CN101297214A - Highly constrained backprojection reconstruction in cardiac gated MRI - Google Patents
Highly constrained backprojection reconstruction in cardiac gated MRI Download PDFInfo
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Abstract
Acquisition of MR data during a fMRI study employs a hybrid PR pulse sequence to acquire projection views from which multi-slice image frames may be reconstructed that depict the BOLD response to an applied stimulus or performed task. Composite images are reconstructed at each slice using the combined interleaved projection views from all the acquired image frames. The composite images are used to reconstruct the highly undersampled image frames using a highly constrained backprojection.
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 magnetic resonance imaging method employing and system.More particularly, the present invention relates to from cardiac gated nuclear magnetic resonance collection, reconstruct the process of image.
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
zMeeting rotation or " inclination " are in the x-y plane, thus the clean laterally magnetic moment M of generation
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 in these measuring periods, these gradients change according to used specific portion method.Each measurement result all is called as " view " in the art, and the number of view has determined the resolution of image.By using one of many known reconfiguration techniques, NMR signal that a winding of gained is received or view or k space sample numeralization and it is handled with reconstructed image.By the number of measuring period or be that the number of the view gathered of an image decides, therefore, by reducing the number of the view of gathering, can be that cost reduces sweep time to sacrifice image resolution ratio total sweep time on the part degree.
A kind of most popular method that is used to gather the NMR data set that can therefrom reconstruct image is called as " Fourier transform " imaging technique or " spin-warpage " technology.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 technology has been discussed and (has been seen for details Physics in Medicine and Biology, volume 25, the 751-756 page or leaf, 1980).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 the NMR signal.In two-dimentional implementation (2DFT), for example, by applying phase encoding gradient (G along a direction
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 acquired 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 the view sequence of above-mentioned scan period collection, increase phase encoding gradient pulses G
yAmplitude (G
y).In three dimensional realization mode (3DFT), before signal is read each time, the 3rd gradient G
zBe added to phase encoding along the 3rd.This second phase encoding gradient pulses G
zAmplitude also traveled through a plurality of numerical value of scan period.These 2DFT and 3DFT method are sampled to the k-space by form of straight lines shown in Figure 2, and the k-space sample is positioned on Descartes's lattice coordinate.
Nuclear magnetic resonance (NMR) vessel visualization (MRA) uses nmr phenomena to produce the image of body vessels system and heart.For the diagnosis capability of Enhanced MRA, before MRA scanning, can earlier the contrast preparation as the gadolinium be injected in the patient body.As United States Patent (USP) 5,417,213 described like that, use the tricks of the trade of this contrast enhancement mode (CE) MRA method to be: that is just flowing through interested vascular system at contrast preparation gathered the k space view at center constantly.CEMRA detects successful key: during the peak value artery strengthens, collect the center line in k space.If just gathered the center line in k space before contrast preparation arrives, then serious image artifacts may limit the diagnostic message in this image.Perhaps, the enhancing of vein sometimes can make the agent of peak value angiography by after the artery image that collects become unclear.In many anatomical area (such as the arteria carotis or the arteria renalis), the separation between artery and vein strengthen may be as little to 6 seconds.
The MRA data acquisition is made and gather the k central zone of space when contrast preparation arrives interested artery by timing.The ability that timing is carried out in the arrival of contrast preparation can change quite big, and in many application, it is useful gathering a series of MRA images in dynamic studies, and artery and vein that this dynamic studies has been described to separate strengthen.A series of images of arranging by the time also can be used for observing the blood vessel pattern filling of the delay that is caused by disease.By using three-dimensional " Fourier " acquisition method to gather a series of time-resolved images, just on the part degree, solved this requirement.The article of Korosec F, Frayne R, Grist T, Mistretta C " Time-Resolved Contrast-Enhanced 3D MR Angiography " (Magn.Reson.Med.1996; 36:345-351) and 5,713,358 pairs of this three-dimensionals of United States Patent (USP) " Fourier " acquisition method be described.
Recently, as United States Patent (USP) 6,487,435 is described, projection reconstruction methods has been used for the MRA data that acquisition time is differentiated.Projection reconstruction methods sometimes is called as " radially " gathers, and this method is just known when Magnetic resonance imaging occurs.By the rectilinear scanning mode sampled (promptly as shown in Figure 2) in the k space unlike the Fourier imaging, the projection reconstruction methods picture is gathered a series of views as shown in Figure 3, 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 if the number of the view of gathering is inadequate, then can produce streak artifacts in the image that reconstructs.Patent 6,487, the technology described in 435 is continuous by gathering, have interleaved views owe sampled images and between continuous images, share peripheral k spatial data, reduced this striped.
At United States Patent (USP) 6,710, in 686, described two kinds and be used for from the method for one group of k space projection view reconstructed image gathering.Prevailing method is that the k space sample is radially fixed Descartes's lattice coordinate the position on the sample track again from it.Then, by the k space sample after fixing is again carried out two dimension or three-dimensional Fourier transform, reconstruct image.The second method that is used for reconstructed image is: by each projection view is carried out Fourier transform, radially the k space projection view transforms to the Radon space.Be backprojected in the field of view (FOV) by these signal projections of filtering and with them, just from these signal projections, reconstruct an image.As known in the art, if the signal projection that collects is not enough to satisfy Nyquist (Nyquist) sampling rule at quantitative aspects, then in the image that reconstructs, can produce streak artifacts.
Fig. 4 shows standard backprojection method.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 backprojected among the FOV 12, we are without any the prior imformation about this experimenter, and the NMR 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. 4 shows signal projection individual signals sample 14 in 10 projection path 8 when passing N pixel among the FOV12 that distributes.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 NMR signal is that this similar supposition is incorrect among the FOV 12.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 the typical, filtered rear projecting method of image reconstruction, 256 * 256 pixel two dimensional images need 400 projections, and 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).
When some artery (such as coronary artery) was carried out imaging, the motion of the heart of beating became a problem.In order to reduce the correction of motion artefacts in MRI or the MRA image, common way is to utilize the ECG signal of expression heart phase (cardiac phase) to carry out cardiac gated to the view gatherer process.As mentioned above, for example, at United States Patent (USP) 5,329, in 925, the one or more heart phase in each cardiac cycle are gathered one group or one section view.For example, can gather 8 different views, and after 16 heartbeats, collect 8 * 16=128 different view altogether, therefrom can construct image in specific heart phase.Normally 16 to 20 heartbeats because single is held the breath are gathered all data so be desirably in very much during holding the breath, thereby have avoided the pseudomorphism that causes because of respiratory movement.
Can the one or more heart phase during single is held the breath gather goodish monolithic two dimensional image although utilize projection reconstruction methods and view to share, but previous method is fast inadequately, can't gather 3-D view or a plurality of two-dimentional sheet in each heart phase.When the experimenter in being in inspection does not lie in the single two dimensional surface (such as coronary artery), or when needing multi-disc or three-dimensional image acquisition, above-mentioned this image is essential.
Summary of the invention
The present invention is a kind of new method that is used to produce cardiac gated MR image, 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 samples are combined and are used for reconstruct one composograph, to describe the experimenter of selected heart phase.Be weighted by the distribution to the rear-projection sample of signal, this composograph is used in the highly constrained backprojection of each projection view.
Discovery of the present invention is: if use about the prior imformation of NMR 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. 5, 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, this distribution is weighted, realizes that sample of signal 14 is distributed in each pixel more accurately by known NMR signal profile according to this pixel position.As a result, the major part of sample of signal 14 will be distributed on 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=NMR sample of signal value; And
C
n=composograph is along the signal value at n pixel place of backprojection path.
Molecule in the formula (2) utilizes in this composograph corresponding NMR 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.Should be noted that, although above-mentioned normalization after carrying out rear-projection, each pixel is carried out separately,, in many clinical practices, it is then easier before rear-projection projection P to be carried out normalization.In this case, passing by same view angle in the projection process of this composograph, by divided by corresponding value P
c, make above-mentioned projection P normalization.Normalized projection P/P
cBy rear-projection, then, the image of gained multiply by this composograph.
Fig. 6 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 through Fourier transform forming the signal profile, and it 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 through the substituting of the rear-projection of filtering (wherein projection signal's profile filtered and be distributed to equably in the continuous Radon plane),, utilize the information in the composograph that projection signal's profile value is distributed in the Radon plane 21 along axle 16.Composograph among Fig. 6 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)(2a)
Wherein summation (∑) is that all projections in the time frame are carried out, and the x in the specific Radon plane, y, and the z value is with 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, this image reconstructing method can be advantageously utilised in the cardiac gated gatherer process, and wherein a series of two field pictures of owing to sample are gathered in same heart phase.By making the image in the continuous images frame gatherer process staggered, can be combined from the view of successive image frame, and be used to the composograph of reconstruct better quality.Then, this composograph is used in the above-mentioned backprojection reconstruction of each picture frame.
Another aspect of the present invention is the restructuring procedure of the picture frame that collects with three-dimensional hybrid reconstruction from projection pulse train in cardiac gated 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 gathered vertically a plurality of.To in a plurality of positions each, reconstruct one composograph, and use these composographs in the backprojection reconstruction of the two-dimentional sheet in each picture frame.
Description of drawings
Fig. 1 is to use the block diagram of MRI of the present invention system;
Fig. 2 is to use the Fourier transform technology to carry out the diagram of k spatial sampling;
Fig. 3 is to use reconstruction from projection's technology to carry out the diagram of k spatial sampling;
Fig. 4 is the diagram of conventional backprojection reconstruction method;
Fig. 5 is the diagram that is used for the rear projecting method of 2DPR image reconstruction according to the present invention;
Fig. 6 is the diagram that is used for the rear projecting method of 3DPR image reconstruction;
Fig. 7 is the diagram of the mixing PR pulse train carried out by the MRI system of Fig. 1 when putting into practice better embodiment of the present invention;
The diagram that Fig. 8 is to use the series of composite of Fig. 5 to carry out the k spatial sampling;
Fig. 9 is the process flow diagram of the many steps in the better embodiment of the present invention;
Figure 10 is about the diagram of the cardiac gated gatherer process of data between a heart beat period;
Figure 11 is the diagram of the k space being carried out interlaced sampling with sample track radially;
Figure 12 is the process flow diagram that is used for many steps of reconstruct two-dimensional image frame according to the present invention;
Figure 13 is to use the diagram of the image that the method for Figure 10 produces;
Figure 14 is the process flow diagram of the many steps in the second embodiment of the invention that contrast strengthens;
Figure 15 is to use the diagram of the image that the method for Figure 14 produces;
Figure 16 is the process flow diagram of the many steps in another better embodiment of the present invention; And
Figure 17 be when putting into practice the method for Figure 16 between a heart beat period about the diagram of the cardiac gated gatherer process of data.
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 instruction 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.
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 working procedure.The description composition that is used for scan instruction 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 program 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 transfiniting 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 navigation 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 flow image 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 7 the sort of) to gather the NMR data.This is a kind of quick gradient-call again echo pulse sequence, wherein under the situation that sheet-selection gradient 202 exists, produce a kind of optionally, the sinc RF excitation pulse 200 of asymmetric intercepting.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.
As hereinafter explaining in detail, this pulse train can be used to gather single two-dimentional sheet by sampling in single k space circle plane, and perhaps it can be used to a plurality of circular k space planes (shown in 204 among Fig. 8,206 and 208) are sampled.When gathering a plurality of two-dimentional sheet, axial gradient 202 is that a slab is selected gradient, is thereafter phase encoding gradient lobe 210 and opposite polarity recoil (rewinder) gradient lobe 212.This axial phase encoding gradient 210 has traveled through a plurality of values of 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 modification 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 modification 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 use with three peacekeepings of these method of samplings two dimension version, and term " pixel " is intended to represent position in two dimension or the 3-D view as hereinafter employed.
The MRI system of Fig. 1 uses above-mentioned pulse train to gather a series of cardiac gated two field pictures.In first better embodiment, in each picture frame, only gather single two-dimentional sheet.With reference to Fig. 1 and 9, be arranged in after the chamber of MRI system and ECG signal be coupled to physiology acquisition controller 36 the experimenter, this system wait ECG trigger pip is shown in decision frame 300.When receiving trigger pip, shown in 302, gather the set of diagrams picture frame.This is illustrated in Figure 10, wherein should cardiac cycle by the ECG start trigger signal at 304 places, and subsequently RR in interim the predetermined moment or " heart phase " gather hexad picture frame 306-311.In better embodiment, each image frame acquisitions process at process frame 312 places all comprises 10 projection views, and these projection views are as far as possible equably the visual angle of sampling in two-dimentional k space to be provided with by those.This is one and highly owes the data set of sampling, and if does not have the present invention then will produce the image of the non-constant of quality when carrying out typical image reconstruction.
When gathering last picture frame in RR interim as decision frame 314 is determined, this systemic circulation is gone back and is waited for next ECG trigger pip at decision frame 300 places.Gathered similar set of diagrams picture frame in next RR interim, difference is, 10 views that each picture frame 306-311 collected in RR interim subsequently are staggered with the view that had before collected.This is illustrated in Figure 11, wherein gathered the projection view shown in the dotted line 230 RR interim, gathered the projection view shown in the dotted line 232 in another RR interim, gathered the projection view shown in the solid line 234 in another RR interim.During typically once holding the breath, can gather 16～20 groups of this staggered projection views.
As mentioned above, the view in each picture frame that collects is aligned to as far as possible equably samples to the k space, and all will satisfy Nyquist sampling rule up to radius r outward, just as shown in Figure 11.Staggered projection 230,232 and 234 through combination is also sampled to the k space as far as possible equably, and they are sampled more thick and fast to the k space, and all satisfies Nyquist sampling rule up to bigger radius R outward.The result, when as decision frame 316 places among Fig. 9 are detected, all having gathered data at heartbeats all in once holding the breath, shown in 318 among Figure 10, gathered considerable staggered and equally distributed view at each heart phase in the generated data group.
Still with reference to Fig. 9, shown in process frame 320, use generated data group 318 to come reconstruct to be used for the composograph of each heart phase.In the process of once typically holding the breath with 16 to 20 heartbeats, the composograph group will comprise 16 to 20 times of contained data in the single image frame, and use the conventional rear-projection technology through filtering can reconstruct the image that appropriateness does not contain pseudomorphism.Shown in process frame 321, the composograph of gained also can be through editor or filtering, to remove undesired structure.By showing composograph and delete undesired structure and just can manually realize above-mentioned this point that perhaps pass filter removes the structure that can detect or organizes just and can automatically realize above-mentioned this point.
Shown in process frame 324, can come reconstruct a series of images frame to each heart phase now.To describe the restructuring procedure of a picture frame now, and an importance of the present invention is that the composograph of a heart phase can be used to the picture frame of this heart phase of reconstruct.
With reference to Figure 12, the first step is especially: shown in process frame 330, by carrying out Fourier transform, picture frame k space projection (having 10 in the better embodiment) is transformed to the radon space.One group of signal distributions 10 as shown in Figure 5 consequently.Shown in process frame 332, each sort signal distributes and next is backprojected among the VOI like that shown in the path among Fig. 58.Described like that in conjunction with equation (2) as mentioned, with composograph this rear-projection is weighted.That is, use the amplitude (C of arbitrary pixel (n) in the composograph
n) rear-projection value (P) that this pixel (n) is located is weighted.
Shown in process frame 334, next, with backprojected signal values (S
n) add to just by the picture frame of reconstruct.Then, this system signal is got back to decision frame 336, so that go the rear-projection next signal to distribute 10 shown in process frame 338 and 332.Therefore, the weighting that is determined with corresponding pixel value in the higher-quality composograph is with the signal value (S in all rear-projection signal distributions 10
n) add above-mentioned picture frame to.The quality of this composograph is higher be because, it be from more projection view, reconstruct and this produce still less pseudomorphism.The quality of this composograph is higher also because its used projection view of reconstruct collects on the long time span.Usually, the SNR of picture frame is proportional to its square root of gathering the duration.Discovery of the present invention is: the highly constrained restructuring procedure by this uniqueness just passes to above-mentioned picture frame with higher-quality composograph.
Turn back to the process flow diagram among Fig. 9, the picture frame that is used for a heart phase comes reconstruct with its corresponding composograph, and then, the picture frame that is used for next heart phase is by reconstruct, shown in process frame 340.When as decision frame 342 is determined, having reconstructed the picture frame that is used for all heart phase, shown in process frame 344, can show them with many modes.
Above-mentioned scanning has all produced a series of images frame in each heart phase.This is illustrated in Figure 13, and wherein each picture frame that reconstructs 345 all is associated with specific heart phase and specific heartbeat.These picture frames 345 can show in many different modes.At first, any selected time point (being heartbeat) during holding the breath can demonstrate the experimenter's who is used for being depicted in the successive heartbeat stage image.If this experimenter is a human heart, then these continuous heart phase images will demonstrate the structure when heart changes between a heart beat period.
Between a succession of heart beat period, also can watch the image 345 of any specific heart phase.In this case, heart movement is frozen, and people can see that cardiac structure changes in time.This display mode is particularly useful when using contrast preparation, and above-mentioned a series of images 345 has been described contrast preparation and flowed into situation in the visual field.The embodiment that this contrast of the present invention strengthens will be described now.
Figure 14 has described a kind of preferred approach of using contrast preparation in ECG gated sweep process.This specific implementations is used and is held the breath for twice, and the first step is that the guiding patient sets up first with reference to holding the breath, shown in process frame 350.This may realize with watch-dog, such as, the United States Patent (USP) 5,363,844 that is entitled as " Breath-holdMonitor For MR Imaging " is described this, and this watch-dog provides about respirometric visual feedback to patient.Shown in process frame 352, next, this initially hold the breath during by such a series of heart phase picture frames of gathering as described above.
Then, shown in process frame 354, supply with contrast preparation, and rebulid as process frame 356 reference position that is shown in and to hold the breath for the second time.By using the above-mentioned watch-dog of holding the breath, patient inhales is also then exhaled, and the feedback lamp indication on watch-dog has arrived the reference position.Shown in process frame 358, during holding the breath for the second time, this when contrast preparation flows in the visual field, gathers another group heart phase picture frame.
Shown in process frame 360, at each heart phase, contrast shielding (mask) image before producing.This is to realize by following process: all projections that each heart phase collected during holding the breath are for the first time all combined; And the back projected picture restructuring procedure of carrying out conventional filtering with the projection after the combination.For example, if 20 heartbeats take place during this holds the breath for the first time and all gather 10 staggered projection views, then always have 10 * 20=200 projection view and be used to each masked images of reconstruct in each heart phase.Thus, produced masked images 362, just as shown in Figure 15 at each heart phase.
Shown in process frame 364, next, at each heart phase, reconstruct unshielded (unmasked) composograph.This is to realize by following process: all interleaved projections that each heart phase collected during back contrast was for the second time held the breath combine; And the back projected picture restructuring procedure of carrying out conventional filtering with (such as 200) interleaved projections that these combine.Thus, produced maskless composograph 366, just as shown in Figure 15 at each heart phase.
Now, shown in process frame 368,, produce final composograph at each heart phase.This realizes by following process: from its corresponding unshielded composograph 366, deduct the masked images 362 that is used for each heart phase.As shown in figure 15, thus,, produced composograph 370 at each heart phase.These shielding composographs 370 have indicated the image pixel that Strength Changes takes place for those arrival because of contrast preparation, and they may be artery in the MRA research or the ventricle in the cardiac studies.Should be clearly, identical shielding composograph 370 also can be produced by following process: from corresponding back contrast projection view, contrast projection view before deducting; And from different projection views, reconstruct the composograph 370 of shielding.
Now, shown in process frame 372, can reconstruct the set of diagrams picture frame at each heart phase.This be as above describe and illustrated in fig. 12 use the shielding composograph 370 that is used for each heart phase and realize at the projection that this heart phase collected between heart beat period each time.In order to produce the sparse data set of the expectation that is used for this highly constrained backprojection reconstruction, deduct corresponding shielding projection view from the projection view that is used for this picture frame of reconstruct.As shown in figure 15, thus,, reconstructed picture frame 374 at heartbeat each time and at each heart phase.These can show in many different modes, just as above discuss and process frame 380 shown in.
Another better embodiment of the present invention has been used the multi-disc ability of the mixing PR pulse train among Fig. 7, so that gathering multi-disc picture frame with each heart phase between heart beat period each time.A plurality of adjacent sheets provide three-dimensional volume, therefrom can produce maximum intensity projection (MIP) image.When also not exclusively being in the two dimensional surface by the structure of imaging, this is important.This multi-disc embodiment can be used in the gatherer process of contrast enhancing above described in conjunction with Figure 14, but will describe the multi-disc embodiment that not contrast strengthens in conjunction with Figure 16 now.All to above embodiment described in conjunction with Figure 10 is similar in many aspects for this embodiment, and substantially the same step all uses identical label to identify in Figure 16.
With reference to Figure 16 and 17, carry out the heart trigger sweep especially, wherein a plurality of heart phase between heart beat period each time in once holding the breath are gathered a series of images frame.Each time between heart beat period, gather a series of images frame 306-311 at process frame 301 places, this is to above similar.Yet, no longer gather the list that is used for single k spatial pieces is sampled and organize 10 projection views, but gather two groups of 10 projection views in each heart phase.Gradient (Fig. 7) is carried out different phase encoding processing to 10 projection views of each group vertically, makes two adjacent two-dimentional sheets in k space be sampled.As now will as described in, in each heart phase, the final picture frame that constitutes by three two-dimentional sheets that forms.With reference to Fig. 8, these comprise center k spatial pieces 206 (hereinafter being called " A ") and two peripheral k spatial pieces 204 and 208 (hereinafter being called " B " and " C ").Yet,,, only gather two in above-mentioned three sheets in any single heart phase in order to reduce to gather each picture frame required sweep time.
Illustrate best as Figure 17, gather each time in the process of a two field picture in specific heart phase, centre slice A is gathered with one of peripheral sheet B or C.Sample mode makes that in any heart phase, centre slice A is gathered, and one of peripheral sheet B or C are gathered, and can produce other peripheral sheet from last adjacent gatherer process of time.For example, in Figure 17, during 20 times of the pulse train of Fig. 7 repeated, the first heart phase picture frame 380 that is collected between the n time heart beat period of once holding the breath had been gathered A and B sheet.In the identical heart phase of n-1 and n+1 heartbeat, A and C sheet have been gathered at 382 and 384 places.Therefore, when being the first heart phase restructuring graph picture frame of the n time heartbeat,, sheet C data have just been calculated by between C sheet adjacent on the time that 382 and 384 places collect between n-1 and n+1 heart beat period, carrying out interpolation.
Referring again to Figure 16, after all images frame of all heartbeats has all been gathered in once holding the breath as decision frame 316 places are determined, shown in process frame 323, from the data that collect, reconstruct one and be combined into image.At first, along the axial phase encoding axle of the k space data set that collects, carry out the one dimension fast fourier transform.As shown in Figure 8, the hybrid space data group of gained constitutes by three axial projection view sheets (A, B and C).To each sheet A, B and C,, three composographs of each heart phase of reconstruct.More particularly, for each heart phase, the sheet A projection that is collected during whole the holding the breath all as shown in Figure 17 second heart phase being combined into synthetic A data set 390, is combined into synthetic B data set 392 to sheet B projection, and sheet C projection is combined into synthetic C data set 394.Be combined with those projections of forming generated data group 390,392 and 394 just as interlocking above with reference to Figure 11 is described, thus, they are sampled to k spatial pieces A, B and C basically equably.Importantly, in this heart phase, generated data group 390,392 and 394 is all sampled to sheet A, B and C more thick and fast than any picture frame that collects.As a result, can use conventional image reconstructing method from the generated data group 390,392 and 394 that forms at each heart phase, to reconstruct composograph.In these three kinds of sheets each all is to utilize conventional reconstruction of two-dimensional images method to reconstruct separately.This may be a kind of backprojection of filtering or the process that fixes again of the two-dimensional projection in each sheet, is thereafter two-dimensional fast fourier transform.
After the restructuring procedure of composograph, shown in process frame 325, reconstruct is used for the picture frame of each heart phase.As above-mentioned embodiment, this image reconstruction procedure has been used highly constrained rear projecting method and composograph, so that the image artifacts in the picture frame that raising SNR and minimizing highly owe to sample.
The restructuring procedure of each picture frame can be realized in many different modes.At first, can carry out Fourier transform to limited one group of A, the B and the C phase encoded projection views that are used for a heartbeat stage along axial phase encoding gradient axle, to form three sheets.In these three sheets each all is to be made of one group of limited projection view, and utilizes method shown in Figure 12 therefrom to reconstruct picture.That is, each projection view is fourier transformed into the Radon space, then, uses the composograph of this sheet it to be carried out rear-projection so that each rear-projection value is weighted.Thus, reconstructing three adjacent picture frame sheets at each heart phase between heart beat period each time, and these can be used as 3-D view and are revealed.In addition, can from this 3-D view, produce maximum intensity pixel projection (MIP) image.
In above-mentioned reconstructing method, at first carry out Fourier transform along axial phase encoding gradient axle.When by the A in the picture frame of reconstruct, B and C phase encoded projection views when staggered each other, above-mentioned this point is preferable.If they interlock, then a kind of alternative approach is preferable, wherein before carrying out Fourier transform, each A, B and C phase encoded projection views are carried out rear-projection individually by using highly constrained rear projecting method and above-mentioned composograph weighting along gradient axes.Then, the data set of gained is fixed again so that aim at those samples along axial phase encoding axle.Then, to the blended data group through fixing again of gained, carry out the Fourier transform of phase encoding gradient axle vertically.
No longer image reconstruction procedure is converted to the restructuring procedure of three two-dimentional sheets, but can directly carry out the three-dimensionalreconstruction process of A, B and C phase encoding data set in each heart phase.In the U.S. Patent application of submitting on July 7th, 2006 that awaits the reply jointly 11/482,372 that is entitled as " HIGHLY CONSTRAINED IMAGE RECONSTRUCTIONMETHOD ", many kinds of methods have been described.These methods are quoted at this as a reference.
Claims (29)
1. the method for an experimenter who is used for producing the field of view (FOV) be positioned at Magnetic resonance imaging (MRI) system image comprises the steps:
A) at each time between heart beat period and of heartbeat repeatedly in each heart phase of a plurality of heart phase, with one group of projection view of MRI system acquisition;
B) projection view that is collected in the corresponding heart phase with repeatedly heartbeat produces a composograph to each heart phase, and each composograph is used to be depicted in the experimenter in the corresponding heart phase;
C) come the experimenter of reconstruct in selected heart phase image by following process:
C) i) will select the one group of projection view that is collected in the heart phase and be backprojected among the FOV, and use the value of corresponding pixel in the composograph that is depicted in the experimenter in the selected heart phase that the value that is backprojected in each image pixel is weighted; With
C) ii) the rear-projection value of each image pixel is sued for peace.
2. the method for claim 1 is characterized in that, the projection view that is collected in each heart phase interlocks.
3. the method for claim 1 is characterized in that, at step c) i) in calculate each image pixel rear-projection value S by following formula
n:
Wherein, P=is by the projection view value of rear-projection;
C
nCorresponding pixel value in the=composograph;
S
n=along the value of n pixel of backprojection path; And
N=is along the sum of the pixel of backprojection path.
4. the method for claim 1 is characterized in that, step b) comprises editor's composograph so that the probability of therefrom removing an object and this object being appeared in the image that reconstructs reaches minimum basically.
5. the method for claim 1 is characterized in that, step c) is included in carries out earlier this projection view being carried out Fourier transform before the rear-projection to each projection view.
6. the method for claim 1 is characterized in that, in each heart phase of a plurality of heart phase between heart beat period each time of heartbeat repeatedly, and repeating step c) so that produce image.
7. the method for claim 1 is characterized in that, under the guidance that mixes 2D PR pulse train execution in step a), this all gathers the projection views of organizing more in each heart phase, these projection views are used to describe corresponding a plurality of of experimenter.
8. method as claimed in claim 7 is characterized in that, step b) is included in the composograph that produces each sheet in each heart phase.
9. method as claimed in claim 8 is characterized in that step c) comprises: each sheet place in selected heart phase, utilize with selected heart phase and the corresponding composograph of sheet and come reconstruct experimenter's image.
10. method as claimed in claim 9 is characterized in that, the number of the picture of institute's reconstruct is greater than the number of the projection view group of utilizing mixing 2D PR pulse train to collect in each heart phase in the heart phase of selecting in step c).
11. method as claimed in claim 10 is characterized in that, also comprises: in selected heart phase, utilize the projection view that does not collect during this selected heart phase to produce one group of additional projection view.
12. method as claimed in claim 11, it is characterized in that, before the heartbeat of this selected heart phase and between twice heart beat period afterwards,, calculate one group of additional projection view by carrying out interpolation between the many groups projection view that in same heart phase, is collected.
13. the method for an experimenter who is used for producing the field of view (FOV) be positioned at Magnetic resonance imaging (MRI) system image comprises the steps:
A) in each heart phase of a plurality of heart phase between heart beat period each time of heartbeat repeatedly, with a plurality of views of this experimenter of MRI system acquisition;
B) utilize in step a) the view that collects from repeatedly heartbeat and selected heart phase to come the reconstruct composograph, this composograph has a numerical value at each composograph pixel place, and this numerical value is used for being illustrated in the experimenter of inherent this pixel position of FOV of selected heart phase; And
C) come this experimenter's of reconstruct image by following process:
C) i) in the view that is collected in the heart phase of from step a), selecting, produce image data set; With
C) ii) utilize this image data set and highly constrained rear projecting method to produce this experimenter's image, this highly constrained rear projecting method is weighted with the image pixel of corresponding pixel value in the composograph to each rear-projection.
14. method as claimed in claim 13, it is characterized in that, step a) is included in the projection view that each heart phase is gathered a plurality of phase encodings, step b) is included in the composograph that selected heart phase reconstruct is used for each phase encoding, and uses these composographs to come this experimenter's of reconstruct described image in step c).
15. method as claimed in claim 13, it is characterized in that, the view that collects in the heart phase of selecting in step a) is the projection view that collects by staggered projected angle between continuous heart beat period, at step c) i) in the image data set that produced comprise and select one group of described projection view, and in step b) from reconstructing composograph all staggered projection views basically.
16. method as claimed in claim 13, it is characterized in that, in step a), gather view in a plurality of selected heart phase, in step b), therefrom reconstruct corresponding a plurality of composograph, and in step c), reconstruct a plurality of images in corresponding a plurality of heart phase.
17. method as claimed in claim 13 is characterized in that, produces a plurality of images the view that collects in the corresponding heart phase of repeatedly selecting between heart beat period in step c).
18. method as claimed in claim 13 is characterized in that, step c) ii) comprises makes each image pixel normalization.
19. a method that produces the cardiac gated image of contrast enhancing with Magnetic resonance imaging (MRI) system comprises the steps:
A) in following the selected heart phase of gating signal and at each time between heart beat period, of heartbeat repeatedly with one group of view of MRI system acquisition;
B) reconstruct masked images all basically views that in selected heart phase, collect;
C) supply with contrast preparation;
D) in following the selected heart phase of gating signal and at each time between heart beat period of heartbeat repeatedly, contrast view with after one group of the MRI system acquisition;
E) reconstruct unshielded composograph all basically views that in selected heart phase, collect;
F) by from unshielded composograph, deducting masked images, produce composograph; And
G) reconstruct a two field picture the contrast view after in heart phase selected between heart beat period, collect one group, wherein use composograph that each pixel in this two field picture is weighted.
20. method as claimed in claim 19, it is characterized in that, described view is a projection view, and uses a kind of highly constrained rear projecting method to come execution in step g), this highly constrained rear projecting method comprises: the back contrast view that collects in selected heart phase is carried out rear-projection; And the rear-projection value is weighted with corresponding value in the composograph.
21. method as claimed in claim 19 is characterized in that, the view that collects in step d) interlocks.
22. method as claimed in claim 19 is characterized in that, at the repeating step g between heart beat period each time of heartbeat repeatedly) so that reconstruct one two field picture.
23. method as claimed in claim 19 is characterized in that, in another selected heart phase, repeating step d), e), f) with g) so that produce a two field picture.
24. method as claimed in claim 23 is characterized in that, heartbeat repeatedly each time between heart beat period in each heart phase of a plurality of selected heart phase, repeating step g) so that reconstruct one two field picture.
25. a method that produces the cardiac gated image of contrast enhancing with Magnetic resonance imaging (MRI) system comprises the steps:
A) in following the selected heart phase of gating signal and at each time between heart beat period of heartbeat repeatedly, with contrast projection view before one group of the MRI system acquisition;
B) supply with contrast preparation;
C) in following the selected heart phase of gating signal and at each time between heart beat period of heartbeat repeatedly, contrast projection view with after one group of the MRI system acquisition;
D) from corresponding back contrast projection view, deduct preceding contrast projection view;
What e) collect in selected heart phase produces composograph all projection views through deducting basically; And
F) reconstruct a two field picture the one group of projection view through deducting that collects in the heart phase of using a kind of highly constrained rear projecting method to select between a heart beat period, this highly constrained rear projecting method comprises: the projection view through deducting that collects in selected heart phase is carried out rear-projection; And the rear-projection value is weighted with corresponding value in the composograph.
26. method as claimed in claim 25 is characterized in that, the view that collects in step d) interlocks.
27. method as claimed in claim 52 is characterized in that, at the repeating step f between heart beat period each time of heartbeat repeatedly) so that reconstruct one two field picture.
28. method as claimed in claim 25 is characterized in that, in another selected heart phase, repeating step c), d), e) with f) so that produce a two field picture.
29. method as claimed in claim 28 is characterized in that, heartbeat repeatedly each time between heart beat period in each heart phase of a plurality of selected heart phase, repeating step f) so that reconstruct one two field picture.
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| PCT/US2006/036836 WO2007038205A1 (en) | 2005-09-22 | 2006-09-21 | Highly constrained backprojection reconstruction in cardiac gated mri |
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| CN200680034795.1A Expired - Fee Related CN101283288B (en) | 2005-09-22 | 2006-09-21 | Highly constrained backprojection reconstruction in diffusion weighted MRI |
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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 |
| EP2681576B1 (en) * | 2011-03-01 | 2020-07-29 | Koninklijke Philips 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 |
| WO2016009844A1 (en) * | 2014-07-15 | 2016-01-21 | 株式会社 日立メディコ | Magnetic resonance imaging device and blood flow drawing method |
| DE102015224162B4 (en) | 2015-12-03 | 2017-11-30 | Siemens Healthcare Gmbh | Method for determining a movement information and a magnetic resonance device describing a movement in an at least partially moved examination area |
| 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 |
| US11085979B1 (en) * | 2020-02-24 | 2021-08-10 | Uih America, Inc. | System and method for magnetic resonance imaging with radial sampling of k-space |
| 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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| 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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