Calibration of 2D images for digital templating using monomarker
Inventors
Assignees
Smith and Nephew Orthopaedics AG • Smith and Nephew Asia Pacific Pte Ltd • Smith and Nephew Inc
Publication Number
US-12303340-B2
Publication Date
2025-05-20
Expiration Date
2041-11-11
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Abstract
A method of calibrating a frontal 2D image of a pelvis of a patient is disclosed. Frontal and lateral 2D images are received, where a fiducial marker is positioned on the patient's suprapubic region during image capture. A first distance of the fiducial marker from the imaging detector is determined based on the fiducial marker's measured diameter in the frontal image. A second distance of the fiducial marker from a coronal plane of the pelvis is determined based on the fiducial marker's measured diameter in the lateral image. The second distance is corrected based on a rotational offset of the patient in the lateral image. A third distance of the coronal plane from the imaging detector in the frontal image is determined from the first distance and corrected second distance. A calibration factor for the frontal image is calculated from the third distance and used to scale the frontal image.
Core Innovation
The invention provides a system and method for calibrating frontal 2D images of a pelvis using a single fiducial marker (monomarker) positioned on the patient’s suprapubic region. The system receives frontal and lateral 2D images where the fiducial marker is visible in both images. The marker’s diameter is measured in the frontal and lateral images to determine its respective distances from the imaging detector and from the coronal plane of the pelvis.
The technique addresses significant challenges encountered with conventional calibration, such as discomfort to patients who must lie on rigid plates, the need for highly precise placement of multiple fiducial markers, and errors arising from misplacement, projectional effects, and rotational offsets. Existing systems often rely on multiple markers and complicated setups that can distort or inaccurately scale the captured images, particularly if fiducial markers are not properly aligned with key anatomical planes and the imaging beam.
Key to the core innovation is a computational correction step: after measuring the marker’s diameters, the system calculates the marker-to-detector and marker-to-coronal-plane distances. The system corrects the marker-to-plane distance for patient rotational offset visible in the lateral image (using factors such as hip-to-hip distances and marker lateral offsets). With these corrections, a calibration factor is determined, and the frontal image is scaled accurately for digital templating using only a single marker in a patient-friendly, repeatable way.
Claims Coverage
The patent contains three independent claims, which together define the inventive system and method for calibrating 2D pelvic images using a single suprapubic fiducial marker and algorithmic corrections for accurate scaling.
System for single-fiducial calibration and digital scaling of 2D pelvic images
A calibration system that uses a calibration device comprising a base positioned proximate to the patient's suprapubic region and a single fiducial marker coupled to this base. The system includes at least one processor and a computer-readable medium with instructions to: - Receive both frontal and lateral 2D images of the pelvis, each including the single fiducial marker. - Measure the diameters of the marker’s representation in both images. - Determine, from these diameters and the known marker size, the first distance (from marker to imaging detector), second distance (from marker to pelvic coronal plane), and modify the second distance based on patient rotational offset in the lateral image. - Compute a third distance (coronal plane to imaging detector), a calibration factor, and scale the frontal image accordingly. - Output the scaled frontal 2D image to a storage device.
Computer-implemented method for monomarker-based calibration using frontal and lateral pelvic images
A method comprising: 1. Receiving frontal and lateral 2D images with a suprapubic single fiducial marker. 2. Measuring marker diameters in both images. 3. Determining the marker-to-detector and marker-to-coronal-plane distances from these measurements and the known marker size. 4. Modifying the second distance based on rotational offset (including steps such as measuring lateral offset, calculating rotational angle using hip distances, determining adjustment distance, and adjusting for directionality). 5. Calculating the third distance (coronal plane to detector), deriving a calibration factor, and applying scaling to the frontal 2D image. 6. Outputting the resulting scaled image to storage.
System for fiducial-based calibration with rotational correction for accurate image scaling
A processor-based system that: - Receives frontal and lateral 2D pelvic images with the fiducial marker positioned on the suprapubic region. - Measures the marker’s diameter in both images. - Determines the marker’s distances from the imaging detector and coronal plane, incorporating rotational offset calculations in the lateral image. - Computes and applies a calibration factor to scale the frontal image, outputting the corrected image to computer-readable storage.
The inventive features collectively support a calibration system and method using a single suprapubic fiducial marker, image-based measurement of anatomical distances, correction for rotational effects, and a computation workflow for obtaining an accurate scaling factor for frontal pelvic images. These are claimed as both a system and a computer-implemented method.
Stated Advantages
Provides more comfortable and less invasive calibration by requiring only a single fiducial marker, allowing patients to be positioned on standard cushions without rigid plates.
Facilitates accurate scaling of 2D images by correcting for projectional and rotational effects, even with variations in fiducial marker placement.
Reduces reliance on precise technical skill from imaging technicians, as the system can correct for placement and orientation errors computationally.
Enables increased accuracy in digital templating for preoperative planning by producing accurately scaled representations of patient anatomy for use in surgical and implant planning workflows.
Documented Applications
Calibration and scaling of 2D pelvic images for digital templating in orthopedic surgical planning, including hip arthroplasty and other surgical interventions such as arthroscopic procedures, spinal procedures, maxillofacial procedures, rotator cuff procedures, and ligament repair and replacement.
Use of the scaled 2D images for anatomy modeling, digital templating, selection, and design of implants.
Generation of patient-specific 3D bone models from multiple accurately scaled 2D images for use in further surgical planning and simulation.
Integration with preoperative planning and simulation systems for optimizing implant orientation and surgical outcomes.
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