FIELD OF THE INVENTION

The present invention relates to X-ray imaging, and relates in particular to an X-ray imaging system for spotlight X-ray mapping, to a method for spotlight X-ray mapping, to a computer program element, and to a computer readable medium.

BACKGROUND OF THE INVENTION

In X-ray imaging, cases may occur where an object of interest is larger than the detector. In order to provide an X-ray image, for example of a patient's leg, i.e. in order to provide a so-called oversized radiograph, multiple exposures may be provided that spatially overlap in order to assemble the oversized radiograph. For this purpose, a digital detector may be moved along the patient's anatomy in-between the exposures or the patient may be moved in relation to the detector. For example, US 6,097,833 relates to image composition of an elongated scene based on a series of sub-images overlapping. Further, "A Stitching Algorithm or Automatic Registration of Digital Radiographs" (by Andre GooBen, Mathias Schluter, Thomas Pralow, and Rolf-Rainer Grigat, ICIAR 2008, Springer Verlag Berlin Heidelberg) describes the use of an external feature brought into the radiographs to facilitate the reconstruction of the multiple spatially overlapping exposures. However, it has been shown that the overlapping exposures mean additional X-ray dose to the patient. SUMMARY OF THE INVENTION

There may be a need to provide X-ray image information of regions of interest larger than the detector's size with reduced X-ray dose for the patient while maintaining the image quality.

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 X-ray imaging system for spotlight X-ray mapping, for the method for spotlight X-ray mapping, for the computer program element, and for the computer readable medium. According to a first aspect of the present invention, an X-ray imaging system for spotlight X-ray mapping is provided, comprising an X-ray image acquisition device with an X-ray source, an X-ray detector, and an X-ray detectable ruler arrangement. Further, the X- ray imaging system comprises an image processor and a display. The X-ray image acquisition device is configured to acquire at least first and second images from different regions of interest of an object, wherein the detectable ruler arrangement and the object are provided in a predetermined spatial relation for each of the images. The image processor is configured to identify at least a segment of the ruler arrangement in each of the at least first and second images, and to assign the identified ruler segment to the respective X-ray image, and to determine a spatial position of the respective segment in relation to the ruler arrangement, and to combine the at least first and second images according to their spatial relation based on the identified segment in the respective image. The display is configured to display the combined images as a spotlight X-ray map.

The term "ruler arrangement" may refer to a continuous scale of a number of equally spaced apart points, for example a metric ruler with millimetres, centimetres, or meters, or an inch-based ruler. "Ruler arrangement" may also refer to differently spaced apart points, wherein the distances of individual points are known. "Ruler arrangement" may also comprise at least two segments, which are provided in a known distance, and wherein one segment is visible, i.e. detectable, in the first image, and one other segment is visible/detectable in the second image. Each segment has at least two distinguishable points spaced apart to allow the detection of the orientation in relation to the other segment, respectively the orientation in space/orientation in relation to a reference in space. The X-ray image acquisition device may be a motorized or unmotorized C-arm system or a U-arm system. Also other movable X-ray imaging systems are provided. Further, also fixed X-ray imaging systems with a movable patient support table or patient support arrangement are provided.

By providing only certain areas of an elongated object, for example the lower limbs of a patient, the particular regions of interest, such as the ankle or the knee or the hip, can be provided as X-ray image, whereas the leg's portion in-between, i.e. the straight bone parts in-between, can be omitted, thereby saving dose to which the patient is exposed. By providing the image portions in the determined spatial position in the spotlight X-ray map, a relation and thus allocation of the different portions of interest is nevertheless provided.

According to an exemplary embodiment, the first and second images are provided in a displaced manner such that a gap between them exists. For example, the images are provided in a non-overlapping manner.

The object may be a long object, which is larger than the size of the detector, or the size of the desired collimation. For the acquisition of the first and second image, the detector is provided at a first and second position. For example, the detector is moved in relation to the object, whereas the ruler arrangement maintains its position in relation to the object. In another example, the detector maintains the position, and the object - together with the ruler arrangement - is moved in relation to the detector. In a further example, object and detector are moved, whereas the ruler arrangement is maintained in its relative position to the object, i.e. moved together with the object.

In a further example, between the first and the second image, the ruler is moved in relation to the object with a predetermined distance, i.e. a known distance. For example the assignment and the determination of the spatial position, the predetermined/known distance is taken into account.

In an example, more than two images are provided, each with a distance to the respective adjacent image(s). In the spotlight map, the ruler arrangement may be provided in the regions of the first and second images only. In another example, the ruler arrangement is provided for the map area between the first and second images. In the spotlight map, the ruler arrangement may provide a map-stitching of the images even though the images do not overlap, i.e. a virtual stitching is provided by stitching the images to the reference system of the ruler arrangement.

The term "spotlight map" relates to the arrangement of non-overlapping image areas provided combined according to their spatial position determined based on the ruler arrangement segments provided in each of the image areas. Thus, a map is provided with image information only in certain areas, which is why the term "spotlight" is used.

According to an exemplary embodiment, the spotlight X-ray map provides the at least first and second images as image portions in the correct geometric relation to each other.

The different regions of interest can also be referred to as different locations of the object. The spotlight X-ray map may comprise non-covered parts between adjacent X-ray images. The ruler arrangement is also referred to as location scale. The ruler arrangement may be provided as a ruler device. For example, the ruler arrangement is provided as a linear ruler between the object and the detector. The ruler arrangement may also be provided in front of the object, i.e. between the object and the X-ray source. The ruler arrangement may be provided integrated with an object support surface.

According to an exemplary embodiment, for the at least first and second images, the ruler arrangement and the object are provided in the same spatial relation to each other.

For example, the ruler arrangement and the object maintain their spatial relation for the at least first and second images.

According to an exemplary embodiment, the ruler arrangement covers at least a part of region of the first image and a part of the second image.

According to an exemplary embodiment, the ruler arrangement is providing an at least one-dimensional geometrical ruler reference coordinate system. The image processor comprises a recognition unit, an assignment unit, and an allocation unit. The recognition unit is configured to recognize predetermined ruler indicators within the first and second image. The assignment unit is configured to assign the respective first or second image to the recognized ruler indicator. The allocation unit is configured to locate the first or second image within the geometrical ruler reference.

For example, a one-dimensional geometrical ruler reference may be provided as a linear ruler. In another example, a two-dimensional geometrical ruler reference in form of a ruler grid is provided.

According to an exemplary embodiment, the ruler arrangement is provided with ruler characters, and the identification of at least a segment of the ruler arrangement is based on optical character recognition (OCR).

The ruler characters are provided as graphic representations of numbers and/or letters. For example, Latin characters are provided for the letters, and Arabic numbers are provided for numbers. In another example, other letters such as Greek or Cyrillic or Hebrew letters are provided. In a further example, Arabic letters are provided. In a still further example, Asian symbols, for example Chinese, Korean, or Japanese symbols, are used for the numbers and/or letters.

In a further example, manual correction is provided for the geometric relation of the image portions when combining them to form the spotlight X-ray map. For example, it is provided to limit or restrict the part of the respective image that is actually used for OCR. In another example, the images can be moved along the combined image manually via an interface such as a keyboard, mouse, graphic pen or touch screw and the like. For example an overlaid ruler may serve as an orientation for the manual correction.

According to a second aspect, a method for spotlight X-ray mapping is provided, comprising the following steps:

a) acquiring at least first and second images from different regions of interest of an object, wherein a detectable ruler arrangement and the object are provided in a determined spatial relation for each of the images;

b) identifying at least a segment of the ruler arrangement in each of the at least first and second images;

c) assigning the identified ruler segments to the respective X-ray image;

d) determining a spatial position of the respective segment in relation to the ruler arrangement;

e) combining the at least first and second images according to their spatial relation based on the identified segments in the respective image; and

f) displaying the combined images as a spotlight X-ray map.

According to an exemplary embodiment, the ruler arrangement is providing an at least one-dimensional geometrical ruler reference coordinate system; and step b) comprises recognizing predetermined ruler indicators within the first and second image; and step c) comprises assigning the respective first or second image to the recognized ruler indicator; and step d) comprises locating the first or second image within the geometrical ruler reference.

According to an aspect, a joint image with correct geometric relations is provided, although this is based on a composition of images, which images do not require overlapping, or which preferably do not overlap in order to save dose. This allows the use of small detectors, as used in particular in interventional or emergency devices producing smaller images. Thus, besides saving patient's radiation dose, also a cumbersome acquisition of a larger plurality of images is not needed. Rather, only those regions of interest need to be radiated, whereas the regions in-between are omitted or left out in the final image and thus do not need to be radiated. This is possible by providing the X-ray detectable ruler arrangement that serves as a basis for the determination of the correct spatial arrangement. The relation of different anatomic structures from several detector positions is thus still provided, and may be of interest, for example for diagnosis or therapy reasons, e.g. measuring the length or joint alignment during fracture treatment. The dose saving aspect considers the ALARA (as low as reasonably achievable) principle in interventional and emergency applications. If, for example, only a hip, knee, or ankle joint is radiated, without producing overlapping images, it is now possible to relate content from one image to content in another image in a geometric way by the spotlight X-ray map. Instead of an image-based composition of images, the proposed example exploits knowledge about the external stitching features, i.e. the X-ray ruler or X-ray ruler arrangement. By means of image processing, optical character recognition (OCR) and image to world coordinate mapping, it is possible to assemble the partial images into a joint image with geometric relations, which is referred to as spotlight X-ray map. According to an example, three steps are carried out for each new image portion to be added to a so-called stitching buffer, i.e. the larger image containing the geometrically aligned smaller images, wherein the term "stitching" relates to virtual stitching, since there is no real overlap that could act for a stitching. In a first step, ruler detection is provided. The X-ray opaque ruler is detected in each of the partial images in terms of orientation (tilt angle), scale marker positions, and digits (for example via OCR). In a second step, a ruler refinement is provided. For each detected scale marker, precise corner detection is carried out, detecting the corner of each marker with sub-pixel accuracy. Thus, the ruler orientation can be estimated with higher precision and the frequency of scale markers can be determined with highest accuracy. In a third step, image-to -world mapping is provided. Digits from each partial image are compared to each other in order to retrieve the closest matching ruler position. Via the scale marker frequency and the precise locations of two scale markers in the different images, the ruler of one image is extrapolated to the exterior of the image. Subsequently, the second image is rotated to the common ruler orientation and translated to the extrapolated scale marker position. Precision may be very high; measured maximum error can be provided as smaller than 2 millimetres for a composite image of 1000 millimetres in height. For the image composition, non-covered image areas may be filled with a uniform background. In case of overlapping areas, these can be blended, using the content of every intersecting image.

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 schematically shows an X-ray imaging system for spotlight X-ray mapping;

Fig. 2 shows an example of an X-ray imaging system with aspects of different embodiments;

Fig. 3 shows different embodiments of a detectable ruler arrangement in Figs. 3A and 3B;

Fig. 4 shows basic steps of an example of a method for spotlight X-ray mapping;

Fig. 5 shows a further example of a method for spotlight X-ray mapping;

Fig. 6 shows an example for ruler detection on two example images of a C-arm series;

Fig. 7 shows a spotlight X-ray map for non-overlapping partial images in a first example;

Fig. 8 shows a further example of a spotlight X-ray map; and

Fig. 9, Fig. 10 and Fig. 11 show photographic illustrations of Fig. 6, Fig. 7 and Fig. 8 respectively.

DETAILED DESCRIPTION OF EMBODIMENTS

Fig. 1 shows an X-ray imaging system 10 for spotlight X-ray mapping, comprising an X-ray image acquisition device 12 with an X-ray source 14, an X-ray detector 16, and an X-ray detectable ruler arrangement 18. The X-ray imaging system 10 further comprises an image processor 20 and a display 22. The X-ray image acquisition device 12 is configured to acquire at least first and second images from different regions of interest of an object, wherein the detectable ruler arrangement and the object are provided in a determined spatial relation for each of the images. The object is indicated with a dotted oval structure 24. The relative movement of the X-ray imaging acquisition device 12 in relation to the object 24 and the ruler arrangement 18 is indicated with first arrows 26 in relation with the X-ray source 14, and second arrows 28 in relation with the detector 16. Connecting lines 30 indicate a data connection between the X-ray source, the X-ray detector 16, and the image processor 20. The image processor 20 is configured to identify at least a segment of the ruler arrangement 18 in each of the at least first and second images, and to assign the identified ruler segment to the respective X-ray image, and to determine a spatial position of the respective segment in relation to the ruler arrangement, and to combine the at least first and second images according to their spatial relation based on the identified segment in the respective image. The display 22 is configured to display the combined images as a spotlight X-ray map 32.

According to an example, the first and second images are provided in a displaced manner such that a gap between them exists.

According to a further example, the spotlight X-ray map 32 provides the at least first and second images as image portions in the correct geometric relation to each other (also further shown in Figs. 6, 7, and 8).

For example, for the at least first and second images, the ruler arrangement 18 and the object 24 are provided in the same spatial relation to each other. The ruler

arrangement 18 may cover at least a part of the region of the first image and a part of the second image.

As indicated in Fig. 2, the ruler arrangement 18 is provided as an at least one- dimensional geometrical ruler reference coordinate system 34. For example, the geometrical ruler reference coordinate system 34 is provided as a one-dimensional geometrical ruler reference in form of a linear ruler 36. In another example, a two-dimensional geometrical ruler reference in form of a ruler grid 38 is provided, which is indicated in Fig. 2 in a dotted manner as an option.

As further indicated in Fig. 2, the image processor 18 may comprise a recognition unit 40, an assignment unit 42, and an allocation unit 44. The recognition unit 40 is configured to recognize predetermined ruler indicators within the first and second image. The assignment unit 42 is configured to assign the respective first or second image to the recognized ruler indicator. The allocation unit 44 is configured to locate the first or second image within the geometrical ruler reference in form of the ruler reference coordinate system 34.

According to a further example, also shown in Fig. 2, but not meaning to represent a necessary requirement for the above-mentioned example of the recognition unit 40, the assignment unit 42 and the allocation unit 44, an alignment unit 46 is provided as an option, which is configured to identify an orientation of the identified ruler segment, and to align the respective image with respect to the ruler. According to a still further example, also shown in combination with Fig. 2, but also meaning not a necessary requirement for the above- mentioned examples of the recognition unit 40, the assignment unit 42, and the allocation unit 44, as well as the alignment unit 46, a registration unit 48 is provided as an option, which is configured to register the identified ruler segment and the assigned X-ray image with respect to the ruler arrangement, and to align the respective X-ray image with respect to the ruler. For example, the respective X-ray image is tilted and/or warped to be aligned to the ruler.

Fig. 3A shows a first example of a portion of a ruler arrangement 18, comprising a plurality of numbers 50. Fig. 3B shows a further example of the ruler

arrangement 18 with a plurality of letters 52.

Fig. 4 shows an example of a method 100 for spotlight X-ray mapping, comprising the following steps: In a first step 110, at least first and second images are acquired from different regions of interest of an object, wherein a detectable ruler arrangement and the object are provided in a determined spatial relation for each of the images. In a second step 112, at least a segment of the ruler arrangement in each of the at least first and second images is identified. In a third step 114, the identified ruler segments are assigned to the respective X-ray image. In fourth step 116, a spatial position of the respective segment in relation to the ruler arrangement is determined. In a fifth step 118, the at least first and second images are combined according to their spatial relation based on the identified segments in the respective image. In a sixth step 120, the combined images are displayed as a spotlight X-ray map 122. The first step 110 is also referred to as step a), the second step 112 as step b), the third step 114 as step c), the fourth step 116 as step d), the fifth step 118 as step e), and the sixth step 120 as step f).

For example, the spotlight X-ray map provides the at least first and second images as image portions in the correct geometric relation to each other.

As shown in Fig. 5, the ruler arrangement is providing an at least one- dimensional geometrical ruler reference coordinate system. Step b) comprises recognizing 124 predetermined ruler indicators within the first and second image; step c) comprises assigning 126 the respective first or second image to the recognized ruler indicator; and step d) comprises locating 128 the first or second image within the geometrical ruler reference.

Fig. 6 shows a first image 210 in the left half and a second image 212 in the right half; a respective portion of the ruler arrangement 18 is shown in both images, and can thus be detected.

Fig. 7 shows a first X-ray image 214, a second X-ray image 216, and a third X- ray image 218 in relation to each other, each image showing a respective segment of the ruler arrangement, for example a first segment 18a in the first image 214, a second segment 18b in the second image 216, and a third segment 18c in the third image 218. As can be seen, the respective images do not overlap and the space between adjacent images is provided with a common background filling 220. The respective image portions, i.e. the first image 214, the second image 216, and the third image 218, are provided in their respective geometric relation representing the combined images as the spotlight X-ray map, as mentioned above.

The ruler may also be shown in the areas between the separate image portions.

Fig. 8 shows a further example of the spotlight X-ray map 34 in form of three images 222 in the left half and further three images 224 in the right half. For example, the left column of the three images 222 relates to the left leg of a patient, whereas the right column of the further images 224 relates to the right leg of a patient. It must be noted that the two columns are spaced apart in a preset distance, which is indicated with a centreline C, indicating the location of the ruler arrangement 18. Of course, in a further example, the two columns are moved closer in relation to each other such that the centrelines overlap, in order to provide not only the correct longitudinal arrangement, i.e. the geometric relation in the length direction of the leg, but also in the direction transverse to the leg direction.

Figures 6 to 8 show line-drawings; respective photographic illustrations are shown in Fig. 9, Fig. 10 and Fig. 11.

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 fulfil 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 fulfil 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.