# US 10,869,724 B2 · Sagittal rotation determination

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- Number: US 10,869,724 B2
- Document ID: US10869724B2
- Status: Granted
- Kind: B2
- Application number: 16/306,991
- Filed: 2018-03-01
- Published: 2020-10-01
- Granted: 2020-12-22
- Earliest claimed: 2017-03-09
- Assignees: Smith & Nephew, Inc.; Smith & Nephew Asia Pacific Pte. Limited; Smith & Nephew Orthopaedics AG
- Applicants: Smith & Nephew, Inc.; Smith & Nephew Asia Pacific Pte. Limited; Smith & Nephew Orthopaedics AG
- Inventors: Steffen Beck; Mario Schubert; Christian Brack; Luise Poitzsch
- Web page: https://patentgrep.com/patent/US10869724B2

## CPC

- A61B 6/505: {for diagnosis of bone}
- A61B 34/10: Computer-aided planning, simulation or modelling of surgical operations
- A61B 5/0059: {using light, e.g. diagnosis by transillumination, diascopy, fluorescence (photoacoustic A61B5/0093; optical measurement of heart rate A61B5/02416; optical measurement of blood flow A61B5/0261; optical measurement of analytes A61B5/1455)}
- A61B 5/1072: {measuring distances on the body, e.g. measuring length, height or thickness (A61B5/1076 takes precedence)}
- A61B 5/1121: {Determining geometric values, e.g. centre of rotation or angular range of movement}
- A61B 6/00: Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment (instruments measuring radiation intensity for application in the field of nuclear medicine, e.g. in vivo counting, G01T1/161)
- A61B 6/5217: {extracting a diagnostic or physiological parameter from medical diagnostic data}
- A61B 6/5223: {generating planar views from image data, e.g. extracting a coronal view from a 3D image}
- A61B 6/5294: {involving using additional data, e.g. patient information, image labeling, acquisition parameters}
- A61B 6/58: Testing, adjusting or calibrating thereof
- A61B 6/582: {Calibration}
- A61B 17/1664: {for the hip}
- A61B 17/1666: {for the acetabulum}
- A61B 17/1703: {using imaging means, e.g. by X-rays}
- A61B 17/1742: {for the hip}
- A61B 17/1746: {for the acetabulum}
- G06T 3/073: Transforming surfaces of revolution to planar images, e.g. cylindrical surfaces to planar images
- G06T 3/18: Image warping, e.g. rearranging pixels individually
- G06T 3/60: Rotation of whole images or parts thereof
- G06T 7/0014: {using an image reference approach}
- G06T 7/80: Analysis of captured images to determine intrinsic or extrinsic camera parameters, i.e. camera calibration
- G06T 12/10: Image preprocessing, e.g. calibration, positioning of sources or scatter correction
- G16H 50/30: for calculating health indices; for individual health risk assessment
- A61B 2017/00725: {Calibration or performance testing}
- A61B 2034/102: {Modelling of surgical devices, implants or prosthesis}
- A61B 2034/105: {Modelling of the patient, e.g. for ligaments or bones}
- A61B 2034/107: {Visualisation of planned trajectories or target regions}
- A61B 2090/061: {for measuring dimensions, e.g. length}
- A61B 2090/376: {using X-rays, e.g. fluoroscopy}
- A61F 2002/4668: {for measuring angles}
- G06T 2207/10064: Fluorescence image
- G06T 2207/10081: Computed x-ray tomography [CT]
- G06T 2207/10116: X-ray image
- G06T 2207/20101: Interactive definition of point of interest, landmark or seed
- G06T 2207/30008: Bone
- G06T 2219/2016: Rotation, translation, scaling
- A61B: DIAGNOSIS; SURGERY; IDENTIFICATION (usefulness limited to only animals A61D)
- G06T: IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G16H: HEALTHCARE INFORMATICS, i.e. INFORMATION AND COMMUNICATION TECHNOLOGY [ICT] SPECIALLY ADAPTED FOR THE HANDLING OR PROCESSING OF MEDICAL OR HEALTHCARE DATA
- A61F: FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS (dental prosthetics A61C)

## Abstract

The invention relates to a method of determining the sagittal rotation of a patient's pelvis based on a standard anterior posterior X-ray-image with known image parameters and a calibration of the image, for example by using at least one King-Mark calibration object. The angle of the pelvic rotation is determined between a pelvic plane which is orthogonal to the midsagittal plane of the pelvis, and the image plane of the X-ray-image. Assuming the patient's position shown on the X-ray-image represents a standard neutral position, the X-ray-image plane can be used as a functional reference plane for further calculations, for example during hip-replacement surgery. The present invention further relates to a corresponding computer program and system.

## Claims

### Claim 1

A computer implemented method for determining a sagittal rotation of a patient's pelvis, the method comprising:
acquiring image data describing a two-dimensional X-ray-image of the patient's pelvis made in an anterior-posterior direction;
determining, based on the image data, position data describing the position of a plurality of pelvic landmarks reproduced in or derivable from the two-dimensional X-ray-image;
acquiring calibration data describing the position of a calibration plane with respect to the patient's pelvis, the calibration plane being perpendicular to the anterior-posterior direction;
determining, based on the position data and the calibration data, calibrated projection data describing a two-dimensional projection representing the plurality of pelvic landmarks of the patient's pelvis being projected into the calibration plane in the anterior-posterior direction;
acquiring distance data describing at least one of a medial-lateral distance and a cranial-caudal distance between at least one first pelvic landmark and at least one second pelvic landmark in the calibrated two-dimensional projection;
acquiring, from a database, regression data describing a linear correspondence between at least one of said medial-lateral distances and cranial-caudal distances, and a pelvic sagittal rotation; and
determining, based on the distance data and the regression data, the sagittal rotation of the patient's pelvis.

### Claim 2 (depends on 1)

The method of claim 1, wherein the determining calibrated projection data involves the use of at least one calibration feature of a predetermined size and/or geometry, which is reproduced in the X-ray-image.

### Claim 3 (depends on 2)

The method of claim 2, wherein at least one calibration feature is disposed anterior to the patient's pelvis and at least one calibration feature is disposed posterior to the patient's pelvis.

### Claim 4 (depends on 1)

The method of claim 1, wherein the determining calibrated projection data comprises:
acquiring source-distance data describing the distance between the X-ray-source and the calibration plane; and
acquiring anterior-posterior-distance data describing the distance of each of the plurality of pelvic landmarks to the calibration plane in the anterior-posterior direction.

### Claim 5 (depends on 4)

The method of claim 4, wherein:
predefined values are set for the anterior-posterior-distances of the plurality of pelvic landmarks, or
wherein the acquiring anterior-posterior-distance data comprises:
matching a three-dimensional pelvis model acquired from an anatomical atlas to the two-dimensional X-ray-image, the model specifying the position of the plurality of pelvic landmarks; and
identifying, based on the three-dimensional pelvis model, statistical values for the anterior-posterior-distances of the plurality of pelvic landmarks to the calibration plane in the anterior-posterior direction.

### Claim 6 (depends on 1)

The method of claim 1, wherein the determining calibrated projection data comprises:
acquiring reference distance data describing the distance in the anterior-posterior direction of each of the plurality of pelvic landmarks to at least one of:
an anterior reference plane defined by the at least one calibration feature disposed anterior to the patient's pelvis; and
a posterior reference plane defined by the at least one calibration feature disposed posterior to the patient's pelvis;
acquiring plane distance data describing the distance in the anterior-posterior direction of the calibration plane to at least one of the anterior reference plane and the posterior reference plane; and
determining, based on the reference distance data and the plane distance data, anterior-posterior-distance data describing the distance of each of the plurality of pelvic landmarks to the calibration plane in the anterior-posterior direction.

### Claim 7 (depends on 1)

The method of claim 1, wherein the determining position data comprises:
matching a three-dimensional pelvis model acquired from an anatomical atlas to the two-dimensional X-ray-image, the three-dimensional pelvis model specifying the position of the plurality of pelvic landmarks; and
identifying, based on the three-dimensional pelvis model, the position of the plurality of pelvic landmarks within the two-dimensional X-ray-image.

### Claim 8 (depends on 1)

The method of claim 1, wherein the at least one first pelvic landmark and the at least one second pelvic landmark are selected from the group consisting of:
left anterior superior iliac spine, right anterior superior iliac spine;
left iliosacral joint, right left iliosacral;
left lateral foramen point, right lateral foramen point;
cranial edge of pubic symphysis; and
center of rotation of left acetabulum, center of rotation of right acetabulum.

### Claim 9 (depends on 1)

The method of claim 1, wherein the at least one of the medial-lateral distance and the cranial-caudal distance between the at least one first pelvic landmark and the at least one second pelvic landmark are selected from the group consisting of:
medial-lateral distance between left anterior superior iliac spine and right anterior superior iliac spine;
medial-lateral distance between iliosacral joint and line connecting anterior superior iliac spines;
cranial-caudal distance between center of rotation of left or right acetabulum and line connecting anterior superior iliac spines;
cranial-caudal distance between center of rotation of left or right acetabulum and intersection point of midsagittal plane and line connecting left lateral foramen point and right lateral foramen point;
medial-lateral distance between center of rotation of left or right acetabulum and midsagittal plane of patient; and
cranial-caudal distance between center of rotation of left or right acetabulum and cranial edge of pubic symphysis.

### Claim 10 (depends on 1)

The method of claim 1, wherein the two-dimensional X-ray-image shows the patient's pelvis of the patient taking a standing posture.

### Claim 11 (depends on 1)

The method of claim 1, wherein the regression data is based on measurements acquired from a plurality of reference patients, wherein for each one of the reference patients, a correspondence between a pelvic sagittal rotation and at least one of a medial-lateral distance and a cranial-caudal distance between the at least one first pelvic landmark and the at least one second pelvic landmark within the calibration plane is described.

### Claim 12 (depends on 1)

The method of claim 1, wherein the sagittal rotation of the patient's pelvis defines the angle between the coronal plane of the patient and an AAC-plane containing the left anterior superior iliac spine, the right anterior superior iliac spine, and at least one of the center of rotation of the left acetabulum and the center of rotation of the right acetabulum.

### Claim 13 (depends on 12)

The method of claim 12, wherein the determined AAC-plane is passed on, for further use as a reference basis, to a registration procedure for surgery.

### Claim 14

A system for determining a sagittal rotation of a patient's pelvis, comprising:
a computer configured to:
acquire image data describing a two-dimensional X-ray-image of the patient's pelvis made in an anterior-posterior direction;
determine, based on the image data, position data describing the position of a plurality of pelvic landmarks reproduced in or derivable from the two-dimensional X-ray-image;
acquire calibration data describing the position of a calibration plane with respect to the patient's pelvis, the calibration plane being perpendicular to the anterior-posterior direction;
determine, based on the position data and the calibration data, calibrated projection data describing a two-dimensional projection representing the plurality of pelvic landmarks of the actual patient's pelvis being projected into the calibration plane in the anterior-posterior direction;
acquire distance data describing at least one of a medial-lateral distance and a cranial-caudal distance between at least one first pelvic landmark and at least one second pelvic landmark in the calibrated two-dimensional projection;
acquire, from a database, regression data describing a linear correspondence between at least one of said medial-lateral distances and cranial-caudal distances, and a pelvic sagittal rotation; and
determine, based on the distance data and the regression data, the sagittal rotation of the patient's pelvis.

### Claim 15 (depends on 14)

The system of claim 14, wherein the determining calibrated projection data involves the use of at least one calibration feature of a predetermined size and/or geometry, which is reproduced in the X-ray-image.

### Claim 16 (depends on 15)

The system of claim 15, wherein at least one calibration feature is disposed anterior to the patient's pelvis and at least one calibration feature is disposed posterior to the patient's pelvis.

### Claim 17 (depends on 14)

The system of claim 14, wherein the determining calibrated projection data comprises:
acquiring source-distance data describing the distance between the X-ray-source and the calibration plane; and
acquiring anterior-posterior-distance data describing the distance of each of the plurality of pelvic landmarks to the calibration plane in the anterior-posterior direction.

### Claim 18 (depends on 14)

The system of claim 14, wherein the determining calibrated projection data comprises:
acquiring reference distance data describing the distance in the anterior-posterior direction of each of the plurality of pelvic landmarks to at least one of:
an anterior reference plane defined by the at least one calibration feature disposed anterior to the patient's pelvis; and
a posterior reference plane defined by the at least one calibration feature disposed posterior to the patient's pelvis;
acquiring plane distance data describing the distance in the anterior-posterior direction of the calibration plane to at least one of the anterior reference plane and the posterior reference plane;
determining, based on the reference distance data and the plane distance data, anterior-posterior-distance data describing the distance of each of the plurality of pelvic landmarks to the calibration plane in the anterior-posterior direction.

### Claim 19 (depends on 14)

The system of claim 14, wherein the determining position data comprises:
matching a three-dimensional pelvis model acquired from an anatomical atlas to the two-dimensional X-ray-image, the three-dimensional pelvis model specifying the position of the plurality of pelvic landmarks; and
identifying, based on the three-dimensional pelvis model, the position of the plurality of pelvic landmarks within the two-dimensional X-ray-image.

### Claim 20

A non-transitory computer readable storage medium storing a computer program for determining a sagittal rotation of a patient's pelvis which, when running on a computer or loaded onto the computer, causes the computer to:
acquire image data describing a two-dimensional X-ray-image of the patient's pelvis made in an anterior-posterior direction;
determine, based on the image data, position data describing the position of a plurality of pelvic landmarks reproduced in or derivable from the two-dimensional X-ray-image;
acquire calibration data describing the position of a calibration plane with respect to the patient's pelvis, the calibration plane being perpendicular to the anterior-posterior direction;
determine, based on the position data and the calibration data, calibrated projection data describing a two-dimensional projection representing the plurality of pelvic landmarks of the patient's pelvis being projected into the calibration plane in the anterior-posterior direction;
acquire distance data describing at least one of a medial-lateral distance and a cranial-caudal distance between at least one first pelvic landmark and at least one second pelvic landmark in the calibrated two-dimensional projection;
acquire, from a database, regression data describing a linear correspondence between at least one of said medial-lateral distances and cranial-caudal distances, and a pelvic sagittal rotation; and
determine, based on the distance data and the regression data, the sagittal rotation of the patient's pelvis.