# US 10,561,466 B2 · Automated planning systems for pedicle screw placement and related methods

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- Number: US 10,561,466 B2
- Document ID: US10561466B2
- Status: Granted
- Kind: B2
- Application number: 16/046,181
- Filed: 2018-07-26
- Published: 2019-02-14
- Granted: 2020-02-18
- Earliest claimed: 2017-08-10
- Assignees: Sectra AB
- Applicants: Sectra AB
- Inventors: Anders Hedblom; Rolf Scheiderbauer; Stefan Lindholm; Ludvig Mangs
- Web page: https://patentgrep.com/patent/US10561466B2

## CPC

- A61B 34/10: Computer-aided planning, simulation or modelling of surgical operations
- A61B 34/25: {User interfaces for surgical systems}
- G06T 7/0012: {Biomedical image inspection}
- G06T 7/62: of area, perimeter, diameter or volume
- G06T 7/75: {involving models}
- G06T 15/06: Ray-tracing
- G06T 19/20: Editing of three-dimensional [3D] images, e.g. changing shapes or colours, aligning objects or positioning parts
- A61B 2034/104: {Modelling the effect of the tool, e.g. the effect of an implanted prosthesis or for predicting the effect of ablation or burring}
- A61B 2034/105: {Modelling of the patient, e.g. for ligaments or bones}
- G06T 2200/24: involving graphical user interfaces [GUIs]
- G06T 2207/10028: Range image; Depth image; 3D point clouds
- G06T 2207/10081: Computed x-ray tomography [CT]
- G06T 2207/10088: Magnetic resonance imaging [MRI]
- G06T 2207/30012: Spine; Backbone
- G06T 2210/21: Collision detection, intersection
- G06T 2210/41: Medical
- G06T 2219/2004: Aligning objects, relative positioning of parts
- G06T 2219/2016: Rotation, translation, scaling
- A61B: DIAGNOSIS; SURGERY; IDENTIFICATION (usefulness limited to only animals A61D)
- G06T: IMAGE DATA PROCESSING OR GENERATION, IN GENERAL

## Abstract

Systems, methods and circuits can perform automated pedicle placement planning on 3D image data sets of the spine using global and local coordinate axes systems and ray casting to identify a center of the vertebral foramen and a center of a solid vertebral body for the local coordinate axis system.

## Claims

### Claim 1

An automated or semi-automated method of planning for placement of pedicle screws, comprising:
providing a three dimensional (3D) image of a target vertebra of a patient;
electronically defining a first coordinate axis system using a first axis extending in an anatomical right to left direction across a target vertebra;
electronically ray casting the 3D image of the target vertebra in an anterior direction that is anterior to the first axis;
electronically identifying a vertebral foramen (VF) based at least in part on the ray casting;
electronically calculating a second coordinate axis system aligned with an orientation of the VF; and
electronically identifying placement and sizing of at least one pedicle screw using the second coordinate axis system.

### Claim 2 (depends on 1)

The method of claim 1, wherein the first and second coordinate systems are Cartesian coordinate systems, wherein the first axis is a first x-axis, a z-axis extends in a superior/inferior direction and a y-axis extends in an anterior/posterior direction.

### Claim 3 (depends on 1)

The method of claim 1, wherein the ray casting identifies points on a boundary of bone tissue.

### Claim 4 (depends on 1)

The method of claim 1, further comprising displaying the provided 3D image of the target vertebra, wherein the first x-axis is generated based on user input of first and second points, spaced apart in the right to left direction, on a posterior of the displayed target vertebra.

### Claim 5 (depends on 4)

The method of claim 4, wherein the identifying the VF is carried out by: i) determining a midpoint between the first and second points from the user input, ii) for points along a line extending in the anterior direction from the midpoint, the electronically ray casting comprises applying a first ray casting that is carried out in the left and right directions to determine an intersection surface associated with bone tissue, iii) from the intersection surface, determining a point or points in an interior of the VF, and iv) from the interior point or points of the VF, applying a second ray casting to determine intersection points with the bone tissue that represent an inner surface of the VF.

### Claim 6 (depends on 5)

The method of claim 5, wherein the step iv) second ray casting comprises spherically distributed ray casting to identify a point cloud having a cylindrical shape, and wherein the method further comprises electronically using the cylindrical shape to identify an orientation of the VF and a middle point of the VF.

### Claim 7 (depends on 6)

The method of claim 6, wherein the second ray casting comprises casting rays in the left and right directions from regularly spaced apart points above and below the middle point of the VF, registering points until rays do not hit bone tissue within a distance of +/−50% of a radius of the cylindrical shape fitted to the VF, and adjusting the middle point of the VF along the z-axis to be an average of the z-axis position of the registered points.

### Claim 8 (depends on 6)

The method of claim 6, wherein identifying the orientation of the VF is performed by electronically fitting a cylindrical model to the VF, comprising: approximating plane normals for each point neighborhood in the point cloud derived from the spherically distributed ray casting, fitting a plane to the collection of normal vectors which represents a cross-section of the cylinder, and using the normal of the cross-section plane to define a cylinder centerline direction of the cylinder.

### Claim 9 (depends on 5)

The method of claim 5, further comprising electronically tilting the z-axis of the second coordinate axis system about 10 degrees in the anterior direction relative to an orientation in the first coordinate system then calculating an anatomical based orientation of the y-axis and x-axis of the second coordinate system based on the tilted z-axis.

### Claim 10 (depends on 1)

The method of claim 1, further comprising electronically ray casting relative to a middle point of the VF in the second coordinate axis system to identify boundary points of cortical bone, then determining a perimeter of a vertebral body from the boundary points, calculating a middle body location of the vertebral body (bodyMid) spaced apart from and adjacent the VF, and updating the second coordinate axis system based on the defined middle body location to thereby adjust for rotation of the vertebra about the z-axis.

### Claim 11 (depends on 1)

The method of claim 1, wherein the pedicle screw placement and sizing comprises determining a first control point left or right of a midpoint of the VF in the second coordinate axis system, the control point being adjacent to the VF and within bone tissue but sufficiently distant to the VF to prevent a properly placed and sized pedicle screw from penetrating the VF.

### Claim 12 (depends on 11)

The method of claim 11, wherein the pedicle screw placement and sizing further comprises determining a second control point anterior to the vertebra, along the y-axis from the midpoint of the VF in the second coordinate axis system, and wherein the pedicle screw placement is defined by a line through the first and second control points.

### Claim 13 (depends on 11)

The method of claim 11, further comprising allowing a manual adjustment of the electronically identified pedicle screw placement, wherein the first control point is set to be a fixed center of rotation for a user for the manual adjustment of the pedicle screw placement.

### Claim 14 (depends on 1)

The method of claim 1, further comprising:
electronically ray casting the target vertebra from a point in the middle of the VF (holeMid) to identify a perimeter of a vertebral body;
electronically calculating a middle body location of the vertebral body (bodyMid);
electronically ray casting the target vertebra laterally in a right to left direction in increments in up and down directions relative to holeMid to identify pedicle heights;
electronically defining a front/anterior position where the pedicle screws will point using the equation: bodyMid+(bodyMid−holeMid)×1.5;
electronically defining right and left lines of a trajectory of respective right and left pedicle screws from a pedicle to a front position;
generating a graphical representation of physical pedicle screws with the graphical representation placing the pedicle screws perpendicular to the cylinder shape in an anterior direction from the pedicles; and
electronically providing size and length parameters of right and left physical pedicle screws as the electronically identifying the placement and sizing.

### Claim 15 (depends on 14)

The method of claim 14, further comprising:
determining the intersection points of vertebra boundary along a pedicle screw trajectory at the front and back of the vertebra, and determining the size of the pedicle screw as a predefined proportion of the distance between the intersection points.

### Claim 16 (depends on 1)

The method of claim 1, wherein the electronically identifying placement and sizing of one or two pedicle screws for a single vertebra is carried out in between 100 and 200 milliseconds.

### Claim 17

A clinician workstation comprising:
at least one display; and
a circuit in communication with the at least one display, the circuit comprising or in communication with at least one processor configured to:
provide a three dimensional (3D) image of a target vertebra of a patient;
define a first coordinate axis system using a first axis extending in an anatomical right to left direction across a target vertebra;
ray cast the 3D image of the target vertebra in an anterior direction that is anterior to the first axis;
identify a vertebral foramen (VF) based at least in part on the ray casting;
calculate a second coordinate axis system aligned with an orientation of the VF; and
identify placement and sizing of at least one pedicle screw using the second coordinate axis system.

### Claim 18 (depends on 17)

The workstation of claim 17, wherein the circuit with the at least one processor directs the display to display the provided 3D image of the target vertebra, and accepts user input of first and second points spaced apart in the right to left direction, on a posterior of the displayed target vertebra, and wherein the first x-axis is generated based on the user input.

### Claim 19 (depends on 18)

The workstation of claim 18, wherein the VF is identified by: i) determining a midpoint between the first and second points from the user input, ii) for points along a line extending in the anterior direction from the midpoint, the electronically ray casting comprises applying a first ray casting that is carried out in the left and right directions to determine an intersection surface associated with bone tissue, iii) from the intersection surface, determining a point or points in an interior of the VF, and iv) from the interior point or points of the VF, applying a second ray casting to determine intersection points with the bone tissue that represent an inner surface of the VF.

### Claim 20 (depends on 17)

The workstation of claim 17, wherein the identification of the pedicle screw placement and sizing comprises determining a first control point left or right of a midpoint of the VF in the second coordinate axis system, the control point being adjacent to the VF and within bone tissue but sufficiently distant to the VF to prevent a properly placed and sized pedicle screw from penetrating the VF.

### Claim 21 (depends on 20)

The workstation of claim 20, wherein the identification of the pedicle screw placement and sizing further comprises determining a second control point anterior to the vertebra, along the y-axis from the midpoint of the VF in the second coordinate axis system, and wherein the pedicle screw placement is defined by a line through the first and second control points.

### Claim 22 (depends on 1)

A system for evaluating 3-D spinal patient image data for pedicle placement planning, comprising:
a pedicle placement planning module comprising at least one processor; and
at least one display in communication with the pedicle placement planning module comprising the at least one processor,
wherein the pedicle planning placement module is configured to carry out the method of claim 1.