Method for calibrating needle tip and needle axial direction

Abstract

The invention discloses a method for calibrating a needle tip and a needle axial direction. The method comprises the following steps: obtaining the position of the needle tip through first-time rotary calibration of a calibration needle; the calibration needle is turned over by 180 degrees in the length direction of the calibration needle, the needle tip and the needle tail are inverted, and then the calibration needle is subjected to second-time rotation calibration to obtain the center position of a hemisphere at the needle tail end; calculating the spatial axial direction of the calibration needle by using a needle point coordinate difference vector obtained by two times of rotation calibration; outputting the coordinate of the needle tip in the coordinate system of the pose sensor and the axial vector of the needle body of the calibration needle to obtain a pose matrix of the calibration needle in the coordinate system of the pose sensor; the needle tip position and the needle body direction can be obtained at the same time, external equipment and a structural device are not depended on, the simplicity and the universality of the calibration process are improved, only two times of normal Pivot rotation are needed for the needle, fine placement and contact control are not needed, and the user experience and the operation stability are greatly improved; and the calibration precision and robustness are enhanced.

Description

Technical Field

[0001] This invention relates to the field of surgical navigation system technology, and in particular to a method for calibrating the needle tip and needle axis. Background Technology

[0002] In modern medicine, industry, and scientific research, calibration needles or guide needles are widely used in navigation systems, stereotactic systems, and image-guided surgery (IGS). Precise needle calibration is crucial for ensuring navigation accuracy, positioning precision, and surgical safety.

[0003] In three-dimensional space, the calibration of a needle typically involves two key issues:

[0004] Tip position calibration: that is, the three-dimensional coordinates of the tip relative to the tracker or sensor;

[0005] The orientation of the needle: that is, the direction of the needle body in space, usually represented by a vector or rotation matrix.

[0006] Currently, in many navigation systems, pivot calibration is a widely used method for calibrating the position of the needle tip. This method calculates the position of the needle tip in the sensor coordinate system by keeping the needle tip fixed and rotating the sensor or tracker around the needle tip, recording multiple attitude data.

[0007] However, Pivot Calibration itself cannot directly obtain the needle's axial information, which limits its application in many practical situations. For example:

[0008] In robot-assisted surgery, puncture path planning, or spatial trajectory tracking, the direction information of the needle axis is crucial.

[0009] The need for manual estimation or measurement of the axial direction after traditional Pivot Calibration increases operational complexity and sources of error.

[0010] There is a lack of automated and easy-to-use methods to simultaneously acquire needle tip position and needle axis direction in standard operating procedures.

[0011] Pivot Calibration, a traditional method for needle tip positioning, is a classic needle tip localization method. Its basic principle is as follows:

[0012] In three-dimensional space, fix the needle tip at a point (a real or virtual fixed point);

[0013] The operator moves the sensor or needle freely in space around the fixed point, causing it to generate multiple sets of attitude data (i.e. multiple transformation matrices).

[0014] Using algorithms such as the least squares method, the fixed coordinates of the needle tip relative to the sensor are solved from these data.

[0015] This method is widely used in the following systems:

[0016] Medical image navigation systems (such as Brainlab, Medtronic StealthStation);

[0017] Reference: Fitzpatrick, JM, West, JB, & Maurer, CR (1998). Predicting error in rigid-body point-based registration. IEEE Transactions on Medical Imaging, 17(5), 694–702.

[0018] The disadvantages of this existing technology are:

[0019] This method can only obtain the tip offset and cannot directly obtain the needle axis direction. In applications that require obtaining the needle axis, it is necessary to use other methods (such as multi-point touch, geometric modeling or manual measurement) to obtain the needle body direction.

[0020] Traditional method for obtaining needle axis direction:

[0021] Existing technologies for determining the needle axis direction mainly include:

[0022] a. Two-point contact method

[0023] The needle is placed on two known contact points, and two attitude data are obtained by combining the three-dimensional tracker. The difference between the two points is used to estimate the axis.

[0024] Advantages: Simple to implement;

[0025] Disadvantages: The error depends on the distance between the two points and is easily affected by the movement of the contact point.

[0026] b. Simulation modeling method

[0027] The needle body is a rigid straight line. A special fixture is designed to fix multiple points of the needle body, and the spatial positions of multiple points are obtained and fitted along the axis.

[0028] c. Optical stereoscopic vision method

[0029] The needle is observed from different angles using multiple cameras, and its orientation is reconstructed through image processing.

[0030] Advantages: Non-contact;

[0031] Disadvantages: It is highly dependent on lighting, occlusion, and camera calibration, and the system is complex.

[0032] d. Spin Calibration

[0033] Fix the tool (such as a needle or cannula) to the tracker; keep the overall position of the tool relatively stable while continuously rotating it around a certain rotation axis (manual or mechanical rotation is acceptable); the tracking system continuously collects multiple poses (position + orientation) of the tool during the rotation process; the tool tip will move around a certain spatial circle during rotation, and its trajectory can be used to deduce the axis of the circle, i.e., the rotation axis of the tool itself; use mathematical models (such as spindle extraction, rigid body motion decomposition, etc.) to solve for the direction and position of the rotation axis.

[0034] Advantages: The direction of rotation axis can be directly determined; the mathematical model is mature; and no needle tip fixing point is required.

[0035] Disadvantages: It requires high precision in rotation operation, demanding stable, continuous, and non-eccentric rotation; it is not suitable for slender, flexible needles and cannot obtain the needle tip position.

[0036] Therefore, a method for calibrating the needle tip and needle axis needs to be developed to solve the above problems. Summary of the Invention

[0037] The purpose of this invention is to design a method for calibrating the needle tip and needle axis in order to solve the above-mentioned problems.

[0038] The present invention achieves the above-mentioned purpose through the following technical solutions:

[0039] A method for calibrating the needle tip and needle axis, comprising the steps of:

[0040] S1. The calibration needle obtains the needle tip position through the first rotation calibration. A position sensor is installed inside the calibration needle.

[0041] S2. Rotate the calibration needle 180° along its own length, invert the needle tip and the needle tail, and then obtain the position of the center of the hemisphere at the needle tail end by a second rotation calibration.

[0042] S3. Calculate the spatial axis of the calibration needle using the needle tip coordinate difference vector obtained from the two rotation calibrations;

[0043] S4 outputs the coordinates of the needle tip in the pose sensor coordinate system and the axial vector of the calibration needle body, which is used to obtain the pose matrix of the calibration needle in the pose sensor coordinate system.

[0044] Furthermore, the needle tip contact point does not move during the first and second rotational calibrations.

[0045] Specifically, step S1 includes:

[0046] Insert the calibration pin with the pose sensor into the adapter;

[0047] The operator holds the calibration needle and, while keeping the needle tip fixed at a single point, freely rotates the needle body around the needle tip.

[0048] The pose sensor acquires multiple sets of pose data, including coordinate data and a rotation matrix. Since the calibration needle is rigidly connected to the pose sensor, the acquired matrix data satisfies the following formula:

[0049] in, Let be the rotation matrix of the i-th set of data acquired by the pose sensor in the world coordinate system; The offset coordinates of the needle tip in the pose sensor coordinate system; Let be the translation vector of the i-th set of data acquired by the pose sensor in the world coordinate system; The coordinates of the needle tip in the world coordinate system;

[0050] Calibration algorithm: In Multiplying the left side by the 3x3 identity matrix does not change the result. The following determinant equation can be constructed:

[0051] Construct the matrix equation:

[0052]

[0053] Preprocessing of data acquired by the pose sensor:

[0054] Orthogonalization of rotation matrices:

[0055] In 3D space, the rotation matrix RRR must satisfy two strict constraints:

[0056]

[0057] Perform singular value decomposition on the rotation matrix to find the distance from R. i The nearest orthogonal rotation matrix:

[0058]

[0059] Outlier removal:

[0060] Substituting the orthogonalized set of pose matrix from the pose sensors, a calibration algorithm is used to construct the matrix equations:

[0061] Solve the equation using the least squares method to obtain the initial needle tip. ,

[0062]

[0063] Residual calculation:

[0064]

[0065] Where, r i This represents the distance between the calculated needle tip position and the needle tip position obtained by combining the pose coordinates; if r i If the threshold is exceeded, it is determined to be an outlier, removed, and the calibration algorithm is rerun.

[0066] The offset vector of the needle tip relative to the tracker is calculated using a least-squares fitting algorithm.

[0067] Preferably, the pose sensor is an optical or electromagnetic marker.

[0068] Furthermore, the second rotation calibration method is the same as the first rotation calibration method, and the offset vector of the needle tail relative to the sensor is obtained through the second rotation calibration.

[0069] Specifically, step S3 includes: mapping the offset vector of the needle tip relative to the pose sensor and the offset vector of the needle tail relative to the pose sensor to two points P1 and P2 in the world coordinate system, respectively, and calculating the vector V = P2 - P1, which is the spatial axial vector of the needle body. The position of the needle tip can be P1 or P2.

[0070] Specifically, step S4 includes: The final output includes:

[0071] Needle tip position: P1 or P2;

[0072] The unit vector along the axial direction of the calibration needle: V.

[0073] The beneficial effects of this invention are as follows:

[0074] 1. Simultaneously obtain the needle tip position and needle body direction:

[0075] By performing two rotational calibrations, one with the needle in normal posture and the other with the needle tip and tail inverted, the position of the needle tip in the posture sensor coordinate system is calculated in both calibrations. The direction of the needle axis can be calculated using the vector between these two needle tip positions. Thus, this method can not only obtain the position of the needle tip, but also accurately deduce the spatial direction of the needle body.

[0076] 2. Avoid relying on external equipment and structural devices:

[0077] This invention eliminates the need for additional fixtures, cameras, lasers, fixed platforms, and other devices, relying solely on the existing 3D spatial tracking system. This simplifies the system structure, saves costs, and improves compatibility.

[0078] 3. Improve the simplicity and versatility of the calibration process:

[0079] Compared to traditional methods that require multiple points of contact or manual assistance, this invention only requires two normal pivot rotations of the needle, eliminating the need for precise placement and contact control. This significantly improves user experience and operational stability, making it suitable for various scenarios such as medical clinical practice, scientific research, and industry.

[0080] 4. Enhance calibration accuracy and robustness:

[0081] Since both rotations use spatial point cloud fitting or least squares solution, the system error is less affected by human intervention, and self-checking or error assessment can be performed based on axial consistency, further improving the reliability of the results.

[0082] 5. Expand the functionality of the existing navigation system:

[0083] This invention can be used as a functional extension module for existing navigation platforms, surgical robots, puncture guidance systems, etc., to enhance their spatial perception and trajectory control capabilities, and has strong engineering practical value and commercial promotion potential. Attached Figure Description

[0084] Figure 1 This is a flowchart illustrating the process of this application;

[0085] Figure 2 This is a schematic diagram of the calibration needle in this application. Detailed Implementation

[0086] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0087] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0088] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0089] In the description of this invention, it should be understood that the terms "upper," "lower," "inner," "outer," "left," "right," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use, or the orientation or positional relationship commonly understood by those skilled in the art. They are only used to facilitate the description of this invention and to simplify the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0090] Furthermore, the terms "first," "second," etc., are used only to distinguish descriptions and should not be interpreted as indicating or implying relative importance.

[0091] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, terms such as "set" and "connection" should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0092] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0093] like Figure 1 and 2 As shown, a method for calibrating the needle tip and needle axis includes the following steps:

[0094] S1. The calibration needle obtains the needle tip position through the first rotation calibration. A position sensor is installed inside the calibration needle.

[0095] S2. Rotate the calibration needle 180° along its own length, inverting the needle tip and the needle tail. Then, obtain the position of the center of the hemisphere at the needle tail end by a second rotation calibration. The needle tip contact point does not move during the first and second rotation calibrations.

[0096] S3. Calculate the spatial axis of the calibration needle using the needle tip coordinate difference vector obtained from the two rotation calibrations;

[0097] S4 outputs the coordinates of the needle tip in the pose sensor coordinate system and the axial vector of the calibration needle body, which is used to obtain the pose matrix of the calibration needle in the pose sensor coordinate system.

[0098] Step S1 specifically includes:

[0099] Insert the calibration pin with the pose sensor into the adapter;

[0100] The operator holds the calibration needle and, while keeping the needle tip fixed at a single point, freely rotates the needle body around the needle tip.

[0101] The pose sensor acquires multiple sets of pose data, including coordinate data and a rotation matrix. A two-dimensional constraint is used to fit the center of the sphere. Since the calibration needle is rigidly connected to the pose sensor, the acquired matrix data satisfies the following formula:

[0102] in, Let be the rotation matrix of the i-th set of data acquired by the pose sensor in the world coordinate system; The offset coordinates of the needle tip in the pose sensor coordinate system; Let be the translation vector of the i-th set of data acquired by the pose sensor in the world coordinate system; The coordinates of the needle tip in the world coordinate system;

[0103] Calibration algorithm: In Multiplying the left side by the 3x3 identity matrix does not change the result. The following determinant equation can be constructed:

[0104] Construct the matrix equation:

[0105]

[0106] Preprocessing of data acquired by the pose sensor:

[0107] Orthogonalization of rotation matrices:

[0108] In 3D space, the rotation matrix RRR must satisfy two strict constraints:

[0109]

[0110] The pose sensor outputs R i It is only a numerical approximation of the actual rotation. Due to quantization errors, pose sensor noise, real-time filtering, etc., it usually does not completely satisfy the above equation.

[0111] Perform singular value decomposition on the rotation matrix to find the distance from R. i The nearest orthogonal rotation matrix:

[0112]

[0113] Outlier removal:

[0114] Substituting the orthogonalized set of pose matrix from the pose sensors, a calibration algorithm is used to construct the matrix equations:

[0115] Solve the equation using the least squares method to obtain the initial needle tip. ,

[0116]

[0117] Residual calculation:

[0118]

[0119] Where, r i This represents the distance between the calculated needle tip position and the needle tip position obtained by combining the pose coordinates; if r i If the threshold is exceeded, it is determined to be an outlier, removed, and the calibration algorithm is rerun.

[0120] The offset vector of the needle tip relative to the tracker is calculated using a least-squares fitting algorithm.

[0121] In some embodiments, the pose sensor is an optical or electromagnetic marker.

[0122] In some embodiments, the method for the second rotation calibration is the same as that for the first rotation calibration, and the offset vector of the needle tail relative to the sensor is obtained through the second rotation calibration.

[0123] In some embodiments, step S3 specifically includes: mapping the offset vector of the needle tip relative to the pose sensor and the offset vector of the needle tail relative to the pose sensor to two points P1 and P2 in the world coordinate system, respectively, and calculating the vector V = P2 - P1, which is the spatial axial vector of the needle body. The position of the needle tip can be P1 or P2.

[0124] In some embodiments, step S4 specifically includes: the final output result includes:

[0125] Needle tip position: P1 or P2;

[0126] The unit vector along the needle body axis of the calibration needle is V (V is normalized to a vector with a magnitude of 1).

[0127] In this invention, the needle tip position and axial direction are calibrated as a whole, integrating needle tip calibration and axial direction derivation into a single process, simplifying operation and improving efficiency;

[0128] In this invention, the results are highly stable and reproducible because the same algorithm and pose sensor are used in both calibrations, thus avoiding registration errors between multi-source systems.

[0129] In terms of axial acquisition, this invention calculates the needle axis by using the difference in needle tip coordinates after two rotational calibrations, whereas traditional techniques rely on geometric modeling, image recognition, or multi-point touch methods. This invention uses the same data source (pose sensor) to calculate the difference vector between two poses, avoiding modeling and visual errors; its unique technical approach ensures stable calculations.

[0130] In terms of rotational motion design, this invention only requires the needle body to rotate around the needle tip, and the operation is repeated after flipping. Traditional techniques require multiple points of contact or additional clamps to support two fixed points. The motion required by this invention is natural and easy to operate, without the need to stabilize the contact points at both ends or reconstruct the field of vision, making it more suitable for practical environments.

[0131] Regarding data acquisition system dependencies, this invention uses only a single tracker system, compatible with both optical and electromagnetic systems. Traditional technologies require the integration of multiple systems such as cameras, scales, CT scanners, and 3D models. This invention does not rely on external vision or CT systems, has a simple system structure, and is conducive to integration and clinical applications.

[0132] In terms of data solving algorithms, this invention uses two least-squares fittings to find the needle tip and calculates the axis using spatial differences. Traditional techniques rely on model fitting, geometric inference, or manual calibration. This method extends the standard Pivot algorithm, with mature mathematical principles, good convergence, and clear error control.

[0133] Regarding the classification of needle tip / axial alignment as step-by-step or step-by-step, this invention uses step-by-step calibration: obtaining both the needle tip and axial alignment in one step. Traditional techniques are step-by-step, first determining the needle tip and then calculating the axial alignment through other steps. The innovation of this method lies in its integrated solution of "tip + axis," resulting in a natural operation process and reduced training costs.

[0134] Regarding the operator's skill requirements, this invention is simple to operate, requiring only the repetition of a known action once. Traditional techniques require precise manual needle placement, alignment with the template, and stabilization of multiple contact points. This invention's technical path is simple, with fewer sources of error, making it more suitable for non-expert operators.

[0135] The above are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for calibrating the needle tip and needle axis, characterized in that, Including the following steps: S1. The calibration needle obtains the needle tip position through the first rotation calibration. A position sensor is installed inside the calibration needle. S2. Rotate the calibration needle 180° along its own length, invert the needle tip and the needle tail, and then obtain the position of the center of the hemisphere at the needle tail end by a second rotation calibration. S3. Calculate the spatial axis of the calibration needle using the needle tip coordinate difference vector obtained from the two rotation calibrations; S4 outputs the coordinates of the needle tip in the pose sensor coordinate system and the axial vector of the calibration needle body, which is used to obtain the pose matrix of the calibration needle in the pose sensor coordinate system.

2. The method for calibrating the needle tip and needle axis according to claim 1, characterized in that, The needle tip contact point does not move during the first and second rotational calibrations.

3. The method for calibrating the needle tip and needle axis according to claim 2, characterized in that, Step S1 specifically includes: Insert the calibration pin with the pose sensor into the adapter; The operator holds the calibration needle and, while keeping the needle tip fixed at a single point, freely rotates the needle body around the needle tip. The pose sensor acquires multiple sets of pose data, including coordinate data and a rotation matrix. Since the calibration needle is rigidly connected to the pose sensor, the acquired matrix data satisfies the following formula: ， in, Let be the rotation matrix of the i-th set of data acquired by the pose sensor in the world coordinate system; The offset coordinates of the needle tip in the pose sensor coordinate system; Let be the translation vector of the i-th set of data acquired by the pose sensor in the world coordinate system; The coordinates of the needle tip in the world coordinate system; Calibration algorithm: In Multiplying the left side by the 3x3 identity matrix does not change the result. The following determinant equation can be constructed: ， Construct the matrix equation: ， Preprocessing of data acquired by the pose sensor: Orthogonalization of rotation matrices: In 3D space, the rotation matrix RRR must satisfy two strict constraints: ， Perform singular value decomposition on the rotation matrix to find the distance from R. i The nearest orthogonal rotation matrix: ， Outlier removal: Substituting the orthogonalized set of pose matrix from the pose sensors, a calibration algorithm is used to construct the matrix equations: ， Solve the equation using the least squares method to obtain the initial needle tip. , ， Residual calculation: ， Where, r i This represents the distance between the calculated needle tip position and the needle tip position obtained by combining the pose coordinates; if r i If the threshold is exceeded, it is determined to be an outlier, removed, and the calibration algorithm is rerun. The offset vector of the needle tip relative to the tracker is calculated using a least-squares fitting algorithm.

4. The method for calibrating the needle tip and needle axis according to claim 3, characterized in that, Pose sensors are optical or electromagnetic markers.

5. The method for calibrating the needle tip and needle axis according to claim 4, characterized in that, The second rotation calibration method is the same as the first rotation calibration method. The offset vector of the needle tail relative to the sensor is obtained through the second rotation calibration.

6. The method for calibrating the needle tip and needle axis according to claim 5, characterized in that, Step S3 specifically includes: mapping the offset vector of the needle tip relative to the pose sensor and the offset vector of the needle tail relative to the pose sensor to two points P1 and P2 in the world coordinate system, respectively, and calculating the vector V=P2-P1, which is the spatial axial vector of the needle body. The position of the needle tip can be P1 or P2.

7. The method for calibrating the needle tip and needle axis according to claim 6, characterized in that, Step S4 specifically includes: The final output results include: Needle tip position: P1 or P2; The unit vector along the axial direction of the calibration needle: V.

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