阅读说明：本技术 X射线照相装置 (X-ray imaging apparatus ) 是由 J·塞内加 S·A·约克尔 H-I·马克 M·贝格特尔特 于 2018-06-15 设计创作，主要内容包括：本发明涉及一种X射线照相装置(10)。描述了以下内容：相对于X射线探测器(30)放置(110)X射线源(20)以形成用于容纳对象的检查区域,其中,基于所述X射线照相装置的几何参数来定义参考空间坐标系；将相机(40)定位(120)在一位置和取向处以查看所述检查区域；利用所述相机在相机空间坐标系内采集(130)所述对象的深度图像,其中,在所述深度图像内,像素值表示针对对应像素的距离；利用处理单元(50)使用映射函数将在所述相机空间坐标系内的所述对象的所述深度图像变换(140)到所述参考空间坐标系,其中,已经相对于所述参考空间坐标系校准了所述相机的位置和取向,以产生将所述相机空间坐标系内的空间点映射到所述参考空间坐标系中的对应空间点的映射函数；在所述参考空间坐标系内生成(150)合成图像；利用输出单元(60)来输出(160)所述合成图像。(The invention relates to X-ray photographing apparatus (10) describing positioning (110) an X-ray source (20) relative to an X-ray detector (30) to form an examination region for accommodating an object, wherein a reference spatial coordinate system is defined based on geometrical parameters of the X-ray photographing apparatus, positioning (120) a camera (40) at a position and an orientation to view the examination region, acquiring (130) a depth image of the object within a camera spatial coordinate system with the camera, wherein within the depth image a pixel value represents a distance for a corresponding pixel, transforming (140) the depth image of the object within the camera spatial coordinate system to the reference spatial coordinate system with a processing unit (50) using a mapping function, wherein the position and orientation of the camera has been calibrated relative to the reference spatial coordinate system to produce a mapping function mapping spatial points within the camera spatial coordinate system to corresponding spatial points in the reference spatial coordinate system, generating (150) a synthetic image within the reference spatial coordinate system, outputting (160) the synthetic image to output (160).)

An X-ray radiography apparatus (10) of the type , comprising:

an X-ray source (20);

an X-ray detector (30);

a camera (40);

a processing unit (50); and

an output unit (60);

wherein the X-ray source is configured to be positioned relative to the X-ray detector to form an examination region for receiving an object, wherein the X-ray source has a collimator configured to limit the range of X-rays;

wherein a reference spatial coordinate system is defined based on geometrical parameters of the radiographic apparatus;

wherein the camera is configured to be positioned at position and orientation to view the examination region, and the camera is configured to acquire a depth image within a camera spatial coordinate system, wherein within the depth image a pixel value represents a distance for a corresponding pixel;

wherein the position and orientation of the camera has been calibrated relative to the reference spatial coordinate system to produce a mapping function that maps spatial points within the camera spatial coordinate system to corresponding spatial points in the reference spatial coordinate system;

wherein the camera is configured to acquire a depth image of the object within the camera spatial coordinate system and to provide the depth image to the processing unit;

wherein the processing unit is configured to transform the depth image of the object within the camera space coordinate system to the reference space coordinate system using the mapping function and generate a composite image within the reference space coordinate system;

wherein the processing unit is configured to generate a representation of the range of X-rays within the reference spatial coordinate system, and wherein the processing unit is configured to generate a composite image with the representation of the range of X-rays at the location of the object;

wherein the output unit is configured to output the composite image.

2. Apparatus according to claim 1, wherein the X-ray detector has at least exposure chambers, the at least exposure chambers being configured to measure exposure levels of X-rays, and wherein the processing unit is configured to generate a representation of a range of the at least exposure chambers within the reference spatial coordinate system, and wherein the processing unit is configured to generate a composite image having the representation of the range of the at least exposure chambers.

3. The apparatus of claim 2, wherein the processing unit is configured to generate a composite image having a representation of the range of the at least exposure chambers at the position of the object.

4. The apparatus of any of claims 1-3, wherein the X-ray detector has an active region configured to detect X-rays, and wherein the processing unit is configured to generate a representation of a range of the active region within the reference spatial coordinate system, and wherein the processing unit is configured to generate a composite image having the representation of the range of the active region.

5. The apparatus of claim 4, wherein the processing unit is configured to generate a composite image having a representation of the extent of the active region at the location of the object.

6. Apparatus according to any of claims 1-5, wherein the X-ray detector has a transverse axis and a longitudinal axis, and wherein the processing unit is configured to generate a representation of the transverse axis and/or the longitudinal axis within the reference space coordinate system, and wherein the processing unit is configured to generate a composite image having a representation of the transverse axis and/or the longitudinal axis.

7. The apparatus of any of claims 1-6, wherein the camera is configured to acquire a 2D image and provide the image to the processing unit, and wherein the processing unit is configured to generate a composite image, including utilizing the 2D image.

a method (100) for providing an image for an X-ray radiography apparatus, comprising:

a) positioning (110) an X-ray source (20) relative to an X-ray detector (30) to form an examination region for accommodating an object, wherein the X-ray source has a collimator configured to limit the range of X-rays, wherein a reference spatial coordinate system is defined based on geometrical parameters of the X-ray photographing apparatus;

b) positioning (120) a camera (40) at a position and orientation to view the examination region;

c) acquiring (130) a depth image of the object within a camera spatial coordinate system with the camera, wherein within the depth image pixel values represent distances for corresponding pixels;

d) transforming (140), with a processing unit (50), the depth image of the object within the camera space coordinate system to the reference space coordinate system using a mapping function, wherein the position and orientation of the camera has been calibrated with respect to the reference space coordinate system, to produce a mapping function that maps spatial points within the camera space coordinate system to corresponding spatial points in the reference space coordinate system;

e) generating (170), with the processing unit, a representation of a range of the X-rays within the reference spatial coordinate system;

i) generating (150) a composite image within the reference spatial coordinate system having a representation of the range of X-rays at the location of the object; and is

j) Outputting (160) the composite image with an output unit.

9. The method according to claim 8, wherein the X-ray detector has at least exposure chambers, the at least exposure chambers being configured to measure exposure levels of X-rays, and wherein the method comprises a step (f) of generating (180) a representation of a range of the at least exposure chambers within the reference spatial coordinate system with the processing unit, and wherein step i) comprises generating a composite image having the representation of the range of the at least exposure chambers.

10. The method according to any of claims 8-9, wherein the X-ray detector has an active zone configured to detect X-rays, and wherein the method comprises a step (g) of generating (190), with the processing unit, a representation of a range of the active zone within the reference spatial coordinate system, and wherein step i) comprises generating a composite image having the representation of the range of the active zone.

11, computer program element for controlling an apparatus according to any of claims 1-7, which, when being executed by a processor, is configured to perform the method of any of claims 8-10.

Technical Field

The invention relates to an X-ray radiography apparatus, a method for providing an image for an X-ray radiography apparatus, and a computer program element and a computer readable medium.

Background

The general background to the present invention is radiography. In radiographic examinations, it is necessary to accurately position the patient with respect to the X-ray detector and to adjust the geometry and system parameters to the patient's anatomy. For example, an exposure chamber for Automatic Exposure Control (AEC) needs to be positioned accurately behind the target anatomy. Similarly, the size of the collimation window needs to be adjusted to fit the size of the body part to be imaged.

On current systems, the prior art is to use visual markers (e.g., a drawing of the exposure chamber on the detector cover) and visible light projected directly on the scene (detector, patient) as a means to guide the operator. For example, using light sources and slide-like devices to project the collimation window and exposure chamber in the scene enables the operator to check the current settings by looking at the projected shape on the patient.

The prior art has obvious limitations: not all the required information is provided and the visibility of the projected light field may be very limited-depending on the lighting conditions in the examination room and the patient's clothing. Also, in an ideal case, the operator needs to look at the patient from a position equal to the X-ray source to avoid any visual obstruction, which needs to be iteratively operated back and forth between the system configuration panel and the observation point.

Other methods using conventional video cameras and overlays also suffer from geometric inaccuracies and occlusion because the video camera cannot be placed at the location of the X-ray source and the captured view of the scene is squinted.

WO 2015/081295 a1 describes a system or method for improving the quality of projected and tomographic X-rays, comprising a depth sensing device for measuring the depth of at least body parts of a patient from the depth sensing device, and a control unit for calculating the thickness and/or circumference of the body parts using the depth information.

WO 2016/001130A 1 describes methods for automatically configuring an X-ray imaging system for taking X-ray images of an object first or more depth images are obtained from or more depth cameras covering at least regions covered by an X-ray beam of an X-ray source then the thickness of the object is determined from the or more depth images.

Disclosure of Invention

It would be advantageous to have an improved apparatus for providing images to an operator of an X-ray radiography apparatus.

The object of the invention is solved by the subject matter of the independent claims, wherein further embodiments are included in the dependent claims. It should be noted that the following described aspects and examples of the invention also apply to the radiographic apparatus, to the method for providing images for a radiographic apparatus, and to the computer program element and the computer readable medium.

According to an th aspect, there is provided a radiography apparatus comprising:

an X-ray source;

an X-ray detector;

a camera;

a processing unit; and

and an output unit.

The camera is configured to acquire depth images of the object within the camera spatial coordinate system and to provide the depth images to the processing unit, the processing unit is configured to transform the depth images of the object within the camera spatial coordinate system to the reference spatial coordinate system using the mapping function and to generate a composite image within the reference spatial coordinate system.

In this way, an image of an object, such as a human subject, can be presented to the operator as if it were acquired by a camera positioned at the location of the X-ray source, rather than acquired by a camera at the actual location of the camera.

In an th aspect, the X-ray source has a collimator configured to limit the extent of the X-rays, and wherein the processing unit is configured to generate a representation of the extent of the X-rays within the reference spatial coordinate system, and wherein the processing unit is configured to generate a composite image having the representation of the extent of the X-rays.

In other words, the X-ray source has a collimation window and the composite image has superimposed thereon an indication of the size of the collimation window at the object. In this way, the operator can move the object within the examination region and/or change the size of the collimation window in order to provide an optimal photographic examination.

In an th aspect, the processing unit is configured to generate a composite image having a representation of a range of X-rays at the location of the object.

In other words, the X-ray source is configured to emit X-rays over an angular and spatial extension, and the processing unit is configured to generate a composite image with a representation of the extended range of X-rays at the location of the object. Thus, the operator is not only provided with an indication of the size of the collimation window from the perspective of the X-ray source, but is also provided with the size of the window at the object. This allows for objects or parts of objects that are very close to the X-ray detector and objects that are further away from the detector.

In an example, the X-ray detector has at least exposure chambers, the at least exposure chambers being configured to measure exposure levels of X-rays, and wherein the processing unit is configured to generate a representation of a range of the at least exposure chambers within the reference spatial coordinate system the processing unit is then configured to generate a composite image having the representation of the range of the at least exposure chambers.

In this way, the operator can ensure that the object (e.g. a patient) is correctly positioned with respect to the exposure chamber for automatic exposure control, taking into account the actual path of the X-rays from the X-ray source to the detector, since the composite image is acquired from the perspective of the X-ray source and its relationship to the X-ray detector.

In an example, the processing unit is configured to generate a composite image having a representation of the range of at least exposure chambers at the position of the object.

In an example, the X-ray detector has an active zone configured to detect X-rays, and wherein the processing unit is configured to generate a representation of a range of the active zone within the reference spatial coordinate system. The processing unit is then configured to generate a composite image with a representation of the extent of the active region.

In an example, the processing unit is configured to generate a composite image having a representation of the extent of the active region at the location of the object.

In an example, the X-ray detector has a transverse axis and a longitudinal axis, and wherein the processing unit is configured to generate a representation of the transverse axis and/or the longitudinal axis within the reference spatial coordinate system. The processing unit is then configured to generate a composite image having a representation of the horizontal axis and/or the vertical axis.

In this way, the operator is provided with another means to help achieve proper alignment of the object (e.g., patient) with the device.

In other words, the axis of symmetry for the X-ray detector can be used to check whether the patient is well aligned with respect to the X-ray detector.

In an example, the camera is configured to acquire a 2D image and provide the image to the processing unit, and wherein the processing unit is configured to generate a composite image, including utilizing the 2D image.

In this way, a composite image having a real texture can be generated.

Thus, although the depth image can be considered as a 2D image (since the depth image has two dimensions), here an additional image is acquired in addition to the depth image, which can be for example a multi-channel (color) image or a single-channel (monochrome) image, wherein the pixel values represent other properties of the scene in addition to depth, such as: the amount of reflected light in a given spectral range; and a thermal image.

According to a second aspect, a method (100) for providing an image for an X-ray radiographic apparatus is provided, comprising:

a) positioning an X-ray source relative to an X-ray detector to form an examination region for accommodating an object, wherein a reference spatial coordinate system is defined based on geometrical parameters of the X-ray radiography apparatus;

b) positioning a camera at position and orientation to view the examination region;

c) acquiring a depth image of the object within a camera spatial coordinate system with the camera, wherein within the depth image pixel values represent distances for corresponding pixels;

d) transforming, with a processing unit, the depth image of the object within the camera space coordinate system to the reference space coordinate system using a mapping function, wherein the position and orientation of the camera has been calibrated with respect to the reference space coordinate system, to produce a mapping function that maps spatial points within the camera space coordinate system to corresponding spatial points in the reference space coordinate system;

i) generating a composite image within the reference spatial coordinate system; and is

j) Outputting the composite image with an output unit.

In a second aspect, the X-ray source has a collimator configured to limit the range of X-rays, and wherein the method comprises step (e): generating, with the processing unit, a representation of the range of X-rays within the reference spatial coordinate system, and wherein step i) comprises generating a composite image with the representation of the range of X-rays.

In a second aspect, step i) comprises generating a composite image having a representation of the extent of the X-rays at the location of the object.

In an example, the X-ray detector has at least exposure chambers, the at least exposure chambers being configured to measure exposure levels of X-rays, and wherein the method comprises a step (f) of generating a representation of a range of the at least exposure chambers within the reference spatial coordinate system with the processing unit, and wherein step i) comprises generating a composite image having the representation of the range of the at least exposure chambers.

In an example, the X-ray detector has an active region configured to detect X-rays, and wherein the method comprises step (g): generating, with the processing unit, a representation of the extent of the active region within the reference spatial coordinate system, and wherein step i) comprises generating a composite image with the representation of the extent of the active region.

According to a further aspect, there is provided computer program element controlling an apparatus and/or system as described above, which, when being executed by a processing unit, is adapted to perform the method steps as described above.

According to a further aspect, there is provided computer readable medium storing the computer program element as described above.

Advantageously, the benefits provided by any of the above aspects apply equally to all other aspects, and vice versa.

The aspects and examples described above will become apparent from and elucidated with reference to the embodiments described hereinafter.

Drawings

Exemplary embodiments will be described below with reference to the following drawings:

fig. 1 shows a schematic arrangement of an example of an X-ray radiography apparatus;

FIG. 2 illustrates a method for providing images for an X-ray radiography apparatus;

figure 3 shows an example of an X-ray source (X-ray tube) with a 3D camera mounted on an X-ray tube support;

figure 4 shows images with and without overlay and overlay which has been geometrically corrected in images, and

fig. 5 shows an image with an overlay that has not been geometrically corrected and an image with an overlay that has been geometrically corrected.

Detailed Description

Fig. 1 shows an example of an X-ray photographing apparatus 10. The radiography apparatus includes an X-ray source 20, an X-ray detector 30, a camera 40, a processing unit 50, and an output unit 60. The X-ray source 20 is configured to be positioned relative to the X-ray detector 30 to form an examination region for receiving an object. The reference spatial coordinate system is defined based on the geometric parameters of the radiographic apparatus 10. The camera 40 is configured to be positioned at a position and orientation to view the examination region, and the camera 40 is configured to acquire a depth image within a camera spatial coordinate system, wherein within the depth image the pixel values represent distances for corresponding pixels. The position and orientation of the camera has been calibrated relative to the reference spatial coordinate system to produce a mapping function that maps spatial points within the camera spatial coordinate system to corresponding spatial points in the reference spatial coordinate system. The camera 40 is configured to acquire a depth image of the object within the camera spatial coordinate system and provide the depth image to the processing unit 50. The processing unit 50 is configured to transform the depth image of the object within the camera space coordinate system to the reference space coordinate system using a mapping function and to generate a composite image within the reference space coordinate system. The output unit 60 is configured to output the synthesized image.

In an example, the mapping function maps spatial points within the reference spatial coordinate system to corresponding spatial points in the camera spatial coordinate system.

In an example, the geometric parameters of the radiography system used to define the reference spatial coordinate system include or more of a position of the X-ray source relative to the X-ray detector, a geometric parameter related to a source-image receptor distance (SID), a height of the X-ray detector, a width of the X-ray detector, a height of the X-ray source, a width of the X-ray source, a rotation angle of the X-ray source, a longitudinal position and a lateral position of the X-ray detector, a longitudinal position and a lateral position of the X-ray source, a rotation angle (roll, pitch, yaw) of the X-ray detector and/or the X-ray source.

In an example, in addition to acquiring a depth image, the camera is configured to acquire a "regular" image of the scene, which is a color image such as R, G or a B color space or a grayscale (monochrome or infrared) image.in an example, the camera is configured to acquire a 3D depth (a.k.a. range) data image and can calculate 3D point coordinates from the depth data image using internal parameters of the camera system.in an example, the regular image is used to generate a composite image on which the overlay is shown.A correspondence (mapping function) between pixels in the regular image and pixels in the depth image is used, which is necessary because the regular image can be acquired by other sensors than the depth sensor and both have different positions and orientations.

Thus, the camera is able to acquire a single depth image and to acquire 3D points from the depth image, which means that the 3D spatial coordinates of these points can be calculated. The 3D point coordinates of the object within the image can be used to implement a transformation from the camera space coordinate system to the reference space coordinate system. Furthermore, the depth image and the calculated 3D points can be used to provide a representation of the 3D points using, for example, a point cloud. Thus, in practice, the depth image can be used to provide a 3D image. A composite image can then be generated in the reference spatial coordinate system using the 2D projection of the 3D image. Alternatively, the camera can acquire a second 2D image (regular image) at the same time as the depth image. As mentioned above, depth images are used to enable a transformation from the camera space coordinate system to the reference space coordinate system, whereas conventional images are used (e.g. from the perspective of the X-ray source) to generate a composite image in the reference space coordinate system on which e.g. an overlay can be shown.

Typically, this requires integrating two different sensors in the camera system. Only in the infrared case can there be only a single sensor.

In an example, the term "camera" actually refers to two or more 2D cameras used together to provide a 3D image, e.g., a stereo system.

According to an example, the X-ray source has a collimator configured to limit the range of X-rays, and wherein the processing unit is configured to generate a representation of the range of X-rays within a reference spatial coordinate system. The processing unit is then configured to generate a composite image having a representation of the range of X-rays.

According to an example, the processing unit is configured to generate a composite image having a representation of a range of X-rays at a location of the object.

According to an example, the X-ray detector has at least exposure chambers, the at least exposure chambers being configured to measure exposure levels of X-rays, and wherein the processing unit is configured to generate a representation of a range of at least exposure chambers within the reference spatial coordinate system the processing unit is then configured to generate a composite image having a representation of a range of at least exposure chambers.

According to an example, the processing unit is configured to generate a composite image having a representation of a range of at least exposure chambers at the position of the object.

According to an example, the X-ray detector has an active zone configured to detect X-rays, and wherein the processing unit is configured to generate a representation of a range of the active zone within the reference spatial coordinate system. The processing unit is then configured to generate a composite image having a representation of the extent of the active region.

According to an example, the processing unit is configured to generate a composite image having a representation of a range of active regions at a location of the object.

According to an example, the X-ray detector has a transverse axis and a longitudinal axis, and wherein the processing unit is configured to generate a representation of the transverse axis and/or the longitudinal axis within the reference spatial coordinate system. The processing unit is then configured to generate a composite image having a representation of the horizontal axis and/or the vertical axis.

According to an example, the camera is configured to acquire a 2D image and provide the image to the processing unit. The processing unit is then configured to generate a composite image, including utilizing the 2D image.

In an example, the 2D image is a monochrome image. In an example, the 2D image is a color image.

Fig. 2 shows a method 100 for providing an image for an X-ray radiography apparatus in basic steps.

The method 100 comprises:

in a placing step 110, also referred to as step (a), the X-ray source 20 is placed relative to the X-ray detector 30 to form an examination region for accommodating the object, wherein a reference spatial coordinate system is defined based on geometrical parameters of the X-ray camera.

In a positioning step 120 (also referred to as step (b)), the camera 40 is positioned at position and orientation to view the examination region;

in an acquisition step 130 (also referred to as step (c)), acquiring a depth image of the object within a camera space coordinate system with the camera, wherein within the depth image the pixel values represent distances to the corresponding pixels;

in a transformation step 140, also referred to as step (d), the depth image of the object within the camera space coordinate system is transformed with the processing unit 50 to the reference space coordinate system using a mapping function, wherein the position and orientation of the camera has been calibrated with respect to the reference space coordinate system, to generate a mapping function that maps spatial points within the camera space coordinate system to corresponding spatial points in the reference space coordinate system;

in a generating step 150 (also referred to as step (i)), a composite image is generated within the reference spatial coordinate system; and is

In an output step 160, also referred to as step (j), the composite image is output with the output unit 60.

According to an example, an X-ray source has a collimator configured to limit the range of X-rays. And wherein the method comprises step (e): generating 170 a representation of the range of X-rays within the reference spatial coordinate system with the processing unit, and wherein step i) comprises generating a composite image having the representation of the range of X-rays.

According to an example, step i) comprises generating a composite image having a representation of the range of X-rays at the location of the object.

In an example, generating the representation of the range of X-rays includes utilizing a ray tracing algorithm.

According to an example, the X-ray detector has at least exposure chambers, the at least exposure chambers being configured to measure exposure levels of the X-rays, and wherein the method comprises the step (f) of generating a representation of a range of 180 at least exposure chambers within a reference spatial coordinate system with the processing unit, and wherein step i) comprises generating a composite image having the representation of the range of at least exposure chambers.

In an example, step i) comprises generating a composite image having a representation of a range of at least exposure chambers at the position of the object.

In an example, generating a representation of the range of at least exposure chambers includes utilizing a ray tracing algorithm.

According to an example, the X-ray detector has an active region configured to detect X-rays, and wherein the method comprises step (g): generating 190 a representation of the extent of the active region within the reference spatial coordinates with the processing unit, and wherein step i) comprises generating a composite image with the representation of the extent of the active region.

In an example, step i) comprises generating a composite image having a representation of the extent of the active region at the location of the object.

In an example, generating the representation of the extent of the active region includes utilizing a ray tracing algorithm.

In an example, the X-ray detector has a transverse axis and a longitudinal axis, and wherein the method comprises step (h): generating 200 a representation of a horizontal axis and/or a vertical axis within the reference spatial coordinate system with the processing unit, and wherein step i) comprises generating a composite image having the representation of the horizontal axis and/or the vertical axis.

In an example, the camera is configured to acquire a 2D image, and the method comprises providing the image to the processing unit, and wherein step i) comprises utilizing the 2D image.

The radiographic apparatus and the method for providing images for the radiographic apparatus will now be described in more detail in connection with fig. 3-5.

A depth camera, a 3D computer vision method and a display capable of acquiring 3D images are used to show an operator an augmented reality composite image with high geometric accuracy according to the following steps:

a depth camera providing depth data and regular video data at an appropriate frame rate is positioned to image the examination region with minimal obstruction (e.g., at the top of a collimator). An example of a 3D camera (depth camera) mounted on an X-ray source (X-ray tube) is shown in fig. 3.

The position and orientation of the camera has been calibrated with respect to the geometry of the camera system. The procedure generates, in combination with real-time values of the geometric parameters of the camera system, a mapping function which allows transforming point coordinates from the camera coordinate system to the X-ray reference coordinate system.

In a lower step, a composite image showing geometrically accurate positions and shapes (as an overlay) of the patient and of the detector, e.g. the exposure chamber, the collimation window and the active area, is reconstructed using known computer vision methods and the coordinate transformations obtained above.

Thus, the composite image seen from the X-ray source is reconstructed from the depth image, but composite images seen from other vantage points can also be reconstructed, and need not necessarily be the composite image seen from the X-ray source. By applying a central projection centered on the X-ray source, an overlay is generated in the scene.

A composite image representing a projection of the patient on the X-ray detector can also be generated from the depth image. The overlay is then generated by calculating the size, shape and position of the different patterns projected on the X-ray detector plane.

The augmented reality composite image is shown to the operator on the display. Different colors can be used to represent each of the different types of overlays.

Fig. 4 shows an example of an overlay for an exposure chamber and a collimation window that can be generated using depth data captured by a 3D camera. Three pictures are shown in fig. 4. The left picture shows an image captured by a 3D camera. In the intermediate image, the stack of exposure chambers and collimation windows is shown as viewed from the perspective of the 3D camera (i.e. in the camera space coordinate system) without applying the proposed mapping function. In the right picture, the overlay has been geometrically corrected based on a mapping function derived from the calibration of the camera and the geometrical parameters of the radiographic apparatus, the geometrically corrected overlay now being positioned exactly at the correct pixel position.

FIG. 5 shows two images of a collimated overlay, where the left image is the image without the collimation corrected and the right image is the image with the collimation corrected.the left image shows the 3D scene as seen from the camera, since the camera is positioned at the side of the X-ray source, the position and size of the collimated overlay (the rectangle projected to the back of the subject) depends on the distance to the X-ray source (which is chosen as the reference). this is represented by two different rectangles.

Camera calibration

In general, it is desirable to express the coordinates of the 3D points in a coordinate system specified with respect to the examination room or with respect to the medical imaging system or the radiographic apparatus. In the following, this reference spatial coordinate system is referred to as the "world" coordinate system, in contrast to the camera spatial coordinate system.

The extrinsic camera parameters describe the 3D point P from the world coordinate system_wTo a 3D point P in the camera coordinate system_cAnd (6) transforming. These parameters are given by:

r and T represent rotations and translations defining external camera parameters, which have the following relationships:

the translation vector T can be regarded as the coordinates of the origin of the world coordinate system expressed in the camera coordinate system. Each column of the rotation matrix represents the coordinates (in the camera coordinate system) of a unit vector oriented along the major axis of the world coordinate system.

To determine the extrinsic parameters for a given camera's position and orientation, the following method can be used. In this approach, it is assumed that the camera's intrinsic parameters defining the mapping of 2D points in image coordinates to 3D points in camera coordinates are already known. These parameters can be calculated using known methods, for example based on an image of a checkerboard pattern. See for example: http:// docs. opencv. org/2.4/doc/tutorials/calib3d/camera _ calibration. html.

First, a depth image of a known object is acquired with a camera. In the image, a plurality of calibration points having known coordinates in a world coordinate system are determined. These points can be located, for example, at specific known locations of the world coordinate system, for example, corners of the sonde bezel. The calibration points are formed to include N pairs

(wherein 0. ltoreq. i<N) to obtain a calibration data setA set of N equations of type. The linear system can then be solved for the unknown coefficients of the rotation matrix R and the translational vector T. Examples of computational algorithms can be found in the following documents: berthold K.P.Horn, "Closed-form solution of adsorption orientation using units" (J.Opt.Soc.am.A., Vol.4, No. 4, p.629-642, 1987).

Enhanced robustness can be obtained if a number N greater than 3 is used (the system is overdetermined) and the calibration points are not coplanar.

Other methods can also be used, for example, instead of using sets of well-defined calibration points, a point cloud describing world coordinates can be used, e.g., a reference 3D object (e.g., part of the detector front cover) with a known pattern.

In a further exemplary embodiment, computer programs or computer program elements are provided, which are characterized in that they are configured to run the method steps of the method according to of the preceding embodiments on a suitable system.

The computer program may be loaded into a working memory of a data processor, the data processor may thus be equipped to perform the methods of the preceding embodiments .

This exemplary embodiment of the invention covers both a computer program that uses the invention from onwards, and a computer program that is updated by means of an existing program to a program that uses the invention.

Further, the computer program element may be able to provide all necessary steps to complete the flow of an exemplary embodiment of the method as described above.

According to a further exemplary embodiment of the present invention, computer-readable media, such as a CD-ROM, a USB-disk, etc., are proposed, wherein the computer-readable media have stored thereon computer program elements, which are described by the preceding sections.

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.

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 the method according to of the previously described embodiments of the present invention.

In particular, some embodiments are described with reference to method type claims and other embodiments are described with reference to apparatus type claims however, unless otherwise stated a person skilled in the art will deduce from the above and the following description that in addition to any combination of features belonging to types of subject matter also any combination between features relating to different subject matters is considered to be disclosed in the present application.

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 the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

The word "comprising" does not exclude other elements or steps and the words "" or "" do not exclude a plurality.A single processor or other unit may fulfill the functions of several items recited in the claims.