Tracking System for 3D Transcranial Tracking of Medical Devices

Abstract

The present invention relates to a tracking system (1) and method for 3D tracking of a medical device comprising at least one ultrasonic sensor within an anatomical region of a subject comprising at least one layer of a first tissue type at least partially surrounding a volume comprising at least one second tissue type, wherein the ultrasonic propagation characteristics in the first and second tissue types are different.

Description

Technical Field

[0001] The present invention relates to the field of position tracking of medical devices for assisting during an intervention on a patient. The present invention particularly relates to the use of ultrasound for the localization and tracking of medical devices within a patient's body.

Background Art

[0002] Advances in recent microtechnologies have made it possible to navigate medical microdevices within the human body and reach deep and difficult-to-access structures. For safety reasons, this micro-robot should be as autonomous as possible and is most preferably controlled in a non-contact manner from outside the patient's body. Therefore, this microdevice requires a non-contact positioning system that defines an internal reference in order to be tracked and accurately positioned during movement inside the target body part. Also, this system must be able to provide accurate 3D localization of the above micro-robot inside the target body part in order to allow the surgeon to fully control the situation.

[0003] There is a need to improve the tracking system of this type of micro-robot, particularly the localization corresponding to the anatomical structure of the target body part. For example, the position of the micro-robot relative to anatomical features such as functional areas, blood vessels, or nerves is of utmost importance for defining the path and target points of the robot inside the target body part. Therefore, a 3D imaging diagnostic method that enables path planning assuming these features is required. Furthermore, the imaging diagnostic method and the positioning of the micro-robot need to be registered together with an accuracy higher than 1 mm. In particular, in neurosurgery, medical microdevices require a non-invasive tracking system with an accuracy at least equivalent to their size.

[0004] Therefore, there is a need to develop a system for tracking medical devices with submillimeter accuracy.

Summary of the Invention

[0005] Accordingly, the present invention relates to a tracking system for estimating the 3D position of a medical device comprising at least one ultrasonic sensor within an anatomical region of a subject comprising at least one layer of a first tissue type that at least partially surrounds a volume comprising at least one second tissue type, wherein the ultrasonic propagation characteristics in the first and second tissue types are different, and the system comprises: at least one input configured to receive the position of each of at least three external ultrasonic sensors relative to at least one first tissue layer, information regarding the geometric shape of at least one first tissue layer, and a 3D map of the speed of ultrasound in the volume of at least one first tissue layer and at least one second tissue; at least one processor, acquire the current position ( ) of the medical device within the volume of at least one second tissue, and, to calculate the current elevation angle ( ) and the current azimuth angle ( ) of the medical device with respect to each external ultrasonic sensor, use the acquired current position ( ) to estimate the current path ( ) through which ultrasound travels between each external ultrasonic sensor and the medical device through at least one first tissue layer, and, to estimate the current elevation angle ( ) and the current azimuth angle ( ​​​​​​ [Number] using For each external ultrasonic sensor, the estimated current path ( [Number] ) and the 3D map of the velocity in the first tissue to obtain the relevant current local velocity ( [Number] ) The current local velocity in at least one first tissue layer related to the corresponding external ultrasonic sensor ( [Number] ) and the estimated current path related to the corresponding external ultrasonic sensor ( [Number] ), the velocity of ultrasonic waves in at least one second tissue, and the measurement time of the propagation of ultrasonic waves between each external ultrasonic sensor and the medical device to calculate the current distance ( [Number] ) between each external ultrasonic sensor and the medical device Using the current distance ( [Number] ) between each external ultrasonic sensor (Si) and the medical device to estimate the new position of the medical device within the volume of at least one second tissue Performing a positioning calculation including Until the exit criteria are met, the new position is the current position ( [Number] ) configured to use and repeatedly perform location-specific calculations, a processor, at least one output configured to provide an estimated position of a medical device that meets an exit criterion comprising.

[0006] According to another advantageous aspect of the present invention, the device comprises, alone or in any possible combination, one or more of the features described in the following embodiments, Current distance (

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[0007] The present disclosure also relates to a computer program comprising software code adapted to execute a method for estimating the position and 3D tracking of a medical device according to any of the above execution modes when the program is executed by a processor.

[0008] As a further object, the present invention has a computer-implemented method for estimating the 3D position of a medical device comprising at least one ultrasonic sensor within an anatomical region of a subject comprising at least one layer of a first tissue type at least partially surrounding a volume comprising at least one second tissue type, wherein the ultrasonic propagation characteristics in the first and second tissue types are different, and the system receiving the position of each of at least three external ultrasonic sensors with respect to at least one first tissue layer, information regarding the geometric shape of at least one first tissue layer, and a 3D map of the speed of ultrasonic waves in at least one first tissue layer and the volume of at least one second tissue; the current position of the medical device within the volume of the second tissue (

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[0009] The method may comprise one or more of the following steps: Calculating the current distance (

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[0010] The present disclosure further relates to a computer-readable non-transitory program storage device tangibly embodying a program of executable instructions for a computer to execute a method for performing position estimation and 3D tracking of a medical device in accordance with the present disclosure.

[0011] Such a non-transitory program storage device may be, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor device, or any suitable combination of the foregoing. Hereinafter, as more specific examples, a portable computer disk, a hard disk, a ROM, an EPROM (erasable programmable ROM), or a flash memory, a portable CD-ROM (compact disk ROM) are mentioned, but these are merely illustrative and are understood to be a non-exhaustive list as easily understood by those skilled in the art. Definitions

[0012] In the present invention, the following terms have the following meanings.

[0013] In the present invention, the following terms have the following meanings.

[0014] In the present disclosure, the terms "adapted" and "configured" are used to broadly encompass, regardless of whether implemented by physical means or (including firmware) software means, the initial configuration of the device, subsequent adaptation or complementation, or any combination thereof.

[0015] The term "processor" should not be construed as limited to hardware capable of executing software, but generally refers to a processing device that may include, for example, a computer, a microprocessor, an integrated circuit, or a programmable logic device (PLD). Also, the processor may include one or more graphics processing units (GPUs), regardless of whether utilized for computer graphics and image processing or other functions. Also, the instructions and / or data that enable the execution of the associated functions and / or the resulting functions may be stored in any processor-readable medium, such as, for example, an integrated circuit, a hard disk, an optical disk such as a CD (compact disc), for example, a DVD (digital versatile disc), a RAM (random access memory), or a ROM (read-only memory). The instructions may be stored, in particular, in hardware, software, firmware, or any combination thereof.

Brief Description of the Drawings

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Mode for Carrying Out the Invention

[0017] This description illustrates the principles of the present disclosure. Accordingly, it is understood that those skilled in the art can devise various configurations that embody the principles of the present disclosure and are included within its scope, although not explicitly described or illustrated herein.

[0018] All of the examples and conditional language recited herein are intended for the educational purpose of helping the reader understand the principles of the present disclosure and the concepts contributed by the inventor to the advancement of the art, and are to be construed as not being limited to such specifically recited examples and conditions.

[0019] Furthermore, all descriptions in this specification that describe the principles, aspects, and embodiments of the present disclosure, as well as specific examples thereof, are intended to encompass both their structural equivalents and functional equivalents. Such equivalents are also intended to include currently known equivalents and equivalents developed in the future, i.e., any elements developed to perform the same function regardless of structure.

[0020] Thus, for example, those skilled in the art will understand that the block diagrams presented herein may represent conceptual diagrams of exemplary circuits embodying the principles of the present disclosure. Similarly, any flowchart, flow diagram, etc. is substantially represented in a computer-readable medium and represents various processes that can be executed by a computer or processor, whether or not a computer or processor is explicitly recited.

[0021] The functions of the various elements shown in the figures can be provided by dedicated hardware, as well as by hardware capable of executing software in association with appropriate software. When provided by a processor, the functions can be provided by a single dedicated processor, a single shared processor, or multiple distinct processors that may be shared.

[0022] It should be understood that the elements shown in the figures can be implemented in various forms of hardware, software, or combinations thereof. Preferably, these elements are implemented in a combination of hardware and software on one or more appropriately programmed general-purpose devices that may include a processor, memory, and an input / output interface.

[0023] The present disclosure is described with reference to a particular functional embodiment of a tracking system 1 for the position estimation and 3D tracking of a medical device, as shown in FIG. 1.

[0024] The medical device of the present invention may be a surgical micro-robot having dimensions in millimeters. Other medical devices that can be placed within a patient by the systems and methods of the present invention are catheters, surgical probes, biopsy needles, laparoscopes, or any other surgical instrument that is inserted into a patient's body and requires tracking during use.

[0025] Medical device M is generally introduced into the anatomical structure of a subject to be examined or treated during surgery. In one example, a hole may be provided in the first tissue layer to directly introduce medical device M into the second tissue volume, particularly when the first tissue type is bone tissue.

[0026] Tracking system 1 is adapted to provide an estimate of the position of medical device M within an anatomical region at a given time. When medical device M moves within the anatomical region, tracking system 1 is configured to provide the position of medical device M as a function of time. As will be described in detail in the following paragraphs, by selection of specific steps implemented by a processor, information regarding the actual position of medical device M can be obtained in real time (i.e., 20 position estimates per second).

[0027] The tracking system 1 described herein is versatile and is provided with several functions that can alternatively or optionally be performed in any cumulative manner. However, other implementations within the scope of the present disclosure include devices having only some of the functions of the present disclosure.

[0028] Tracking system 1 is advantageously a device or a physical part of a device that is designed, configured, and / or adapted to perform the functions recited and to produce the effects or results recited. In alternative implementations, any of tracking system 1 may be embodied as a set of devices or physical parts of a device, whether grouped on the same machine or grouped on different, possibly remote machines. Tracking system 1 may, for example, have functions distributed across a cloud infrastructure and be available to a user as a cloud-based service, or have remote functions accessible via an API.

[0029] In the following, a module is understood as a functional entity rather than a materially physically different component. Thus, a module can be embodied by being grouped into the same tangible and specific components or being distributed among several such components. Also, each of these modules can, in some cases, itself be shared between at least two physical components. Additionally, a module is similarly implemented in hardware, software, firmware, or any mixed form thereof. Preferably, a module is embodied in at least one processor of the tracking system 1.

[0030] The tracking system 1 comprises a module 11 for receiving a plurality of inputs necessary for steps to be carried out. In particular, the module 11 is configured to receive the position 20 of each of at least three external ultrasonic sensors Si with respect to at least one first tissue layer, information on the geometric shape 21 of at least one first tissue layer, and a 3D map of the speed of ultrasonic waves within at least one first tissue layer and at least one second tissue 22. These inputs 20, 21, and 22 may be stored in one or more local or remote database(s) 10. The latter may take the form of storage resources available within an SSD (solid state disk), for example, from any suitable type of storage means, which may in particular be a RAM or an EEPROM (electrically erasable programmable read-only memory) such as a flash memory.

[0031] As shown in FIG. 2, at least three external ultrasonic sensors Si (i = 1, ···, N, where N is 3 or more) are arranged at three different positions with respect to the anatomical region and can be brought into contact with at least one layer of the first tissue layer L1. Depending on the anatomical region, the external ultrasonic sensors Si may or may not be firmly fixed to a part of the anatomical region. For example, when the first tissue layer is bone tissue, the external ultrasonic sensors Si can be firmly fixed to the bone or to a surgical instrument whose relative position with respect to the anatomical structure does not change. Similarly, during the operation, at least three external ultrasonic sensors Si can be arranged on a part of the anatomical structure that can drift, expand, or be modified during the operation so that the positions of the at least three external ultrasonic sensors Si with respect to the first tissue layer L1 or the second tissue volume V change. In that case, each of the at least three external ultrasonic sensors Si may be provided with a reference coupled to a navigation system capable of tracking the position of each external ultrasonic sensor Si with respect to the first tissue layer L1. The tracking information can be used to correct the position of each external ultrasonic sensor Si in real time so as not to lose the accuracy in the 3D tracking of the medical device M.

[0032] When the external ultrasonic sensors Si are firmly fixed to the anatomical structure (i.e., their positions do not change during the operation), their positions 20 can be obtained before the start of the operation (but after being fixed to the subject) using medical imaging techniques such as CT scans or MRI imaging. In an alternative example, when no firm fixation is possible and no navigation system is used, the positions 20 of the external ultrasonic sensors Si can be directly measured in the operating room at the start of the operation and tracked throughout the operation.

[0033] Information regarding the geometry 21 of at least one first tissue layer and ultimately the second tissue volume of the anatomical structure can be derived from medical imaging data such as CT scans and / or MRI, depending on the nature of the first tissue type and at least one second tissue type. The information regarding the geometry 21 includes, for example, the thickness of the first tissue layer at each point on the surface. In addition, the second layer

[0034] A 3D map of the speed of ultrasound in the volume of at least one first tissue layer and at least one second tissue 22 can be derived from CT scan imaging data or any other medical imaging technique known to those skilled in the art. In fact, the actual speed of sound (i.e., ultrasound) varies depending on tissue structure characteristics. By using a 3D map of the speed of ultrasound rather than just an approximation of the speed of sound for the first and second tissue types, better tracking accuracy can be obtained.

[0035] The receiving module 11 can be further configured to communicate with the medical device M and the external ultrasound sensor Si, particularly via a wireless communication network. Thus, the receiving module 11 can be configured to receive in real time the measurements made by the ultrasound sensor of the medical device M and the external ultrasound sensor Si. In one example, the ultrasound sensor of the medical device M is an ultrasound emitter and the external ultrasound sensor Si is an ultrasound receiver, or vice versa, where the ultrasound sensor of the medical device M is a receiver and the external ultrasound sensor Si is an ultrasound emitter. In both cases, the ultrasound sensor of the medical device M and the external ultrasound sensor Si make it possible to measure the time required for sound to propagate between the medical device and the external ultrasound sensor. This configuration of the external ultrasound sensor Si and the medical device sensor is particularly advantageous with respect to the use of a standard ultrasound probe configured to perform both ultrasound emission and reception, for example when a first type of tissue, such as bone tissue, strongly attenuates the intensity of the ultrasound. In fact, by separating the emitter and the receiver, the emitted ultrasound passes through the first tissue layer only once before being received by the receiver. Conversely, when a standard probe is used, the ultrasound first passes through the first layer, then reflects off the tissue and the medical device within the volume, and the reflected ultrasound passes through the first tissue layer a second time and is detected by the receiver. However, the signal-to-noise ratio of these ultrasounds is degraded by passing through the first tissue layer twice.

[0036] The tracking system 1 further comprises an initialization module 12 for obtaining a first position of the medical device M within the volume of at least one second tissue, which is then used by the localization module 13 as a starting position for the localization calculation loop.

[0037] According to one embodiment, the initialization module 12 receives imaging data (obtained from a medical imaging technique other than the ultrasonic sensors described above) and analyzes the imaging data to obtain a first approximation calculation of the position

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[0038] According to one alternative embodiment shown in FIG. 3, the initialization module 12 is configured to use measurements obtained from the external ultrasonic sensors Si and the ultrasonic sensor of the medical device M to obtain an approximate calculation of the position

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[0039] The initialization module 12 may be configured to perform steps 121, 122, and 123 for each of the external ultrasonic sensors Si. The results of the three steps obtained for each external ultrasonic sensor Si are then combined in step 124. Step 121 is the thickness of at least one first tissue layer at the position of each external ultrasonic sensor Si

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[0040] Step 122 is configured to obtain a local velocity in a first tissue type corresponding to the propagation speed of ultrasound through at least one first tissue layer corresponding to the external ultrasound sensor position.

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[0041] Step 123 consists of estimating a first distance

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[0042] The first distance for each external ultrasound sensor Si is given by the following formula:

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[0043] The first distance between each external ultrasound sensor Si and the medical device M

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[0044] This first current position

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[0045] In one example, the measurement time T of the propagation of ultrasonic waves between each external ultrasonic sensor Si and the medical device M i is based on the direct time-of-flight measurement values measured using at least one ultrasonic sensor of each external ultrasonic sensor Si and the medical device M. The propagation time means the time required for ultrasonic waves to propagate from one of each external ultrasonic sensor Si to the medical device M. The measurement of the propagation time can be of several types, including the use of a threshold to detect an ultrasonic pulse with an amplitude exceeding the threshold, the use of cross-correlation, the use of a maximum value to detect the ultrasonic pulse with the highest amplitude, the use of a Hilbert-transformed maximum value to detect the ultrasonic pulse corresponding to the transformed maximum value, or any other measurement type known to those skilled in the art.

[0046] According to one alternative embodiment, particularly when a tracking system is used to estimate at least one 3D position of the medical device M, the module 12 [Number] is configured to be obtained as the last estimated position of the medical device M that meets the exit criteria.

[0047] The tracking system 1 further includes a localization calculation loop module 13 for performing localization calculations. The above-mentioned localization calculation loop module 13 uses the first current position obtained by the initialization module 12 [Number] is configured to receive as input. Module 13 is this first current position [Number] is set as the initial value of the current position for the first iteration (j = 1) of the localization calculation loop. In fact, the present invention uses the first approximate estimated value of the current position as information for increasing the accuracy in the next calculation of the current position regarding one actual given position of the medical device until the calculation converges to an optimal estimated value of the current position of the medical device having an error of only sub-millimeters with respect to the estimated value. More precisely, by using the steps of module 13, an error of about 1 - 2 mm (i.e., 1 mm when considering only the thickness of the first tissue layer in front of each external ultrasonic sensor, and 2 mm when considering only one average thickness of the first tissue layer) can be reduced to an error of 100 - 900 micrometers.

[0048] As shown in FIG. 4, module 13 may be configured to perform successive steps 131 - 136, and steps 131 - 133 are performed for each external ultrasonic sensor until a predetermined exit criterion is verified. The current position used in step 131 for the first iteration (j = 1) is the first current position obtained by module 12, and when j > 2, the current position used in step 131 is the new (current) position obtained as a result of iteration j - 1.

[0049] Step 131 uses the obtained current position [Number] to calculate the current elevation angle [Number] and the current outer angle [Number] configured to calculate (see FIG. 5). The current elevation angle of the medical device M

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[0050] The next step 132 is to determine the current path estimated in step 131 in order to know with high accuracy which part of the first tissue layer the ultrasonic wave passes through to reach each of the external ultrasonic sensors Si

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[0051] The successive step 133 is the current distance (relating to the j-th iteration) between each external ultrasonic sensor Si and a medical device M within the volume of at least one second tissue

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[0052] Alternatively, optionally, step 133 is configured to use a numerical simulation of the propagation of ultrasound in the volume of at least one first tissue layer and at least one second tissue of the subject to calculate the current distance

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[0053] Next, step 134 is configured to estimate a new position (i.e., a new corrected position) of the medical device M within the volume of at least one second tissue using the current distance between each external ultrasonic sensor Si calculated in step 133 and the medical device M. The new position is calculated by triangulation or trilateration using the current distance

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[0054] Next, step 135 is performed to verify whether the estimated new position meets a predetermined exit criterion. When the exit criterion is not met, step 135 is configured to define the new position as the current position for the next iteration j + 1, and the current position received at the input of step 131

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[0055] The exit criterion may simply consist of verifying whether one iteration of steps 131 - 134 has been performed. In this example, the final estimated position 31 is the first new position estimated at the end of the first iteration. Similarly, the exit criterion may be configured to be met when a predetermined number of iterations are completed

[0056] Alternatively, the exit criterion may be such that the iteration is stopped when the result converges to one value, for a given number of (i.e., not predefined) iterations, for example 3 iterations, Current position

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[0057] As described above, the external ultrasonic sensor Si may be an ultrasonic emitter, and the medical device may include an ultrasonic receiver. The external ultrasonic sensor Si may be an ultrasonic emitter configured to modify the emission direction of the ultrasonic wave. In this case, the system 1 is further configured to include a module 14 (not shown) configured to wirelessly communicate with the external ultrasonic sensor to provide an instruction to modify the emission direction of the ultrasonic wave of each external ultrasonic sensor Si according to the final estimated position of the medical device M. Advantageously, the emission direction of the external ultrasonic sensor Si is modified to concentrate the ultrasonic wave on the medical device M, thereby improving the signal-to-noise ratio and the accuracy of the 3D position reconstruction. This embodiment of the present invention is particularly advantageous when a small number (i.e., three) of external ultrasonic sensors Si are used.

[0058] The tracking system 1 interacts with the user interface 16 through which information can be input and retrieved by the user. The user interface 16 includes visual, tactile, and / or auditory functions suitable for inputting or retrieving data, information, or instructions, in particular, any one or more of a screen, keyboard, trackball, touchpad, touch screen, loudspeaker, and voice recognition system well known to those skilled in the art.

[0059] Thus, the tracking system 1 of the present invention enables the position of a medical device within a patient's body to be estimated at a given location. The tracking system 1 can similarly be used to track in real time the position of a medical device moving within a second tissue volume. By repeating the steps described above for a plurality of actual positions of the medical device, it is possible to monitor the trajectory of the medical device M. Further, the implementation of the steps is fast enough to enable the estimated position 31 of the medical device M to be obtained 20 times per second in response to real-time tracking of the medical device.

[0060] FIG. 6 shows an example of an application of the system 1 in which there are three external ultrasonic sensors S1, S2, and S3, which are fixed to a patient's head. In this case, the first tissue layer L1 is the skull, and the second tissue volume V is the soft tissue of the brain. The medical device M shown in this figure is a micro-robot configured to move within the brain of a subject.

[0061] In the scenario of this example, as in other practical examples, the ultrasonic waves need to move not only through the skull but also through the skin, which may have ultrasonic propagation characteristics different from those of the first and second tissue types. Since the skin is a low-density tissue, the fact that the presence of the skin layer is ignored and only the first tissue layer is considered in the calculation does not threaten the results with sub-millimeter accuracy, as disclosed above.

[0062] However, the modules 12 and 13 can be configured to take into account the presence of a second layer of a third tissue that is different from (or not different from) the first and second tissues. Those skilled in the art will know how to take into account the presence of a second layer covering the first layer or located between the first layer and the volume V in the steps performed by the modules 12 and 13. This embodiment may further reduce the accuracy of 3D localization.

[0063] In an automatic action, the tracking system 1 is, for example, the following process, Receiving, for each of at least three external ultrasonic sensors Si, the location 20 thereof with respect to at least one first tissue layer, information regarding the geometric shape 21 of the at least one first tissue layer, and a 3D map of the speed of ultrasound in the volume of the at least one first tissue layer and at least one second tissue 22 (step 41), First current position [Number] Obtaining the same (step 42), Executing a positioning calculation loop using the first current position as the starting position (step 43), Obtaining a final estimated value of the position 31 of the medical device M (step 44) May be executed (Figure 7).

[0064] A specific device 9 as shown in Figure 8 embodies the tracking system 1 described above. This corresponds to, for example, a workstation, laptop, tablet, smartphone, or head-mounted display (HMD).

[0065] The device 9 is suitable for estimating the 3D position of a medical device within a patient's body. The device 9 includes the following elements connected to each other by an address and data bus 95 that carries a clock signal, A microprocessor (or CPU) 91, A graphics card 92 having several graphics processing units (or GPUs) 920 and a graphics random access memory (GRAM) 921, the GPUs being very suitable for image processing due to their highly parallel structure, A ROM-type non-volatile memory 96, A RAM 97, One or several I / O (input / output) devices 94 such as, for example, a keyboard, mouse, trackball, webcam, etc., and other command introduction modes such as voice recognition are also possible, A power supply 98, and A high-frequency unit 99 Is provided.

[0066] According to a modification, the power supply 98 is external to the device 9.

[0067] The device 9 also includes a display screen type display device 93 directly connected to the graphics card 92 in order to display a composite image of the trajectory of the medical device calculated and created in the graphics card. By using a dedicated bus to connect the display device 93 to the graphics card 92, a significantly larger data transmission bit rate is achieved, and the latency time regarding the display of the image created by the graphics card is reduced. According to a modification, the display device is external to the device 9 and is connected by cable or wirelessly to transmit a display signal. For example, the device 9 includes an interface for transmission or connection adapted to transmit a display signal to an external display means such as an LCD or a plasma screen or a video projector through the graphics card 92. In this regard, the RF unit 99 can be used for wireless transmission.

[0068] However, hereinafter, the term "register" used in the description of the memories 97 and 921 may refer to a low-capacity memory area (some binary data) as well as a high-capacity memory area (where the entire program is stored, or all or part of the data representing the data is calculated or displayed) in each of the memories referred to. Also, the registers meaning RAM 97 and GRAM 921 may be arranged and configured in any manner, and each of them does not necessarily correspond to adjacent memory locations and may be distributed in other ways (in particular, including the situation where one register includes several small registers).

[0069] When the switch is turned on, the microprocessor 91 loads and executes the program instructions contained in the RAM 97.

[0070] As will be understood by those skilled in the art, the presence of the graphics card 92 is not essential and may be replaced by overall CPU processing and / or a more simple visualization implementation.

Claims

1. In an anatomical region of a subject comprising at least one layer (Li) of a first tissue type that at least partially surrounds a volume (V) comprising at least one second tissue type, a tracking system (1) for estimating the 3D position of a medical device (M) comprising at least one ultrasonic sensor, wherein the ultrasonic propagation characteristics in the first and second tissue types are different, and the system (1) is configured to: at least one input configured to receive the position (20) of each of at least three external ultrasonic sensors (Si) relative to the at least one first tissue layer, information regarding the geometric shape (21) of the at least one first tissue layer, and a 3D map (22) of the speed of ultrasound in the volume of the at least one first tissue layer and the at least one second tissue; at least one processor, acquire the current position ( 【Number 1】 ) of the medical device (M) within the volume of the at least one second tissue, use the acquired current position ( 【Number 2】 ) and the positions (20) of the at least three external ultrasonic sensors (Si) to calculate the current elevation angle ( [Number 3] ) and current azimuth angle ( [Number 4] ) of the medical device (M) with respect to each external ultrasonic sensor (Si), and use the current elevation angle ( [Number 5] ) and current azimuth angle ( 【Number 6】 ) to estimate the current path ( 【Number 7】 ) through which the ultrasound travels between each external ultrasonic sensor (Si) and the medical device (M) through the at least one first tissue layer; for each external ultrasonic sensor (Si), use the estimated current path ( 【Number 8】 ) and the 3D map of the speed in the first tissue to obtain the associated current local speed ( 【Number 9】 ) in the first tissue; calculate the current distance ( 【Number 10】 ) between each external ultrasonic sensor (Si) and the medical device (M) by considering the current local speed ( 【Number 11】 ) in the at least one first tissue layer associated with the corresponding external ultrasonic sensor (Si), the estimated current path ( 【Number 12】 ) associated with the corresponding external ultrasonic sensor (Si), the speed of ultrasound in the at least one second tissue, and the measured time of propagation of the ultrasound between each external ultrasonic sensor (Si) and the medical device (M); the current distance between each external ultrasonic sensor (Si) and the medical device (M) 【Number 13】 using () to estimate a new position of the medical device (M) within the volume of the at least one second tissue performing a location calculation comprising repeating execution of the location calculation using the new position as the current position () until an exit criterion is met 【Number 14】 a processor configured to at least one output configured to provide an estimated position of the medical device (M) that meets the exit criterion (31) comprising a system, wherein a measurement time of ultrasonic propagation between each external ultrasonic sensor (Si) and the medical device (M) is based on a direct time-of-flight measurement value measured using at least one ultrasonic sensor of each external ultrasonic sensor (Si) and the medical device (M). **Claim 2** Calculating the current distance () comprises 【Number 15】 using a numerical simulation of ultrasonic propagation in at least one first tissue layer of the subject and in the volume of the at least one second tissue, the numerical simulation being based on medical imaging data of at least a part of the anatomical region of the subject. The system according to claim 1 **Claim 3** Obtaining the current position () of the medical device (M) within the volume of the second tissue for the first iteration comprises 【Number 16】 using the 3D geometric shape of at least one first tissue layer of the subject to obtain the thickness () of the at least one first tissue layer at the position of each external ultrasonic sensor (Si) for each external ultrasonic sensor (Si), using a 3D map of velocities in the first tissue to obtain a local velocity () in the first tissue corresponding to the propagation velocity of ultrasonic waves through the at least one first tissue layer corresponding to the external ultrasonic sensor position 【Number 17】 for each external ultrasonic sensor (Si), based on the corresponding obtained thickness (), the corresponding obtained local velocity () in the at least one first tissue layer propagating through the at least one first tissue layer along a path equal to the thickness, the velocity of ultrasonic waves in the second tissue, and the measurement time of ultrasonic propagation between each external ultrasonic sensor (Si) and the medical device (M), estimating a first distance () between the external ultrasonic sensor (Si) and the medical device (M) comprising, for the first iteration, the current position () of the medical device (M) within the volume of the at least one second tissue 【Number 18】 ​ ​ 【Number 19】 ​ 【Number 20】 ​ 【Number 21】 ​ ​ 【Number 22】 ), a system according to either claim 1 or 2, obtained using the estimated first distance ( 【Number 23】 ) between the medical device (M) and each external ultrasonic sensor (Si). **Claim 4** For the first iteration, obtaining the current position ( [24 Points] ) of the medical device (M) within the at least one second volume comprises using medical imaging data, a system according to any one of claims 1 or 2. **Claim 5** The exit criterion is configured to stop the iteration when, for a given number of iterations, the difference between the current position ( 【Number 25】 ) and the estimated new position is less than a predetermined threshold, a system according to any one of claims 1 to 4. **Claim 6** The external ultrasonic sensor (Si) is an ultrasonic emitter configured to modify the emission direction of the ultrasonic wave, the medical device comprises an ultrasonic receiver, and the at least one processor is further configured to use the estimated position (31) of the medical device to modify the emission direction of the ultrasonic wave so as to concentrate the ultrasonic waves of the at least three external ultrasonic sensors (Si) on the position of the medical device (M), a system according to any one of claims 1 to 5. **Claim 7** At least one layer of the first tissue type is the subject's skull, the at least one volume of the second tissue is the subject's brain, or at least one layer of the first tissue type is fat and the at least one volume is the liver, a system according to any one of claims 1 to 6. **Claim 8** A computer-implemented method for estimating the 3D position of a medical device (M) comprising at least one ultrasonic sensor within an anatomical region of a subject comprising at least one layer of a first tissue type surrounding at least partially a volume comprising at least one second tissue type, wherein the ultrasonic propagation characteristics in the first and second tissue types are different, and the system (1) comprises receiving the position (20) of each of at least three external ultrasonic sensors (Si) with respect to the at least one first tissue layer, information on the geometric shape (21) of the at least one first tissue layer, and a 3D map (22) of the speed of ultrasonic waves in the at least one first tissue layer and the volume of the at least one second tissue Obtaining the current position ( 【Number 26】 ) of the medical device (M) within the volume of the second tissue, Using the obtained current position ( 【Number 27】 ) to calculate the current elevation angle ( 【Number 28】 ) and the current lateral angle ( 【No. 29】 ) of the medical device (2) with respect to each external ultrasonic sensor (Si), and estimating the current path ( 【30】 ) through which the ultrasonic wave travels between each external ultrasonic sensor (Si) and the medical device (2) through the at least one first tissue layer using the current elevation angle ( 【Number 31】 ) and the current lateral angle ( 【Number 32】 ), For each external ultrasonic sensor (Si), estimating the relevant current local velocity ( 【Number 33】 ) in the first tissue using the current path ( 【Number 34】 ) and the 3D map of the velocity in the first tissue, Calculating the current distance ( 【Number 35】 ) between each external ultrasonic sensor (Si) and the medical device (M) by considering the current local velocity ( 【Number 36】 ) in the at least one first tissue layer associated with the corresponding external ultrasonic sensor (Si), the estimated current path ( 【Number 37】 ) associated with the corresponding external ultrasonic sensor (Si), the velocity of the ultrasonic wave in the at least one second tissue, and the measured time of propagation of the ultrasonic wave between each external ultrasonic sensor (Si) and the medical device (M), Using the current distance ( 【Number 38】 ) between each external ultrasonic sensor (Si) and the medical device (M) to estimate a new position of the medical device (M) within the volume of the at least one second tissue, Performing a positioning calculation comprising: Repeating the execution of the positioning calculation using the new position as the current position ( 【Number 39】 ) until an exit criterion is met, Comprising: The measured time of propagation of the ultrasonic wave between each external ultrasonic sensor (Si) and the medical device (M) is based on a direct time-of-flight measurement value measured using at least one ultrasonic sensor of each external ultrasonic sensor (Si) and the medical device (M). A method.

9. Calculating the current distance ( 【Number 40】 ) comprises using a numerical simulation of the propagation of ultrasonic waves in the first type of tissue and the second type of tissue of the subject, the numerical simulation being based on medical imaging data of at least a part of the anatomical region of the subject. The method according to claim 8.

10. Obtaining the current position ( 【Number 41】 ) of the medical device (M) within the volume of the second tissue is Using the 3D geometric shape of at least one first tissue layer of the subject, the thickness of the at least one first tissue layer at the position of each external ultrasonic sensor (Si) ( 【Number 42】 ) is obtained; For each external ultrasonic sensor (Si), corresponding to the external ultrasonic sensor position, the local velocity in the first tissue corresponding to the propagation velocity of ultrasonic waves passing through the at least one first tissue layer ( 【Number 43】 ) is obtained by using a 3D map of velocities in the first tissue; For each external ultrasonic sensor (Si), for a path equal to the corresponding obtained thickness ( 【Number 44】 ), the corresponding obtained local velocity in the first tissue propagating through the at least one first tissue layer ( 【Number 45】 ), the velocity of ultrasonic waves in the second tissue, and based on the measurement time of the propagation of ultrasonic waves between each external ultrasonic sensor (Si) and the medical device (M), the first distance ( 【Number 46】 ) between the external ultrasonic sensor (Si) and the medical device (M) is estimated; comprising, the current position ( 【Number 47】 ) of the medical device (M) within the volume of the at least one second tissue is obtained using the estimated first distance ( 【Number 48】 ) between the medical device (M) and each external ultrasonic sensor (Si), the method according to any one of claims 8 or 9.

11. The exit criterion is configured to stop the iteration when, for a given number of iterations, the difference between the current position ( 【Number 49】 ) and the new position ( 【Number 50】 ) is less than a predetermined threshold value, the method according to any one of claims 8 to 10.

12. The external ultrasonic sensor (Si) is an ultrasonic emitter configured to modify the emission direction of the ultrasonic waves, the medical device comprises an ultrasonic receiver, and the at least one processor is further configured to use the new position ( 【Number 51】 ) to modify the emission direction of the ultrasonic waves so as to concentrate the ultrasonic waves of the at least three cranial ultrasonic sensors (Si) at the position of the medical device (M), the method according to any one of claims 8 to 11.

13. A computer program product comprising instructions for causing the computer to execute the method according to any one of claims 8 to 12 when the program is executed by the computer.

14. A computer-readable medium comprising instructions that cause a computer to execute the method according to any one of claims 8 to 12 when executed by the computer.

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