CN100526906C - Degenerate birdcage coil and transmit/receive apparatus and method for same - Google Patents
Degenerate birdcage coil and transmit/receive apparatus and method for same Download PDFInfo
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- CN100526906C CN100526906C CNB2003801041812A CN200380104181A CN100526906C CN 100526906 C CN100526906 C CN 100526906C CN B2003801041812 A CNB2003801041812 A CN B2003801041812A CN 200380104181 A CN200380104181 A CN 200380104181A CN 100526906 C CN100526906 C CN 100526906C
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Abstract
A birdcage coil (16) used in conjunction with a magnetic resonance imaging apparatus includes a first conductive loop (81, 581), a second conductive loop (82, 582), and a plurality of first conductor rungs (80, 580) disposed between the first and second conductive loops. A third conductor (83, 83'', 583) is coupled to the second conductive loop at resonance frequencies, such as by second conductor rungs (84, 84'', 584). The birdcage coil also includes switches (590) for switching the birdcage coil at least among: 1) an RF transmit mode to operate as an RF transmit coil; and 2) an RF receive mode to operate as an RF receive coil.
Description
Technical field
The present invention relates to magnetic resonance imaging (MRI) technology.The application that is particularly suitable for combining of this technology with pass MRI scanning machine, and will be described with particular reference to pass MRI scanning machine.Yet, should being understood, the present invention also can be used for the MRI scanning machine of other similar application and other type.
Background technology
Usually, in MRI, uniform substantially, time-invariant main field B
0Be based upon in the inspection area, be placed in this zone by imaging object.By magnetic resonance radio-frequency (RF) excited and operation, chosen magnetic dipole (by the RF pulse) is tilted in the plane in this main field zone of crosscut in this subject, thereby can precession and resonance, under the situation that is not subjected to magnetic resonance radio-frequency (RF) excited and operation, these magnetic dipoles are aimed at main field.Then, this resonance dipole can be decayed or be rearranged to cause magnetic resonance (MR) echo or MR signal according to this main field.The various echoes of forming this MR signal are encoded by the magnetic field gradient of setting up in this main field.Be collected in the matrix that is commonly referred to the K space from the raw data of this MRI scanning machine or device.Usually, each echo is generated data line or the data line point in the K space by repeatedly sampling.At last, use inverse fourier transform or other known conversion, rebuild the image expression of this object from this K spatial data.
Usually, when to relatively large zone (for example trunk) imaging, transmit and receive the radio-frequency coil of having used whole health in the pattern at RF.Difference is, when to head, neck, shoulder or other relatively during less regional imaging, local coil is used as the RF receiving coil in conjunction with the transmitting coil of whole health usually.A reason using local coil is near having been improved signal to noise ratio (S/N ratio) and resolution by imaging region with this local coil.
It also is useful in some processes local coil being launched as RF.A benefit is, compares with RF from people's body coil, uses the influence that local coil can reduce the heat of supervening in absorptance (SAR) and the body in the RF emission process.
A kind of local coil of using in the MRI scanning machine is called as " birdcage " coil.The so-called birdcage RF coil that is used to receive the MR signal is known.For example, referring to No. the 4680548th, United States Patent (USP).Usually, birdcage coil is cylindrical and comprises by even number rod or axial two the conducting end loops or the ring that connect of conductor, this rod or axially conductor two end ring are divided into two arc or sections that are defined between the two.This structure makes this RF coil have the shape of birdcage.Correspondingly, " birdcage " speech typically refers to this geometric configuration.
This birdcage coil has many different resonant frequencies usually.Each resonant frequency is relevant with different resonance modes.Usually, this birdcage coil moves under selected resonance mode, to obtain in this coil inside: (i) field distribution as far as possible uniformly (as under the situation of emitter coil); And/or, the (ii) constant sensitivity of location independent (under situation) as receiving coil.The location independent of sensitivity is favourable, particularly with this coil axes plane orthogonal in provide convenience because it is the reconstruction from the image of MR signal that receives.
Referring to Fig. 2, the electrical characteristic of birdcage coil has been described, Fig. 2 shows various resonant frequencies (ordinate) and resonance mode (horizontal ordinate).On the principle, birdcage coil can be counted as has a plurality of resonance modes or resonant frequency, and the number of these resonance modes or resonant frequency equals pin that end ring is linked together or axial half of number of conductors.Therefore, the birdcage with eight pins has four different resonant frequencies and four kinds of different resonance modes (having different field distribution or the different relevant sensitivity in position).Interconnect by dashed curve with give the certainty ratio relevant resonant frequency and the resonance mode of this coil.Supposed to build the birdcage of eight pins, different birdcage coil types can be distinguished as follows:
A) low-pass type is characterised in that this end ring does not have electric capacity, thereby only has the single arc of this ring or the inductance of local distribution of section to activate.Four kinds of different resonant frequencies are arranged, and the uniform field distribution that lowest resonance frequency is interior with occurring in this coil area surrounded or the resonance mode of sensitivity are relevant, therefore, recommend to use this pattern.The field distribution of other resonance mode that is in higher resonant frequency is not too suitable, does not therefore use usually.The curve of this type coil is referring to the LP among Fig. 2.
B) when only in end loop, electric capacity being arranged, just formed high-pass type, thereby and pin do not comprise electric capacity and activate by the inductance that continuous conductor is formed the local distribution of having only single pin.This type also has four kinds of resonant frequencies that have four kinds of resonance modes, yet preferred resonance mode is positioned at highest frequency.The curve of this type coil is referring to the HP among Fig. 2.
C) the logical type of band all has electric capacity in two end ring and axial legs.Described in United States Patent (USP) the 4680548th, for example, " high pass " and " low pass " characteristic can be endowed the logical type of this band, depends on whether the electric capacity in this pin or this end ring shows inductance (characteristic of other part performance separately is an electric capacity).
Above-mentioned band with low-pass characteristic leads to the curve of type referring to the BP among Fig. 2
1, preferred resonance mode (having local uniform sensitivity) is positioned at lowest resonance frequency.The curve of the logical type of band with high pass characteristic is referring to the BPh among Fig. 2, and preferred resonance mode is positioned at the highest resonant frequency.
Coil array (be also referred to as phased-array coil, be made up of a plurality of overlapping plane subcoils usually) with the signal to noise ratio (S/N ratio) that is better than this birdcage coil is also arranged.Therefore, this coil is used to obtain and the coil array advantages associated in the birdcage geometric configuration.
For example, United States Patent (USP) No. 6043658 (the ' No. 658 patents) has been introduced a kind of birdcage coil with logical type, all comprises electric capacity in this axial legs and two end ring.Yet, thereby these electric capacity are balanced high pass or low-pass characteristic of not occurring, but seek curve B P among Fig. 2
dShown characteristic, wherein all resonance modes all occur or converge on same frequency substantially.In the paper of the 11st the nd Annual Meeting collection of medical magnetic resonance association (1992) that Troop holds " mixed the birdcage resonator ", this characteristic was called as " degeneration ".Therefore, has the birdcage coil that is called as degeneration to the logical type birdcage coil of band of common frequency (nominally being called as the degeneration frequency of this coil) convergent resonant frequency.
Should ' No. 658 patent think, thereby make it suitably balanced that other a plurality of resonant frequencies that have to the logical type birdcage coil of band of certainty ratio or size can degenerate to single resonant frequency by the electric capacity in the axial legs of two end ring of suitable selection and interconnection.At the resonant frequency of this degeneration, the single adjacent grid of forming birdcage is by decoupling zero mutually.Because this decoupling zero, these grids can effectively move or be operated as a coil array, and the MRI signal that receives from single grid can be according to similar manner by independent processing.Notice that single grid is meant the circular arc or the part in two adjacent axial legs or conductor and two end ring between them or loop.
Preferably, according to the ' No. 658 patents, the single MR signal reconstruction common image that can receive from single grid separately, wherein this common image has higher relatively signal to noise ratio (S/N ratio), especially in this coil near the location of these grids.In other words, single grid has the relevant sensitivity in position,, has higher relatively sensitivity from the signal that closes on this net region that is, has relatively low sensitivity from the signal in farther zone.For example, when the single MR signal that receives from single grid forms overview image, compare with other the birdcage coil of traditional approach operation, externally the zone can obtain high 2 to 4 the signal to noise ratio (S/N ratio) of coefficient, and the heart then has with conventional coil and operates essentially identical value therein.
Though quoted above-mentioned patent, still required further improvement.For example forming the importance of the minimum coupling between the single coil of phased array is understood in this technical field well.Similarly, the birdcage coil of degeneration also need have more minimized coupling between grid.In other words, bigger insulation is favourable between the grid, and not only for the grid of direct neighbor, and for farther grid (be next adjacent mesh or meshes near grid).The traditional regression birdcage coil provides the insulation that is not better than about 10dB usually, and usually this grid only by relative its direct meshes by effectively decoupling zero.In addition, need other a plurality of resonance frequencies converge or degenerate to each other difference within less number percent.By contrast, traditional degenerate birdcage coil can still have very little unlike a desired frequency distribution.Usually, traditional degenerate birdcage coil can have in resonant frequency greater than 5% or bigger frequency range.It should be noted that equally difficulty is to adjust degenerate birdcage coil to obtain required operation characteristic.Developing a kind of device that is used for more easily regulating this coil is favourable to solve this difficulty.Correspondingly, wish to have an additional degree of freedom also to facilitate for suitably regulating.
For example SENSE and SMASH imaging and other are relevant especially in using in the parallel image technology for the birdcage coil of degenerating.For example SENSE is based on the application of a plurality of RF coils and receiver.Use a plurality of coil units, only need make the phase encoding step of limited number and utilize same resolution to measure the same area of view: the acquisition time of Jian Shaoing equals coil unit quantity like this.Yet unlike phased-array coil, this coil unit is not used to cover independent anatomic region.But being used to measure simultaneously the same area, the single coil element sensitivity is used to the minimizing of phase encoding step is proofreaied and correct thus.
Usually, alternately utilize a RF coil (for example people's body coil) and second coil (for example local birdcage coil of Tui Huaing), collect sensitivity information by receiving the RF signal to inspection area transmitting RF signal and from the inspection area.When a RF coil received signal, second coil is by from this MR system decoupling.Similarly, when the 2nd RF signal received signal, first coil is by decoupling zero.The signal reconstruction image that from the signal that two coils receive, obtains the sensitivity information relevant and be used for only receiving from second coil with second coil.
Summary of the invention
The present invention proposes a kind of new improved birdcage coil and technology, thereby overcome above-mentioned and other problem.
According to an aspect, disclosed birdcage coil system is used in conjunction with MR imaging apparatus.Birdcage coil comprises first and second galvanic circles, and a plurality of first stub is arranged between first and second galvanic circles that electric power connects with it.Provide a kind of switchgear to be used between RF emission mode and RF receiving mode, this birdcage coil being changed at least.In the RF receiving mode, this birdcage coil is adjusted the receiving coil as phased array RF.
According to the another one aspect, a kind of birdcage coil in conjunction with the MR imaging apparatus application is disclosed.This birdcage coil comprises first and second galvanic circles, places between first and second conductive coils and a plurality of first stubs that while electric power connects and the 3rd conductor that separates and be connected at radio frequency second loop with second galvanic circle.
An advantage is to have reduced the local absorption rate.
The another one advantage is to finish parallel imaging technique, for example SENSE.
Another advantage is to have improved coil efficiency.
Yet the another one advantage is to have improved the insulativity of the grid of the birdcage coil of degenerating.
After reading and having understood the following description of preferred embodiment, further advantage of the present invention will be conspicuous for those skilled in the art.
Description of drawings
Realization of the present invention can be the layout by various piece and various piece, and operates and handle the arrangement of operation with various processing.Accompanying drawing only is used to illustrate preferred embodiment, is not to be counted as limitation of the present invention.
Fig. 1 is a synoptic diagram of having described MR imaging apparatus.
Fig. 2 is the figure that helps to describe the various action types of birdcage coil.
Fig. 3 is a synoptic diagram of describing birdcage RF coil.
Fig. 4 is used for the layout synoptic diagram of transmitting RF signal to birdcage coil.
Fig. 5 is the layout synoptic diagram that is used for the MR signal is fed to from birdcage RF coil processing channel.
Fig. 6 is the synoptic diagram that is used for the MR signal is fed to from birdcage RF coil another layout of processing channel.
Fig. 7 A, 7B, 7C and 7D have formed the planimetric map of electric current in the expression birdcage RF coil together.
Fig. 8 is the connection diagram that is used for providing the birdcage coil of Fig. 3 that radio frequency receives grid array.
Fig. 9 is a synoptic diagram of describing another exemplary embodiments of birdcage radio frequency coil.
Figure 10 is a synoptic diagram of describing another exemplary embodiments of birdcage radio frequency coil.
Figure 11 is a synoptic diagram of describing another exemplary embodiments of birdcage radio frequency coil.
Figure 12 is the planimetric map that is similar to the birdcage coil of coil among Fig. 3, and wherein each wire loop links to each other with independent transmit/receive switch.
Figure 13 is the synoptic diagram of one of them transmit/receive switch of Figure 12.
Preferred implementation
Referring to Fig. 1, a kind of MRI scanning machine has been described.Main field controller 10 control main magnetic field magnet 12, for example superconduction or resistive magnet.Main magnet 12 Be Controlled are used to generate even, stable substantially main field area B
0, this main field area B in test zone or zone 14
0Intensity with expection, for example | B
0|=3.0Tesla, wherein those who are investigated are placed in this inspection area.As shown in the figure, inspection area 14 has cylindrical inner diameter, but also can adopt other shape such as open area test zone.Typically, B
0Be set on Z-direction, the Z axle is the longitudinal central axis of test zone 14.
Pulse train is stored in the sequence memory 32 and by sequence controller 30 and carries out.Sequence controller 30 control gradient pulse amplifiers 20 are also controlled the first and second RF transmitters 24,25 as required.More specifically, sequence controller 30 control gradient pulse amplifiers 20 and this transmitter produce a plurality of MRI pulse trains, the MR signal that these pulse trains generate and gradient coding (that is section,, phase place and/or frequency coding) finally is received and samples.
The gradient coil 22 that gradient pulse amplifier 20 is applied to current impulse to select is along creating magnetic field gradient with the orthogonal axes of inspection area 14.These magnetic fields basically with B
0Extend on the same direction, but on x, y and/or z direction, have gradient respectively.
In this inspection area, arrange the 2nd RF coil 16, and can come in inspection area 14, to generate selectively the RF pulse by 25 controls of the 2nd RF transmitter alternatively.As shown in Figure 1, the 2nd RF coil 16 is birdcage head coil.The same with a RF coil 26, a B has been set up in these RF pulses in this test zone
1Magnetic field.
No matter adopt which kind of RF transmitter, typical radio-frequency pulse is mutually combined by the short-time pulse section of one group of direct neighbor and forms, and any gradient that is employed realizes a selected magnetic resonance operation.The MRI pulse train of optional employing is that two dimension (2D) or three-dimensional (3D) imaging generate the MR signal.The MRI pulse train of optional employing comprises a plurality of arbitrarily single echoes or many echo-wave imagings sequence.Can use an arbitrarily individual existing MRI technology and carry out imaging, for example area echo (FE) imaging, rotation echo (SE) imaging, echo-planar imaging (EPI), echoing volume imaging, gradient and rotation echo-wave imaging (GSE), fast rotational echo (FSE) imaging, single photography FSE imaging, three-D volumes FSB imaging, parallel imaging technique (for example sensitivity encoding (SENSE), space harmonics obtain simultaneously (SMASH) etc.) and/or similar techniques.Under the situation of 2D imaging, the region of interest domain representation passes by the 2D cross-sectional slices of imaging object.Under the situation of 3D imaging, the region of interest domain representation is by the 3D volume of imaging object.
14 magnetic resonance signals that produce are received by the RF receiving coil from the inspection area, and this RF receiving coil is placed near this inspection area.Alternatively, this RF receiving coil can be human body RF coil 26 or local RF coil 16.First receiver 38 is separated from whole body RF coil 26 receiving magnetic resonance signals and with this signal and is transferred to a plurality of data lines.If this receiver is simulated, first analog to digital converter 40 becomes digital form with each data line transitions.Alternatively, this analog to digital converter is placed between RF receiving coil 26 and the receiver 38 and is used for digit receiver.
It will be appreciated that local coil 16 is subdivided into a plurality of parts or grid (for example 8), each part links to each other with second receiver 34.Therefore, second receiver 34 can comprise a plurality of receivers and relevant analog to digital converter, and for example, each grid of local coil 16 comprises a receiver and relevant with it analog to digital converter.Alternatively, can adopt single multi-channel receiver.
Reconstruction processor uses inverse fourier transform or other reconstruction algorithm that is fit to is reconstructed into image expression with this data line.This image can represent to pass this patient's planar slice, parallel planar slice array, three-D volumes or analog.This electronic image is expressed and is stored in the video memory 52 subsequently, wherein this image can be visited selectively by video processor 54, and this video processor 54 is that display (monitor 56 of the readable demonstration of people of composograph for example is provided) converts suitable form to the other parts of section, projection or this image expression.
Referring to Fig. 3, show local RF coil 16 in further detail.Thereby local RF coil 16 can be used as emission/reception birdcage coil and can be used as quadrature transmit coil and phased array receiving coil.As shown in the figure, this phased array comprises eight independently coil or grids.In addition, local RF coil 16 can be that the sequence decoupling zero wherein only has health RF coil 26 to be used as receiving coil from the MR system.
As shown in the figure, thereby local birdcage coil 16 is created normally with respect to the axis of symmetry that extends along the z direction and becomes rotational symmetry, and comprises with this axis of symmetry arranged in co-axial alignment and be in first, second and the 3rd radio frequency conductor or loop 81,82 and 83 in the basic thus normal plane of extending.In an illustrated embodiment, this loop is isodiametric substantially.First and second conductor circuits 81 and 82 pass through first stub 80 by electrical interconnection.As shown in the figure, have eight rods 80, but can use the similar conductor of other even number.Each rod 80 comprises first leg capacitor C
1First and second loops 81 and 82 be divided into its separately with rod 80 be connected between defined part or circular arc.Each part of first conductor circuit 81 comprises a tuning capacity C
4With a matching capacitance C
5Similarly, each part of second conductor circuit 82 comprises the second tank capacitance C
2The part of two adjacent rods 80 and the loop between rod 81 and 82 has defined a single grid.
In the embodiment shown, end conductor is a loop.Yet also can adopt other end conductor, for example distal end cap or dish, other electric capacity or feedback circuit and analog.
Forward Fig. 4 to, show the end-view of first conductor circuit 81, together with single first stub 80 in this page or leaf
1, 80
2... 80
8For quadrature emission, second (promptly local) RF transmitter 25 links to each other with quadrature splitter and is used to generate two and has 90 RF that spend phase relations substantially and transmit.These two RF signals are launched into local RF coil 16 by first and second concentric cable 220,225, as shown in Figure 4.First concentric cable 220 and 200 couplings of first half-wavelength coaxial cables, two feeding points 201,202 of first half-wavelength coaxial cables 200 on coil 81 are connected to local RF coil 16.These two feeding points and first contact rod 80
2With 80
6Electric power connects.Second concentric cable 225 and the coupling of second half-wavelength coaxial cables, 210 electric power, second half-wavelength coaxial cables 210 is connected with local RF coil 16 electric power with 212 at feeding point 211.This latter two feed points and first stub 80
4With 80
8Electric power connects.Though 4 layouts of feeding have been shown among Fig. 4, can only use two feeding points, or implement alternatively more than four feeding points.
Fig. 5 shows the RF signal how acquisition receives from single grid.Show the end-view of first conductor circuit 81 simultaneously.Each capacitor C
5As matching capacitance, cross-over connection therebetween be a balanced-to-unbalanced transformer 300.This balanced-to-unbalanced transformer is the other suitable shape of butterfly balanced-to-unbalanced transformer or balanced-to-unbalanced transformer.Note, for clarity sake, not shown C among Fig. 5
4Electric capacity, and only show two output units.It will be appreciated that other C
5Electric capacity has similar output unit.
The capacitor C of each balanced-to-unbalanced transformer by providing prime amplifier to isolate
8Be installed on high-impedance amplifier or the prime amplifier 310.Because each capacitor C
5Only with separately grid is relevant, crosses over specific C
5The voltage of electric capacity is represented the MR signal of that grid induction.From C
5The MR signal that electric capacity the obtains amplifier 310 by separately subsequently is applied to second (promptly local) RF receiver.
Referring to Fig. 6, show a kind of optional feed arrangements, advantageously reduced the number of used processing channel 320.That is to say that the processing channel quantity that the embodiment of Fig. 5 uses equals the meshes number that adopted in this coil, and the quantity of the processing channel 320 that the embodiment of Fig. 6 uses is less than the meshes number that adopts in the coil 16.Note, for clarity sake, not shown C among Fig. 6
4Electric capacity, and only show two C
5The feed arrangements of electric capacity.It will be appreciated that other C
5Electric capacity has similar feed arrangements.
Therefore Fig. 6 shows an embodiment, and wherein a pair of processing channel 320 is merged, and has only used half of used processing channel 320 numbers among Fig. 5 embodiment.Yet more multiprocessing channel 320 also can be merged with similar fashion.
As shown in Figure 6, be applied to the input of phase shifter 330 (for example grouping circuits) by amplifier 310 separately from the MR signal of two adjacent mesh.The adjustable phase shift of grouping circuits 330 usefulness will appear at the signal plus of two input end.Subsequently, the output signal of grouping circuits 330 is handled by processing channel 320.The image that forms from the MR data from single processing channel 320 has accessible optimum signal to noise ratio (S/N ratio) this zone, this regional position depends on the phase place that is used for making up from the MR signal of two grids.Therefore, by changing phase position, this optimal value can move to favored area alternatively.
Continuation there is shown the circuit of local birdcage coil 16 referring to Fig. 3-6 and more detailed in Fig. 7 on the plane.It will be appreciated that in operation, this coil forms around the longitudinal axis, thereby some A, B, C and the D on Fig. 7 left side are connected to some A, B, C and the D on Fig. 7 right side, have therefore formed common cylindrical birdcage coil 16.
Except having the sensitivity (for example birdcage coil of Tui Huaing) that in fact position is relevant, may wish to have such coil, promptly in test zone 14, have basic sensitivity uniformly, for example can obtain by conventional birdcage coil.For this reason, pass through switchgear, gate-controlled switch (as PIN diode D1 or analog) for example, the capacitor C 1 in first stub 80 and first and second conductor circuits 81,82 can be changed alternatively, this gate-controlled switch and each self-capacitance are parallel to be arranged or each self-capacitance of bridge joint, thereby makes same capacitance short-circuit when switch closure.By closed or open separately switch selectively, thereby can obtain the birdcage coil of different electricity characteristics.Correspondingly, can between dissimilar birdcage coils, change (promptly launch, reception, low pass, high pass, band are logical or degenerate, or decoupling zero) and need not the exchange physical coil.
Correspondingly, in each first stub 80, first leg PIN diode D1 and capacitor C 1 parallel the layout.As shown in the figure, the PIN diode in the rod that closes on is to arrange in the opposite direction each other.In every section of first conductor circuit 81 be and the parallel coupling PIN diode D5 that arranges of matching capacitance C5.First and second half-wavelength coaxial cables 200,210 are connected to its feeding point 201,202,211,212 separately by emission PIN diode D6 and emission matching capacitance C9.As shown in the figure, this emission concentric cable is grounding to basic ring 85.Be furnished with the second eddy current capacitor C 7 in the basic ring 85 and handle the interior eddy current of this coil.This switchgear is biased between emission, reception and the decoupling zero pattern and changes based on being applied to DC on cage voltage input V1 and the prime amplifier voltage input V2.
In an embodiment of local birdcage RF coil 16, excellent conductor 80,84 and conductor or loop 81,82,83 comprise and have about 1.0cm of width and the about 0.009cm of thickness and be arranged in copper strips on the cylindrical support unit that is suitable for electric insulation.In the application-specific that is used for the anatomy imaging, for example to the head imaging, the about 12cm of the length of the first leg 80, the about 25.0cm of the diameter of this conductor circuit.In other was used, the length of first leg conductor 80 can be about 24.5cm, and the diameter in this loop can be about 23.0cm.The length of second leg conductor 84 can be about 2.0cm, and length can be less than 1.0cm alternatively.Under any circumstance, herein the size of indication only be example and can be by appropriate change to different scale to be suitable for application-specific.
Electric capacity is selected to obtain the resonant frequency decay of desired level and the insulation between the grid.In one embodiment, the resonance frequencies converge of coil 16 or the difference that decays to each other are less than in 5%.In another embodiment, the resonance frequencies converge of coil 16 or the difference that decays to each other are less than in 2%.By adding prime amplifier decoupling zero device, mesh isolation can be greater than 20dB.
For example, in an experiment, use the birdcage coil 16 of having created above-mentioned copper strips size, the first leg conductor 80 that to have eight length be 24.5cm, the conductor 81,82 and 83 of loop diameters 23.4cm, with eight length second leg conductor 84 that is 2.0ch, and C1=45.8pf, C2=56pf, C3=4.7pf, and C4+C5=56pf, the scope of the normal mode frequencies that measures approximately is 980kHz, and centre frequency approximately is 65MHz, and the insulation that reaches when having the prime amplifier decoupling zero is greater than 18dB.Correspondingly, have been found that adding tertiary coil or conductor 84 in the mode that is provided can support improved mesh isolation and resonant frequency decay.Further, tertiary circuit or conductor 83 provide the additional degrees of freedom that is used for tuning this coil.
Notice that capacitor C 4 and C5 are called single first loop capacitance by merging in this experimental example.Alternatively, in actual applications, they are merged.Yet when the two separated, C5 electric capacity was used to receiver channels 320 feeds as matching capacitance, and C4 electric capacity is as the device of this coil of fine setting.
In the operation, in inspection area 14, generate main field B
0, inspected object places this magnetic field.Use a series of RF and magnetic field gradient pulse with counter-rotating or excite the resonance of magnetic spin, induced magnetism, focus magnetic resonance, operation magnetic resonance, space and other coding magnetic resonance again, make the saturated and similar fashion of spin generate MRI pulse train.More specifically, gradient pulse amplifier 20 with current impulse be applied to selected or paired gradient coil 22 along the inspection area 14 x, y and z axle create magnetic field gradient.Whole RF transmitter 24 drives whole RF transmitting coil 26 and comes transmitting RF pulse or packet of pulses in inspection area 14.Alternatively, local RF transmitter 25 drives local RF coil 16 transmitting RF pulses or packet of pulses in a similar manner in inspection area 14.
According to above-mentioned RF emission, in the operation of first pattern, local birdcage coil 16 transmitting RF pulses are in the inspection area.When local RF coil was employed with emission mode, this coil was operated as quadrature transmit coil.In this emission mode, cage voltage input V1 and prime amplifier voltage input V2 are applied in negative potential.This negative potential at V1 and V2 place makes emission PIN diode D6, coupling PIN diode D5, first leg PIN diode D1 and preposition PIN diode D7 by forward bias.The loop construction that obtains is a four-point fed high pass birdcage.The feed of this birdcage is connected to this coil by emission PIN diode D6.Matched diodes D5 short circuit receive to regulate telefault L5 and matching capacitance C5, as shown in Figure 7.When the protection level was applied to prime amplifier 310, work can carry out tuning to birdcage like this.The first leg PIN diode D1 short circuit first leg capacitor C 1 make this coil become a high pass birdcage.Prime amplifier diode D7 short circuit the input of prime amplifier 310, for this prime amplifier provide another the protection level.The 3rd conductor or loop 83 (the supporting the degeneration birdcage mode) influence under this pattern is very little.Radio-frequency choke PRF and partiting dc capacitor C-DCBlock are used for guaranteeing suitable DC bias voltage.Quadrature splitter 230 provides two to become the quadrature that transmits of 90 degree to excite this birdcage.
No matter which kind of MRI pulse train and technology what adopt is, sequence controller 30 coordinates to generate a plurality of MRI pulse trains of MR signal, and this MR signal finally is received from this inspection area.For selected sequence, each echo of the MR signal that receives is received by a RF coil 26 or local RF coil 16.
Be used to receive from this inspection area under the situation of this signal at local RF coil 16, this local coil moves with second operator scheme.Under this pattern, local RF coil 16 is used as the phased array receiving coil, and this phased array receiving coil is including (for example) eight circuit coils or grid.DC bias voltage at cage voltage input V1 and prime amplifier voltage input V2 is positive, therefore applies reverse biased for all diodes.Under this pattern, selected correct reactance at second leg capacitor C 3, the second tank capacitance C2, first leg capacitor C 1, tuning capacity+reception tuning coil L5 and matching capacitance C4, generate eight passage birdcages of degeneration.Closing emission PIN diode D6 makes radiating portion and this birdcage insulate fully.All eight circuit coils are fully insulated and can be used to separate receiver, as shown in Figure 5, are used for optimum SENSE or other parallel processing imaging.Alternatively, this signal can be merged into any number of one to eight in prime amplifier output, as shown in Figure 6.
Be used to receive from this inspection area under the situation of this signal at a RF coil 26, this local coil moves with the 3rd operator scheme.Under this pattern, local RF coil 16 is by from this MR system decoupling, because only be used to from the inspection area 14 couplings that just need local RF coil 16 and MR system when receiving the RF signals when a RF coil 26.Under this pattern, the DC bias voltage at cage voltage input V1 place is positive, and bears at the DC bias voltage at prime amplifier voltage input V2 place.Correspondingly, all cage diodes all are in and receive or degradation modes, and prime amplifier diode D7 is applied in bias voltage.Thereby the matching capacitance C5 that is combined in of prime amplifier capacitor C 8 chosen matching capacitance C5, coaxial balanced-to-unbalanced transformer 300 and prime amplifier capacitor C 8 obtains a high impedance.So just to local RF coil 16 decoupling zeros, thereby allow the RF of a RF coil 26 to receive.
No matter which coil is as the RF receiving coil, the MR signal that receives is all by relevant RF receiver 38,36 and analog to digital converter 40, more than 36 sampling, thereby obtains representing the data line of each echo or the array of sampled data points.This undressed MR signal is loaded in this MR datarams or the buffer zone 42 subsequently.This MR data-carrier store represents to be commonly referred to as the data matrix in k-space.Based on the specific gradient coding to each echo, corresponding M R data are mapped or be endowed a position in the k-space.
By using inverse fourier transform or other reconstruction algorithm that is fit to, reconstruction processor 50 is reconstructed into these data in the image expression.This electronic image is expressed and is stored in the video memory 52 subsequently, video processor 54 is the image in the access images storer 52 selectively, and video processor 54 is that display (monitor 56 of the readable demonstration of people of composograph for example is provided) converts suitable form to the other parts of section, projection or this image expression.
Based on comprise eight conductors 80,84 promptly the embodiment of eight grids coil 16 has been described.Yet, also may use different even number of conductors or grid, for example 6 or 32.It also is favourable adding electric capacity in the part of tertiary coil or conductor 83 or circular arc, particularly when number of grid under the situation between 8 to 16.Similarly, the 4th or more galvanic circles can advantageously add in a similar manner in the tertiary circuit 83, particularly in this meshes number under the situation about 32.The 4th or the galvanic circle of more interpolations can be added to any end of coil 16.Yet, because physical restriction, preferably with the 4th or more galvanic circles add an end identical to the 3rd conductor 83, thereby make conductor 81 freely this MR signal to be fed to this processing channel.The 4th or the introducing of additional loops, though increased complexity, also have the favourable influence that has increased more freedom for coil tuning.
Referring to Fig. 8, show connection diagram as the coil 16 of receiving coil array.The MR signal is received by coil 16.Coil 16 is subdivided into a plurality of parts or grid (shown in coil 16 in be eight), and each part all is connected to independent signal processing channels 400, is illustrated by dash line in the layout of Fig. 8.In each processing channel 400, the MR signal that the MR signal that receives is distributed by the nuclear-magnetism in the zone of grid covering separately with the generation expression by demodulation, decoding and digitizing.For example, by the algorithm that inverse fourier transform and/or other are fit to, MR signal separately is rebuilt and/or merge with generation and be illustrated in the image that object that coil 16 surrounds and/or space center magnetic dipole distribute by reconstructing device 402.After rebuilding, this image formatted being used for shows on display 404, for example the display that can watch of video monitor or other people or the output device that the description of this composograph or image can be provided selectively.Alternatively, this formatted image can be other visual representation of surperficial skeleton view, 3D volume, 2D sectional view or this object.Each processing channel 400 comprises a receiver that is used for the MR signal that its corresponding grid of demodulation, decoding and/or digitizing detects alternatively.Alternatively, use single multichannel receiver.
Referring to Fig. 9, show an optional embodiment of degenerate birdcage coil 16 '.In this embodiment, second stub 84 and relevant with it electric capacity have been omitted.In other words, the 3rd conductor circuit 83 is not connected electrically to conductor circuit 82 by the physical power source joint in coil 16 '.Thereby but the 3rd conductor circuit 83 be arranged as far as possible near conductor circuit 82 there by electric capacity and/inductive coupling.This capacitive/inductive coupling has replaced second stub 84 and the relevant with it electric capacity.It will be appreciated that in addition, when tertiary circuit 83 when 82 next doors are illustrated in the loop, thereby tertiary circuit 83 have alternatively be slightly less than or greater than the diameter loop 83 in loop 82 can with loop 82 arranged concentric.If be placed in 82 the insides, loop, for example, conductor 83 can be loop or disk.
Figure 10 shows degenerate birdcage coil 16 " another one embodiment, wherein second stub is retained, and has omitted stub 84 " capacitor C 1, and the telefault that wherein has an induction coefficient L1 has been added to the 3rd conductor circuit 83 " part in.
In order to reach similar effects, in degenerate birdcage coil 16 " ' another one embodiment in, tertiary circuit 83 is omitted fully and L1 telefault and C2 electric capacity are parallel arranges, as shown in figure 11.Yet, omit tertiary circuit 83 and removed intercoupling of the tertiary circuit and second loop 82, and the additional degree of freedom of the coil tuning that is used for being obtained by additional tertiary circuit is had a negative impact.
Referring to Figure 12 and 13, degenerate birdcage coil 516 is similar with birdcage coil 16, and this degenerate birdcage coil 516 comprises first stub 580, first, second and the 3rd conductor or the loop 581,582,583 and second stub 584.With the same in the birdcage coil 16, thus the reactance birdcage coil 516 of selected stub 580,584 and conductor circuit 581,581 be a degenerate coil wherein by the grid of the coupling part definition in rod 580 that closes on and loop 581,582 basically at least with nearest and inferior near adjacent mesh decoupling zero.Each grid effectively is connected with independent emission/reception (T/R) switch 590 that is used to operate this grid.Rod, coil and the shunt capacitor C-Rung of selected coil 516, the coefficient of C-Ring and C-Shunt is to produce the high-insulativity of loop to the loop at the frequency of operation place.The T/R switch 590 independent to each grid application allows the independent electric current of controlling in the different grids.Basic and the nearest meshes decoupling zero of this degenerate coil.Compare with two loop degenerate birdcage coil, the application of the 3rd conductor circuit 583 provides improved basically mesh isolation.Tertiary circuit conductor 583 reduced basically time close on RF-coupled.Compare with the two loop birdcage coils of degenerating, improved insulativity provides more excellent efficient and to the improved control of electric current in the single grid.
Referring to Figure 12, and mark " meet R[] ", wherein the scope of [] is 1-8, expression is connected to the radio frequency signal receiver R1-R8 that is used for receiving magnetic resonance signals.Similarly, and mark " meet T[] ", wherein the scope of [] is 1-8, expression is used to have the emission of radio frequency signals device T1-T8 of the selected grid of selecting excitation radio frequency coil 516.
Figure 13 has schematically shown the details of one of them T/R switch 590.In the emission cycle, conversion bias voltage 600 is applied to one of telefault 601 and brings in and transmitter input 602 and radio shielding trap effectively be connected also so and effectively be connected with the matching capacitance C-Match of the pickup coil grid of birdcage coil 516.In receiving cycle, thereby conversion bias voltage 600 is switched on PIN diode 606 with transmitter input 602 and trap 604 insulation, and be launched into prime amplifier 614 by the magnetic resonance signal that the pickup coil grid of birdcage coil 516 picks up by quarter-wave emission line 610,612, prime amplifier 614 produces the conditioning signal of presenting to receiver coupling 616.
The degenerate birdcage coil 516 to the high-insulativity of single grid that is provided by first, second and the 3rd conductor circuit 581,582 and 583 is provided in utilization, together with the T/R switch 590 of each independent grid of operation separately, can be under various patterns operating coil 516.For example, by this launcher signal being carried out suitable relative phase adjustment, coil 516 can be used as volume resonator.In the highfield (for example at B
0--under 3.0Telsa or the higher situation), can reduce radiation loss by this coil mesh part of control separately.Degenerate coil 516 also can be used as coil array and be used to launch radio-frequency pulse or be used to survey magnetic resonance.For example, this coil mesh can be used as emission or receiving sensitivity coding (SENSE) coil array, as the parallel imaging coil array, or analog.
Though what describe is the round conductor loop, also can consider to adopt other shape, for example polygon (having and the as many angle of number of conductors) or ellipse.This conductor circuit alternatively can be not closed yet, and one of them grid can be omitted.In addition,, it will be appreciated that similarly reactance unit, distributed reactance unit or equivalent electrical circuit with similar reactance can suitably be substituted though mentioned concrete capacitor and/or electric capacity and telefault and/or inductance.And, can consider to make the 3rd conductor circuit to have and compare different diameters or other sectional dimension with second conductor circuit, thereby one of them loop can place inside, another one loop.In such layout, the second and the 3rd conductor circuit can be coplane or can be axially separating along this coil.Can consider that further the 3rd conductor can be end cap or end plate.
Invention has been described with reference to preferred embodiment.Obviously, for those readings and understood the people of aforementioned content, can modify and change.It should be understood that the present invention has been counted as comprising all such modifications and changes, because they are included within the scope of accessory claim or its equivalent.
Claims (28)
1. birdcage coil system of using in conjunction with MR imaging apparatus, this birdcage coil system comprises:
By the birdcage coil of tuning degeneration (16,16 ', 16 ", 16 " ', 516), this coil comprises:
First galvanic circle (81,581) is divided into a plurality of parts, each part be defined in they separately with the corresponding connection of first stub (80,580) between, and each part all comprises matching capacitance (C5),
Second galvanic circle (82,582) and
Place between first and second galvanic circles and a plurality of first stubs (80,580) that are connected with the described first and second galvanic circle electric power; And
Be used at least the RF emission mode and wherein this birdcage coil be suitable for the conversion equipment of this birdcage coil of conversion between the RF receiving mode of making phased array RF receiving coil, this conversion equipment comprises:
Be connected, be used to this coil to present a plurality of RF emission feed point (201,202,211,212) that RF transmits with first galvanic circle (81) electric power;
Be used for a plurality of emission PIN diode (D6) that are coupled with this feed point are presented in the RF emission;
A plurality of RF that cross-over connection matching capacitance (C5) is arranged receive output point;
With the parallel a plurality of coupling PIN diode (D5) of arranging of this matching capacitance (C5); With
Be connected, be used for this emission and coupling P IN diode are applied a plurality of cage DC bias voltages inputs (V1) of bias voltage with matched diodes electric power with this emission.
2. the birdcage coil system described in claim 1, wherein:
This birdcage coil is suitable for and makes quadrature RF transmitting coil in this emission mode.
3. the birdcage coil system described in claim 1, wherein:
This birdcage coil is suitable for and makes phased array RF transmitting coil in this emission mode.
4. the birdcage coil system described in claim 1, wherein
In emission mode, described emission and coupling PIN diode are by cage DC bias voltage (V1) forward bias, thereby this emission PIN diode connects lead to this birdcage coil for providing from transmitting of RF transmitter (25), and this coupling PIN diode makes this matching capacitance short circuit and avoid the output of RF signal.
5. the birdcage coil system described in claim 4, wherein:
In this receiving mode, described emission and coupling PIN diode are by cage DC bias voltage (V1) reverse biased, thereby this emission PIN diode disconnects being connected of this birdcage coil and this RF transmitter (25), and should mate the output that PIN diode allows the RF signal.
6. the birdcage coil system described in claim 5, wherein this conversion equipment further comprises:
A plurality of prime amplifier PIN diode (D7), wherein each prime amplifier PIN diode (D7) all connects with corresponding RF receiving preamplifier (310) electric power;
The a plurality of prime amplifier DC bias voltages inputs (V2) that are connected with this prime amplifier PIN diode electric power are used to this prime amplifier PIN diode to apply bias voltage and make this RF receiving preamplifier (310) short circuit.
7. the birdcage coil system described in claim 6, wherein:
This conversion equipment further is applicable to this birdcage coil is transformed into the decoupling zero pattern, in this decoupling zero pattern, this cage DC bias voltage (V1) is that this emission (D6) and coupling PIN diode (D5) apply reverse deflection voltage, and this prime amplifier PIN diode (D7) of this prime amplifier DC bias voltage (V2) forward direction deflection, thereby this RF coil and this magnetic resonance device decoupling zero.
8. the birdcage coil system described in claim 1 further comprises:
Three conductor RF-coupled (83,83 ", 583) with second galvanic circle (82,582).
9. the birdcage coil system described in claim 8, wherein this birdcage coil is a degenerate birdcage coil, this degenerate birdcage coil has defined a plurality of grids, this grid at least with close on most and time meshes decoupling zero, and this conversion equipment comprises:
Be connected a plurality of transmit/receive switch (590) with a plurality of decoupling zero grids of independent operation with this grid.
10. the birdcage coil system described in claim 9, wherein each this transmit/receive switch (590) comprises:
Connect this transmit/receive switch (590) and with the grid of the corresponding decoupling zero grid of this transmit/receive switch (590) coupling (C-match);
The receiving circuit (610,612,614) that links to each other with this grid coupling; With
Transmitter input (602); With
Be used for selectively this transmitter being imported the device (606) that (602) and this grid are of coupled connections.
11. a birdcage coil that uses in any the described birdcage coil system as claim 1-10, this birdcage coil comprises:
First galvanic circle (81,581);
Second galvanic circle (82,582);
A plurality of first stubs (80,580) that are arranged between first and second galvanic circles and are connected with the first and second galvanic circle electric power; With
Separate with second galvanic circle (82,582) and to arrange and three galvanic circle RF-coupled (83,83 ", 583) with second galvanic circle.
12. the birdcage coil described in claim 11, wherein:
First and second galvanic circles (81,82,581,582) are arranged in the opposite end of first stub (80,580), described a plurality of first stub is connected with the first and second galvanic circle electric power, thereby described first and second galvanic circles have first and second parts between the electric power of the first adjacent stub connects, and a pair of adjacent first stub and defining a grid with the first and second galvanic circle parts between this electric power to first stub is connected; And
This birdcage further comprises:
(C1 C-Rung) is arranged in first stub in the first stub reactance;
(C5, C-Tune C-Match) are arranged in the first galvanic circle part in the first galvanic circle reactance; And
(C2 C-Ring) is arranged in the second galvanic circle part in the second galvanic circle reactance.
13. the birdcage coil described in claim 12 further comprises:
A plurality of second stubs (84 that between second galvanic circle and the 3rd galvanic circle, extend, 84 "; 584); thereby the 3rd galvanic circle (83; 83 ", 583) be arranged in and first galvanic circle (81,581) side of the second relative galvanic circle, described a plurality of second stub (84,84 "; 584) be connected with the second galvanic circle electric power and described a plurality of second stub (84,84 ", 584) thus being connected described the 3rd galvanic circle with the 3rd galvanic circle electric power has part between the electric power of adjacent second stub connects.
14. the birdcage coil described in claim 13, wherein:
Second stub (84,84 ", 584) identical with the number of first stub (80,580), and first stub is connected to second galvanic circle (82,582) with second stub at identical position electric power.
15. the birdcage coil described in claim 14, wherein first stub and second stub (80,84,84 "; 580; 584) form single stub, this single stub has the electrical interconnection with second galvanic circle (82,582); and the end of this single stub respectively electric power be connected to first galvanic circle (81; 581) and the 3rd galvanic circle (83,83 ", 583).
16. the birdcage coil described in claim 15 further comprises:
Be arranged in the second stub reactance in second stub (84,84 ", 584) (C3, C-Shunt).
17. the birdcage coil described in claim 16, wherein:
The first stub reactance, the second stub reactance, the first galvanic circle reactance and the second galvanic circle reactance comprise the first stub electric capacity, the second stub electric capacity, the first galvanic circle electric capacity and the second galvanic circle electric capacity respectively.
18. the birdcage coil described in claim 11 further comprises:
Be arranged in second with the 3rd galvanic circle and with second a plurality of second stubs that are connected with the 3rd galvanic circle electric power (84,84 ", 584).
19. the birdcage coil described in claim 18, the wherein chosen inferior meshes of coming this birdcage coil of decoupling zero of at least one in the reactance of the reactance of the 3rd galvanic circle (83,583) and a plurality of second stub (84,584).
20. the birdcage coil described in claim 11, wherein second galvanic circle and the 3rd galvanic circle the two one of place these two another inside.
21. the birdcage coil described in claim 20, wherein second galvanic circle and the 3rd galvanic circle coplane.
22. the birdcage coil described in claim 11, wherein the 3rd galvanic circle (83) and second galvanic circle (82) induction coupling.
23. the birdcage coil described in claim 22, wherein the 3rd galvanic circle (83 ") comprise the chosen inductance that comes the inferior meshes in this birdcage coil of decoupling zero.
24. the birdcage coil described in claim 11, thereby the reactance of the reactance of the reactance of wherein said stub, galvanic circle and conductor is to have to close on most and the degenerate birdcage coil of inferior meshes decoupling zero by so selected this birdcage coil.
25. the birdcage coil described in claim 11, wherein this birdcage coil is the degenerate birdcage coil that has defined a plurality of grids, and from closing on most and time meshes decoupling zero, this birdcage coil further comprises these a plurality of grids at least:
The a plurality of transmit/receive switch (590) that link to each other with these grids come a plurality of decoupling zero grids of independent operation as in radiofrequency launcher and the radio frequency receiver at least one.
26. birdcage coil as claimed in claim 25, wherein this transmit/receive switch (590) is suitable for and operates this birdcage coil to be used as one of the following at least:
Volume resonator,
Emission SENSE coil array,
Receive the SENSE coil array and
The parallel imaging coil array.
27. a magnetic resonance method comprises:
The time-invariant magnetic field of the birdcage coil inside of claim 11 is passed in generation; With
Birdcage coil in one of following at least pattern operational rights requirement 11:
The volume resonator pattern,
Emission SENSE pattern,
Receive the SENSE pattern,
The parallel imaging pattern.
28. a magnetic resonance imaging system comprises:
The main magnet (12) of rise time stationary magnetic field;
On time-invariant magnetic field, apply the magnetic field gradient coils (22) of selected magnetic field gradient selectively; With
Birdcage coil system as claimed in claim 1.
Applications Claiming Priority (3)
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| US42950902P | 2002-11-27 | 2002-11-27 | |
| US60/429,509 | 2002-11-27 | ||
| US60/457,039 | 2003-03-24 |
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| CNB2003801041812A Expired - Fee Related CN100526906C (en) | 2002-11-27 | 2003-11-25 | Degenerate birdcage coil and transmit/receive apparatus and method for same |
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| US10254360B2 (en) * | 2010-07-08 | 2019-04-09 | Koninklijke Philips N.V. | Router and coil array for ultra high field MRI |
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