US-20260123849-A1 - DISTORTION MODELING AND COMPENSATION IN A CURVE-TRACKED DETECTOR ARRAY

US20260123849A1US 20260123849 A1US20260123849 A1US 20260123849A1US-20260123849-A1

Abstract

A system for position and/or shape-tracking of an elongated device including a shape sensor to estimate a position and orientation of the device at a plurality of points along the device, and a processor configured to: obtain a plurality of predetermined points along a tracked portion of the device; allocate, for each of the plurality of the predetermined points, a local energy function dependent on the estimated position and orientation of device that incorporates relevant mechanical and sensor measurement constraints; generate a resultant unified energy function for the full shape and position of the entire tracked portion of the device with respect to relative locations and orientation of adjacent plurality of the predetermined points, the unified energy function is constructed based on the allocated local energy functions and segmental energy functions; and calculate a fully localized curve along the tracked portion of the device by minimizing the energy function.

Inventors

RON BARAK
BENJAMIN GREENBURG
Amit Cohen
EYAL KLEIN

Assignees

Magnisity Ltd.

Dates

Publication Date: 20260507
Application Date: 20231003

Claims (20)

1 . A system for position and/or curve/shape-tracking of an elongated device, comprising: a. a curve/shape sensor comprising a plurality of sensor elements positioned on said elongated device; b. one or more transmitters; c. a controller comprising a processor; said processor comprising instructions for: i. obtaining a plurality of points along a tracked portion of said elongated device; ii. allocating, for each point from said plurality of points, a local energy function dependent on an estimated position and orientation of said tracked portion of said elongated device; iii. generating a resultant unified energy function for a full shape and a position of an entire tracked portion of said elongated device; iv. calculating a fully localized curve along said tracked portion of said elongated device by minimizing said unified energy function.
2 . The system according to claim 1 , wherein said local energy function incorporates relevant mechanical and sensor measurement constraints for said each point; and wherein said unified energy function is constructed based on said allocated local energy functions and segmental energy functions that relate to said constraints of mechanical properties of said elongated device, with respect to relative locations and orientation of adjacent plurality of the predetermined points.
3 . (canceled)
4 . The system according to claim 1 , wherein said fully localized curve is calculated relative to said one or more transmitters.
5 . The system according to claim 1 , wherein said plurality of points are one or more of: a. a predetermined plurality of points; b. a sensor point, which is a point in which said sensor elements of said shape sensor are located; and c. a curve point, which is a virtual predetermined point positioned at predetermined intervals between sensor points.
6 . (canceled)
7 . The system according to claim 5 , wherein there are one or more of: a. a plurality of sensor points along said tracked portion of said elongated device; and b. one or more curve points between sensor points.
8 . (canceled)
9 . The system according to claim 1 , wherein said local energy function incorporates constraints related to a sensed magnetic field.
10 . The system according to claim 1 , wherein the processor further comprises instructions for allocating a weight for each local energy function, based on a certainty value, related to a certainty that a measurement is accurate.
11 . The system according to claim 2 , wherein said segmental energy function is characterized by being one or more of: a. a length energy function, related to known distances along said elongated device between adjacent points from said plurality of points or a known length of said tracked portion of said elongated device; b. an orientation energy function, related to a limited possible orientation difference between adjacent points from said plurality of points; c. at least one selected from the group consisting of: i. at least one energy function corresponding to the tracking approximation of a sensor point; ii. at least one energy function corresponding to the length approximation between adjacent points; iii. at least one energy function corresponding to the distortion approximation of a sensor point; iv. at least one energy function corresponding to the orientation difference between adjacent points; wherein said orientation energy function grows in accordance with said orientation difference between said adjacent points; v. at least one energy function corresponds to the twist difference between adjacent points; vi. at least one energy function corresponds to the smoothness/curvature difference between adjacent points; and vii, wherein at least one energy function corresponds to the motion difference between a point and a motion model of that point; d. a smoothness energy function configured for minimizing a curvature along a sequence of adjacent points; and e. a motion energy function configured for minimizing a jitter of said calculated fully localized curve.
12 . The system according to claim 11 , wherein said length energy function is characterized by one or more of: a. incorporating an approximation of a total curve length between two points, and a known distance along said elongated device between said two points; b. relating to a length along said elongated device between two adjacent curve points, and is proportional to the squared difference between a known distance and a linearly approximated distance according to momentarily calculated positions.
13 - 18 . (canceled)
19 . The system according to claim 1 , wherein said processor further comprises instructions for calibrating said curve/shape sensor with respect to a magnetic field distortion imposed by a tool inserted into said elongated device; and wherein said calibration includes one or more of: a. obtaining a plurality of distortion samples; b. finding distortion calibration parameters by reducing a distortion matrix based on said distortion samples; c. using said distortion calibration parameters to adjust said calculated fully localized curve of said tracked portion of said elongated device; d. monitoring a location of a tool tip; wherein said monitoring comprises comparing and fitting a theoretical diagram of a distortion distribution to a series of distortion values calculated for a plurality of points along said tracked portion of said elongated device; and wherein said distortion value for a certain sensor element is calculated by a rooted mean square of said reduced distortion matrix.
20 - 23 . (canceled)
24 . The system according to claim 1 , wherein said one or more transmitters are configured for transmitting one or more multi-frequency EM fields comprising one or more harmonies of a base frequency; and wherein said processor comprises further instructions for: a. analyzing sensed magnetic fields; b. comparing said sensed magnetic fields with an expected frequency profile; c. extracting a distortion field; and d. utilizing said distortion field in said calculating.
25 . (canceled)
26 . A computer implemented method for position and/or curve/shape-tracking of an elongated device performed by a curve/shape sensor comprising a plurality of sensor elements positioned on said elongated device, the method comprising: a. obtaining a plurality of points along a tracked portion of said elongated device; said plurality of points corresponding to readings from said plurality of sensor elements; b. allocating, for each point from said plurality of points, a local energy function dependent on an estimated position and orientation of said tracked portion of said elongated device; c. generating a resultant unified energy function for a full shape and a position of an entire tracked portion of said elongated device; d. calculating a fully localized curve along said tracked portion of said elongated device by minimizing said unified energy function.
27 . The computer implemented method according to claim 26 , wherein said local energy function incorporates relevant mechanical and sensor measurement constraints for said each point; and wherein said unified energy function is constructed based on said allocated local energy functions and segmental energy functions that relate to said constraints of mechanical properties of said elongated device, with respect to relative locations and orientation of adjacent plurality of the predetermined points.
28 . (canceled)

Description

RELATED APPLICATION/S This application claims the benefit of priority of U.S. Provisional Patent Application No. 63/412,559 filed on 3 Oct. 2022 and further claims the benefit of priority of U.S. Provisional Patent Application No. 63/536,467 filed on 4 Sep. 2023, the contents of which are incorporated herein by reference in their entirety. FIELD AND BACKGROUND OF THE INVENTION The present invention, in some embodiments thereof, relates to system and methods for position and/or shape-tracking of an elongated device and, more particularly, but not exclusively, to system and methods for performing corrections on position and/or shape-tracking of an elongated device, optionally taking under consideration electromagnetic distortions. Electromagnetic tracking systems are widely used in clinical applications to track certain instruments inside the patient's body in 3D. A common electromagnetic tracking system usually consists of an electromagnetic transmitter, which generates a number of different alternating electromagnetic fields, commonly at different frequencies (for example, 3 different fields at frequencies 1 Khz, 2 Khz, 3 Khz) and an electromagnetic sensor which usually consists of one or more electromagnetic coils (for example, 3 concentric small electromagnetic coils). The alternating fields generate Electromotive Force (EMF) in the sensor's coils which are sensed on the receiving end. The measured fields are then used to compute the position and orientation of the electromagnetic sensor. The solution of a 6 Degrees-of-Freedom (6-DOF) or 5-DOF or any other configuration of solved position and orientation of the sensor relative to the transmitter relies on the knowledge of the values of the generated EM fields at each point in space relative to the transmitter. By knowing the values of the generated fields, the receiver is able to determine the position and orientation of the sensor in space relative to the transmitter such that the measured fields correspond to its solved position and orientation. Certain objects are known to create an electromagnetic distortion in space and impact the accuracy of the solved position and orientation relative to the transmitter. For example, certain ferromagnetic/paramagnetic/diamagnetic materials (collectively, magnetic materials) may be magnetized due to the electromagnetic fields generated by the transmitter and become sources for electromagnetic fields (of similar frequencies). Conductive materials may serve as receivers in the sense that they experience EMF due to the generated electromagnetic fields. These EMF create electrical currents (eddy currents) inside the conductive metals which generate secondary fields, such that the conductive metals may also become sources for electromagnetic fields (of similar frequencies) on their own. In a static environment, where all magnetic and conductive materials are positioned and oriented statically relative to the transmitter and/or the receiver, the distortion fields can be modeled and learned in a mapping and calibration process prior to operating the tracking system. For example, in a clinical environment, where a transmitter is fixed to a patient's bed, conductive metals on the bed are located in a static position relative to the transmitter. In this case, the distortion fields which are caused by eddy currents flowing through the conductive metals or by magnetization of magnetic metals are static in the sense that they do not change during operation of the tracking system. By mapping the total field generated in the sensing volume surrounding the transmitter, the system can then use the mapped fields (rather than the “neutral” or theoretically expected fields) to perform the tracking. In another example, a magnetic stainless-steel metal is located inside an endoscope, having a magnetic sensor (EM sensor). The magnetic metal creates a distortion field as described above. Since the magnetic sensor is fixed to the distorter, the distortion field moves together with the magnetic sensor and its effect is static and can be modeled in a calibration process. For example, the distortion field's effect may be modeled as increased sensing gain of the EM sensor, or more generally, as a gain matrix applied to measurements of three concentric sensing coils, regardless of the sensor's position and orientation in space. Additional background art includes U.S. Pat. No. 11,712,309 disclosing an EM shape sensor which consists of a sensor-array made of multiple discrete digital 3D magnetometers assembled on a Flexible Printed Circuit (FPC). The sensor-array may be embedded in an endoscope (or other tubular device) to enable EM shape sensing of that endoscope. SUMMARY OF THE INVENTION Following is a non-exclusive list including some examples of embodiments of the invention. The invention also includes embodiments which include fewer than all the features in an example and embodiments using features from multiple examples, also if not expressl