EP-4742163-A1 - CT IMAGING METHOD AND APPARATUS, AND CBCT DEVICE

EP4742163A1EP 4742163 A1EP4742163 A1EP 4742163A1EP-4742163-A1

Abstract

The present disclosure provides a CT imaging method, an apparatus, and a CBCT device. The method comprises: performing several scans on an object to be scanned and obtaining one set of projection images respectively for each scan of the several scans; performing a backprojection weighting on several projection images at the same scan angle after obtaining at least two sets of projection images, or performing the backprojection weighting on the projection images obtained at a current scan angle during each scan, to obtain weighted projection data; and obtaining volume data of the object based on the weighted projection data.

Inventors

YU, Wenrui
MA, JUNQI
XU, RAN
LIU, Zhe
CAI, Yunyan
Guan, Xianjin

Assignees

Yofo (Hefei) Medical Technology Co., Ltd.

Dates

Publication Date: 20260513
Application Date: 20231220

Claims (20)

A CT imaging method, characterised in that the method comprises: performing several scans on an object to be scanned and obtaining one set of projection images respectively for each scan of the several scans, the several scans comprise N circular scans and M helical scans with N≥2 and N>M≥1, the several scans respectively correspond to scan layers at different axial positions, and the scan layer of the helical scans is adjacent only to the scan layer of the circular scans; performing a backprojection weighting on several projection images at the same scan angle after obtaining at least two sets of projection images, or performing the backprojection weighting on the projection images obtained at a current scan angle during each scan, to obtain weighted projection data, wherein the at least two sets of projection images comprise the projection images obtained from one circular scan and one helical scan, the scan layer of the one circular scan are axially adjacent to the scan layer of the one helical scan; and obtaining volume data of the object based on the weighted projection data.
The CT imaging method of claim 1, characterised in that during each scan of the several scans, the scan angle is changed by controlling a scanning device to rotate around the object.
The CT imaging method of claim 1, characterised in that in a scanning device used for scanning the object, a detector is offset-installed relative to an X-ray source.
The CT imaging method of claim 1, characterised in that during the circular scans, an axial position of the scanning device remains unchanged, while during the helical scans, the axial position of the scanning device changes unidirectionally along an axial direction.
The CT imaging method of claim 1, characterised in that M is equal to N-1, and the scan layers of the circular scans and the scan layers of the helical scans are alternately distributed in an axial direction.
The CT imaging method of claim 5, characterised in that M is equal to 1.
The CT imaging method of claim 1, characterised in that when performing the several scans on the object, the object is scanned sequentially according to an axial position distribution of the scan layers of the serval scans.
The CT imaging method of claim 7, characterised in that when two adjacent scan layers correspond to different scan ways, an earlier-executed scan of two scans corresponding to the two adjacent scan layers is designated as a prior scan, and the other scan of the two scans is designated as a subsequent scan, after completing the prior scan, a first helical motion is performed by controlling a scanning device, and after completing the first helical motion, the subsequent scan is performed.
The CT imaging method of claim 8, characterised in that an axial travel distance of the first helical motion is not less than a height of a cone angle deficiency at an outermost edge of a scanning field of view of two adjacent circular scans of the subsequent scan.
The CT imaging method of claim 7, characterised in that performing a backprojection weighting on several projection images at the same scan angle after obtaining at least two sets of projection images comprises: designating, according to a scanning sequence, two circular scans adjacent to the helical scan as a first circular scan and a second circular scan respectively, for each scan angle of the second circular scan, when obtaining a projection image at a current scan angle of the second circular scan, performing the backprojection weighting based on the projection images at the current scan angle obtained from the helical scan, the first circular scan, and the second circular scan.
The CT imaging method of claim 10, characterised in that during the helical scan and the first circular scan, the projection images obtained from the helical scan and the first circular scan are cached.
The CT imaging method of claim 10, characterised in that performing the backprojection weighting based on the projection images at the current scan angle obtained from the helical scan, the first circular scan, and the second circular scan comprises: performing the backprojection weighting on the projection images at the current scan angle obtained from the first circular scan and the helical scan to obtain a first weighted result; performing the backprojection weighting on the projection images at the current scan angle obtained from the helical scan and the second circular scan to obtain a second weighted result; and negating the projection image of the helical scan to obtain a negated image.
The CT imaging method of claim 7, characterised in that performing the backprojection weighting on the projection images obtained at a current scan angle during each scan comprises: for each scan angle in a current scan, obtaining a projection image at the current scan angle as a current projection image; obtaining backprojection geometry parameters at the current scan angle for a scan task associated with the current scan, wherein a scan way of the scan task is different from a scan way of the current scan, the scan layer of the scan task is adjacent to the scan layer of the current scan, and the backprojection geometry parameters are pre-obtained based on geometric relationships between components of a scanning device; and performing the backprojection weighting based on the backprojection geometry parameters, the current projection image, and a corresponding zero-value image having the same size as the current projection image, to obtain a weighted result.
The CT imaging method of claim 13, characterised in that when several scan tasks are associated with the current scan, the backprojection geometry parameters at the current scan angle are obtained for each scan task respectively, and the backprojection weighting is performed respectively based on the backprojection geometry parameters, the current projection image, and the corresponding zero-value image, to obtain the weighted result.
The CT imaging method of claim 14, characterised in that when the several scan tasks are associated with the current scan, during performing the backprojection weighting based on the backprojection geometry parameters, the current projection image, and the corresponding zero-value image, a negated image is also obtained by taking the negative of the current projection image of the current scan.
The CT imaging method of claim 1, characterised in that a way for performing the backprojection weighting on the projection images comprises: taking spatial points that have projection points in a ray reception area at the corresponding scan angle in two images to be backprojection weighted as first spatial points; for each of the first spatial points, calculating a backprojection value of the first spatial point based on positions of the projection points of the first spatial point in the two images and a height of the ray reception area, wherein one of the two images is a projection image and the other image is either a projection image or a zero-value image.
The CT imaging method of claim 16, characterised in that the two images include a first image A and a second image B, and the backprojection value S of the first spatial point is calculated by the following formula: S = A u a ν a ν a + B u b ν b H − ν b H − ν b + ν a , where A ( u a , v a ) is a projection value of a projection point of the first spatial point on the first image A, B ( u a , v a ) is a projection value of a projection point of the first spatial point on the second image B, u a and v a are a horizontal coordinate and a vertical coordinate respectively of the projection point of the first spatial point on the first image A, u b and v b are a horizontal coordinate and a vertical coordinate respectively of the projection point of the first spatial point on the second image B, and H is the height of the ray reception area.
The CT imaging method of claim 1, characterised in that when performing the backprojection weighting on the projection images, the method further comprises: taking spatial points that do not have projection points on two images being backprojection weighted as second spatial points; for each of second spatial points, determining a nearest point in an axial direction to the second spatial point as a substitute projection point.
The CT imaging method of claim 1, characterised in that after obtaining the volume data of the object, the method further comprises: in a simulation projection step, performing a simulation projection on the volume data at each scan angle of the helical scan to obtain a simulation image, wherein a region range of the projection image is contained within a region range of the simulation image, and a height of the simulation image is greater than a height of the projection image; replacing an overlapping region between the simulation image and the projection image with the projection image at the corresponding scan angle; reconstructing based on the replaced simulation image and projection images of the circular scans adjacent to the helical scans in scanning sequence, to obtain new volume data; and substituting the new volume data into the simulation projection step until predetermined requirements are met.
A CT imaging apparatus, characterised in that the apparatus comprises: a memory storing execution instructions; and a processor executing the execution instructions stored in the memory to perform the CT imaging method of claim 1.

Description

TECHNICAL FIELD The present disclosure relates to a CT imaging method, an apparatus, and a CBCT device. BACKGROUND During a measurement of a CBCT (Cone Beam CT) device, an X-ray source and a detector are controlled to rotate around a patient's head to complete scanning. To increase a field of view in an axial direction, a dual-source single-detector system can be employed to expand the axial field of view. A dual-source single-detector system having two X-ray sources and one detector is used to increase the field of view in the axial direction. The two X-ray sources are arranged in the axial direction and alternately emit the X-rays. However, due to limitations of a cone angle and a detector dimension, an axial separation between the two X-ray sources should be set to a relatively small value, making it difficult for the axial field of view expansion capability to meet requirements, which significantly restricts the expansion capability of the field of view. SUMMARY The present disclosure provides a CT imaging method, an apparatus, and a CBCT device. In a first aspect, the present disclosure provides a CT imaging method, comprising: performing several scans on an object to be scanned and obtaining one set of projection images respectively for each scan of the several scans, the several scans comprise N circular scans and M helical scans with N≥2 and N>M≥1, the several scans respectively correspond to scan layers at different axial positions, and the scan layer of the helical scans is adjacent only to the scan layer of the circular scans; performing a backprojection weighting on several projection images at the same scan angle after obtaining at least two sets of projection images, or performing the backprojection weighting on the projection images obtained at a current scan angle during each scan, to obtain weighted projection data, wherein the at least two sets of projection images comprise the projection images obtained from one circular scan and one helical scan, the scan layer of the one circular scan are axially adjacent to the scan layer of the one helical scan; and obtaining volume data of the object based on the weighted projection data. In a second aspect, the present disclosure provides a CT imaging apparatus, comprising: a memory storing execution instructions; and a processor executing the execution instructions stored in the memory to perform the aforementioned CT imaging method. In a third aspect, the present disclosure provides a CBCT device, comprising: an X-ray source emitting X-rays to irradiate a head of an object; a detector being arranged opposite to the X-ray source and receiving the X-rays; a support arm fixing the X-ray source and the detector, wherein the support arm, the X-ray source, and the detector form a laterally open shape, and the lateral open shape allowing the head to be inserted into the lateral open shape from a lateral direction of the CBCT device; a driving device supporting and rotating the support arm, thereby causing the X-ray source and the detector to rotate; and the aforementioned CT imaging apparatus for obtaining dental images of the object based on the X-rays received by the detector, wherein the CBCT device is configured to allow measurement in a sitting position mode or a lying/prone position mode; in the sitting position mode, the head of the object is positioned inside the lateral open shape in a sitting posture; in the lying/prone position mode, the head of the object is positioned inside the lateral opening shape in a lying/prone posture. BRIEF DESCRIPTION OF DRAWINGS The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure. These drawings are included to provide further understanding of the present disclosure and form a part of this specification. Fig. 1 is a flowchart schematic diagram of a CT imaging method of large field of view according to an embodiment of the present disclosure.Fig. 2 is a flowchart schematic diagram of a method for weighting projection images according to an embodiment of the present disclosure.Fig. 3 is a flowchart schematic diagram of a method for weighting projection images according to an embodiment of the present disclosure.Fig. 4 is a flowchart schematic diagram of a method for weighting projection images according to an embodiment of the present disclosure.Fig. 5 is a schematic diagram of an axial longitudinal cross-section showing effective fields of view for several circular scans.Fig. 6 is a flowchart schematic diagram of a method for supplementing cone angle deficiency according to an embodiment of the present disclosure.Fig. 7 is a flowchart schematic diagram of a method for supplementing cone angle deficiency according to an embodiment of the present disclosure.Fig. 8 is a schematic diagram of a CT imaging apparatus implemented with a processing system hardware according to an embodiment of the present disclos