WO2011135290A1

WO2011135290A1 - Apparatus and method for implanting a medical device

Info

Publication number: WO2011135290A1
Application number: PCT/GB2011/000641
Authority: WO
Inventors: Mathew David Frederick Stratton; Hugo George Derrick; James David Mortimer
Original assignee: Renishaw (Ireland) Limited
Priority date: 2010-04-26
Filing date: 2011-04-26
Publication date: 2011-11-03
Also published as: GB201006971D0

Abstract

This invention concerns a computer aided method of selecting at least one anatomical site for receiving at least one implantable device. The method may comprise taking a digital model of said at least one implantable device, taking a model of an anatomical region of interest of a patient and comparing the model of said at least one implantable device with the model of the anatomical region of interest of a patient to establish one or more suitable anatomical sites within the anatomical region of interest where the at least one implantable device can be implanted.

Description

Apparatus and Method for Implanting a Medical Device

The present invention relates to a method and associated apparatus that aids in the selection of an anatomical site or sites for receiving a medical implant. In particular, the invention relates to a computer implemented method for helping a surgeon to select the preferred site(s) on the skull for mounting one or more implantable devices.

It is known to mount implantable devices in recesses or holes formed in the skull. Previously, the selection of the anatomical site or sites where such devices are to be mounted was determined manually by a surgeon; this is often done "in-theatre" during a surgical implantation procedure. Such a manual site selection process can lead to sub-optimal device placement.

According to the present invention, a computer aided method of selecting at least one anatomical site for receiving at least one implantable device is provided. The method preferably comprises the step of taking a digital (preferably three-dimensional) model of said at least one implantable device. For example, the step may comprise taking a 3D CAD representation of the device(s) to be implanted. A step of taking a (preferably three dimensional) model of an anatomical region of interest of a patient may also be performed. This step may comprise, for example, taking a 3D image (e.g. derived from a CT or MRI scan) of a patient's skull.

The method preferably includes a step of comparing the model of said at least one implantable device with the model of the anatomical region of interest of a patient. Advantageously, this step comprises establishing one or more suitable anatomical sites

(e.g. within the anatomical region of interest) where the at least one implantable device may be implanted. This step may also comprise finding a preferred orientation of the at least one implantable device relative to the model of the anatomical region. As described in more detail below, preferred or optimised anatomical site(s) for implanting each implantable device may be calculated using a suitable algorithm based on a set of preferred (e.g. weighted) criteria for implantable device placement. The method may be implemented on a computer. A computer program for implementing the method may be provided. A computer programmed to implement the method may be provided. The method may include the further step of implanting the implantable device. The implantation may be performed in an automated or semi- automated manner using a surgical robot or by a manual process.

The invention also extends to apparatus for selecting at least one anatomical site for receiving at least one implantable device. The apparatus may include means for taking a digital (preferably three-dimensional) model of said at least one implantable device. The apparatus may include means for taking a (preferably three dimensional) model of an anatomical region of interest of a patient. Means may also be provided for comparing the model of said at least one implantable device with the model of the anatomical region of interest of a patient.

The invention will now be described, by way of example only, with reference to figures 1 to 3.

Figure 1 shows a first stage in the process of identifying the location of implant.

The process shown in figure 1 may include any one or more of the following steps in any suitable order:

Step 1 - Plan stereotactic target co-ordinates. This may include generating a stereotactic surgical plan including at least one of defining target structures / volumes / points, co-ordinates of such and initial planned trajectories / safety corridors through which you can safely traverse brain tissue.

Step 2 - Identify implantable device. This may comprise selecting a device from the software, generating a foot print manually etc. The implantable device may comprise a pump, port, catheter, guide tube, DBS electrode etc. Step 3 - Load 3D model of implantable device. This may be from CAD or similar as described above. Step 4 - Refer to and/or load appropriate dataset containing patient data. This may, for example, comprise taking the data that has been used for surgical planning in step 1. Alternatively, it is possible to load and register a dataset (such as CT data of the patient) that it is to be used specifically for this stage in the planning process. Step 5 - Segment skull. This involves distinguishing between skull bone and surrounding tissue and may be done using known segmentation algorithms.

Step 6 - Create a 3D model of the skull from the segmented data. Step 7 - Segment bone / structure type. This allows classification of the different structures within the skull bone.

Step 8 - Assign material values (e.g. softness, thickness etc) to segmented bone volumes. Using previously generated classification for bone data, it is possible to assign different material properties to different bone structures / sections. It is also possible for additional loading to be applied to certain structures in cases of osteoporosis etc.

Step 9 - Segment fissures and/or any other areas of concern.

Step 10 - Identify anchor points and/or the location of related devices. This can be done from the surgical plan where DBS lead / catheter positions have been defined or via previously implanted devices such as implanting drug delivery systems in patients that have had DBS.

It should be noted that in place of some or all of steps 7 to 10 , a full FEA analysis could be conducted on the 3D skull model.

Step 1 1 - A number of potential implant sites for the device can be established. This can be constrained by other planned implants / sites of previously implanted devices and any cable routings required. Factors that can be used to calculate such site options can be classified as fit (optionally including aesthetics) and structural strength of skull once implant is secured.

Step 12 - Present / display options to clinician. There are various ways to present this - e.g. via volumes within which devices can be implanted, actual device positions or a mixture of the two where a device is initially located within a volume that it can moved around in. At this point, the surgeon can take in to account patient aesthetics (such as hairlines) etc. when selecting the best option or the software can provide additional tools / weighting etc. for this.

Implantable device placement can be chosen by the surgeon in step 12 from a selection of possible solutions offered by the system as calculated in step 1 1. Algorithms for creation of possible solutions take into account many factors and multiple solutions are found each with a rating giving their suitability. A search algorithm could be utilised whereby a cost function is minimised by translating and rotating (optimising) the position of the implantable device. Such search algorithms "search" the solution space, in this case the position of the implantable device. Optimisation of the position, in a bid to minimise the cost function, could be controlled by using the well known Matlab function "fininsearch()" or some other widely used and well documented optimisation algorithm, such as a genetic search algorithm. The cost function could be based on metrics such as the distance of the implantable device's surface to the skull surface (both internal and external) and/or the amount of implantable sticking out above the skull surface. Further constraints would be imposed on the proposed positions to take into account metrics such as proximity to sinus, vessels, fissures, skull plates and electrodes etc from previous surgeries and data such as the skull thickness, bone type etc. Rather than use the full model the surgeon / software could narrow the search and analysis down through gross factors (such as how the patient will be held in the operating room) or surgical preference.

Step 13 - Save device location. If automated implantation is to be implemented, a cutting programme for a surgical robot may be generated.

The output of step 13 may be used in an automatic, semi-automatic or manual surgical procedure. The automatic and/or semi-automatic procedure may be implemented using a Neuromate robot produced by Renishaw Mayfield SA, Nyon, Switzerland.

Figure 2 shows a process of auto drilling / machining. The process shown in figure 2 may include any one or more of the following steps in any suitable order:

Step 20 - Saved device position and macliining programme. Either pull through all saved devices / positions or one at a time dependent on surgical workflow.

Step 21 - Register patient to robot co-ordinate system. Using known techniques such as via fitting the stereotactic frame to a receiving plate permanently attached (and calibrated) to the robot OR using known frameless techniques such as optimal those based on optimal, magnetic inductance or ultrasound technologies.

Step 22 - Demonstrate machining in software. Or alternatively a dry run on a model skull.

Step 23 - Robot creates burr hole / volume etc. Preferably with constant feedback on position either or from torque feedback on the motors, strain gauges, piezo sensing technologies, acoustically, optically etc.

Step 24 - Device is implanted. Either using the robot to implant the device or the surgeon.

Referring to figure 3, a manual or constrained robotics machining option is described. The process shown in figure 3 may include any one or more of the following steps in any suitable order:

Step 30 - Implant / patient skull Boolean intersection generates extents of volume to be machined / removed from skull. Step 31 - Results of bone classification / analysis used to define maximum tool feed- rates through out volume.

Step 32 - Machining protocol downloaded to robotic arm. Step 33 - Robotic arm, equipped with a bone machining end-effector, manually guided / 'pencil traced' over area to be machined.

Step 34 - Robotic arm constrains motion such that (1) the cutting tool is prevented from straying beyond the previously defined volume boundary (2) optimal feed-rates are not exceeded.

Step 35 - Cutting tool automatically stops once the volume has been cleared of bone.

Step 36 - Turn to next feature to be machined.

The cutting tool used in the above method may include one or more of a rotary cutter, a reactionless rotary cutter, a non-rotating ultrasonic cutter and a rotating ultrasonic cutter. The method may comprise a step of sensing using , for example, strain gauges, piezo-sensing, motor torque and/or natural frequency shift / acoustic behaviour.

The above examples are merely illustrative and should not be seen as limited the scope of the present invention. The skilled person would be aware of the many variants and alternative applications of the above described methods.

Claims

1. A computer aided method of selecting at least one anatomical site for receiving at least one implantable device, the method comprising taking a digital model of said at least one implantable device, taking a model of an anatomical region of interest of a patient, comparing the model of said at least one implantable device with the model of the anatomical region of interest of a patient to establish one or more suitable anatomical sites within the anatomical region of interest where the at least one implantable device can be implanted.

2. A computer aided method according to claim 1 , comprising finding a preferred orientation of the at least one implantable device relative to the model of the anatomical region.

3. A computer aided method according to claim 1 or claim 2, wherein taking a model of an anatomical region of interest comprises taking a three dimensional image of a patient's skull.

4. A computer aided method according to claim 3, wherein the 3D image is derived from a CT or MRI scan.

5. A computer aided method according to any one of the preceding claims, wherein the model of the implantable device is a three dimensional model.

6. A computer aided method according to any one of the preceding claims, wherein anatomical site(s) for implanting each implantable device are established by calculating using a suitable algorithm based on a set of preferred criteria for implantable device placement.

7. A computer aided method according to claim 6, wherein the criteria include distance of the implantable device's surface to the external and/or internal surface of the anatomical region, an amount of the implantable device sticking above the surface of the anatomical region, a proximity of the implantable device to sinus, vessels, fissures, skull plates and electrodes, skull thickness, bone type, a fit of the implantable device in the anatomical region and/or a structural strength of the anatomical region once the implantable device is implanted.

8. A computer aided method according to any one of the preceding claims comprising segmenting the image of the anatomical region and assigning material values to segmented volumes/regions.

9. A computer aided method according to claim 8, wherein the segmented volumes/regions are assigned material values using previously generated classification of bone data.

10. A computer program for implementing the method as claimed in any one of the previous claims.

11. A computer programmed to implement the method according to any one of claims 1 to 9.

12. Apparatus for selecting at least one anatomical site for receiving at least one implantable device, the apparatus comprising means for taking a digital model of said at least one implantable device, means for taking a model of an anatomical region of interest of a patient, means for comparing the model of said at least one implantable device with the model of the anatomical region of interest of a patient to establish one or more suitable anatomical sites within the anatomical region of interest where the at least one implantable device can be implanted..

13. A surgical robot for implanting an implantable device in a patient in an automated or semi- automated manner, the surgical robot having loaded therein a location of an anatomical site determined in accordance with any one of claims 1 to 9.

14. A method of operating a surgical robot for preparing a site for the implantation of an implantable device in a patient in an automated or semi-automated manner, the method comprising loading into the surgical robot a location of an anatomical site determined in accordance with any one of claims 1 to 9.

15. A method according to claim 14, comprising receiving data on surgical workflow and adjusting the position of the surgical robot in response to the received data.

16. A method according to claim 15, wherein the data is received from a sensor providing data on the torque feedback on motors of the robot for drilling a burr hole.

17. A computer aided method comprising taking a digital model of said at least one implantable device, taking a model of an anatomical region of interest of a patient, comparing the model of said at least one implantable device with the model of the anatomical region of interest of a patient to establish a volume to be removed from the anatomical region.

18. A computer aided method comprising taking a digital model of said at least one implantable device, taking a model of an anatomical region of interest of a patient, comparing the model of said at least one implantable device with the model of the anatomical region of interest of a patient to establish a maximum tool feed rate when machining a volume to be removed from the anatomical region.

1 . A computer aided method according to claim 18, wherein the maximum tool feed rate is determined from a tissue type identified from the model of the anatomical region of interest.

20. A method of programming a surgical robot for machining an anatomical region of a patient in an automated or semi-automated manner, the method comprising loading into the robot a protocol that constrains motion of the robot during machining of the anatomical region.

21. A method according to claim 20, wherein the protocol constrains motion such that a cutting tool of the robot is prevented from straying beyond a defined volume boundary.

22. A method according to claim 20 or claim 21 , wherein the protocol constrains motion such that a cutting tool of the robot is prevented from exceeding defined feed- rates.