Visualization of a medical device

Abstract

Method for visualizing the position of a medical object (O) in a body (K), comprising the steps: - Providing a stack (S) of sectional images (SB0, SB1, SB2, SB3, SB4) through the body (K) recorded by means of a magnetic resonance imaging system (1), - cross-sectional image-specific coding of at least some of the various cross-sectional images (SB0, SB1, SB2, SB3, SB4), whereby for coding purposes, pixels of a cross-sectional image (SB0, SB1, SB2, SB3, SB4) receive a coding associated with this cross-sectional image (SB0, SB1, SB2, SB3, SB4), - Creating a combination image (KB) from a combination of a number of coded sectional images (SB1b, SB2w, SB3r) from the stack (S), wherein to obtain the combination image, the pixels of different sectional images (SB0, SB1, SB2, SB3, SB4) which lie in a predetermined projection direction (PR) are combined with one another using a predetermined combination function, - Display of the combination image (KB).

Description

[0001] The invention relates to a method for visualizing the position of a medical object, a related visualization device, a control device for controlling a magnetic resonance imaging system, and a magnetic resonance imaging system with such a control device.

[0002] In a magnetic resonance imaging system, also known as a magnetic resonance imaging system, the body to be examined is typically exposed to a relatively high basic magnetic field, for example, 1, 5, 3, or 7 Tesla, using a basic field magnet system. A gradient system is also used to create a magnetic field gradient. High-frequency excitation signals (RF signals) are then emitted via a radio-frequency transmission system using suitable antenna devices. This is intended to cause the nuclear spins of certain atoms resonantly excited by this radio-frequency field to be tilted by a defined flip angle relative to the magnetic field lines of the basic magnetic field. During the relaxation of the nuclear spins, high-frequency signals, so-called magnetic resonance signals, are emitted, which are received by suitable receiving antennas and then further processed. The desired image data can then be reconstructed from the raw data thus acquired.

[0003] For a specific measurement, a specific pulse sequence must be emitted. This consists of a series of radio-frequency pulses, in particular excitation pulses and refocusing pulses, as well as gradient pulses that are to be emitted in different spatial directions in a coordinated manner. Readout windows must be set to match the timing of this. These specify the time periods in which the induced magnetic resonance signals are acquired. The timing within the sequence, i.e. the time intervals at which different pulses follow one another, is particularly crucial for imaging. Many of the control parameters are usually defined in a so-called measurement protocol, which is created in advance and can be retrieved from a memory for a specific measurement, for example, and modified on-site by the operator if necessary. The operator can then enter additional control parameters such as a specific slice spacing of a stack of slices to be measured, a slice thickness, etc.can be specified. Based on all these control parameters, a pulse sequence, also known as a measurement sequence, is then calculated.

[0004] Due to the relatively strict timing of the pulse sequences, a measurement time must be estimated for the acquisition of image data, the duration of which cannot be shortened arbitrarily.

[0005] Therefore, capturing multiple slices to cover large body volumes is generally not possible in real time. This is particularly true when tracking a medical device, such as a catheter, within the body or verifying its current position, or is only possible with considerable technical effort. Acquiring larger 3D volumes or thicker slices of 1 to 2 cm instead of several thinner slices of 1 to 3 mm would also be unhelpful, as these are also time-consuming to create and there is also a risk that the object, especially a thin catheter, can no longer be detected because its signal component is essentially lost in the thick volume or layer.

[0006] Methods in which magnetic resonance imaging is performed during interventional procedures are known, for example, from DE102015215476A1, from US20150294082A1, from US 20150258349A1, from DE102014218445A1 and from DE102014218454A1.

[0007] From WO 2014 / 001 974 A2, a magnetic resonance system for guiding a needle or shaft to a target in a patient is known. The system comprises a user interface with a frame for positioning on a patient, with an opening above the entry point of a planned trajectory, extending from the entry point to the target. The user interface further comprises one or more visible markers on the frame around the opening. The visible marker indicates a deviation of the shaft or needle from the planned trajectory or a real-time position of a slice of the real-time MR image.

[0008] It is an object of the present invention to provide a method, a visualization device and a corresponding control device for controlling a magnetic resonance imaging system, with which the disadvantages described above are avoided.

[0009] This object is achieved by a method according to claim 1, by a visualization device according to claim 10 and by a control device according to claim 11 and a magnetic resonance imaging system according to claim 12.

[0010] The inventive method for visualizing the position of a medical device allows the user to easily display or detect the position of this object, e.g., the catheter, in the body. The inventive visualization method comprises the following steps: a) Provision of a stack of cross-sectional images through the body acquired using a magnetic resonance imaging system. Such cross-sectional images are acquired in multiple layers of the body, as described in the introductory section, and are initially available as acquisition data and, after standard processing, as image data. The term "stack" indicates that the image planes of the cross-sectional images, i.e., the sectional planes in which these images were acquired, are parallel to each other and that the images represent successive sectional planes within the body.

[0011] At least two, particularly preferably at least three, cross-sectional images are acquired, in particular images from three directly adjacent sectional planes. Care should preferably be taken to ensure that the sectional plane runs in a plane approximately parallel to the longitudinal axis of the medical device, which will be explained in more detail below.

[0012] b) Next, possibly after preprocessing the images, a cross-sectional image-specific coding of at least one part, preferably at least two, of the various cross-sectional images takes place. This cross-sectional image-specific coding is preferably a visual coding, particularly preferably a color coding. Pixels, in particular all pixels, of a coded cross-sectional image receive a coding assigned to this cross-sectional image, at least if they have a certain intensity. The assigned coding is preferably characteristic of the cross-sectional images in such a way that the relative position of a cross-sectional image in the part of the stack under consideration to the other cross-sectional images under consideration always has a comparable coding. For example, the topmost cross-sectional images in a (partial) stack under consideration are coded comparably, and the bottommost cross-sectional images are likewise coded.

[0013] The assignment of the unique code to the individual slices can preferably be freely chosen. Since slices typically consist of grayscale, the individual slices are marked, for example, by coloring them. For example, if there are three slices, the top slice in the stack is colored red, the middle slice is colored white, and the bottom slice is colored blue. This order is also freely selectable.

[0014] c) A combination image is then created by combining a number of coded cross-sectional images from the stack. Depending on the type of combination, this combination can also be referred to as a type of projection, and the resulting image as a "projection image." As a rule, a projection direction is preferably specified which runs through the stack in plan view, in particular orthogonal to the cross-sectional images, and which combines all areas (pixels) that lie one behind the other in this projection direction. In a particularly preferred case, in which the cross-sectional images each have the same format and the same number of pixels, pixels at the same positions in the cross-sectional images (same image coordinates) are combined, or a projection of pixels whose position is identical in the different cross-sectional images is carried out.

[0015] d) The combination image or projection image is then displayed. Although this combination image is two-dimensional, the position of the medical instrument can be easily determined from the image-specific coding. Using the example given above with the three cross-sectional images, the top one is coded red, the middle one white, and the bottom one blue, a medical object displayed in white will lie exactly in the center of the stack, i.e., exactly between the outermost images. If the medical object is colored blue or red, it will lie at the edge of the stack. A red color indicates that it is too high up in the stack, and a blue color indicates that it is too far down.It's important to note that the coded representation of the object alone does not provide direct information about the position of the medical device within the body. However, the user of the magnetic resonance imaging system learns how to adjust the sectional planes for further observation of the object. However, the position of the object within the body can easily be determined from the remaining image information of the combined image. Due to their coding, the image areas of the body structures also contain deep genetic information, even though they are only a 2D representation.

[0016] With regard to the invention, it should be noted that it is suitable both for locating the medical object within a body and aligning the cross-sectional plane according to the object's dimensions, as well as for tracking the object as it moves through the body. This is achieved by applying the method multiple times, i.e., repeatedly acquiring a stack of cross-sectional images, encoding them, and creating the corresponding combined image. Based on the combined image, the magnetic resonance imaging system can be controlled, and the next stack can then be acquired.

[0017] Since only at least two, or preferably at least three, cross-sectional images need to be acquired per scan, which takes relatively little time, even tracking in near real time is possible. With faster measurement methods, multiple cross-sectional images can also be acquired, allowing for better classification of the object. However, the combined image should preferably not be created from too many cross-sectional images. It is particularly preferred to combine no more than 10 cross-sectional images. For up to 10 images, it can be ensured that depth information does not become blurred due to the different coding.

[0018] A visualization device according to the invention for visualizing the position of a medical object in a body, in particular according to the method according to the invention, comprises the following components. a) An image interface for providing a stack of cross-sectional images acquired using a magnetic resonance imaging system. This can also be a pure software interface that receives data from other units or software modules, e.g., an image reconstruction unit. This applies in particular if the visualization device itself is part of a control device of the magnetic resonance imaging system. b) A coding unit for the slice-specific coding of at least one part, preferably at least two, of the various slices. This coding unit is designed, as already described above, to code pixels of a slice with a code assigned to the slice or, as explained above, with a code characteristic of this slice. This can be done, for example, by characteristically coloring the slices, which allows conclusions to be drawn about the position of the slices in the stack and, if several stacks are considered, contains comparable codes for corresponding positions of the slices in the stack. c) An image creation unit for creating a combination image from a combination of the coded slice images from the stack, as already explained above.

[0019] The coding unit and the image creation unit can in particular be part of a common computing unit which encodes and combines the pixels by means of calculation and conversion, or carries out a projection. d) An output interface for outputting the combination image for display.

[0020] The device may also have an output unit, such as a display. If it is part of a medical technology system, such as a magnetic resonance imaging system, it can also use the system's output units via the output interface.

[0021] The visualization device preferably additionally comprises a recognition unit for automatically recognizing the medical device. Such a recognition unit automatically recognizes the medical device in the image data generated by the magnetic resonance imaging system or in the cross-sectional images or the combined image.

[0022] A control device according to the invention for controlling a magnetic resonance imaging system comprises a visualization device according to the invention and preferably an aforementioned recognition unit. It is also particularly preferably designed for automatically tracking the acquisition of a further stack of cross-sectional images, so that the medical object is substantially captured by the further stack of cross-sectional images (preferably at least with the most relevant part, usually a front part with which the object is inserted into the body), i.e., is recognizable in at least one of the cross-sectional images.

[0023] Particularly preferably, the tracking is carried out such that the medical object is located substantially within the further stack of cross-sectional images. With regard to the stack, “within” means that the medical object can be seen substantially in a number of cross-sectional images which lie between the cross-sectional images at the top and bottom edges of the stack. The “number” can also be regarded as a single cross-sectional image here. In the aforementioned example with three cross-sectional images, the medical object should therefore preferably always be seen substantially in the middle cross-sectional image. If this is not the case, the recording position of the next stack of cross-sectional images will preferably be adjusted accordingly by the control device.

[0024] A magnetic resonance imaging system according to the invention comprises a control device according to the invention.

[0025] In a stack according to the invention of at least three sectional images acquired by means of a magnetic resonance imaging system, at least two of these sectional images have a coding in such a form that pixels of each encoded sectional image contain a coding characteristic of the sectional image in question or its position in the stack.

[0026] It is not absolutely necessary for all slices to be coded differently. Furthermore, leaving some slices in a stack in their original state, e.g. not coloring them, can be regarded as coding within the stack if other slices in the stack are coded in such a way that they differ from the original slices. For example, it may be sufficient for only those slices on the outside of the stack to be coded, and for the slices inside to continue to display their shades of gray. In particular, the slices inside the stack can all have the same coding, e.g. be white or in grayscale with no coding, while the top slice in the stack is blue and the bottom one is red.

[0027] However, it is preferable for all cross-sectional images to have different coding, as this allows for particularly good position detection of the medical device within the stack when there are more than three cross-sectional images, and its orientation can be more accurately determined. For example, with five cross-sectional images, the coding can run in the form of a color gradient from blue for the top cross-sectional image, to light blue, followed by white for the middle cross-sectional image, then light red to red for the bottom cross-sectional image.

[0028] Another possible color coding is based on the standardized color coding according to diffusion tensor imaging. Diffusion tensor imaging (abbreviated DTI from English diffusion tensor imaging or DT-MRI from diffusion tensor magnetic resonance imaging) is a frequently used variant of diffusion-weighted magnetic resonance imaging, which also records the directionality of diffusion. For each pixel, not only the intensity is recorded, but also a tensor that describes the three-dimensional diffusion behavior. The color coding preferably depends on the anatomical orientation of the stack. Each of the three directions is assigned one of the primary colors red, green, and blue, which are mixed for directions in between. Pixels without a clear main direction may appear gray. Red coding is preferred in the left-right direction, green in the anterior-superior direction, and blue in the inferior-superior direction.

[0029] A large part of the aforementioned components of the visualization device and / or the control device, in particular the coding unit and the image creation unit and, if applicable, the optional recognition unit, can be implemented entirely or partially in the form of software modules in a processor of a corresponding control device. A largely software-based implementation has the advantage that even previously used control devices can be easily retrofitted with a software update in order to operate in the manner according to the invention. In this respect, the object is also achieved by a corresponding computer program product with a computer program that is directly integrated into a memory device of a visualization device ora control device of a magnetic resonance imaging system, with program sections for executing all steps of the method according to the invention when the program is executed in the visualization device or control device. Such a computer program product may, in addition to the computer program, optionally include additional components such as documentation and / or additional components, including hardware components such as hardware keys (dongles, etc.) for using the software.

[0030] A computer-readable medium, such as a memory stick, a hard drive, or another portable or permanently installed data storage device, can be used for transport to the visualization device or control unit and / or for storage on or in the control unit / visualization device. The computer-readable medium stores the program sections of the computer program that can be read and executed by a computer unit of the control unit or visualization device. For this purpose, the computer unit can, for example, have one or more cooperating microprocessors or the like.

[0031] Further, particularly advantageous embodiments and developments of the invention emerge from the dependent claims and the following description, wherein the independent claims of one claim category can also be developed analogously to the dependent claims of another claim category and, in particular, individual features of different embodiments or variants can be combined to form new embodiments or variants.

[0032] The cross-sectional image-specific coding can be performed in various ways. However, an embodiment of the method according to the invention is preferred in which the cross-sectional image-specific coding is a visual coding, as already mentioned above.

[0033] Typically, the magnetic resonance signal is represented as a variation of the brightness signal, often by a grayscale graphic. Therefore, color coding is preferred for the depth information, i.e., the information about the cross-sectional image or its position in the stack. When color-coding a cross-sectional image, the pixels of this cross-sectional image are preferably color-coded with a color assigned to the respective cross-sectional image or its position in the stack, and thus characteristic of the respective cross-sectional image or said position of the cross-sectional image. For clarification, reference is made to the above example with three cross-sectional images, in which the top cross-sectional image was always coded blue, the bottom always red, and the middle one always white.

[0034] In principle, however, the coding described above could also be applied in a reversed manner, namely in a form in which the magnetic resonance signal is represented in the form of colored image information and the depth information is brightness-coded.

[0035] In general, it would also be possible for the two aforementioned pieces of information, image information and depth information, to be encoded in the same way, but with different colors or intensity ranges, or for the types of representation or encoding to overlap. For example, the magnetic resonance signal can be displayed in the red channel, and the encoding of the cross-sectional images can be in the blue channel.

[0036] To obtain the combined image, the pixels of different sectional images that lie one behind the other or one above the other in a predetermined projection direction are preferably combined with a predetermined combination function. As already mentioned above, a projection direction orthogonal to the sectional images of the stack is preferred, whereby a combination of the pixels lying one above the other in the stack (pixels with the same image coordinates in the respective sectional images) takes place together with an adoption of the respective coding of the respective pixels.

[0037] The combination function preferably comprises an intensity value-dependent projection, such as a maximum or minimum intensity projection, a projection of pixels in a predetermined intensity interval or a peak-to-peak projection, i.e. a projection in which the maximum intensity difference of the pixels is calculated.

[0038] According to a preferred combination function, a mask image, e.g., a color mask, is created from the coded sectional images, which is then combined with a projection image based, in particular, on the uncoded sectional images. This mask image comprises the coding information of the combined pixels of the respective sectional images, and the projection image comprises intensity information of the combined pixels.

[0039] According to a preferred embodiment, the pixels of the sectional images are coded according to the invention with the coding assigned to the respective sectional image, and a mask image is created in which each pixel at a specific position comprises proportional coding information of the pixels of the sectional images at the corresponding position with regard to their intensity. In particular, each pixel of the mask image is normalized with regard to the overall intensity, so that the intensity of all pixels of the mask image is the same. In the example with three sectional images, each pixel triplet of an image coordinate of the three sectional images is added to a mask image pixel with regard to its color value and preferably normalized to a specific intensity. A mask image is obtained in which the color of each pixel indicates the proportion of the intensity influence of the individual sectional images at this position.Before coding, the slice images can be inverted if this seems appropriate.

[0040] According to a preferred embodiment, the pixels of the cross-sectional images are projected onto one another in a suitable manner, creating a projection image in which each pixel of the projection image indicates the pixel(s) of the cross-sectional images that dominate there in terms of their intensity. This is preferably done using the aforementioned projection types, e.g., a peak-to-peak projection.

[0041] Now, in a preferred further step, the mask image and the projection image are combined, e.g. by multiplying the values ​​of the individual pixels.

[0042] Preferably, the pixel values ​​of the cross-sectional images and / or the type of projection are adapted to anatomical structures and / or the medical object. Certain anatomical structures and / or the medical object are preferably represented and thus identified with different colors in each cross-sectional image. An example of this is given above in the description of different visual codings. In this case, a preferred visual coding of the pixels of the cross-sectional images or information in the cross-sectional image planes is preferably brightness coding.

[0043] Preferably, further graphical preprocessing of the encoded cross-sectional images is performed before combining them, in particular before encoding. Graphical preprocessing techniques from the group of edge enhancement ("edge detection filters" such as Sobel, Prewitt-Compass, Roberts, Laplace, or differential), posterization, deflickering, blurring, sharpening, inversion, brightness modification, and contrast modification are preferred. A Hough transform can also be used as part of preprocessing, which—as explained below—can be advantageous for automatic detection of image elements.

[0044] As already mentioned above, the medical device is preferably automatically recognized. For this purpose, the visualization device or the control device preferably comprises a recognition unit.

[0045] Recognition of the medical object is preferably based on a comparison with reference images. For example, cross-sectional images without the medical object are subtracted from cross-sectional images with the medical object with regard to the pixel intensity values. Furthermore, the use of the Hough transformation is preferred for recognition. For example, by exploiting knowledge of the geometry of the medical object, a Hough transformation could be used to recognize and highlight straight lines, circles, or other geometric shapes. Likewise, the geometry of the medical object can be combined with factors, particularly if the object is equipped with a marker element such as a contrast agent or small MR receiver coils (coils for detection by a magnetic resonance imaging system).The areas of such marking elements can be recognized as particularly bright points in the grayscale image and can be used as prominent start / end points with Active Contours algorithms (algorithms for active contour detection).

[0046] Automatic recognition of elements, e.g. the medical object, in the individual images can also be carried out before the combination image is created in order to use the information obtained in the combination, for example to limit the combination to the relevant image areas around the medical object.

[0047] Preferably, when a further stack of cross-sectional images is acquired, as also mentioned above, the cross-sectional planes are automatically tracked. This tracking preferably occurs in such a way that the position of the medical object is determined inside the stack or at its edge, and for a further acquisition of a stack, the planes of the cross-sectional images are changed such that the position of the medical object determined in this way moves further towards the center of the newly acquired stack or is selected as the new center point. It is particularly preferred to select the cross-sectional planes such that the medical object is located substantially inside the further stack of cross-sectional images, i.e., not at the edge of the stack, but somewhere inside it.With three slices, this would be the middle slice; with seven slices, with slices 1 and 7 at the edge, this would be one or more of slices 2 to 6.

[0048] The orientation of the cross-sectional images is preferably aligned in such a way that an axis of greatest extent of the medical object, the expected path of which is predetermined, for example, by the course of a hollow organ into which the object is inserted, runs essentially in the plane of the cross-sectional images. The term “essentially” means that a tilt of the plane of the cross-sectional images with respect to this axis of the medical object is less than 30°, preferably less than 10°, particularly preferably less than 5°. The aim is for the object to be aligned parallel to the cross-sectional planes. The orientation of the cross-sectional images is preferably adjusted automatically in such a way that the pixels representing the medical object are encoded as uniformly as possible.The statement "as uniform as possible coding" refers to the change in coding that the medical device undergoes when it is tilted to the cutting plane and is therefore partially displayed in adjacent cross-sectional images. The coding should be so uniform that the above-mentioned maximum tilt (30° or 10° or 5°) is not exceeded. In the example with the three cross-sectional images in red, white and blue, an obliquely arranged, elongated medical device would, for example, be red at one end, white in the middle and blue at the other end. Due to the known length of the medical device and the known distance between the cutting planes, the angle of the tilt can be determined from the change in coding.

[0049] Preferably, graphical post-processing of the combined image is performed to improve the representation of the medical device. This is done based on one or more of the following assumptions. a) There should be no overlap of structures of the medical device in two adjacent cross-sectional images. This would be the case, for example, if the medical device is thinner than the distance between two cross-sectional images and is parallel to the cross-sectional planes. b) The medical device should have a continuous contour. This is the case if the device consists of a single, continuous body, which is true for most medical devices. c) The medical device should exhibit a uniform gradient across its contour. This would be the case if the device has a uniform surface without protrusions or depressions. For example, a uniform gradient can be expected along a catheter, with a sharp demarcation from the surrounding tissue perpendicular to its axis, especially at its tip.

[0050] Preferably, the position of the stack of cross-sectional images is chosen in a special way, at least during the initial acquisition or “initial recording” before or at the start of a procedure in which the object is inserted into the body, i.e. at the start of the measurement sequence, in order to increase the probability that the object will also be captured by the layer stack of the initial recording. The location in the body at which the cross-sectional images are acquired and their orientation can preferably be determined based on the presumed position of the medical object, so that this lies inside the stack. The orientation of the cross-sectional images is chosen so that it corresponds to the presumed orientation of the longest dimension of the medical object. If, for example, the medical object is to be located in a hollow organ, such as a blood vessel, or is to be inserted into it, the approximate position of the hollow organ orblood vessel and its orientation in the body are known due to previous measurements or general knowledge of human anatomy. The cross-sectional images can therefore be acquired specifically at the location of this hollow organ with the hollow organ running in the plane of the cross-sectional images. The medical instrument will most likely then be in a good position in the stack. For this reason, it is preferable to take more tomographic images for the initial acquisition than later on when the orientation or position of the object is already known from the preliminary measurement. This initial acquisition is usually taken at a time when the measurement time is not yet critical and there is still plenty of time left to select the appropriate position and orientation.

[0051] With this approach, the stack preferably initially includes more slice images than are intended to be used in the combination image (the initial acquisition). This allows multiple initial combination images to be created from adjacent, coded slice images. Preferably, a corresponding coding is always applied to the respective slice images, so that for different combination images, the xth slice image always has a comparable coding. Thus, one and the same slice image is coded differently for different combination images depending on its position in the stack.

[0052] The medical device object is located on the initial combination images, and the initial combination image in which the medical device object is located within the stack is selected. The respective settings that were present for the selected initial combination image when acquiring the respective cross-sectional images are used as the settings for acquiring the next stack.

[0053] A significant advantage of the procedure is that only a few cross-sectional images with small thicknesses need to be acquired, e.g., thicknesses of approximately 1 to 3 mm. Time-consuming images of large volumes, e.g., in the range of 1 to 2 cm, are not necessary.

[0054] The invention is explained in more detail below with reference to the accompanying figures using exemplary embodiments. In the various figures, identical components are provided with identical reference numerals. The figures are generally not to scale. They are not essential for understanding the invention, but can facilitate understanding. They show: Fig. 1 a flowchart to explain the sequence of an example of a preferred embodiment of a method according to the invention, Fig. 2 a detailed flow chart to explain the process of a preferred concrete embodiment of the process according to Fig. 1, Fig. 3 a simple flow chart for the formation of different combination images from a selection of three sectional images from a total of five sectional images, Fig. 4 a simple flow chart for the formation of a combination image from the five sectional images from Fig. 3, Fig. 5 a schematic representation of a magnetic resonance imaging system according to an embodiment of the invention, Fig. 6 a schematic representation of the evaluation unit in Fig. 5.

[0055] In the Fig. In the example of a preferred method sequence shown in Figure 1, a stack S comprising three cross-sectional images SB1, SB2, SB, SB3, representing adjacent, parallel sections through a heart, is provided in step I. In the middle cross-sectional image SB2, the medical device O can be seen in the lower right corner.

[0056] Arrows are intended to illustrate the further processing of the data, with dashed arrows symbolizing optional processing.

[0057] In step II, the color coding of the slice images takes place as already explained above, as is illustrated by the palette shown. In the detailed Fig. 2, Step II, shows, for example, that each slice image, or rather its pixels, receives an individual color marking. For example, the top slice image can be colored blue, the middle one white, and the bottom slice image red, as in Fig. 2 is shown.

[0058] Optionally, as in Fig. 2, before the color coding in an intermediate step Ia, an inversion of the slice images takes place and the inverted slice images SB1i, SB2i, SB3i are color-coded, which leads to the color-coded slice images SB1b (blue), SB2w (white), SB3r (red) in Fig. 2. In this case, this inversion serves to better emphasize the contours. Theoretically, further graphic preprocessing is possible, such as sharpening the edges.

[0059] In step III, a combination to a combination image KB takes place. In this case, the projection direction is as in Fig. 1 on the stack S orthogonal to the plane of the slice images SB1, SB2, SB3. Pixels at the same slice image coordinates are thus combined with each other and result in a pixel in the combination image KB or initially in a mask image FM as in step IIIa in Fig. 2 is shown.

[0060] At the Fig. 2, the combination step III comprises Fig. 1 three sub-steps IIIa, IIIb and IIIc.

[0061] In step IIIa, the original slice images SB1, SB2, and SB3 are accessed directly, and a peak-to-peak projection image PTP is created. Theoretically, the inverted slice images SB1i, SB2i, and SB3i could also be used for this purpose. This highlights the maximum differences in the pixel intensities of the individual slice images SB1, SB2, and SB3. Areas of large differences are imaged brighter than areas of small differences. It should be noted that this peak-to-peak projection image PTP contains no information about which of the slice images SB1, SB2, and SB3 has the greatest intensity or which of the slice images SB1, SB2, and SB3 has the greatest influence on the respective peak-to-peak value of an image coordinate.

[0062] This information is obtained from the mask image FM, which is created in step IIIb from the color-coded slice images SB1b, SB2w, and SB3r. In the color mask image FM, the intensity of each pixel is normalized to a common value, and each pixel proportionally comprises the color values ​​of the pixels in the slice images SB1b, SB2w, and SB3r. This color mask image FM thus shows which pixel of a slice image SB1, SB2, and SB3 is dominant.

[0063] In step IIIc, the peak-to-peak projection image (PTP) is combined with the color mask image (FM). This is preferably done by multiplying the respective intensities pixel by pixel. The peak-to-peak projection image (PTP) is colored according to the intensities in the individual cross-sectional images.

[0064] At the end, in step IV, the Fig. 1 and Fig. 2 the calculated combination image KB is output.

[0065] It is not necessary to take three slice images SB1, SB2, SB3. In principle, two slice images are sufficient. As shown in the Fig. 3 and Fig. 4, several slice images SB0, SB1, SB2, SB3, SB4 can also be recorded. From these slice images, several different combination images KB1, KB, KB2 can be created, each from three consecutive slice images SB0, SB1, SB2, SB3, SB4, as shown in Fig. 3, which is very suitable for locating the medical object O.

[0066] To localize or locate the medical device, the user can use the various combination images KB1, KB, KB2 and see which of the combination images KB1, KB, KB2 the medical device O has a coding, in this case a color, that indicates that it is located within the stack. This stack is then selected. Scrolling through the individual combination images KB1, KB, KB2 can be done relatively quickly and easily. To subsequently track the medical device, the settings of the selected stack can be selected—that is, the settings that were used to acquire the relevant cross-sectional images of this stack.For example, for the respective combination images KB1, KB, and KB2, the coding for the cross-sectional images is selected such that the topmost cross-sectional image in the sub-stack under consideration is always coded blue, the bottom one is always coded red, and the middle one is always coded white. The combination image KB is then advantageously selected in which the medical device object appears white, i.e., is located in the middle.

[0067] In Fig. 3 For a better comparison of the combination images KB1, KB, and KB2, it is advisable to always code the slice images used for this purpose so that identical positions each have the same coding. For example, slice image SB2 is colored red to create the upper combination image KB1, colored white to create the middle combination image KB, and colored blue to create the lower combination image KB2.

[0068] Likewise, the Fig. 3 sectional images SB0, SB1, SB2, SB3, SB4 shown at the beginning can also be combined into a single combination image KB3, as in Fig. 4 is shown.

[0069] In Fig. 4 For better comparison of the combination images KB1, KB, KB2, it is advisable to code all of the cross-sectional images used for this purpose differently, or at least the two outer cross-sectional images SB0 (e.g. blue) and SB4 (e.g. red), so that when the medical object O leaves the stack it can be reliably detected by its coloring. The inner cross-sectional images SB1, SB2, SB3 could theoretically all be coded similarly, e.g. white or without coloring. However, a color gradient can also be selected preferably, as already described above. For example, with five cross-sectional images the coding can run from blue for the top cross-sectional image, via light blue, followed by white for the middle cross-sectional image, then via light red to red for the bottom cross-sectional image.

[0070] In Fig. Figure 5 shows a roughly schematic representation of a magnetic resonance imaging system 1. It comprises, on the one hand, the actual magnetic resonance scanner 2 or a magnetic resonance tomograph 2 with an examination room 3 or patient tunnel, in which a patient or test subject is positioned on a couch 8, in whose body K the actual medical device O, here a catheter O, is located, which is to be visualized within the scope of the method according to the invention.

[0071] The magnetic resonance scanner 2 is conventionally equipped with a basic field magnet system 4, a gradient system 6, an RF transmit antenna system 5, and an RF receive antenna system 7. In the illustrated embodiment, the RF transmit antenna system 5 is a whole-body coil permanently installed in the magnetic resonance scanner 2, whereas the RF receive antenna system 7 consists of local coils arranged on the patient or test subject (symbolized in this figure only by a single local coil). In principle, however, the whole-body coil can also be used as an RF receive antenna system and the local coils as an RF transmit antenna system, provided these coils can each be switched to different operating modes. The basic field magnet system 4 is conventionally designed to generate a basic magnetic field in the longitudinal direction of the patient, i.e., along the longitudinal axis of the magnetic resonance scanner 2, which runs in the z-direction.The gradient system 6 comprises, in the usual way, individually controllable gradient coils for independently switching gradients in the x, y, or z directions. Furthermore, the magnetic resonance scanner 2 contains shim coils (not shown), which can be designed in the usual way.

[0072] In the Fig. The MR system shown in Figure 5 is a whole-body system with a patient tunnel into which a patient can be completely inserted. In principle, however, the invention can also be used with other MR systems, e.g., with a C-shaped housing that is open at the side. The only essential requirement is that appropriate images of the medical object O can be taken. In this way, this object, which could be a catheter, for example, can be tracked "online," i.e., in near real time, with regard to its course and movement within the body, even during an examination.

[0073] The MR system 1 further comprises a central control device 13, which is used to control the MR system 1. This central control device 13 comprises a sequence control unit 14. This controls the sequence of radio-frequency pulses (RF pulses) and gradient pulses as a function of a selected pulse sequence PS or a sequence of multiple pulse sequences for acquiring multiple slices in a volume region of interest of the examination subject within a measurement session. Such a pulse sequence PS can, for example, be specified and parameterized within a measurement or control protocol P. Typically, different control protocols P for different measurements or measurement sessions are stored in a memory 19 and can be selected by an operator (and modified if necessary) and then used to perform the measurement.

[0074] To output the individual RF pulses of a pulse sequence PS, the central control device 13 has a radio-frequency transmitter 15, which generates and amplifies the RF pulses and feeds them into the RF transmit antenna system 5 via a suitable interface (not shown in detail). To control the gradient coils of the gradient system 6 in order to switch the gradient pulses appropriately according to the predetermined pulse sequence PS, the control device 13 has a gradient system interface 16. The sequence control unit 14 communicates in a suitable manner, e.g., by transmitting sequence control data SD, with the radio-frequency transmitter 15 and the gradient system interface 16 to execute the pulse sequences PS.

[0075] The control device 13 also has a radio-frequency receiving device 17 (which also communicates in a suitable manner with the sequence control unit 14) in order to receive magnetic resonance signals within the readout window specified by the pulse sequence PS in a coordinated manner by means of the RF receiving antenna system 7 and thus to acquire the raw data.

[0076] A reconstruction unit 18 receives the acquired raw data and reconstructs magnetic resonance image data from it. This reconstruction is also generally performed based on parameters that may be specified in the respective measurement or control protocol P. This image data can then be stored, for example, in a memory 19.

[0077] How suitable raw data can be acquired in detail by irradiating RF pulses and switching gradient pulses and how MR images (magnetic resonance images, i.e. the cross-sectional images required in the procedure) can be reconstructed from them is generally known to the person skilled in the art and will therefore not be explained in more detail here.

[0078] The required sectional images can then be transferred to an evaluation unit 20, which here has the visualization device 212 for carrying out the method according to the invention. The visualization device 21 and the evaluation unit 20 are in Fig. 6 is shown in more detail.

[0079] The visualization device 21 comprises an image interface 22 for receiving the cross-sectional images, an image output interface 22a for outputting the combination images KB, a coding unit 23 for individually coding the cross-sectional images, and an image creation unit 24 for creating the combination images. The arrows in the figure represent data flows. For example, both the coding unit 23 and the image creation unit 24 can access the image interface 22 to obtain cross-sectional image data; however, it is also possible for the image creation unit 24 to obtain its data solely from the coding unit, which is indicated by a dashed arrow to the image interface 22.

[0080] All the units of the visualization device 21 can be present as software modules.

[0081] Optionally, the evaluation unit 20 comprises a recognition unit 25, which can also be present as a standalone unit in the control device 13 or can be part of the visualization unit 21. This recognition unit 25 automatically recognizes the medical object O and, if necessary, via its coding and the known position of the planes of the cross-sectional images SB1, SB2, SB3, also its orientation relative to the cross-sectional images and generates information on how the positioning and, if necessary, the orientation of the cross-sectional planes should be changed for a further acquisition of a new stack S of cross-sectional images.

[0082] The recognition unit 25 can in turn be present as a software module.

[0083] The data required for this purpose, for example the coordinates of the new desired layer positions (which may also be defined only relative to the current layers), are transferred here via the control interface 20a to the other components of the control device 13, in particular the sequence control unit 14.

[0084] The central control unit 13 can be operated via a terminal 11 with an input unit 10 and a display unit 9, via which the entire MR system 1 can also be operated by an operator. MR images can also be displayed on the display unit 9, and using the input unit 10, optionally in combination with the display unit 9, measurements can be planned and started, and in particular, control protocols P can be selected and modified if necessary.

[0085] Likewise, the combination images KB can be output on the display unit 9 of the terminal 11, and the recording of cross-sectional images can be controlled based on the information of the combination images KB.

[0086] The visualization device 21 or the evaluation unit 20 do not necessarily have to be part of the control device 13. For example, one or both components can also be located in an evaluation computer or a diagnostic station, which are connected to the control device 13, for example, via a radiological network. However, it is advantageous if these components are located directly in the control device 13, as this facilitates quick and uncomplicated tracking and online monitoring during the procedure.

[0087] The magnetic resonance imaging system 1 according to the invention and in particular the control device 13 can furthermore have a plurality of further components, not shown in detail here, but usually present in such systems, such as a network interface in order to connect the entire system to a network and to be able to exchange raw data and / or image data or parameter maps, but also further data, such as patient-relevant data or control protocols.

[0088] Finally, it should be noted once again that the methods described in detail above, as well as the magnetic resonance imaging system illustrated, are merely exemplary embodiments that can be modified in a variety of ways by those skilled in the art without departing from the scope of the invention. Furthermore, the use of the indefinite articles "a" or "an" does not exclude the possibility that the respective features may be present in multiple instances. Likewise, the terms "unit" and "module" do not exclude the possibility that the respective components consist of several interacting subcomponents, which may also be spatially distributed.

Claims

[1] Method for visualising the position of a medical object (O) in a body (K), comprising the steps: - Providing a stack (S) of sectional images (SB0, SB1, SB2, SB3, SB4) through the body (K) recorded by means of a magnetic resonance imaging system (1), - cross-sectional image-specific coding of at least some of the various cross-sectional images (SB0, SB1, SB2, SB3, SB4), whereby for coding purposes, pixels of a cross-sectional image (SB0, SB1, SB2, SB3, SB4) receive a coding associated with this cross-sectional image (SB0, SB1, SB2, SB3, SB4), - Creating a combination image (KB) from a combination of a number of coded sectional images (SB1b, SB2w, SB3r) from the stack (S), wherein to obtain the combination image, the pixels of different sectional images (SB0, SB1, SB2, SB3, SB4) which lie in a predetermined projection direction (PR) are combined with one another using a predetermined combination function, - Display of the combination image (KB). [2] Method according to claim 1, wherein the cross-sectional image-specific coding is a visual coding, preferably a color coding, and preferably the pixels of a cross-sectional image (SB0, SB1, SB2, SB3, SB4) are color-coded with a color assigned to the respective cross-sectional image (SB0, SB1, SB2, SB3, SB4). [3] Method according to one of the preceding claims, wherein the combination function comprises an intensity value-dependent projection and wherein particularly preferably a mask image (FM) is created from the coded sectional images (SB1b, SB2w, SB3r), which is combined with a projection image (PTP) which is based on the uncoded sectional images (SB0, SB1, SB2, SB3, SB4). [4] Method according to one of the preceding claims, wherein before the combination of the coded sectional images, in particular before the coding, a further graphic preprocessing of the sectional images (SB0, SB1, SB2, SB3, SB4) is carried out, preferably a graphic operation from the group of edge enhancement, Hough transformation, posterization, deflickering, blurring, sharpening, inversion, change of brightness and change of contrast. [5] Method according to one of the preceding claims, wherein an automatic recognition of the medical object (O) takes place, preferably based on a comparison with reference images or based on a Hough transformation. [6] Method according to claim 5, wherein an automatic tracking is carried out when recording a further stack (S) of sectional images (SB0, SB1, SB2, SB3, SB4), so that the medical object (O), which is essentially captured by the further stack (S) of sectional images (SB0, SB1, SB2, SB3, SB4), is preferably located within the further stack (S) of sectional images (SB0, SB1, SB2, SB3, SB4). [7] Method according to one of the preceding claims, wherein an alignment of the orientation of the sectional images (SB0, SB1, SB2, SB3, SB4) is carried out in such a way that an axis of greatest extent of the medical-technical object (O) or its expected path runs substantially in the plane of the sectional images (SB0, SB1, SB2, SB3, SB4), wherein an automatic tracking of the orientation of the sectional images (SB0, SB1, SB2, SB3, SB4) is preferably carried out in such a way that the most uniform coding possible of the pixels representing the medical-technical object (O) is sought. [8] Method according to one of the preceding claims, wherein a graphic post-processing of the combination image (KB) is carried out to improve the representation of the medical object (O), based on one or more of the assumptions that - there is no overlap of structures of the medical device (O) in two adjacent cross-sectional images (SB0, SB1, SB2, SB3, SB4), - the medical-technical object (O) has a continuous contour, - the medical object (O) has a uniform gradient over its contour. [9] Method according to one of the preceding claims, wherein the stack (S) of sectional images (SB0, SB1, SB2, SB3, SB4), in particular initially, is selected such that the presumed position of the medical-technical object (O) lies inside the stack (S) and the orientation of the sectional images (SB0, SB1, SB2, SB3, SB4) corresponds to the presumed orientation of a longest extent of the medical-technical object (O). [10] Visualization device (21) for visualizing the position of a medical object (O) in a body (K), comprising - an image interface (22) for providing a stack (S) of sectional images (SB0, SB1, SB2, SB3, SB4) recorded by means of a magnetic resonance imaging system (1), - a coding unit (23) for the slice-image-specific coding of at least some of the various slice images (SB0, SB1, SB2, SB3, SB4), wherein the coding unit is designed to encode pixels of a slice image with a coding assigned to this slice image (SB0, SB1, SB2, SB3, SB4), - an image generation unit (24) for generating a combination image (KB) from a combination of the coded sectional images (SB1b, SB2w, SB3r) from the stack (S), wherein the image generation unit (24) is designed to combine the pixels of different sectional images (SB0, SB1, SB2, SB3, SB4) lying in a predetermined projection direction (PR) with one another using a predetermined combination function to obtain the combination image, - an output interface (22a) for outputting the combination image (KB) for display. [11] Control device (13) for controlling a magnetic resonance imaging system (1) comprising a device according to claim 10. [12] Magnetic resonance imaging system (1) comprising a control device (13) according to claim 11. [13] Combination image (KB) for visualizing the position of a medical-technical object (O) in a body (K), created by a method according to one of claims 1 to 9, wherein the combination image (KB) is a projection image (PTP) of a projection of pixels of sectional images (SB0, SB1, SB2, SB3, SB4), wherein each pixel of the projection image (PTP) indicates the pixel or pixels of the sectional images (SB0, SB1, SB2, SB3, SB4) which dominate there in terms of their intensity. [14] Computer program product with a computer program which can be loaded directly into a memory device of a visualization device (21) or a control device (13) of a magnetic resonance imaging system (1), with program sections to carry out all steps of the method according to one of claims 1 to 9 when the computer program is executed in the visualization device (21) or control device (13). [15] Computer-readable medium on which program sections are stored which can be read and executed by a computer unit in order to carry out all the steps of the method according to one of claims 1 to 9 when the program sections are executed by the computer unit.

Images