A double-needle conformal ablation planning method and device for liver cancer microwave ablation

Abstract

The present application belongs to the technical field of medical image processing, and provides a double-needle conformal ablation planning method for liver cancer microwave ablation, which comprises the following steps: S1, performing ex vivo pig liver microwave ablation experiment and measuring the axial length of the ablation injury area; using a distance field with weights, obtaining a simulation model of the ablation injury area in the double-needle simultaneous ablation mode with different intervals; S2, scaling the target ablation area along the needle insertion direction; S3, clustering the scaled target ablation area into a plurality of unit blocks, and obtaining the closest paired double-unit blocks; S4, covering the unit blocks with the simulation model to obtain the needle arrangement planning scheme before ablation. The method can solve the problem of rapid conformal ablation needle arrangement of liver tumors in the double-needle ablation mode, and quickly calculate an ablation preoperative planning scheme for conformally covering the target ablation area, thereby providing an optimized preoperative planning reference scheme for liver tumor ablation.

Description

Technical Field

[0001] This invention belongs to the field of medical image processing technology, specifically relating to a dual-needle conformal ablation planning method and device for microwave ablation of liver cancer. Background Technology

[0002] Microwave ablation is a novel, minimally invasive treatment method targeting specific tumor sites, and it is currently one of the most commonly used methods for treating solid tumors in clinical practice. Microwave ablation works based on the biothermal effect of high-frequency electromagnetic waves, converting microwave energy into heat energy to precisely heat and inactivate lesions. The key to its successful treatment lies in creating an appropriately sized area of ​​thermal damage to achieve complete conformal inactivation of the tumor. Therefore, using medical imaging to design preoperative ablation plans can provide practical assistance to the ablation procedure.

[0003] The preoperative planning for microwave ablation generally includes two parts: simulation of the ablation zone and needle placement planning. To achieve conformal ablation needle placement, the location of the ablation zone needs repeated adjustments and optimization during planning, requiring very high real-time simulation capabilities. Therefore, a simple ellipsoidal geometric model is typically used to simulate the ablation zone. However, the commonly used dual-needle simultaneous ablation mode in clinical practice results in significant differences between the ablation zone and the dual-ellipsoidal simulation model due to the thermal interaction between the two needles. This greatly reduces the guiding significance of the preoperative planning for assisting ablation treatment. Summary of the Invention

[0004] To address the significant discrepancy between the actual ablation damage area and the dual-ellipsoidal simulation model, this invention provides a dual-needle conformal ablation planning method for microwave ablation of liver cancer. This method can solve the real-time simulation problem of the ablation damage area under the dual-needle simultaneous ablation mode and quickly calculate a preoperative planning reference scheme that conformally covers the target ablation area.

[0005] To achieve the above objectives, the present invention adopts the following technical solution.

[0006] A dual-needle conformal ablation planning method for microwave ablation of liver cancer includes the following steps:

[0007] S1. Conduct microwave ablation experiments on isolated pig liver and measure the axial length of the ablation damage area; use a weighted distance field to obtain simulation models of the ablation damage area of ​​the dual-needle simultaneous ablation mode with different spacings.

[0008] S2. Scale the target ablation area along the needle insertion direction;

[0009] S3. Cluster the scaled target ablation region into several unit blocks and obtain the closest paired double unit blocks;

[0010] S4. Use the simulation model to cover the unit block to obtain the needle placement plan before ablation.

[0011] In step S1, the needle type, ablation power, and ablation time are fixed, and single-needle and double-needle ablation experiments with different spacings are conducted. After the ablation experiments, pig liver samples are cut along the largest cut surface. For the single-needle ablation experimental group, the axial length of the ablation damage area along the needle path is measured and defined as the major axis. l 1. Measure the axial length of the ablation zone of the vertical ablation needle path, defined as the transverse diameter. l 2; For the dual-needle ablation model, the axial length of the ablation zone parallel to the needle path and equidistant from the dual needles is measured and defined as the intermediate major diameter formed by the thermal interaction of the dual needles. l 3.

[0012] The weighted distance field is configured as follows:

[0013] For single-needle ablation, an ellipsoidal geometry is used to simulate the ablation damage area, assuming the ablation center point is... o Then the ablation damage area E 单 Represented as:

[0014] ,

[0015] in, x Represents any point in three-dimensional space. R 3 For a three-dimensional spatial region, superscript T Represents the transpose of a matrix. Q It is a positive definite matrix whose eigenvectors represent the directions of the principal axes of the ellipsoid and whose eigenvalues ​​represent the reciprocals of the square of the semi-axis length;

[0016] Define distance d for:

[0017] ;

[0018] Then around the ablation center point o A distance field is formed, distance d The region with a value greater than 1 is the ablation damage region represented by the ellipsoidal model;

[0019] When two needles are used for simultaneous ablation, the ablation damage area E 双 This can be represented as a weighted superposition of the distance fields of two single-needle ablation techniques:

[0020] ,

[0021] In the above formula, d 1 and d 2 represents the distance from the center point of the two single-needle ablation points, respectively;

[0022] Weight oh 1 and oh 2 represents the distance between two needles. u Functions:

[0023] ,

[0024] in, e The base of the natural logarithm function is given by . α , c , d These are parameters to be determined.

[0025] Based on two extreme cases, when the ablation needles are infinitely close together, the ablation effect is similar to that of a single needle; when the distance between the ablation needles is sufficiently large, the thermal interaction between the two needles can be ignored; therefore, the following conclusions can be drawn:

[0026] ;

[0027] ;

[0028] Therefore, c =1, d =0;

[0029] parameter α The value is the optimal value determined by the grid search algorithm.

[0030] Specifically, the parameters in the grid search algorithm α The search range is [1, 100], and the search step size is 0.5; the intermediate major diameter obtained under the dual-needle ablation mode with different spacing is compared with the measured intermediate major diameter. l The smallest sum of the squares of 3 α The value is the optimal value.

[0031] In step S2, a three-dimensional image of the liver, tumor, intrahepatic blood vessels, skin, and ribs on a cross-section of the liver region is obtained. The skin surface of the intercostal space closest to the tumor is selected as the target point, and the direction from the target point to the center of gravity of the tumor is set as the needle insertion direction.

[0032] The target ablation zone is defined as the tumor and the area within 5 millimeters of its periphery;

[0033] The unit vector along the needle insertion direction is denoted as v 1. Place the tumor voxel along... v Scaling is performed in one direction, with the scaling factor being the horizontal diameter. l 2 and major axis l The ratio of 1.

[0034] In step S3, the number of ablation needle insertions is set. n The initial value is ,

[0035] in, The rounding up symbol, V t The volume of the target ablation zone. V b The volume of the ablation zone of a single needle ellipsoid;

[0036] Clustering algorithms were used to segment the scaled target ablation region into voxel points. n Each unit block, and obtain n The center of gravity of each unit block; pairing unit blocks in pairs according to the distance between the centers of gravity; if n If the number is even, then the unit blocks are formed after pairing and combining. A double-unit block; if n If the number is odd, then the unit blocks are formed after pairing and combining. One double-cell block and one single-cell block.

[0037] In step S4, the clustered cell blocks are restored to their original positions and sizes. For bi-cell blocks, the centroid of the two cell blocks is used as the center point, and the clustering is performed according to… E 双 Perform needle placement planning; if the number of needle insertions... n If the number is odd, then the remaining 1 unit block is centered on the centroid position, according to... E 单 Perform needle placement planning; if the simulation model can completely cover the target tumor area, then the above needle placement plan is the final preoperative planning plan; if the simulation model cannot completely cover the target ablation area, then the number of ablation needle insertions will be determined. n Automatically increment by one and repeat S3 until the obtained simulation model completely covers the target ablation area to obtain the final preoperative planning scheme.

[0038] A microwave ablation planning system for implementing the above method includes:

[0039] The simulation module is configured to obtain a simulation calculation method for the ablation damage area in the dual-needle ablation mode.

[0040] The scaling module is configured to scale the target ablation area along the needle insertion direction, with the scaling ratio being the measured transverse diameter of the single-needle ablation lesion area. l 2 and major axis l The ratio of 1;

[0041] The clustering module is configured to cluster the target ablation region into several unit blocks and calculate the closest pairwise unit blocks.

[0042] The planning module is configured to use a dual-needle ablation damage area simulation model to cluster the unit blocks. E 双 and single-needle ellipsoid model E单 Coverage should be implemented, and a preoperative ablation needle placement plan should be established.

[0043] The present invention has the following advantages:

[0044] This invention proposes a real-time simulation method for the ablation damage area of ​​a dual-needle simultaneous ablation mode with different spacings by establishing a weighted distance field model. This method can simulate the irregular ablation damage range formed by the thermal interaction between the two needles. For the target ablation area of ​​liver tumor, the method scales it along the needle insertion direction. The scaled target ablation area voxel set is clustered, and the optimal pairwise pairing is obtained based on the nearest distance. Finally, the clustered unit blocks are covered by a single-needle ellipsoid model and a dual-needle ablation damage area simulation model. An iterative method is used to determine the minimum number of needle insertions and the final optimized needle placement scheme. Therefore, this method can solve the problem of rapid conformal ablation needle placement for liver tumors under dual-needle ablation mode and quickly calculate a preoperative planning scheme for conformal coverage of the target ablation area, providing an optimized preoperative planning reference scheme for liver tumor ablation. Attached Figure Description

[0045] Figure 1 This is a flowchart of the dual-needle conformal ablation planning method for microwave ablation of liver cancer.

[0046] Figure 2 The results of double-needle ablation of pig liver with a spacing of 20 mm, the effect diagram of the double ellipsoid model in the prior art, and the simulation effect diagram of the damage area of ​​double-needle ablation according to the present invention;

[0047] Figure 3 This is an image showing the effect of needle placement planning in the dual-needle conformal ablation planning method for microwave ablation of liver cancer. Detailed Implementation

[0048] The present invention will be further described below with reference to the embodiments and accompanying drawings, but the present invention is not limited to the following embodiments.

[0049] Example 1: Two-needle conformal ablation planning method for microwave ablation of liver cancer

[0050] The procedure for planning the dual-needle conformal ablation method in microwave ablation of liver cancer is as follows: Figure 1 As shown, the specific steps include:

[0051] S1. Conduct microwave ablation experiments on isolated pig liver and measure the axial length of the ablation damage area; use a weighted distance field to obtain simulation models of the ablation damage area of ​​the dual-needle simultaneous ablation mode with different spacings.

[0052] The extracted pig liver must be fresh. In the pig liver microwave ablation experiment, the needle type, ablation power, and ablation time are fixed. The specific selection can be made according to individual cases or commonly used clinical combinations. In this embodiment, a PTFE slit microwave ablation antenna (KY2450B) is used, with an ablation power of 60W and an ablation time of 8min. The experiment is divided into 4 groups according to the ablation method: one group of single needle ablation and one group of double needle ablation with parallel spacing of 10 mm, 15 mm, and 20 mm, respectively. Each group is repeated 5 times.

[0053] After the ablation experiment, the pig liver sample was cut along the largest cut surface. The following data were measured and the average of 5 parallel experiments was calculated as the parameter value:

[0054] For the single-needle ablation experimental group, the axial length of the ablation damage area along the needle path was measured and defined as the major axis. l 1. Measure the axial length of the ablation zone of the vertical ablation needle path, defined as the transverse diameter. l 2;

[0055] For the dual-needle ablation model, the axial length of the ablation zone parallel to the needle path and equidistant from the needles is measured and defined as the mid-length diameter formed by the thermal interaction of the two needles. l 3;

[0056] In this embodiment, l 1. l 2 are 45 mm and 36 mm respectively; when the needle spacing is 10 mm, l 3 is 49.8 mm; when the needle spacing is 15 mm, l 3 is 48 mm; when the needle spacing is 20 mm, l 3 is 45.1 mm.

[0057] The weighted distance field is configured as follows:

[0058] For single-needle ablation, an ellipsoidal geometry is used to simulate the ablation damage area, assuming the ablation center point is... o Then the ablation damage area E 单 Represented as:

[0059] ,

[0060] in, x Represents any point in three-dimensional space. R 3 For a three-dimensional spatial region, superscript T Represents the transpose of a matrix. Q It is a positive definite matrix whose eigenvectors represent the directions of the principal axes of the ellipsoid and whose eigenvalues ​​represent the reciprocals of the square of the semi-axis length;

[0061] Define distanced for:

[0062] ;

[0063] Then around the ablation center point o A distance field is formed, distance d The region with a value greater than 1 is the ablation damage region represented by the ellipsoidal model.

[0064] When two needles are used for simultaneous ablation, the ablation damage area E 双 This can be represented as a weighted superposition of the distance fields of two single-needle ablation techniques:

[0065] ,

[0066] In the above formula, d 1 and d 2 represents the distance from the center point of the two single-needle ablation points, respectively;

[0067] Weight oh 1 and oh 2 represents the distance between two needles. u Functions:

[0068] ,

[0069] in, e The base of the natural logarithm function is given by . α , c , d These are parameters to be determined.

[0070] Based on two extreme cases, when the ablation needles are infinitely close together, the ablation effect is similar to that of a single needle; when the distance between the ablation needles is sufficiently large, the thermal interaction between the two needles can be ignored; therefore, the following conclusions can be drawn:

[0071] ;

[0072] ;

[0073] Therefore, c =1, d =0;

[0074] parameter α The value is the optimal value determined by the grid search algorithm: setting parameters α The search range is [1, 100], and the search step size is 0.5. During the search process, parameters are selected from the search range. α One value can determine the double-needle ablation damage area with different spacing. E 双 By sequentially selecting all parameters within the search rangeα The experimental values ​​were used to determine the median major diameter obtained under dual-needle ablation modes with spacings of 10 mm, 15 mm, and 20 mm, and compared with the measured median major diameter. l The optimal parameters are obtained by minimizing the sum of the squares of 3. The value of .

[0075] S2. Scale the target ablation area along the needle insertion direction;

[0076] In particular, for cases where three-dimensional CT images of the abdominal liver region are obtained, existing technologies such as MITK medical segmentation software are used to segment the tumor, liver, intrahepatic blood vessels, abdominal skin, and ribs, and to perform three-dimensional visualization. The skin surface of the intercostal space closest to the tumor is selected as the target point, and the direction from the target point to the center of gravity of the tumor is set as the needle insertion direction.

[0077] The target ablation zone is defined as the tumor and the area within 5 millimeters of its periphery;

[0078] The unit vector along the needle insertion direction is denoted as v 1. Place the tumor voxel along... v Scaling is performed in one direction, with the scaling factor being the horizontal diameter. l 2 and major axis l The ratio of 1.

[0079] S3. Cluster the scaled target ablation region into several unit blocks and obtain the closest paired double unit blocks;

[0080] First, set the number of ablation needle insertions. n The initial value is ,

[0081] in, The rounding up symbol, V t The volume of the target ablation zone. V b The volume of the ablation zone of a single needle ellipsoid;

[0082] Then, the scaled target ablation region voxel points were segmented using the K-Means clustering algorithm. n Each unit block, and obtain n The center of gravity of each unit block; pairing unit blocks in pairs according to the distance between the centers of gravity; if n If the number is even, then the unit blocks are formed after pairing and combining. A double-unit block; if n If the number is odd, then the unit blocks are formed after pairing and combining. One double-cell block and one single-cell block.

[0083] S4. Use the simulation model to cover the unit block to obtain the needle placement plan before ablation.

[0084] First, the clustered cell blocks are restored to their original positions and sizes; then, the bi-cell blocks are centered on the centroids of the two cell blocks, and then... E 双 Perform needle placement planning; if the number of needle insertions... n If the number is odd, then the remaining 1 unit block is centered on the centroid position, according to... E 单 Perform needle placement planning.

[0085] If the simulation model can completely cover the target tumor area, then the above needle placement plan is the final preoperative planning plan; if the simulation model cannot completely cover the target ablation area, then the number of ablation needle insertions will be [number missing]. n Automatically increment by one and repeat step S3 until the obtained simulation model completely covers the target ablation area, thus obtaining the final preoperative planning scheme.

[0086] Figure 2 The figures show the experimental results of pig liver ablation using a double-needle ablation with a 20 mm spacing, the effect diagram of the existing technology using a double ellipsoidal model, and the simulation effect diagram of the ablation damage area obtained according to this embodiment. It is evident that the existing technology using a double ellipsoidal model cannot simulate the impact of the thermal interaction of double-needle ablation on the ablation damage area, and the simulation effect of the ablation damage area differs significantly from the in vitro experimental results. In contrast, the simulation effect of the ablation damage area obtained according to this embodiment shows a very high degree of consistency with the in vitro experimental results. Figure 3 This is a diagram illustrating the effect of needle placement planning using the dual-needle conformal ablation planning method for microwave ablation of liver cancer according to the present invention.

[0087] All or part of the steps in the above method can be implemented by a program instructing related hardware. The program can be stored in a computer-readable storage medium. When the program is executed, it includes the steps of the method in the above embodiments. The storage medium can be: ROM / RAM, magnetic disk, optical disk, or memory card.

[0088] Example 2: Dual-needle conformal ablation planning device for microwave ablation of liver cancer

[0089] This embodiment provides an apparatus for implementing a dual-needle conformal ablation planning method for microwave ablation of liver cancer. The apparatus is represented by functional modules corresponding to the steps of the method. The apparatus includes:

[0090] The simulation module is configured to obtain a simulation calculation method for the ablation damage area in the dual-needle ablation mode.

[0091] The scaling module is configured to scale the target ablation area along the needle insertion direction, with the scaling ratio being the measured transverse diameter of the single-needle ablation lesion area.l 2 and major axis l The ratio of 1;

[0092] The clustering module is configured to cluster the target ablation region into several unit blocks and calculate the closest pairwise unit blocks.

[0093] The planning module is configured to use a dual-needle ablation damage area simulation model to cluster the unit blocks. E 双 and single-needle ellipsoid model E 单 Coverage should be implemented, and a preoperative ablation needle placement plan should be established.

Claims

1. A dual-needle conformal ablation planning method for liver cancer microwave ablation, characterized in that, The method comprises the following steps: S1, microwave ablation experiment of ex vivo pig liver is carried out, and the axial length of the ablation lesion area is measured; a weighted distance field is used to obtain a simulation model of the ablation lesion area in the double-needle simultaneous ablation mode with different intervals; S2, scaling the target ablation area along the needle insertion direction; S3, clustering the scaled target ablation area into a plurality of unit blocks, and obtaining the closest interval paired double unit blocks; S4, covering the unit blocks with the simulation model to obtain the needle arrangement planning scheme before ablation; In step S1, the weighted distance field is set as follows: For single needle ablation, ellipsoid geometry is used to simulate the ablation lesion area. The center point of ablation is assumed to be o The ablation lesion area is E 单 is represented as: ， wherein x denotes an arbitrary point in three-dimensional space, R 3 is a three-dimensional space region, the superscript T denotes the transpose of a matrix, Q is a positive definite matrix whose eigenvectors represent the principal axis directions of the ellipsoid and whose eigenvalues represent the reciprocals of the squares of the half-axis lengths; Defining a distance d is: ； then the ablation center point o A distance field is formed, distance d Regions with a distance greater than 1 are the ablation lesion region represented by an ellipsoid model; Ablation lesion zone when both needles are simultaneously ablated E 双 Represented as a weighted superposition of two single needle ablation distance fields: ， In the above formula, d 1 and d 2 represent the distance from the two single needle ablation center points, respectively; weight ω 1 and ω 2 are functions of the double needle spacing u : ， wherein e denotes the base of the natural logarithm function, α , γ , δ is a pending parameter; According to two extreme cases, when the ablation needle distance is infinitely close, the ablation effect is similar to that of single needle ablation; when the ablation needle interval distance is large enough, the heat interaction between the two needles can be ignored; the following conclusions can be obtained: ； ； Thus, we have γ = 1, δ = 0; Parameters α have values that are optimal values determined by a grid search algorithm; The search range of the parameter in the grid search algorithm is [1, 100], and the search step is 0.5; the value of the square sum of the intermediate long diameter obtained in the double-needle ablation mode with different intervals and the measured intermediate long diameter l 3 is the optimal value; the value of the square sum of the intermediate long diameter obtained in the double-needle ablation mode with different intervals and the measured intermediate long diameter α 3 is the optimal value; the value of the square sum of the intermediate long diameter obtained in the double-needle ablation mode with different intervals and the measured intermediate long diameter 3 is the optimal value. In step S1, for the double needle ablation model, the ablation zone axial length parallel to the double needle needle tract and equidistant from the double needle is measured, defined as the intermediate major axis formed by the thermal interaction of the double needle l 3.

2. The dual needle conformal ablation planning method of claim 1, wherein, In step S1, the needle type, ablation power and ablation time are fixed, and single-needle and double-needle ablation experiments with different spacings are performed; after the ablation experiment, the pig liver sample is cut along the maximum section; for the single-needle ablation experiment group, the axial length of the ablation damage zone along the needle path of the ablation needle is measured, which is defined as the long diameter l 1. The axial length of the ablation zone perpendicular to the needle path of the ablation needle is measured, which is defined as the transverse diameter l 2.

3. The dual needle conformal ablation planning method of claim 1, wherein, In step S2, the three-dimensional images of the liver, tumor, intrahepatic blood vessels, skin and ribs on the cross section of the liver region are obtained; the skin surface of the rib gap closest to the tumor is selected as the target point, and the direction from the target point to the tumor center is set as the needle insertion direction; The target ablation area is defined as the tumor and the surrounding area of 5mm; The unit vector along the needle insertion direction is denoted as v 1. The tumor voxel is scaled along the v 1 direction by a scale factor of the ratio of the transverse diameter l 2 to the longitudinal diameter l 1.

4. The dual needle conformal ablation planning method of claim 1, wherein, In step S3, the number of needle insertion for ablation is set n with an initial value of , wherein, is a ceiling symbol, V t is a volume of a target ablation zone, V b is a single-needle ellipsoidal ablation zone volume.

5. The dual needle conformal ablation planning method of claim 1, wherein, In step S3, the scaled target ablation region voxel points are segmented into n unit blocks by using a clustering algorithm, and the centers of gravity of the n unit blocks are obtained; the unit blocks are paired two by two according to the interval distances between the centers of gravity; If n is even, then the unit blocks form double unit blocks after pairing combination; if n is odd, then the unit blocks form double unit blocks and 1 single unit block after pairing combination.

6. The dual needle conformal ablation planning method of claim 1, wherein, In step S4, the clustered cell blocks are restored to their original positions and sizes. For bi-cell blocks, the centroid of the two cell blocks is used as the center point, and the clustering is performed according to… E 双 Perform needle placement planning; if the number of needle insertions... n If the number is odd, then the remaining 1 unit block is centered on the centroid position, according to... E 单 A needle placement plan is then developed. If the simulation model can completely cover the target tumor area, the needle placement plan becomes the final preoperative plan. If the simulation model cannot completely cover the target ablation area, the number of ablation needle insertions is determined. n Automatically increment by one and repeat S3 until the obtained simulation model completely covers the target ablation area to obtain the final preoperative planning scheme.

7. A microwave ablation planning system for implementing the dual-needle conformal ablation planning method of any one of claims 1-6, characterized in that, It comprises: a simulation module configured to obtain a simulation calculation method of the ablation lesion area in the double-needle ablation mode; a scaling module configured to scale the target ablation zone in the needle insertion direction by a scaling ratio of a measured cross-diameter of a single needle ablation lesion l 2 to the ratio of the long diameter l 1; a clustering module configured to cluster the target ablation area into a plurality of unit blocks, and to calculate and obtain the closest interval paired unit blocks; a planning module configured to simulate the lesion using a double needle ablation lesion model E 双 and a single needle ellipsoid model E 单 perform coverage, establish a pre-operative ablation needle planning scheme.

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