A personalized screw trajectory planning method combining computer-assisted planning and 3D printing

Abstract

This invention provides a personalized screw trajectory planning method combining computer-aided planning and 3D printing, belonging to the field of personalized screw trajectory planning technology. First, the screw position is initially calculated using a screw trajectory planning algorithm. Second, a 1:1 model of the vertebral body and screw is printed using 3D printing technology. The screw is then assembled on the vertebral body model according to the calculated path. Next, the screw path is fine-tuned on the model based on the actual clinical situation. Finally, the fine-tuned screw position is matched to the patient's preoperative CT or intraoperative CBCT to achieve more accurate screw trajectory planning. This method allows for fine-tuning of the screw position according to specific circumstances to adapt to specific clinical environments and conditions, reducing limitations imposed by image display technology and human information processing capabilities. Through computer-aided planning and 3D printing, it ensures that the planning results do not lead to unsatisfactory planning effects.

Description

Technical Field

[0001] This invention belongs to the field of personalized screw trajectory planning technology, and in particular relates to a personalized screw trajectory planning method that combines computer-aided planning and 3D printing. Background Technology

[0002] Currently, in robot-assisted surgery, screw trajectory planning methods rely on intraoperative CBCT images and are performed on a visualization workstation. Surgeons must manually adjust the screw trajectory using drag-and-drop strategies until the ideal path is achieved. However, this process can disrupt the surgical flow and potentially lead to human error. Therefore, to improve the planning process and outcomes, various computer-aided screw planning methods have been developed. Lee J and Wicker R et al. manually extracted the pedicle region and reconstructed its geometry and features to plan the optimal screw trajectory. Knez D, Wi W, Soliman MA, Caprara S, and Mischler D et al. calculated the optimal screw trajectory using bone mechanics or bone mineral density features obtained from CT images. Daemi N and Solitro GF et al. calculated the preoperative screw trajectory based on the correlation between the screw placement trajectory at different angles and vertebral body bone mineral density. Knez D and Xiaozhao C et al. developed a method for automatically segmenting the vertebral body and pedicle and planning the screw trajectory based on the pedicle's geometric features. Vijayan R and Goerres J et al. used a graphical method to align known screw paths on vertebrae with target vertebrae for screw trajectory planning. Kausch L, Ma C, Qi X, and Cai D et al. developed an AI-based method for spinal segmentation and preoperative screw trajectory planning. In actual clinical practice, doctors need to fine-tune screw positions according to specific circumstances to adapt to the specific clinical environment and conditions. Due to factors such as image display technology and human information processing capabilities, manually adjusting the planning results through drag-and-drop strategies in a computer can lead to difficulties in achieving ideal planning results. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention proposes a personalized screw trajectory planning method that combines computer-aided planning and 3D printing. This method allows for fine-tuning of screw positions based on specific circumstances to adapt to specific clinical environments and conditions, reducing constraints imposed by factors such as image display technology and human information processing capabilities. By combining computer-aided planning and 3D printing, the method ensures that the planning results do not lead to unsatisfactory planning outcomes.

[0004] To solve the above problems, the present invention adopts the following technical solution: A personalized screw trajectory planning method combining computer-aided planning and 3D printing, characterized in that the method includes the following steps: S1: Initially calculate the screw position using a screw trajectory planning algorithm; S2: Segment the vertebral body and select and mark feature points on the segmented vertebral body; S3: 3D printing of the vertebral body and screw model; S4: Assemble the screws and vertebral body on the 3D model and fine-tune the screw positions according to clinical requirements; S5: Calculate the screw position after fine-tuning; S6: Register the fine-tuning results onto the image to complete the screw trajectory planning.

[0005] Furthermore, in S1, let... To avoid any point in the area, The screw insertion point is on the surface of the vertebral body. Let be the unit vector of the screw. The optimal screw path can be obtained using the following formula: .

[0006] Furthermore, in S1, the optimal placement trajectory of the screw is planned by calculating the optimal trajectory of the screw on the projection surface and then reconstructing it into a three-dimensional screw trajectory, and a parallel light ray-driven projection algorithm is used to generate a simulated projection.

[0007] Furthermore, in S2, to ensure accurate segmentation of the vertebral body, at least three marked feature points are selected.

[0008] Furthermore, in S2, to facilitate the assembly of screws on the 3D model, the screw entry and exit points need to be marked on the segmented cones. and nail tail point The following relationship is obtained: where For screw length, It is the unit vector of the screw: .

[0009] Furthermore, in S6, the image is a preoperative CT or intraoperative CBCT image of the patient.

[0010] The beneficial effects of this invention are as follows: This method allows for fine-tuning of screw positions to adapt to specific clinical environments and conditions. Through computer-aided planning and 3D printing, the morphology, location, and surrounding structures of the pedicle can be observed intuitively and clearly during screw trajectory planning, resulting in a more comprehensive anatomical understanding. This intuitive visual aid significantly improves the accuracy of screw trajectory planning, helps avoid potential errors, optimizes the operational process, and increases the success rate. The trajectory planning success rate of this study's method reached 92.5%. Attached Figure Description

[0011] To more clearly illustrate the specific embodiments of the present invention, the accompanying drawings used in the description of the specific embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0012] Figure 1 This is a flowchart of the algorithm of the present invention; Figure 2 A schematic diagram of vertebral body segmentation and feature point marking; Figure 3 This is a schematic diagram of the fine-tuning results; Figure 4 A schematic diagram for determining the screw position; Figure 5 This is a 3D-printed model of the vertebral body and screws in the embodiment; Figure 6 This is a schematic diagram showing the distance a pedicle screw penetrates the pedicle cortex. Detailed Implementation

[0013] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0014] like Figures 1-4 As shown, this invention proposes a personalized screw trajectory planning method that combines computer-aided planning and 3D printing. First, the screw position is initially calculated using a screw trajectory planning algorithm. Second, a 1:1 model of the vertebral body and screw is printed using 3D printing technology. The screw is then assembled on the vertebral body model according to the calculated path. Next, the screw path is fine-tuned on the model based on the actual clinical situation. Finally, the fine-tuned screw position is matched to the patient's preoperative CT or intraoperative CBCT to achieve more accurate screw trajectory planning.

[0015] The method includes the following steps: S1: Initially calculate the screw position using a screw trajectory planning algorithm; set up To avoid any point in the area, The screw insertion point is on the surface of the vertebral body. Let be the unit vector of the screw. The optimal screw path can be obtained using the following formula: .

[0016] The optimal placement trajectory of the screw is planned by calculating the optimal trajectory of the screw on the projection surface and then reconstructing it into a three-dimensional screw trajectory. A parallel light ray-driven projection algorithm is used to generate a simulated projection.

[0017] S2: Segment the vertebral body and select and mark feature points on the segmented vertebral body; To ensure accurate segmentation of the vertebral body, at least three feature points should be selected for marking; to facilitate screw assembly on the 3D model, screw entry and exit points need to be marked on the segmented vertebral body. and nail tail point The following relationship is obtained: where For screw length, .

[0018] S3: 3D printing of the vertebral body and screw model; S4: Assemble the screws and vertebral body on the 3D model and fine-tune the screw positions according to clinical requirements; S5: Calculate the screw position after fine-tuning; S6: Register the fine-tuning results onto the image, which is usually the patient's preoperative CT or intraoperative CBCT image, to complete the screw trajectory planning.

[0019] The method will now be described in detail with reference to the preferred embodiment. The present invention includes the following steps: 1. Screw trajectory planning The trajectory of a pedicle screw can be defined as a straight line passing through a fixed point. This straight line must lie within the pedicle and not penetrate the vertebral body. Therefore, in this study, we define the vertebral foramen and the surrounding soft tissue of the vertebral body as the avoidance zone. The optimal screw trajectory should be as far away from the avoidance zone as possible to ensure screw safety. Therefore, let... To avoid any point in the area, The screw insertion point is on the surface of the vertebral body. Let be the unit vector of the screw. The optimal screw path can be obtained using the following formula:

[0020] Theoretically, given the optimal 3D screw trajectory, multi-angle reprojection of the vertebral body around the pedicle can yield the optimal screw insertion trajectory on a 2D projection plane at each angle. Conversely, given the optimal screw trajectory on a 2D projection, reconstructing the projections of the optimal screw trajectories at different angles can also estimate the optimal 3D screw insertion trajectory. Therefore, this study employs a method of calculating the optimal screw trajectory on the projection plane and then reconstructing it into a 3D screw trajectory to plan the optimal screw insertion trajectory.

[0021] Digitally Reconstructed Radiograph (DRR) simulates the process of X-rays passing through a three-dimensional object and accumulating their attenuation values ​​as they fall onto the detector plane. Methods for generating DRR are mainly divided into two categories: voxel-driven projection algorithms and ray-driven projection algorithms. Compared to voxel-driven projection algorithms, ray-driven projection algorithms yield more accurate results; therefore, this study adopts a parallel-light ray-driven projection algorithm to generate the DRR. The Siddon algorithm is one of the most classic ray-driven projection methods. Projection at an angle As shown in the following formula. It is the voxel of the intersection of light rays and the object being projected. CT value, It is the length of light passing through that voxel. Indicates the projection angle.

[0022]

[0023] Assumption Is it a CT image in Projection of an angle The optimal screw placement trajectory can be determined by and Confirmed, among which and These are parameters of the screw trajectory. Assuming... It is M in The boundary of the upper projection, then Two boundaries can be marked with -1 or +1. It can be represented as... ,Then, The optimal screw implantation trajectory can be represented as follows:

[0024] The constrained optimization problem described above can be transformed into an unconstrained optimization problem using Lagrange multipliers:

[0025] in It is a Lagrange multiplier, and It can be solved using the Support Vector Machine (SVM) method.

[0026] Assumption It is the optimal screw implantation trajectory The optimal screw implantation trajectory is obtained by (3) and (4) through angular projection, where the point on the optimal screw implantation trajectory is marked as 1 and the other points are marked as 0. Therefore, the three-dimensional image, i.e. the three-dimensional screw trajectory, can be reconstructed layer by layer by the filtered back projection method during the reconstruction process. The filtered back projection algorithm is shown in the following formula.

[0027]

[0028] In the above formula For the third three-dimensional image layer, Indicates the first Layer in Screw trajectory projection at an angle, For ramp filters, This is a 3D image containing the screw trajectory. In fact, the final result is a binary 3D image containing only the screw trajectory, with the image value at the screw trajectory being 1 and others being 0. The filtering process can be ignored during reconstruction, and the optimal 3D screw trajectory can be simplified as follows:

[0029] In fact, the final result is a binary 3D image containing only the screw trajectory, with a value of 1 at the screw trajectory and 0 elsewhere. Therefore, in practical deployment, we can estimate the screw trajectory using only two projections, as the screw trajectory is simple enough as a line segment. In this work, we use a horizontal projection ( , ) and sagittal projection ( , To estimate the optimal screw implantation trajectory. Assume... and They are exist and Boundary points on the projection can be used Optimal screw implantation trajectory parameters as well as Optimal screw implantation trajectory parameters Determine the three-dimensional screw trajectory

[0030] More concisely, (7) can be equivalently expressed as

[0031] Where x, y, and z represent the coordinates on the CT image.

[0032] The final preliminary calculation of the screw trajectory is as follows: , , .

[0033] 2. Vertebral body segmentation and feature point construction Accurately segment the vertebral body and select at least 3 marker points on the segmented vertebral body. , , To facilitate screw assembly on the 3D model, the screw entry and exit points need to be marked on the segmented cone. and nail tail point ,in For the screw length, such as Figure 1 As shown.

[0034]

[0035] 3. 3D printing of vertebral body and screw models Using 3D printing technology, cones and screws with feature point markings are printed at a 1:1 scale.

[0036] 4. Assemble the screws and the cone. like Figure 2 As shown, according to the calculated screw trajectory, the screw model is implanted into the 3D model, and the insertion point is located at... The position of the nail tail point is .

[0037] 5. Fine-tuning like Figure 3 As shown, fine-tune the screw position according to clinical requirements, i.e., adjust. and To achieve the desired clinical planning effect, and to mark the screw trajectory as... .

[0038] 6. Calculate the screw position after fine-tuning. like Figure 4 As shown, measure the nail insertion point. and nail tail point to , , The distance. Let the pin tail point be... arrive , , The distance is , , , The coordinates are Then it can be calculated by solving the system of equations (10). Coordinates:

[0039] Similarly, the point of entry arrive , , The distance is , , , The coordinates are Then it can be calculated by solving the system of equations (11). Coordinates:

[0040] 7. Register the fine-tuning results onto the image. The final screw trajectory is .

[0041]

[0042] like Figure 5 As shown, the printed model and visualization results in this embodiment allow for a direct visual understanding of the pedicle structure within the physical model, enabling more accurate planning. Specifically, during screw trajectory planning, the morphology, location, and surrounding structures of the pedicle can be clearly and intuitively observed, resulting in a more comprehensive anatomical understanding. This intuitive visual aid significantly improves the accuracy of screw trajectory planning, helps avoid potential errors, optimizes the operational process, and increases the success rate.

[0043] like Figure 6 As shown, this embodiment tested the implantation trajectory planning of 40 pedicle screws in the L1-L5 segments and compared it with cutting-edge image-based screw trajectory planning algorithms. The left figure shows the minimum distance from the pedicle screw to the pedicle cortex obtained by this method, and the right figure presents the corresponding measurement results of the image-based algorithm. It should be noted that MGM indicates no pedicle cortex breach, while CAE indicates pedicle cortex breach. Experimental results show that the method in this study resulted in pedicle cortex breach in 3 out of 40 screw implantations (7.5%), with a trajectory planning success rate of 92.5%; while the image-based algorithm group resulted in cortex breach in 8 out of 10 cases (20.0%), with a success rate of 80.0%.

[0044] The present invention has been described in detail above through embodiments, but the content described is only a preferred embodiment of the present invention and should not be considered as limiting the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A personalized screw trajectory planning method combining computer-aided planning and 3D printing, characterized in that: The method includes the following steps: S1: Initially calculate the screw position using a screw trajectory planning algorithm; S2: Segment the vertebral body and select and mark feature points on the segmented vertebral body; S3: 3D printing of the vertebral body and screw model; S4: Assemble the screws and vertebral body on the 3D model and fine-tune the screw positions according to clinical requirements; S5: Calculate the screw position after fine-tuning; S6: Register the fine-tuning results onto the image to complete the screw trajectory planning.

2. The personalized screw trajectory planning method combining computer-aided planning and 3D printing according to claim 1, characterized in that: In S1, let To avoid any point in the area, The screw insertion point is on the surface of the vertebral body. Let be the unit vector of the screw. The optimal screw path can be obtained using the following formula: 。 3. The personalized screw trajectory planning method combining computer-aided planning and 3D printing according to claim 1, characterized in that: In S1, the optimal placement trajectory of the screw is planned by calculating the optimal trajectory of the screw on the projection surface and then reconstructing it into a three-dimensional screw trajectory. A parallel light ray-driven projection algorithm is used to generate a simulated projection.

4. The personalized screw trajectory planning method combining computer-aided planning and 3D printing according to claim 1, characterized in that: In S2, to ensure accurate segmentation of the vertebral body, at least three feature points are selected for marking.

5. The personalized screw trajectory planning method combining computer-aided planning and 3D printing according to claim 1, characterized in that: In S2, to facilitate screw assembly on the 3D model, the screw entry and exit points need to be marked on the segmented cone. and nail tail point The following relationship is obtained: where For screw length, It is the unit vector of the screw: 。 6. The personalized screw trajectory planning method combining computer-aided planning and 3D printing according to claim 1, characterized in that: In S6, the image is a preoperative CT or intraoperative CBCT image of the patient.

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