Systems and methods for tracking sensors comprising ferrofluids

Abstract

A system and method of tracking a sensor comprising a ferrofluid are provided. The system comprises: one or more field generating coils configured to generate a magnetic field; a sensor comprising a housing containing a ferrofluid, the sensor configured to be introduced in proximity to the magnetic field, wherein the ferrofluid causes a distortion of the magnetic field when the ferrofluid is in proximity to the magnetic field; and one or more field measurement coils configured to: measure a characteristic of the magnetic field when the ferrofluid is in proximity to the magnetic field; and provide a signal to a computing device representing the measured characteristic of the magnetic field, wherein the computing device is configured to determine one or both of a position and an orientation of the sensor based on the measured characteristic of the magnetic field.

Description

[0001] This application is a divisional application of the invention patent application filed on August 9, 2018, entitled "System and method for tracking a sensor including a ferrofluid", application number 201810903541.3. Technical Field

[0002] This disclosure relates to sensors that track ferrofluids. Background Technology

[0003] Electromagnetic tracking (EMT) systems are used to aid in the localization of instruments and anatomical structures in medical procedures, virtual reality (VR) setups, and augmented reality (AR) setups. Such systems determine the position of sensors based on the distortion of the transmitted magnetic field being measured. Summary of the Invention

[0004] Electromagnetic tracking (EMT) systems can be used to track medical devices during medical procedures. For example, in a surgical setting, an EMT system can be used to track the position and / or orientation of sensors incorporated into a medical device. The sensor may include a housing filled with a ferrofluidic core. The magnetic properties of the sensor are configured to induce distortion in a generated magnetic field, and a field measurement coil is configured to measure the characteristics of the distortion and provide this measurement to a computing device. The computing device can then determine the position and / or orientation of the sensor (and, for example, the position and / or orientation of the medical device) based on the received measurement.

[0005] In some implementations, the sensor can be inserted into a hard-to-access and / or dangerously accessible location within the patient's body. For example, a flexible housing of the sensor can be inserted into the body before the presence of ferrofluid. The flexible housing allows insertion with minimal or no damage to the patient's anatomy. The ferrofluid can then be supplied to the flexible housing (e.g., by injection into the housing). Once the medical procedure is complete, some or all of the sensor can be removed from the body. For example, the ferrofluid can be removed by puncturing the housing and magnetically pulling it out using a permanent magnet. The housing can then be removed. Alternatively, the housing can be made of biocompatible and / or biodegradable materials and can therefore remain inside the patient.

[0006] In one aspect, an electromagnetic tracking system is provided, comprising one or more field-generating coils configured to generate a magnetic field. The system also includes a sensor comprising a housing containing a ferrofluid, the housing including one or more flexible walls and configured to be introduced into a patient's body. The sensor is configured to be introduced into the vicinity of the magnetic field. When the ferrofluid is in the vicinity of the magnetic field, the ferrofluid causes magnetic field distortion, and the ferrofluid is configured to be removed from the housing by piercing it and introducing a magnetic force in the vicinity of the housing. The system also includes one or more field measurement coils configured to measure the characteristics of the magnetic field when the sensor containing the ferrofluid is not in the vicinity of the magnetic field; to measure the characteristics of the magnetic field when the sensor containing the ferrofluid is in the vicinity of the magnetic field; and to provide a signal representing the measured characteristics of the magnetic field to a computing device, the computing device including a processor capable of executing instructions stored on a storage device; wherein the computing device is configured to determine one or both of the position and orientation of the sensor by comparing the characteristics of the magnetic field measured when the sensor containing the ferrofluid is not in the vicinity of the magnetic field with the characteristics of the magnetic field measured when the sensor containing the ferrofluid is in the vicinity of the magnetic field.

[0007] The implementation may include one or more of the following features.

[0008] In some implementations, the sensor is flexible.

[0009] In some implementations, one or more magnetic properties of the sensor remain unchanged when mechanical stress is applied to the sensor.

[0010] In some implementations, one or both of the shell and the ferrofluid are biocompatible or biodegradable, or both biocompatible and biodegradable.

[0011] In some implementations, ferrofluids include one or both of liquids and powders.

[0012] In some implementations, the ferrofluid includes superparamagnetic iron oxide nanoparticles (SPION).

[0013] In some implementations, SPION includes one or both of magnetite (Fe3O4) and maghemite (γ-Fe2O3).

[0014] In some implementations, the shell comprises a polymer.

[0015] In some implementations, the shell is configured to receive the ferrofluid via injection after it has been introduced into the patient's body.

[0016] In some implementations, the sensor has an ellipsoidal shape.

[0017] In some implementations, the ellipsoid is defined by three axes of unequal length.

[0018] In some implementations, the sensor has a cuboid shape.

[0019] In some implementations, the sensor has a cylindrical shape.

[0020] In some implementations, the sensor has a pill shape.

[0021] In some implementations, the sensor is wireless.

[0022] In another aspect, a sensor configured for use in an electromagnetic tracking system is provided, the sensor comprising: a housing including one or more flexible walls configured to be introduced into a patient's body; a ferrofluid contained within the housing, the ferrofluid being configured to be removed from the housing by piercing the housing and introducing a magnetic force in the vicinity of the housing, wherein the ferrofluid causes a measurable distortion of a magnetic field, the position and orientation of the sensor being determined by a computing device by comparing the characteristics of the magnetic field measured when the ferrofluid is not in the vicinity of the magnetic field with the characteristics of the magnetic field measured when the ferrofluid is in the vicinity of the magnetic field.

[0023] In another aspect, a method for tracking a sensor using an electromagnetic tracking system is provided. The method includes: initiating the generation of a magnetic field; receiving from one or more magnetic field measuring coils a signal representing the characteristics of the magnetic field measured when the sensor is introduced into the magnetic field, the sensor including a housing comprising one or more flexible walls and containing a ferrofluid, the housing being configured to be introduced into a patient's body. Wherein, when the ferrofluid is in the vicinity of the magnetic field, the ferrofluid causes distortion of the magnetic field, and the ferrofluid is configured to be removed from the housing by piercing the housing and introducing a magnetic force in the vicinity of the housing; and determining one or both of the sensor's position and orientation by comparing the characteristics of the magnetic field measured when the ferrofluid is not in the vicinity of the magnetic field with the characteristics of the magnetic field measured when the ferrofluid is in the vicinity of the magnetic field using a computing device including a processor capable of executing instructions stored on a storage device.

[0024] Details of one or more embodiments of the subject matter described herein are set forth in the accompanying drawings and the following description. Other features, objects, and advantages of this subject matter will become apparent from the specification, the drawings, and the claims. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of an electromagnetic tracking (EMT) system that includes a field generating coil, a field measuring coil, and a sensor.

[0026] Figure 2 An example of the magnetic field present in an EMT system is shown.

[0027] Figure 3 An example of a sensor for an EMT system with an ellipsoidal shape is shown.

[0028] Figures 4A to 4C Other examples of sensors used in EMT systems are shown.

[0029] Figure 5 This is a block diagram of an example computer system.

[0030] In the various figures, the same reference numerals indicate the same elements. Detailed Implementation

[0031] Electromagnetic tracking (EMT) systems can be used in medical settings, virtual reality (VR) settings, augmented reality (AR) settings, and more to track devices. For example, in a surgical setting, an EMT system can be used to track medical devices, robotic arms, etc., allowing medical professionals (such as surgeons) to know the three-dimensional position and orientation of the device during the procedure. This electromagnetic tracking within the patient can be used for guidance purposes in image-guided surgery and, in some cases, can allow for a reduction in reliance on other imaging modalities such as fluorescence examinations, which may expose the patient to the health risks of ionizing radiation.

[0032] Figure 1 and Figure 2 An exemplary implementation of an EMT system 100 is presented, which can be used for image-guided medical procedures on a patient 102. The system can allow targeting of anatomical organs, structures, or blood vessels for visualization, diagnostic, interventional purposes, etc. Typically, system 100 includes components configured to generate a magnetic field 112 (…). H ext The system 100 includes one or more field generating coils 104. The system 100 also includes one or more field measuring coils 106 configured to measure the characteristics of a magnetic field 112. When an object with magnetic properties is introduced into the system 100 (e.g., in the vicinity of field generating coils 104 and / or field measuring coils 106), the resulting magnetic field 112 is distorted. Field measuring coils 106 are configured to measure the characteristics of this distortion and provide the measurement results to a computing device 110. The computing device 110 is configured to determine information related to the object (e.g., one or both of position and orientation information) based on the measurement results. The distorted characteristics may include properties such as field strength. In some implementations, the field strength projected onto the field measuring coils 106 is measured (i.e., a field component of a 3D field vector in the local coil coordinate system). In some implementations, full 3D knowledge can be obtained from the measurement results of the characteristics of the distorted magnetic field.

[0033] For example, the object introduced into system 100 may be a sensor 108 employing a wired or wireless architecture (wireless in the illustration). Sensor 108 includes a ferrofluid that may have one or more magnetic properties. Figure 3 304). Specifically, the ferrofluid 304 is a fluid that is magnetized in the presence of a magnetic field (e.g., magnetic field 112). Therefore, when the sensor 108 is near the magnetic field 112, the sensor 108 causes distortion of the magnetic field 112. In other words, the sensor 108 interacts with the magnetic field 112 generated by the field generating coil 104 to produce a distorted magnetic field 114 ( H int A sensed torque 116 (η) is also generated in sensor 108. ind The characteristics of the distorted magnetic field 114 can correspond to the position of the sensor 108 (e.g., x , y , z Coordinates) and orientation (azimuth) ψ ),high( θ ), roll ( Therefore, the field measurement coil 106 can measure the characteristics of the magnetic field (e.g., magnetic field 112 when sensor 108 is absent and / or distorted magnetic field 114 when sensor 108 is present), providing a signal representing the measured characteristics to the computing device 110, and the computing device 110 can determine one or both of the position and orientation of sensor 108 based on the measurement results. In this way, sensor 108 can be used as a six-degree-of-freedom (6DoF) sensor, which is configured to allow the measurement of position and orientation information related to forward / backward position, up / down position, left / right position, azimuth angle, altitude, and roll.

[0034] like Figure 1 As shown, the field generating coil 104 (sometimes referred to as the field coil) and the field measuring coil 106 (sometimes referred to as the pickup coil) can be connected to the computing device 110 via a wired connection, but a wireless connection is also possible. The positions of the field generating coil 104 and the field measuring coil 106 can be known to the computing device 110 (e.g., relative to the computing device 110). x , y and z (Coordinates). For example, the field measuring coil 106 can measure one or more characteristics of the magnetic field 112 generated by the field generating coil 104 in the absence of a sensor to obtain a baseline magnetic field measurement. The signal representing the measured characteristic can be provided to the computing device 110.

[0035] In some implementations, the field generating coil 104 may be positioned at a surgical drill, a surgical table (e.g., integrated into a surgical table), and / or placed somewhere at / near the patient 102. The field measuring coil 106 may be positioned at a location spaced apart from the field generating coil 104 (e.g., at a different location than the field generating coil 104). In some implementations, the field measuring coil 106 may be positioned at a surgical drill, a surgical table, and / or placed somewhere at / near the patient 102. In some implementations, the field generating coil 104 or the field measuring coil 106 may be integrated into a loop placed around the leg of the patient 102.

[0036] In some implementations, a sensor array can be used to track the location where the field generating coil 104 is positioned. For example, the sensor array (e.g., a repeater) can be positioned at a location spaced apart from the field generating coil 104 to track the position of the field generating coil 104 (and, for example, a surgical drill). In some implementations, such as in those where the EMT system 100 is relatively over-defined (e.g., including a relatively large number of field generating coils 104 and field measuring coils 106, such as eight or more per coil), a solution for determining the relative positions of the field generating coils 104, field measuring coils 106, and sensor array can be determined digitally. In such implementations, the sensor array can also be positioned at the surgical drill such that the field generating coils 104 and sensor array have fixed positions relative to each other.

[0037] Sensor 108 can be wirelessly introduced into the vicinity of magnetic field 112 (e.g., so that sensor 108 is not physically connected to computing device 110). For example, sensor 108 can be incorporated into a medical device to be tracked during medical procedures. The ferrofluid 304 of sensor 108 (and any other magnetic and / or metallic portion of sensor 108, for example) causes the magnetic field 112 generated by field generating coil 104 to be distorted. That is, the magnetic properties of sensor 108 cause the magnetic field 112 in the vicinity of sensor 108 to be distorted. This change and / or distortion is illustrated by a distorted magnetic field 114. The characteristics of the distorted magnetic field 114 depend on the position and orientation of sensor 108. For example, when sensor 108 is located in a first position, distorted magnetic field 114 may have a first shape and / or intensity; when sensor 108 is located in a second position, distorted magnetic field 114 may have a second shape and / or intensity; when sensor 108 is located in a second position but with a different orientation, distorted magnetic field 114 may have a third shape and / or intensity, etc. The field measurement coil 106 is configured to measure one or more characteristics of the distorted magnetic field 114 (e.g., characteristics corresponding to the shape and / or strength of the magnetic field) and provide a signal representing the measured characteristics to the computing device 110.

[0038] The computing device 110 is configured to determine one or both of the position and orientation of the sensor 108 based on a received signal representing a measurement characteristic of the distorted magnetic field 114. In some examples, the computing device 110 may determine the position and / or orientation of the sensor 108 relative to the computing device 110, the position and / or orientation of the field generating coil 104, the position and / or orientation of the field measuring coil 106, etc. In some implementations, the computing device 110 may determine the position and / or orientation of the sensor 108 by comparing the characteristics of the measured magnetic field 112 (e.g., when sensor 108 is not present) with the characteristics of the measured distorted magnetic field 114 (e.g., when sensor 108 is present). The position and / or orientation of the sensor 108 may be determined using one or more algorithms or mathematical formulas.

[0039] Figure 3 It shows Figure 1 and Figure 2 An example of sensor 108 is provided. Sensor 108 includes a housing 302 containing ferrofluid 304. In the example shown, sensor 108 has an ellipsoidal shape defined by three axes: a-axis 310, b-axis 320, and c-axis 330. In the example shown, the axes have unequal lengths. That is, the length of a-axis 310 is not equal to the length of b-axis 320, and the length of c-axis 330 is not equal to the length of either a-axis 310 or b-axis 320. This configuration ensures that sensor 108 can provide 6DoF tracking. For example, because the three axes have unequal lengths, the exact position and orientation of sensor 108 can be definitively determined. For example, if the lengths of b-axis 320 and c-axis 330 were the same, the azimuth angle ( ψ The orientation component may be unmeasurable. In some implementations, the relationship between the dimensions of sensor 108 can be related to... Figure 3 The differences shown are (e.g., depending on the specific application).

[0040] Ferrofluid 304 may comprise any material having magnetic properties that can influence the generated magnetic field. In some implementations, ferrofluid 304 comprises one or both of a liquid and a powder. In some implementations, ferrofluid 304 comprises iron oxide particles, such as superparamagnetic iron oxide nanoparticles (SPION). SPION may comprise magnetite (Fe3O4), maghemite (γ-Fe2O3), etc. In some implementations, SPION may have a diameter between about 1 and 100 nanometers.

[0041] In some implementations, one or both of the shell 302 and the ferrofluid 304 may be biocompatible and / or biodegradable. For example, the shell 302 and / or the ferrofluid 304 may be made of materials harmless to living tissue. In some implementations, the shell 302 is made of a biocompatible and biodegradable polymer and / or wax. In this way, the shell 302 can remain in the patient's body and decompose in a manner that does not harm the patient.

[0042] In some implementations, sensor 108 can be configured to be introduced into the patient's body. For example, sensor 108 can be incorporated into a surgical tool (e.g., a drill, scalpel, etc.) to be used during a medical procedure. In some implementations, sensor 108 can be incorporated into a surgical implant (e.g., an intramedullary (IM) nail) to be inserted into the patient's body. In particular, sensor 108 can be positioned within the orifice (e.g., screw hole) of the IM nail so that the position and / or orientation of the orifice can be tracked after the IM nail has been placed in the patient's body (e.g., after the IM nail has been inserted into the patient's bone). By tracking the positioning and orientation of sensor 108, a medical professional can, for example, determine the location on the patient's exterior where a screw should be inserted, to align the screw hole and secure the implant against the bone.

[0043] In some implementations, sensor 108 can be configured to be located in a hard-to-access location within the patient's body. For example, sensor 108 can be located near the patient's delicate anatomical structures (e.g., structures that could harm the patient if damaged), such as in a blood vessel (e.g., in blood flow) or a tumor.

[0044] In some implementations, the sensor 108 can be flexible (e.g., the structure, housing, etc., can have limited rigidity). By providing a flexible sensor 108, potential damage to the patient's anatomy during insertion can be minimized or eliminated. In some implementations, the sensor 108 can be introduced into the patient in multiple stages. For example, the housing 302 can be introduced into the patient first, followed by the introduction of the ferrofluid 304. In this way, the housing 302 can be inserted into a hard-to-access area of ​​the patient's body (e.g., due to the reduced size of the unfilled housing 302), and the ferrofluid 304 can subsequently be injected into the housing 302. Similarly, the sensor 108 can be removed from the patient's body in multiple stages. For example, after a medical procedure, the housing 302 can be punctured and the ferrofluid 304 can be removed. In some implementations, the ferrofluid 304 is removed by puncturing the housing 302 and introducing a magnetic force (e.g., a permanent magnet) near the punctured housing 302. After the ferrofluid 304 is removed, the housing 302 can be removed from the patient's body. In some implementations (e.g., where the housing 302 is biocompatible and / or biodegradable), the housing 302 can remain inside the patient.

[0045] In some implementations, the sensor 108 possesses properties such that its magnetic properties remain unchanged when mechanical stress is applied to it. For example, the ferrofluid 304 can retain its magnetic properties when exposed to mechanical stress. In this way, the sensor 108 can distort the magnetic field 112 in a defined manner, enabling the field measuring coil 106 to measure the characteristics of the distorted magnetic field 114, which provides a precise indication of the sensor 108's position and / or orientation. This precise measurement can be provided even when the sensor 108 is subjected to stress due to its introduction into a patient's body.

[0046] Although sensor 108 is largely depicted as having an ellipsoidal shape, it may employ one or more geometries (i.e., it may or may not include an ellipsoidal shape). Figures 4A to 4C Examples of other sensors with various shapes are shown. For example... Figure 4A As shown, in some implementations, the sensor 410 for the EMT system 100 can have a cylindrical shape. For example... Figure 4B As shown, in some implementations, the sensor 420 for the EMT system 100 can have a pill shape (e.g., a cylinder with hemispheres at the top and bottom). Figure 4C As shown, in some implementations, the sensor 430 for the EMT system 100 can have a cuboid shape, such as a cube or rectangular prism. Sensors 410, 420, and 430 can have any of a plurality of dimensions. For example, as referenced above... Figure 3 The axes (e.g., a-axis, b-axis, and c-axis) of each of the sensors 410, 420, and 430 may have unequal lengths. In some implementations, the length of one or more of these axes may be equal to the length of one or more of the other axes.

[0047] One or more field generating coils 104 (e.g., sometimes referred to as transmitters) may comprise a single field generating coil or an array of field generating coils. Similarly, one or more field measuring coils 106 (e.g., sometimes referred to as receivers) may comprise a single field measuring coil or an array of field measuring coils. When a coil array is used for one or more field generating coils 104, each coil may be sequentially excited, each coil generating its own magnetic field and evoking a different response in sensor 108. When a coil array is used for one or more field measuring coils 106, each coil may be sequentially excited during the excitation of each field generating coil 104, each coil measuring the characteristics of the resulting magnetic field (e.g., one or both of magnetic field 112 and distorted magnetic field 114).

[0048] In some implementations, one or more of the field generating coils 104 can be used for measurement purposes, and one or more of the field measuring coils 106 can be used for field generating purposes. In other words, one or more of the field generating coils 104 can be used as field measuring coils 106 and / or one or more of the field measuring coils 106 can be used as field generating coils 104. The field generating coils 104 and the field measuring coils 106 can have configurations and structures that allow for such interchangeability.

[0049] The aforementioned EMT system 100 can be used on a computer-readable medium to be displayed on a computer (e.g., Figure 1 The software is implemented by software executing on a computing device 110. For example, the software may form a process in one or more computer programs that execute on one or more programmed or programmable computer systems (which may be of various architectures).

[0050] Figure 5 This is a block diagram of example computer system 500. Figure 1The computing device 110 may be an example of the computer system 500 described herein. System 500 may include a processor 510, memory 520, storage device 530, and input / output device 540. For example, each of components 510, 520, 530, and 540 may be interconnected using a system bus 550. Processor 510 is capable of processing instructions for execution within system 500. Processor 510 may be a single-threaded processor, a multi-threaded processor, or a quantum computer. Processor 510 is capable of processing instructions stored in memory 520 or on storage device 530. Processor 510 may perform operations such as causing EMT system 100 to determine the position and / or orientation of sensor 108.

[0051] Memory 520 stores information within system 500. In some implementations, memory 520 is a computer-readable medium. Memory 520 may be, for example, a volatile memory cell or a non-volatile memory cell.

[0052] Storage device 530 provides high-capacity storage for system 500. In some implementations, storage device 530 is a non-transitory computer-readable medium. Storage device 530 may include, for example, hard disk drives, optical disk drives, solid-state drives, flash drives, magnetic tapes, or other high-capacity storage devices. Alternatively, storage device 530 may be a cloud storage device, such as a logical storage device comprising multiple physical storage devices distributed across a network and accessed via a network. In some implementations, information stored on memory 520 may also be stored on storage device 530 or alternatively stored on storage device 530.

[0053] Input / output device 540 provides input / output operations for system 500. In some implementations, input / output device 540 includes one or more network interface devices (e.g., Ethernet cards), serial communication devices (e.g., RS-23210 ports), and / or wireless interface devices (e.g., short-range wireless communication devices, 502.11 cards, 3G wireless modems, or 4G wireless modems). In some implementations, input / output device 540 includes driver devices configured to receive input data and send output data to other input / output devices such as keyboards, printers, and display devices. In some implementations, mobile computing devices, mobile communication devices, and other devices are used.

[0054] In some implementations, system 500 is a microcontroller. A microcontroller is a device that contains multiple components of a computer system in a single electronic package. For example, the single electronic package may contain a processor 510, a memory 520, a storage device 530, and an input / output device 540.

[0055] Despite Figure 5An example computer system is described herein, but the above-described subject matter and functional operations can be implemented in other types of digital electronic circuits, or as computer software, firmware, or hardware (including the structures disclosed herein and their equivalents), or in a combination thereof. Implementations of the subject matter described herein can be implemented as one or more computer program products, i.e., one or more modules of computer program instructions encoded on a tangible program carrier such as a computer-readable medium, said modules being executed, for example, by a processing system or used to control the operation of a processing system. The computer-readable medium can be a machine-readable storage device, a machine-readable storage substrate, a memory device, a combination of substances affecting machine-readable propagation signals, or a combination thereof.

[0056] The term "computer system" can include all means, devices, and machines used for processing data, such as programmable processors, computers, or multiprocessors or computers. In addition to hardware, a processing system can also include code that creates an execution environment for the computer program in question, such as code that constitutes processor firmware, protocol stacks, database management systems, operating systems, or one or more combinations thereof.

[0057] Computer programs (also known as programs, software, software applications, scripts, executable logic, or code) can be written in any form of programming language, including compiled or interpreted languages, or declarative or procedural languages, and can be deployed in any form, including as standalone programs or as modules, components, subroutines, or other units suitable for use in a computing environment. A computer program does not necessarily correspond to a file in a file system. A program can be stored as part of a file that holds other programs or data (e.g., stored in one or more scripts in a markup language document), in a single file dedicated to the program in question, or in multiple collaborating files (e.g., a file storing one or more modules, subroutines, or code sections). A computer program can be deployed to execute on a single computer or on multiple computers located at a single site or distributed across multiple sites and interconnected by a communication network.

[0058] Computer-readable media suitable for storing computer program instructions and data include all of the following forms: non-volatile or volatile memory, media, and memory devices, including, for example, semiconductor memory devices such as EPROM, EEPROM, and flash memory devices; magnetic disks, such as internal hard disks or removable disks or magnetic tapes; magneto-optical disks; and CD-ROM and DVD-ROM disks. Processors and memory may be supplemented by or incorporated into dedicated logic circuitry. Components of the system may be interconnected via digital data communication, such as communication networks, in any form or medium. Examples of communication networks include local area networks (“LANs”) and wide area networks (“WANs”), such as the Internet.

[0059] Many embodiments have been described. However, it should be understood that various modifications may be made without departing from the spirit and scope of the subject matter described herein. Other such embodiments are within the scope of the appended claims.

Claims

1. An electromagnetic tracking system, comprising: One or more field-generating coils are configured to generate a magnetic field; A sensor, comprising a housing including one or more flexible walls, the housing containing a ferrofluid and configured to be introduced into a patient's body, wherein, when the sensor is in the vicinity of a magnetic field, the ferrofluid causes distortion of the magnetic field, and the ferrofluid is configured to be removed from the housing by piercing the housing and introducing a magnetic force in the vicinity of the housing; and One or more magnetic field measuring coils are configured as follows: The characteristics of the magnetic field are measured when the sensor containing the ferrofluid is not near the magnetic field. When the sensor containing the ferrofluid is near the magnetic field, it measures the characteristics of the magnetic field; and A signal representing a measured characteristic of the magnetic field is provided to a computing device, the computing device including a processor capable of executing instructions stored on a storage device; The computing device is configured to determine one or both of the position and orientation of the sensor by comparing the characteristics of the magnetic field measured when the sensor containing the ferrofluid is not near the magnetic field with the characteristics of the magnetic field measured when the sensor containing the ferrofluid is near the magnetic field.

2. The electromagnetic tracking system according to claim 1, wherein, The characteristics of the magnetic field measured when the sensor containing the ferrofluid is in a first position include a first magnetic shape and a first magnetic intensity, and the characteristics of the magnetic field measured when the sensor containing the ferrofluid is in a second position include a second magnetic shape and a second magnetic intensity.

3. The electromagnetic tracking system according to claim 1, wherein, When mechanical stress is applied to the sensor, one or more magnetic properties of the sensor remain unchanged.

4. The electromagnetic tracking system according to claim 1, wherein, One or both of the shell and the ferrofluid are biocompatible or biodegradable, or both are biocompatible and biodegradable.

5. The electromagnetic tracking system according to claim 1, wherein, The ferrofluid includes one or both of liquid and powder.

6. The electromagnetic tracking system according to claim 1, wherein, The ferrofluid comprises superparamagnetic iron oxide nanoparticles.

7. The electromagnetic tracking system according to claim 6, wherein, The superparamagnetic iron oxide nanoparticles include one or both of magnetite (Fe3O4) and maghemite (γ-Fe2O3).

8. The electromagnetic tracking system according to claim 1, wherein, The shell comprises a polymer.

9. The electromagnetic tracking system according to claim 1, wherein, The housing is configured to receive the ferrofluid by injection after being introduced into the patient's body. The ferrofluid causes a measurable distortion of the magnetic field, which can be compared by the computing device with one or more other measured characteristics of the one or more magnetic fields.

10. The electromagnetic tracking system according to claim 1, wherein, The sensor has an ellipsoidal shape.

11. The electromagnetic tracking system according to claim 10, wherein, The ellipsoid is defined by three axes, and the length of the ellipsoid along each axis is different.

12. The electromagnetic tracking system according to claim 1, wherein, The sensor has at least one of the following: (i) a cuboid shape; (ii) a cylindrical shape; or (iii) a pill shape.

13. The electromagnetic tracking system according to claim 1, wherein, The computing device does not receive signals from the sensor.

14. A sensor configured for use in an electromagnetic tracking system, the sensor comprising: A housing comprising one or more flexible walls, the housing being configured to be introduced into a patient's body; A ferrofluid contained within the housing, and the ferrofluid being configured to be removed from the housing by piercing the housing and introducing a magnetic force in the vicinity of the housing, wherein the ferrofluid causes a measurable distortion of the magnetic field, and the location and orientation of the sensor can be determined by a computing device by comparing the characteristics of the magnetic field measured when the ferrofluid is not in the vicinity of the magnetic field with the characteristics of the magnetic field measured when the ferrofluid is in the vicinity of the magnetic field.

15. A method for tracking a sensor using an electromagnetic tracking system, the method comprising: The magnetic field begins to be generated; The sensor receives signals from one or more magnetic field measuring coils that represent the characteristics of the magnetic field measured when the sensor is introduced into the magnetic field. The sensor includes a housing comprising one or more flexible walls and containing a ferrofluid. The housing is configured to be introduced into a patient's body, wherein the ferrofluid causes distortion of the magnetic field when it is in the vicinity of the magnetic field, and the ferrofluid is configured to be removed from the housing by piercing the housing and introducing a magnetic force in the vicinity of the housing. as well as The location and orientation of the sensor are determined by comparing the characteristics of the magnetic field measured when the ferrofluid is not near the magnetic field with the characteristics of the magnetic field measured when the ferrofluid is near the magnetic field using a computing device including a processor capable of executing instructions stored on a storage device.

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