CN106683142B - Dynamic pitch CT image reconstruction method and device - Google Patents
Dynamic pitch CT image reconstruction method and device Download PDFInfo
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- CN106683142B CN106683142B CN201611235824.2A CN201611235824A CN106683142B CN 106683142 B CN106683142 B CN 106683142B CN 201611235824 A CN201611235824 A CN 201611235824A CN 106683142 B CN106683142 B CN 106683142B
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G06T11/00—2D [Two Dimensional] image generation
- G06T11/003—Reconstruction from projections, e.g. tomography
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- A61B6/00—Apparatus for radiation diagnosis, e.g. combined with radiation therapy equipment
- A61B6/02—Devices for diagnosis sequentially in different planes; Stereoscopic radiation diagnosis
- A61B6/03—Computerised tomographs
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B6/00—Apparatus for radiation diagnosis, e.g. combined with radiation therapy equipment
- A61B6/52—Devices using data or image processing specially adapted for radiation diagnosis
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- G06—COMPUTING; CALCULATING OR COUNTING
- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G06T2207/00—Indexing scheme for image analysis or image enhancement
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- G06T2207/10072—Tomographic images
- G06T2207/10081—Computed x-ray tomography [CT]
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- G06T2211/40—Computed tomography
- G06T2211/416—Exact reconstruction
Abstract
The embodiment of the invention provides a dynamic pitch CT image reconstruction method and a device, wherein the method comprises the following steps: rearranging the cone beam into a parallel beam; determining the focal point position information of the parallel beam according to the focal point position information of the cone beam and the position deviation information of the scanning bed; determining at least one PI ray according to the focal point position information of the parallel beam and the position information of the target voxel point; and obtaining a target CT image according to the at least one PI ray and a back projection reconstruction algorithm. By adopting the technical scheme, all PI rays contributing to the target voxel point to be reconstructed can be found out according to the rearranged focal point position information and the position information of the target voxel point, so that the CT value of the target CT image obtained by reconstruction is more uniform, and the quality of the reconstructed image is greatly improved.
Description
Technical Field
The embodiment of the invention relates to the technical field of medical image processing, in particular to a dynamic pitch CT image reconstruction method and device.
Background
With the progress of the technology, the CT scanning mode and the imaging method are also continuously improved, the three-dimensional cone-beam CT has become the mainstream of research and application, the CT scanning has been widely applied in the fields of medical clinical, safety inspection, nondestructive testing and the like, especially in the medical clinical diagnosis, the CT scanning has become one of the indispensable inspection means, and the CT scanning imaging technology is a key link for determining whether the inspection result is accurate. The current CT scanning imaging technology generally performs CT image reconstruction based on CT scan data by spirally moving a CT device around a scanned object, emitting rays through a bulb, and receiving projection data, i.e. CT scan data, passing through the scanned object by a detector row.
The existing helical reconstruction algorithm generally selects the beams in a certain scanning range of the current beams according to a fixed helical pitch for normalization processing, but some clinical applications need to use a dynamic helical pitch scanning technology, such as dynamic perfusion, that is, in the process of helical movement, the moving speed of a scanning bed along a Z axis is not fixed, so that the helical pitch of some scanning positions is larger, and the helical pitch of some scanning positions is smaller. The existing method calculates the beam information required by a certain voxel to be reconstructed in a scanning object based on a fixed screw pitch, if the current beam is at a position with a larger screw pitch, when the beam passing through the voxel is searched, the search range may be set too large, and the beam without contribution to the voxel to be reconstructed is normalized; similarly, if the current beam is at a position with a small pitch, the search range may be too small to normalize all beams passing through the voxel to be reconstructed, thereby affecting the reconstruction effect of the CT image.
Disclosure of Invention
In view of this, embodiments of the present invention provide a method and an apparatus for reconstructing a dynamic pitch CT image, so as to solve the technical defect that a CT value of a CT image obtained by an existing spiral CT reconstruction algorithm is not uniform.
In a first aspect, an embodiment of the present invention provides a method for reconstructing a dynamic pitch CT image, including:
rearranging the cone beam into a parallel beam;
determining the focal point position information of the parallel beam according to the focal point position information of the cone beam and the position deviation information of the scanning bed;
determining at least one PI ray according to the focal point position information of the parallel beam and the position information of the target voxel point;
and obtaining a target CT image according to the at least one PI ray and a back projection reconstruction algorithm.
In a second aspect, an embodiment of the present invention further provides an apparatus for reconstructing a dynamic pitch CT image, including:
a rebinning module for rebinning the cone beam into a parallel beam;
the focal point position determining module is used for determining the focal point position information of the parallel beam according to the focal point position information of the cone beam and the position deviation information of the scanning bed;
the PI ray determining module is used for determining at least one PI ray according to the focal point position information of the parallel beams and the position information of the target voxel point;
and the reconstruction module is used for obtaining a target CT image according to the at least one PI ray and the back projection reconstruction algorithm.
According to the technical scheme provided by the embodiment of the invention, after the cone beam is rearranged into the parallel beam, all focus position information obtained after rearrangement is determined, then at least one PI ray is determined according to the focus position information after rearrangement and the position information of the target voxel to be reconstructed, and the back projection image reconstruction is carried out according to the selected PI ray to obtain the target CT image. By adopting the technical scheme, all PI rays contributing to the target voxel point to be reconstructed can be found out according to the rearranged focal point position information and the position information of the target voxel point, so that the CT value of the target CT image obtained by reconstruction is more uniform, and the quality of the reconstructed image is greatly improved.
Drawings
FIG. 1a is a schematic structural diagram of a spiral CT scanning apparatus according to an embodiment of the present invention;
FIG. 1b is a schematic partial structure diagram of a spiral CT scanning apparatus to which the present invention is applied;
fig. 1c is a schematic flowchart of a dynamic pitch CT image reconstruction method according to an embodiment of the present invention;
FIG. 1d is a schematic diagram illustrating a beam rebinning principle according to an embodiment of the present invention;
FIG. 1e is a schematic view of a rearranged beam focus distribution according to an embodiment of the present invention;
fig. 1f is a schematic diagram illustrating comparison of reconstruction effects according to a first embodiment of the present invention;
fig. 2 is a schematic flowchart of a dynamic pitch CT image reconstruction method according to a second embodiment of the present invention;
fig. 3 is a schematic flow chart of a dynamic pitch CT image reconstruction method according to a third embodiment of the present invention;
fig. 4 is a schematic structural diagram of a dynamic pitch CT image reconstruction apparatus according to a fourth embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting of the invention. It should be further noted that, for the convenience of description, only some of the structures related to the present invention are shown in the drawings, not all of the structures.
Before discussing exemplary embodiments in more detail, it should be noted that some exemplary embodiments are described as processes or methods depicted as flowcharts. Although a flowchart may describe the steps as a sequential process, many of the steps can be performed in parallel, concurrently or simultaneously. In addition, the order of the steps may be rearranged. The process may be terminated when its operations are completed, but may have additional steps not included in the figure. The processes may correspond to methods, functions, procedures, subroutines, and the like.
To clearly describe the technical solution of the embodiment of the present invention, first, a helical CT scanning apparatus and a scanning principle thereof applied to the embodiment of the present invention are described. Fig. 1a is a schematic structural diagram of a spiral CT scanning apparatus suitable for use in the embodiment of the present invention, the apparatus includes a scanning bed and a scanning frame, the scanning frame is provided with a scanner, the scanner is in a ring shape and surrounds the scanning bed, and the scanning bed moves horizontally along the length direction of the scanning bed (the height direction of the person, referred to as the Z axis) at a uniform speed or a variable speed according to the set scanning requirement. While moving horizontally, the inside of the scanner will rotate around the Z-axis, forming a helical scanning trajectory as shown in fig. 1 a. The scanner has the specific structure that the ray emission source and the detector are arranged on the inner wall of the scanner and are symmetrically arranged relative to the Z axis. Referring to FIG. 1b, which is a partial schematic view of a helical CT scanner, the radiation source is typically a bulb, which emits a cone beam. The plurality of detectors are arranged in a matrix form to form a detection plate, the direction parallel to the Z axis on the detection plate is the detector row direction, the direction vertical to the detector row direction is called the detector channel direction, in the figure, an arrow A represents the rotation direction of the bulb, an arrow B represents the rotation direction of the detector, an arrow Z represents the moving direction of the scanning bed, the beam emitted by the bulb penetrates through the body of a patient to be scanned and is received by the opposite detector as scanning projection data, and the scanning track of the scanner moves in a spiral shape, so that the scanning projection data of the beam emitted by the bulb at a plurality of positions can correspond to any one voxel point in the body of the patient. These scan projection data are image reconstructed to form an image of the voxel point in the patient's body. All voxel points in the patient's body are thus processed, a scanned image can be formed for each section of the patient's body. The embodiment of the invention provides a solution for the image reconstruction process of the spiral CT scanning equipment based on the structure.
Example one
Fig. 1c is a schematic flow chart of a dynamic pitch CT image reconstruction method according to an embodiment of the present invention, which is suitable for use in a CT image reconstruction situation, and the method can be executed by a dynamic pitch CT image reconstruction apparatus, where the apparatus can be implemented by software and/or hardware, and can be generally integrated into a CT imaging device. As shown in fig. 1c, the method comprises:
First, all scan projection data of one helical scan are acquired, and during the scan, although the scanner is continuously rotated, the scan data are acquired according to the set sampling frequency. Throughout the scan there is a cone beam emitted by the bulb at each sampling instant, as shown in diagram a of fig. 1d for any instant. As shown in diagram B of fig. 1d, when the bulb is continuously rotated, the cone beam will have scan range coverage. As shown in a diagram C in fig. 1d, the cone beams covered by the scanning range are rearranged into parallel beams according to a plurality of rotations of the bulb, each parallel beam is formed by converging rays in a plurality of cone beams, for example, the parallel beams can be converged according to the angle relationship between the angle of each ray in the cone beam and the angle relationship between the parallel beams, and after the rearrangement, the cone beams emitted by the bulb are rearranged into parallel beams with a certain opening angle.
And 102, determining the focal point position information of the parallel beam according to the focal point position information of the cone beam and the position deviation information of the scanning bed.
Fig. 1e is a schematic diagram of the distribution of the rearranged beams, where the focus is a place where the anode target surface of the bulb is bombarded by the electron beam, and the X-ray is emitted from the area, as shown in fig. 1e, the focus of the cone beam is located on a spiral line relative to the moving track of the scanned object, and the intersection point of the parallel beam and the spiral line is the focus of each parallel beam. The focal point of the primary cone beam is usually one, which may be called the central focal point, and after the beams are rearranged, the focal point of the parallel beams is no longer a fixed focal point, but a series of focal points. The position of the "x" symbol in fig. 1e may indicate the position of each focal point after rearranging the cone beam into parallel beams, and the positional information of the series of focal points of the parallel beams after beam rearranging may be determined from the focal point positional information of the cone beam. The distance in the Z direction between two adjacent circles of helices in the helix in fig. 1e is the pitch, the helix that obtains under static pitch is standard helix, and the pitch is fixed, and the helix under the dynamic pitch is nonstandard helix, and is great at some scanning position pitch promptly, and some scanning position pitch is less, and the pitch is not fixed.
For example, when calculating the position of a certain ray in the parallel beam on the detector, the position information of the focus corresponding to the ray is needed, the position information can be in the form of (x, y, Z) coordinate, and the Z coordinate information of the focus corresponding to the ray in the parallel beam can be determined according to the focus Z coordinate information of the cone beam and the Z direction offset information of the scanning bed.
And 103, determining at least one PI ray according to the focal point position information of the parallel beam and the position information of the target voxel point.
Scanning projection data will generally have a corresponding scanned region, with a target voxel point being any point in the scanned region, which generally corresponds to the portion of the scanned patient's body currently being scanned, between the bulb and the probe plate.
For example, the position information may be coordinate information, and a connection line between the coordinates of each focal point in the parallel beam and the coordinates of the target voxel point is established and an extension line of the connection line is determined as a virtual ray. And calculating the position of the virtual ray in the direction of the detector, and determining at least one PI ray which is effective for image reconstruction according to the position, wherein the ray which can generally fall into the position range of the detection row is an effective ray, and otherwise, the ray is an ineffective ray.
And step 104, obtaining a target CT image according to at least one PI ray and a back projection reconstruction algorithm.
Illustratively, back projection reconstruction is performed according to the projection data corresponding to the at least one PI ray to obtain a target CT image.
According to the technical scheme provided by the embodiment, after the cone beam is rearranged into the parallel beam, all focus position information obtained after rearrangement is determined, at least one PI ray is determined according to the rearranged focus position information and the position information of the target voxel point to be reconstructed, and the back projection image reconstruction is performed according to the selected PI ray to obtain the target CT image. According to the rearranged focal point position information and the position information of the target voxel point, all PI rays contributing to the target voxel point to be reconstructed can be found out, so that the CT value of the target CT image obtained by reconstruction is more uniform, and the quality of the reconstructed image is greatly improved.
Optionally, normalization processing is performed in the back projection reconstruction process according to at least one PI ray, so as to obtain a target CT image.
Illustratively, in the back projection reconstruction process, normalization processing is performed on data acquired by a detector corresponding to the determined at least one PI ray, and a target CT image is reconstructed according to the processed data.
Specifically, a corresponding weight is set for each PI ray, the corresponding weight of the PI ray is usually determined according to the position of the ray in the direction of the detector row, the position on the detector row opposite to the central focus is the central position of the detector row, and the closer the position of the PI ray on the detector row is to the central position, the greater the weight is, and the farther the position is from the central position, the smaller the weight is. Suppose the weight corresponding to each PI ray is [ w ]1，w2，……wN]The corresponding value collected on the detector is [ v ]1，v2，….vN]Then, the normalization process can be performed according to the following formula:
where v is a value of projection data used for reconstructing the target image after the normalization process, and i is 1, 2, 3 … … N.
Fig. 1f is a schematic diagram illustrating comparison of reconstruction effects according to an embodiment of the present invention, where an a diagram in fig. 1f is a CT image obtained by searching for a PI ray with a fixed pitch and performing normalization processing, and a B diagram in fig. 1f is a CT image obtained by searching for a PI ray with a dynamic pitch method according to the embodiment and performing normalization processing.
Example two
Fig. 2 is a flowchart of a dynamic helical pitch CT image reconstruction method according to a second embodiment of the present invention, and this embodiment optimizes "determining the focal position information of the parallel beam according to the focal position information of the fan beam and the position offset information of the scanning bed" based on the first embodiment. As shown in fig. 2, the method includes:
Illustratively, the focal point of the cone beam is centered on the detector, e.g., the detector has 40 channels, the focal point of the cone beam may correspond to the position of channel 20 on the detector, the center channel on the detector being designated as chanl20After the cone beam is rearranged into parallel beams, the focus corresponding to the ray i in the parallel beams is struck to the channel chanl corresponding to the position on the detectoriWherein i is 1, 2, 3 … … 40, according to chanliAnd chanl20Obtaining the channel offset information, e.g. channel offsetThe shift is 20-i.
For example, when performing a helical CT scan, the X-ray emitted by the tube is used to scan the human body to acquire projection data, and the beam information corresponding to each focal point j included in the parallel beam after beam rearrangement can be recorded as viewjThe beam information may include: acquiring information such as data time, acquired projection data, a scanning angle, a Z-axis position and the like, obtaining rearranged X and Y coordinate offset information of a parallel beam focus according to channel offset information, and determining position offset information of a scanning bed, as shown in FIG. 1e, obtaining a view offset M of the parallel beam relative to a cone beam according to a mapping relation between a channel position on a detector and a view, determining a moving time T of the scanning bed according to the view offset, and determining offset information of the scanning bed in a Z direction according to a relation curve of the time and the position of the scanning bed, namely Z coordinate offset of the parallel beam focus shown in FIG. 1e, or directly searching corresponding Z position information of the scanning bed according to the view offset, thereby determining offset information of the scanning bed in the Z direction and obtaining Z coordinate offset information of the parallel beam.
And step 204, determining the focal point position information of the parallel beam according to the focal point position information and the focal point offset information of the cone beam.
Illustratively, the beam rebinned individual focal point position information is derived from the focal point position information of the cone beam and the corresponding X, Y and Z-shift information for each focal point in the rebinned parallel beam.
and step 206, obtaining a target CT image according to at least one PI ray and a back projection reconstruction algorithm.
After the offset of the view is determined, a fixed value is generally determined according to a fixed pitch and multiplied by the offset of the view, so that focal position information of the parallel beam is obtained and used for searching the PI ray, namely the PI ray is calculated and searched by adopting the fixed pitch, so that the searched PI ray is inaccurate, and the reconstruction effect of the image is influenced. According to the technical scheme provided by the embodiment, after the cone beam is rearranged into the parallel beam, view offset information is obtained according to channel offset information of the cone beam and the parallel beam, and accurate Z offset information is determined by combining an actual moving curve of a scanning bed, so that the focal position information of the parallel beam obtained after the beam is rearranged is more accurate, the accuracy of subsequent searching for PI rays is ensured, the algorithm is reliable, the CT value of a target CT image obtained through reconstruction is more uniform, and the quality of the reconstructed image is greatly improved.
EXAMPLE III
Fig. 3 is a schematic flow chart of a dynamic pitch CT image reconstruction method according to a third embodiment of the present invention, in this embodiment, based on the foregoing embodiments, at least one PI ray is determined according to focal point position information of a parallel beam and position information of a target voxel point, and as shown in fig. 3, the method includes:
step 310 rebinning the cone beam into a parallel beam.
And step 320, determining the focal point position information of the parallel beam according to the focal point position information of the cone beam and the position deviation information of the scanning bed.
And step 330, determining at least one PI ray according to the focal point position information of the parallel beam and the position information of the target voxel point.
And 340, obtaining a target CT image according to at least one PI ray and a back projection reconstruction algorithm.
Wherein step 330 comprises:
for example, any one of the parallel beams obtained by rearranging the beams may be selected as an initial beam, which is denoted as view0。
for example, according to the coordinate information of the initial beam corresponding to the focal point and the coordinate information of the target voxel point, a straight line L where the initial beam corresponding to the focal point and the target voxel point are located may be determined in a manner of finding a straight line, and an intersection position of the straight line L and a plane or a curved surface where the detector row is located may be calculated, so as to obtain a position where the initial beam impinges on the detector, i.e., a beam landing position.
for example, the detector row position range refers to a physical position range of the detector row, and may specifically be a coordinate range of positions of the detector row, for example, according to the space coordinate system established in fig. 1e, the coordinate ranges of the positions of all detectors on the detector row are determined, and then it is determined whether the coordinates of the beam falling point are within the coordinate range of the position of the detector.
for example, if the coordinates of the beam drop point are within the coordinate range of the position of the detector, it indicates that the selected initial beam satisfies the PI ray condition, and the selected initial beam is determined as a PI ray. When the helix turns up one turn as shown in FIG. 1e, the scan angle of the ray changes to 2 π, and the initial beam view is obtained0And view0Beam view with 1/2 turns out of phase0+ pi or view0And determining the-PI as a current beam, stopping searching the PI ray if the coordinates of the beam falling point are not in the coordinate range of the position of the detector, and reselecting a new initial beam.
illustratively, will be related to view0View with integer number of turns difference0+2 π or view0Beams corresponding to-2 PI, i.e. even number of PI-rays, and view0+ pi difference integer turn view0+ π +2 π, or with view0View with-pi difference by integer turns0-π-Beams corresponding to 2 PI, namely odd PI rays are respectively updated to be current beams, so that circular calculation can be carried out when PI rays are searched.
336, calculating the position of the ray determined by the focus of the current beam and the target voxel point in the row direction of the detector as the beam falling point position;
illustratively, the process is similar to step 332, with the calculation based on the focal coordinate information corresponding to the current beam.
Optionally, determining the focal point position information of the current beam and the position information of the target voxel point; and calculating the position of the current beam focus and the position of the ray determined by the target voxel point in the row direction of the detector as the beam falling point position according to the focus position information and the position information of the target voxel point.
337, judging whether the beam landing position of the current beam is in the detector row position range, if not, executing 339, and if so, executing 338.
and step 339, ending.
Exemplarily, whether the beam falling point position of the current beam is within the position range of the detector row is judged, if yes, the current beam is determined to be the PI ray, and the searching is continued until all PI rays meeting the conditions are found, and the end refers to stopping the determining operation of the PI ray.
According to the technical scheme provided by the embodiment, after the initial beam meeting the PI ray condition is selected, the odd number PI rays and the even number PI rays are searched in a circulating mode, the calculation method is simple and convenient, the accuracy of the searched PI rays is guaranteed until the PI rays with all beam falling point positions falling on the row direction of the detector are searched, the target CT image is reconstructed according to all data contributing to the reconstructed voxel point, the CT value of the reconstructed target CT image is more uniform, and the quality of the reconstructed image is greatly improved.
Optionally, determining at least one PI-ray according to the focal point position information of the parallel beam and the position information of the target voxel point may further include:
step A, selecting an initial beam from the parallel beams; b, calculating the position of the ray determined by the focus of the initial beam and the target voxel point in the detector row direction as the beam falling point position; step C, judging whether the beam falling point position of the initial beam is in the detector row position range, if not, stopping the determining operation of the PI ray, if so, determining the initial beam as the PI ray, determining the initial beam and the beam which is 1/2 circles different from the initial beam as reference beams, and executing subsequent operation;
d, determining a beam which is different from the reference beam by n circles as a standby beam, wherein n is an integer;
illustratively, n may be an integer within the (- ∞, + ∞) interval, assuming that the determined initial beam is view0Then the initial beam view is0And view0Beam view with 1/2 turns out of phase0+ pi or view0-pi is determined as a reference beam, after which view is taken0+2n π and view0+ π +2n π or view0- π +2n π is determined as a backup beam.
E, sequentially calculating the focal position of each standby beam and the position of a ray determined by the target voxel point in the row direction of the detector as the beam falling point position according to the direction of the increase of the absolute value of n;
and F, sequentially judging whether the beam falling point position of each spare beam is in the detector row position range, if not, stopping the determining operation of the PI ray, and if so, determining the corresponding spare beam as the PI ray.
For example, the PI rays are searched in directions of which the absolute value of n is 1, 2, and 3 … … in sequence, and first, whether the spare beam when n is 1 or-1 is a PI ray is searched, that is, view is calculated0+2 π or view0-2 pi corresponding to the beam landing position of the backup beam, and calculating view0+ π +2 π or view0+ π -2 π, or calculate view0-pi +2 pi or view0-pi-2 pi and determining whether the calculated beam landing position is under detectionAnd if so, determining the corresponding spare beam as the PI ray, continuously judging whether the spare beam with the n being 2 or-2 meets the PI ray condition, if so, determining the spare beam with the n being 2 or-2 does not meet the PI ray condition, stopping searching the PI ray, and determining the spare beam with the n being-2, -1, 1 and 2 and the initial beam as all beams contributing to the reconstruction voxel point.
Example four
Fig. 4 is a schematic structural diagram of a dynamic pitch CT image reconstruction apparatus according to a fourth embodiment of the present invention, which may be implemented by software and/or hardware, and may be generally integrated in a CT imaging device, and may perform CT image reconstruction by executing a dynamic pitch CT image reconstruction method. As shown in fig. 4, the apparatus includes:
a rebinning module 401 for rebinning the cone beam into a parallel beam; a focal point position determining module 402, configured to determine focal point position information of the parallel beam according to the focal point position information of the cone beam and the position offset information of the scanning bed; a PI ray determining module 403, configured to determine at least one PI ray according to the focal point position information of the parallel beam and the position information of the target voxel point; and a reconstruction module 404, configured to obtain a target CT image according to at least one PI ray and a back projection reconstruction algorithm.
According to the technical scheme provided by the embodiment, after the cone beam is rearranged into the parallel beam, all focus position information obtained after rearrangement is determined, at least one PI ray is determined according to the rearranged focus position information and the position information of the target voxel to be reconstructed, and the back projection image reconstruction is performed according to the selected PI ray to obtain the target CT image. According to the rearranged focal point position information and the position information of the target voxel point, all PI rays contributing to the target voxel point to be reconstructed can be found out, so that the CT value of the target CT image obtained by reconstruction is more uniform, and the quality of the reconstructed image is greatly improved.
On the basis of the above embodiment, the focus position determining module 402 includes: a channel offset determination unit for determining channel offset information from the beams within the parallel beams and the cone beam; the focus offset determining unit is used for determining focus offset information according to the channel offset information and the position offset information of the scanning bed; and a focal position determining unit for determining focal position information of the parallel beam based on the focal position information and the focal shift information of the cone beam.
On the basis of the above embodiment, the PI ray determination module 403 includes: a first initial beam determination unit for selecting an initial beam among the parallel beams; the first drop point determining unit is used for calculating the position of a ray determined by the focus of the initial beam and the target voxel point in the detector row direction as a beam drop point position; the current beam determining unit is used for judging whether the beam falling point position of the initial beam is in the position range of the detector row, if not, stopping the determining operation of the PI ray, if so, determining the initial beam as the PI ray, determining the initial beam and the beam which is 1/2 circles different from the initial beam as the current beam, and executing the subsequent operation; the current beam updating unit is used for determining a beam which is 1 circle away from the current beam by taking the current beam as a reference, and updating the beam into the current beam; the second drop point determining unit is used for calculating the position of a ray determined by the focus of the current beam and the target voxel point in the row direction of the detector as the beam drop point position; and the first PI ray determining unit is used for judging whether the beam falling point position of the current beam is in the detector row position range, stopping the determining operation of the PI ray if the beam falling point position of the current beam is not in the detector row position range, determining the current beam as the PI ray if the beam falling point position of the current beam is in the detector row position range, and returning to execute the operation of updating the current beam.
On the basis of the above embodiment, the second drop point determining unit includes: the position information determining subunit is used for determining the focal position information of the current beam and the position information of the target voxel point; and the drop point determining subunit is used for calculating the positions of the current beam focus and the ray determined by the target voxel point in the detector row direction according to the focus position information and the position information of the target voxel point, and taking the positions as beam drop point positions.
On the basis of the above embodiment, the PI ray determination module 403 further includes: a second initial beam determination unit for selecting an initial beam among the parallel beams; the third drop point determining unit is used for calculating the position of the ray determined by the focus of the initial beam and the target voxel point in the detector row direction as the beam drop point position; a reference beam determining unit, configured to determine whether a beam landing point position of the initial beam is within a detector row position range, if not, stop a determination operation of a PI ray, if so, determine the initial beam as the PI ray, determine the initial beam and a beam that differs from the initial beam by 1/2 circles as reference beams, and perform a subsequent operation; a spare beam determination unit for determining a beam differing by n turns from the reference beam as a spare beam, wherein n is an integer; the fourth falling point determining unit is used for sequentially calculating the focal position of each standby beam and the position of a ray determined by the target voxel point in the detector row direction according to the direction of increasing the absolute value of n, and taking the focal position of each standby beam and the position of the ray determined by the target voxel point as beam falling point positions; and the second PI ray determining unit is used for sequentially judging whether the beam falling point position of each spare beam is in the detector row position range, stopping the determining operation of the PI ray if the beam falling point position of each spare beam is not in the detector row position range, and determining the corresponding spare beam as the PI ray if the beam falling point position of each spare beam is in the detector row position range.
The dynamic pitch CT image reconstruction device provided in the above embodiment can execute the dynamic pitch CT image reconstruction method provided in any embodiment of the present invention, and has corresponding functional modules and beneficial effects for executing the method. The technical details not described in detail in the above embodiments can be referred to a dynamic pitch CT image reconstruction method provided in any embodiment of the present invention.
It is to be noted that the foregoing is only illustrative of the preferred embodiments of the present invention and the technical principles employed. It will be understood by those skilled in the art that the present invention is not limited to the particular embodiments described herein, but is capable of various obvious changes, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, although the present invention has been described in greater detail by the above embodiments, the present invention is not limited to the above embodiments, and may include other equivalent embodiments without departing from the spirit of the present invention, and the scope of the present invention is determined by the scope of the appended claims.
Claims (6)
1. A dynamic pitch CT image reconstruction method is characterized by comprising the following steps:
rearranging the cone beam into a parallel beam;
determining the focal point position information of the parallel beam according to the focal point position information of the cone beam and the position deviation information of the scanning bed;
determining at least one PI ray according to the focal point position information of the parallel beam and the position information of the target voxel point;
obtaining a target CT image according to the at least one PI ray and a back projection reconstruction algorithm;
wherein the focal point of the cone beam is positioned on a spiral line relative to the moving track of the scanned object; the focus of the parallel beam is the intersection point of the parallel beam and the spiral line;
the determining at least one PI ray according to the focal point position information of the parallel beam and the position information of the target voxel point includes:
selecting an initial beam among the parallel beams;
calculating the position of a ray determined by the focus of the initial beam and the target voxel point in the row direction of the detector as the beam falling point position;
judging whether the beam falling point position of the initial beam is in the detector row position range, if not, stopping the determining operation of the PI ray, if so, determining the initial beam as the PI ray, determining the initial beam and the beam which is 1/2 circles different from the initial beam as the current beam, and executing the subsequent operation;
determining a beam which is 1 circle away from the current beam by taking the current beam as a reference, and updating the beam into the current beam;
calculating the position of a ray determined by the focus of the current beam and the target voxel point in the row direction of the detector as the beam falling point position;
judging whether the beam falling point position of the current beam is in the detector row position range, if not, stopping the operation of determining the PI ray, if so, determining the current beam as the PI ray, and returning to execute the operation of updating the current beam;
the determining at least one PI ray according to the focal point position information of the parallel beam and the position information of the target voxel point further includes:
selecting an initial beam among the parallel beams;
calculating the position of a ray determined by the focus of the initial beam and the target voxel point in the row direction of the detector as the beam falling point position;
judging whether the beam falling point position of the initial beam is in the detector row position range, if not, stopping the determining operation of the PI ray, if so, determining the initial beam as the PI ray, determining the initial beam and the beam which is 1/2 circles different from the initial beam as reference beams, and executing subsequent operation;
determining a beam that differs from the reference beam by n turns as a backup beam, where n is an integer;
sequentially calculating the positions of the focal points of the standby beams and the positions of rays determined by the target voxel points in the row direction of the detector as beam falling point positions according to the direction of increasing the absolute value of n;
and sequentially judging whether the beam falling point position of each spare beam is in the range of the detector row position, if not, stopping the determining operation of the PI ray, and if so, determining the corresponding spare beam as the PI ray.
2. The method of claim 1, wherein determining the focus position information of the parallel beam based on the focus position information of the cone beam and the position offset information of the scan bed comprises:
determining channel offset information from beams within the parallel beams and the cone beam;
determining focus offset information according to the channel offset information and the position offset information of the scanning bed;
and determining the focal position information of the parallel beam according to the focal position information and the focal offset information of the conical beam.
3. The method of claim 1, wherein calculating the position of the ray defined by the focal point of the current beam and the target voxel point in the detector row direction as the beam landing position comprises:
determining focal point position information of the current beam and position information of the target voxel point;
and calculating the position of the current beam focus and the position of the ray determined by the target voxel point in the detector row direction according to the focus position information and the position information of the target voxel point, and taking the position as the beam falling point position.
4. A dynamic pitch CT image reconstruction device, comprising:
a rebinning module for rebinning the cone beam into a parallel beam;
the focal point position determining module is used for determining the focal point position information of the parallel beam according to the focal point position information of the cone beam and the position deviation information of the scanning bed;
the PI ray determining module is used for determining at least one PI ray according to the focal point position information of the parallel beams and the position information of the target voxel point;
the reconstruction module is used for obtaining a target CT image according to the at least one PI ray and a back projection reconstruction algorithm;
wherein the focal point of the cone beam is positioned on a spiral line relative to the moving track of the scanned object; the focus of the parallel beam is the intersection point of the parallel beam and the spiral line;
the PI ray determination module comprises:
a first initial beam determination unit for selecting an initial beam among the parallel beams;
the first drop point determining unit is used for calculating the position of a ray determined by the focus of the initial beam and the target voxel point in the detector row direction as a beam drop point position;
the current beam determining unit is used for judging whether the beam falling point position of the initial beam is in the position range of the detector row, if not, stopping the determining operation of the PI ray, if so, determining the initial beam as the PI ray, determining the initial beam and the beam which is 1/2 circles different from the initial beam as the current beam, and executing the subsequent operation;
the current beam updating unit is used for determining a beam which is 1 circle away from the current beam by taking the current beam as a reference, and updating the beam into the current beam;
the second drop point determining unit is used for calculating the position of a ray determined by the focus of the current beam and the target voxel point in the row direction of the detector as the beam drop point position;
the first PI ray determining unit is used for judging whether the beam falling point position of the current beam is in the detector row position range or not, if not, stopping the determining operation of the PI ray, if so, determining the current beam as the PI ray, and returning to execute the operation of updating the current beam;
a second initial beam determination unit for selecting an initial beam among the parallel beams;
the third drop point determining unit is used for calculating the position of the ray determined by the focus of the initial beam and the target voxel point in the detector row direction as the beam drop point position;
a reference beam determining unit, configured to determine whether a beam landing point position of the initial beam is within a detector row position range, if not, stop a determination operation of a PI ray, if so, determine the initial beam as the PI ray, determine the initial beam and a beam that differs from the initial beam by 1/2 circles as reference beams, and perform a subsequent operation;
a spare beam determination unit for determining a beam differing by n turns from the reference beam as a spare beam, wherein n is an integer;
the fourth falling point determining unit is used for sequentially calculating the positions of the focal points of the standby beams and the positions of the rays determined by the target voxel points in the detector row direction according to the direction of increasing the absolute value of n, and the positions are used as beam falling point positions;
and the second PI ray determining unit is used for sequentially judging whether the beam falling point position of each spare beam is in the detector row position range, stopping the determining operation of the PI ray if the beam falling point position of each spare beam is not in the detector row position range, and determining the corresponding spare beam as the PI ray if the beam falling point position of each spare beam is in the detector row position range.
5. The apparatus of claim 4, wherein the focal position determining module comprises:
a channel offset determination unit for determining channel offset information from the beams within the parallel beams and the cone beam;
a focus offset determining unit, configured to determine focus offset information according to the channel offset information and the position offset information of the scanning bed;
a focal position determining unit for determining focal position information of the parallel beam based on the focal position information of the cone beam and the focal offset information.
6. The apparatus of claim 4, wherein the second drop point determining unit comprises:
a position information determining subunit, configured to determine position information of the focal point of the current beam and position information of the target voxel point;
and the drop point determining subunit is configured to calculate, according to the focal point position information and the position information of the target voxel point, a position in the detector row direction of a ray determined by the focal point of the current beam and the target voxel point, as the beam drop point position.
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