Method and system for position determination during X-ray imaging

The invention relates to a method for position determination in the X-ray imaging as well as an arrangement for carrying out such a Method with an X-ray machine, a detector array having at least two Detector elements and with a marker arrangement.

An arrangement for determining the position in medical imaging is in PCT / IB 96/00384 (PHN 15775 WO) described. Two cameras can detect visible light or infrared light, there are stationary at the room a tripod mounted. At a treatment instrument are diodes of the cameras detectable emit light attached. With the cameras, the coupled position of the treatment instrument in the cameras Coordinate system are determined. This position can by means of a pre specific transformation matrix in an image position be converted, wherein the image before using computed tomography (CT) or Magnetic resonance imaging (MRI) has been detected. To achieve the above Transformation matrix for converting coordinates in the camera image coordinates to determine markers are attached to the patient during image acquisition, which are also displayed and are visible in the image. These markers then the diodes provided with treatment instrument or a approached separate, provided with diodes pointing instrument, whereby their Position is detected in the camera coordinate. This is the required compound manufactured between camera coordinates and image coordinates and the position of the Treatment instrument during treatment in the image can be displayed.

Also, in the conventional X-ray imaging, in particular in the intraoperative imaging, the exact allocation of a point in a X-ray image to a point in or on the object under examination, for example a Patient, be of great importance. The exact position of a Treatment instrument or another medical device, such as For example, a radiation therapy device is desirable. In the known A process is required that the object to be examined over longer time marker at fixed positions are installed, namely already in the imaging by CT or MR and later in the position detection means of the cameras. Also the Arrangement of the cameras on a stationary tripod for a position determination not ideal in X-ray imaging. Particularly, in the intraoperative Ray imaging with a pivoting X-ray machine would at a such an arrangement of cameras often the lines of sight of the cameras by either the X-ray machine are covered itself or by treating people.

The invention is therefore based on the object, a suitable method for Positioning in the X-ray imaging and an arrangement for specifying implementation of such a method.

The object relating to the method is achieved by the fact that<ul><li>with an X-ray machine at least one X-ray image of a Examination object is created and with the X-ray machine arranged detector arrangement, the position of the object to be examined or arranged relative to the examination object stationary coupled arrangement of markers in one with the detector array Detector coordinate system is detected,</li><li>the position of the X-ray machine in one with the object to be examined coupled object coordinate system is determined</li><li>and then the position of a pixel in an X-ray image Imaged object point is determined in the object coordinate system.</li></ul>

The position of the marker arrangement is in the same position of the X-ray machine detected, in which also the X-ray image was created. These two operations can done so at the same time. By detecting the position of the Marker arrangement in the detector coordinate system is automatically the position won the detector array in the object coordinate system, since the Marker assembly stationary relative to the object under examination is arranged and the object coordinate system fixed to the object to be examined and thus laid is coupled to the marker array. This automatic recovery of Position the marker arrangement in object coordinates from the detected position in Detector coordinates by the functionality of the of the detector array and where the marker arrangement existing position measuring system.

Since the detector array is arranged in a fixed X-ray unit, may consist of now known position of the detector array in the object coordinate system easily the position of the X-ray apparatus are determined in the object coordinate system. Preferably, in the determination of the position of the x-ray device characteristic points as the position of the focal point and the location of Imaging plane determined. Subsequently, from an association between a pixel in an x-ray and an objective point of Examination object in the object coordinate system take place. If only one single X-ray image has been detected, the position of a pixel to a corresponding object point will only be determined as a pixel a lying between the focal point and image plane of the X-ray can be assigned. Only when more, from different positions of the X-ray machine detected X-ray images, a more accurate position determination of the Object point occur.

In one embodiment of the invention it is provided that at least two detects X-rays of the object under examination from different directions be and at the same X-ray imaging, the position of the focal point and the position of the imaging plane of the X-ray apparatus in the object coordinate system be determined. the position already at two X-ray images of a Object point, which is displayed in the two X-ray images as a pixel, in Object coordinate system can be determined exactly. For example, sufficient to two X-ray images, which detects from mutually perpendicular directions were.

A further development of this method provides the invention provides that the position the object point is determined by means of two lines, the first line through the object point corresponding pixel in a first x-ray image and passes the first position of the focal point and the second line through the for Object point corresponding pixel in a second X-ray image and through the second Position of the focal point passes, wherein the object point of the intersection two lines, or as the center of the shortest link between the two Line gives. The object point can thus be very accurately by simple Calculating the intersection of two lines or by calculating a Point, which in the middle of the shortest link between the Line is, determine.

Another mode of the invention provides that with the detector array, the position of a further arrangement of markers provided the medical device is detected in the detector coordinate system and that from the position of the medical device in the detector coordinate system whose position is determined in the image coordinate system of an X-ray image. By means of certain already beginning conversion rule between Detector coordinates and object coordinates can first of the detected position of the medical device in the detector coordinate system whose position in Object coordinate system and then from its position in are determined image coordinate system of an X-ray image. Thereby, it is possible, the position of the medical device, which for example, a may be treatment instrument immediately display the radiograph so that the practitioner knows at all times, at which point on or in the to study object the treatment instrument is straight, even if Part of the treatment instrument from the outside are not visible. The medical Device can for example be a radiation therapy device, the position of which in the Image coordinate system by the novel accurately determined may be, whereby an exact alignment of the therapy beam on to is treated point possible.

In one of them late development of the method provided that the position of the medical device in the image coordinate system from the intersection of a through the focus point and the position of the medical device in the object coordinate system extending straight line with the Imaging plane is calculated. Since the position of the X-ray apparatus, in particular the position of the focus point and the imaging plane of the X-ray apparatus, and Position of the medical apparatus in the object coordinate system in the detection of an X-ray image can be determined, by simple Intersection under a straight line with the imaging plane of the position medical device are determined in the image coordinate system.

The object relating to an arrangement for implementing the method is achieved by an aforementioned arrangement characterized is characterized in that the detector arrangement is arranged on the X-ray apparatus and that the marker arrangement on the examination subject or relative to Examination object is stationary. It is thereby achieved that the Field of view of the detector array and the illumination region of the X-ray device is substantially or at least largely identical. While in the known arrangement, in which the detector array at one disposed tripod, the field of view of the detector array by a treating person or device may be covered, whereby a Positioning an object point or a treatment instrument in Using an optical detector array is prevented, this may in the Inventive arrangement hardly occur. During a Fluoroscopy is free of definitely the illumination region Treatment instruments or treating them, so that at the same time a Position detection of attached to the object under examination marker arrangement by means of the detector array is possible. Even during the time in which no Fluoroscopy takes place, usually is the area between X-ray machine and examination object free from other devices and treated Persons, so that the position of also during this time Treatment instruments by means of the detector array in detected Detektorkoordinateiisystem and then in the image coordinate system can be determined.

A further development of the inventive arrangement provides that the Detector array at the X-ray source or the Röntgenbildaufnahme- or Ray image intensifier device is arranged. In this arrangement, the Detector arrangement is the risk that the lines of sight of the detector arrangement could be interrupted, very low. In the choice of position of the Detector arrangement is natural to consider that the line of sight of Detector array in certain positions of the X-ray machine by buying parts the X-ray apparatus itself, such as the patient table, be covered. The detector array is therefore preferred in most positions on a the X-ray apparatus situated above the object under examination part of the Ray device arranged.

According to a development of the invention provides that a further Marker assembly to a medical device, in particular a Treatment instrument or radiotherapy assembly is disposed. The Detecting the position of this medical device can simultaneously capture a radiographic image take place, but also at any other desired time. However, the prerequisite is always that the current position of the X-ray machine was detected and measured by the detector array, as this position data for determining the position of the medical device in the image coordinate system required are.

Preferably, the invention provides that the optical marker arrays Light source markers, for example, infrared light or visible light emitting LEDs, retroreflective markers or with a recognition pattern have provided markers. For the detector array corresponding optical detectors are used which are sensitive to the respective radiation. at the use of retroreflective marker is also near the Detector array another radiation source provided, the radiation from the markers reflected and is then detected by the detector arrangement, whereby the position of the markers can be determined. When using with Detecting patterns provided markers, the detector array corresponding Detectors, which determine a position of the detection of such patterns can.

A further development of the inventive arrangement also stipulates that the Two detector array, each two-dimensional position detecting or three, each a one-dimensional position detecting optical detectors comprises, can detect which infrared light or visible light, preferably infrared CCD cameras, and that the marker arrangement at least three infrared light or visible light-emitting diodes comprise. This provides a simple and cost-effective solution, as determined by the positions with high accuracy can be.

An alternative embodiment of the inventive arrangement provides that the Marker arrangement at least one electromagnetic transmitter assembly and the Detecting device at least one electromagnetic receiver assembly having. The electromagnetic transmission arrangement orthogonal can produce standing electromagnetic fields, and the electromagnetic Receiving device which can detect electromagnetic fields, can be used in place of the optical marker and detector array. The Problem of the line of sight obstruction created by personnel or equipment plays Using electromagnetic devices, such as small Coil assemblies, not very large rolls, which, however, the optical marker and detector array has a greater reach.

A preferred embodiment of the invention provides that the X-ray device is a C-arm X-ray device is. Such X-ray machine is widely used to intraoperative uses X-ray imaging to the from different positions during create operational radiographs from patients. Since the detector array fixed is attached to the X-ray machine, changed at a rotation of the C-arm immediately the position of the detector array, while the position of arranged marker assembly securely to the patient or stationary relative to the patient is. As a fixed reference coordinate system, therefore, is the coordinate system of Marker array (the object coordinate system) used.

The invention will be explained in more detail with reference to the drawings. Show it:<dl tsize="6" compact="compact"><dt>Fig. 1</dt><dd>a schematic representation of an inventive arrangement with a C-arm X-ray device,</dd><dt>FIG. 2</dt><dd>a flowchart of the inventive method,</dd><dt>Fig. 3</dt><dd>a schematic diagram for explaining the position determination by The inventive method and</dd><dt>Fig. 4</dt><dd>another flowchart illustrating an embodiment of Inventive method.</dd></dl>

In Fig. 1 is an inventive arrangement with a C-arm X-ray device 1 shown. At the bottom of the C-arm 2 is an X-ray source 3, at the top of the C-arm 2 there is a video recording or Image intensifier device 4. The electronics for control and data processing the X-ray machine is located in the control and processing unit 5. The to examined patient 6 lies on a patient table 7 so that an X-ray image its head can be detected. At the image pickup device 4 are laterally two infrared CCD cameras installed 8,9 which form the detector array. The Cameras 8,9 are mounted so that their field of view the Fluoroscopy range of X-ray apparatus 1, so the the X-ray source 3 corresponds screened area substantially. The cameras can 8.9 consequently detect infrared light signals which are arranged three on the patient table Infrared LEDs are emitted. The LEDs 10 are such on Patient table 7 arranged that it overlaps on the patient's head 6 will. Furthermore, an example of a treatment instrument 11 in Fluoroscopic area shown on the also three infrared light emitting diodes 12 are attached. In addition, still as an example of a further medical Device symbolically a radiation therapy machine 13, which is also three IRED 14 is provided. Although there is not this the is screening area of ​​the X-ray apparatus 1, the field of view of the cameras 8,9 however, so large that also signals are detected by the light-emitting diodes 14 can, if the radiation therapy device 13 is not too far removed from the patient 6 is.

The three infrared light emitting diodes 10 on the patient table form a marker arrangement. Likewise, the three light-emitting diodes 12 on the treatment instrument 11 and the three LEDs 14 at the radiation therapy device 13 is a marker arrangement. Each of the two cameras 8,9 can detect the two-dimensional position of a light emitting diode. From 8.9 sensed by the two cameras, the signals of a light-emitting diode three-dimensional position of a light-emitting diode can be determined. To the position a device, such as the patient table 7 in three-dimensional coordinates to determine, are shown per marker arrangement three LEDs required.

The positions are first determined in the detector coordinate system D, the by the coordinate axes x_D, y_D, z_D is formed. The detector coordinate system D is laid with the detector array, in the example shown by the camera 9 coupled. By functionality of the cameras 8,9 and LEDs 10,12,14 existing position measuring system can positions in Detector coordinate system D were determined easily in object coordinates an object coordinate system O are converted. The by Coordinate axes x_O,y_O,z_O formed object coordinate system O is fixed to the Examination object, here the patient 6 and secured to the patient table 7, the is stationary relative to the patient 6, coupled. The position measuring system allows So the detection of three-dimensional position of a marker arrangement equipped device in Detetektorkoordinatensystem D and converting them Position in object coordinates of the object coordinate system O.

Reference to the flow scheme shown in Fig. 2, the method is intended for determining the an imaged position as pixel in at least one X-ray image Object point are described in the object coordinate system O closer. First in block 101 in a first position the C-arm, a first X-ray image detected. Simultaneously with this is with the cameras 8.9 the position of the LED 10 in Detector coordinates detected. From the position of the light-emitting diodes 10 results at the same time also the position of the patient table 7 and the position of the Object coordinate system O (or the position of the origin of the Object coordinate system O).

In block 102, then the position of the cameras in the object coordinate 8.9 determines what the function of the position and due Knowing the position of the object coordinate system O in detector coordinates is easily possible.

In block 103 after which the position of the X-ray apparatus 1 in Object coordinate system O determined. The characteristic points of the Ray device 1, the focal point will be in the X-ray source 3 and the Imaging plane selected in the image pickup device 4, whose positions in Object coordinates are determined. Given the positions of the focal point are and the imaging plane of detector coordinates into object coordinates converted. The positions in detector coordinates are in carrying out the presuppose the inventive method as known and for example, a one-time basis ray device 1 to be carried out won calibration procedure using a calibration phantom, what more detail below will be explained.

In block 104, is now a straight line through the focal point and the image point in the Imaging plane, whose associated object point in the object coordinate system to be determined down. On this straight line is the searched object point.

A more accurate determination is not possible with only one X-ray image. Should the Position of the object point in the object coordinate system are determined exactly, so a second X-ray image required that in another position the C-arm is detected as in the detection of the first X-ray image. In the second position of the C-arc can be carried out in the first position the C-arm The method steps of blocks 101 to 104 is also performed, which by Blocks 201 illustrates to 204th As a result, there will again be a Straight through the focal point of the X-ray device in the second position the C-arm and by the pixel in the second X-ray image, its associated to be determined object point. The pixel in the first and second Radiograph should this possible belong to the same object point.

In the selection of pixels in two different X-ray images, the Users are supported. After the determination of the first pixel in the first X-ray image, the connecting line between the first pixel and the first focus point can be determined. This connecting line can on the second X-ray image are projected, whereby the information is obtained that the second pixel (the second X-ray image) projected on this line in the second must be x-ray image. the user now selects a pixel on this projected Just now, the connecting line between the selected determined second pixel and the second focus point and this in turn on the first X-ray image can be projected. The user can thus iteratively in two X-ray images, the position of the selected pixels vary until sufficient accuracy is achieved.

The position of this object point finally obtained in block 105 by Calculation of the intersection of the two lines, resulting in the calculation of blocks 104 and 204 resulted. Thus, the exact position of the object point known in the object coordinate system of a pixel in two X-ray images is depicted. This can be used, for example, a point in is displayed in one or two X-ray images, the patient, for example, one equipped with LEDs treatment instrument later on.

In three-dimensional space to have the two straight not necessarily to cut. If there is no intersection, the searched object point lies on in the middle of the shortest link between the two lines.

The method illustrated in FIG. 2 will be illustrated in FIG. 3 again. With Q, a section of an object under examination is denoted by P is the searched object point indicated. In a first position of the X-ray source 31 the examination object Q is illuminated with a first radiation beam S1. The radiation S1 starts out from the focal point F1 of the X-ray source 31 and the X-ray image is displayed in the image plane A1. The object point P is thereby ready for example, as pixel C1 whose coordinates in Image coordinate system of the first X-ray image (coordinate axes x_B1, y_B1, z_B1) are known. In a second position of the X-ray source 32 is another X-ray image detected, which is imaged in the imaging plane A2. Of the Object point P is in this case as a pixel in the second image coordinate system C2 (Coordinate axes x_B2, y_B2, z_B2) Ready.

According to the procedure to be a line through the points F1 and C1 (G1) or F2 and C2 (line G2) placed and calculates the intersection. This intersection is the searched object point P, the two in the X-ray images is displayed as a pixel C1 and C2, and whose position is now in is known object coordinates.

As readily apparent from Fig. 3 can be seen, the two X-ray images must not mutually perpendicular directions are included. In addition, can also more than two X-ray images are used to determine position.

Another application of the method is by the flowchart are described in Fig. 4. This application possibility is to determine the position of a medical device and display example, in an X-ray image.

The process steps shown symbolically in the blocks 301 to 303 corresponding to in FIG. 2 in the blocks 101 to 103 shown Method steps, that is, there is detected an X-ray image and the position of Focus and imaging plane of the X-ray device determines in object coordinates. In block 304 is the position of another medical device, such as a Treatment instrument 11 or a radiation therapy device 13 (see FIG. 1) with the cameras 8, 9 detected in the detector coordinate system D. With this acquisition must either the position of the X-ray machine to be unchanged from the Position, was detected in the in the X-ray image, or it must be the first item be saved. The step was taken in block 304 may also simultaneously to the Process steps of blocks 301 to 303 take place. The detector coordinates of medical device then in block 305 in object coordinates converted. To determine the position of the device in image coordinates and expand this position in the radiograph, first, in block 306 a Straight line through the focal point of the X-ray source and the position of the device in Object coordinate system drawn, intersecting the imaging plane. In block 307. This point of intersection is then computed, from which the position of the device results in the image coordinate system of the X-ray image.

If the position of the X-ray source in the detection of the position of the a medical device was different from the position at the X-ray imaging, the position of the medical device of Object coordinates using the stored Positon of the X-ray machine in Detector coordinates of the X-ray machine in the X-ray imaging converted. It can then position the device in the Bildkoodinatensystem X-ray image as described above are determined.

The process described in Fig. 4 for example, is used to the Position of a surgical instrument is guided inside the patient and from the outside is not visible to its LED arrangement, the view radiograph or show the instrument itself. This can be both carried out at x-ray apparatus is turned off when the x-ray images created in advance were, as a uch when not connected radiograph and settled Fluoroscopy. if for example a guided body in the biopsy needle in Röntbild is not visible.

The position of the instrument can also be updated by in blocks repeated 304 process steps described to 307 ongoing will.

In the event that the position of a radiation therapy device continuously with the Position measuring system is determined, it can be used to Therapeutic beam precisely to a predetermined point, for example, by way of is selected X-ray image to position.

To determine the position of the focal point and the position of the imaging plane in the detector coordinate system is unique for an X-ray device, for example in the installation of a position measuring system described, a calibration process required. For this, a calibration phantom is quasi as the object in the Field of view of the cameras and the illumination region of the X-ray machine brought. This calibration phantom is absorbent at a first, X-rays Marker array and a second marker array for the cameras, For example, infrared LEDs when using infrared cameras. provided. The relative position of the two marker arrays each other is known. Subsequently, a simultaneously to both the X-ray machine X-ray image of the calibration phantom in the ready to the first marker arrangement with is as detects the position of the second marker array with the cameras. The position of the second marker array (the light-emitting diodes) in Detector coordinates is thus immediately known, this is also where the position the first marker array in detector coordinates can easily calculate, since the relative position of the two arrangements of markers each other is known. at arranged selection of a suitable calibration phantom with appropriately can marker arrays using geometric considerations from now known position of the first marker array and mapping the Radiograph very easily the position of the focal point of the X-ray machine and the Location of the imaging plane of the x-ray device can be calculated. If the Arrangement of the cameras is not subsequently changed the X-ray machine, remain these values ​​unchanged and can virtually as fixed values ​​for the X-ray machine as are assumed known and used for the novel process.

To ensure the accuracy of the position determination to further increase or in the event that the lines of sight of the cameras could be concealed, may additionally comprise a further detector array, for example as in the known case of a is attached to a tripod, may be used.

For diagnostic purposes, the method according to the invention and Inventive arrangement can be used. For example, is the positionally accurate combination of multiple X-ray images at different Positions of the X-table has been added, into a single radiograph possible. For this example, are the focus and the imaging plane retained and the patient table is moved, wherein different in two Positions of the patient table in each case an X-ray picture is taken. The Position of the patient table is on the patient table or the patient arranged arrangement of markers detected.

The invention is not limited to that shown in the drawings applied to an C-arm X-ray device is limited. It is also possible with other X-ray equipment X-ray images from different positions with respect to a Examination object are obtained, for example, with a swiveling Patient table using a fixed X-ray source and image receptor. at Such X-ray equipment could, for example, the cameras on X-ray and the LEDs can be arranged on the pivotable table. Even with increasingly used mobile X-ray or computed tomography systems can the invention can be used. In a CT system, the cameras at the Scanning unit (gantry) and the LEDs to be mounted on the patient table.