Tracking system for 3D transcranial tracking of medical devices

Abstract

The invention relates to a tracking system (1) and a method for 3D tracking of a medical device equipped with at least one ultrasound sensor within an anatomical region of a subject, the anatomical region of the subject comprising at least one layer of a first tissue type, the at least one layer of the first tissue type at least partially encloses a volume comprising at least one second tissue type wherein the propagation characteristics of the ultrasound waves in the first tissue type and the second tissue type differ.

Description

Technical Field

[0001] The present invention relates to the field of tracking the position of medical devices used to assist during patient interventions. In particular, the present invention relates to the use of ultrasound to locate and track medical devices within a patient's body. Background Art

[0002] Recent breakthroughs in microtechnology offer the possibility to navigate medical microdevices inside the human body to reach deep and hard-to-reach structures. For safety reasons, such microrobots should be as autonomous as possible and most preferably controlled from outside the patient's body in a contactless manner. Therefore, such microdevices require a contactless positioning system that defines internal references so that they can be tracked and accurately positioned while moving inside the target body. To give the surgeon a complete picture of the situation, the system should also be able to accurately position the microrobot in 3D within the target body part.

[0003] There is a need to improve tracking systems, in particular to improve the positioning of such microrobots with respect to the anatomy of the target body part. The position of the microrobot relative to anatomical features (e.g., functional areas, vessels, or nerves) is crucial, as this will determine the path and target point of the robot within the target body part. Therefore, 3D imaging modalities are necessary to visualize these features and allow path planning. Furthermore, the imaging modalities as well as the positioning of the microrobot must be registered with an accuracy better than 1 mm. In particular, in neurosurgery, medical microdevices require a non-invasive and non-invasive tracking system with an accuracy at least comparable to their size.

[0004] In this context, there is a need to develop a system for tracking medical devices with sub-millimeter accuracy. Summary of the invention

[0005] The present invention thus relates to a tracking system for estimating the 3D position of a medical device equipped with at least one ultrasound sensor within an anatomical region of a subject, the anatomical region comprising at least one layer of a first tissue type, the at least one layer of the first tissue type at least partially surrounding a volume comprising at least one second tissue type, wherein propagation characteristics of ultrasound waves in the first tissue type and the second tissue type are different, the system comprising:

[0006] - at least one input configured to receive a position of each of the at least three external ultrasound sensors relative to at least one first tissue layer, information about the geometry of the at least one first tissue layer, and a 3D velocity map of ultrasound waves within the volume of the at least one first tissue layer and at least one second tissue;

[0007] - at least one processor configured to:

[0008] o obtaining a current position of the medical device within a volume of at least one second tissue ( );

[0009] oPerform positioning calculations, including:

[0010] ·Use the current location obtained ( ) to calculate the current elevation angle of the medical device relative to each external ultrasonic sensor ( ) and the current horizontal angle ( ), and using the current elevation angle ( ) and the current lateral angle ( ) to estimate a current path traveled by ultrasound waves through at least one first tissue layer between each external ultrasound sensor and the medical device ( );

[0011] For each external ultrasonic sensor (Si), use the estimated current path ( ) and the 3D velocity map in the first tissue to obtain the relevant current local velocity in the first tissue ( );

[0012] By taking into account the current local velocity in at least one first tissue layer associated with the corresponding external ultrasound sensor ( ), the estimated current path associated with the corresponding external ultrasonic sensor ( ), the speed of ultrasound in at least one second tissue, and the measured time for ultrasound to propagate between each external ultrasound sensor and the medical device to calculate the current distance between each external ultrasound sensor and the medical device ( );

[0013] · Use the current distance between each external ultrasonic sensor (Si) and the medical device ( ), to estimate a new position of the medical device within at least one second tissue volume;

[0014] o Use the new position as the current position ( ), repeat the positioning calculation until the exit criteria are met;

[0015] oAt least one output configured to provide an estimated position of a medical device that meets an exit criterion.

[0016] According to other advantageous aspects of the present invention, the device comprises one or more features described in the following embodiments, which can be used alone or in any possible combination:

[0017] - Calculate the current distance ( ) comprising using a numerical simulation of ultrasound wave propagation within a volume of at least one first tissue layer and at least one second tissue of a subject, the numerical simulation being based on medical imaging data of at least a portion of an anatomical region of the subject;

[0018] - For the first iteration, obtain the current position of the medical device within the volume of the second tissue ( )include:

[0019] i. Using the 3D geometry of at least one first tissue layer of the subject to obtain the thickness of at least one first tissue layer at the location of each external ultrasound sensor ( );

[0020] ii. For each external ultrasonic sensor, using the 3D velocity map in the first tissue to obtain the local velocity within the first tissue ( ), the local velocity corresponding to the propagation velocity of ultrasound through at least one first tissue layer corresponding to the location of the external ultrasound sensor;

[0021] iii. For each external ultrasonic sensor, based on the thickness equal to the corresponding obtained thickness ( ) propagates through at least one first tissue layer, the corresponding local velocity obtained in the at least one first tissue layer , the ultrasonic velocity in the second tissue, and the measured time of ultrasonic propagation between each external ultrasonic sensor (Si) and the medical device to estimate the first distance ( );

[0022] wherein the current position of the medical device in the volume of the at least one second tissue of the first iteration ( ) is the estimated first distance between the medical device and each external ultrasonic sensor using ( ) to obtain,

[0023] - for a first iteration, obtaining a current position of the medical device within the volume of at least one second tissue ( ) including the use of medical imaging data;

[0024] - the measured time of propagation of an ultrasonic wave between each external ultrasonic sensor and the medical device is based on a direct time-of-flight measurement measured using each external ultrasonic sensor and at least one ultrasonic sensor of the medical device,

[0025] - The exit criteria are configured as: for a given number of iterations, the current position ( ) and the estimated new position is less than a predetermined threshold, the iteration is stopped.

[0026] - the external ultrasonic sensors are ultrasonic transmitters configured to modify the emission direction of ultrasonic waves, and the medical device is equipped with an ultrasonic receiver, and wherein the at least one processor is further configured to modify the emission direction of ultrasonic waves using the estimated position of the medical device so as to focus the ultrasonic waves of the at least three external ultrasonic sensors to the position of the medical device,

[0027] - the at least one layer of the first tissue type is a skull of the subject and the at least one volume of the second tissue is a brain of the subject, or the at least one layer of the first tissue type is a fat layer and the at least one volume is a liver.

[0028] Furthermore, the present disclosure relates to a computer program comprising software code, which, when executed by a processor, is adapted to perform a method for estimating the position and 3D tracking of a medical device in accordance with any of the above-mentioned execution modes.

[0029] Another object of the invention is a computer-implemented method for estimating a 3D position of a medical device equipped with at least one ultrasound sensor within an anatomical region of a subject, the anatomical region comprising at least one layer of a first tissue type, the at least one layer of the first tissue type at least partially surrounding a volume comprising at least one second tissue type, wherein propagation characteristics of ultrasound waves in the first tissue type and the second tissue type are different, the system comprising:

[0030] - receiving a position of each of the at least three external ultrasound sensors relative to at least one first tissue layer, information about the geometry of the at least one first tissue layer, and a 3D velocity map of ultrasound waves within the volume of the at least one first tissue layer and at least one second tissue;

[0031] - Obtaining the current position of the medical device within the volume of the second tissue ( );

[0032] -Perform positioning calculations, including:

[0033] ·Use the current location obtained ( ) to calculate the current elevation angle of the medical device relative to each external ultrasonic sensor ( ) and the current horizontal angle ( ), and using the current elevation angle ( ) and the current lateral angle ( ) to estimate a current path traveled by ultrasound waves through at least one first tissue layer between each external ultrasound sensor and the medical device ( );

[0034] For each external ultrasonic sensor (Si), use the current path ( ) and the 3D velocity map in the first tissue to estimate the relevant current local velocity in the first tissue ( );

[0035] By taking into account the current local velocity in at least one first tissue layer associated with the corresponding external ultrasound sensor ( ), the estimated current path associated with the corresponding external ultrasonic sensor ( ), the speed of ultrasound in at least one second tissue, and the measured time of ultrasound propagation between each external ultrasound sensor and the medical device to calculate the current distance ( );

[0036] · Using the current distance between each external ultrasonic sensor and the medical device ( ), to estimate a new position of the medical device within at least one second tissue volume;

[0037] - Use the new location as the current location ( ), repeat the positioning calculation until the exit criteria are met;

[0038] The method may include one or more of the following steps:

[0039] - Calculate the current distance ( ) comprises using a numerical simulation of propagation of ultrasound waves in a first type of tissue and a second type of tissue of a subject, the numerical simulation being based on medical imaging data of at least a portion of an anatomical region of the subject,

[0040] - obtain the current position of the medical device (M) within the volume of the second tissue ( )include:

[0041] iv using the 3D geometry of at least one first tissue layer of the subject to obtain the thickness ( );

[0042] v. For each external ultrasonic sensor (Si), use the 3D velocity map in the first tissue to obtain the local velocity in the first tissue ( ), the local velocity corresponding to the propagation velocity of ultrasound through the at least one first tissue layer corresponding to the location of the external ultrasound sensor;

[0043] vi. For each external ultrasonic sensor, based on the thickness equal to the corresponding obtained ( ) propagates through at least one first tissue layer in the first tissue. , the ultrasonic velocity in the second tissue and the measured time of ultrasonic propagation between each external ultrasonic sensor and the medical device to estimate the first distance ( );

[0044] wherein the current position of the medical device within the volume of the at least one second tissue ( ) is the estimated first distance between the medical device and each external sensor ( ) obtained.

[0045] - The exit criteria are configured as: for a given number of iterations, the current position ( ) and the new position ( ) is less than a predetermined threshold, the iteration is stopped.

[0046] - the external ultrasonic sensor is an ultrasonic transmitter configured to modify the transmission direction of the ultrasonic wave, and the medical device is equipped with an ultrasonic receiver, and wherein the at least one processor is further configured to use the new position ( ) to modify the emission direction of ultrasound, thereby focusing the ultrasound from at least three skull ultrasound sensors (Si) at the location of the medical device.

[0047] The present disclosure also relates to a non-transitory program storage device readable by a computer, tangibly embodying program instructions executable by the computer to perform a method for estimating position and 3D tracking of a medical device consistent with the present disclosure.

[0048] Such non-transitory program storage devices can be, but are not limited to: electronic devices, magnetic devices, optical devices, electromagnetic devices, infrared devices or semiconductor devices, or any suitable combination of the foregoing devices. It should be understood that although more specific examples are provided below, they are only illustrative and not exhaustive, which are easily understood by those skilled in the art: portable computer floppy disk, hard disk, ROM, EPROM (erasable programmable read-only memory) or flash memory, portable CD-ROM (compact disk read-only memory).

[0049] definition

[0050] In the present invention, the following terms have the following meanings:

[0051] In the present invention, the following terms have the following meanings:

[0052] The terms "adaptation" and "configuration" as used in this disclosure broadly cover the initial configuration of the device, subsequent adaptation or supplementation, or any similar combination thereof - whether these are achieved by material or software means (including firmware).

[0053] The term "processor" should not be construed as limited to hardware that executes software, but rather generally refers to a processing device, which can include, for example, a computer, a microprocessor, an integrated circuit, or a programmable logic device (PLD). A processor may also include one or more graphics processing units (GPUs), whether for computer graphics and image processing or other functions. In addition, instructions and / or data capable of performing related and / or resulting functions may be stored on any processor-readable medium, such as an integrated circuit, a hard disk, a CD (compact disk) such as a DVD (digital versatile disk), a RAM (random access memory), or a ROM (read-only memory). Instructions may be stored in hardware, software, firmware, or any combination thereof. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 is a schematic block diagram representing a particular mode of a system for estimating a 3D position of a medical device.

[0055] Figure 2 is a schematic diagram showing a tracking system, a medical device, and an external ultrasonic sensor arranged relative to an anatomical region of a subject.

[0056] Figure 3 is a schematic block diagram showing a specific mode of a module for obtaining a first current position.

[0057] Figure 4 is a schematic block diagram representing a specific mode of modules for executing a positioning calculation loop.

[0058] Figure 5 is a schematic diagram showing a current elevation angle and a lateral angle for estimating a current path of ultrasound waves passing through at least one first tissue layer.

[0059] Figure 6 is a schematic diagram showing the estimation of the position and 3D tracking of a medical device located inside a subject's brain using a tracking system.

[0060] Figure 7 Shows the use of Figure 1 Flowchart of sequential steps performed for a 3D tracking device.

[0061] Figure 8 Schematically shows the integration of Figure 1 The 3D tracking device is a functional device of the device. DETAILED DESCRIPTION

[0062] This specification explains the principles of the present disclosure. Therefore, it should be understood that those skilled in the art can design various arrangements, although these arrangements are not explicitly described or shown in the present disclosure, they embody the principles of the present disclosure and are included in the scope of the present disclosure.

[0063] All examples and conditional language described herein are intended for educational purposes to help the reader understand the principles of the present disclosure and the concepts contributed by the inventors to advance the art, and should not be construed as being limited to only these explicitly recited examples and conditions.

[0064] In addition, all statements of the principles, aspects, embodiments and specific examples of the present disclosure described herein are intended to cover equivalents of both structure and function. In addition, these equivalents are intended to include both currently known equivalents and equivalents developed in the future, that is, any element developed to perform the same function regardless of its structure.

[0065] Thus, for example, it will be appreciated by those skilled in the art that the block diagrams described herein may represent conceptual views of illustrative circuitry embodying the principles of the present disclosure. Similarly, it will be appreciated that any flow charts, flowcharts, and the like represent various processes that may be substantially represented in a computer-readable medium and executed by a computer or processor, whether or not such computer or processor is explicitly shown.

[0066] The functions of the various elements shown in the drawings can be provided by using dedicated hardware and hardware capable of executing software in conjunction with appropriate software. When provided by a processor, these functions can be provided by a single dedicated processor, a single shared processor or multiple separate processors, wherein some processors can be shared.

[0067] It should be understood that the various elements shown in the drawings can be implemented by various forms of hardware, software or a combination thereof. Preferably, these elements are implemented on one or more appropriately programmed general-purpose devices by a combination of hardware and software, and these general-purpose devices may include a processor, a memory and an input / output interface.

[0068] Reference will be made to Figure 1 The present disclosure is described with reference to a specific functional embodiment of the tracking system 1 shown for estimating the position and 3D tracking of a medical device.

[0069] The medical device of the present invention may be a surgical microrobot with millimeter-scale dimensions. Other medical devices that can be positioned in a patient's body with the system and method of the present invention are catheters, surgical probes, biopsy needles, laparoscopes, or any other surgical instruments that need to be inserted into a patient's body and need to be tracked during use.

[0070] Medical device M is usually introduced into the subject's anatomical structure for examination or treatment during surgery. In one example, a hole can be opened in a first tissue layer, especially when the first tissue type is bone tissue, to introduce the medical device M directly into a second tissue volume.

[0071] The tracking system 1 is adapted to provide an estimate of the position of the medical device M in the anatomical region at a given time. As the medical device M moves within the anatomical region, the tracking system 1 is configured to provide the position of the medical device M as a function of time. As will be explained in detail in the following paragraphs, the specific selection of steps implemented by the processor enables information on the actual position of the medical device M to be obtained in real time (i.e.: 20 position estimates per second).

[0072] Although the presently described tracking system 1 is multifunctional and provides several functions that can be performed alternatively or in any cumulative manner, other embodiments within the scope of the present disclosure include devices having only some of the present functions.

[0073] Advantageously, the tracking system 1 is a device, or a physical part of a device, which is designed, configured and / or adapted to perform the above-mentioned functions and produce the above-mentioned effects or results. In alternative embodiments, any part of the tracking system 1 is implemented as a set of devices or physical parts of devices, whether they are in the same machine or in different (possibly remote) machines. The tracking system 1 may, for example, have functions distributed on a cloud infrastructure and provided to users as a cloud-based service, or have remote functions accessible via an API.

[0074] In the following, modules should be understood as functional entities rather than material, physically distinct components. Therefore, they can be embodied both as being concentrated and combined in the same tangible and concrete component, and as being distributed in several such components. Moreover, each of these modules itself may be shared between at least two physical components. Furthermore, these modules may also be implemented in hardware, software, firmware or any hybrid thereof. They are preferably embodied in at least one processor of the tracking system 1.

[0075] The tracking system 1 comprises a module 11 for receiving a plurality of inputs required for the implementation steps. It is noteworthy that the module 11 is configured to receive the position 20 of each of the at least three external ultrasonic sensors Si relative to at least one first tissue layer, information about the geometry 21 of at least one first tissue layer, and a 3D velocity map 22 of ultrasound in the volume of at least one first tissue layer and at least one second tissue. These inputs 20, 21 and 22 may have been stored in one or more local or remote databases 10. The remote database may take the form of a storage resource available from any type of appropriate storage device, which may in particular be a RAM or an EEPROM (Electrically Erasable Programmable Read-Only Memory), such as a flash memory, and may also be an SSD (Solid State Drive).

[0076] like Figure 2 As shown, at least three external ultrasonic sensors Si (i=1, ..., N, where N is equal to or greater than 3) are located at three different positions relative to the anatomical region and may have been in contact with at least one layer L1 of the first tissue type. Depending on the anatomical region, the external ultrasonic sensor Si may be rigidly fixed to a portion of the anatomical region or may not be fixed. For example, when the first tissue type is bone tissue, the external ultrasonic sensor Si may be rigidly fixed to the bone, or to a surgical tool whose relative position relative to the anatomical structure does not change. It is also possible to place at least three external ultrasonic sensors Si on a portion of the anatomical structure that may be displaced, swollen or changed during surgery, so that the position of the at least three external ultrasonic sensors Si relative to the first tissue layer L1 or the second tissue volume V changes during surgery. In this case, the at least three external ultrasonic sensors Si may each be equipped with a reference coupled to a navigation system that is capable of tracking the position of each external ultrasonic sensor Si relative 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 that there is no loss of accuracy in the 3D tracking of the medical device M.

[0077] When the external ultrasound sensors Si are rigidly fixed relative to the anatomy (i.e. their position does not change during the operation), their position 20 can already be obtained before the start of the operation (but after they have been fixed to the subject) using medical imaging techniques such as CT scanning or MRI imaging, etc. In another case where rigid fixation is not possible and a navigation system is used, the position 20 of the external ultrasound sensors Si can be measured directly in the operating room at the start of the operation and can be tracked throughout the operation.

[0078] Based on the properties of the first tissue type and the at least one second tissue type, information about the geometry 21 of the at least one first tissue layer of the anatomical structure and the final second tissue volume can be derived from medical imaging data (e.g., CT scan and / or MRI). For example, the information about the geometry 21 can include the thickness of the first tissue layer at each point of its surface, plus the second layer.

[0079] A 3D velocity map 22 of ultrasound waves in at least one first tissue layer and at least one second tissue volume can be obtained from CT scan imaging data, or any other medical imaging technology known to those skilled in the art. In fact, the actual speed of sound (i.e., ultrasound waves) varies depending on the structural characteristics of the tissue. Using a 3D ultrasound velocity map, rather than just using an approximation of the speed of sound for the first tissue type and the second tissue type, can achieve higher tracking accuracy.

[0080] The receiving module 11 can also be configured to communicate with the medical device M and the external ultrasonic sensor Si, in particular via a wireless transmission network. Therefore, the receiving module 11 can be configured to receive in real time the measurements performed by the ultrasonic sensor of the medical device M and the external ultrasonic sensor Si. In one example, the ultrasonic sensor of the medical device M is an ultrasonic transmitter, and the external ultrasonic sensor Si is an ultrasonic receiver, or conversely, the ultrasonic sensor of the medical device M is a receiver, and the external ultrasonic sensor Si is an ultrasonic transmitter. In both cases, the ultrasonic sensor of the medical device M and the external ultrasonic sensor Si are capable of measuring the time required for the sound to propagate between the medical device and the external ultrasonic sensor. In the case where the first type of tissue (such as bone tissue) strongly attenuates the intensity of the ultrasonic wave, this configuration of the external ultrasonic sensor Si and the medical device sensor is particularly advantageous relative to the use of a standard ultrasonic probe configured to both transmit and receive ultrasonic waves. In fact, by separating the transmitter and the receiver, the emitted ultrasonic wave only passes through the first tissue layer once before being received by the receiver. In contrast, when a standard probe is used, the ultrasonic wave passes through the first tissue layer for the first time, then is reflected by the tissue and the medical device in the volume, and the reflected ultrasonic wave passes through the first tissue layer for the second time and is detected by the receiver. However, since the ultrasound waves pass through the first tissue layer twice, their signal-to-noise ratio is reduced.

[0081] The tracking system 1 further comprises an initialization module 12 for acquiring a first position of the medical device M within the volume of at least one second tissue, which first position is then used in the localization module 13 as a starting position for a localization calculation cycle.

[0082] According to one embodiment, the initialization module 12 is configured to receive imaging data (ie, obtained from a medical imaging technique other than the above-mentioned ultrasonic sensor) and analyze the imaging data in order to obtain the position of the medical device M. For example, the position can be expressed as a triplet of coordinates in a reference system where the position of each external ultrasonic sensor Si is also known.

[0083] according to Figure 3 In an alternative embodiment shown, the initialization module 12 is configured to use the measurement results obtained from the external ultrasonic sensor Si and the ultrasonic sensor of the medical device M to obtain the position of the medical device M ( ) That is, the approximate calculation result of the first current position).

[0084] The initialization module 12 may be configured to perform steps 121, 122 and 123 for each external ultrasonic sensor Si. The results of the three steps obtained for each external ultrasonic sensor Si are then combined in step 124. Step 121 is configured to obtain the thickness of at least one first tissue layer at the location of each external ultrasonic sensor Si. The thickness is obtained using the received 3D geometry of at least one first tissue layer of the subject. The average thickness is defined as the length of the first tissue layer in the normal direction of the area in front of the location where the external ultrasound sensor Si is placed.

[0085] Step 122 is configured to obtain the local velocity in the first tissue type , the local velocity corresponding to the propagation velocity of ultrasound through at least one first tissue layer corresponding to the location of the external ultrasound sensor. The local velocity in the first tissue type is obtained using the 3D velocity map in the first tissue In fact, as described above, the speed of sound in one tissue type may vary depending on several physical parameters. Therefore, the positions of the received external ultrasound sensors Si are used to estimate the propagation speed of the sound in the first tissue layer in front of each external ultrasound sensor Si.

[0086] Step 123 comprises estimating a first distance between each external ultrasonic sensor Si and the medical device M To obtain these first distance estimates , it is necessary to use information on the velocity of the ultrasound wave through the tissue present between the actual position of the medical device M and the external ultrasonic sensor Si under consideration, and also to consider the time required for the ultrasound wave to propagate between the medical device M and the external ultrasonic sensor Si under consideration. Two velocity values ​​need to be considered: the local velocity obtained in the first tissue type and and the ultrasound velocity in the second tissue type (which can be obtained from the 3D velocity map). For the ultrasound velocity in the second tissue type, an average value can be considered. Regarding the time measurement, the module 12 is configured to receive the measured time of the ultrasound propagation between each external ultrasound sensor Si and the medical device M. The measured time can be obtained from the flight time measurement between the medical device M and the external ultrasound sensor Si considered.

[0087] The first distance of each external ultrasonic sensor Si can be calculated using the following formula: ,in is the average speed of sound in the second tissue type, is the measured time for the ultrasonic wave to propagate between each external ultrasonic sensor Si and the medical device M.

[0088] After determining a first distance between each external ultrasonic sensor Si and the medical device M Then, step 124 is configured to calculate the first current position The first current position is only an approximation of the 3D position of the medical device M, since it is calculated using the assumption that the propagation path traversed by the ultrasound wave in the first tissue layer is equal to the average thickness of the first tissue layer, however, depending on the actual position of the medical device, the propagation path may be longer.

[0089] The first current position (i.e., the current position for the first iteration , j = 1, for initialization of the positioning loop) is achieved by using the first distance estimated between the medical device M and each external ultrasonic sensor Si Obtained by triangulation or trilateration.

[0090] In one example, the measurement time of the ultrasonic wave propagating between each external ultrasonic sensor Si and the medical device M is It is based on direct flight time measurement measured using each external ultrasonic sensor Si and at least one ultrasonic sensor of the medical device M. The propagation time refers to the time it takes for an ultrasonic wave to propagate from one of each external ultrasonic sensor Si to the medical device M. There are many types of measurement of the propagation time: using a threshold to detect ultrasonic pulses with amplitudes above the threshold; using a cross-correlation method; using a maximum value to detect ultrasonic pulses with the highest amplitude; using a Hilbert transform maximum to detect ultrasonic pulses corresponding to the transform maximum; or using any other measurement type known to those skilled in the art.

[0091] According to an alternative embodiment, in particular when the tracking system has been used to estimate at least one 3D position of the medical device M, the module 12 is configured to obtain the first current position The last estimated position of the medical device M that satisfies the exit criteria.

[0092] The tracking system 1 further comprises a positioning calculation loop module 13 for performing positioning calculation. The positioning calculation loop module 13 is configured to receive the first current position obtained from the initialization module 12 As input, module 13 takes the first current position is set to the initial value of the current position of the first iteration (j=1) of the positioning calculation loop. In fact, the invention uses the first approximate estimate of the current position as information to improve the accuracy of the next calculation of the current position of a given actual position of the medical device, until the calculation converges to an optimal estimate of the current position of the medical device, which has an error of only sub-millimeter. More precisely, the use of the steps of module 13 makes it possible to reduce the error from about 1 to 2 mm (i.e., 1 mm if only the thickness of the first tissue layer in front of each external ultrasonic sensor is considered; 2 mm if only the average thickness of the first tissue layer is considered) to 100 to 900 microns.

[0093] like Figure 4 As shown, module 13 can be configured to continuously implement steps 131 to 136, wherein steps 131 to 133 are performed for each external ultrasonic sensor Si until a predefined exit criterion is verified. In step 131, the current position used 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 the j-1th iteration.

[0094] Step 131 is configured to use the current location obtained To calculate the current elevation angle of the medical device M relative to each external ultrasonic sensor Si and the current horizontal angle (See Figure 5 ). The current elevation angle of the medical device M and the current horizontal angle is relative to Figure 5 shown Coordinate reference system. The coordinate reference system can be defined relative to the first tissue layer L1, wherein the Z axis is perpendicular to the main direction of the first tissue layer L1. It is the XZ-plane and the current position The angle between the current horizontal angle Then, in step 131, the current elevation angle and the current horizontal angle For estimating the current path traveled by ultrasound waves through at least one first tissue layer between each external ultrasound sensor Si and the medical device M .

[0095] The next step 132 uses the current path estimated in step 131 , with higher accuracy, understand which part of the first tissue layer the ultrasound waves pass through to reach each external ultrasound sensor Si. This information is then used in conjunction with the 3D velocity map in the first tissue to obtain the current path of the ultrasound waves obtained for each external ultrasound sensor Si. The current local velocity in the first tissue layer when passing through the first tissue layer This step advantageously allows taking into account heterogeneities in the structure of the first tissue layer, which may result in variations in the speed of the ultrasound waves in the first tissue type. This is the case with bone tissue. In fact, since the density of the skull depends on age as well as other factors (e.g. pathology), it varies not only from patient to patient but also from one area of ​​the skull to another in the same patient.

[0096] The subsequent step 133 is configured to calculate the current distance between each external ultrasound sensor Si and the medical device M located within the volume of at least one second tissue (i.e., for the jth iteration). To calculate the current distance , step 133 uses the estimated current path associated with the corresponding external ultrasonic sensor Si , the current local velocity in at least one first tissue layer associated with the corresponding external ultrasonic sensor Si (ie, obtained in step 132), the ultrasonic velocity in at least one second tissue, and the measured time for the ultrasonic wave to propagate between each external ultrasonic sensor Si and the medical device M. It is worth noting that the current path Used to estimate the length of ultrasound waves passing through the second tissue volume and the length of ultrasound waves passing through the first tissue layer. In one example, for the ultrasound velocity in at least one second tissue, the average velocity is used. Used to estimate the current distance The formula is: .

[0097] Alternatively and optionally, step 133 is configured to use a numerical simulation of the propagation of ultrasound waves within the volume of at least one first tissue layer and at least one second tissue of the subject to calculate the current distance of each external ultrasound sensor Si . These numerical simulations can take into account the reflection, refraction, diffraction, diffusion and other phenomena of ultrasound in at least one first tissue layer and at least one second tissue volume of the subject. The numerical simulation is based on medical imaging data of at least a part of the anatomical region of the subject. The numerical simulation can rely on numerical finite difference methods, or k-space methods, or semi-analytical ray tracing methods, or use transfer functions, or hybrid methods combining semi-analytical methods with analytical methods, etc. Advantageously, the use of numerical simulations helps to improve the current distance of each external ultrasonic sensor Si The calculation accuracy of .

[0098] Then, step 134 is configured to use the current distance between each external ultrasonic sensor Si and the medical device M calculated in step 133 , to estimate the new position (i.e., the new corrected position) of the medical device M within the volume of at least one second tissue. The new position is calculated by using the current distance Calculated by triangulation or three-sided measurement.

[0099] Step 135 is then executed to verify whether the estimated new position meets the predefined exit criteria. When the exit criteria are not met, step 135 is configured to define the new position as the current position for the next iteration (j+1), so that the current position received at the input of step 131 This is the new position estimated at the jth iteration. Step 135 is configured to stop the iteration of the module 13 in response to the exit criterion being met, and define a final estimated position 31 that meets the exit criterion.

[0100] The exit criterion may simply consist of verifying that one iteration of steps 131 to 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. Likewise, the exit criterion may be configured such that the criterion is deemed to be met when a predefined number of iterations has been completed.

[0101] Optionally, the exit criteria can be configured as follows: for a given number of iterations (i.e., not a predefined number), such as three iterations, at the current position The iteration is stopped when the difference between the new position and the position is less than a predetermined threshold, so that the iteration stops when the results converge to a value. In this case, the final estimated position 31 is defined as the new estimated position of the jth iteration that meets the exit criterion. This optional approach can stop the iteration when the value of the new position converges to a stable estimate of the "actual" position of the device M.

[0102] As described above, the external ultrasonic sensor Si can be an ultrasonic transmitter, and the medical device can be equipped with an ultrasonic receiver. The external ultrasonic sensor Si can be an ultrasonic transmitter configured to modify the ultrasonic emission direction. In this case, the system 1 is also configured to include a module 14, not shown, which is configured to wirelessly communicate with the external ultrasonic sensor so as to provide instructions to modify the ultrasonic emission direction 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 so as to focus the ultrasonic wave on the medical device M, which allows the signal-to-noise ratio to be improved, thereby improving the accuracy of 3D position reconstruction. Embodiments of the present invention are particularly advantageous when a small number (i.e., three) of external ultrasonic sensors Si are used.

[0103] The tracking system 1 interacts with a user interface 16 through which information can be input and retrieved by the user. The user interface 16 comprises any means suitable for inputting or retrieving data, information or instructions, in particular visual, tactile and / or audio capabilities, which may include any one or more of the following means known to those skilled in the art: screen, keyboard, trackball, touchpad, touch screen, speaker, voice recognition system.

[0104] Thus, the tracking system 1 of the present invention is able to estimate the position of the medical device at a given position in the patient's body. The tracking system 1 can also be used to track the position of the medical device M being moved in the second tissue volume in real time. By repeating the above steps for multiple actual positions of the medical device, it is possible to monitor the trajectory of the medical device M. In addition, these steps are performed quickly enough to obtain an estimated position 31 of the medical device M twenty times per second, which corresponds to real-time tracking of the medical device.

[0105] Figure 6 An example of application of the system 1 is shown, wherein there are three external ultrasonic sensors S1, S2 and S3 fixed to the head of a patient. 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 the figure is a microrobot configured to travel in the brain of a subject.

[0106] In this scenario, as in other practical cases, the ultrasound wave must not only pass through the skull, but also through the skin, which has different ultrasound wave propagation characteristics from the first tissue type and the second tissue type. Since the skin is a low-density tissue, ignoring the existence of the skin layer in the calculation and only considering the first tissue layer does not affect the results, which, as disclosed above, have sub-millimeter accuracy.

[0107] However, modules 12 and 13 may be configured to take into account the presence of a second layer of a third tissue that is different from (or not) the first tissue and the second tissue. A person skilled in the art will understand how to take into account the presence of a second layer covering the first layer or between the first layer and the volume V in the steps implemented by modules 12 and 13. This embodiment will allow the accuracy of 3D positioning to be further improved.

[0108] During its automatic operation, the tracking system 1 may, for example, perform the following process: Figure 7 ):

[0109] - receiving a position 20 of each of the at least three external ultrasound sensors Si relative to at least one first tissue layer, information about the geometry 21 of the at least one first tissue layer and a 3D velocity map 22 of ultrasound waves in the volume of the at least one first tissue layer and at least one second tissue (step 41 );

[0110] - Get the first current position (step 42);

[0111] - executing a positioning calculation loop using the first current position as a starting point (step 43);

[0112] - Obtaining a final estimate 31 of the position of the medical device M (step 44 ).

[0113] Figure 8 The specific device 9 shown in the figure embodies the above-mentioned tracking system 1. For example, the device corresponds to a workstation, a laptop, a tablet, a smartphone or a head mounted display (HMD).

[0114] The device 9 is suitable for estimating the 3D position of a medical device in a patient's body. The device 9 comprises the following elements interconnected by an address and data bus 95, which also transmits a clock signal:

[0115] - microprocessor 91 (or CPU);

[0116] - Graphics card 92, which includes several graphics processing units (or GPUs) 920 and graphics random access memory (GRAM) 921; GPUs are well suited for image processing due to their highly parallel structure;

[0117] - a non-volatile memory 96 of the ROM type;

[0118] - RAM 97;

[0119] - one or more I / O (input / output) devices 94, for example, keyboard, mouse, trackball, webcam; other modes of introducing commands such as voice recognition are also possible;

[0120] - Power supply 98;

[0121] - Radio frequency unit 99.

[0122] According to a variant, the power supply 98 is located outside the device 9 .

[0123] The device 9 also includes a display device 93 of the display screen type, which is directly connected to the graphics card 92 for displaying a composite image of the trajectory of the medical device calculated and synthesized in the graphics card. Using a dedicated bus to connect the display device 93 to the graphics card 92 advantageously provides a greater data transmission bit rate, thereby reducing the display delay time of the graphics card synthesized image. According to a variation, the display device is located outside the device 9 and is connected to the device 9 by a cable or wirelessly to transmit a display signal. The device 9 (for example, through the graphics card 92) includes an interface for transmission or connection, which is suitable for transmitting the display signal to an external display device, such as an LCD or plasma display screen or a video projector. In this regard, the RF unit 99 can be used for wireless transmission.

[0124] It is worth noting that the word "register" used below in the description of the memories 97 and 921 can refer to both low-capacity memory areas (some binary data) and large-capacity memory areas (enabling the storage of entire programs or representing all or part of the data to be displayed or calculated) in each of the memories mentioned. For this reason, the registers represented by the RAM 97 and the GRAM 921 can be arranged and constituted in any way, and each of them does not necessarily correspond to adjacent storage locations, and can be distributed in other ways (this especially covers the case where one register includes several smaller registers).

[0125] When turned on, microprocessor 91 loads and executes program instructions contained in RAM 97 .

[0126] Those skilled in the art will appreciate that the presence of graphics card 92 is not mandatory and that full CPU processing and / or simpler visualization implementations can be used instead.

Claims

1. A tracking system (1) for estimating the 3D position of a medical device (M) equipped with at least one ultrasound sensor within an anatomical region of a subject, the anatomical region of the subject comprising at least one layer (Li) of a first tissue type, the at least one layer of the first tissue type at least partially surrounding a volume (V) comprising at least one second tissue type, wherein: The propagation characteristics of ultrasound waves in a first tissue type and a second tissue type are different, and the system (1) comprises: - at least one input configured to receive a position (20) of each of at least three external ultrasound sensors (Si) relative to at least one first tissue layer, information about the geometry (21) of the at least one first tissue layer, and a 3D velocity map (22) of ultrasound waves in the volume of the at least one first tissue layer and the at least one second tissue; - at least one processor configured to: o obtaining a current position of the medical device (M) within a volume of at least one second tissue ( ); oPerform positioning calculations, including: ·Use the current location obtained ( ) and the positions (20) of the at least three external ultrasonic sensors (Si) to calculate a current elevation angle ( ) and the current horizontal angle ( ), and using the current elevation angle ( ) and the current lateral angle ( ) to estimate a current path ( ); For each external ultrasonic sensor (Si), use the estimated current path ( ) and the 3D velocity map in the first tissue to obtain the relevant current local velocity in the first tissue ( ); By taking into account the current local velocity ( ), the estimated current path ( associated with the corresponding external ultrasonic sensor (Si) ), the speed of ultrasound in at least one second tissue, and the measured time of ultrasound propagation between each external ultrasound sensor (Si) and the medical device (M), to calculate the current distance ( ); · Using the current distance ( ), to estimate a new position of the medical device (M) within a volume of at least one second tissue; o Use the new position as the current position ( ), repeat the positioning calculation until the exit criteria are met; o at least one output configured to provide an estimated position (31) of the medical device (M) that meets an exit criterion, Wherein the measured time of propagation of an ultrasonic wave between each external ultrasonic sensor (Si) and the medical device (M) is based on a direct time-of-flight measurement measured using at least one ultrasonic sensor of each external ultrasonic sensor (Si) and the medical device (M).

2. The system according to claim 1, wherein: Calculate the current distance ( ) comprises using a numerical simulation of ultrasound wave propagation within a volume of at least one first tissue layer and at least one second tissue of the subject, the numerical simulation being based on medical imaging data of at least a portion of an anatomical region of the subject.

3. The system according to claim 1 or 2, wherein: For the first iteration, the current position ( )include: - using the 3D geometry of at least one first tissue layer of the subject, obtaining the thickness ( ); - For each external ultrasound sensor (Si), using the 3D velocity map in the first tissue to obtain the local velocity in the first tissue , the local velocity corresponds to a propagation velocity of ultrasound waves through the at least one first tissue layer corresponding to a location of an external ultrasound sensor; - For each external ultrasonic sensor (Si), based on the thickness equal to the corresponding obtained ( ) propagates through at least one first tissue layer, the corresponding local velocity obtained in the at least one first tissue layer , the speed of ultrasound in the second tissue, and the measured time of ultrasound propagation between each external ultrasound sensor (Si) and the medical device (M), to estimate the first distance ( ); wherein the current position ( ) is an estimated first distance ( ) to obtain.

4. The system according to any one of claims 1 or 2, wherein: For a first iteration, a current position ( ) including the use of medical imaging data.

5. The system according to any one of claims 1 to 4, wherein: The exit criteria are configured as follows: for a given number of iterations, when the current position ( ) and the estimated new position is less than a predetermined threshold.

6. The system according to any one of claims 1 to 5, wherein: The external ultrasonic sensors (Si) are ultrasonic transmitters configured to modify the emission direction of ultrasonic waves, and the medical device is equipped with an ultrasonic receiver, and wherein the at least one processor is further configured to modify the emission direction of ultrasonic waves using the estimated position (31) of the medical device so as to focus the ultrasonic waves of the at least three external ultrasonic sensors (Si) on the position of the medical device (M).

7. The system according to any one of claims 1 to 6, wherein: the at least one layer of the first tissue type is a skull of the subject, and the at least one volume of the second tissue is a brain of the subject; Alternatively, the at least one layer of the first tissue type is a fat layer and the at least one volume is a liver.

8. A computer-implemented method for estimating a 3D position of a medical device (M) equipped with at least one ultrasound sensor within an anatomical region of a subject, the anatomical region of the subject comprising at least one layer of a first tissue type, the at least one layer of the first tissue type at least partially surrounding a volume comprising at least one second tissue type, wherein The propagation characteristics of ultrasound waves in a first tissue type and a second tissue type are different, and the system (1) comprises: - receiving a position (20) of each of at least three external ultrasound sensors (Si) relative to at least one first tissue layer, information about the geometry (21) of the at least one first tissue layer, and a 3D velocity map (22) of ultrasound waves in the volume of the at least one first tissue layer and at least one second tissue; - obtaining a current position of the medical device (M) within the volume of the second tissue ( ); - Perform positioning calculations, including: ·Use the current location obtained ( ) to calculate the current elevation angle ( ) and the current horizontal angle ( ), and using the current elevation angle ( ) and the current lateral angle ( ) to estimate the current path ( ) traveled by the ultrasound wave through at least one first tissue layer between each external ultrasound sensor (Si) and the medical device (2) ); For each external ultrasonic sensor (Si), use the current path ( ) and the 3D velocity map in the first tissue to estimate the relevant current local velocity in the first tissue ( ); By taking into account the current local velocity ( ), the estimated current path ( associated with the corresponding external ultrasonic sensor (Si) ), the speed of ultrasound in at least one second tissue, and the measured time of ultrasound propagation between each external ultrasound sensor (Si) and the medical device (M), to calculate the current distance ( ); · Using the current distance ( ), to estimate a new position of the medical device (M) within a volume of at least one second tissue; - Use the new location as the current location ( ), repeat the positioning calculation until the exit criteria are met; Wherein the measured time of propagation of an ultrasonic wave between each external ultrasonic sensor (Si) and the medical device (M) is based on a direct time-of-flight measurement measured using at least one ultrasonic sensor of each external ultrasonic sensor (Si) and the medical device (M).

9. The method according to claim 8, wherein: Calculate the current distance ( ) comprises using a numerical simulation of ultrasound wave propagation in a first type of tissue and a second type of tissue of the subject, the numerical simulation being based on medical imaging data of at least a portion of an anatomical region of the subject.

10. The method according to any one of claims 8 or 9, wherein: Obtain the current position ( )include: - using the 3D geometry of at least one first tissue layer of the subject, obtaining the thickness ( ); - For each external ultrasound sensor (Si), using the 3D velocity map in the first tissue to obtain the local velocity in the first tissue , the local velocity corresponds to a propagation velocity of ultrasound waves through the at least one first tissue layer corresponding to a location of an external ultrasound sensor; - For each external ultrasonic sensor (Si), based on the thickness equal to the corresponding obtained ( ) propagates through at least one first tissue layer in the first tissue. , the speed of ultrasound in the second tissue, and the measured time of ultrasound propagation between each external ultrasound sensor (Si) and the medical device (M), to estimate the first distance ( ); wherein the current position ( ) is an estimated first distance ( ) to obtain.

11. The method according to any one of claims 8 to 10, wherein: The exit criteria are configured as follows: for a given number of iterations, when the current position ( ) and the new position ( ) is less than a preset threshold, the iteration is stopped.

12. The method according to any one of claims 8 to 11, wherein: The external ultrasonic sensor (Si) is an ultrasonic transmitter configured to modify the transmission direction of ultrasonic waves, and the medical device is equipped with an ultrasonic receiver, and wherein the at least one processor is further configured to use the new position ( ) to modify the emission direction of ultrasound so as to focus the ultrasound from at least three skull ultrasound sensors (Si) on the position of the medical device (M).

13. A computer program product comprising instructions which, when executed by a computer, cause the computer to perform the method according to any one of claims 8 to 12.

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

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