CN103714513A - Artifact correction method and equipment in CT imaging - Google Patents

Artifact correction method and equipment in CT imaging Download PDF

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Publication number
CN103714513A
CN103714513A CN201210375800.2A CN201210375800A CN103714513A CN 103714513 A CN103714513 A CN 103714513A CN 201210375800 A CN201210375800 A CN 201210375800A CN 103714513 A CN103714513 A CN 103714513A
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projected image
certain objects
projection
image
data
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CN103714513B (en
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李亮
张丽
陈志强
赵自然
邢宇翔
肖永顺
王清礼
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Tsinghua University
Nuctech Co Ltd
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Tsinghua University
Nuctech Co Ltd
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Abstract

Disclosed are a method and a piece of equipment for correcting artifacts caused by a plurality of specific objects in a CT image. The method comprises the steps of using three projection images under an approximately vertical angle of view to realize three-dimensional space positioning of an object and then pre-processing the projection data to realize metal artifact correction. For a situation in which a plurality of metal implants exist in a scanning field of view, metal artifacts in a CT image can still be quickly removed, no pre-reconstruction on a CT image is required, the algorithm does not involve iterative steps, and the method is fast and effective and can be well applied to engineering applications.

Description

Artifact correction method and equipment in CT imaging
Technical field
The present invention relates generally to radiant image, more specifically, relates to artifact correction method and equipment in CT imaging.
Background technology
Since Hounsfield in 1972 has invented First CT machine, CT technology has been brought revolutionary impact to medical diagnosis and industrial nondestructive testing, and CT has become one of important detection means of the industries such as medical treatment, biology, Aero-Space, national defence.Along with the progress of technology, CT scan pattern and formation method are also constantly improving, and 3 D pyramidal CT has become the main flow of research and application.X ray Cone-Beam CT is widely used in fields such as clinical medicine, safety inspection, Non-Destructive Testings, and particularly, in medical clinic applications, CT has become one of indispensable detection methods.
1989, spiral CT starts to drop into clinical medicine application, huge advantage due to spiral CT, make it progressively substitute tomography CT in the past, spiral CT is with respect to the advantage of tomography CT: spiral CT is recording projection data uninterruptedly, and by custom-designed reconstruction algorithm, obtains the three-dimensional data of object, and the time of CT scan is shortened greatly, the Z axis resolution of rebuilding image is provided, has reduced motion artifacts.Spiral CT has been obtained huge success in clinical practice, very fast, the detector that spiral CT is used develops into bilayer, four layers, 8 layers, 16 layers from individual layer, and develops into gradually 32 layers, 64 layers, 128 layers, has taken the lead in releasing the spiral CT of 320 layers to Toshiba company in 2007.In the time of spiral develop rapidly, an other technology is also quietly progressive: flat panel detector technology.Be different from the detector array that a lot of separate detectors module spliced that multi-layer spiral CT uses are dressed up, flat panel detector is directly used the large-area flicker body of monoblock, after encapsulate extensive photosensitive unit array (such as CCD, CMOS, TFT etc.), be then converted to X ray intensity data through A/D.The development of flat panel detector technology impels the Cone-Beam CT that a class is new (CBCT) to be emerged, use the CBCT system of flat panel detector generally only need rotate a circle and can complete the CT scan of larger region (for example 30cm*30cm), reconstructed the three dimensional CT image in this scan vision (FOV) scope.
In safety inspection and industrial nondestructive inspection (NDI) field, CT technology is also obtaining development fast in recent years, for example based on dual intensity technology safety check CT owing to having possessed the ability of good differentiation material, obtained the approval in safety check field, progressively promote; And also aspect spatial resolution, density resolution, obtaining larger progress for the industry CT in industrial nondestructive testing field.
In CT image, often there is multiple artifact, for example: strip artifact, windmill artifact, metal artifacts etc., wherein metal artifacts is one of modal artifact.Metal artifacts is normally owing to existing density to be significantly higher than the metal of surrounding tissue density in scanned object, thereby in CT scan image, at metal, there is bright streak artifact around, have influence on to a great extent the normal discriminating of metal itself and its surrounding tissue.Particularly, in medical CT and safety check CT, the existence of metal artifacts tends to diagnosis or material identification to affect greatly, and therefore, how to eliminate metal artifacts is all an important subject in CT field all the time.
Summary of the invention
Consider one or more problems of prior art, proposed artifact correction method and equipment in CT imaging.
According to embodiments of the invention, the method for the artifact that in a kind of correcting CT image, a plurality of certain objects cause, comprises step:
Thereby from data for projection, calculate described a plurality of certain objects three each other the position on the perspective view of perpendicular determine the position of described a plurality of certain objects in three dimensions;
Utilize the barycentric coordinates of described a plurality of certain objects to carry out object segmentation to the projected image under all angles;
With the data for projection of having cut apart after the plurality of certain objects, the data for projection of the plurality of certain objects is repaired;
Utilize the data for projection after repairing to carry out the CT image that CT reconstruction acquisition does not comprise the plurality of certain objects.
According to embodiments of the invention, thus from data for projection, calculate described certain objects three each other the position on the perspective view of perpendicular determine that the step of the position of described a plurality of certain objects in three dimensions comprises:
Utilize projection composition algorithm from data for projection, to calculate its direction of observation perpendicular to the first projected image of CT fault plane;
In the cone beam projection perpendicular to described direction of observation, select two width projected images, i.e. the second projected image and the 3rd projected image, described the second projected image and described the 3rd projected image be quadrature substantially;
Determine the position of described a plurality of certain objects in described the first projected image, described the second projected image and described the 3rd projected image;
The position of a plurality of certain objects in three dimensions described in position calculation based on described a plurality of certain objects in described the first projected image, the second projected image and described the 3rd projected image.
According to embodiments of the invention, utilize the step that the barycentric coordinates of described a plurality of certain objects are carried out object segmentation to the projected image under all angles to comprise: the projected position of the center of gravity of calculating described a plurality of certain objects under each projection angle on flat panel detector; And based on this projected position, the view field of described a plurality of certain objects is cut apart.
According to embodiments of the invention, with having cut apart the step that the data for projection after the plurality of certain objects repairs the data for projection of the plurality of certain objects, comprise:
View field based on having cut apart data for projection usability interpolation method after the plurality of certain objects and repair the plurality of certain objects.
According to embodiments of the invention, select the step of two width projected images to comprise:
Based on described the first projected image, select the second projected image and the 3rd projected image, so that the overlapping region between a plurality of certain objects in the second projected image and the 3rd projected image is minimum.
According to embodiments of the invention, based on described the first projected image, select the step of the second projected image and the 3rd projected image to comprise:
Described the first projected image is cut apart, obtained only comprising the binary image of certain objects area information;
Described binary image is carried out to the forward projection of fan-beam, obtains the sinogram of fan-beam projection, used herein to the fan angle of fan-beam need to equal the subtended angle of cone-beam system central core corresponding light source target spot;
For every row of sinogram, by peak-seeking algorithm, calculate the number at peak;
For all peak value numbers, equal the projection angle of certain objects number in the first projected image, selecting angle between the two is the projection angle of 90 degree, thereby determines the second projected image and the 3rd projected image.
According to embodiments of the invention, determine that the step of the position of a plurality of certain objects in described the first projected image, described the second projected image and described the 3rd projected image comprises:
In the first projected image, each certain objects is cut apart, determined each certain objects region center of gravity in the first image;
In the second projected image and the 3rd projected image, each attention object region is cut apart, and determined the center of gravity of each certain objects in the second projected image and the 3rd projected image.
According to embodiments of the invention, described certain objects is metal object.
According to embodiments of the invention, the equipment of the artifact that in a kind of correcting CT image, a plurality of certain objects cause, comprising:
Thereby from data for projection, calculate described a plurality of certain objects three each other the position on the perspective view of perpendicular determine the device of the position of described a plurality of certain objects in three dimensions;
Utilize the barycentric coordinates of described a plurality of certain objects the projected image under all angles to be carried out to the device of object segmentation;
The device of the data for projection of the plurality of certain objects being repaired with the data for projection of having cut apart after the plurality of certain objects;
Utilize the data for projection after repairing to carry out the device that CT reconstruction obtains the CT image that does not comprise the plurality of certain objects.
In the method for this embodiment, in scan vision, exist in the situation of many metal implants, still can remove fast the metal artifacts of rebuilding in image.Its unique advantage is image not to be rebuild in advance, does not also relate to iterative step in algorithm, only adopts the perspective view at three (being similar to) vertical visual angle to carry out positioning metal, therefore can to data for projection, repair fast and accurately.
Accompanying drawing explanation
For a better understanding of the present invention, will describe the present invention according to the following drawings:
Fig. 1 is according to the structural representation of the CT equipment of embodiment of the present invention;
Fig. 2 shows the structured flowchart of computer data processor as shown in Figure 1;
Fig. 3 shows according to the structured flowchart of the controller of first embodiment of the invention;
Fig. 4 shows according to the schematic diagram of the procedure of the positioning object of the embodiment of the present invention;
Fig. 5 is the schematic diagram of describing CBCT system;
Fig. 6 describes the schematic diagram that synthesizes the algorithm of depression angle collimated beam perspective view by data for projection;
It is the schematic diagram of all alternative MAP in location that Fig. 7 shows;
Fig. 8 describes the horizontal projection of being selected two width quadratures by vertical view;
Fig. 9 shows the method flow diagram of eliminating according to another embodiment of the present invention the artifact in CT imaging;
Figure 10 shows the experimental result that artifact is eliminated.
Embodiment
To describe specific embodiments of the invention in detail below, it should be noted that the embodiments described herein, only for illustrating, is not limited to the present invention.In the following description, in order to provide thorough understanding of the present invention, a large amount of specific detail have been set forth.Yet, for those of ordinary skills, it is evident that: needn't adopt these specific detail to carry out the present invention.In other examples, for fear of obscuring the present invention, do not specifically describe known circuit, material or method.
In whole instructions, " embodiment ", " embodiment ", " example " or mentioning of " example " are meaned: special characteristic, structure or characteristic in conjunction with this embodiment or example description are comprised at least one embodiment of the present invention.Therefore phrase " in one embodiment ", " in an embodiment ", " example " or " example ", occurring in each place of whole instructions differs to establish a capital and refers to same embodiment or example.In addition, can with any suitable combination and or sub-portfolio by specific feature, structure or property combination in one or more embodiment or example.In addition, it should be understood by one skilled in the art that the diagram providing at this is all for illustrative purposes, and diagram is not necessarily drawn in proportion.Should be appreciated that it can be directly connected or coupled to another element or can have intermediary element when claiming " element " " to be connected to " or " coupling " arrives another element.On the contrary, when claiming element " to be directly connected to " or during " being directly coupled to " another element, not having intermediary element.
According to some embodiments of the present invention, can in CT imaging, locate a plurality of attention objects.Utilize projection composition algorithm from data for projection, to calculate its direction of observation perpendicular to the first projected image of CT fault plane.Then in the cone beam projection perpendicular to described direction of observation, select two width projected images, i.e. the second projected image and the 3rd projected image, described the second projected image and described the 3rd projected image be quadrature substantially.Determine the position of a plurality of attention objects in described the first projected image, described the second projected image and described the 3rd projected image.The position of each attention object of position calculation based on a plurality of attention objects in described the first projected image, the second projected image and described the 3rd projected image in three dimensions.
According to other embodiments of the present invention, can eliminate the artifact in CT imaging.Thereby from data for projection, calculate described a plurality of certain objects three each other the position on the perspective view of perpendicular determine the position of described a plurality of certain objects in three dimensions.Utilize the barycentric coordinates of described a plurality of certain objects to carry out object segmentation to the projected image under all angles.With the data for projection of having cut apart after the plurality of certain objects, the data for projection of the plurality of certain objects is repaired.Utilize the data for projection after repairing to carry out the CT image that CT reconstruction acquisition does not comprise the plurality of certain objects.
Fig. 1 is according to the structural representation of the CT equipment of embodiment of the present invention.As shown in Figure 1, according to the CT equipment of present embodiment, comprise: send the radiographic source 10 checking with X ray, such as X-ray machine; Load carrier 40, its carrying inspected object is rotated around axle Z, and can lifting, make tested object enter surveyed area, thereby the ray being sent by radiographic source 10 can see through tested object; Survey and harvester 30, it is detector and the data acquisition unit with integral module structure, flat panel detector for example, for surveying the ray of transmission inspected object, obtain simulating signal, and convert simulating signal to digital signal, thereby output inspected object is for the data for projection of X ray; Controller 50, it is for controlling the various piece synchronous working of whole system; And computer data processor 60, it is used for processing the data that gathered by data acquisition unit, data is processed and is rebuild, Output rusults.
As shown in Figure 1, radiographic source 10 is placed in load carrier 40 1 sides that can place tested object, detection and harvester 30 are placed in the opposite side of load carrier 40, comprise detector and data acquisition unit, for obtaining inspected object projection data and/or multi-angle projection data.Data acquisition unit comprises data amplification wave-shaping circuit, and it can work in (electric current) integral way or pulse (counting) mode.Survey and be connected with computer data processor 60 with the data output cable of harvester 30, according to trigger command, the data of collection are stored in computer data processor 60.
In addition, checkout facility can also comprise the tubular object passage 20 being made of metal, and it is arranged on load carrier 40, and inspected object is placed in tested object passage.
Fig. 2 shows the structured flowchart of computer data processor 60 as shown in Figure 1.As shown in Figure 2, the data that data acquisition unit gathers are stored in storer 61 by interface unit 68 and bus 64.In ROM (read-only memory) (ROM) 62, store configuration information and the program of computer data processor.Random access memory (RAM) 63 is for keeping in various data in processor 66 courses of work.In addition, in storer 61, also store for carrying out the computer program of data processing.Internal bus 64 connects above-mentioned storer 61, ROM (read-only memory) 62, random access memory 63, input media 65, processor 66, display device 67 and interface unit 68.
After operational order user by input media 65 inputs such as keyboard and mouse, the instruction code instructs processor 66 of computer program is carried out predetermined data processing algorithm, after obtaining data processed result, be presented in the display device 67 such as LCD display, or the direct formal output result with hard copy such as printing.
Fig. 3 shows according to the structured flowchart of the controller of embodiment of the present invention.As shown in Figure 3, controller 50 comprises: control module 51, according to the instruction from computing machine 60, control radiographic source 10, load carrier 40 and detection and harvester 30; Trigger pip generation unit 52, for producing the trigger command of the action be used for triggering radiographic source 10, detection and harvester 30 and load carrier 40 under the control of control module; The first drive motor 55, it drives load carrier 40 to rise or decline at the trigger command producing under the control of control module 51 according to trigger pip generation unit 52; Elevation information acquiring unit 53, it is along with the motion of load carrier 40, to the elevation information of control module 51 feedback load carriers; The second drive motor 56, the trigger command that it produces under the control of control module 51 according to trigger pip generation unit 52 drives load carrier 40 rotations; Angle information acquiring unit 54, it obtains the anglec of rotation of load carrier 40 in load carrier 40 rotary courses, feeds back to control module 51.According to the embodiment of the present invention, above-mentioned elevation information acquiring unit 53 and angle information acquiring unit 54 are all photoelectric code disks, and it possesses jamproof advantage.
Below introduce in detail the method for certain objects (attention object) in the location CT imaging based on three-view diagram.Fig. 4 shows according to the schematic diagram of the procedure of the positioning object of the embodiment of the present invention.
If the system of CBCT is as follows: reconstruction regions is described with three-dimensional cartesian coordinate system Oxyz, the rotation center that wherein true origin O is system.S (β) is the position at place, cone beam of rays source, the rotation angle value that wherein β is system.Flat panel detector 30 is placed in rotation center opposite side, and rotates with light source synchronous.Data for projection on detector is with P (β, u, v) expression, and wherein u, v are the rectangular coordinate on flat panel detector.CBCT system schematic as shown in Figure 5.
At step S41: utilize projection composition algorithm to calculate its direction of observation perpendicular to the first projected image of CT fault plane from data for projection.
By Cone-Beam CT (CBCT) data for projection gathering, calculate the depression angle collimated beam perspective view in visual field.For example utilize the relation of data for projection and Radon transform numerical value, based on data for projection, calculate the thunder corresponding with the first projected image when the partial derivative of data.For example, can pass through the partial derivative that formula (1) calculates the thunder (Radon) on duty that vertical view (in this example corresponding to the first projected image) is corresponding:
∂ ∂ u R f ( s , m → ) = 1 cos 2 γ ∫ t 1 t 2 ∂ ∂ u ( SO SA ( t ) × P ( β , u ( s , m → ) , v ( s , m → , t ) ) ) dt - - - ( 1 )
As shown in Figure 6, some C is arranged in central plane Ω, and the length correspondence of OC the s among formula 1,
Figure BDA00002215319700072
for vector
Figure BDA00002215319700073
vector of unit length, γ represents ∠ CSO.Integral and calculating is along a line segment t of ordering perpendicular to surface level and through C 1t 2complete.
Then, the partial derivative that utilizes filter back-projection algorithm and described thunder to work as data calculates the first projected image.For example, utilize formula (2) to obtain the collimated beam perspective view of depression angle:
Pf ( r → ) = 1 2 π ∫ 0 π [ ∂ Rf ( s ) ∂ s * h H ( s ) ] | s = r → · m → dβ - - - ( 2 )
H wherein h(s) be Hilbert filtering, its concrete form is:
h H ( s ) = ∫ - ∞ + ∞ ( - i · sign ( ρ ) ) · e 2 πiρs dρ - - - ( 3 )
At step S42, in the cone beam projection perpendicular to described direction of observation, select two width projected images, i.e. the second projected image and the 3rd projected image, described the second projected image and described the 3rd projected image be quadrature substantially.
In the present embodiment, with three coordinates of certain 1 MAP (metal anchor point) in derby, represent the position of metal.Perspective view by three visual angles is located all MAP in three dimensions, and wherein a width is the depression angle perspective view obtaining in upper step, and other two width are to select from all cone beam projection figure.Depression angle collimated beam perspective view is by helping to select the cone beam projection of this two width level, so that the metal overlapping region occurring in this two width projection is minimum, and the corresponding anglec of rotation of two width projections is as far as possible vertical, to reduce the error of calculation.
Fig. 7 be take one group of real data and has been introduced by the method for image selection level visual angle, depression angle image as example.First we cut apart depression angle image, obtains only comprising the binary image of metallic region information; Then this binary image is carried out the forward projection of fan-beam, obtains the sinogram of fan-beam projection, used herein to the fan angle of fan-beam need to equal the subtended angle of cone-beam system central core corresponding light source target spot, with this, simulate the situation of cone beam projection process under depression angle; For every row of sinogram, by peak-seeking algorithm, calculate the number at peak; For all peak value numbers, equal the projection angle of metal number in the image of depression angle.For example by formula (4), select two comparatively vertical angle angle 1and angle 2, these two angles are selected.
(angle 1，angle 2)＝arg?min||angle 1-angle 2|-90°|(4)
At step S43, determine the position of a plurality of attention objects in described the first projected image, described the second projected image and described the 3rd projected image, then, the position of each attention object of position calculation in described the first projected image, the second projected image and described the 3rd projected image in three dimensions based on a plurality of attention objects.
For example, in picked out Liang Fu horizontal projection, metallic region is cut apart, and calculated the center of gravity of every metallic region, as shown in formula (5):
u c ( i ) = Σ ( u , v ) ∈ M i P ( u , v ) · u Σ ( u , v ) ∈ M i P ( u , v ) v c ( i ) = Σ ( u , v ) ∈ M i P ( u , v ) · v Σ ( u , v ) ∈ M i P ( u , v ) - - - ( 5 )
(u wherein c(i), v c(i)) be i piece metallic region M icorresponding barycentric coordinates.
In three dimensions, above-mentioned three width images are used for locating all MAP.If derby is convex geometry body, the straight line that links so light source point and metallic region focus point is bound to through derby, and two intersection points through the known straight line of same metal just can be construed to be the MAP of this piece metal.Therefore as shown in Figure 8, in actual conditions, two, space straight line is disjoint often, can calculate the least square solution of these two straight lines as the coordinate of MAP, as formula (6):
(x m，y m，z m)＝arg?min(d 2(x，y，z，l 1)+d 2(x，y，z，l 2))(6)
D (x, y, z, l wherein 1) and d (x, y, z, l 2) representative (x m, y m, z m) to two straight line l 1and l 2distance.
Calculate M (x m, y m, z m) afterwards, can check M (x with the 3rd perspective view m, y m, z m) whether be projected in corresponding metallic region, in this way, M (x m, y m, z m) can be recorded as MAP.
Depression angle collimated beam projected image is with helping selection level projection, to avoid as far as possible the occurring situation that metal is overlapping in horizontal projection.In practical application, situation is comparatively complicated, actual conditions is discussed herein.Suppose to have m piece metal in the visual field, in the collimated beam projected image of depression angle, comprise n opiece metallic region, comprises respectively piece n in two width horizontal projections 1and n 2metallic region, might as well suppose n here 1>=n 2.We can divide three kinds of situations to be discussed.
(1) if m=n o=n 1=n 2, meaning so the equal zero lap of metal in the image that three width choose, all metallic region centers of gravity of calculating in formula (5) are so accurately.We can select any two width in three width images, use formula (6) to calculate possible MAP coordinate, and with the option of the 3rd width image examination debug.
(2) if m=n o=n 1> n 2or m=n 1=n 2> n 0, mean so in three width images, have in two width images metal be separate completely nonoverlapping.We can select the nonoverlapping image of this two width metal, utilize formula (6) to calculate possible MAP coordinate, and with the option of the 3rd width image examination debug.
(3) if m=n o> n 1>=n 2or m=n 1> n 0∩ n 1> n 2, only have piece image not have metal overlapping; If m > max is (n o, n 1), three width images all comprise the overlapping region of metal.In these two kinds of situations, cannot apply said method and calculate MAP coordinate.
By said process, can from CT data for projection, determine the position of attention object.
In addition, for the metal artifacts problem extensively existing in CT imaging, another embodiment of the present invention has proposed a kind of CT metal artifacts bearing calibration based on three-view diagram, utilize projection synthetic technology and the coordinate setting of the many object dimensionals based on three-view diagram technology, the metal artifacts of realizing in CT imaging is eliminated.The method of the embodiment of the present invention belongs to the bearing calibration of projection pre-service class, without CT, rebuilds in advance, and algorithmic procedure is simple and direct, speed is fast, can meet well engineering application to rebuilding the requirement of speed.
In the method for this embodiment, in scan vision, exist in the situation of many metal implants, still can remove fast the metal artifacts of rebuilding in image.Its unique advantage is image not to be rebuild in advance, does not also relate to iterative step in algorithm, only adopts the perspective view at three (being similar to) vertical visual angle to carry out positioning metal, therefore can to data for projection, repair fast and accurately.
Fig. 9 shows the method flow diagram of eliminating according to another embodiment of the present invention the artifact in CT imaging.As shown in Figure 9, at step S91, thereby from data for projection, calculate described a plurality of certain objects three each other the position on the perspective view of perpendicular determine the position of described a plurality of certain objects in three dimensions.
According to another embodiment, thus from data for projection, calculate described a plurality of certain objects three each other the position on the perspective view of perpendicular determine that the location method process of described a plurality of certain objects in three dimensions is as follows:
1) first utilize projection composition algorithm directly from data for projection, to calculate the collimated beam projected image of position, depression angle, by investigating the position relationship of metallic region in the perspective view of depression angle, at the cone beam projection clock of all horizontal directions, select two width projections, in this two width horizontal projection, metal is not overlapped as much as possible, and the difference of the anglec of rotation of two width horizontal projections will approach 90 ° as much as possible, to guarantee the accuracy of subsequent calculations.
2) utilize the three width projected images of selecting, in this three width image, metallic region is cut apart, then the position in three dimensions according to this metal object of position calculation of metal in three width images, and the three-dimensional coordinate note of this object center of gravity is done to the anchor point (metal anchor point is called for short MAP) of this metal.In practical application, can run into unavoidably in selected projected image metal object has overlappingly each other, and through demonstration, as long as there is at least two sub-pictures metal not overlapping in three width images, this algorithm can be oriented the MAP of all metals accurately.
At step S92, utilize the barycentric coordinates of described a plurality of certain objects to carry out object segmentation to the projected image under all angles.
At step S93, with the data for projection of having cut apart after the plurality of certain objects, the data for projection of the plurality of certain objects is repaired.
At step S94, utilize the data for projection after repairing to carry out the CT image that CT reconstruction acquisition does not comprise the plurality of certain objects.
For example, MAP is projected on the detector plane under all angles to the subpoint called after seed metallization point obtaining (metal seed point is called for short MSP).MSP point sets out thus, and the projected image of each angle is carried out to pre-service, and the MSP of take is cut apart all metallic region in this perspective view as Seed Points.After metallic region in being partitioned into all projected images, the data for projection of the metallic region position being partitioned into is repaired to (adopting general interpolation method).Utilize revised data for projection, use existing CT reconstruction algorithm to reconstruct and do not wrap metallic CT image.
For example, located all MAP in three dimensions after, we can calculate the projection of MAP on flat panel detector under each projection angle, are denoted as MSP (metal seed point).Because MAP is positioned at derby inside in three dimensions, MSP is bound to be positioned at the inside in metal shadowing region in perspective view so.Based on this, can utilize comparatively ripe algorithm of region growing in perspective view, to be partitioned into all metal shadowing regions.
After marking the metallic region of perspective view, we utilize the algorithm of bilinear interpolation to repair metal shadowing region.The method is as shown in formula (7):
I = ( d up × I down + d down × I up ) ( d up + d down ) × ( d left + d right ) + ( d left × I right + d right × I left ) ( d left + d right ) × ( d up + d down ) d up + d down + d left + d right - - - ( 7 )
Wherein, I is the repair data of inserting corresponding pixel points, d up, d down, d leftand d rightthat this pixel is apart from the distance at metallic region edge, I up, I down, I leftand I rightit is the gray-scale value of the image on corresponding edge.
Utilize said method to complete after the pre-service of data for projection, just can use existing CT method (such as circular orbit FDK algorithm, helical orbit FDK algorithm etc.) to reconstruct and do not wrap metallic CT image.
On real system, above-mentioned theory and method have been carried out to experimental verification.The CBCT system of using is as shown in Figure 10 (a).Flat panel detector is of a size of 243.84mm * 195.07mm, and each Pixel Dimensions is 0.127mm * 0.127mm, this means that array comprises 1920 * 1536 pixels.X source is positioned at detector opposite, and voltage is 120keV, and electric current is 1.7mA.Turntable is between detector and light source, and light source target spot is apart from rotation center 750mm, light source target spot range finder center 1050mm.Scan at every turn and within the scope of 360 °, gather uniformly 360 projections.We have made a model algorithm (as Figure 10 (b)) have been described, fix a plastic flask in plastic beaker, in fixing some the Metal Ball in flask outside.In order to apply by simulative medicine, in scanning process, beaker and flask all will be filled with water.
Experimental result as shown in figure 10.Metal Ball has been fixed on flask outside with two kinds of different disposing ways, to investigate diverse location relation, for location algorithm, whether has impact.Wherein, Figure 10 (a1, b1, b3) is the CT image that does not give processing, and the inventive method of utilizing that Figure 10 (a2, b2, b4) is correspondence is carried out metal artifacts correction CT image afterwards.Can find that near artifact strip artifact between derby and metal can remove effectively by metal artifacts bearing calibration of the present invention.
Above-mentioned artifact correction method is started with from projection domain image processing method, and the metal artifacts in the time of can solving quickly and efficiently a plurality of metal objects and coexist is eliminated problem.In addition, the method, without iteration, can be conveniently used in Practical Project.
Above detailed description, by user's block diagram, process flow diagram and/or example, has been set forth the method for positioning object and/or has proofreaied and correct numerous embodiment of artifact correction method.In the situation that this block scheme, process flow diagram and/or example comprise one or more functions and/or operation, it will be understood by those skilled in the art that each function in this block scheme, process flow diagram or example and/or operation can by various hardware, software, firmware or in fact their combination in any come separately and/or jointly realize.In one embodiment, described in embodiments of the invention, some parts of theme can realize by special IC (ASIC), field programmable gate array (FPGA), digital signal processor (DSP) or other integrated forms.Yet, those skilled in the art will recognize that, some aspects of embodiment disclosed herein can realize in integrated circuit on the whole or partly equally, (be for example embodied as one or more computer programs of moving on one or more computing machine, be embodied as one or more programs of moving in one or more computer system), (be for example embodied as one or more programs of moving on one or more processors, be embodied as one or more programs of moving on one or more microprocessors), be embodied as firmware, or be embodied as in fact the combination in any of aforesaid way, and those skilled in the art are according to the disclosure, to possess design circuit and/or write software and/or the ability of firmware code.In addition, those skilled in the art will recognize that, described in the disclosure, the mechanism of theme can be distributed as the program product of various ways, and regardless of the actual particular type that is used for carrying out the signal bearing medium of distribution, and the exemplary embodiment of theme is all applicable described in the disclosure.The example of signal bearing medium includes but not limited to: recordable-type media, as floppy disk, hard disk drive, compact-disc (CD), digital universal disc (DVD), numerical tape, computer memory etc.; And transmission type media, for example, as numeral and/or analogue communication medium (, optical fiber cable, waveguide, wire communication link, wireless communication link etc.).
Although described the present invention with reference to several exemplary embodiments, should be appreciated that term used is explanation and exemplary and nonrestrictive term.The spirit or the essence that because the present invention can specifically implement in a variety of forms, do not depart from invention, so be to be understood that, above-described embodiment is not limited to any aforesaid details, and explain widely in the spirit and scope that should limit in the claim of enclosing, therefore fall into whole variations in claim or its equivalent scope and remodeling and all should be the claim of enclosing and contain.

Claims (15)

1. a method for the artifact that in correcting CT image, a plurality of certain objects cause, comprises step:
Thereby from data for projection, calculate described a plurality of certain objects three each other the position on the perspective view of perpendicular determine the position of described a plurality of certain objects in three dimensions;
Utilize the barycentric coordinates of described a plurality of certain objects to carry out object segmentation to the projected image under all angles;
With the data for projection of having cut apart after the plurality of certain objects, the data for projection of the plurality of certain objects is repaired;
Utilize the data for projection after repairing to carry out the CT image that CT reconstruction acquisition does not comprise the plurality of certain objects.
2. the method for claim 1, thus wherein from data for projection, calculate described certain objects three each other the position on the perspective view of perpendicular determine that the step of the position of described a plurality of certain objects in three dimensions comprises:
Utilize projection composition algorithm from data for projection, to calculate its direction of observation perpendicular to the first projected image of CT fault plane;
In the cone beam projection perpendicular to described direction of observation, select two width projected images, i.e. the second projected image and the 3rd projected image, described the second projected image and described the 3rd projected image be quadrature substantially;
Determine the position of described a plurality of certain objects in described the first projected image, described the second projected image and described the 3rd projected image;
The position of a plurality of certain objects in three dimensions described in position calculation based on described a plurality of certain objects in described the first projected image, the second projected image and described the 3rd projected image.
3. the method for claim 1, wherein utilizes the step that the barycentric coordinates of described a plurality of certain objects are carried out object segmentation to the projected image under all angles to comprise: the projected position of the center of gravity of calculating described a plurality of certain objects under each projection angle on flat panel detector; And based on this projected position, the view field of described a plurality of certain objects is cut apart.
4. the method for claim 1, wherein comprises with having cut apart the step that the data for projection after the plurality of certain objects repairs the data for projection of the plurality of certain objects:
View field based on having cut apart data for projection usability interpolation method after the plurality of certain objects and repair the plurality of certain objects.
5. method as claimed in claim 2, wherein, select the step of two width projected images to comprise:
Based on described the first projected image, select the second projected image and the 3rd projected image, so that the overlapping region between a plurality of certain objects in the second projected image and the 3rd projected image is minimum.
6. method as claimed in claim 5, wherein, based on described the first projected image, select the step of the second projected image and the 3rd projected image to comprise:
Described the first projected image is cut apart, obtained only comprising the binary image of certain objects area information;
Described binary image is carried out to the forward projection of fan-beam, obtains the sinogram of fan-beam projection, used herein to the fan angle of fan-beam need to equal the subtended angle of cone-beam system central core corresponding light source target spot;
For every row of sinogram, by peak-seeking algorithm, calculate the number at peak;
For all peak value numbers, equal the projection angle of certain objects number in the first projected image, selecting angle between the two is the projection angle of 90 degree, thereby determines the second projected image and the 3rd projected image.
7. method as claimed in claim 2, wherein, determine that the step of the position of a plurality of certain objects in described the first projected image, described the second projected image and described the 3rd projected image comprises:
In the first projected image, each certain objects is cut apart, determined each certain objects region center of gravity in the first image;
In the second projected image and the 3rd projected image, each attention object region is cut apart, and determined the center of gravity of each certain objects in the second projected image and the 3rd projected image.
8. method as claimed in claim 2, wherein said certain objects is metal object.
9. an equipment for the artifact that in correcting CT image, a plurality of certain objects cause, comprising:
Thereby from data for projection, calculate described a plurality of certain objects three each other the position on the perspective view of perpendicular determine the device of the position of described a plurality of certain objects in three dimensions;
Utilize the barycentric coordinates of described a plurality of certain objects the projected image under all angles to be carried out to the device of object segmentation;
The device of the data for projection of the plurality of certain objects being repaired with the data for projection of having cut apart after the plurality of certain objects;
Utilize the data for projection after repairing to carry out the device that CT reconstruction obtains the CT image that does not comprise the plurality of certain objects.
10. equipment as claimed in claim 9, thus wherein from data for projection, calculate described certain objects three each other the position on the perspective view of perpendicular determine that the device of the position of described a plurality of certain objects in three dimensions comprises:
Utilize projection composition algorithm from data for projection, to calculate its direction of observation perpendicular to the device of the first projected image of CT fault plane;
In the cone beam projection perpendicular to described direction of observation, select the device of two width projected images, select the second projected image and the 3rd projected image, described the second projected image and described the 3rd projected image be quadrature substantially;
Determine the device of the position of described a plurality of certain objects in described the first projected image, described the second projected image and described the 3rd projected image;
The device of the position of a plurality of certain objects in three dimensions described in position calculation based on described a plurality of certain objects in described the first projected image, the second projected image and described the 3rd projected image.
11. equipment as claimed in claim 9, wherein utilize the device that the barycentric coordinates of described a plurality of certain objects are carried out object segmentation to the projected image under all angles to comprise: the device of the projected position of the center of gravity of calculating described a plurality of certain objects under each projection angle on flat panel detector; The device of the view field of described a plurality of certain objects being cut apart based on this projected position.
12. equipment as claimed in claim 9, wherein comprise with having cut apart the device that the data for projection after the plurality of certain objects repairs the data for projection of the plurality of certain objects:
Data for projection usability interpolation method based on having cut apart after the plurality of certain objects is repaired the device of the view field of the plurality of certain objects.
13. equipment as claimed in claim 10, wherein, select the device of two width projected images to comprise:
Based on described the first projected image, select the second projected image and the 3rd projected image, so that the device of the overlapping region minimum between a plurality of certain objects in the second projected image and the 3rd projected image.
14. equipment as claimed in claim 13, wherein, based on described the first projected image, select the device of the second projected image and the 3rd projected image to comprise:
Described the first projected image is cut apart, obtained only comprising the device of the binary image of certain objects area information;
Described binary image is carried out to the forward projection of fan-beam, obtains the device of the sinogram of fan-beam projection, used herein to the fan angle of fan-beam need to equal the subtended angle of cone-beam system central core corresponding light source target spot;
For every row of sinogram, by peak-seeking algorithm, calculate the device of the number at peak;
For all peak value numbers, equal the projection angle of certain objects number in the first projected image, selecting angle between the two is the projection angle of 90 degree, thereby determines the device of the second projected image and the 3rd projected image.
15. equipment as claimed in claim 10, wherein, determine that the device of the position of a plurality of certain objects in described the first projected image, described the second projected image and described the 3rd projected image comprises:
In the first projected image, each certain objects is cut apart, determined the device of each center of gravity of certain objects region in the first image;
In the second projected image and the 3rd projected image, each attention object region is cut apart, and determined the device of the center of gravity of each certain objects in the second projected image and the 3rd projected image.
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