Imaging system for a vertebral level

The present invention relates to an imaging system (10) for a vertebral level, an identification method for a vertebral level, a computer program element for controlling such system and a computer readable medium having stored such computer program element. The imaging system (10) comprises a determination unit (11), a definition unit (12), an imaging unit (13), and a processing unit (14). The determination unit (11) determines a target vertebral level. The definition unit (12) defines an anatomical landmark of a spine. The imaging unit (13) provides a series of X-ray images along the spine based on the landmark. The processing unit (14) identifies the target vertebral level in at least one of the X-ray images. The processing unit (14) further stitches the X-ray images to a continuous panoramic image of the spine and identifies the target vertebral level in the panoramic image.

CROSS-REFERENCE TO PRIOR APPLICATIONS

This application is the U.S. National Phase application under 35 U.S.C. § 371 of International Application No. PCT/EP2015/062150, filed on Jun. 1, 2015, which claims the benefit of European Patent Application No. 14171512.8, filed on Jun. 6, 2014. These applications are hereby incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to an imaging system for a vertebral level, an identification method for a vertebral level, a computer program element for controlling such system and a computer readable medium having stored such computer program element.

BACKGROUND OF THE INVENTION

In minimally invasive spine interventions, it is very important to localize the correct vertebral level for treatment. The interventions are usually performed under X-ray guidance, with the X-ray system offering only a limited field-of-view. However, only few vertebral levels can reliably be identified from their shape or the surrounding anatomy in such assembled image. Therefore, the vertebral level has to be identified by palpitation and counting of landmarks or from visually assessing projection images from the limited X-ray field-of-view. As a result, the process is complicated and error-prone.

In digital X-ray imaging, a composition of an image from sub-images is generally used to form a composite image of an elongate scene which is too long to be reproduced in one operation. Using a contemporary digital X-ray examination apparatus, it is difficult or even impossible to form an X-ray image of the complete region of the spinal column of the patient to be examined in one exposure. A number of successive X-ray images of portions of the region to be examined are formed, which images together cover the entire region. A method of this kind is also called the translation reconstruction technique and is known from EP 0 655 861 A1.

Further, US2011/0276179 A1 discloses designating beginning and end points of a desired AP radiograph. A robotic system can retrace this path obtaining a contiguous X-ray image. The entire scan can be displayed on a computer screen. A surgeon can designate one or more desired surgical levels in the displayed scan. A further robotic system may hold a marker in place over the designated vertebral body while a confirmatory radiograph is obtained.

SUMMARY OF THE INVENTION

Hence, there may be a need to provide an imaging system for a vertebral level, which enables an easier and more reliable identification of the target vertebral level in an interventional setting.

The problem of the present invention is solved by the subject-matters of the independent claims, wherein further embodiments are incorporated in the dependent claims. It should be noted that the aspects of the invention described in the following apply also to the imaging system for identification of a vertebral level, the identification method for a vertebral level, the computer program element, and the computer readable medium.

According to the present invention, an imaging system for a vertebral level is presented. The imaging system comprises a determination unit, a definition unit, an imaging unit, and a processing unit. The determination unit is configured to receive pre-interventional image data and determine a target vertebral level using this pre-interventional image data. The determination may be made automatically. The determination unit may be an interface to an input device, so that the input regarding the target vertebra level may be provided manually by a user.

The imaging unit is configured to provide a series of X-ray images along the spine based on a landmark. The landmark may be a characteristic of a 1st thoracic vertebrae, a 12th thoracic vertebrae, a 1st cervical vertebrae, a 2nd cervical vertebrae, a 7th cervical vertebrae, a sacrum and/or the like. The term “based on” means that the series of X-ray images is taken based on one of more landmarks. Thereby, the landmark can be a start, end or center point for the images, a particular point of interest, and/or the images can be taken along a series of at least two landmarks and the like. The X-ray images can be stitched together to form a panoramic image of the spine.

The definition unit is configured to define an anatomical landmark of a spine. The definition of a landmark can be done by registration of the pre-interventional data (CT, MR or else) to a panoramic image and/or by registration of a patient-specific or general model to the panoramic image. The processing unit is configured to identify the target vertebral level in at least one of the X-ray images based on the determination in the pre-interventional image data.

In other words, a target vertebral level or disk space is determined. The target vertebral level or disk space is e.g. known by name (e.g., L2—second lumbar vertebra) or it can be known from pre-interventional CT or MRI data or else.

A reliably identifiable anatomical landmark of a spine is defined, which indicates preferably a characteristic as e.g. a center, uppermost or lowest point of a 1st thoracic vertebrae, a 12th thoracic vertebrae, a 1st cervical vertebrae, a 2nd cervical vertebrae, a 7th cervical vertebrae, a sacrum and/or the like.

Based on or starting from the landmark, a series of X-ray images or frames is provided or preferably acquired while moving a patient table or an imaging system in-between the frames e.g. towards a region near the target vertebral level or starting from a region near the target vertebral level. A limited overlap between the frames is preferred.

The target vertebral level is then identified in at least one of the X-ray images. Having a reliably identifiable landmark in the same (panoramic) image as the target vertebral level, this identification can be done based on a pre-interventional data set with marked target position, whereby an identification of the target vertebral level can be done automatically through registration of the pre-interventional data set or of a projective view of the pre-interventional data to the series of X-ray images along the spine or to the panoramic image. Such registration may advantageously include or rely on registration of the defined anatomical landmark, which provides a registration having a relatively high level of accuracy.

Once the target vertebral level is identified in a e.g. current or last X-ray image, which means it is within the field of view of the imaging device, it can be marked either physically e.g. by placing a position marker on the patient skin and/or electronically e.g. by storage of current x-ray system and patient table positions. At this point, the X-ray image acquisition may either be stopped to keep the X-ray dose received by the patient to a minimum, or it may continue in order to obtain a more complete panoramic image covering a larger region of the spine.

As the imaging system for a vertebral level according to the invention is based on a series of images and as the series of images is based on a defined anatomical landmark of the spine, the device according to the invention enables a very easy and reliable identification of the target vertebral level in an interventional setting. In particular, a risk of mis-identifying the treated vertebral level is greatly reduced.

Further, the dose of the acquisition can be chosen very low, as the spine X-ray images are not used for direct diagnostic use. Furthermore, the device according to the invention can be implemented on existing imaging systems even without availability of C-arm motion tracking or table motion tracking.

In an example, the determination unit is further or additionally configured to indicate the target vertebral level in the pre-interventional image data.

In an example, the determination unit is further or additionally configured to extract the spine in the pre-interventional image data by segmentation and in particular by model-based segmentation using a model of the spine. The output of the segmentation is then a patient-specific spine model.

In an example, the determination unit is further or additionally configured to provide a general spine model, to determine the target vertebral level based on the general spine model and to indicate the target vertebral level in the general spine model. The imaging system may further comprise a registration unit configured to register the general spine model with at least one X-ray image and/or a panoramic image (explained below) and to indicate the target vertebral level in the at least one X-ray image and/or the panoramic image based on the indication in the general spine model.

In an example, the processing unit is further configured to stitch the X-ray images or frames to a preferably continuous panoramic image of the spine and to identify the target vertebral level in the panoramic image. An overlap between the frames is required for a continuous panoramic image. The stitching can be based on e.g. the image content and/or external markers attached to the patient and/or the table. The stitched panoramic image offers a preferably continuous view from the known and identified landmark up to the current imaging position, which makes an identification of the target vertebral level in the current image easy and safe.

If a pre-interventional data set (CT, MR or else) with marked target position is available, an identification of the target vertebral level can be done automatically through registration of the pre-interventional data set or of a projective view of the pre-interventional data to the series of X-ray images along the spine or to the panoramic image.

Additionally, model-based segmentation methods may be used to extract the spinal column in the pre-interventional data and to register it to the panorama image. Even without a patient-specific model, a general model of the spinal column can be registered to the panoramic image to facilitate vertebral level identification.

Once a target vertebral level has been identified and is in the field-of-view of the X-ray system, it can be marked on the patient's skin or recorded electronically from tracked positions of the patient table and imaging system.

In an example, the imaging system for a vertebral level further comprises an input device configured to enable the determination of the target vertebral level. The input device may be instead or additionally configured to enable the identification of the target vertebral level in the at least one X-ray image and/or in the panoramic image.

In an example, the imaging system for a vertebral level further comprises a motion unit configured to provide a motion signal for moving a patient table and/or the imaging unit.

The imaging system may further comprise a tracking unit configured to provide a tracking signal for tracking the motion of the patient table and/or of the imaging unit. The tracking unit may be at least one sensor positioned at the patient table and/or the imaging unit. The sensor may be a position sensor and/or an acceleration sensor or the like.

If a tracking of the table or the X-ray system motion is available, the device can give guidance to a user at which position to acquire the next frame for stitching to minimize dose while retaining sufficient coverage.

In an example, the imaging system for a vertebral level further comprises a recording unit configured to record the position of the target vertebral level based on the tracked position of the patient table and/or of the imaging unit.

The imaging system may further comprise a marking unit configured to mark the target vertebral level on the patient's skin.

In an example, the imaging system for a vertebral level further comprises a registration unit configured to register the pre-interventional image data with the at least one X-ray image and/or the panoramic image. The registration unit may be further configured to indicate the target vertebral level in the at least one X-ray image and/or in the panoramic image based on the indication in the pre-interventional image data.

The imaging system may further comprise an X-ray acquisition device for acquiring a series of X-ray images and a display unit. The system may further comprise a patient table.

According to the present invention, also an identification method for a vertebral level is presented. It comprises the following steps, not necessarily in this order:a) determining a target vertebral level,b) defining an anatomical landmark of a spine,c) providing a series of X-ray images along the spine based on the landmark, andd) identifying the target vertebral level in at least one of the X-ray images.

The definition of a landmark can be done by registration of pre-interventional data to a panoramic image and/or by registration of a patient-specific or general model to the panoramic image.

The identification can be done by a ‘counting’ method, manually or automatically. Alternatively, if a pre-interventional data set (CT, MR or else) with marked target position is available, an identification of the target vertebral level can be done automatically through registration of the pre-interventional data set or of a projective view of the pre-interventional data to the series of X-ray images along the spine or to the panoramic image.

Of course, both approaches can be combined to use a single, reliably identifiable landmark to guide the registration of the pre-interventional image data or of the model.

According to the present invention, also a computer program for controlling an imaging system for a vertebral level is presented, wherein the computer program comprises program code means for causing an imaging system as defined in the independent device claim to carry out the steps of the identification method for a vertebral level as defined in the independent method claim, when the computer program is run on a computer controlling the imaging system.

It shall be understood that the imaging system for a vertebral level, the identification method for a vertebral level, the computer program element for controlling such system and the computer readable medium having stored such computer program element according to the independent claims have similar and/or identical preferred embodiments, in particular, as defined in the dependent claims. It shall be understood further that a preferred embodiment of the invention can also be any combination of the dependent claims with the respective independent claim.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1shows schematically and exemplarily an embodiment of an imaging system1an X-ray acquisition device3for acquiring a series of X-ray images and a display unit2for displaying images. The system further comprises a patient table (not shown).

The imaging system10comprises a determination unit11, a definition unit12, an imaging unit13and a processing unit14.

The determination unit11determines a target vertebral level. The determination may be made automatically. The determination unit may be an interface to an input device15, so that the determination may be made manually by a user.

The definition unit12defines an anatomical landmark of a spine and is connected with the imaging unit13. The imaging unit13provides a series of X-ray images along the spine based on the landmark. For receiving X-ray image data, the imaging unit13is connected with the X-ray acquisition device3. Thus, the imaging unit13provides images based on X-ray image data from the X-ray acquisition device3, the image data being acquired e.g. starting at a landmark and/or along a series of at least two landmarks. The processing unit14identifies the target vertebral level in at least one of the X-ray images. The processing unit14further stitches the X-ray images to a continuous panoramic image of the spine and identifies the target vertebral level in the panoramic image. The stitching can be based on e.g. the image content and/or external markers attached to the patient and/or the table. The processing unit14may be connected with the determination unit11and the display unit2for displaying one of more of the X-ray images and/or the panoramic image of the spine.

The imaging system10further comprises an input device15to enable the determination of the target vertebral level and to enable the identification of the target vertebral level in the X-ray image and/or in the panoramic image. The determination may be made manually by a user and/or automatically be the device. The input device15may be connected with the determination unit11and the processing unit14.

The imaging system10further comprises a motion unit17connected with the processing unit14to provide a motion signal for moving a patient table and/or the imaging unit13. The imaging system10further comprises a tracking unit18connected with the processing unit14to provide a tracking signal for tracking the motion of the patient table and/or of the imaging unit13. The tracking unit18may be also connected with the motion unit17and/or the table (not shown).

The imaging system10further comprises a recording unit19connected with the processing unit14to record the position of the target vertebral level based on the tracked position of the patient table and/or of the imaging unit13. The recording unit19may be also connected with the tracking unit18and/or the imaging unit13(connection not shown).

The imaging system10further comprises a marking unit20connected with the processing unit14to mark the target vertebral level on the patient's skin.

The imaging system10further comprises a registration unit16to register pre-interventional image data with the X-ray image and/or the panoramic image. Based on this registration, the target vertebral level may be indicated in the X-ray image and/or in the panoramic image based on the in accordance with the determined target vertebral level in the pre-interventional image data. The registration unit16may be connected with the imaging unit13, the determination unit11and the processing unit14.

Instead or additionally, also model-based segmentation methods may be used to extract the spinal column in the pre-interventional data and to register it to the panoramic image. Even without a patient-specific model, a general model of the spinal column can be registered to the panoramic image to facilitate vertebral level identification.

Once a target vertebral level has been identified and is in the field-of-view of the X-ray system, it can be marked on the patient's skin, or tracked positions of the patient table and imaging system can be recorded electronically.

FIG. 2ashows a pre-operative MRI (magnetic resonance imaging) or CT (computed tomography) image of a spine. The pre-interventional image data is provided to determination unit11, which uses this data to determine the target vertebral level. The target vertebral level is, for illustrative purposes only, indicated in the drawing by a star-shaped marker. The determination may be made based on user input on an input device, so that the target vertebral level may be provided manually by a user. The target vertebral level may also be determined automatically, for example, based on a diagnosis or treatment indication stored in an electronic patient record or otherwise.

FIG. 2bshows a panoramic image stitched from several single images of a series of X-ray images along the spine. The single images or separate frames are shown by differently broken boxes. The image is based on a reliably identifiable anatomical landmark, the sacrum. The five round markers symbolize ‘counting’ i.e. intermediate vertebrae between the sacrum and the target vertebral level.

The pre-operative image is registered to the panoramic image. As shown by the arrow betweenFIG. 2aandFIG. 2c(another panoramic image of the spine), the registration allows for the position of the target vertebral level to be accurately inferred from the pre-operative image to the panoramic image. Once the target vertebral level is identified in the X-ray image or panoramic image, i.e. the X-ray imaging system has been positioned so that the target vertebra is within its field-of-view, the target vertebral level may be indicated with a star-shaped marker or any other suitable marker.

FIG. 3shows schematically an X-ray imaging system10. It comprises the X-ray image acquisition device3with a source of X-ray radiation100provided to generate X-ray radiation. The X-ray acquisition device3acquires a series of X-ray images to be provided by the imaging unit13(not shown). A table111is provided to receive a subject to be examined. An X-ray image detection module101is located opposite the source of X-ray radiation100, i.e. during the radiation procedure, the subject is located between the source of X-ray radiation100and the detection module101.

The X-ray source100and a detector101are mounted to the ends of a C-arm102. The C-arm102is held by curved rail, the “sleeve”103. The C-arm can slide in the sleeve103, thereby performing a “roll movement” about the axis of the C-arm. The sleeve103is attached to an L-arm104via a rotational joint and can perform a “propeller movement” about the axis of this joint. The L-arm104is attached to the ceiling via another rotational joint and can perform a rotation about the axis of this joint. The various rotational movements are effected by servo motors. The axes of the three rotational movements and the cone-beam axis always meet in a single fixed point, the “isocenter”105of the rotational X-ray scanner. The various rotational movements are controlled by a control unit112. Each triple of C-arm angle, sleeve angle, and L-arm angle defines a position of the X-ray source100. By varying these angles with time, the source100can be made to move along a prescribed source trajectory. The detector101at the other end of the C-arm102makes a corresponding movement. The source trajectory will be confined to the surface of an isocentric sphere. It is noted that the example shown is of a so-called C-type X-ray imaging system10. Of course, the invention also relates to other types of imaging systems10. The processing unit14identifies the target vertebral level in at least one of the X-ray images provided by the imaging unit13(not shown) and acquired by the X-ray acquisition device3. The processing unit14further stitches the X-ray images to a continuous panoramic image of the spine and identifies the target vertebral level in the panoramic image. The processing unit14is connected with the determination unit11(not shown) and the display unit2for displaying one of more of the X-ray images and/or the panoramic image of the spine. The display unit2is arranged in the vicinity of the table111to display information to the person operating the X-ray imaging system, i.e. a clinician. The input device15is arranged to input information by the user, as to determine a target vertebral level.FIG. 4shows a schematic overview of steps of an identification method for a vertebral level. The method comprises the following steps, not necessarily in this order:

In a first step S1, a target vertebral level is determined.

In a second step S2, an anatomical landmark of a spine is defined.

In a third step S3, a series of X-ray images along the spine based on the landmark is provided.

In a fourth step S4, the target vertebral level is identified in at least one of the X-ray images.

With pre-interventional data being used, the definition of a single landmark in step S2and the identification of the target vertebral level in step S4can be done by registration of the pre-interventional data to the panoramic image. Also with a patient-specific or a general model being used, the definition of a single landmark in step S2and the identification of the target vertebral level in step S4can be done by registration of the model to the panoramic image. Of course, both approaches can be combined to use a single, reliably identifiable landmark to guide the registration of the pre-interventional image data or of the model.

Further on, the computer program element might be able to provide all necessary steps to fulfil the procedure of an exemplary embodiment of the method as described above.