CN101273276A - Backprojection reconstruction method for ct imaging - Google Patents
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Abstract
Projection views of the moving heart and stationary background tissues are acquired and processed to provide corresponding moving tissue projection views. An average image is reconstructed in a conventional manner and a moving tissue image is reconstructed using a highly constrained backprojection method and a composite image formed from selected moving tissue projection views. The average image is then combined with the moving tissue image. The method is disclosed in a cardiac gated MRI scan.
Description
The cross reference of relevant application
The application is based on following two U.S. Provisional Patent Application: the application 60/719,445 that is entitled as " HIGHLY CONSTRAINED IMAGE RECONSTRUCTION METHOD " that on September 22nd, 2005 submitted to; And the application 60/738,444 that is entitled as " IMAGE RECONSTRUCTIONMETHOD FOR CARDIAC GATED MAGNETIC RESONANCE IMAGING " of submission on November 21st, 2005.
Background of invention
The field of the invention is the imaging of medical method and system.More particularly, the present invention relates to the imaging process of the object (such as the heart of beating) that moves.
When object (such as the heart of beating) when carrying out imaging, if, then can obtain higher-quality image with medical imaging system image data very rapidly to motion.For example, when using the X ray CT system, x-ray source and detecting device all rotate so that gather the projection view of sufficient amount around the experimenter, can reconstruct tomographic image from these projection views.This needs the time, usually, certain balance is being arranged by gathering that still less projection view shortens sweep time and improving picture quality with more projection view between the two.
Although there is this problem in X ray CT, this problem is then more outstanding in Magnetic resonance imaging (MRI).When the material such as tissue is subjected to uniform magnetic field (polarization field B
0) do the time spent, the magnetic moment of each spin in this tissue attempts to aim at this polarization field, but by its feature Larmor frequency with any order around its precession.If this material or tissue are subjected to being in the x-y plane and near magnetic field (the exciting field B of Larmor frequency
1) effect, then aim at magnetic moment M only
zCan rotate or " inclination " thus produce clean laterally magnetic moment M in the x-y plane
tA kind of signal is sent in the spin of these excited target, and at pumping signal B
1After the termination, form image thereby can receive and handle this signal.When adopting these signals to produce image, can use magnetic field gradient (G
x, G
yAnd G
z).Usually, the zone that is treated as picture by a series of measuring periods is scanned, and above-mentioned these gradients change according to used specific portion method in these measuring periods.By using one of many known reconfiguration techniques, the NMR that a winding of gained is received is signal digitalized and it is handled with reconstructed image.
The most popular method that is used to gather NMR signal and reconstructed image has been used the variant of known " Fourier transform " imaging technique, and it usually is called as " spin-warpage ".In people's such as W.A.Edelstein the article that is entitled as " Spin-Warp NMR Imaging and Applications to Human Whole-Body Imaging ", this spin-warpage technology has been discussed and (has been seen for details Physics in Medicine and Biology, volume 25, the 751-756 page or leaf, 1980).Thereby it had used a kind of amplitude variable phase encoding magnetic field gradient pulse that the spatial information on this gradient direction is carried out phase encoding before gathering NMR spin-echoed signal.In two-dimentional implementation (2DFT), for example, by along a cartesian coordinate system direction application phase encode gradient (G
y), on this direction, spatial information is encoded, then, with a direction of this phase-encoding direction quadrature on have the magnetic field gradient (G that reads
x) situation under gather a spin-echoed signal.The readout gradient that exists during the spin-echo acquirement is encoded to the spatial information on the orthogonal directions.In typical 2DFT pulse train, in " view " sequence of above-mentioned scan period collection, increase progressively phase encoding gradient pulses G
yAmplitude (Δ G
y), to produce one group of NMR data, from these data, can reconstruct entire image.
In order to increase the speed of acquired image frames, by gathering phase encoding view still less, or, just may sacrifice picture quality by using faster pulse train (this itself just cause picture quality lower).Therefore, when using spin-warpage method, between the speed of the NMR data of the number of the view of gathering in order to realize desired images resolution and quality and collection complete image, a kind of balance is arranged.
Recently, use a kind of alternative approach that is used to gather the NMR view data, wherein do not used phase encoding gradient.On the contrary, in the gatherer process of each NMR signal (i.e. " view "), only used readout gradient, and, just gathered a series of different views by rotating the angle of readout gradient.By the rectilinear scanning mode sampled in the k space no longer in the Fourier imaging, this " reconstruction from projection " method is sampled to the k space with a series of views, and these views are to sampling from the outward extending radial line in the center in k space.The sample number of required view of k space has been determined the length of scanning, and if gathered the insufficient view of number, then in the image that reconstructs, produced streak artifacts.
Because the heart of beating is a steady motion, thus between a series of heart beat periods in cardiac cycle approximately identical point or " stage " locate, gathered to reconstruct and do not had the required many different view of pseudomorphism image.Use the ECG trigger pip that image acquisition process is carried out gate, usually, the time interval selected after the heart trigger pip is located, and gathers four to eight views (being called as " figure section ").The image displaying that reconstructs by the heart in the selected specific heart phase that determined time delay.
Fig. 2 shows the standard backprojection method that is used in MRI and the X ray CT.By come along the projection path shown in the arrow 16 projection each distribute in 10 sample of signal 14 and make it pass FOV 12, each signal projection that collects distributes and 10 just is backprojected on the visual field 12.In the process that each sample of signal 14 is projected among the FOV 12, we are without any the priori about this experimenter, and the signal among the supposition FOV 12 is similar and sample of signal 14 should be assigned in each pixel that projection path passes equably.For example, Fig. 2 shows projection path 18, and when it was passed in N pixel among the FOV 12, it was corresponding to distribute individual signals sample 14 in 10 of a signal projection.The signal value (P) of between this N pixel, cutting apart this sample of signal 14 equably:
S
n＝(P×1)/N (1)
Wherein: S
nIt is the NMR signal value of in projection path, distributing to n pixel with N pixel.
Obviously, the signal among the FOV 12 is that this similar supposition is incorrect.Yet, as known in the art, proofread and correct if each signal distributions 10 is carried out some filtering, and the distribution through filtering of gathering sufficient amount with the projection angle of respective amount, then the caused mistake of this wrong supposition reaches minimum and image artifacts is inhibited.In typical, filtered rear projecting method about image reconstruction, for 256 * 256 pixel two dimensional images, need 400 projections, for 256 * 256 * 256 volume elements 3-D views, then need 203,000 projections.If use above-mentioned United States Patent (USP) 6,487, the method described in 435, then the number of the required projection view of these identical images may be reduced to 100 (two dimensions) and 2000 (three-dimensionals).
Before more than 20 year, McKinnon and Bates are at " Towards Imaging The Beating HeartUsefully With A Conventional CT Scanner " this piece article (IEEE Transactions onBiomedical Engineering, volume BME-28, No.2, February .1981) in a kind of method that is used to be reduced to the number of the required projection view of the image that produces the satisfactory heart of beating has been proposed.These authors recognize, when gathering view by different heart phase, static tissue remains constantly around the heart, and all views that collect can be used to the high quality graphic of reconstruct about these static tissues.By with of the organize data combination of these higher-quality static tissue images with the motion that collects, just can reconstruct an image, wherein can be removed by the static streak artifacts that tissue caused.Yet this method had not found that great clinical practice was arranged because design this method at the multi-source CT scanner do not have commercialization at that time.
Can the one or more heart phase during single is held the breath gather goodish monolithic two dimensional image although utilize known method, but previous method is fast inadequately, can't gather 3-D view or a plurality of two-dimentional sheet in each heart phase during single is held the breath.When the experimenter in being in inspection (such as coronary artery) does not lie in the single two dimensional surface, or need multi-disc or three-dimensional image acquisition so that when diagnosing, above-mentioned this image is essential.
Summary of the invention
The present invention is a kind of new method of image of the tissue that is used to produce heart and other motion, particularly a kind ofly is used to improve the method for quality that the height that collects in specific heart phase is owed sampled images.The heart phase of selecting between continuous heart beat period has been gathered a series of picture frames of owing to sample.The view of being gathered during the successive heartbeat is sampled to track staggered in the k space, and these samplings are combined and are used to reconstruct one composograph, and this composograph is used to describe above-mentioned experimenter.By highly constrained rear projecting method and above-mentioned McKinnon and Bates method are combined use, this composograph is used to reconstruct picture frame from collect image frame views.
Discovery of the present invention is: if use about the priori of the signal profile among the FOV 12 in the back projected picture restructuring procedure is not that the putative signal profile is even, then can produce the top-quality frames image with few view that collects.With reference to Fig. 3, for example, the signal profile among the FOV 12 may comprise the structure as blood vessel 18 and 20.In this case, when backprojection path 8 is passed these structures, by known NMR signal profile this distribution is weighted, thereby sample of signal 14 is assigned in each pixel more accurately according to this pixel position.As a result, the major part of sample of signal 14 will be assigned to and structure 18 and 20 those pixel places of intersecting.For the backprojection path 8 with N pixel, this can be expressed as:
Wherein: P=sample of signal value; And
C
n=along the signal value of the composograph at n pixel place of backprojection path.
Molecule in the formula (2) utilizes in this composograph corresponding signal value to come each pixel is weighted, and denominator makes this value normalization, make all rear-projection sample of signal reflected picture frame projection and and not multiply by this composograph with.
Fig. 4 shows a three-dimensional embodiment of the present invention, corresponding to being the single 3 D projection view of feature with view angle theta and φ.This projection view be along axle 16 by rear-projection and be extended in the Radon plane 21 at distance r place along rear-projection axle 16.As substituting of filtered rear-projection (wherein projection signal's profile is filtered and is assigned to equably in the continuous Radon plane),, utilize the information in the composograph that projection signal's profile value is assigned in the Radon plane 21 along axle 16.Composograph among Fig. 4 comprises blood vessel 18 and 20.Based on relevant position x in the composograph, y, the intensity at z place will leave the picture position x in the Radon plane 21 through the signal profile value of weighting in, y, z place.This is the simple multiplication processes of signal distributions value and corresponding composograph voxel values.Then, by making this product, make this product normalization divided by the distribution value in the respective image space distribution that from composograph, forms.The formula that is used for three-dimensionalreconstruction is:
I(x，y，z)＝∑(P(r，θ，φ)＊C(x，y，z)
(r，θ，φ)/P
c(r，θ，φ) (3)
Wherein summation (∑) is to carry out in all projections in time frame, and the x in the specific Radon plane, y, and the z value is to use at the suitable r in this plane, θ, (r, θ φ) calculate the distribution value P at φ value place.P
c(r, θ φ) are corresponding distribution value from composograph, and C (x, y, z)
R, θ, φBe (r, θ, the composograph value of φ) locating.
Another discovery of the present invention is: particularly useful when highly constrained rear projecting method and McKinnon and Braes method combine.McKinnon and Bates method need deduct static tissue signal from the projection view that collects.This has produced one group of sparse data for projection, and therefrom restructural goes out composograph, and it comprises the prior imformation that is limited to structure of interest.
Another aspect of the present invention is the restructuring procedure of the nuclear magnetic resonance image frame that collects with three-dimensional hybrid reconstruction from projection pulse train in cardiac gating scan period.The acquired projections view is so that sample to the k space with the radial trajectories in the two-dimentional sheet, and the use phase encoding is so that gather a plurality of along axial direction.At each multi-disc position, the reconstruct composograph, and in each picture frame, used these composographs during the backprojection reconstruction about two-dimentional sheet.
Description of drawings
Fig. 1 is to use the block diagram of MRI of the present invention system;
Fig. 2 is the diagram of conventional backprojection reconstruction method;
Fig. 3 is the diagram that is used for the rear projecting method of 2D PR image reconstruction according to the present invention;
Fig. 4 is the diagram that is used for the rear projecting method of 3DPR image reconstruction;
Fig. 5 is by the diagram of the performed mixing PR pulse train of the MRI system of Fig. 1 when putting into practice better embodiment of the present invention;
Fig. 6 is to use the diagram of k spatial sampling of the series of composite of Fig. 3;
Fig. 7 is the process flow diagram of the many steps in better embodiment of the present invention;
Fig. 8 has the radially diagram of the interlaced sampling in the k space of sample track;
Fig. 9 is the figure that is used to show by the data structure that method produced of Fig. 7;
Figure 10 is the diagram of the step of projection again in the method for Fig. 7; And
Figure 11 is the process flow diagram that is used for many steps of reconstruct two-dimensional image frame according to the present invention.
Embodiment
With reference to Fig. 1, in the MRI system, used better embodiment of the present invention especially.This MRI system comprises workstation1 10, and workstation1 10 has display 112 and keyboard 114.Workstation1 10 comprises processor 116, and processor 116 is the commercial programmable machines that can move commercial operation system.Workstation1 10 provides operation interface, and the indication that will be imported in this MRI system can be scanned in this interface.
Workstation1 10 is coupled to four station servers: pulse sequence server 118; Data acquisition server 120; Data processing server 122; With data storage server 23.In better embodiment, data storage server 23 is to be realized with relevant disc drive interface circuit by workstation processor 116.Its excess-three station server 118,120 and 122 all is by being installed in the single chassis and with 64 backplane bus the different processor of its interconnection to be realized.Pulse sequence server 118 adopts commercial microprocessor and commercial four worker's communication controlers.Data acquisition server 120 all adopts identical commercial microprocessor with data processing server 122, and data processing server 122 also comprises one or more array processor based on the parallel vector processor of commercialization.
Workstation1 10 all is connected to serial communication network with each processor that is used for server 118,120 and 122.This serial network transmits the data that download to server 118,120 and 122 from workstation1 10, and it also is transmitted between each server and the label data that transmits between workstation and server.In addition, between data processing server 122 and workstation1 10, also provide high speed data link, so that image data transmission is arrived data storage server 23.
The RF excitation waveform is applied to RF coil 34 by RF system 26, thereby carries out the magnetic resonance pulse sequence of appointment.RF system 26 receives the NMR signal by the 34 detected responses of RF coil, under the commander of the order that pulse sequence server 118 is produced, to these signals amplify, demodulation, filtering and digitizing.RF system 26 comprises the RF transmitter, and this RF transmitter produces the multiple RF pulse that is used in the MR pulse train.This RF transmitter has the RF pulse of expected frequency, phase place and pulse amplitude waveform in response to scanning indication and commander from pulse sequence server 118 with generation.The RF pulse that is produced can be applied to monoblock type RF coil 34 or be applied to one or more local coils or coil array.
And the phase place of the NMR signal that receives also can be determined:
φ＝tan
-1Q/I.
Should be clearly, in scanning process, 118 pairs of MRI system elements of pulse sequence server are carried out control in real time.As a result, must operate its hardware element with the programmed instruction of carrying out in good time mode by the program of working time.The description composition that is used for scanning indication is that form is downloaded from workstation1 10 with the object.Pulse sequence server 118 comprises some programs like this, and they receive these objects and convert thereof into by the employed object of the program of working time.
The digitized NMR sample of signal that RF system 26 is produced is received by data acquisition server 120.Data acquisition server 120 is operated in response to the description composition of downloading from workstation1 10, so that receive real-time NMR data and buffer-stored is provided, makes and loses according to overload without any the data factor.In some scanning process, data acquisition server 120 is just given data processing server 122 with the NMR data transfer that collects.Yet, need from the NMR data that collect, obtain information so that in those scanning processes of other performance of gated sweep, data acquisition server 120 just is programmed to produce this category information and it is transferred to pulse sequence server 118.For example, in the process of prescan, gather the NMR data, and use it for calibration by the performed pulse train of pulse sequence server 118.Equally, in scanning process, can gather navigator signal and use it for and adjust RF or gradient system running parameter or be used to control the view order of being sampled in the K space.In addition, data acquisition server 120 can be used for handling the NMR signal, and these signals are used to detect the arrival of the contrast preparation in MRA scanning.In all these examples, data acquisition server 120 is gathered the NMR data and in real time it is handled, thereby produces the information that is used to control this scanning.
The NMR data that data processing server 122 receives from data acquisition server 120, and according to from the description composition of workstation1 10 downloads it being handled.This class is handled and can be comprised: produce bidimensional or 3-D view thereby original K space NMR data are carried out Fourier transform; Image applications filtering to reconstruct; The NMR data that collect are carried out back projected picture reconstruct; Computing function MR image; Calculate motion or stream picture etc.
The image of 122 reconstruct of data processing server back is transferred to workstation1 10 again, and stores.Realtime graphic is stored in the archival memory high-speed cache (not shown), and exports it to operating personnel's display 112 or display 42 from this high-speed cache, and this display is placed near the magnet assembly 30 so that doctor's use.The realtime graphic of batch mode image or selection is stored in the master data base on the disk storage device 44.When this class image by reconstruct and when being transferred to memory device, data processing server 122 is the data storage server 23 of notice on workstation1 10 just.Workstation1 10 can be used by the operator, so that archival image, produce film or send image by network to miscellaneous equipment.
In order to put into practice better embodiment of the present invention, use reconstruction from projection or radial, pulse sequence (such as shown in Figure 5 the sort of) to gather the NMR data.This is a kind of quick gradient-recurrence echo pulse sequence, wherein a kind of optionally, the asymmetric sinc RF driving pulse 200 that blocks of generation under the situation that sheet-selection gradient 202 exists.The flip angle of RF pulse 200 is set as near being used for T
1Shorten the Ernst angle of blood, this angle is 30 °～40 ° usually.
This pulse train can be used to gather single two-dimentional sheet by sampling in single k space circle plane, but in better embodiment, like that a plurality of circular k space planes is sampled shown in 204 among Fig. 6,206 and 208.When gathering a plurality of two-dimentional sheet, axial gradient 202 is that a plate is selected gradient, is thereafter phase encoding gradient lobe 210 and opposite polarity recoil (rewinder) gradient lobe 212.This axial phase encoding gradient lobe 210 has traveled through a plurality of values of above-mentioned scan period, so that sample from two-dimentional k space plane 204,206 and 208.
For a person skilled in the art, should be clearly, can use the sample track except that above-mentioned preferable straight path, these preferable straight lines from the peripheral edge of k space one light begin to extend and pass arrive behind the center in k space on the peripheral edge of k space relative a bit.A kind of variant is a collecting part NMR echoed signal 218, and it is sampled along the track across the gamut of the k spatial volume that is sampled not.The variant that another kind is equivalent to linear projection's reconstruction pulse sequence is along the path of bending and non-rectilinear is sampled.This pulse train has been described: people's such as F.E.Boada " FastThree Dimensional Sodium Imaging ", MRM, 37:706-715,1997 in following document; People's such as K.V.Koladia " Rapid 3D PC-MRA Using Spiral Projection Imaging ", Proc.Intl.Soc.Magn.Reson.Med.13 (2005); And people such as J.G.Pipe and Koladia " Spiral ProjectionImaging:a new fast 3D trajectory ", Proc.Intl.Soc.Mag.Reson.Med.13 (2005).Also should be clearly, the present invention also can be with the three-dimensional of these method of samplings but not two-dimentional version use, and term " pixel " is intended to represent position in two dimension or the 3-D view as hereinafter employed.
With reference to Fig. 7, gathered a series of cardiac gating picture frames especially, they have described to be in the heart in corresponding a plurality of different heart phase.As determine shown in the frame 300, system wait ECG gate-control signal, when this signal is received, the pulse train of execution graph 5 is so that gather projection view about the heart of positive motion and static tissue on every side from a plurality of (such as N=20) heart phase, just as shown in the process frame 302.In each heart phase, use this specific pulse train, gather three kinds of two-dimentional sheets effectively, projection view be interlock and by spaced apart equably, just as shown in Figure 8, the k spatial sampling track that its dotted line 230 expressions are gathered at a sheet, the k spatial sampling track that dotted line 232 expressions are gathered at second sheet, solid line 234 expressions are used for the k spatial sampling figure of the 3rd sheet.This gatherer process continues, up to the projection view (such as n=30) of having gathered defined amount in each heart phase at three kinds of two-dimentional sheets, just as determining that frame 304 is detected.Shown in the frame among Figure 12 305, thus, gathered N=20 picture frame, n=30 staggered projection view arranged in each two-dimentional picture frame.The projection view that is collected in each heart phase is not only staggered as mentioned above, they also with other heart phase in the projection view that collected interlock.
Have many different modes can produce the tabulation of scan period projection visual angle φ, it will make all views that collect staggered.This visual angle φ will depend on following factors: in the number (N) of the heart phase that will gather between heart beat period each time; Number (n at the projection view that will gather at each heart phase between heart beat period each time
Pr); Number of times (H) in the scan period heartbeat.The formula that is used to calculate the visual angle of n heart phase between the k time heart beat period in better embodiment is:
φ＝Δ
1×K+Δ
2×B(n)+[0:180/n
pr:180]
Wherein: Δ
1=180/ (H * n
Pr)
Δ
2＝180/(H×N×n
pr)
B (n)=be used to produces the bit reversal algorithm of the pseudo-random permutation of a series of integers.
The visual angle φ that is used for each sheet also interlocks, and this is to realize by making initial angle in each sheet increase progressively " 180 °/sheet number ".
Still with reference to Fig. 7 and 9, shown in process frame 306, use and come reconstructed image 307 at all projection views that collect (nxN) of each sheet position.This is a kind of restructuring procedure of routine, the NMR signal that wherein collects at first vertically gradient direction through Fourier transform, so that produce projections in three sheet positions along this.Then, the radially k space sample point that is used for each two-dimentional sheet is regridded to cartesian grid, then, carries out two-dimensional Fourier transform.The average image of gained is depicted heart as fuzzy appearance, because heart is in motion, but there is the staggered projection view that collects in each sheet place in each heart phase because used in restructuring procedure, so static structure will be described very accurately and pseudomorphism is seldom arranged.
Shown in process frame 310, at one of N heart phase, by all projection visual angles projection average image 309 again.This is illustrated in Figure 10, and be to realize with conventional Radon conversion, such as, " Computed Tomography Principles; Design; Artifacts andRecent Advances " book of Jiang Hsieh (SPIE publishes, and 2003, chapter 3) this is described.Thus, each visual angle according to gathering at each sheet in this heart phase produces projected outline.At each heart phase, repeat again projection step 310, and when as decision frame 312 detects again projection during last heart phase projection, shown in Fig. 9 center 311, produced the projection again of mean chart picture frame.
Shown in process frame 314, next step is to deduct the projection again of each the average image from the projection 313 that collects accordingly.This causes in each heart phase of the N=20 that a collects heart phase, and at each two-dimentional sheet and n=30 projection view of Yan Youyi group, they only are used to the tissue describing to move, with regard to such shown in the frame 313.Signal from stationary has been cut, and remaining signal all is the motor tissue signal through high-pass filtering basically.This be a kind of data set of " sparse " promptly only comprises motion structure among the FOV at these projection views that are used for each two-dimentional picture frame.
Next, shown in process frame 316, by carry out conventional image reconstruction with motor tissue projection view 313, just reconstruct composograph.In each heart phase, at each two-dimentional picture frame, reconstruct composograph, hereinafter this is explained in more detail.Because composograph 315 is to reconstruct from a large amount of different projection views, so compare with the image that reconstructs in the usual way in n=30 the projection from single two-dimentional picture frame, they have much higher SNR.
This systemic circulation goes back so that come the reconstruct composograph at each two-dimentional picture frame that collects, just as shown in the process frame 412.When all composographs during by reconstruct, shown in decision frame 414, just this process has been finished.
Shown in process frame 318, next step is: by carrying out each the highly constrained backprojection in n=30 the motor tissue projection, reconstruct the two-dimentional picture frame of each motor tissue.Hereinafter describe this step in more detail, and this result is the preferable image of the motion structure among the FOV, with regard to shown in the frame 317 like that.Each motor tissue two dimension picture frame all comes reconstruct by this way in each heart phase, to the last a picture frame is by reconstruct, just as determining that frame 320 places are detected.Shown in process frame 322, final step is: at each heart phase, each motor tissue picture frame 317 is combined to form final picture frame 319 with the average image 309.This is to realize by the value of adding respective pixel place in the image.This has added good stationary signal, and it has added the low frequency movement tissue signal that is before cut at process frame 314 places again.
As mentioned above, at each motor tissue two dimension picture frame, produce composograph, so that the prior imformation about the experimenter among the FOV is provided.Tricks of the trade are to select those collected and motor tissue projection views that can accurately describe the experimenter of two-dimentional sheet position.The projection view that is used for current two-dimentional picture frame comprised, but because this experimenter move, must be careful in the process of the additional projection view in the composograph so will be included in selection.
Especially with reference to Figure 12, based on the amount of the experimenter's motion that has taken place, be chosen in collect in the adjacent heart phase, from the projection view of identical sheet position, and these projection views are included in the composograph.Shown in process frame 400, calculate the barycenter (" COM ") of each motor tissue projection view, to locate the position of these motor tissues roughly.This calculating utilizes the following fact to realize,, from the average first moment of corresponding sinogram, can obtain the projection of the COM of object to the Radon line that is:
COM
x*cosθ+COM
y*sinθ＝∫rR(r，θ)dr/∫R(r，θ)dr
Wherein: COM
xCOM
yThe coordinate of=COM
R (r, θ)=Radon projection (sinogram)
Next, enter a circulation, wherein the difference between the COM of the projection view in the COM of the projection view in current two-dimentional picture frame and the adjacent heart phase is calculated, just as shown in the process frame 402.If this difference is lower than default amplitude (as decision frame 414 is determined), the motor tissue projection view that then is used for this adjacent heart phase is added to composograph, shown in process frame 406.At other adjacent heart phase, repeat this evaluation process, shown in process frame 408, be exceeded, just as determining what frame 404 places were determined up to default motion value.
The amount that is used for experimenter's motion that special exercise organizes the number of the included motor tissue projection view of the composograph of two-dimensional image frame to depend on just to occur.During diastole, seldom there is the experimenter to move, and may comprises, and will produce the very high composograph of SNR from the projection view that reaches 6 heart phase.On the other hand, during aroused in interest fast, may successfully be combined from the projection view of one or two heart phase.No matter how many numbers of included staggered projection view is, the composograph that is used for current two-dimentional picture frame is by reconstruct, shown in process frame 410.This is a kind of image reconstruction procedure of routine, and it is exactly to fix again in better embodiment, is thereafter two-dimensional Fourier transform, just as described above.
Above-mentioned highly constrained backprojection reconstruction method uses corresponding composograph to retrain the backprojection of each motor tissue projection view 313.With reference to Figure 11, the first step is by carrying out Fourier transform motor tissue picture frame k space projection to be transformed to the Radon space, shown in process frame 330 especially.This result is one group of signal distributions 10 as shown in Figure 3.Shown in process frame 332, next each in these signal distributions all is backprojected among the FOV, just as shown in the path among Fig. 38.Described like that in conjunction with equation (2) as mentioned, with composograph this backprojection is weighted.That is, use the normalized amplitude (C of pixel identical in the composograph
n) rear-projection value (P) that any pixel (n) is located is weighted.
Shown in process frame 334, next, backprojected signal values (S
n) be added to just by the two-dimentional picture frame of reconstruct.This systemic circulation is got back to decision frame 336, so that rear-projection is carried out in next signal distribution 10, shown in process frame 338 and 332.Therefore, the signal value (S of all rear-projection signal distributions 10
n) being added to this picture frame, its weighting is then decided by corresponding pixel value in the higher-quality composograph 315.Composograph 315 quality are higher, because it reconstructs from more projection view, and this produces pseudomorphism still less.The composograph quality is higher, also is used for its projection view of reconstruct because gathered on long a lot of time span.Usually, the SNR of picture frame is proportional to its square root of gathering the duration, and by this unique restructuring procedure, the composograph 315 that SNR is higher is passed to this picture frame.
Although better embodiment of the present invention is used in the MRI system, should be clearly, the present invention also can be used in the CT system.As above-mentioned MRI system, in one or more heart phase and one or more axial sheets position, gather staggered cardiac gating projection view with the CT system.Use and approaching identical step shown in Figure 7, these projection views are used to the one or more two field pictures of reconstruct.No longer as above, the k space projection view that collects is fixed and Fourier transform again, and be to use the conventional filtration rear projecting method to reconstitute an image with the Radon space projection view that CT scanner collects.
Should be clearly, the present invention can be used to reconstruct two-dimentional picture or 3-D view from the data for projection that collects.Under latter event, highly constrained rear-projection step will be used the three-dimensional method of equation (3) but not the two-dimension method of equation (2).
Claims (19)
1. the method for the image of a moving object that is used for producing the field of view (FOV) that is positioned at medical imaging system comprises the steps:
A), gather one group of projection view about this object with this medical imaging system in a series of images frame each;
B) in the projection view that collects from step a), produce corresponding motor tissue projection view, these motor tissue projection views have only been described the tissue of motion basically;
C) in the more than one group of projection view that from step a), collects, produce the average image;
D) utilize the pairing motor tissue projection view of projection view that collects at described picture frame, add other selected motor tissue projection view, come reconstruct to be used for the composograph of one of described picture frame;
E) come reconstruct to be used for the motor tissue of described picture frame by following process:
E) the pairing motor tissue projection view of projection view that collects at described picture frame of rear-projection i), and with the value of corresponding pixel in the composograph value that is backprojected in each image pixel is weighted; With
E) ii) the rear-projection value that is used for each image pixel is sued for peace; And
F) altogether with motor tissue image and average image sets.
2. the method for claim 1 is characterized in that, step c) comprises: reconstruct the average image in the projection view of the enough numbers that collect from step a), wherein described tissue static among the FOV and pseudomorphism seldom.
3. the method for claim 1 is characterized in that, step b) comprises:
B) i) again the projection average image so that produce the average image projection again; With
B) ii) from the projection view that collects accordingly, deduct the average image again projection so that produce corresponding motor tissue projection view.
4. method as claimed in claim 3 is characterized in that, all basically projection views that collect in the step a) all are used to the reconstruct the average image in step c).
5. method as claimed in claim 4 is characterized in that, comes projection average image again by each visual angle of the projection view that collected in a) set by step, just produces the motor tissue projection view in step b).
6. the method for claim 1 is characterized in that, the gatherer process in the step a) is subjected to cardiac gating, and described a series of images frame has described to be in the moving object in a succession of heart phase.
7. method as claimed in claim 6 is characterized in that the projection view that is collected in the step a) is repeatedly being gathered between heart beat period.
8. method as claimed in claim 7 is characterized in that described medical imaging system is a nuclear magnetic resonance imaging system.
9. the method for claim 1 is characterized in that, selects described other motor tissue projection view by following process in step d):
D) i) when collection is used for the projection view of described picture frame, in each group projection view of station acquisition, determine how many described objects moved with respect to described object; With
D) ii) select those to work as the motor tissue projection view that is collected when described object is within the position-scheduled distance of described picture frame.
10. the method for claim 1 is characterized in that, repeating step d), e) with f) so that from other multiple series of images frame projection view, produce additional image.
11. the method for claim 1 is characterized in that, calculates each image pixel rear-projection value S through weighting by following formula in step e)
n:
Wherein: P=is by the projection view of rear-projection;
C
nCorresponding pixel value in the=contour images;
S
n=along the value of n pixel of backprojection path; And
N=is along the sum of the pixel of backprojection path.
12. the method for claim 1 is characterized in that the projection view that is collected in the step a) interlocks.
13. the method for claim 1 is characterized in that, employed motor tissue projection view interlocks in the step d).
14. the method for claim 1 is characterized in that, the sheet position that is collected in the many groups projection view that is collected in the step a) each heart phase corresponding to a plurality of heart phase.
15. method as claimed in claim 14 is characterized in that, the projection view of gathering at described position interlocks.
16. method as claimed in claim 15 is characterized in that, utilizes at described and the pairing motor tissue projection view of gathering of interleaved projection views forms composograph.
17. method as claimed in claim 16 is characterized in that, repeating step d), e) with f) so that produce the image be used to describe to be in the moving object in each heart phase.
18. method as claimed in claim 16, it is characterized in that, many groups projection view of being gathered in the step a) is corresponding to the additional sheet position of being gathered in each heart phase, and repeating step d), e) with f) so that produce the image that is used to describe be in the moving object of each sheet position.
19. method as claimed in claim 18 is characterized in that, repeating step d), e) and f) be used to be depicted in the image that is in the moving object of each sheet position in each heart phase so that produce.
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| CN200680035048XA Active CN101287997B (en) | 2005-09-22 | 2006-09-08 | Highly constrained reconstruction of motion encoded mr images |
| CN200680034795.1A Expired - Fee Related CN101283288B (en) | 2005-09-22 | 2006-09-21 | Highly constrained backprojection reconstruction in diffusion weighted MRI |
| CN2006800351783A Active CN101297214B (en) | 2005-09-22 | 2006-09-21 | Highly constrained backprojection reconstruction in cardiac gated MRI |
| CNA2006800347947A Pending CN101287995A (en) | 2005-09-22 | 2006-09-21 | Highly constrained backprojection reconsruction in mr spectroscopy |
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| CNA2006800347947A Pending CN101287995A (en) | 2005-09-22 | 2006-09-21 | Highly constrained backprojection reconsruction in mr spectroscopy |
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| CN107015182A (en) * | 2015-12-03 | 2017-08-04 | 西门子保健有限责任公司 | It is determined that describing the method and magnetic resonance device of the movable information of the motion in test zone |
| CN113296038A (en) * | 2020-02-24 | 2021-08-24 | 上海联影医疗科技股份有限公司 | Magnetic resonance imaging system and method based on K-space radial sampling |
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| CN102008307B (en) * | 2010-12-29 | 2012-07-25 | 中国科学院深圳先进技术研究院 | Magnetic resonance diffusion tensor imaging method and system |
| CN102018514B (en) * | 2010-12-30 | 2015-07-08 | 中国科学院深圳先进技术研究院 | Magnetic resonance diffusion tensor imaging method and system |
| DE102011004881B4 (en) * | 2011-03-01 | 2012-10-31 | Siemens Aktiengesellschaft | Processing complex image data of an examination object with different spin species in MR imaging |
| WO2012117303A1 (en) * | 2011-03-01 | 2012-09-07 | Koninklijke Philips Electronics N.V. | Accelerated mr thermometry mapping involving an image ratio constrained reconstruction |
| DE102011077197B4 (en) * | 2011-06-08 | 2013-05-16 | Siemens Aktiengesellschaft | Distortion correction in magnetic resonance imaging |
| KR101351583B1 (en) * | 2012-10-10 | 2014-01-16 | 한국과학기술원 | Medical image imaging method, medical diagnostic apparatus thereof, and recording device thereof |
| CN103048632B (en) * | 2012-12-19 | 2015-11-25 | 北京大学 | A kind of quick fine angular resolution diffusion imaging method based on compressed sensing |
| CN103932707B (en) * | 2013-01-21 | 2015-07-22 | 上海联影医疗科技有限公司 | Phase contrast magnetic resonance flow velocity and flow rate measuring method and device |
| CN106470605A (en) * | 2014-07-15 | 2017-03-01 | 株式会社日立制作所 | MR imaging apparatus and blood flow discharge drawing method |
| KR102449249B1 (en) * | 2015-05-27 | 2022-09-30 | 삼성전자주식회사 | Magnetic resonance imaging apparatus and method thereof |
| EP3483619A1 (en) * | 2017-11-13 | 2019-05-15 | Technische Universität München | Automated noninvasive determining the sex of an embryo of and the fertility of a bird's egg |
| CN109696647B (en) * | 2019-02-21 | 2021-05-28 | 奥泰医疗系统有限责任公司 | K space acquisition method and reconstruction method for three-dimensional multi-excitation diffusion weighted imaging |
| CN113281282B (en) * | 2021-06-17 | 2022-05-13 | 四川九洲电器集团有限责任公司 | Image acquisition and reconstruction method, equipment and storage medium |
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| DE4319539A1 (en) * | 1993-06-12 | 1994-12-15 | Philips Patentverwaltung | Method for generating an MR image sequence and arrangement for carrying out the method |
| US6078176A (en) * | 1996-11-08 | 2000-06-20 | General Electric Company | Fast spin echo pulse sequence for diffusion weighted imaging |
| DE10119660B4 (en) * | 2001-04-20 | 2006-01-05 | Siemens Ag | Method for the rapid acquisition of a magnetic resonance image |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN107015182A (en) * | 2015-12-03 | 2017-08-04 | 西门子保健有限责任公司 | It is determined that describing the method and magnetic resonance device of the movable information of the motion in test zone |
| US10564244B2 (en) | 2015-12-03 | 2020-02-18 | Siemens Healthcare Gmbh | Ascertaining an item of movement information describing a movement in an at least partially moved examination region |
| CN113296038A (en) * | 2020-02-24 | 2021-08-24 | 上海联影医疗科技股份有限公司 | Magnetic resonance imaging system and method based on K-space radial sampling |
| CN113296038B (en) * | 2020-02-24 | 2022-11-25 | 上海联影医疗科技股份有限公司 | Magnetic resonance imaging system and method based on K-space radial sampling |
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| CN101297214B (en) | 2011-06-29 |
| CN101287996A (en) | 2008-10-15 |
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| CN101283288A (en) | 2008-10-08 |
| CN101283288B (en) | 2012-12-26 |
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| CN101297214A (en) | 2008-10-29 |
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