since the volume acquisition. It is assumed that the system angles, at which the new image is acquired, can be obtained precisely. Even though the volume is recorded at another time, the volume is still representative on the patient's internals.
As an alternative to using a previously acquired 3D rotational reconstruction, also another 3D dataset can be used, e.g. a preoperative CT or MRI dataset.
In another exemplary embodiment of the present invention, a computer program or a computer program element is provided that is characterized by being adapted to execute the method steps of the method according to one of the preceding embodiments, on an appropriate system.
The computer program element might therefore be stored on a computer unit, which might also be part of an embodiment of the present invention. This computing unit may be adapted to perform or induce a performing of the steps of the method described above. Moreover, it may be adapted to operate the components of the above described apparatus. The computing unit can be adapted to operate automatically and/or to execute the orders of a user. A computer program may be loaded into a working memory of a data processor. The data processor may thus be equipped to carry out the method of the invention.
This exemplary embodiment of the invention covers both, a computer program that right from the beginning uses the invention and a computer program that by means of an up-date turns an existing program into a program that uses the invention.
Further on, the computer program element might be able to provide all necessary steps to fulfill the procedure of an exemplary embodiment of the method as described above.
According to a further exemplary embodiment of the present invention, a computer readable medium, such as a CD-ROM, is presented wherein the computer readable medium has a computer program element stored on it, which computer program element is described by the preceding section.
A computer program may be stored and/or distributed on a suitable medium, such as an optical storage medium or a solid state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the internet or other wired or wireless telecommunication systems. However, the computer program may also be presented over a network like the World Wide Web and can be downloaded into the working memory of a data processor from such a network. According to a further exemplary embodiment of the present invention, a medium for making a computer program element available for downloading is provided, which computer program element is arranged to perform a method according to one of the previously described embodiments of the invention.
It has to be noted that embodiments of the invention are described with reference to different subject matters. In particular, some embodiments are described with reference to method type claims whereas other embodiments are described with reference to the device type claims. However, a person skilled in the art will gather from the above and the following description that, unless otherwise notified, in addition to any combination of features belonging to one type of subject matter also any combination between features relating to different subject matters is considered to be disclosed with this application.
However, all features can be combined providing synergetic effects that are more than the simple summation of the features.
While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. The invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing a claimed invention, from a study of the drawings, the disclosure, and the dependent claims.
In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may fulfill the functions of several items re-cited in the claims. The mere fact that certain measures are re-cited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.