EP-4740181-A1 - COMPUTER-IMPLEMENTED METHOD FOR CORRECTING ARTEFACTS DUE TO ELECTROMAGNETIC DISTURBANCES CAUSED IN X-RAY PROJECTION IMAGES

Abstract

The present invention relates to computer-implemented methods for correcting artefacts in x-ray projection images caused by electromagnetic disturbances on an x-ray detector (4) and for generating a corrected three-dimensional volume image or a corrected tomosynthesis based image or a corrected cephalometric image of a patient based on the artefact corrected projection images.

Inventors

• BACHMANN, OLIVER
• Eichner, Stefan

Assignees

• SIRONA Dental Systems GmbH
• DENTSPLY SIRONA Inc.

Dates

Publication Date

20260513

Application Date

20240703

Claims (4)

1. 1. Computer-implemented method for correcting artefacts in x-ray projection images caused by electromagnetic disturbances on an x-ray detector (4) and for generating a corrected three-dimensional volume image or a corrected tomosynthesis based image or a corrected cephalometric image of a patient, comprising the steps of: providing (SI 00) one or more projection images by means of an x-ray source (3), an x-ray collimator and the x-ray detector (4); characterized by further comprising the steps of: determining (S300) for each projection image the spatial components corresponding to the artefacts in the two-dimensional spatial domain respectively, wherein the spatial components corresponding to the artefacts are determined in one or more separate regions (Rl, R2) of the projection image which has been obscured by the x-ray collimator; suppressing (S400) the artefacts by subtracting the determined spatial components corresponding to the artefact from the corresponding projection image to obtain an artefact corrected projection image, wherein in the suppressing step (S400) the determined artefacts are subtracted at least from one or more regions (Rl', R2') in the corresponding projection image which has not been obscured by the x-ray collimator; reconstructing (S600) a corrected three-dimensional volume image or a corrected tomosynthesis based image or a corrected ceph image based on the artefact corrected projection images.
2. 2. The computer-implemented method according to claim 1, characterized in that in the determining step (S300) the spatial components corresponding to the artefacts determined in said one or more separate regions (Rl, R2) are weighted, and in the subtracting step (S400) the said weighted artefacts are subtracted at least from one or more regions (Rl', R2') in the corresponding projection image which has not been obstructed by the x-ray collimator.
3. 3. A computer program comprising computer-readable code which, when executed by a computer-assisted x-ray imaging system (1), causes said system (1) to perform the method of any one of the preceding claims.
4. 4. A computer-assisted x-ray imaging system (1) comprising a computing unit (8) configured to execute the computer program according to claim 3.

Description

COMPUTER-IMPLEMENTED METHOD FOR CORRECTING ARTEFACTS DUE TO ELECTROMAGNETIC DISTURBANCES CAUSED IN X-RAY PROJECTION IMAGES TECHNICAL FIELD OF THE INVENTION The present invention relates to methods and systems for x-ray imaging of patients in the dental field. The present invention more particularly relates to extraoral x-ray imaging in which artefacts due to electromagnetic disturbances caused in x-ray projection images are suppressed in the reconstruction of three-dimensional (3D) volume images, tomosynthesis based images (panoramic images), and/or cephalometric (ceph) images. BACKGROUND ART OF THE INVENTION Volume images, tomosynthesis based images such as panoramic images, and ceph images are among the standard imaging procedures of all extraoral dental radiographic examinations. Volume images, tomosynthesis based images, and ceph images provide the dentist with information about the patient's dental condition. These images are used by dentists to diagnose problem cases and prepare for treatment. Generally, an extraoral x-ray imaging system has an x-ray source and an x-ray detector that are rotated around the patient's head during the x-ray imaging. The trajectory of the x-ray source and the x-ray detector during the imaging can describe various paths. During the rotation, the x-ray detector acquires x-ray projection images of the patient. The panoramic image is generally reconstructed from the x-ray projection images using standard techniques such a shift-and-add or other techniques known to those skilled in the art. A panoramic image shows the structures located in a physical layer to be sharply viewed within the patient's jaw. The Volume image is generally reconstructed from the x-ray projection images using a standard technique such as the filtered back projection algorithm (e.g., the Feldkamp algorithm). The cheph image can be generated from the volume image. Alternatively, a separate x-ray detector on a cantilever arm can be used for generating a ceph image. Ambient electromagnetic fields can adversely affect the proper functioning of the x-ray detector, its electrical components, and cabling, so that the acquired x-ray projection images may contain image artefacts due to the electromagnetic disturbances. These image artefacts may lead to misdiagnosis and incorrect therapies, which must, however, be avoided accordingly. SUMMARY OF THE INVENTION The inventors are not aware of any prior art technique in which the image artefacts due to electromagnetic disturbances are determined in a frequency domain of the Fourier transformed x-ray projections images, and then subsequently suppressed in the frequency domain or, alternatively, in the spatial domain accordingly to obtain artefact-corrected x- ray projection images for the reconstruction of a corrected three-dimensional volume image or a corrected tomosynthesis based image or a corrected ceph image. Furthermore, the inventors are also not aware of any prior art technique in which the image artefacts due to electromagnetic disturbances are determined at least in a region of the x- ray projection image which has been obscured by the x-ray collimator (i.e., unexposed region of the acquired projection image), and subsequently suppressed in the spatial domain accordingly to obtain artefact-corrected x-ray projection images for the reconstruction of a corrected three-dimensional volume image or a corrected tomosynthesis based image or a corrected ceph image. An objective of the present invention is to provide computer-implemented methods for reducing image artefacts in dental volume images and/or dental tomosynthesis based images and/or ceph images caused by electromagnetic interferences. A further objective of the present invention is to provide an extraoral x-ray imaging system that performs the methods according to the present invention. These objectives have been achieved by the computer-implemented methods as defined in claim 1, and the x-ray imaging system as defined in claim 4. The subject-matters of the dependent claims define further developments and preferred embodiments. The methods according to the present invention are computer-implemented methods and are each used to correct artefacts in x-ray projection images caused by electromagnetic disturbances on an x-ray detector. These methods are respectively used to generate a corrected three-dimensional volume image or a corrected tomosynthesis based image or a corrected ceph image of a patient. According to a first aspect of the present invention the image artefacts due to electromagnetic disturbances are determined in a two-dimensional frequency domain of the Fourier transformed x-ray projections images, and then suppressed in the frequency domain. According to this first aspect of the present invention the method comprises the steps of: providing one or more projection images by means of an x-ray source, an x-ray collimator and the x-ray detector, wherein each projection image is a two-dimensi