Stereotactic device for cutting hard tissue on the cranial bone using energetic radiation

Abstract

A stereotactic device for cutting hard tissue on the cranial bone using energetic radiation has a stereotactic frame (22) and a stereotactic bow (25) fastened to the stereotactic frame (22) by at least one rotary joint. A laser applicator (17) is attached to the stereotactic bow (25) and can be moved along the stereotactic bow (25) via a motorised drive (28´´), said bow also being able to be tilted on the stereotactic frame (22) via a motorised drive (28, 28´). The laser applicator (17) has a dynamic 2D beam deflection apparatus (11) for a processing laser beam (2), focusing optics (12) with an adjustable focal position and a measuring apparatus (6) or is connected thereto, by means of which the cutting depth and the remaining thickness of the cranial bone (15) in the kerf can be measured. The device permits a safe opening of the cranium which is vibration-free and silent for the patient.

Description

[0001] Stereotactic device for cutting hard tissue on the skull bone with energetic radiation Technical field of application The present invention relates to a stereotactic device for cutting hard tissue on the skull bone of a patient, which device has a stereotactic frame that is designed to be attached to the patient's head and a stereotactic arch that is attached to the stereotactic frame via at least one pivot joint and that can be tilted over the head by the pivot joint when the stereotactic frame is attached to the patient's head. In neurosurgery, new therapy methods have been developed in recent years that significantly improve the quality of life and survival rate of seriously ill patients. These methods require that the patient is operated on while awake, since complex functions such as speech must be tested during the operation.On the one hand, this applies to deep brain stimulation (DBS) operations, in which electrodes are implanted with high precision in defined target areas of the brain in order to treat complex movement disorders (e.g. Parkinson's disease, dystonia or essential tremor). Deep brain stimulation enables patients whose motor skills were so severely impaired that they became socially isolated and required care to live permanently symptom-free. Awake operations are also becoming increasingly important in the treatment of low-grade gliomas (the most common brain tumor), as it has been shown that with these infiltratively growing tumors, the most extensive tumor removal possible, up to the point of loss of brain function, is necessary in order to achieve the longest possible survival with a good quality of life. Despite these successes, the majority of patients with severe movement disorders or a brain tumor forgo surgery while awake.The reason for this is the traumatic experience of drilling or milling into the skull bone. This process, accompanied by immense noise and strong vibrations, is perceived as frightening and extremely stressful. State of the art Currently, deep brain stimulation uses a mechanical drill (12 mm diameter) to open the skull, the rotation of which stops automatically at the point of penetration. Unfortunately, in around 10% of cases, this results in injuries to the meninges beneath the bone. In rare cases, the brain is also injured. During awake surgery for brain tumors, a hole is drilled and then a large area of ​​the skull is milled open using a hand-held mill (craniotomy). An angled metal shoe is attached to the mill to protect the meninges (dura) and the brain from injury.Nevertheless, injuries to the meninges or even the blood vessels beneath the bone (sinus) frequently occur during craniotomy. Laser-assisted cutting techniques are also well-known in the field of medical surgery. For example, a system for robot-assisted osteotomy has been developed. A robotic arm moves a laser head with a scanner over the bone tissue to be cut or positions it in front of the surgical site to cut bone tissue by distributing the laser energy via the scanner. However, the robotic arm and processing head move considerable masses, which poses a very high safety risk during head surgery. The required precise incision on the patient's head also presents a challenge.The object of the present invention is to provide a stereotactic device for cutting hard tissue on the skull of a patient using energetic radiation, which device entails a lower risk of injury to the patient, ensures high cutting precision, and enables a largely stress-free opening of the skull for the patient. Description of the invention This object is achieved with the device according to patent claim 1. Advantageous embodiments of the device are the subject of the dependent patent claims or can be derived from the following description and the exemplary embodiment. The proposed device has a stereotactic frame designed for attachment to the head of a patient.A stereotactic arch in the form of an arcuate rail, also known as an aiming bar, is attached to the stereotactic frame via at least one pivot joint. When the stereotactic frame is attached to the patient's head, the aiming bar can be tilted over the head using the pivot joint, for example, along the head, i.e., in the sagittal direction. The proposed device is characterized by a laser applicator attached to the stereotactic arch and movable along the stereotactic arch via a motor drive. The stereotactic arch itself can also be tilted via a further motor drive on the stereotactic frame. The laser applicator has a dynamic 2D beam deflection device and focusing optics. The focus position can be adjusted via the focusing optics or other optical elements in the laser applicator.The 2D beam deflection device allows a processing laser beam coupled into the laser applicator to be guided over a section of the hard tissue to be cut with the laser beam. The focusing optics with adjustable focus position enable the focus of the processing laser beam to be adjusted depending on the respective cutting depth and any changes in the distance of the laser applicator from the skull during processing. The laser applicator also has a measuring device or is connected to a measuring device with which the cutting depth of the cutting kerf created with the processing laser beam and the residual thickness of the skull bone in the cutting kerf – at least with a small residual thickness of ≤ 200 μm – can be measured. Various measuring techniques, such as ultrasonic or optical measuring technology, can be used for this purpose.Preferably, an OCT measuring device (OCT = Optical Coherence Tomography) is used, which directs a measuring beam to measure the cutting depth and the residual thickness of the skull cap coaxially to the processing laser beam onto the hard tissue to be cut. With the proposed device, the skull bone can be opened safely, noise- and vibration-free, with local anesthesia and almost imperceptibly for the patient. By monitoring the residual thickness of the skull bone with the measuring device, unintentional injury to the tissue beneath the skull bone is avoided. The laser cutting process is carried out using the laser applicator, which distributes laser pulses from a short-pulse laser along the cutting line using the dynamic 2D beam deflection device so that the laser cut in the bone is carried out efficiently and without thermal tissue damage. The measuring device, which is arranged in the laser applicator or connected to the laser applicator, measures the depth of cut in the bone during cutting or sawing.The cutting depth and residual bone thickness are measured during ablation, in the case of an OCT measuring device, for example, by the measuring beam carried along with the processing laser beam. This online control prevents injury to the dura mater beneath the bone and to the brain. For small cranial openings, the laser applicator remains stationary, and the incision is guided by the dynamic 2D beam deflection device, which can be formed, for example, by a 2D scanner mirror or by two separate 1D scanner mirrors arranged along two mutually orthogonal axes of rotation for beam deflection. For large cranial openings, the laser applicator is additionally moved along the arc using a motor drive, and the arc as a whole is tilted using another motor drive, for example, along the longitudinal axis of the skull.To move the laser applicator along the arc, it preferably has a carriage that can be moved along the arc. The laser applicator is attached to the carriage, preferably via a detachable connection, and the carriage is moved along the arc using the motor drive. Since the patient's head is fixed in the stereotactic frame during the procedure or incision, no unwanted relative movement between the laser beam and the skull can occur. The incision is planned before the start of the procedure by taking a CT or MRI scan of the head with the stereotactic frame attached to it in order to obtain the exact reference position of the stereotactic frame and the respective incision position. The guidance of the laser applicator and thus of the processing laser beam is carried out fully automatically by controlling the motor drives according to the incision plan using a specially designed control unit.The movement of the laser applicator is monitored and controlled with high precision via a measuring system, e.g., using suitable incremental encoders. This automated stereotactic system, also referred to below as a stereotactic robot, enables material removal with an accuracy in the submillimeter range (approx. 0.1 mm). This opens up the possibility of safely ablating bone even very close to critical structures (e.g., in the area of ​​the skull base and the caudal cranial nerves). Injury to the meninges underlying the bone is avoided by controlling the process with continuous measurement of the residual bone thickness, preferably using optical coherence tomography (OCT). The control unit is preferably designed to stop processing with the processing laser beam when a target residual thickness is reached. The control unit can, for example, be arranged in or on the laser applicator, but can also be separate from it.The automation of the stereotaxic system allows complex surgeries requiring multiple holes to be drilled in the skull and electrodes to be placed at various defined locations in the brain (stereo electroencephalogram, stereo EEG). These locations can be automatically approached by the system according to preoperative planning. This relieves the surgeon, who previously had to manually adjust the coordinates, and reduces the risk of errors in electrode positioning. The stereotaxic robot does not move large masses like a robotic arm. Due to its design, the moving mass of the applicator cannot collide with the patient's head.The processing laser used in the proposed device is preferably a CO2 laser, which emits pulsed laser radiation with pulse lengths in the picosecond, nanosecond, or microsecond range, preferably with emission wavelengths between 9.3 µm and 10.6 µm, or a pulsed solid-state laser with pulse lengths in the picosecond, nanosecond, or microsecond range, preferably with wavelengths between 2.7 µm and 3.3 µm. In an advantageous embodiment, the processing laser beam is guided to the laser applicator via a flexible or articulated beam guide. This can, for example, be a suitably designed articulated mirror arm. A fiber guide to the laser applicator can also be used. The proposed device preferably also has a spray system with one or more nozzles that generates a spray mist, preferably of water, for local humidification and cooling of the bone in the processing area.In an advantageous embodiment of the proposed device, the laser applicator is attached to the stereotactic arch via a motorized linear adjustment unit. This linear adjustment unit allows the laser applicator to be moved radially relative to the stereotactic arch. This additional motorized drive is in turn controlled by the control unit. This allows a constant distance between the laser applicator and the bone surface to be maintained during processing. In a further development of the device, the stereotactic frame has an inner ring-shaped frame part that is fixed to the patient's head, and an outer frame part that can be rotated around the inner ring-shaped frame part (in the ring plane), to which outer frame part the stereotactic arch is attached via at least one rotary joint. This further development offers the advantage that the stereotactic arch can then also be rotated on the stereotactic frame.This allows all trajectories to be set at the target points (located in the center of the arch). This avoids the need to set the stereotactic arch in a position that is disruptive to the surgeon, or certain trajectories that are technically impossible. This is particularly important for complex stereotactic surgeries such as stereo-EEG or posterior fossa biopsies, as fewer technical limitations mean the anatomically optimal trajectory can be selected more often. The motorized stereotactic system or stereotactic robot, with its motor drives for tilting the stereotactic arch and moving a carriage along the arch, can also be operated without the laser applicator, for example, to position a large number of electrodes deep within the brain.The stereotactic frame can also, as described above, have an inner ring-shaped frame part that is fixed to the patient's head, and an outer frame part that can be rotated around the inner ring-shaped frame part and to which the stereotactic arch is attached via at least one pivot joint. To position electrodes deep within the brain, a holder for thin, cylindrical electrodes with multiple contacts is attached to the carriage of the stereotactic arch instead of the laser applicator. This holder is equipped with a micrometer screw to enable sub-millimeter-precise advancement of the electrodes. The motorized stereotactic system can now be used to move to a multitude of positions with sub-millimeter precision where, based on preoperative planning, electrodes are to be positioned deep within the brain.Holes are first drilled at the appropriate positions using the laser applicator so that the electrodes can be inserted into the brain. This is important, for example, for so-called stereo-EEGs, which are used to determine the source of epileptic seizures. Based on this localization, a tailored surgical therapy (“tailored resection”) is then carried out to treat the epilepsy. Other applications of the motorized stereotaxic system without the laser applicator are also possible. Brief description of the drawings The proposed device is explained in more detail below using an exemplary embodiment in conjunction with the drawings. Herein: Fig. 1 shows a schematic representation of an example of the laser applicator used in the proposed device and Fig. 2 shows a schematic representation of the proposed device with the stereotactic frame fixed to the head of a patient.Ways of carrying out the invention The proposed device can be used to carry out a safe, noise- and vibration-free ablation process on the skull of a patient. In the proposed device, the drills and milling cutters previously used are replaced by a laser beam source that emits short-pulsed laser radiation with pulse energies preferably in the range of 0.1 mJ to 10 J. This radiation can be used to cut narrow and deep gaps in bone tissue to create access to the brain. In order for the cutting process to be efficient and without thermal tissue damage, the laser pulses must be distributed along the cutting line at repetition rates in the range between 0.1 and 1000 kHz in such a way that, on the one hand, the resulting process heat does not accumulate locally and, on the other hand, a continuous, deep cutting gap is created.The pulses are distributed by the dynamic 2D beam deflection device of the laser applicator, which is controlled accordingly via the control unit. Suitable wavelengths for the processing laser beam are those that are well absorbed by bone tissue. Examples of suitable wavelengths for this are the CO2 laser wavelengths between 9.3 µm and 10.6 µm, as well as wavelengths between 2.7 and 3.3 µm. The process is controlled via a laser applicator 17, an example of which is shown in Fig. 1 and described below. In this example, the laser beam 2 from a laser beam source 1 is transmitted via a beam guide 3 through two weakly reflecting planar glass plates 4 and 4'. The small portion of the laser radiation reflected by the glass plates 4, 4' is detected by two position sensors 5, 5'. The position sensors determine the position and propagation direction of the laser beam 2 within the laser applicator.In the event of misalignment, the beam position can be adjusted to the optical axis of the laser applicator using two automatically adjustable mirrors in the beam guidance system (not shown here) using position measurement. The laser beam is guided via a deflection element 8 via a telescopic optics 9 and, via a beam combiner 10, strikes a dynamic 2D beam deflection unit 11. Behind the beam deflection unit 11, the laser beam 2 is focused by a focusing optics 12 onto the bone surface 15 to be cut, where it leaves the applicator housing 14 through an exit opening 13. Depending on the design, the exit opening 13 can be closed off by the focusing optics 12 or a protective window 13'. An OCT sensor 6 emits an OCT measuring beam 7, which is guided to the applicator 17 via a beam guidance system 6', e.g. an optical fiber.This measuring beam 7 is superimposed on the laser beam 2 at the beam combiner 10 and then strikes the deflection unit 11. The deflection unit 11 distributes the focuses of the two coaxial beams 2, 7 in the processing plane on the bone 15 in the feed direction (x-direction) of the cutting process and perpendicular to it (y-direction). During the ablation process, the bone surface is wetted with a water spray to ensure a carbonization-free and efficient laser ablation process. The spray comes from fine atomizer nozzles 16 arranged concentrically around the outlet opening 13 of the applicator housing 14. The OCT sensor 6 uses the OCT measuring beam 7 to measure the cutting depth ds and the remaining thickness dr. The measuring light runs antiparallel to the excitation direction of the OCT measuring beam 7 and is detected in the OCT sensor 6.The measurement signal controls the cutting process so that a defined thin residual thickness remains, preventing laser beam 2 from damaging the brain tissue or dura beneath bone 15. As the ablation depth increases, the position of the laser focus is shifted in depth (z-direction) into bone 15 by adjusting a positionally displaceable lens 9' of telescope 9. Laser applicator 17 is located on a stereotaxic robot 21 (see Figure 2). This robot has a stereotactic frame 22 and a stereotactic arch 25. In this example, stereotactic frame 22 has an inner ring 22' with a platform 22'' that is rotatably mounted relative to ring 22'. Inner ring 22' is secured to the patient's skull 40 via brackets 23 with screws 24. The stereotactic arch 25 is attached to the platform 22'' of the stereotactic frame 22 via pivot joints.The arch plane is thus rotatably mounted so that it can be folded toward or away from the ring plane. A carriage 26, which can be moved along the arch, is located on the stereotactic arch 25. The applicator housing 14 is attached to the arch by a motorized linear adjustment unit 27. The applicator tip, from which the laser beam 2 emerges, can be moved in space by tilting the stereotactic arch 25, moving the carriage 26 along the arch 25, and linearly adjusting the applicator 17 with the adjustment unit 27. In contrast to conventional stereotactic systems, the stereotactic system of the proposed device is motorized. The stereotactic arch 25, the carriage 26, and the linear adjustment unit 27 are moved by motors 28, 28', 28'' via a sequence control (see Figure 2).Furthermore, the stereotactic system has additional degrees of freedom, via which the position of the arc center can be manually adjusted to a target point in the head (center-of-arc principle). This adjustment allows the surgeon to reach the preset arc center as the target point for any position of the arc 25 and the carriage 26 by radially guiding a surgical instrument in the arc plane. Using surgical planning software, the target trajectory for the cutting process of the proposed device, hereinafter also referred to as a laser osteotome, is determined based on preoperative image data. The stereotactic laser osteotome can be operated in two application modes. For cutting small access openings, the laser applicator 17 is stationary. The laser focus is then moved along a closed cutting line via the beam deflection unit 11.The movement of the laser beam 2 transverse to the cutting direction defines the width of the cutting kerf, while the movement in the cutting direction defines the length of the cutting kerf. Adjusting the laser focus in depth via the telescope 9 ensures an efficient cutting process even with increasing depth. During the cutting process, the cutting depth and residual thickness are measured via the OCT sensor 6 in order to regulate the local cutting depth and prevent the tissue from being processed beyond the bone. In the second application, larger access openings are cut out using the stereotactic laser osteotome. The distribution of the laser focuses on the bone surface is achieved by a combined movement of the applicator 17 via the stereotactic robot 21, of the laser beam 2 via the beam deflection unit 11, and the focus adjustment of the telescope 9. The beam deflection unit 11 can be designed as a 2D scanner mirror.A 2D scanner mirror is a mirror with a pivot point that can deflect a laser beam in two spatial directions. Alternatively, the beam deflection unit 11 can consist of 2D scanner mirrors with two mutually orthogonal axes of rotation.

[0002] List of reference symbols Laser beam source Laser beam Beam guidance Glass plate ' Glass plate Position sensor ' Position sensor OCT sensor ' Beam guidance system OCT measuring beam Deflection element Telescopic optics ' Adjustable telescopic lens 0 Beam combiner 1 2D beam deflection unit 2 Focusing optics 3 Exit opening 3' Protective window 4 Applicator housing 5 Bone 6 Atomizer nozzle 7 Laser applicator 1 Stereotaxy robot 2 Stereotactic frame 2' Ring 2'' Platform 3 Holder 4 Screw 5 Stereotactic arch 6 Slide 7 Linear adjustment unit 8 Motor 8' Motor 8'' Motor 0 Skull

Claims

1. Stereotactic device for cutting hard tissue on the skull bone, with - a stereotactic frame (22) which is designed to be attached to the head of a patient, and - a stereotactic arch (25) which is attached to the stereotactic frame (22) via at least one rotary joint and which, when the stereotactic frame (22) is attached to the head of a patient, can be tilted over the head by means of the rotary joint, characterized in that a laser applicator (17) is attached to the stereotactic arch (25) and can be moved along the stereotactic arch (25) via a motor drive (28''), and the stereotactic arch (25) can be tilted on the stereotactic frame (22) via a further motor drive (28, 28'), wherein the laser applicator (17) has a dynamic 2D beam deflection device (11),via which a processing laser beam (2) coupled into the laser applicator (17) can be guided over an area of ​​the hard tissue to be cut, and a focusing optic (12) with a focus position for the coupled processing laser beam (2) that can be adjusted by the focusing optic (12) or other optical elements, and wherein a measuring device (6) is arranged in the laser applicator (17) or connected to the laser applicator (17), with which a cutting depth of a cutting joint produced with the processing laser beam (2) and a residual thickness of the skull bone (15) in the cutting joint can be measured.

2. Stereotactic device according to claim 1, characterized in that the measuring device (6) is an OCT measuring device that directs a measuring beam (7) for measuring the cutting depth and the residual thickness of the cranial bone (15) coaxially to the processing laser beam (2) onto the hard tissue to be cut.

3. Stereotactic device according to claim 1 or 2, characterized in that the laser applicator (17) has a spray device with which a liquid film that moistens and cools the bone surface can be applied to the cranial bone (15) during cutting.

4. Stereotactic device according to one of claims 1 to 3, characterized in that the laser applicator (17) is connected to a flexible or articulated beam guide device (3), via which the processing laser beam (2) is coupled into the laser applicator (17). 5.Stereotactic device according to claim 4, characterized in that the beam guiding device (3) is formed by an articulated mirror arm or a fiber optic system with an optical fiber.

6. Stereotactic device according to one of claims 1 to 5, characterized in that the stereotactic arch (25) has a carriage (26) which can be moved along the stereotactic arch by the motor drive (28") and on which the. Laser applicator (17) is attached.

7. Stereotactic device according to claim 6, characterized in that the laser applicator (17) is attached to the carriage (26) via a detachable connection.

8. Stereotactic device according to one of claims 1 to 7, characterized in that the stereotactic frame (22) has an inner annular frame part (22') and an outer frame part (22'') rotatable about the inner annular frame part (22'), to which outer frame part the stereotactic arch (25) is attached via the at least one rotary joint.

9. Stereotactic device according to one of claims 1 to 8, characterized in that the laser applicator (17) is attached to the stereotactic arch (25) via a motorized linear adjustment unit (27), via which the laser applicator (17) can be moved in a direction radial to the arch (25). 10.Stereotactic device according to one of claims 1 to 9, characterized in that the dynamic 2D beam deflection device (11) has a 2D scanner mirror or two 1D scanner mirrors designed for beam deflection along two mutually orthogonal axes of rotation.

11. Stereotactic device according to one of claims 1 to 10, characterized in that the motor drives (28, 28', 28'') that... The measuring device (6) and the laser applicator (17) are connected to a control unit which controls them for cutting guidance when cutting the hard tissue on the skull bone.

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