Non-invasive system for fixing navigational reference

A fixing system and method for fixing a navigational reference array for image-assisted medical treatment with respect to a patient, wherein the reference array is arranged the patient's body with the assistance of an immobilizing device, and wherein the immobilizing device is a vacuum mattress or a vacuum mattress patient jacket, and at least one anchoring for the reference array is provided on or in the vacuum mattress or a vacuum mattress patient jacket.

FIELD OF THE INVENTION

The present invention relates to non-invasively fixing a navigational reference which can be positionally determined and tracked by a localizing system of a medical navigation system. More particularly, the invention relates to the field of intra-operative navigation with non-contact registering of the reference or reference array, respectively, specifically for applications in the spinal area.

BACKGROUND OF THE INVENTION

In medical navigation, a patient reference or reference array is fixed with respect to a part of the body to be treated. In the area of spinal treatment, for example, this conventionally has been achieved by attaching the reference array to an exposed section of bone and then registering, i.e., positionally assigning, the reference array in a navigation system. A disadvantage of such conventional methods is that in order to gain access to the section of bone (e.g. vertebra) to which the reference array is to be attached, relatively large incisions into the skin and through the tissue must be performed. In cases where the actual surgery can be performed using a thin and/or small instrument, the problem then arises that attaching the reference array represent the most invasive aspect of the entire treatment.

A localizing device for determining the position of a patient is known from DE 102 06 166 A1, wherein a vacuum mattress is used to place the patient. A box-like couch, which includes two side walls that stand up on both sides of the patient, is placed around the vacuum mattress and the patient. Navigational markings are arranged on the sidewalls, and the patient is immobilized and fixed with respect to the markings. A disadvantage of this is approach is that the patient and/or the area to be treated is relatively far from the markings, which can reduce the accuracy of the navigation. Also, the proposed box-like arrangement is very bulky and difficult to handle, and can obstruct the area to be treated.

DE 197 31 040 A1 describes a device and a method for fixing parts of a body, wherein a patient is positioned on a bearing surface and then covered with a foil. The patient is immobilized by suctioning air from under the foil, thereby collapsing the foil around the patient. The reference, as a secondary aspect, also describes how holding arms can be used that include a base beneath the foil, wherein the holding arms pass through the foil and are attached at the other end to the patient couch. The holding arms are designed with joints and are attached both to the patient and to the couch only via the suctioning effect created by the partial vacuum. DE 197 31 040 A1 also proposes attaching a marker system to the holding arms. However, attaching the holding arms via the foil and partial vacuum may not offer a sufficient holding force to rigidly fix such markings with respect to the patient. As a result, accuracy in navigation can be affected. Further, due to the holding arm joints and the unstable fixing by means of the foil, a fixed arrangement of such markings with respect to the parts of the body cannot be ensured.

SUMMARY OF THE INVENTION

The present invention relates to a fixing system for fixing a navigational reference device for image-assisted medical treatment with respect to a patient, so as to enable one to treat a patient with navigational assistance. Data on the patient's body structure, captured beforehand, can be visibly displayed in its correct positional relation with respect to instruments or other treatment means. The reference device, which is arranged in a fixed position with respect to the part of the patient's body, provides reference data to the navigation system. The data can be used by the navigation system to display the location of a treatment instrument and/or body structure in real time.

In accordance with the present invention, a fixing system includes a reference device that can be arranged outside the patient's body. An immobilizing device, such as a vacuum mattress or a vacuum mattress patient jacket, includes at least one anchor point (also referred to as an anchor) for the reference device, wherein the reference device can be attached directly to the immobilizing device. By attaching the reference device to the immobilizing device, the location of the reference device relative to the area to be treated can be ensured. Further, since the reference device can be attached to the immobilizing device (as opposed to the area to be treated), the reference device does not obstruct the area to be treated. Additionally, since the immobilizing device can be a vacuum mattress or a vacuum mattress patient jacket, which, once evacuated, is completely rigid, a stable and immovable location can be provided for fixing the reference device with respect to the patient. For at least this reason, it is sufficient to provide one anchor point for the reference device; on which the reference device can then be fixed.

In a preferred embodiment of the present invention, the anchor point includes a base, e.g. base plate, (the base need not necessarily be rigid, but can also be made of a flexible material and become rigid during evacuation) which can be rigidly fixed in a known position with respect to the immobilizing device when the immobilization device is evacuated. Such a base can ensure a sufficient hold in order to provide a rigid and stable anchor point. The base can be embedded within filling material of the immobilizing device and can include a connection to the reference device. The connection can protrude to the outer side of the immobilizing device through a sealed, air and/or gas-tight opening. This arrangement in the interior of the immobilizing device can ensure that following evacuation, the base is held firmly in place.

The reference device can be integrally formed with the connection and the base. It also is possible to form the reference device as a separate component, such that the reference device can be placed onto the connection via an adaptor. This arrangement allows very simple handling and provides the option of only attaching the reference device when it is needed, e.g., after immobilizing the patient and/or shortly before or during treatment.

A number of anchor points may be provided at spaced locations on the immobilizing device. This enables the patient to be immobilized via the immobilizing device, and a reference device to then be placed on one of the anchor points. The reference device can be attached, for example, using a plug connection, latch connection, threaded connection or other detachable connection. Preferably, the reference device can be attached to an anchor point that is as near as possible to the part of the patient's body to be treated or operated on. By providing a number of anchor points at spaced and likely suitable locations, e.g., in the peripheral area of the immobilizing device, a location near the area to be treated typically can found. Accordingly, the immobilizing device can be used for a number of different treatments or procedures.

In addition, using an immobilization device such as a vacuum mattress or vacuum mattress patient jacket also offers another advantage. Such immobilizing devices can be freely configured in their shape, such that in accordance with one aspect of the invention, it is possible to provide at least one recess or transit window that allows access to parts of the patient's body in need of treatment. It is thus possible on the one hand to effectively immobilize the patient and fixedly anchor the reference device, and on the other to achieve optimum access to the region of the patient to be treated. It is advantageous if the anchor points are arranged around the periphery of the transit window, in order to place them in the vicinity of the treatment location.

The immobilizing device may be dimensioned such that it can envelope the torso area of the patient, wherein it can be pre-fixed to the patient with the aid of clasps on its peripheral areas, before the patient is conclusively immobilized by evacuating the mattress.

In the following, the invention is explained in more detail on the basis of a preferred embodiment. The features of the invention cited in this description can be implemented individually and in any combination.

DETAILED DESCRIPTION

FIG. 1illustrates a patient in a face-down position, on whom an operation is to be performed in the vertebral area. The patient is held on a couch (not shown) with the aid of a strap6. In the present example, it is noted that in accordance with the present invention, the patient need not necessarily be fixed in a completely rigid manner. This is due to the fact that the patient is enclosed by a vacuum mattress patient jacket which bears the reference numeral1. A plurality of anchor points2for securing a plurality of navigational reference devices (illustrated inFIG. 3as exemplary reference arrays5) are provided on vacuum mattress patient jacket1. The patient can therefore only move together with the jacket1, and since the reference arrays5in the anchor points2would move with the jacket1, the corresponding movement is taken into account by the navigation system and, thus, no errors arise. It is therefore unnecessary to completely fix the patient on the couch. Only the anchor points2(and therefore the reference arrays) cannot move with respect to the patient. Maintaining the anchor points2in a fixed relation is ensured by the fixed vacuum mattress jacket, thus allowing some patient movement. Accordingly, the patient is substantially more comfortable than when completely immobilized.

The vacuum mattress jacket1envelopes the patient in the torso area and can be pre-fixed using clasps3before the air is suctioned off from the jacket's interior. In the embodiment shown, the jacket1includes a window10which ensures access to the area of operation.

At this point, it is noted that it is not absolutely necessary to provide such a jacket. In some cases, it can be sufficient to immobilize the patient simply by placing the patient onto a vacuum mattress (not shown), wherein the vacuum mattress includes anchor points for attaching reference arrays at locations next to the patient.

In the case shown, however, the patient is enveloped in the torso area, andFIG. 2shows section A-A inFIG. 1, from which it is clear how the anchor point2is inserted within filling material (not shown) of the jacket1. A clasp3can also be seen inFIG. 2.

The anchor point2inFIG. 2is the same as that which can be seen inFIG. 3and includes a base plate4and a connection or connection section9. The base plate4is embedded within the filling material of the vacuum jacket1(or vacuum mattress), wherein the connection section9protrudes upwards out through the upper material of the jacket1. The resultant opening in the jacket is sealed using an air or gas-tight seal. By embedding the base plate4, it is enveloped on all sides by the filling material of the jacket1and rigidly fixed once the jacket has been evacuated. Rigidly fixing the base plate4with respect to the jacket1and, therefore, with respect to the patient, ultimately leads to the reference array5being rigidly and immovably fixed with respect to the parts of the patient's body to be treated.

On its upper side, the reference array5includes, for example, three markers8. The markers can be reflective passive markers that can be detected using infrared cameras. Markers for visible light also can be used, or markers which passively or actively indicate their position within electrical or magnetic fields. Each of the above markers8can be localized by the navigation system. Navigation systems are well known in the art and will not be discussed herein. Further information regarding medical navigation systems can be found in U.S. Patent Publication No. 2003/0225329, which is hereby incorporated by reference.

In the present example, the reference array5is placed onto the connection section9of the base2via a connector7(adaptor), resulting in a rigid and immovable mount. The adaptor7is shown only schematically; any positionally fixed plug connection, threaded connection, latch connection or similar type of connection can be utilized for the adapter.

As can be seen again fromFIG. 1, the anchor points2in the present example are arranged around the window10, such that they are situated in the vicinity of the treatment location and therefore enable precise navigation of the area to be treated. The present invention allows a navigational reference device or reference array to be stably and reliably fixed with respect to the patient, without requiring invasive surgery to attach the navigational reference device or reference array to the area to be treated. Using the present invention, and with highly precise navigational assistance, minimally invasive operations can be performed, particularly in the spinal area, e.g., administering injections in the intervertebral area, or using vertebroplasty in which cannulae have to be positioned in order to introduce supporting mass into vertebrae. However, the invention is also suitable for any other applications in which minimal invasive surgery is performed.

In conclusion, it is noted that when using the invention intra-operatively, the base of a reference array attached in accordance with the invention is advantageously registered in the navigation system in a non-contact process. It is then advantageous if a material is used for the jacket1and filling material which is permeable to x-rays, since in such cases, the base can be registered in a non-contact process via x-ray C-arcs, navigation systems with fluoro-to-CT or fluoro-to-MR registration or via 3D C-arcs which produce three-dimensional images from a number of individual recordings.