Magnetic flexible catheter tracking system and method using digital magnetometers

Abstract

To provide a method for magnetic tracking of a flexible catheter device or a flexible elongated device.SOLUTION: The method comprises: receiving by a host server 10 a plurality of sensed values of a local magnetic field, sensed by a respective plurality of sensors 31 located along a flexible tube of a device, where the sensed values are at least partially due to at least one of an alternating magnetic field generated by at least one magnetic field generator, and the source amplitude and frequency of each generated magnetic field given by the host server 10; and calculating a measurement position of the flexible tube by the host server 10 based on the sensed magnetic field values and the given source amplitude and frequency of each generated magnetic field.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a system and method for magnetic tracking of a flexible catheter using a digital magnetometer. [Background technology]

[0002] Known electromagnetic (EM) localization systems are sometimes used in the medical field to track small catheters inside the body. EM systems are well suited for such applications because the human body is transparent to near-field electromagnetic fields. This allows for real-time tracking of catheters or any other tools inside (or outside) the body without the need for line of sight and without the use of potentially harmful imaging modalities such as X-ray or computed tomography (CT).

[0003] Some known systems may include an electromagnetic field sensor / receiver and an electromagnetic field generator / transmitter that transmits multiple different alternating current ("AC") electromagnetic fields, e.g., sinusoidal electromagnetic fields. The receiver typically receives a combination of the multiple electromagnetic fields from the transmitter and distinguishes between the different fields, for example, by performing a fast Fourier transform (FFT) and / or a discrete Fourier transform (DFT) or any other suitable method. By analyzing the phase and / or amplitude, the receiver identifies a unique electromagnetic signature associated with a specific six-degree-of-freedom (6DOF) state, such as a specific position and orientation, e.g., three coordinates of position and three angles of orientation. In other systems, the electromagnetic signature is used to recover only five degrees of freedom (5DOF). In these systems, the roll angle of the sensor is typically not present. In other systems, only the position is resolved (3DOF), and the sensor orientation remains unknown.

[0004] To resolve the combination of received fields and / or distinguish between received fields and identify the unique 6DOF (or 5DOF) state of the monitored object, the transmitter must transmit multiple electromagnetic sinusoidal field signals, for example, at carefully selected frequencies so that the sinusoidal field signals are orthogonal to one another. Some systems may include N transmit coils that generate electromagnetic fields of different geometric shapes. The number N must be large enough to enable identification of the 6DOF (or 5DOF) state of the monitored object. In other systems, there may be a smaller number of coils that generate orthogonal (at the source) and / or otherwise highly distinctive electromagnetic field signals. To facilitate separation between fields and increase system availability, the system may use high-frequency electromagnetic fields, typically on the kHz scale.

[0005] In a conventional electromagnetic tracking catheter setup, the catheter has one or more microcoils positioned at its tip. For example, three micro-sized coils are traditionally placed at the catheter tip in an orthogonal fashion, and wires must be pulled outward from an external DSP. Some specialized systems use a single coil instead of three orthogonal coils, but this requires a specialized electromagnetic field generator to generate many different unique fields and, in addition, can only provide a maximum of five degrees of freedom (lacking roll angle) of measured position. Generally, one-coil systems are inferior in terms of accuracy and overall stability. The electromagnetic field generator generates a high-frequency (e.g., >1 kHz) alternating magnetic field, which will induce an electromotive force (EMF) on the catheter coil (according to Faraday's law of induction). The coil is connected through wires to an external digital signal processor (DSP) unit, which amplifies the induced voltage and then samples it, for example, using an analog-to-digital (A2D) converter. A dedicated processor then analyzes the sensed signal and decomposes it into distinct sinusoidal amplitudes using an FFT or DFT (or any other suitable method), and passes the DFT results to another processing stage, which is responsible for converting the calculated field amplitudes into the position and orientation of the sensor in three-dimensional space, relative to the field generator.

[0006] The DSP unit must include a high-quality, low-noise amplifier to amplify the minute voltages captured by the microcoils for the A2D transducer so that they can be sampled with a good signal-to-noise ratio (SNR). Every such coil requires a separate processing channel with a dedicated high-quality amplifier and A2D input. Furthermore, maintaining a good SNR is difficult; even the smallest noise can be amplified and obscure the signal of interest. For example, the wires connecting the coils to the DSP form loops through which some magnetic flux flows and therefore pick up a certain amount of parasitic, undesired signals from the transmitted field. This requires that the wires be wound across the catheter in a twisted-pair fashion. In addition to the wires, the connectors connecting the catheter to the DSP can also form undesired loops that can pick up a certain amount of parasitic signals. Therefore, conventional EM catheters involve complex designs with specialized, complex, and expensive complementary DSP units. The complexity of such systems increases approximately linearly with the number of desired sensors (number of coils, number of twisted-pair wires, number of DSP input channels, including more expensive amplifiers and A2Ds). For all these reasons, it should be understood why it is substantially impractical to build a conventional EM catheter with only a very small number of EM sensors.

[0007] Some devices, such as mobile phones, include an inertial measurement unit (IMU) that provides information about the device's motion and orientation. An IMU typically includes digital sensors such as a three-axis accelerometer and a three-axis gyro, and often also a three-axis magnetometer. The accelerometer detects acceleration in local 3D coordinates. In a typical configuration, the accelerometer primarily detects the gravity vector (plus some local linear acceleration, which can be filtered using various sensor fusion methods) and thus may allow detection of a partial orientation, such as the device's screen orientation (landscape / portrait). The gyroscope detects the device's angular velocity. In many applications, data received from the accelerometer and gyroscope are combined to provide robust device orientation tracking. Because these two sensors have no reference other than gravity (which points to the sky), the orientation calculated from the accelerometer and gyroscope typically drifts slowly around the gravity vector. In this sense, orientation tracking based solely on the accelerometer and gyroscope is considered "drifting" because it lacks a stable reference. A magnetometer may be used to sense the DC Earth magnetic field, for example, using a Hall-effect sensor, a magnetoresistive sensor, a magnetic induction sensor, and / or any other suitable sensor type. The sensed DC Earth magnetic field may be used to correct drift in accelerometer and gyroscope orientation detection in Earth coordinates. However, magnetometer readings are often distorted by various elements in their environment, such as nearby metals (soft iron, distortion of hard iron). Furthermore, low-cost magnetometer sensors are prone to bias calibration issues, in which the sensor's internal bias drifts over time. Therefore, in many applications, magnetometer data is ignored, and orientation is detected solely by the accelerometer and gyroscope. However, because magnetometer data is ignored and other sensors are not used as additional references for orientation, the determined orientation typically drifts relative to Earth's north. IMUs are primarily used for orientation detection, but may also be used for relative positioning. Using sensor fusion techniques, local acceleration can be extracted from accelerometer readings (minus gravity).The velocity of the device can then be calculated by integrating over a short period of time. Double integration gives the relative position of the device. However, these methods are sensitive to bias noise and are therefore typically only used with high-end, high-precision IMU sensors or over very short periods of time (e.g., for motion gesture detection). While an IMU can be used in a typical setting to calculate the absolute orientation of a device relative to Earth's coordinates (by using data from all three sensors: accelerometer, gyroscope, and magnetometer), none of the IMU readings provide information about the device's position relative to an absolute reference. To use an IMU for accurate absolute positioning, some external reference must be added. Summary of the Invention [Means for solving the problem]

[0008] An aspect of some embodiments of the invention provides a method for magnetic tracking of a flexible catheter device or other flexible elongate device, the method comprising receiving, by a host server, a plurality of sensed local magnetic field values sensed by each of a plurality of sensors positioned along a flexible tube of the device, the sensed values resulting from at least one of an alternating magnetic field generated by at least one magnetic field generator and an amplitude and frequency of a source of each generated magnetic field provided by the host server, and calculating, by the host server, a measured position of the flexible tube based on the sensed magnetic field values and the amplitude and frequency of the source of each provided generated magnetic field.

[0009] Optionally, the method includes receiving, by a host server, an instantaneous phase value of the generated magnetic field from at least one generator of the alternating magnetic field; associating, by the host server, between the instantaneous phase value and at least one of some of the sensed values of the magnetic field received from the sensor; and calculating, by the host server, a measured position of the flexible tube based on the magnetic field value and the associated phase value.

[0010] Optionally, the associating step is based on corresponding clock readings that are shared or synchronized between the magnetic field generator, the sensor's controller and the host server.

[0011] Optionally, the phase data is received from at least one generator with a magnetometer located on the at least one generator at full rate.

[0012] Optionally, the clock readings are shared by the field generators or by a clock source shared between the field generators, the sensor's controller and the host server.

[0013] Optionally, the method comprises receiving, at the source, an amplitude value of the generated magnetic field from the at least one generator.

[0014] Optionally, the calculating step includes calculating the positions and orientations of the plurality of sensors.

[0015] Optionally, the calculating step includes using an extended Kalman filter to fuse the sensor data, and imposing a motion model or shape constraints on the calculation.

[0016] Optionally, at least one sensor is a sensor bundle, and the calculation incorporates accelerometer or gyroscope readings of a corresponding sensor included in the sensor bundle.

[0017] Optionally, the calculation incorporates known structural relationships between the sensors to calculate the position, orientation or curvature of the tube as a whole.

[0018] Optionally, the sensed value is at least partially due to at least two generated magnetic fields generated by at least two corresponding generators.

[0019] Optionally, the at least two generated magnetic fields operate at different frequencies.

[0020] Optionally, at least two generators share the same clock, or have synchronized clocks, or share a clock source.

[0021] Another aspect of some embodiments of the invention is a system for magnetic tracking of a flexible catheter device or a flexible elongate device, the system comprising: an apparatus having at least one generator each configured to generate an alternating magnetic field, each generated magnetic field having a determined source amplitude and frequency; a flexible tube; and a plurality of sensors disposed along the flexible tube and each configured to communicate sensed values of a local magnetic field attributable at least in part to the generated magnetic field; and a host server that receives the sensed values of the local magnetic field from the corresponding sensors and calculates a measured position of the flexible tube based on the determined source amplitude and frequency, optionally the host server being included in a controller of the sensors.

[0022] Optionally, the host server receives an instantaneous phase value of the generated magnetic field from at least one generator of the alternating magnetic field, associates by the host server between the instantaneous phase value and at least one of some of the sensed values of the magnetic field received from the sensor, and calculates by the host server a measured position of the flexible tube based on the magnetic field value and the associated phase value.

[0023] Optionally, the correlating is based on readings of corresponding clock sources shared between the field generators, the controllers of the sensors and the host server.

[0024] Optionally, the apparatus further comprises a flexible PCB along the tube, the sensor being disposed along the flexible PCB.

[0025] Optionally, the flexible PCB is spirally wrapped around the wall of the tube.

[0026] Optionally, the apparatus further comprises a communication bus configured to digitally carry data of the sensed values from the plurality of sensors to a server.

[0027] Optionally, the communication bus includes up to four wire lines capable of carrying digital data sensed values from and supplying power to the multiple sensors.

[0028] Optionally, at least one generator includes an internal clock and is configured to share its clock readings with the sensor and the host server.

[0029] Optionally, the at least one generator includes a magnetometer for detecting phase data.

[0030] Optionally, at least one of the sensors is a sensor bundle comprising an accelerometer or a gyroscope sensor.

[0031] Optionally, the system includes at least two generators that respectively generate at least two magnetic fields operating at different frequencies.

[0032] Optionally, at least two generators share the same clock, or have synchronized clocks, or share a clock source.

[0033] Optionally, the at least one generator comprises at least one permanent magnet and a motor arrangement for rotating the magnet at the determined frequency.

[0034] Optionally, the at least one generator comprises an electromagnetic coil that generates a sinusoidal magnetic field at a particular known frequency.

[0035] Optionally, the apparatus includes a plurality of dipole magnets positioned between the sensors.

[0036] Optionally, the dipole magnets are positioned at equal distances and orientations such that when the tube is in a straight state, the two magnets positioned on either side of the sensor have opposite dipole directions. [Brief explanation of the drawings]

[0037] Certain non-limiting exemplary embodiments or features of the disclosed subject matter are illustrated in the following drawings. [Figure 1] FIG. 1 is a schematic diagram of a catheter tracking system for tracking with a digital magnetometer, according to some embodiments of the present disclosure. [Figure 2] FIG. 2 is a schematic diagram of an exemplary magnetic field generator / transmitter for digital magnetometer tracking, according to some exemplary embodiments of the present disclosure. [Figure 3] FIG. 3 is a schematic flow chart illustrating a method for tracking with a digital magnetometer, according to some embodiments of the present disclosure. [Figure 4] FIG. 4 is a schematic illustration of a catheter according to some embodiments of the present disclosure. [Figure 5] FIG. 5 is a schematic illustration of a catheter device according to some other embodiments of the present disclosure. [Figure 6] FIG. 6 is a schematic illustration of a catheter device according to some other embodiments of the present disclosure.

[0038] Referring now specifically to the drawings in detail, it is emphasized that the particulars shown are by way of example and for purposes of illustrative discussion of embodiments of the present disclosure. In this regard, the description given with the drawings will make apparent to those skilled in the art how embodiments of the present disclosure may be practiced.

[0039] Identical or duplicated or equivalent or similar structures, elements, or portions that appear in more than one drawing are generally labeled with the same reference number, optionally with one or more additional characters to distinguish between similar entities or variations of entities, and may not be repeatedly labeled and / or described. Reference to previously presented elements is implied without necessarily further citation to the drawing or description in which they appear.

[0040] Dimensions of components and features shown in the figures are chosen for convenience or clarity of presentation and are not necessarily shown to scale or in true perspective. For convenience or clarity, some elements or structures are shown only in part and / or in or from different perspectives, or are not shown at all. DETAILED DESCRIPTION OF THE INVENTION

[0041] Before describing at least one embodiment of the present disclosure in detail, it is to be understood that the present disclosure is not necessarily limited in its application to the details of construction and arrangement of components and / or methods set forth in the following description and / or illustrated in the drawings and / or examples. The present disclosure is capable of other embodiments or of being practiced or carried out in various ways.

[0042] Some embodiments of the present disclosure provide a magnetic tracking system for a fully curved catheter. A magnetic field generator / transmitter according to some embodiments of the present disclosure can induce an electromagnetic field to multiple magnetometers positioned along a flexible catheter tube. In some embodiments, the provided system may include at least one specialized magnetic field generator and / or may use specialized magnetic field generation and / or transmission methods. The magnetic field generator / transmitter provided according to some embodiments of the present invention may be constructed from low-cost components.

[0043] The provided system can receive sensor readings of local electromagnetic field values from multiple magnetometers and calculate a full curvilinear measurement position of the catheter tube along its length based on the received readings. This is in contrast to conventional EM catheter tracking systems, in which only the tip of the catheter is typically tracked. In some embodiments, the provided system can calculate and / or determine a 6DOF measurement position, e.g., a three-dimensional position and orientation, of each magnetometer based on its magnetic sensor readings relative to a field generator. In some embodiments, the sensing radius of the magnetometer is up to about 50 centimeters. Thus, in some embodiments, the distance of at least one field generator from the multiple magnetometers is up to 50 centimeters.

[0044] According to some embodiments, the provided system includes multiple digital magnetometers, e.g., off-the-shelf magnetic sensors, similar or identical to magnetometers included in an IMU. In some embodiments, a complete IMU sensor bundle is used. The digital magnetometers may have a small footprint and / or size suitable for catheters for insertion into various body cavities. For example, the magnetometers can be inserted into the catheter tube and / or the body cavity and / or the catheter tube wall. For example, multiple magnetometers may be disposed on a flexible printed circuit board (PCB) along the catheter tube, e.g., within an integrated circuit and / or silicon die. Multiple magnetometers may be packaged, e.g., within an ultra-compact wafer-level BGA (ball grid array) package, potentially enabling placement on a very thin flexible PCB.

[0045] Magnetometers referenced throughout this specification typically operate at sampling rates on the order of several hundred Hz, e.g., about 100 Hz and / or 500 Hz to 1000 Hz. To use a direct current (DC) magnetometer (measuring DC magnetic fields) as an alternating current (AC) magnetic sensor (intended for use with AC magnetic fields), the detected AC magnetic field may be at a frequency significantly lower than the sampling rate of the magnetometer, e.g., an order of magnitude lower. The detected magnetic field should be in a range detectable by a DC magnetometer. For example, in order to be detected by the magnetometer, the detected magnetic field should be about 10 times the sensitivity of the magnetometer as it occurs, taking into account noise levels. For example, a DC magnetometer can detect magnetic fields of several μT to several thousand μT (e.g., 1 to 4000 μT) with a sensitivity, e.g., resolution, of about 0.1 μT. Since the magnetic field strength is inversely proportional to the cube of the distance between the dipole source and the receiver, the detection range should have a range of about 10 times the minimum to maximum distance, e.g., 10 cm to 1 m or 1 m to 10 m.

[0046] According to some embodiments, multiple magnetometers are located along the same data bus and transmit their sensed values over the same data bus. Any number of magnetometers located along and / or transmitting data over the data bus requires, for example, no more than four electrical wires running along the catheter tube. This is in contrast to conventional analog catheter tracking systems, which may require a large number of wires that grow linearly with the number of magnetic sensors.

[0047] Some embodiments of the present disclosure provide a method for measurement position calculation that can calculate the full curve measurement position of a catheter at a rate exceeding 30 Hz. This rate is suitable for most real-time medical applications. Therefore, some embodiments of the present invention provide a solution to the problem of obtaining the full curve measurement position of a small diameter catheter in real time without the high cost of conventional EM sensors and DSP. In addition, in some embodiments, the provided system has low power consumption, for example, at both the receiving and transmitting ends, which may enable operation of the full curve catheter position measurement system with a significantly smaller wireless and / or battery footprint.

[0048] The ability to build a full curve tracking catheter in a low cost, uncomplicated configuration, as provided by some embodiments of the present disclosure, is important for many potential medical applications.

[0049] Reference is now made to FIG. 1 , which is a schematic diagram of a catheter tracking system 100 for tracking with a digital magnetometer, according to some embodiments of the present disclosure. According to some embodiments of the present disclosure, the system 100 provides a solution for full-curvilinear catheter position measurement. The system 100 may include a catheter 30, a hardware host server 10, and at least one magnetic field generator / transmitter 20, e.g., magnetic field generators / transmitters 20a and 20b. As described herein, the system 100 is capable of providing full-curvilinear position measurement of the catheter 30 over its length. In some embodiments of the present disclosure, the host server 10 is included in a controller within the catheter 30, e.g., all functions of the host server 10 described herein are performed by the controller within the catheter 30. The terms “controller” and “microcontroller” are sometimes used interchangeably throughout this disclosure and may refer to or include a microprocessor.

[0050] The transmitters 20 may generate a magnetic field. For example, the transmitters 20 may be electromagnetic generators of a magnetic field, e.g., including at least one electromagnetic coil. Each generator 20 may generate an alternating magnetic field. Each generated magnetic field has a determined source amplitude and frequency. In some embodiments, the transmitters 20 may include sensors that sense the instantaneous phase of the generated electromagnetic field or calculate the instantaneous phase of the generated electromagnetic field by using synchronized electromagnetic field generator drivers and communicate the instantaneous phase value, e.g., periodically, along with a timestamp, to the host server 10.

[0051] In some embodiments of the present disclosure, transmitter 20 may include at least one rotating magnet, as shown in more detail in Figure 2. As described in more detail herein, in some embodiments, transmitter 20 may include a sensor that senses the instantaneous phase of the rotating magnet or calculates the instantaneous phase of the rotating magnet by using a synchronous motor driver and communicates the instantaneous phase value along with a timestamp to host server 10, for example, periodically.

[0052] The catheter 30 may include a microcontroller 32, a flexible tube 36, and multiple magnetometer sensors 31 mounted, for example, on a flexible PCB (shown in more detail in FIG. 4) along the tube 36. The magnetometer sensors 31 may be positioned at predetermined locations along the tube 36 and / or at predetermined distances between them. According to some embodiments, the magnetometer sensors 31 may be or include off-the-shelf magnetic sensors, for example, magnetometers similar to or the same as those included in an IMU or a stand-alone off-the-shelf magnetic sensor. In some embodiments, each of the magnetometer sensors 31 may be or include a complete IMU sensor bundle.

[0053] Each of the magnetometer sensors 31 can sense a corresponding local magnetic field value resulting from the magnetic field generated by the transmitter 20. The host server 10 / microcontroller 32 can receive the magnetic field values from the sensors 31, and / or the microcontroller 32 can communicate the sensed values along with a timestamp to the host server 10 / microcontroller 32. The microcontroller 32 can be located at the proximal end of the catheter 30, e.g., in the communication path between the sensors 31 and the host server 10. For example, the microcontroller 32 can receive and / or collect at least one local magnetic field value and instantaneous magnetic field value, e.g., sensed values at a given moment, from each of the at least one sensor 31 and transmit the collected values along with a corresponding timestamp, e.g., via USB, wireless communication, etc. For example, the microcontroller 32 can communicate the collected sensed values, e.g., along with the identification of each sensing sensor 31 for each sensed value. As described in more detail herein, the sensors 31 can be communicatively connected to the microcontroller 32 and / or the host server 10 by the same data bus 34 located along the tube 36. In some embodiments of the present disclosure, at least some of the functions of host server 10 described throughout this specification are performed by microcontroller 32. In some embodiments, all of the functions of host server 10 are performed by microcontroller 32 and / or processor / controller 27 described with reference to FIG.

[0054] The flexible tube 36 may be positioned in a variety of positions and may have a variety of instantaneous curved shapes, for example, according to the shape of the body organ into which it is inserted and / or according to obstacles the catheter tube may encounter.

[0055] The host server 10 / microprocessor 32 may include at least one hardware processor 12 and / or at least one hardware memory 14. The memory 14 may include a tangible, non-transitory, processor-readable storage medium that stores processor-readable program instructions for causing the processor 12 to perform aspects of the present disclosure. The system 100 may include a display device 16 configured to receive data and / or instructions from the host server 10 and display information in accordance with the received data and / or instructions. The display device 16 may, for example, show navigation instructions to instruct a physician to reach a particular point of interest within the body.

[0056] The magnetometer sensors 31 may be and / or include a digital magnetometer configured to provide a sensor digital output, and / or may be low-cost and / or have a small footprint. In some embodiments, each of the sensors 31 may be or include a standard IMU, which may include a magnetometer, an accelerometer, and / or a gyroscope. Multiple sensors 31 may be located along the same digital communication bus 34 and / or communicate the sensor digital output to the microcontroller 32 and / or server 10 via the same digital communication bus 34. For example, the sensors 31 may sense local electromagnetic field values along the curve of the tube 36 simultaneously or within a very short period of time, such as a few milliseconds, and / or transmit these values via the same bus 34 to the microcontroller 32 and / or server 10, for example, simultaneously or within a very short period of time, such as a few milliseconds or up to tens of milliseconds. The host server 10 / microprocessor 32 can receive sensed local magnetic field values from the corresponding sensors 31 and / or can calculate the measured position of the flexible tube 36 based on, for example, the sensed magnetic field values and the amplitude and frequency of the determined source of the magnetic field generated by the transmitter 20.

[0057] Each sensor 31 may be separately identified by the microcontroller 32 and / or the server 10. For example, the microcontroller 32 and / or the server 10 may associate each received electromagnetic field value with the respective sensor 31 that sensed that value. For example, the microcontroller 32 may transmit the sensed value to the server 10 along with an identifier code that identifies the sensor that sensed the value. In some embodiments, the sensed value and / or identifier code may be transmitted along with a timestamp that verifies, for example, the time of sample reading. As described in more detail herein, the host server 10 / microprocessor 32 may calculate the 6DOF measured position of each sensor based on the received sensed values and / or timestamps, and / or phase data received from at least one generator 20, and / or calculate the full curve position of the catheter tube 36 based on multiple sensed values received from multiple sensors 31. For example, the calculation may be performed by imposing certain shape and / or curvature constraints. In some embodiments of the present invention, system 100 may include any suitable number of sensors 31 along tube 36 without substantially increasing the complexity of the system, for example, because sensors 31 transmit sensed values over the same data bus 34. For example, in some embodiments, no DSP input channels are required to amplify, sample, and transmit magnetic values from sensors 31 to microcontroller 32 and / or server 10.

[0058] In some embodiments, system 100 is synchronous, e.g., shares a single clock among its components. For example, generator / transmitter 20 can include an internal clock and / or share its clock readings with sensors 31, microcontroller 32, and / or server 10, and / or other generator / transmitters, as described in more detail herein. In some embodiments of the present disclosure, at least some of the components of system 100 synchronize their respective clocks with an external clock. Microcontroller 32 can receive respective sensed values from sensors 31. For example, microcontroller 32 can receive sensed data sampled by sensors 31 and written to data bus 34 via data bus 34. In some embodiments, microcontroller 32 transmits data to host 10, e.g., with a corresponding timestamp. For example, the timestamp corresponds to the respective clock reading received from transmitter 20 or is based on another shared clock. Server 10 can receive data from transmitter 20 and sensors 31 and / or synchronize the data according to the timestamps. For example, the shared or external clock may include a dedicated crystal oscillator physically connected to all devices, a USB hub clock shared among all devices connected to a USB hub, a clock generated by an RF (radio frequency) main source and shared wirelessly among RF devices, or a GPS clock that is sensed by at least some devices in system 100.

[0059] In some exemplary embodiments, the transmitter 20 may generate a low-frequency magnetic field using an electromagnetic coil. The frequency may be sufficiently low (e.g., below 500 Hz) to be perfectly matched by the sampling rate of the sensor 31, e.g., the sensor 31 may sample the magnetic field at at least the minimum rate required to retain all necessary information about the sensed magnetic field, e.g., amplitude, frequency, and / or phase. The generated magnetic field may be sufficiently strong within the sensing radius (e.g., greater than 1 μT) to obtain quality samples within the magnetometer's sensitivity and / or signal-to-noise ratio ("SNR"). The sensor 31 may collect enough samples to perform a discrete Fourier transform ("DFT") or similar algorithm to separate the generated magnetic field and solve for the 6 DOF measured position of the sensor 31 and / or the tube 36. In some cases, phase information may be provided by the transmitter 20 and synchronized between the transmitter 20 and the sensor 31 and / or the microcontroller 32 to provide a low-latency, high-speed 6 DOF solution. In this way, the microcontroller 32 and / or host server 10 can know the instantaneous phase of the generated magnetic field and can generate a quick 6DOF solution by using the synchronized phase information and timestamps in an extended Kalman filter setup (as described herein).

[0060] As described in more detail herein, for example, with reference to Figure 2, according to some embodiments of the present invention, the magnetic field generator / transmitter 20 includes a rotating magnet and a rotation sensor (e.g., a magnetometer) that senses the instantaneous phase of the magnet rotation, e.g., the position where the magnet is located within its rotational orbit at a given moment. For example, the rotation sensor is configured to communicate the instantaneous phase information to the server 10, e.g., along with a timestamp for each of the full-rate clock readings.

[0061] For example, according to their corresponding timestamps, the server 10 can associate a certain phase state of the generated magnetic field with a corresponding local magnetic field reading received from the sensor 31 that was detected and / or transmitted simultaneously with the phase reading. Based on the magnetic field readings and the associated instantaneous phase readings, the server 10 / microprocessor 32 can calculate, e.g., in real time, a measured position of the fully curved catheter. For example, the host server 10 / microprocessor 32 can receive from at least one generator 20 of the alternating magnetic field an instantaneous phase value of the generated magnetic field, correlate the instantaneous phase value with at least a portion of the sensed magnetic field values received from the sensor 31, and / or calculate a measured position of the flexible tube 36 based on the magnetic field values and the associated phase values.

[0062] It will be appreciated that the system 100 may include multiple catheters 30 and the server 10 may calculate full curvilinear catheter measurement positions for multiple catheters 30, eg, simultaneously.

[0063] Reference is now made to Figure 2, which is a schematic diagram of an exemplary magnetic field generator / transmitter 20 for tracking with a digital magnetometer, according to some exemplary embodiments of the present disclosure. The generator / transmitter 20 may include at least one permanent magnet 22, a processor / controller 27 having an internal clock 28 and a communications interface 29, a motor device 21, a magnetometer 25, and a power supply 24.

[0064] The configuration of generator / transmitter 20 shown in FIG. 2 and described herein is not required by some embodiments of the present invention, and other suitable configurations, components, and / or structures of generator / transmitter 20 are possible in accordance with some embodiments of the present invention.

[0065] In some embodiments, the generator / transmitter 20 generates a low-frequency electromagnetic field, e.g., below 60 Hz, having a strength of, e.g., about 1 μT, or stronger at, e.g., about 1 meter from the transmitter. Typically, generating such a strong field with AC current according to Ampere's law requires a very large transmitter with very high power consumption. However, according to some embodiments of the present invention, the generator / transmitter 20 includes at least one permanent magnet 22 that generates the magnetic field. By generating the magnetic field with at least one permanent magnet, the magnetic field generated by the generator / transmitter 20 can be approximately 100 times stronger than the magnetic field generated by AC current and can be generated by a transmitter of similar dimensions, resulting in an extremely low-power transmitter. The material of the magnet can be selected to maximize the generated magnetic field strength relative to the size of the generator / transmitter 20. For example, the generator / transmitter 20 can include a rare-earth magnet, e.g., a neodymium magnet, or a magnet of another suitable material.

[0066] To generate an AC magnetic field, in some embodiments of the present invention, magnet 22 is mounted on an axis that is rotated at a desired operating frequency f, for example, by motor device 21, e.g., a direct current (DC) motor, or by an electromagnetic coil wound around magnet 22 that generates a weak AC magnetic field strong enough to rotate the magnet about its center with applied torque, or by an off-the-shelf single-axis electromagnetic coil positioned near magnet 22 that generates a weak AC magnetic field strong enough to rotate the magnet with applied torque, or by any other suitable device. Thus, for example, rotating magnet 22 generates an AC magnetic field in the surrounding space. The magnetic field generated by rotating magnet 22 can be expressed as the superposition of two AC magnetic fields of frequency f and quadrature phase, as follows, generated by two separate imaginary coils x and y:

number

number

[0067] In some embodiments, magnet 22 may be controlled by generator 20 to rotate about an additional, secondary, axis to obtain a more complex magnetic field sensed by receiver 20 and thus provide more information for, for example, position and orientation calculations. Magnetometer 25 can sense the corresponding generated magnetic field, calculate the instantaneous phase of magnet 22 in rotation about the first and second axes accordingly, and transmit the calculated instantaneous phase to receiver 20. For example, periodic motion of magnet 22 may be generated by attaching magnet 22 and / or a first motor to a camshaft of a second motor. For example, periodic motion about the first and second axes may be applied to magnet 22 by mounting magnet 22 on a shaft that is free to rotate and move axially and includes a radial pin that engages a groove in a surrounding sleeve. Optionally, the groove is in the shaft and the pin extends radially from the sleeve into the groove.

[0068] A processor / controller 27, e.g., a microcontroller / controller, can maintain a permanent desired frequency f at which motor 21 operates and / or magnet 22 rotates. For example, the desired frequency f may be inherent in and / or embedded within the hardware of controller 27 and / or transmitter 20. For example, motor device 21 may be a highly stable motor and / or a specially designed motor that operates according to, e.g., a clock 28 of controller 27 or that otherwise maintains a substantially constant frequency. In some embodiments, controller 27 can switch between various possible frequencies to cause transmitter 20 to generate an AC field within the desired, maintained frequency f, e.g., by maintaining corresponding voltage levels provided to motor 21 in a closed feedback loop with the transmitter's magnetometer 25 (rotation sensor). In some embodiments, controller 27 can include hardware and / or software components for varying frequency f. The maintained frequency f can be communicated to receiver / sensor 20, e.g., by controller 27, via communication interface 29. The communication interface 29 may include a low-power wireless transmitter / receiver, for example a 2.4 GHz transmitter / receiver, and / or a low-energy Bluetooth® device, a WiFi communication device, a USB cable, or any other suitable communication device.

[0069] According to some embodiments of the present invention, magnetometer 25 may be positioned at a fixed position relative to rotating magnet 22. Magnetometer 25 may sense the rotation period of magnet 22 and where magnet 22 is located in the period, e.g., the instantaneous rotational phase Φ(t) of magnet 22. As shown in more detail herein, the rotational phase of magnet 22 may include one or two rotational phases about one or two corresponding axes. For example, magnetometer 25 may provide an estimate of the phase of magnet 22, e.g., by principal component analysis (PCA) of magnetic samples collected over many rotation periods, e.g., by extracting the axes of an ellipse drawn in a local coordinate system centered on transmitter 20 by rotating magnet 22, or any other suitable method for detecting the phase of magnet 22, e.g., by fitting an ellipse to samples collected over many periods of the rotating magnet by means of optimization. According to some embodiments of the present invention, magnetometer 25 is positioned at and / or on the rotational axis of the rotating magnet. Due to symmetry, the sensed magnetic field forms an approximation of a circle or ellipse at the location of the magnetometer 25 while the magnet is rotating. The formed ellipse / circle can be identified, for example, by the server 10 / microcontroller 32. For example, the ellipse / circle can be fitted to the periodic curved shape of the sensed magnetic field, for example, by the host server 10 / microprocessor 32. For example, the server 10 / microprocessor 32 can approximate the periodic curved shape of the sensed magnetic field to a circle and / or calculate the instantaneous phase state of the magnetic field generated within this circle.

[0070] The rotation frequency of magnet 22 can be significantly lower than the sampling rate of magnetometer 25, e.g., a sampling rate in the range of about 100 Hz to 1000 Hz, thereby enabling, for example, a more accurate estimation of the rotation phase of magnet 22. Thus, in some embodiments of the present invention, the rotation frequency of magnet 22 is much lower than the sampling rate of magnetometer 25, e.g., an order of magnitude lower than the sampling rate of magnetometer 25, e.g., about 10 Hz to 100 Hz. Thus, processor / controller 27 can calculate the rotation phase of magnet 22 and / or communicate the calculated phase to receiver server 10, e.g., via interface 29. Magnetometer 25, in some embodiments, may be included in a sensor bundle, e.g., an IMU chip.

[0071] According to some embodiments of the present disclosure, unlike conventional magnetic / electromagnetic field transmission units, transmitter 20 may generate a magnetic field without using an electric current to induce the magnetic field. Transmitter 20 utilizes an already-existing field generated by permanent magnet 22. Therefore, the power consumption of transmitter 20 is much lower compared to conventional transmitter units, allowing it to operate, for example, on standard batteries for tens of hours. Thus, for example, power source 24, which may power transmitter 10, may be a low-power source, such as a disposable and / or rechargeable battery and / or any other suitable low-power source. Rotating a magnet using a standard DC motor or by a weak AC magnetic field generated by a coil near the magnet that applies a torque to the magnet, causing it to rotate, consumes much less power than generating the same AC magnetic field using a standard EM transmitter.

[0072] Reference is now made to FIG. 3 , which is a schematic flowchart illustrating a method 300 for tracking with a digital magnetometer, according to some embodiments of the present disclosure. As indicated in block 310, the server 10 may receive data regarding the instantaneous phase of the generated AC magnetic field, e.g., the instantaneous rotational phase of the permanent magnet 22, from the generator / transmitter 20, e.g., along with a corresponding clock reading from the clock 28. For example, the server 10 may receive the phase data from the generator / transmitter 20 at predetermined time periods and / or each time the magnetometer 25 detects the phase of the generated AC magnetic field. Additionally, the server 10 may receive and / or extract the amplitude and / or magnitude of the generated magnetic field at a source, i.e., the transmitter 20, e.g., from the magnetometer 25 and / or via predefined calibration data stored on the server 10.

[0073] As shown in block 320, the server 10 may receive a sensed value of the local magnetic field sensed by at least one of the sensors 31 along the flexible tube 36 that senses the magnetic field generated by the generator / transmitter 20. Because the sensor 31 senses the generated magnetic field in its local coordinate system, the magnetic field reading is rotated according to its orientation relative to the generator / transmitter 20, resulting in, for example, the next magnetic field measurement by the sensor 31.

number

[0074] In the case of a single generator / transmitter 20 included in system 100, in some embodiments of the present invention, the local magnetic field at the location of one of the sensors 31 can be represented as a superposition of two AC magnetic fields of frequency f and quadrature phase, generated by two separate virtual coils x and y of transmitter 20.

number

[0075] As shown in block 330, the server 10 may associate the sensed instantaneous phase of the magnet 22 sensed and / or communicated by the magnetometer 25 and / or generator / transmitter 20 with the sensed value of the magnetic field received from the sensor 31 based on a shared clock reading of the corresponding clock 28 or a shared clock reading of an external clock source shared between the server 10 and components of the system 100, such as the sensor 31 and / or microcontroller 32.

[0076] As shown in block 340, the server 10 may calculate the magnetic field sensing values, e.g., the position and orientation of the sensors 31 based on the received magnetic field sensing values and the associated phase of the magnets 22, providing the measured position of each of the sensors 31, e.g., 6DOF or 5DOF, and / or the overall position, orientation, and / or curve of the tube 36. According to some embodiments, the server 10 may use accelerometer and / or gyroscope readings for the measured position calculation of the corresponding sensors included in the sensors 31 in some embodiments of the present disclosure.

[0077] According to some embodiments of the present disclosure, sensor 31 is required to have a minimum size and therefore may not include, for example, a gyroscope and / or an accelerometer and / or other additional sensors. In such cases, system 100 may include multiple generator / transmitters 20, e.g., generators / transmitters 20a and 20b, to enable more accurate calculation of, for example, 6DOF or 5DOF position measurements.

[0078] Generators / transmitters 20a and 20b may both generate alternating magnetic fields, for example, at different frequencies (not necessarily orthogonal). Generators / transmitters 20a and 20b may be located at fixed positions and orientations relative to one another, and / or the relative positions and / or orientations of generators / transmitters 20a and 20b may be calculated and / or adjusted, for example, by manual and / or computerized calibration.

[0079] Similar to a single generator / transmitter 20, generator / transmitters 20a and 20b generate magnetic fields M1(t), M2(t), respectively, which can be expressed as:

number

number

[0080] The magnetic field sensed by the sensor 31 can be expressed as:

number

number

[0081] Of course, the solution for the 6DOF measurement position of the sensor 31 and / or tube 36 is flexible enough and does not depend on any particular implementation, structure and / or configuration of the transmitter 20, as long as the instantaneous generated magnetic field at various positions in space is known. In a general setup, the magnetic field reading by the sensor 31 can be written as:

number

number

[0082] In some embodiments of the present disclosure, a Kalman filter may be used to track the position and / or orientation state of the sensor 31. Using a Kalman filter algorithm may result in a faster refresh rate for updating the detected state of the sensor 31 and better overall tracking performance. It will be appreciated that in a low-frequency magnetometer-based localization system, where the sampling rate of the sensor 31 may be, for example, 100 Hz to 1000 Hz, the magnetic field frequency of the transmitter 20 may be constrained to approximately 10 to 100 Hz. In this case, a localization algorithm that relies on decomposing a full cycle of a sine wave into field amplitudes would result in a slow refresh rate and poor overall tracking performance, making it unacceptable for most medical applications. In some embodiments of the present disclosure, the server 10 solves the problem of a slow refresh rate by using a Kalman filter algorithm incorporated into its catheter localization algorithm, which in some embodiments can result in a refresh rate of at least 100 Hz, which is fast enough for most medical applications.

[0083] The server 10 can use a mathematical model to describe the motion of the catheter tube 36. In some embodiments, the server 10 can track each sensor 31 independently. For example, the server 10 can predict the state of the sensor 31 for the next time frame, e.g., based on the state in the current time frame and / or based on IMU sensor flux measurements, which can be used to correct the prediction. For example, the motion model can use a constant and / or decaying rate for the position and / or orientation of the sensor 31. For example, the server 10 can use a state vector for the sensor 31 for a Kalman filter algorithm. The state vector can be composed of parameters such as, for example, sensor bias, environmental magnetic bias, position in the coordinates of the transmitter 20 / 20a, orientation in the coordinates of the transmitter 20 / 20a (represented as a quaternion), velocity in the coordinates of the transmitter 20 / 20a, and angular velocity in local coordinates (also sometimes represented by ω, not to be confused with the frequency of the transmitted magnetic field).

number

[0084] After defining the state vector and its dynamic model, the server 10 can predict the state vector of the sensor 31 and / or the state covariance between successive time frames. The state vector can then be corrected according to the prediction to provide a better fit to newly obtained sensor magnetic field readings. For example, if the magnetic measurements are M RX (DUAL)The tracking state vector, modeled as (t), may yield a vector that deviates from the most recent sensed magnetic reading by a small amount of random noise, and its standard deviation may be set according to its typical value, e.g., from the data sheet of the respective magnetometer.

[0085] In some embodiments, the motion model used by server 10 is modular and / or extensible. For example, if an optional accelerometer or gyroscope sensor is present, e.g., in sensors 31, the Kalman filter can be expanded to include an additional state for linear acceleration r··→. The accelerometer-gyroscope readings can be processed with an IMU fusion filter to separate between gravitational acceleration and linear acceleration. The calculated linear acceleration can then be fed to the Kalman filter as the measurement r··→ when correcting the state vector, while the gyroscope readings can serve as the measurement ω→. The extra accelerometer-gyroscope readings can significantly reduce the latency of the filter, providing even faster and more stable position measurements.

[0086] In another configuration, for example, instead of separating between "classical" IMU-fused orientation tracking and magnetometer-based 6DOF tracking, additional IMU data (accelerometer, gyroscope) can be combined with magnetometer readings in a single unified extended Kalman filter, whose states (as described above) can be:

number

[0087] The use of an extended Kalman filter to solve for 6 DOF measured position of the sensor 31 and / or tube 36 is not limited to the transmitter 20 described with reference to FIG. 2, but can be easily generalized to any type of transmitter 20. As long as each magnetic measurement can be explained using the filter's states, the filter will work perfectly and provide a fast 6 DOF solution. This is an excellent property of the extended Kalman filter; all that is required for a high-quality solution of the states is to be able to model the measurements using those states.

[0088] For example, if an electromagnetic generator / transmitter 20 is used that generates the magnetic field with an electromagnetic coil, the following more general equation may be substituted:

number

[0089] where M(r→,t) depends on the magnetic field generated by the transmitter 20 used. This allows the use of an extended Kalman filter for a 6DOF measurement position solution of the sensor 31 / tube 36 that is invariant to the choice of transmitter, which is extremely powerful and flexible for many general purposes.

[0090] According to some embodiments of the present disclosure, the server 10 may, for example, use known structural relationships between the sensors 31 in a catheter localization algorithm to calculate an estimate of the position, orientation, and / or curve of the tube 36 as a whole, rather than calculating the position and / or orientation for each of the sensors 31 separately.

[0091] Reference is now made to Figure 4, which is a schematic illustration of a catheter 30, according to some embodiments of the present disclosure. The catheter 30 may include a flexible PCB 33 disposed within and / or along a catheter tube 36. The PCB 33 may be communicatively connected to a microcontroller 32 by a data bus 34, which may include a small number of wire lines 35, e.g., two to four wires 35. For example, an Inter-Integrated Circuit (I2C) may be used as a digital connection interface between the microcontroller 32 and sensors 31 located along the PCB 33. In some embodiments, only two wires 35 are required to exchange data between the sensors and the microcontroller 32, which may be beneficial for small catheters where wire count should be kept low.

[0092] In an exemplary configuration, the flexible PCB 33 can have eight, five, ten, or any suitable number of sensors 31 mounted thereon, all connected, for example, to the same I2C bus (e.g., serial data and serial clock lines). In some embodiments, the microcontroller 32 is connected to the flexible PCB 33 using, for example, a four-wire shielded cable including a voltage and / or ground wire. The microcontroller 32 can provide voltage and / or ground for the digital sensors 31, for example, in addition to two data lines for reading digital measurements by the sensors 31. The microcontroller 32 can, for example, sequentially read the sensors 31 and transmit the sensor readings to the server 10, for example, via wired and / or wireless communication. In a slightly different configuration, five wires 35 can be used to connect between the microcontroller 32 and the flexible PCB 33 and / or sensors 31. For example, additional data lines may be added. For example, some of the sensors 31 can use a first data line wire, and other sensors 31 can use a second data line wire. Thus, for example, the microcontroller 32 may sample and / or read several of the sensors 31 simultaneously, thereby, for example, reducing the overall I2C sampling time. For example, in the case of two parallel data line wires, the sampling time may be halved.

[0093] The design of the flexible PCB 33 and / or the positioning of the sensor 31 thereon can provide, for example, the position and / or orientation of the sensor 31 when the PCB 33 is straight. For example, during the manufacturing process, the PCB 33 can be mounted within and / or along the tube 36 in a manner that determines, for example, the position and / or orientation of the sensor 31 relative to the tube 36. The server 10 can be calibrated to provide the server 10 with an initial 6DOF orientation and / or position of the sensor 31, for example, the 6DOF orientation and / or position of the sensor 31 when the tube 36 is straight. The initial 6DOF orientation and / or position data, along with information about the stiffness and / or flexibility limits of the tube 36, can be incorporated into the catheter localization algorithm as a geometric constraint. For example, based on the incorporated geometric constraint, two adjacent sensors 31 cannot point in opposite directions.

[0094] In this manner, more sophisticated localization algorithms that take shape constraints into account can make the system 100 compact and robust. Solving the 6DOF positions and / or orientations of all sensors 31 while imposing a physical shape constraint on the complete curved shape of the catheter tube 36 can essentially reduce the number of parameters in the motion model, thus preventing, for example, overfitting of the measured data. By using shape constraints, the server 10 can refrain from miscalculating the position and / or orientation of a sensor 31 due to noisy or distorted measurements, for example, because the position and / or orientation solutions must follow those of neighboring sensors 31, and thus, for example, because they together describe a smooth, physically plausible catheter tube 36.

[0095] A common challenge in electromagnetic positioning systems is to be as accurate as possible in the presence of magnetic distortion. In low-frequency systems, the primary distortions are objects made of ferromagnetic materials. In hospital settings, these can be found in patient bed frames or as part of instruments used by physicians during medical procedures (e.g., surgical instruments). If a positioning system does not consider magnetic distortion, it can be highly inaccurate (position error >1 cm) and unsuitable for medical applications. Magnetic distortion devices can be divided into static distortion devices, whose position relative to the system can be fixed, and dynamic distortion devices, which can move between and / or during medical procedures. Static magnetic distortion devices are objects that can be fixed relative to the magnetic field generators during deployment of the positioning system and remain permanently fixed during the lifetime of the positioning system. In some embodiments of the present disclosure, static distortions can be addressed through a process of magnetic mapping, in which the magnetic field within a sensing radius around the transmitter(s) 20 is no longer assumed to be a perfect dipole field, but rather is "mapped" in an offline process with calibrated sensors 31 and later used by a real-time solver to solve for accurate 6DOF position and orientation even under distorted fields. In some embodiments, the server 10 can take dynamic distortions into account, for example, by incorporating the distortions into the positioning algorithm to provide an accurate solution.

[0096] Different methods can be used to compensate for dynamic magnetic distortion. One method would be to incorporate a physical distortion model within the model of the sensed magnetic field of the sensor 31. Even in the case of multiple transmitters 20, this addition of parameters can result in a less robust solution if each sensor 31 is solved independently due to the solver's ability to overfit the 6DOF and distortion model parameters to the measured sensor 31 data. For this reason, the solver should be constrained to parameters that make "mechanical sense" with respect to both the solved geometry of the sensor 31 within the catheter tube 36 and the geometric properties of the distortion field. Another method for addressing dynamic distortion includes imposing shape constraints on the entire curved shape of the catheter tube 36. The 6DOF orientation and position solutions calculated by the server 10 may deviate less from the actual position and orientation of the sensor 31 along the curve of the tube 36, for example, because they are regularized by the shape constraints, as described above. While dynamic distortions are typically local artifacts that distort position and orientation calculations in entirely different ways, the imposed shape constraints will ensure that the position and / or orientation solutions of the multiple sensors 31 are still meaningful with respect to the fully solved curve of the catheter tube 36. The undesirable effects of distortions are naturally reduced simply because of the imposed shape constraints.

[0097] There are several ways to impose shape constraints on the localization algorithm. One option is to approximate the shape of the catheter as a set of line segments 37 with a single sensor 31 at the end of each segment 37. The orientation of each sensor 31 relative to its surrounding catheter and its distance to its neighboring receiver are assumed to be fixed and known, for example, by calibration of the localization algorithm. Thus, according to some embodiments of the present disclosure, the entire catheter curve is modeled by a single set of 6 DOFs that may belong to one of the sensors 31, e.g., the first sensor 31 along the tube 36, e.g., the first sensor 31 closest in the communication path to the server 10 and / or microcontroller 32, along with two spherical angles corresponding to the bending of the catheter within the segment 37 between the sensor 31 and the sensor 31, and / or an additional angle to represent the internal twist of the tube 36 within the corresponding line segment 37. In some embodiments of the present invention, PCB 33 includes thinner portions 33a, e.g., between sensors 31, that are thinner than portions of PCB 33 in which sensors 31 are located, e.g., to facilitate increased flexibility and / or bendability of PCB 33 in portions 33a.

[0098] Reference is now made to Figure 5, which is a schematic illustration of a catheter 30a, according to some embodiments of the present disclosure. In some embodiments, the flexible PCB 33 is spirally wound on and / or along the inner or outer wall of the tube 36, as shown in Figure 5, to facilitate, for example, improving the flexibility and / or bendability of the catheter 30a, e.g., of the tube 36 along with the PCB 33. As will now be described in more detail, e.g., with reference to Figure 6, the PCB 33 can further carry sensors 31, e.g., multiple dipole magnets, and / or a data bus 34.

[0099] Thus, in some embodiments, the number of parameters in the catheter geometry is significantly reduced from 6 DOF orientations and positions for each sensor 31 to 6 DOF orientations and positions for the first sensor 31 plus three angles for each additional sensor 31. In this manner, the solved sensor 31 orientations and positions are less prone to overfitting due to hard constraints that assume, for example, fixed distances between sensors 31, e.g., fixed orientations of each sensor 31 relative to some surrounding segment of the tube 36. An alternative is to use a soft model, in which, for example, the position and orientation of a sensor 31 relative to neighboring sensors 31 is parameterized, e.g., with a regularization term to penalize the parameters.

number

number

[0100] Another possible approach is to solve for the orientation and / or position of the sensors 31, e.g., using an independent solver. This may involve fitting a mechanical model to the curve of the catheter tube 36 in the segments 37 between the sensors 31, and then fitting each individual sensor 31 as closely as possible to its associated position and orientation along the curve of the tube 36. This may be achieved, for example, by fitting a low-degree polynomial between the solved positions of the sensors 31 and then using the model positions of the sensors 31 as (noisy) position measurements in the independent solver. Another more general way to achieve this is by describing the curve of the tube 36 as a general curve with an energy function that may encode catheter geometry constraints (e.g., position and orientation smoothness constraints, distance along the curve between successive sensors, etc.). The curve of the tube 36 can then be fitted to the noisy or distorted measurements of the sensors 31 by nonlinear optimization, simultaneously minimizing the errors of the sensors 31 and the energy function of the curve of the tube 36. The method of alternating between individual sensor 31 measurement position calculations and full curve fit calculations can be beneficial because the calculations can be performed in parallel. Instead of solving for the entire curve shape of the tube 36 as a whole inside a potentially huge extended Kalman filter, the task may be broken down into smaller subtasks, such as solving for the localization of each sensor 31 individually, and the sub-results may then be glued together to form the final catheter curve fit.

[0101] In some embodiments, it is further possible to reduce the number of degrees of freedom of the system by assuming that the environmental magnetic field (e.g., the Earth's magnetic field) is uniform along the catheter curve. The solved environmental magnetic field is denoted by B0 (in the transmitter coordinate system) and is solved independently for each sensor on the catheter. By assuming that the environmental magnetic field is uniform along the catheter, B0 can be solved jointly for all sensors on the catheter, thus reducing the degrees of freedom of the system and the risk of overfitting. Intuitively, sharing B0 among sensors imposes constraints on the relative orientation between sensors (which, together with the complete catheter shape constraint, also imposes constraints on the relative positions of the sensors). Assuming B0 is uniform along the entire catheter may not be correct in the presence of magnetic distortions; in these cases, the environmental magnetic field may deform and vary slowly in space, especially along the catheter curve. In this case, a more flexible assumption can be utilized, assuming it is approximately constant between adjacent sensors. This flexible assumption is expressed as an energy function as follows and minimized in a least-squares sense (as part of the complete catheter solver optimization):

number

[0102] In another embodiment, instead of using natural environmental magnetic fields (e.g., the Earth's) to constrain the resolved 6 DOF of the sensor, an artificial, constant magnetic field can be created by incorporating small magnets along the catheter curve. With magnets positioned at known positions and orientations, B can be perfectly predicted for any given configuration of the complete catheter curve. B may also depend on the relative position and orientation of the sensors (where the relative positions and orientations of the incorporated magnets are also uniquely defined by the geometric smoothness constraint). This is because each such different configuration could potentially introduce other DC magnetic fields (e.g., magnetic fields with substantially zero frequency) along the curve into each sensor due to the differently positioned and oriented incorporated small magnets. Knowing the exact position and orientation of each incorporated magnet for each complete curve configuration allows prediction of B for each sensor, potentially further reducing the number of degrees of freedom of the system.

[0103] Reference is now made to FIG. 6, which is a schematic diagram of a catheter 30b according to some embodiments of the present disclosure. The catheter 30a can include multiple dipole magnets 38, for example, equidistantly spaced between sensors. For example, the dipole magnets 38 are oriented so that when the tube 36 is in a straight state, the two magnets 38 located on the two sides of the sensor 31 have opposite dipole directions. When the catheter tube 36 is straight, each sensor can sense the superposition of perfectly aligned positive and negative dipole fields, thereby canceling out the contributions of the two magnets located on the two sides of the sensor 31. Thus, for example, the B sensed by the sensor 31 can include substantially only the Earth's magnetic field. As the catheter begins to bend, the contributions of the two magnets located on the two sides of the sensor 31 grow linearly as Csin(α), where α is the angle of bending and C is some known constant depending on the relative positions and strengths of the magnets 38. In this example, it is clear how B encodes more information about the relative orientation between adjacent sensors. By incorporating a magnet 38 along the catheter, as in this example, more efficient constraints on relative sensor orientation can be achieved in terms of SNR (by incorporating a relatively strong magnet), reliability (the incorporated magnet is much less prone to magnetic distortion), geometry (by positioning the magnet in a carefully selected orientation, tuning the constraint as desired for a particular application), and relative sensor orientation than when using the Earth's magnetic field.

[0104] In some embodiments of the present invention, system 100 may be used for organ deformation tracking in minimally invasive surgery. For example, fully curvilinear catheter measurement positions are used to track deformations imposed on internal organs by some external means. For example, during laparoscopic procedures, organs may be manipulated using tools to such an extent that it is difficult to know which parts of the organ are visible in live laparoscopic video. For that reason, visual markers are sometimes utilized; at the beginning of the procedure and before any manipulation is applied to the organ, the markers are placed on the surface of the organ at known anatomical landmarks. The organ is then visually tracked throughout the procedure and used as a registration reference to enable some kind of anatomical position measurement, even when the organ is highly manipulated and deformed compared to its initial, known state.

[0105] Unfortunately, in some procedures, such as pulmonary laparoscopy, where measurement location is crucial for identifying hidden vessels, the lung surface does not contain sufficient visual information to place anatomical markers (i.e., markers whose location in the anatomy is well known). Furthermore, due to the lung's highly flexible morphology, tracking anatomical features on the lung's surface does not necessarily stretch sufficiently for tracking important anatomical features inside the lung, such as airways and blood vessels, and the surface does not adequately predict the lung's internal condition. Finally, visual markers and optical tracking systems are prone to occlusion, motion blur, three-dimensional (3D) out-of-two-dimensional (2D) computational problems, and other issues that make most optical-based systems unsuitable for the purpose of highly accurate laparoscopic guidance.

[0106] The newly invented fully curved, bent catheter tracking can very easily address the problem of flexible alignment. During the preoperative phase, one or more bent-tracked catheters are inserted into known airways using a bronchoscope. Each catheter remains stationary relative to the anatomical structures (as described below) and provides fully curved measurement locations for airways near some region of interest (ROI). Then, by using real-time alignment between the fully tracked catheter and the preoperative CT scan, all important anatomical features in some ROI can be displayed in real time. During the laparoscopic procedure, the catheter (or catheters) bend and twist but still maintain their anatomical location within some known airway. The catheter (or catheters) can then be fully tracked in real time and serve as a lung skeleton, providing smooth, real-time, flexible alignment between important anatomical features from the preoperative CT and the deforming lung in real time. By placing additional sensors on the laparoscopic camera, these anatomical features can be displayed as an overlay on the live laparoscopic video, thus providing guidance for laparoscopic procedures in the lungs, which are fully real-time and flexible in nature.

[0107] To ensure that the catheter remains stationary relative to the anatomical structure, especially in organs containing tubes (blood vessels or airways), the catheter should be attached to the anatomical tube. The catheter should be attached distally so that it tracks the organ from the distal point of the catheter and allows the organ to freely expand and contract. Attachment can be achieved using a balloon or hook, or by friction with the tissue. To conform to the anatomical structure without deforming the catheter, the catheter must be highly flexible. Flexibility is achieved by using flexible plastic tubing in the construction of the catheter shaft. Reducing the stiffness of the flexible PCB is also important. The stiffness of the flexible PCB material comes from the polyimide stiffness, the number of PCB layers, and the amount of copper used. Increased flexibility can be achieved through the geometric design of the PCB, for example, by reducing the width of the PCB 33 between the sensors 31 and / or by routing the conductors in a serpentine manner and cutting the PCB 33 parallel to the serpentine path to reduce rotational stiffness.

[0108] In some embodiments of the present invention, the system 100 can be used for electromagnetic navigation bronchoscopy (ENB). A fully curved, real-time local catheter offers significant advantages in terms of registration accuracy during an ENB procedure. Instead of relying solely on past samples of the catheter tip, which can be very "noisy" due to respiratory and cardiac motion, the entire catheter is always visible within the system and can be used as a whole for registration between the transmitter 20 coordinates and the airway map. The very specific bend and shape of the catheter within the airway can teach the system the most likely location of the catheter as a complete curve within the airway. That shape can be matched to the map and used as a unique signature for its anatomical location within the airway. For initial registration, the measured position of the complete curve provides more samples during an unsupervised survey of the lung compared to only the catheter tip, and the entire path can be drawn in transmitter 20 coordinates and matched to the map in an unsupervised manner, thus improving the stability and accuracy of the registration. In adaptive registration, the curve of the fully positioned catheter can be fitted to the airway within the region of interest (ROI) until the most likely airway is found. This better adapts to changes in breathing and body posture. Unlike history-based approaches, where cumulative samples within a time window may undergo different deformations over time (e.g., if they are taken during different phases of breathing), the measurement positions of the full curve are instantaneous. Another form of adaptive registration is also possible, where the measurement positions of the full curve are used as a skeletonization of the lung and can serve as a basic component for a flexible, deformable lung model. By analyzing the full curve of the catheter, we can understand how the specific major airways through which the catheter passes are deformed, and then, by using some kind of extrapolation model, we can conclude how the surrounding areas are deformed.

[0109] Additionally, the catheter can be more easily steered; it is not uncommon for physicians to experience difficulty while attempting to execute sharp turns with the catheter inside the lung. The physician then attempts multiple times to pull, rotate, and push the catheter based on the single sensor feedback received from the system. The full curve measurement position allows the physician to see the full bend of the catheter and gain a better understanding of how applied forces, under the stress of the surrounding tissue, translate into distal catheter movement. Based on this much more informative feedback, the user can generate more precise steering gestures that translate into the precise desired distal movement with much less trial and error.

[0110] Furthermore, measuring the full curve of the catheter's position makes it much easier to align with other modalities, such as fluoroscopy. During fluoroscopy, the entire length of the catheter is visible in the x-ray image due to the catheter's radiopacity. With conventional EM localization systems, only the tip is visible. In this situation, it would be difficult for a physician to match the fluoroscopic image with the image displayed by the localization system. By measuring the catheter's position completely, the entire length of the catheter is visible in both the fluoroscopic image and the magnet localization system, making it much easier for a physician to align between different modalities.

[0111] In some embodiments of the present disclosure, the system 100 may be used for electromagnetically guided colonoscopy, where complete catheter measurement location has proven beneficial.

[0112] It will be understood that some embodiments of the present invention are applicable, mutatis mutandis, to any elongate flexible body and not just to catheters.

[0113] Some embodiments of the present disclosure may include a system, a method, and / or a computer program product. The computer program product may include a tangible, non-transitory, computer-readable storage medium (or media) having computer-readable program instructions thereon for causing a processor to perform aspects of the present disclosure. The computer-readable program instructions for performing the operations of the present disclosure may be assembler instructions, instruction set architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcode, firmware instructions, state setting data, or source code or object code written in any combination of one or more programming languages, including any object-oriented programming language and / or conventional procedural programming languages.

[0114] In the context of some embodiments of the present disclosure, by way of example and not limitation, terms such as "operate" or "execute" also connote the capability such as "operable" or "executable," respectively.

[0115] For example, a conjugated term such as "the nature of a thing" means the nature of a thing unless otherwise clearly evident from the context.

[0116] The terms "processor" or "computer" or systems thereof are used herein in their normal context in the art to refer to general purpose processors, portable devices such as smartphones or tablet computers, or microprocessors, or RISC processors or DSPs, etc. (which may include additional elements such as memory and communication ports). Optionally or additionally, the terms "processor" or "computer" or derivatives thereof refer to a device that can execute programs provided or embedded therein and / or that can control and / or access data storage devices and / or other devices, such as input and output ports. The terms "processor" or "computer" also refer to multiple processors or computers that are connected and / or linked and / or otherwise in communication, and possibly sharing one or more other resources, such as memory.

[0117] The terms "software," "program," "software procedure" or "procedure" or "software code" or "code" or "application" may be used interchangeably according to the context and generally refer to one or more instructions or directives or electronic circuitry for performing a sequence of operations that represent an algorithm and / or other process or method. The program is stored on a medium such as RAM, ROM, or disk, or embedded in circuitry accessible and executable by a device such as a processor or other circuitry. The processor and program may, at least in part, constitute the same device designed to perform a programmed sequence of operations, such as an array of electronic gates like an FPGA or ASIC, optionally comprising or linked with the processor or other circuitry.

[0118] The terms "configure" and / or "adapt" for purposes herein, or variations thereof, mean using at least software and / or electronic circuitry and / or auxiliary devices that are designed and / or implemented and / or operative or capable of operating to accomplish a purpose.

[0119] An apparatus that stores and / or includes the program and / or data constitutes an article of manufacture. Unless otherwise specified, the program and / or data are stored in or on a non-transitory medium.

[0120] Where electrical or electronic equipment is disclosed, it is assumed that a suitable power source is used for its operation.

[0121] The flowcharts and block diagrams illustrate the architecture, functionality, or operation of possible implementations of systems, methods, and computer program products according to various embodiments of the subject matter of this disclosure. In this regard, each block in the flowcharts or block diagrams may represent a module, segment, or portion of program code, comprising one or more executable instructions for implementing the specified logical function(s). It should also be noted that in some alternative implementations, the operations shown or described may occur in a different order, or in combination, or as parallel operations instead of sequential operations, to achieve the same or equivalent effect.

[0122] The corresponding structure, material, acts, etc. of all means or steps, as well as functional elements recited in the claims, are intended to include any structure, material, or act that performs that function in combination with the other elements defined in the claims. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms unless the context clearly dictates otherwise. Furthermore, it should be understood that the terms "comprise," "include," and / or "have," and / or other variations of "have," when used herein, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0123] The terms used herein, unless otherwise specified, should not be construed as limiting, and are for the purpose of describing particular embodiments only, and are not intended to limit the subject matter disclosed. While particular embodiments of the disclosed subject matter have been illustrated and described, it will be apparent that the disclosure is not limited to the embodiments described herein. Numerous modifications, changes, variations, substitutions, and equivalents are not excluded.

Claims

1. 1. A method of magnetic tracking of a flexible device, the flexible device being a flexible catheter device or other flexible elongate device, the flexible device comprising an elongate flexible body; The method comprises: a) receiving, by a host server, a plurality of sensed values of local magnetic fields sensed by a plurality of digital magnetometers positioned at corresponding locations along the elongated flexible body of the flexible device, the sensed values being at least partially attributable to at least one alternating magnetic field generated by at least one magnetic field generator; b) a host server calculating an estimate of a curvilinear localization of the elongated flexible body based on the sensed magnetic field values and the amplitude and frequency of each generated magnetic field source; Equipped with The calculating step incorporating the sensed magnetic field values and source values for each generated magnetic field into a localization algorithm; incorporating shape constraints of the elongated flexible body of the flexible device into the localization algorithm; and performing a curve optimization based on the embedded values and the embedded shape constraints to determine the estimate of the curve localization of the elongated flexible body; characterized in that it comprises method.

2. the flexible device has a tip; the digital magnetometer is located along the flexible device at least on the tip and / or the elongated flexible body of the flexible device; The method of claim 1.

3. the localization algorithm includes an energy function of the curve of the elongated flexible body and errors of the plurality of digital magnetometers; The curve optimization includes minimizing the energy function. The method of claim 1.

4. the host server is calibrated using the initial orientations and positions of the plurality of digital magnetometers. The method of claim 1.

5. the shape constraints include information regarding the stiffness and / or flexibility limits of the elongated flexible body; The method of claim 1.

6. the shape constraints include a known structural relationship between positions and orientations of the plurality of digital magnetometers along the elongated flexible body of the flexible device. The method of claim 1.

7. the shape constraint includes an approximation of the shape of the elongated flexible body as a set of line segments, each line segment connecting two of the plurality of digital magnetometers. The method of claim 1.

8. the shape constraints include a fixed and known orientation and distance each magnetometer has to its neighboring magnetometers; The method of claim 1.

9. the shape constraints further include a constraint on the smoothness of the shape of the elongated flexible body; The method of claim 1.

10. the localization algorithm describes the curve of the elongated flexible body by an energy function that encodes the shape constraints of the elongated flexible body; The method of claim 1.

11. the host server is configured to fit the curve to the measurements of the plurality of digital magnetometers by minimizing an error in the measurements of the plurality of digital magnetometers and an error in the curve. The method of claim 1.

12. The digital magnetometer is a digital DC magnetometer. The method of claim 1.

13. a plurality of the digital magnetometers are arranged on the same digital communication bus; The method of claim 1.

14. the calculating step includes incorporating a physical distortion model into the localization algorithm to compensate for dynamic magnetic distortion. The method of claim 1.

15. 1. A system for magnetic tracking of a flexible device, the flexible device being a flexible catheter device or other flexible elongate device, comprising: The system comprises: a) at least one generator each configured to generate at least one alternating magnetic field; b) a flexible device; and c) a host server; Equipped with The flexible device i) an elongated flexible body; ii) a plurality of digital magnetometers; Equipped with the plurality of digital magnetometers are disposed at corresponding locations along the elongated flexible body of the flexible device, each of the plurality of digital magnetometers configured to transmit a sensed value of a local magnetic field, the sensed value attributable at least in part to the generated magnetic field; The host server iii) receiving the sensed local magnetic field values from the corresponding digital magnetometers; iv) calculating an estimate of a curvilinear localization of the elongated flexible body based on the sensed magnetic field values and the amplitude and frequency of each generated magnetic field source; Equipped with The calculation is incorporating the sensed magnetic field values and source values for each generated magnetic field into a localization algorithm; incorporating shape constraints of the elongated flexible body of the flexible device into the localization algorithm; and performing a curve optimization based on the embedded values and the embedded shape constraints to determine the estimate of the curve localization of the elongated flexible body; characterized in that it comprises system.

16. the flexible device has a tip; the digital magnetometer is located along the flexible device at least on the tip and / or the elongated flexible body of the flexible device; 16. The system of claim 15.

17. the localization algorithm includes an energy function of a curve of the elongated flexible body and errors of the plurality of digital magnetometers, and the curve optimization includes minimizing the energy function.

16. The system of claim 15.

18. the flexible device further comprises a flexible PCB disposed along the flexible device; The digital magnetometer is disposed along the flexible PCB.

16. The system of claim 15.

19. The flexible PCB is spirally wound around the wall of the flexible device.

20. The system of claim 18.

20. the flexible device further comprising a communication bus configured to digitally convey data of the sensed values from the plurality of digital magnetometers to the host server.

16. The system of claim 15.

21. the communication bus includes up to four wire lines capable of carrying digital data of the detected values from the plurality of digital magnetometers and supplying power to the plurality of digital magnetometers.

21. The system of claim 20.

22. The plurality of digital magnetometers are mounted on the same flexible printed circuit.

16. The system of claim 15.

23. the flexible printed circuit includes a thinned portion between the plurality of digital magnetometers.

23. The system of claim 22.

24. the plurality of digital magnetometers are arranged on the same digital communication bus, 16. The system of claim 15.

25. the at least one generator includes one or more transmit coils that generate electromagnetic fields of different geometries; 16. The system of claim 15.

26. The digital magnetometer is a digital DC magnetometer.

16. The system of claim 15.

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