A Suturing Interaction Simulation Method in Virtual Surgery

Abstract

A virtual surgical suture interaction simulation method includes the following steps: Step 1, constructing a suture needle and suture line model; Step 2, setting the maximum static friction between the suture needle and the soft tissue surface, and performing puncture; Step 3, the suture needle penetrates the soft tissue, while simultaneously pulling the suture line to slide within the soft tissue; Step 4, introducing position constraints and updating the position of the suture line in the sliding state; Step 5, the suture needle completely penetrates the soft tissue, pulling the suture line to tighten the wound; Step 6, controlling the entire suture interaction process, adjusting and updating the suture point position in real time. This invention ensures the stability of the interaction process by applying position constraints to the sliding constraint points during the sliding process within the soft tissue, and by employing a suture control method to adjust the entire interaction process, it can avoid situations where the wound cannot close or re-opens, thereby effectively improving the suture interaction effect with the soft tissue model.

Description

Technical Field

[0001] This invention belongs to the field of medical technology of virtual reality, and specifically relates to an interactive simulation method for wound suturing in a virtual surgical simulation system. Background Technology

[0002] Virtual surgery, as a significant application of virtual reality technology, integrates knowledge from multiple disciplines such as robotics, computer science, medicine, biomechanics, mechanics, and materials science. Starting with medical images from CT and MRI scans of human organs, it uses multidisciplinary technologies to simulate and guide various processes involved in medical surgery, playing a crucial role in medical training. Compared to traditional surgical training methods, virtual surgical training offers several advantages, including reduced consumable costs, minimizing ethical risks associated with human or animal testing, and lowering the risks of surgical training.

[0003] Suturing is one of the most common surgical training procedures. Because real-world sutures are extremely fine and suturing techniques are highly complex, surgeons need extensive training to master them. Furthermore, surgical instruments cause complex deformations of soft tissue during suturing, and the quality of these deformations directly impacts the realism of virtual surgical simulation systems. Therefore, achieving a realistic suturing simulation in virtual surgery is crucial.

[0004] Currently, interactive suturing simulation still faces several challenges, primarily falling into three categories. The first is the real-time performance issue. As the physical modeling of suture needles, sutures, and soft tissue models becomes increasingly sophisticated, the computational load of the simulation increases significantly, potentially impacting its real-time performance. The second is the accuracy issue. While meeting real-time requirements, simulation accuracy still needs improvement, including studying the physical properties of friction and self-collision during the suturing interaction process. The third is the stability issue. Improving stability during interaction ensures a smoother and more realistic suturing effect throughout the simulation. Existing sliding constraint methods involve setting sliding constraint points to drive the sliding of the suture and wound closure, achieving the simulated effect of interactive suturing. However, this method can lead to instability in the interactive system and secondary dehiscence of already closed wounds. Therefore, a suitable method needs to be developed to improve the realism and stability of suturing simulation. Summary of the Invention

[0005] The purpose of this invention is to provide a suturing interaction simulation method in virtual surgery to improve the stability and realism of the suturing effect.

[0006] This invention is achieved through the following technical solution.

[0007] The present invention discloses a suture interaction simulation method in virtual surgery, comprising the following steps:

[0008] Step 1: Construct a model of the suture needle and suture thread;

[0009] First, the suture line is discretized into a line consisting of a series of vertices x0, x1, x2, ..., x using a Kirchhoff elastic rod method. n-1 The curve is formed, and then the center line is extracted to simplify the suture needle into an arc. The arc is then segmented. Assuming that the arc PQ represents the suture needle, then point P and point Q correspond to the tip and root of the suture needle, respectively.

[0010] Step 2: Set the maximum static friction between the suture needle and the soft tissue surface, and perform the puncture. If the applied puncture force is greater than the maximum static friction, the suture needle will penetrate into the soft tissue; otherwise, the soft tissue surface will not be penetrated. Specifically, the puncture is divided into two processes:

[0011] 1) When the suture needle begins to penetrate the soft tissue, the apex of the segmented suture needle will follow the needle tip's path into the soft tissue and begin its movement. At this point, a set of puncture points p0, p1, ..., p... is set. n This is used to record the process of the suture needle gradually penetrating the soft tissue, and to store all puncture points in a puncture point linked list in the order of puncture.

[0012] 2) When the suture needle fully penetrates the soft tissue and pulls the suture to slide inside the soft tissue, the positional relationship between the two changes from the puncture state to the sliding state. The movement process of the suture is recorded by setting a series of sliding constraint points, and all sliding constraint points are stored sequentially in the sliding point linked list according to the movement order of the suture. At the same time, it is also necessary to store the suture vertex number corresponding to the sliding constraint point at the current moment and the node information of the soft tissue.

[0013] Step 3: The suture needle penetrates the soft tissue, while the suture is pulled and slids within the soft tissue. The frictional force between the suture and the soft tissue is calculated based on the movement of the suture.

[0014] 1) When the surface tension generated by soft tissue is less than the maximum static friction force, the static friction force F_static is equal to the total force F_total. sum The component of force in the direction of the motion trend is opposite to the direction of the motion trend.

[0015]

[0016] Where α represents the angle between the direction of the total force and the direction opposite to the movement of the suture.

[0017] 2) When the surface tension generated by soft tissue is less than the maximum static friction, sliding friction will replace the static friction. The formula for calculating sliding friction Fkinetic is as follows:

[0018]

[0019] μ represents the coefficient of kinetic friction, which is related to factors such as the roughness of the material itself and the temperature and humidity of the contact surface.

[0020] Step 4: Introduce position constraints and update the position of the suture line in the sliding state.

[0021] Under the continuous action of external force, the distance between two adjacent vertices on the suture line will be lengthened. Once the distance exceeds the safety threshold L0, the positional relationship between the suture line vertex and its corresponding sliding constraint point can be adjusted immediately to produce a sliding effect.

[0022] To avoid instability caused by excessively large spacing between adjacent sliding constraint points and inability to slide due to excessively small spacing, positional constraints are applied to adjacent sliding constraint points for positional correction. For any sliding constraint point n, the constraint equation can be approximated by Taylor's formula as follows:

[0023]

[0024] Where Δn represents the change in position, This represents the gradient on the constraint equation corresponding to the sliding constraint point n. The position change of a single sliding constraint point can be expressed as:

[0025]

[0026] in m i The mass of the preset sliding constraint point. The proportional coefficient s is:

[0027]

[0028] Since the sliding constraint points are also particles in the soft tissue model, when the soft tissue deforms, stretching constraints are applied to all particles in the sliding constraint point list. At this time, the stretching constraints between adjacent sliding constraint points n1 and n2 can be expressed as:

[0029] C stretch (n1,n2)=|n1-n2|-d0

[0030] Where d0 is the initial length between particles n1 and n2. The gradients of n1 and n2 are respectively:

[0031]

[0032] After applying positional constraints, if the distance between two sliding constraint points is still less than the safety threshold L0, either point will be deleted to avoid redundant sliding constraint points interfering with the stitching interaction simulation process.

[0033] Step 5: The suture needle is fully inserted through the soft tissue. The suture is pulled to tighten the wound, and the position and speed of the suture point are updated.

[0034] By setting the sliding constraint point as the stitching point, and according to Newton's laws of motion, the following equation of motion can be established for the stitching point:

[0035]

[0036] Where F stretch F is the tensile force at suture point i. spring F represents the surface tension of the soft tissue at suture point i. damp F is the damping force at the suture point i. tense The force between the suture points at the left and right ends of the wound, m i For the quality of suture point i, Let F be the acceleration at suture point i. Since the tension of the suture always points in the direction of suture contraction, and the magnitude of the tension on a single suture is equal everywhere, we can obtain F. tense Size equal to F stretch .

[0037] Finally, determine the position of suture point i at the next moment. With speed The update is performed using the following calculation formula:

[0038]

[0039] Step 6: Control the entire interactive process of suturing, and adjust and update the suture point position in real time.

[0040] A pair of matching suture points on both sides of the wound were set as a suture group. The initial position, real-time position, and distance change between the two points in the suture group were recorded, and a data table was created based on the corresponding position information. As shown in Table 1, the initial distance between suture points... Real-time distance relative error If the relative error RE i If the size exceeds the set value, the stitching points that caused the offset will be adjusted and their positions updated. and

[0041] Since the stitching point, as a surface sliding constraint point, is formed after the stitching interaction has already occurred, there is no need to distinguish between stitched and unstitched points.

[0042] Table 1 Data on Suture Control Methods

[0043]

[0044] Compared with the prior art, the beneficial effects of the present invention are:

[0045] This invention provides a suturing interaction simulation method in virtual surgery. By introducing position constraints into the traditional sliding constraint point method and using a suturing control method to supervise the interaction process, the stability of the interaction process can be guaranteed. At the same time, it can avoid problems such as the suture line not being able to slide and secondary wound dehiscence, effectively improving the suturing interaction effect with the soft tissue model. Attached Figure Description

[0046] Figure 1 This is a schematic diagram of a suture needle model.

[0047] Figure 2 This is a schematic diagram of a suture needle penetrating into soft tissue.

[0048] Figure 3 A schematic diagram illustrating the interaction between sutures and soft tissue constructed from point springs.

[0049] Figure 4 This is a schematic diagram illustrating the suture position update during sliding.

[0050] Figure 5 This is a schematic diagram of the stress analysis at the suture point.

[0051] Figure 6 Interactive simulation of liver suturing. (a) shows the initial state, (b) shows the start of suturing, (c) shows the completion of suturing, and (d) shows the state without suturing control methods. Detailed Implementation

[0052] The present invention will be further described in conjunction with the accompanying drawings through the following embodiments, so that those skilled in the art can implement it based on the description.

[0053] The present invention discloses a suture interaction simulation method in virtual surgery, comprising the following steps:

[0054] Step 1: Construct a model of the suture needle and suture. First, the suture is discretized into a line consisting of a series of vertices x0, x1, x2, ..., x6. n-1 The curve is formed; then the suture needle is treated, as shown in the attached diagram. Figure 1The suture needle is segmented by extracting its centerline and simplified as an arc PQ, where P and Q correspond to the needle tip and root, respectively. γ represents the tangent vector at the needle tip P, R represents the radius of the arc, and O represents the center point of the suture needle model. When the suture needle punctures soft tissue under external force, the needle tip moves along the tangent of γ, and the component of the external force in the γ direction is equal to the puncture force of the suture needle into the soft tissue.

[0055] Step 2: Set the maximum static friction force between the suture needle and the soft tissue surface to force = 2.8N, and perform the puncture. If the applied puncture force is greater than the maximum static friction force, the suture needle will penetrate into the soft tissue; otherwise, the soft tissue surface will not be penetrated. Penetration occurs in two specific ways:

[0056] 1) As the suture needle begins to penetrate the soft tissue, the apex of the segmented needle will follow the needle tip's path into the soft tissue and begin its movement. (See attached image.) Figure 2 In (1), a set of puncture points p0, p1, ..., p are set. n This is used to record the process of the suture needle gradually penetrating the soft tissue, and to store all puncture points in a puncture point linked list in the order of puncture.

[0057] 2) When the suture needle fully penetrates the soft tissue and pulls the suture to slide within the soft tissue, the positional relationship between the two changes from the puncture state to the sliding state. A series of sliding constraint points are set to record the movement of the suture, and all sliding constraint points are stored sequentially in a sliding point linked list following the order of the suture movement. Simultaneously, the suture vertex number corresponding to each sliding constraint point at the current moment, as well as the node information of the soft tissue, also needs to be stored. (See attached...) Figure 2 In (2), after the suture needle has completely penetrated the soft tissue, the suture will pass through the last puncture point p1 left by the needle tail Q and enter the soft tissue. Since the first vertex x0 on the suture is always fixed at the needle tail Q, when the second vertex x1 slides to the puncture point p1, p1 will be deleted from the puncture point list, and a new sliding constraint point n0 will be generated at the same time. As the suture gradually enters the soft tissue, the puncture points will be deleted one by one until the list is cleared. At this time, the suture needle is once again in the external position of the soft tissue.

[0058] Step 3: The suture needle penetrates the soft tissue, while the suture slides within the soft tissue under traction. The frictional force between the suture and the soft tissue is calculated based on the suture's movement. First, the frictional force between the suture and the soft tissue is divided into static friction and sliding friction for calculation. (See attached diagram) Figure 3The suture and soft tissue are simplified as two objects with a tendency to move relative to each other, and frictional force analysis is performed. The line segment formed by vertices x0 to x4 represents the suture, the line segment formed by particles n0 to n4 represents the soft tissue surface composed of a spring, F1 and F3 represent the surface tension of the soft tissue on particle n2, and f... 12 with f 23 The tension of the suture on particle n2.

[0059] 1) When the surface tension generated by soft tissue is less than the maximum static friction force, the static friction force F_static is equal to the total force F_total. sum The component of force in the direction of the motion trend is opposite to the direction of the motion trend.

[0060]

[0061] Where α represents the angle between the direction of the total force and the direction opposite to the movement of the suture.

[0062] 2) When the surface tension generated by soft tissue is less than the maximum static friction, sliding friction will replace static friction. Sliding friction F 动 The calculation formula is as follows:

[0063]

[0064] The coefficient of kinetic friction, μ = 0.2, is related to factors such as the roughness of the material itself and the temperature and humidity of the contact surface.

[0065] Step 4: Introduce position constraints to update the position of the suture line in the sliding state. Under the continuous action of external force, the distance between two adjacent vertices on the suture line will be stretched. Once the distance exceeds the safety threshold L0 = 0.75mm, the positional relationship between the suture line vertex and its corresponding sliding constraint point can be adjusted immediately, thereby producing the sliding effect. (See attached...) Figure 4 The position update process in the sliding state is shown, with appendix. Figure 4 (1) The sliding constraint point n0 corresponds to the apex x of the seam line. i , attached Figure 4 (2) Vertex x appears i-1 With x i If the distance between them is greater than the safety threshold L0, the suture will continue to slide, and the vertex of the suture corresponding to the sliding constraint point n0 will be adjusted to x. i+1 As attached Figure 4 As shown in (3).

[0066] To avoid instability caused by excessively large spacing between adjacent sliding constraint points and inability to slide due to excessively small spacing, positional constraints are applied to adjacent sliding constraint points for positional correction. For any sliding constraint point n, the constraint equation can be approximated by Taylor's formula as follows:

[0067]

[0068] Where Δn represents the change in position, This represents the gradient on the constraint equation corresponding to the sliding constraint point n. The position change of a single sliding constraint point can be expressed as:

[0069]

[0070] in The mass m of the preset sliding constraint point i =0.01g. The proportionality constant s is:

[0071]

[0072] Since the sliding constraint points are also particles in the soft tissue model, when the soft tissue deforms, stretching constraints are applied to all particles in the sliding constraint point list. At this time, the stretching constraints between adjacent sliding constraint points n1 and n2 can be expressed as:

[0073] C stretch (n1,n2)=|n1-n2|-d0

[0074] Where d0 is the initial length between particles n1 and n2. The gradients of n1 and n2 are respectively:

[0075]

[0076] After applying positional constraints, if the distance between two sliding constraint points is still less than the safety threshold L0, either point will be deleted to avoid redundant sliding constraint points interfering with the stitching interaction simulation process.

[0077] Step 5: After the suture needle has completely penetrated the soft tissue, pull the suture to tighten the wound, and update the position and speed of the suture point. (See attached image) Figure 5 By setting the sliding constraint point as the stitching point, and according to Newton's laws of motion, the following equation of motion can be established for the stitching point:

[0078]

[0079] Where F stretch F is the tensile force at suture point i. spring F represents the surface tension of the soft tissue at suture point i. dampF is the damping force at the suture point i. tense Let m be the mass of suture point i, representing the force between the suture points on the left and right sides of the wound. i =0.01g, Let F be the acceleration at suture point i. Since the tension of the suture always points in the direction of suture contraction, and the magnitude of the tension on a single suture is equal everywhere, we can obtain F. tense Size equal to F stretch .

[0080] Finally, determine the position of suture point i at the next moment. With speed The update is performed using the following calculation formula:

[0081]

[0082] Step 6: Control the entire interactive process of suturing, and adjust and update the suture points in real time.

[0083] A pair of matching suture points on both sides of the wound were designated as a suture group. The initial position, real-time position, and distance changes between the two points in each suture group were recorded, and a data table was created using the corresponding positional information. The initial distance between suture points is also recorded. Real-time distance relative error If the relative error RE i If the size exceeds the set value by 10%, the stitching points that caused the offset will be adjusted and their positions updated. and As shown in Table 1.

[0084] Since the stitching point, as a surface sliding constraint point, is formed after the stitching interaction has already occurred, there is no need to distinguish between stitched and unstitched points.

[0085] Table 1 Data on Suture Control Methods

[0086]

[0087] As attached Figure 6 This is the effect of the interactive simulation process of liver suturing, among which Figure 6 (a) is the initial state of the suturing process; Figure 6 (b) The suturing effect after the first stitch is completed after the suturing begins; Figure 6 (c) shows the completed suture state, where it can be seen that the liver wound gradually closes under the action of the suture, eventually achieving closure. Figure 6(d) demonstrates the problem of secondary dehiscence of the wound after suturing when no suture control method is added. It can be seen that the system can effectively simulate soft tissue suturing operations, without the phenomenon of sutures not being able to slip, and has a high degree of realism. Furthermore, the suture control method can effectively solve the problem of wound failure to close after suturing.

Claims

1. A suture interaction simulation method in virtual surgery, characterized by: Includes the following steps: Step 1: Construct a model of the suture needle and suture thread; First, the suture line is discretized into a line consisting of a series of vertices x0, x1, x2, ..., x using a Kirchhoff elastic rod method. n-1 The curve is formed, and then the center line is extracted to simplify the suture needle into an arc. The arc is then segmented. Assuming that the arc PQ represents the suture needle, then point P and point Q correspond to the tip and root of the suture needle, respectively. Step 2: Set the maximum static friction between the suture needle and the soft tissue surface, and perform the puncture. If the applied puncture force is greater than the maximum static friction, the suture needle will penetrate into the soft tissue; otherwise, the soft tissue surface will not be penetrated. The puncture is specifically divided into two processes: 1) When the suture needle begins to penetrate the soft tissue, the apex of the segmented suture needle will follow the needle tip's path into the soft tissue and begin to move; at this time, a set of puncture points p0, p1, ..., p are set. n To record the process of the suture needle gradually penetrating into the soft tissue, and at the same time store all puncture points in the puncture point linked list in the order of puncture; 2) When the suture needle fully penetrates the soft tissue and pulls the suture to slide inside the soft tissue, the positional relationship between the two will change from the puncture state to the sliding state; the movement process of the suture is recorded by setting a series of sliding constraint points, and all sliding constraint points are stored in the sliding point linked list in the order of the suture movement. At the same time, it is necessary to store the suture vertex number corresponding to the sliding constraint point at the current moment and the node information of the soft tissue. Step 3: The suture needle penetrates the soft tissue, while the suture is pulled and slids within the soft tissue. The frictional force between the suture and the soft tissue is calculated based on the movement of the suture. 1) When the surface tension generated by the soft tissue is less than the maximum static friction force, the static friction force F 静 Equivalent to the total force F sum The component of the force in the direction of the trend of motion has the opposite direction to the direction of the trend of motion: Where α represents the angle between the direction of the total force and the direction opposite to the movement of the suture line; 2) When the surface tension generated by soft tissue is less than the maximum static friction, sliding friction will replace static friction; sliding friction F 动 The calculation formula is as follows: μ represents the coefficient of kinetic friction, which is related to factors such as the roughness of the material itself and the temperature and humidity of the contact surface. Step 4: Introduce position constraints and update the position of the suture line in the sliding state; Under the continuous action of external force, the distance between two adjacent vertices on the suture line will be lengthened. Once the distance exceeds the safety threshold L0, the positional relationship between the suture line vertex and its corresponding sliding constraint point can be adjusted immediately to produce a sliding effect. To avoid instability caused by excessively large spacing between adjacent sliding constraint points and inability to slide due to excessively small spacing, positional constraints are applied to adjacent sliding constraint points for positional correction. For any sliding constraint point n, the constraint equation can be approximated by Taylor's formula as follows: Where Δn represents the change in position, This represents the gradient on the constraint equation corresponding to the sliding constraint point n; the position change of a single sliding constraint point can be expressed as: in m i The mass of the preset sliding constraint point; the proportional coefficient s is: Since the sliding constraint points are also particles in the soft tissue model, when the soft tissue deforms, stretching constraints are applied to all particles in the sliding constraint point list. At this time, the stretching constraints between adjacent sliding constraint points n1 and n2 can be expressed as: C stretch (n1,n2)=|n1-n2|-d0 Where d0 is the initial length between particles n1 and n2; the gradients of n1 and n2 are respectively: After applying positional constraints, if the distance between two sliding constraint points is still less than the safety threshold L0, either point will be deleted to avoid redundant sliding constraint points interfering with the stitching interaction simulation process. Step 5: The suture needle is fully inserted through the soft tissue. The suture is pulled to tighten the wound, and the position and speed of the suture point are updated. By setting the sliding constraint point as the stitching point, and according to Newton's laws of motion, the following equation of motion can be established for the stitching point: Where F stretch F is the tensile force at suture point i. spring F represents the surface tension of the soft tissue at suture point i. damp F is the damping force at the suture point i. tense The force between the suture points at the left and right ends of the wound, m i For the quality of suture point i, Let F be the acceleration at suture point i; since the tension of the suture always points in the direction of suture contraction, and the magnitude of the tension on a single thread is equal everywhere, we can obtain F. tense Size equal to F stretch ; Finally, determine the position of suture point i at the next moment. With speed The update is performed using the following calculation formula: Step 6: Control the entire interactive process of suturing, and adjust and update the suture point position in real time; Set a pair of matching suture points on both sides of the wound as a suture group, record the initial position, real-time position and distance change of each point in the suture group, and build a data table based on the corresponding position information; Initial distance in suture point spacing Real-time distance relative error If the relative error RE i If the size exceeds the set value, the stitching points that caused the offset will be adjusted and their positions updated. and Since the stitching point, as a surface sliding constraint point, is formed after the stitching interaction has already occurred, there is no need to distinguish between stitched and unstitched points.

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