CN85101788A - Produce and/or receive the rf coil system of alternating magnetic field - Google Patents
Produce and/or receive the rf coil system of alternating magnetic field Download PDFInfo
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- CN85101788A CN85101788A CN85101788.6A CN85101788A CN85101788A CN 85101788 A CN85101788 A CN 85101788A CN 85101788 A CN85101788 A CN 85101788A CN 85101788 A CN85101788 A CN 85101788A
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Abstract
One produces and/or receives the rf coil system of alternating magnetic field, in nuclear magnetic resonance apparatus.This system is positioned in around the columniform detection space, comprises at least 4 conductor segment, and formation one closed-loop path that is connected, and is uniform radio-frequency alternating magnetic field substantially to receive or to produce.Size is similar to the space of the magnitude of radio-frequency (RF) magnetic field wavelength at least and can detects.In this system, it is axial arranged along detecting space center that conductor segment is connected to the conductor group, and the conductor group is coupled together along the connecting line that detects the space circumference.The length of connecting line is selected to such an extent that the amplitude maximum point of radio-frequency current is formed in the central authorities of each conductor segment, and has at least a radio-frequency current smallest point to appear on each connecting line.
Description
The invention belongs to be used for producing and/or to receive and come down to uniform alternating magnetic field at least, particularly be used in the rf coil system in the nuclear magnetic resonance apparatus, described system is positioned in one and comes down to columniform detecting around the space; And comprises at least four and in fact is parallel to longitudinal center's axis, the And that detects the space and is symmetrical at least one with respect to the conductor segment of settling by the plane of longitudinal center's axis on circumference, and described these conductor segment are connected to each other to constitute a closed-loop path with connecting line.
European patent application 83201449.2, particularly figure two and corresponding narration have proposed a kind of transmitter/measurement coil, and it is arranged in and is used for the detecting around the space of measurand in the nulcear magnetic resonance (NMR) tomographs.Described transmitter/measurement coil is made by the coil of two one side of something and is formed the shape of a saddle.For two half of coils giving coil excitation , And connection by the radio-frequency electric current source feed.Each half of coil is made up of two conductor segment, and conductor segment extends axially along transmitter/measurement coil, on the circumferencial direction of transmitter/measurement coil same two parts is arranged.Whole four element connected in series and constitute a Huan , And and on this end that is connected in series that constitutes coil connecting terminal, be connected to radio-frequency power supply by power line.
Go back tuning capacitor of cross-over connection on this coil connecting terminal.Coil is Chenged the And circuit that shakes of allying the communists with tuning capacitor Gou together, it is tuned on the frequency of radio-frequency power supply and resonates.Purpose is the efficient for the radio-frequency (RF) magnetic field of improving this transmitter/measurement coil.
When the frequency of radio frequency source is higher, the formula known according to resonant circuit, be tuned to resonance tuning capacitor numerical value must reduce.Transmitter/measurement coil individually, the Calipering resonance frequency that do not add tuning capacitor in addition is called the natural frequency of coil.The conductor structure length of saddle-type coil 15 to 20% of the Swing wavelength that normally when the coil natural frequency, shakes.Its exact value is decided by coil dimension and the coil stray capacitance to peripheral conductor.Running on the natural frequency scope simultaneously, the radio-frequency current of flowing through coil is along demonstrating significant phase shift on the coil conductor structure length.Therefore, produce by coil, especially the radio-frequency (RF) magnetic field that produces by its axially oriented conductor segment when the running frequency of saddle-type coil just become during in the natural frequency scope can aware inhomogeneous.Have only the frequency of radio frequency source to be lower than the natural frequency of saddle-type coil significantly, saddle-type coil just produces and comes down to uniform radio-frequency (RF) magnetic field at least.
Radio-frequency (RF) magnetic field is needed to the nulcear magnetic resonance (NMR) tomography for example uniformly.There, checked object may be a living tissue, is placed in the fixing uniform former magnetic field.Because their nuclear spin, atomic nucleus are subjected to a magnetic moment and are arranged neat in former magnetic field.The magnetic induction in former magnetic field strengthens, and this degree that comes into line increases.
When an alternating magnetic field with perpendicular to former magnetic field magnetic line directive effect on the atomic nucleus of inspected object, then magnetic moment causes the precession campaign, it causes with respect to the rightabout magnetic moment in former magnetic field.From quantum-mechanical viewpoint, be used for magnetic moment being mentioned higher energy state from the energy of alternating magnetic field; This requires certain quantity of energy under the given frequency in the grand magnetic field of excitation friendship.This frequency is called nmr frequency f
0, And is according to the magnetic induction B in following equation and former magnetic field
0(* represent multiplication mark) interrelates:
f
0=g×B
0
Here, g is a gyromagnetic ratio, and is relevant with nuclide, and for example its numerical value is 42.58 megahertzes/tesla to hydrogen, is 17.23 megahertzes/tesla to phosphorus, is 11.26 megahertzes/tesla to sodium.With the frequency of suitable selection alternating magnetic field, independent nuclide can be encouraged selectively, becomes possibility thereby close the measurement selectively have no progeny when being activated in the decay from the tension and relaxation signal of atom at alternating magnetic field.
The image quality that has been found that the nulcear magnetic resonance (NMR) Laminographic increases with the magnetic induction in former magnetic field and improves, and therefore increases because arrange consistent magnetic moment number in the atomic nucleus proportionally.Yet to various nuclides, nmr frequency also improves thereupon.So, detecting magnetic field of the necessary generation of rf coil system (transmitter/receiving coil) that the space produces radio-frequency alternating magnetic field and receives the tension and relaxation signal from atomic nucleus, even under higher like this frequency occasion, its uniformity should satisfy the requirement by nulcear magnetic resonance (NMR) Laminographic institute.
Only having been found that structure length at the saddle-type coil conductor constitutes is no more than coil frequency, and the wavelength of measured in other words nmr frequency could produce enough uniform radio-frequency alternating magnetic field with saddle-type coil at about 1/12 o'clock.Yet, because the structure length of such saddle-type coil is determined that by the dimension of object of being detected saddle-type coil only just can be suitable for producing uniform alternating magnetic field below a certain given frequency.For example, when saddle-type coil will be substantially equal to the human head of its diameter corresponding to the measurement lengthwise dimension, its structure length was approximately three times of coil diameter.When coil diameter is defined as about 30 centimetres, still nmr frequency that can be measured on be limited to about 20 megahertzes.For the nulcear magnetic resonance (NMR) of measuring hydrogen atom, the magnetic induction in former magnetic field can be to be no more than 0.5 tesla so.Yet, for satisfied image quality is arranged, particularly good resolution to be arranged to being used for living tissue nuclear magnetic resonance spectrometer in the nulcear magnetic resonance (NMR) Laminographic, the magnetic induction in the former magnetic field of requirement is up to 2 to 2.5 teslas.
The shortcoming of known radio-frequency coil had been narrated for the nulcear magnetic resonance (NMR) Laminographic in the above, but these shortcomings require at the wavelength than the radio-frequency (RF) magnetic field that should produce at those, and its size no longer is to produce in all devices that are actually uniform radio-frequency alternating magnetic field at least in the less space all will take place.
Target of the present invention is the coil system that proposes a kind of described kind, and its allows to reach in its size the magnitude of radio-frequency (RF) magnetic field wavelength, thereby constitutes to produce and receive in the space of signal portion of wavelength numerical value and be actually uniform radio-frequency alternating magnetic field at least.
In the coil system of described kind, this target has been reached by the present invention, it is that to flow into respect to longitudinal center's axis of detecting the space all be in equal some conductor segment in energising, they are located substantially on the conductor of detecting on the circumferencial direction of space again its adjacent termination are connected to each other formation conductor group, this conductor group is connected to each other by the connecting line of receiving on the conductor that is positioned at circumferencial direction, the length of connecting line is selected to such an extent that make radio-frequency current amplitude maximum point appear at the central authorities of each conductor segment, and at least one radio-frequency current amplitude smallest point appears on each root connecting line.
Opposite with the coil system that proposes at european patent application 83201449.2, the conductor part of all saddle-type coils of there must have than wavelength dimension as far as possible little, to avoid radio-frequency current along the phase shift in the conductor of coil total length, this phase shift then is used for rf coil system of the present invention carefully, in single conductor segment, to produce a given phase place, given with respect to coil longitudinal center axis one in other words direction.Utilizing standoff distance in so true , Calipering conductor to multiply by electric current in 2 of half-wavelength for integer, is homophase when this multiplier is even number, then anti-phase when this multiplier is odd number.Therefore there is no need to produce the whole electric currents that constitute radio-frequency alternating magnetic field has the same phase place, as long as and satisfy and have 180 ° of phase shift , Calipering that multiply by integer to be equivalent to integer between these electric currents to multiply by half-wavelength.Like this, just can obtain size and can reach the coil system that is approximately the radio-frequency alternating magnetic field wavelength magnitude that gives off at least.Jiao Bian Ci Chang And is inoperative frequently to producing She for electric current in connecting line, so do not influence the shape of alternating magnetic field along the current phase Yi And of connecting line.Mate by the conductor segment that connecting line connects, so the electric current of flowing through wherein has only very less important phase shift along conductor segment length under the coil system running frequency, the uniformity of the alternating magnetic field that is produced thereby be not subjected to significantly to influence consequently.
Select to obtain resonance in running frequency lower coil system when the length of connecting line and conductor segment by the present invention, the result is the current strength in conductor segment, and the magnetic field intensity of the alternating magnetic field that thereupon gives off is high.
For the application in the nulcear magnetic resonance (NMR) Laminographic, this means that coil system of the present invention can have the space of detecting that its size reaches the running frequency wavelength magnitude.Otherwise one has by the testee size and has determined the coil system of its size can be used in upper frequency.Therefore, the magnetic induction B in former magnetic field
0Can bring up to the numerical value of from 2 to 2.5 teslas from the normally used numeral that is lower than 0.5 tesla greatly; This causes improving image quality thereupon or improve resolution in nuclear magnetic resonance spectrometer in the nulcear magnetic resonance (NMR) Laminographic.
Also have, coil system of the present invention has simple in structure, the characteristics that the requirement of manufacturing tolerance is lower.
Design that induces one of the present invention is the characteristic impedance Z of a conductor group and a connecting line
0, Z
1Ratio and their length L
0, L
1With propagation constant β
0, β
1Between following relationship arranged:
Z
0/Z
1=|tan(β
0×L
0/2)×tan(β
1×L
1/2)
Or Z
0/ Z
1=| tan(β
1* L
1/ 2) | tan(β
0* L
0/ 2)
Or it is high slightly.First relational expression can be used for selecting to constitute the connecting line length of odd number amplitude smallest point; Second relational expression then is used to constitute the situation of even number amplitude smallest point.These relational expressions are only considered a connecting line length L
0With a conductor group, the length L of a conductor segment in other words
1During for more accurate calculating, must take into account the influence that is positioned at the circumferencial direction upper conductor, for example with being used for L
1Numerical value increased a bit, for example 10%, for known Z
0/ Z
1Ratio will obtain low slightly β
0And β
1Value, resonance frequency is low slightly in other words.
In the design of an invention, connecting line comprises a screen that conducts electricity aspect electric.This makes to have only conductor segment to give off the radio frequency alternating electromagnetic field, and its spatial form is only relevant with numerical value, direction and the phase position of radio-frequency current in these conductor segment as a result.Electric current in connecting line does not influence the alternating magnetic field of generation, and on the contrary, they do not absorb energy from the alternating field that receives yet.The spatial placement of connecting line just can be simplified in the coil system.Connecting line is preferably made coaxial leads.Like this, connecting line has fixing characteristic impedance and simple especially, has guaranteed the suitable propagation performance and the accurate possibility of coupling.
In further design of the present invention, each only comprises two adjacent conductor segment the conductor group.The conductor group that therefore can obtain to form simply, and that it is placed in the conductor length of detecting the space circumferencial direction is the shortest.
In the present invention further conceived, several conductor segment were positioned in respect in two conductor groups of arranging by the plane symmetry ground of longitudinal center's axis.Utilize such arrangement, the alternating magnetic field that obtains, its magnetic line of force vertically are passed in the longitudinal center's axis in the above-mentioned plane of detecting in the space, and And is in this plane and highly even on its each limit.
In the present invention further conceived, per two the conductor segment arrangements that feed same electric current must be approximately 60 ° of angles of circumference at least for the subtended angle of detecting in the space.Like this, detecting in the space, Calipering makes also can obtain radio-frequency alternating magnetic field magnetic line of force result especially uniformly when the conductor hop count is minimum.Every group of situation that only comprises two conductor segment is desirable especially for having only two conductor groups for this.
In further design of the present invention, conductor segment by a conduction and the screen of saturating magnetic surround, this screen is aspect electric and the insulation of said conductor segment.
When radio-frequency alternating magnetic field is radiated testee, electricity with dielectric property the intensity and the shape in magnetic field had decisive influence.They have determined radio-frequency alternating magnetic field to enter the penetrability of testee and the quality factor of resonance frequency and coil system.Also have, particularly rf electric field also may have interference effect to testee.
For example, when living cell tissue was carried out the nulcear magnetic resonance (NMR) Laminographic, the discovery testee was put coil system into and has been changed the quality factor of coil system and moved its resonance frequency.To the situation of static fully object, signal to noise ratio has reduced; Under the situation of testee activity, comprise the motion of testee inside, relevant with the quality factor change in received alternating magnetic field, additional amplitude or phase noise take place, cause moving of coil system resonance frequency thereupon.Have been found that the radio frequency alternating field of shielding from testee, the light object dielectric property of Ke Yi Minus to make an uproar than adverse effect.
Coil system of the present invention in the conductor segment scope, forms radio-frequency current wave amplitude maximum point (current loop) and the smallest point (voltage node) of the voltage followed on connecting line.Thereby be exactly little from the beginning by the radio frequency alternating electric field that coil system of the present invention is added to conductor segment.In order to reduce the influence of residual field to testee, conductor segment is surrounded by the screen of describing.This screen outside testee, makes that the dielectric loss in the object is avoided the harmful effect of image quality with them with residual radio frequency alternating electric field retaining.This screen has also been got rid of testee simultaneously and has been exposed danger under voltage to the open air.This particular importance when coil system of the present invention uses aspect medical.
In the present invention further conceived, each only surrounded the interior conductor segment of same conductor group an enclosure portion of the screen of magnetic conduction and saturating.Therefore, the interior conductor segment of conductor group has just been shielded around following effectively; Especially influencing each other between these conductor segment and connecting line and other conductor group also forgone.
In the present invention further conceives, each comprises one towards detecting internal shield and outer shielding layer in its outside that Kong Jian And surrounds this space the screen of magnetic conduction and saturating, is that the sector of cylindrical surface is formed with screen and outer shielding layer basically by several parts.Outer shielding layer is blocked in the radiation of coil system radio frequency alternating field nearby, and internal shield then is blocked in the radio frequency alternating electric field the inside will put detecting outside the space of testee, but can see through radio-frequency alternating magnetic field, so that allow it reach on the testee.
This inner barrier is to the magnetic permeability of radio-frequency alternating magnetic field and shield the another further design of alternating electric field formation the present invention simultaneously, and it is to contain the slit at screen along detecting the space circumferencial direction in the conductor segment scope.
During the present invention further conceived, the width in this slit was little to Minus along detecting longitudinal center axis side, space to its two ends from the coil system center.When coil system of the present invention be tuned to resonance, there is radio-frequency current wave amplitude maximum point (" current loop ") in central authorities in conductor segment length, corresponding to the smallest point (" voltage node ") of voltage on the conductor segment, thereby also be rf electric field minimum by the conductor segment radiation.This voltage increases towards the conductor segment two ends.Thereby the validity of shielded radio frequency electric field must strengthen towards the conductor segment two ends; This reaches with the way of having narrated at the width of Minus small gap on the direction at conductor segment two ends.
During the present invention further conceives, the barrier that this is inner is made at one by longitudinal center's axis, and relatively it is that the area and being positioned on the area at the conductor place on the circumferencial direction on the plane of symmetrical placement seals to the conductor group, thereby internal shield is impervious in these places to radio frequency alternating electric field and magnetic field.The slit or other otch that on these areas, do not have description.Have in the coil system of the present invention a place by one by longitudinal center's axis; And and be to be placed in the place that intersect on plane and internal shield and outer shielding layer symmetrically with respect to its conductor group, it is positioned at somewhere on the circumference of detecting the space, presents the density of line of magnetic force of lower radio-frequency alternating magnetic field there.Thereby be called as " neutral zone ".For example, come less for the influence of the shape of radio-frequency alternating magnetic field compared with the influence of detecting the structure of other local internal shield on the circumference of space in the structure of internal shield in this zone.Particularly the structure of internal shield goes into to detect the space moment-less influence in this zone for the alternating magnetic field radiation.Because the enclosed construction in the conductive region of internal shield on being placed in circumferencial direction makes the radio frequency alternating electric field of these conductors and magnetic field be suppressed the influence of detecting the field in the space.
During the present invention further conceived, the connecting line total length all was placed in the closed area of internal barrier.Therefore, radio-frequency alternating magnetic field is disturbed just to having been avoided by the Ying Xiang Calipering of connecting line.As long as connecting line itself comprises a screen, at least it has one to be in electric go up and internal barrier is connected, ES preferably also like this, so that cause common earth potential, make radio-frequency current in the uncontrollable screen, thereby the distortion in the magnetic field in detecting the space is avoided.
In the further design of the present invention, internal shield and outer shielding layer are to couple together to the conducting strip of settling with the width of cloth in the end of coil system, these conducting strips with conductor segment and be placed in the rf electric field of detecting space circumferencial direction end conductor be shielded from detect around space and the coil system outside.On the one hand, just can avoid the capacitive coupling of testee and last resonance shift and the degenerating of image quality of nulcear magnetic resonance (NMR) Laminographic.And on the other hand, testee also can not be subjected to the harm of electric field.
In the further design of the present invention, screen is the structure of layering at least in part, and like this, screen can be made up of for example one or more layers electric conducting material, or constitutes with metal forming or similar material, and this structure material saving is with the Minus light weight.
Further in the design, screen is positioned in the non-conductive supporting in the present invention, this supporting can by, for example, dielectricity polymethyl methacrylate or other dielectric substance are made; On the one hand its firm screen of forming a lightweight props up thing, and the aspect also is screen and detects electric insulation between the space with the protection testee in addition, or the electric insulation between screen and the conductor segment, to prevent the lighting network.Screen can be for example layer of metal paper tinsel or one deck steam-spraying layer in the supporting.
Further in the design, screen is a network structure in the present invention, in this case it preferably a gauze form, such gauze mechanically is firm, inexpensive and processing easily.
And then screen should be done so that it still can see through the low frequency alternating magnetic field in a few khz frequency scopes.This magnetic field also is called gradient magnetic, and it is superimposed on the former magnetic field and is used for to the testee image scanning in the nulcear magnetic resonance (NMR) Laminographic.This gradient magnetic is produced by the gradient coil that is placed in the rf coil system outside.Postponed by the eddy current in the conductive component in rf coil system the settling time of gradient magnetic in detecting the space.When rf coil system is sure when allowing gradient magnetic see through, this delay can not considered over time for gradient magnetic.Therefore in fact must be by the eddy current De Shuai Minus time constant that gradient magnetic produces less than the rise time of gradient magnetic, like this, in above-mentioned example, it in fact must be less than one millisecond.
In further design of the present invention, this makes thickness for reaching several times of radio-frequency current frequency next part effect penetration depth with screen.For example bed thickness is following three the collection effect penetration depths of coil system running frequency.The influence of radio-frequency current conduction just can be ignored during bed thickness, and for the low frequency eddy current that is produced by gradient magnetic, screen has sufficiently high damping resistance.
The network structure of screen, particularly gauze form also are attracting for Shuai Minus soon by the eddy current aspect that gradient magnetic produces.Yet when the applied metal silk screen, empty coil system , Calipering puts into the quality factor before the testee, and surface conductivity is lower reduces because it is effective compared with the conductive layer of closed in itself.Yet, the reduction of this quality factor, compared with because the reduction of putting into the caused quality factor of testee is little, the result uses gauze in ES, when putting into testee the reduction of actual quality factor very little, can disregard.
In the present invention further in the design, conductor segment and/or the conductor that is placed in circumferencial direction are made the tubulose of the conduction of thin-walled.With settle in a circumferential direction conductor together, conductor segment forms a suitable conduction closed-loop path, it can apply strong influence to postponing gradient magnetic.Conductor segment is made light-wall pipe, do not change actually that loop resistance rises to this degree under the self-induction, in fact the Minus time constant that declines for the eddy current that produces in the loop was become less than the gradient magnetic rise time in the nulcear magnetic resonance (NMR) Laminographic.Conductor segment just can be avoided for the harmful effect of for example image quality of nulcear magnetic resonance (NMR) Laminographic.
In the present invention further conceived, it was concentric with respect to detecting space longitudinal center axis basically that outer shielding layer and internal shield are settled feasiblely.Between internal shield and outer shielding layer, in fact formed a hollow cylinder intermediate space under this situation, said intermediate space can supply conductor segment, connecting line and any optional feature, for example is the usefulness of the screening arrangement of the tuning of coil system and the parts that mate usefulness.Like this, the diameter of internal shield is by the testee size, when when the nulcear magnetic resonance (NMR) tomographs is used for medical application, deciding in other words by human body or anthropolith, the diameter of outer shielding layer must be considered the space that conductor segment and connecting line need on the one hand, also will consider on the other hand for coil system in the required space of device that produces fixing uniform former magnetic field.
In the further design of the present invention, the cross-sectional profiles of detecting the space that is surrounded by internal shield comes down to perpendicular to an ellipse in the plane of longitudinal center's axis.The structure of this internal shield induces one for the nulcear magnetic resonance (NMR) tomography with human body especially owing to the elliptic cross-section of human body.Than perpendicular to detecting the circular outline line in space on the plane of longitudinal center's axis, internal shield is positioned in now near patient's chest, abdomen, back of the body district, and the result conductors section also can be settled near patient, testee in other words.The vertical range that is inversely proportional to approx from conductor segment owing to the magnetic field intensity of radio-frequency alternating magnetic field under the condition that known radio-frequency current amplitude is arranged in conductor segment reduces, the coupling of the tension and relaxation signal from the testee to the conductor segment also reduces to the same extent, the sensitivity of rf coil system is with little rising of distance De Minus between testee and conductor segment, because the power of necessary radio-frequency alternating magnetic field reduces and signal to noise ratio has risen for excited nuclear magnetization resonates.Also have, when outer shielding layer is kept intact, the distance between this screen and the conductor segment has changed, and result's uniformity of radio-frequency alternating magnetic field in detecting face has been improved.
In further design of the present invention, outer shielding layer and internal shield have the radius of curvature that is actually same at least, because this, for internal shield and outer shielding layer, or the non-conductive supporting of using for internal shield and outer shielding layer be because of using same member, for example the pipe sector of same diameter and reach designs simplification.
In further design of the present invention, screen is made up of the two parts that itself are sealing, every part constitutes the shielding box of the part of a part that comprises internal shield and outer shielding layer, distance between these two parts can be regulated on the direction perpendicular to longitudinal center's axis of detecting the space, thereby the size of detecting the space also can be regulated the size that , Calipering detects the testee that the space can be adapted to be correlated with.Thereby, to each testee, the improvement of the coil system sensitivity of speaking of in order to reach, distance is adjustable between object and conductor segment.
In the present invention further conceived, shielding box can move on perpendicular to the direction of detecting space longitudinal center axis each other.For example, shielding box is contained on the railway line guide rail that conductor segment remains parallel each other when guaranteeing that distance changes between shielding box.
In the present invention further in the design, shielding box is arranged to such an extent that can be parallel to the axle revolution of longitudinal center's axis each other around of the plane that is arranged in conductor group symmetrical placement.This can reach, for example connect shielding box in " neutral zone " zone with joint, coil system just can be opened, and testee is no longer needed from axially, on longitudinal center's axis direction, put in other words and detect the space, and can be the width of cloth concerning longitudinal center's axis to direction put into.The operation of coil system has been simplified greatly, when particularly the nulcear magnetic resonance (NMR) tomographs being used for human body.
In the present invention further conceived, connecting line was made soft.Particularly connecting line is made soft coaxial line.Thereby on the one hand the arrangement of the structure , Calipering connecting line of coil system has been simplified, aspect in addition, and the simple connection between the coil system each several part that the locus will become also may obtain.
In further design of the present invention, conductor segment has the bending that is tubbiness detecting on longitudinal center's axis in space.Under straight conductor section arranged parallel situation, find that magnetic field intensity its direction of both ends of mind-set from conductor segment of radio-frequency alternating magnetic field reduces.This reduction can be used on its end direction by the few conductor segment of Minus gradually and the way of detecting the vertical central axis wire spacing in space and compensate, thereby has improved the uniformity of radio-frequency alternating magnetic field on longitudinal center's axis direction.
If desired, the resonance Zhen Swing that in the coil system of the central authorities that are positioned at conductor segment length at current loop and corresponding " voltage node ", had spoken of, also have a Ge Zhen Swing can be activated at " potential loop " and accordingly " current node " be positioned in the coil system of central authorities of conductor segment length, type shakes like this
Be undesirable in rf coil system, around conductor segment, produce rf electric field because it consumes radio frequency electromagnetic energy , And.Shake in order to suppress such
, at one further in the design of the present invention, additional connection line segment is received connecting line and on the binding post between the conductor of detecting on the circumferencial direction of space, this is its first line end.These are additional to connect the shaking of type that line segments disturb the needs of coil system hardly
Resonance frequency, the resonance frequency of unwanted Zhen Swing type then reduces significantly.The coupling (degeneration) of two Zhong Zhen Swing has been prevented from owing to the interval between their resonance frequency increases.When radio-frequency current was energized with given frequency in conductor segment, two kinds were shaken
In have only a kind ofly, needed in other words, containing the sort of of " current loop " in conductor segment will be energized.
In further design of the present invention, additional connection line segment is made coaxial line, and its second end is unsettled.Because the additional coaxial configuration that connects line segment, radio-frequency alternating magnetic field does not have influence in the space to detecting in the field that is produced.Best, the additional line segment that connects is installed parallelly with the conductor that is positioned at circumferencial direction, make their by a part of the internal shield of sealing itself with its with detect the space and separate.
In the further design of the present invention, there is the coupling line segment of a conduction to be placed at least between the internal shield and outer shielding layer in a conductor class range, therefore to the conductor segment symmetry.Above-mentioned line is arranged essentially parallel to longitudinal center's axis of detecting the space, and its head end is received outer shielding layer, and second termination is received radio frequency electromagnetic energy.By the coupling line of conduction, coil system is excited to resonance Zhen Swing , Zhen Swing electric current and is detecting space generation radio-frequency alternating magnetic field.On the contrary, in the situation of nulcear magnetic resonance (NMR) Laminographic, in order to be used as a receiving system, the tension and relaxation signal can pass to coupling line from testee by rf coil system.This situation is preferably in the there and pacifies a switching device, and coupling line is alternately received power supply with radio frequency electromagnetic energy to be provided and to receive receiving system to receive and to identify the value of this tension and relaxation signal, and at this moment coil system is as long as a coupling line.
The present invention is further in the design, and coupling line is done to such an extent that can be out of shape, so that the surface area that is surrounded by coupling line and outer shielding layer can change.Like this, coupling line can be simply be complementary with the characteristic impedance of connecting line, and by this connecting line, radio frequency electromagnetic energy is supplied into and the tension and relaxation signal is spread out of.When coupling line is constructed by this way, radio frequency high tension capacitor that just needn't application of expensive.
In the present invention further in the design, on circumference, be parallel to and detect space longitudinal center axis and settling an auxiliary conductor, thereby may be parallel to the coupling line of each conductor group in fact.Above-mentioned auxiliary conductor is also linked on the conductor that is positioned on the circumferencial direction.The auxiliary conductor that like this one is parallel to the coupling line of conductor group has improved the coupling of the radio frequency electromagnetic energy from the coupling line to the coil system.For the cause of symmetry, each conductor group comprises a similar auxiliary conductor.
In the present invention further conceived, radio frequency electromagnetic energy was added on second end of coupling line by a variable capacitor, and this variable capacitor is complementary the characteristic impedance of coupling line and connecting line.Like this, it is one firm that coupling line has, mechanically stable structure more.
In the further design of the present invention, have at least one to comprise the power supply branch line in the connecting line, be added on the loop of forming by connecting line and capacitor by this branch line radio frequency electromagnetic energy.When radio frequency electromagnetic energy applies by this way, coupling line and auxiliary conductor can be removed, and the layout of result conductors is just simple especially.The power supply branch line preferably is contained in place such on the connecting line, and the there forms coil system " potential loop " of required type De Zhen Swing under running frequency.Yet the power supply branch line also can be placed in and leave this " potential loop " known distance place, can cause the coupling of characteristic impedance between the connecting line that is connected to the power supply branch line and coil system by this distance.Such characteristic impedance coupling also can be from obtaining from the inventive concept of connecting line supply radio frequency electromagnetic energy by variable capacitor.
For the situation that is applied to the nulcear magnetic resonance (NMR) Laminographic, the resonance frequency of coil system of the present invention must be able to have the tuning range of a few percent, this puts into coil system because of ten fens obvious Calipering of the following fact work as testee, load forms on the coil system connecting line, and resonance frequency has also changed.The resonance frequency of coil system for example also may perhaps be adjusted capacitor and be moved with the surface area of adjusting between coupling line and the outer shielding layer, and these capacitors are used for the input radio frequency electromagnetic energy, also be for the coupling institute of load Pi Pei Calipering characteristic impedance essential.Resonance frequency be tuned to by the value that self-induction determined in the former magnetic field of determined nulcear magnetic resonance (NMR), be to use outer shielding layer is linked through variable capacitor in second termination of coupling line to finish in the another design of the present invention.
Use any additional circuit hardly, further can obtain bigger significantly frequency tuning range in the design in the present invention, this design is that each connecting line comprises a tuning branch line, by it, connecting line is received screen and is got on, and every place is with a variable capacitor.Tuning branch line preferably is contained under the resonance frequency, and the place of " potential loop " appears in Calipering on connecting line under the coil running frequency.In order to obtain the arrangement of symmetry, each connecting line comprises a tuning branch line.
In the further design of the present invention, every connecting line comprises a tuning branch line, and each part has first line end of a coaxial resonance line to receive its there, and the crust of said resonance line is received on the screen, and its length is variable.For tuning branch line device use as before.When using adjustable coaxial line, so-called " radio frequency U-shaped waveguide cell " can save the variable radio frequency high-voltage capacitor.
A kind of simple especially and reliable tuner can obtain in further design of the present invention, and it is that second line end of resonance line is unsettled, and intracutaneous is equipped with the length direction that dielectric can be online and slides outside.Such resonance line manufacturing is cheap, and does not comprise movable direct current contact, so can guarantee not safeguard for a long time reliability service.
Go through some embodiment below with reference to the accompanying drawings:
Fig. 1 represents an example according to the conductor segment layout plan of a coil system of the present invention.
The example of the connection conductor arrangement figure of the example shown in Fig. 2 presentation graphs 1.
The modified model of the example of the conductor arrangement figure of company of example shown in Fig. 3 presentation graphs 1.
The characteristic impedance of the coil system shown in Fig. 4 presentation graphs 2 and 3, propagation velocity, voltage and current.
Fig. 5 represents that a coil system according to the present invention is at the sectional drawing of longitudinal center's axis direction perpendicular to it.
Fig. 6 represents the layout plan according to conductor segment and interior external shield in the coil system of the present invention.
Fig. 7 represents that a coil system modified model example according to the present invention is at the sectional drawing of longitudinal center's axis direction perpendicular to it.
The fragmentary cross-sectional view of the coil system shown in Fig. 8 presentation graphs 7.
Fig. 9 represents modified model according to one embodiment of present invention.
Figure 10 represents follow-on according to one embodiment of present invention vertical sectional drawing.
Figure 11 represents according to another embodiment of the present invention at the sectional drawing perpendicular to longitudinal center's axis direction.
Figure 12 represents that modified model is at the sectional drawing perpendicular to longitudinal center's axis direction according to one embodiment of present invention.
Figure 13 represents that coil system according to a different structure of the present invention is at the sectional drawing perpendicular to longitudinal center's axis direction.
Figure 14 represents a follow-on according to one embodiment of present invention example.
The modified model that the conductor segment of embodiment shown in Figure 15 presentation graphs 1 is arranged.
Figure 16 represents follow-on according to one embodiment of present invention fragmentary cross-sectional view.
Figure 17 represents fragmentary cross-sectional view according to another embodiment of the invention.
Figure 18 represents modified model according to one embodiment of present invention.
Figure 19 represents follow-on according to one embodiment of present invention conductor segment and the layout plan that is connected lead.
Figure 20 represents conductor segment and the layout plan that is connected lead according to another embodiment of the invention.
Figure 21 represents according to a tuning lead in the coil system of the present invention.
Fig. 1 represents the conductor segment layout plan according to the simple embodiment of a coil system of the present invention.At their adjacent end portion, with conductor 2, all conductor segment 1 is coupled together at every turn, conductor 2 is positioned at circumferencial direction Shang And and is connected on the link Z3,4,5,6, to form the first conductor group 7 and the second conductor group 8.Conductor segment 1 and conductor 2 are positioned at circumferencial direction, and they are arranged on the circumference of detecting the space.Detecting the space in the present embodiment is the cylindrical of a ring-type, and its profile with dashed lines 13 shows, and its longitudinal center's axis is represented with chain-dotted line 9.Each conductor segment 1 of conductor group 7,8 with respect to longitudinal center's axis 9 of detecting the space, surrounds an angle of circumference 10, and in the present embodiment, this angle of circumference 10 equals 60 °.
By link Z3,4,5,6, conductor segment 1 receives R, F electric current, and at the sense of current with reference to the moment, for example they reach positive amplitude, represent with arrow 11.Electric current in all conductor segment always has identical numerical value at any time.Detecting the space, producing a uniform R, F AC magnetic field by electric current at least basically, the magnetic line of force is parallel to each other basically, and a branch of magnetic line of force of Xing Chenging is perpendicular to longitudinal center's axis 9 of detecting the space like this.
Fig. 2 represents, the conductor group 7,8 that may connect in order to form a closed-loop path.At this, first bonding conductor 20 is connected on link Z3 and 6, and the 2nd connection lead 21 is connected on link Z4 and 5.The length that connects lead 20,21 is selected like this, make under R, F electric current running frequency, amplitude maximum (" current loop ") is formed centrally in each conductor segment 1, and between maximum, amplitude minimum value (" current node ") is positioned at each center that connects lead 20,21.Between the electric current of the second conductor group 8 of the electric current of on one side the first conductor group 7 and another side, cause one 180 ° phase difference.Because " across " connection lead 20,21, then arrow 11 has just been represented R in the conductor segment 1, F sense of current.
Fig. 3 represents the connection conductor arrangement figure of a modified model (Further) embodiment.There, the 3rd connects lead 30 links link Z3 and 5, and the 4th connection lead 31 is linked link Z4 and 6.The length that connects lead 30,31 designs like this, so that under the running frequency of R, F electric current, " current loop " is in the centre of each conductor segment 1, and " current loop " three, two " current node " is positioned at each centre that connects lead 30,31.Under identical running frequency, the length that connects lead 30,31 is longer than the connection lead among Fig. 2 20,21.Like this, between the electric current of on one side the first conductor group 7 and electric current, there are 360 ° of phase differences in the second conductor group 8 of another side.This layout that connects lead 30,31 produces the sense of current indicated by the arrow once more.When (how much) length of the connection lead 20,21 of Fig. 2 concerning the structural design of coil system not during Enough, can consider has increased the connection lead 30,31 of length with respect to connecting lead 20,21.
Fig. 4 a represent as a kind of prolongation by conductor group 7,8 be connected the closed-loop path that lead 20,21 constitutes.Corresponding to coil system shown in Figure 3, caused variation has also showed between the support.The same with other accompanying drawing, appropriate section all uses same reference number to mark.
Fig. 4 b representation feature impedance Z and propagation velocity V are along the variation in loop.They by conductor segment 1 be connected lead 20,21 and 30,31 in the propagation decision of R, F electric current.Expression in this example, conductor segment has high characteristic impedance Z
1With high propagation velocity V
1; Yet connect lead 20,21 and 30,31 and have low characteristic impedance Z
0With low propagation speed V
0Like this, to the geometrical length that is limited by the volume of given coil system, conductor segment 1 has minimum electrical length, that is to say, for the maximum electrical length that the maximum by R, F alternating magnetic field allows distortion to be limited, the geometrical length of conductor segment can have the amplitude of a growth.And for connecting lead 20,21 and 30,31, under the alap situation of running frequency, its electrical length is determined by the distribution of required " current loop " and " current node ".
Fig. 4 c is illustrated in a kind of layout that Fig. 2 represents, under the resonance situation, along the situation of change of R, F electric current and the voltage of closed-loop path length.To conductor group 7,8 be connected lead 20,21 and measure, can obtain the length in whole loop, represent with L.At the center of conductor segment 1, that is to say at the center of conductor group 7,8, there be " current loop " and corresponding " voltage node ".Because the electrical length of conductor segment 1 is indefinite, current strength I is little to the Minus of end portion of conductor segment 1, but according to the sine effect, this kind Minus is micro-for a short time.Voltage U on the conductor segment 1 increases to the conductor segment end direction on the both sides of " voltage node ", and the voltage on the conductor segment 1 will be represented as the shade curved portion 40 of Fig. 4 c like this.For the holding current intensity I is little to two extreme direction Minus of conductor in conductor segment 1, cause the Minus that declines of R, F magnetic field allowable limit, And and in order to guarantee that conductor segment both end voltage U can too not increase the length L of conductor segment 1
1Should be restricted to 1/8 of wavelength.
When as shown in Figure 3, when conductor group 7,8 usefulness connect lead 30,31 and connect, then along obtaining voltage U that Fig. 4 d represents and the distribution situation of current strength I on the whole length L in loop.Two " current nodes " are arranged connecting on the lead 30,31, and be one " current loop " between the two at it.In the coil system of reality, with the represented arrangement of Fig. 2, frequency range is mainly decided by the length that connects lead 20,21, the coil system of representing with Fig. 3, also may operate in higher frequency range, the connection lead 30,31 of the coil system of Fig. 3, its electrical length is longer.At the coil system of Fig. 3, frequency range is mainly decided by the length of conductor segment 1.
Fig. 5 is the sectional drawing of a modified model (Further) embodiment of coil system of the present invention, and it is perpendicular to longitudinal center's axis 9 of detecting the space.Conductor group 7 and 8 conductor segment 1 are perpendicular to the figure paper plane, and And represents with sectional drawing.To the conductor segment 1 of the first conductor group 7, R, F electric current flow out from the drawing plane, and to the conductor segment 1 of the second conductor group 8, electric current is to flow to the figure paper plane.Dotted line 50 is represented the direction and the variation of R, F alternating magnetic field with arrow, and this is corresponding with arrow 12 among Fig. 1.The conductor segment 1 of each conductor group 7,8 is arranged to the angle of circumference 10 of a closure, and this angle is for longitudinal center's axis 9 of detecting the space, and this angle equals 60 °.When this angle is got this numerical value, in the coil system of forming by 4 conductor segment, just can obtain the even variation of a specific R, F alternating magnetic field detecting the space.
In conductor group 7,8 with detect between the space and to also have an inner shield 51, shielding is made up of electric conducting material, it shields the electric field of detecting space and 7,8 generations of conductor group around detecting space And mutually, like this, in detecting the space, can not produce unwanted induced current because of R, F alternating magnetic field.R, F alternating magnetic field just can pass through it like this.The whole winding system also has one deck external shield 52 to surround, in the electromagnetic field of coil system generation just is limited in like this.
Fig. 6 is the layout plan of the first conductor group 7 between inner shield 51 and the external shield 52.Conductor segment 1 and shielding 51,52 mutually insulateds, conductor segment 1 is approaching as much as possible with inner shield 51, so that obtain strong as far as possible R, F alternating magnetic field, conductor segment 1 should approachingly as far as possible be detected the space, and detects the restriction that the space is subjected to inner shield 51.Like this, between conductor segment 1 and external shield 52, maintain a bigger distance, so big distance for detect the R in the space, the uniformity of F alternating magnetic field has remarkable effect.Inner shield 51 and external shield 52 are one deck structure sheafs.In conductor segment 1 zone, inner shield 51 has many seams, and these seams are positioned at the circumferencial direction of detecting the space, in other words perpendicular to conductor segment 1.Outer shielding 52 has closing structure, thus the R of conductor segment 1, F field be completely shielded in coil system around, and the R of conductor segment 1, F alternating magnetic field penetrate region probed by the seam 60 of inner shield 51.The R of conductor segment 1, F electric field then are kept away from basically by inner shield 51 and detect the space.
Fig. 7 is the sectional drawing perpendicular to longitudinal center's axis 9 of detecting the space according to the coil system of a modified model embodiment of the present invention of Fig. 5 mode.Inner shield 51 is arranged in cylinder shape medium that mechanically stable uses and supports 70 Shang , And and inner shield 51 and detect space d.c insulation.As discussing in an embodiment, 2 groups of conductor groups 7,8 are equipped with in the outside of inner shield 51, and each group is made up of two conductor segment 1 and two conductors 2, and conductor 2 is arranged in the circumferencial direction of detecting the space.Link two at the link Z3,4,5,6 of the conductor group of not seeing on Fig. 7 and connect on the leads 20,21, as shown in Figure 2.It is each all from link Z3,4,5,6 one to connect lead, around the circumferencial direction of detecting the space, along inner shield 51, up to zone line 53,54, is parallel to longitudinal center's axis 9 of detecting space other end to conductor group 7,8 then.Whole layout is all surrounded by external shield 52, and external shield is contained in the inner face of a medium supporting 71 of present embodiment.The required media supporting 71 of external shield 52 has annulus one cylindrical structural, is used for inner shield 51 as medium supporting 70, with longitudinal center's axis 9 of detecting the space be concentric.Medium supporting 71 is used for the mechanically stable of external shield 52, makes shielding and coil system insulation mutually on every side simultaneously.Supporting 70,71 only is used for inner shield and external shield, and for example available plexiglass is made.
In the end of coil system, inner shield 51 and external shield 52 are to be electrically connected with the conductor piece 72 that radiation shape is arranged.These conductor pieces are arranged in the zone of conductor 2 in a circumferential direction significantly, just in zone line 54,55.They are used for electric field shielding, are limited in the maximum field intensity on the conductor 2 of circumferencial direction.At zone line 54,55, connect lead 20,21 and shield mutually with R, F alternating-current field, for this purpose, inner shield 51 is closed. Connect lead 20,21 at zone line, the influence on the space geometry of R, F alternating field is to eliminate like this, the result, and there for example have the lead of connection 20,21 to arrange to be inhomogeneous, and perhaps its position is moved, and can not influence the uniformity of R, F alternating magnetic field.
Compare with Fig. 2, connect lead the 20, the 21st, be arranged in the opposite of detecting the space.Obviously, when the first connection lead 20 can connect leads 21 by zone line 54 by zone line 55, the second, can not change to the connection of link Z.
Fig. 8 represents the plane graph of coil system shown in Figure 7.Its B-M-F line in Fig. 7 partly launches.Visible inner shield 51 comprises seam 60 on plane graph, and seam 60 is positioned on the circumferencial direction, and the first conductor group 7 is arranged in above the inner shield.External shield 52 and the supporting 71 of its circle and radiation conductor slice 72 are arranged in conductor 2 zones of circumferencial direction.Line H-K represents the cross section of the coil system represented by Fig. 7.The extention of coil system had been discussed , And and had been illustrated among Fig. 7.Fig. 8 represents two insulating lids 80.Insulating lid 80 makes coil system and , And and supporting 70, the 71 insulation chamber bodies that link to each other and form a closure of insulating on every side.
Fig. 9 represents a perspective view of coil system, basically with Fig. 7 and Fig. 8 represent identical.Part was said in front, also represented with identical numeral at this.In order to simplify accompanying drawing, supporting 70,71 and insulating lid 80 have omitted, and the quantity also Yi Minus of the seam 60 in the inner shield 51 is few.Inner shield and external shield 51,52 disconnect in zone line 54,55 scopes, so that see the path that this position connects lead 20,21 clearly.Connect lead the 20, the 21st, coaxial line, with Fig. 7 Fig. 8 represent the same.What the embodiment that represents with Fig. 7 Fig. 8 was different is, as shown in Figure 9, inner shield 51 and external shield 52 can disconnect at zone line 54,55 places really, and detect the R in space, the F alternating magnetic field does not take place significant how much and changes or influence.With half inner shield 51 and half external shield 52, single shielding box 90,91 connects with connecting lead 20,21 at every turn.Might support inner shield 51 and external shield 52 if support 70,71, and be spaced in zone line 54,55, if connect lead 20,21 structures are flexible coaxial electrical rheniums, the coil system that obtains so comprises two closing sections, each part comprises a shielded conductor group, and the distance between two parts is transformable.
Figure 10 represents along a simple sectional drawing of A-E-G line work among Fig. 7.Coil system is consistent with the coil system among Fig. 1 basically.Opposite with coil system among Fig. 1 is, the seam 60 wide degree Minus of inner shield 51 are few, and when detecting longitudinal center's axis 9 orientation measurements in space, inner shield is towards the end of conductor segment 1.But, the same with Fig. 8 Fig. 9, Figure 10 represents that conductor 2 is positioned at circumferencial direction, and as seen connection lead 20,21(show from Fig. 8) be arranged in inner shield 51 zones, inner shield is closed.
Figure 11 represents the sectional drawing according to a modified model coil system of the present invention, along the H-K line of Fig. 8, perpendicular to longitudinal center's axis 9 of detecting the space.Embodiment was discussed relatively with the front, the supporting 71 of external shield 52 does not improve, yet the supporting 70 of inner shield 51 comprises two periphery parts 113 now, and its radius of curvature is identical with the supporting 71 of external shield 52.Detect the space and be supported 70 part 113 closures, have oval cross-section basically.In order to compare, dashed circle is represented the profiled outline of concentric inner shield, as is used in Fig. 7 to the system as shown in Fig. 9, and the position of conductor segment 1.When inner shield as shown in this embodiment, conductor segment 1 more close longitudinal center's axis of detecting the space, also more close testee just.So the sensitivity of coil system improves.This layout is specially adapted to detect on human body, and the profile in human body cross section is oval-shaped basically.Figure 11 represents the cross-sectional view of a human body, and it is approaching in the thorax level.Numeral 111 expression thorax sections, and the section of numeral 112 expression arms, measured human body is positioned on the desk 110, and And introduces in the coil system with obliquity.
As among the embodiment in front, in the zone of conductor segment 1, inner shield 51 comprises seam 60, and seam 60 is positioned at circumferencial direction, and inner shield 51 comprises seam 60, and seam 60 is positioned at circumferencial direction, and inner shield is a closing structure in zone line 54,55.
Figure 12 represents the follow-on hasty profile of coil system shown in Figure 9.Along H-K line among Fig. 8, perpendicular to longitudinal center's axis of detecting the space.This figure represents two closed shielding boxs 90,91, shielding box 90,91 usefulness connect lead 20,21 and connect, zone line at coil system, shielding box 90,91 is supported by guide rail 120, guide rail 120 allows shielding box 90,91 to move mutually, and guide rail 120 and conductor group 7,8 are together perpendicular to longitudinal center's axis of detecting the space.Moving direction is represented with double-head arrow 121.
The modified model embodiment of a coil system of the same expression of Figure 13, this coil system is the same with Figure 12 basically.Compare with the coil system of Figure 12, shielding box 90,91 is connected on the zone line 55 by joint (hinge) 130 pivots now.Joint 130 also can comprise a hollow shaft, and second connects lead 21 can pass through wherein.First connects lead 20 comprises R, F connector, and R, F connector are made up of shielded plug 132 and shielding socket 131, and when shielding box 90,91 was separated by joint, plugs and sockets disconnected.
Figure 14 is follow-on perspective view of system shown in Figure 13.For fear of a R, F connector used in Figure 13, two connection leads 20 and 21 in coil system of representing in Figure 14 are received a zone line.Although the coil system uniformity is subjected to some influences, omit R, F connector, enlarged has also saved.Two connect leads 20,21 and can be arranged together, for example at the quill shaft of joint in the heart.
Obviously, in the coil system that Figure 13 represents, each connects lead 20,21 can comprise a R, F connector.Shielding box 90,91 can be separated from each other fully.A kind of like this advantage of system is, shielding box 91 can with shielding box 90 structures on inequality, for example can comprise different matching elements, also can combine 90,91.
Figure 15 represents modified model shown in Figure 1, and on the direction of longitudinal center's axis 9, conductor segment 1 can bend to barrel shape.Detect the R in space, the uniformity of F alternating magnetic field so that improve.Remaining discusses identical with the discussion carried out among Fig. 1.
Figure 16 represents the perspective view of coil system shown in Figure 8.Get section along Fig. 7 B-M-F line, be added in Fig. 8 system, additive wire 160,161 links that each link Z3,4,5,6(are connected to link Z5,6 lead is not shown among the figure), lead the 160, the 161st, coaxial line, one end scatters (float), is used for suppressing the unwanted Zhen Swing in the coil system.Be positioned at conductor 2 zones of circumferencial direction, additive wire 160,161 is arranged like this, reaches the enclosed region back of inner shield 51 abreast, with this part with detect the space and shield mutually.The advantage of the layout of this additive wire 160,161 is that the symmetry of all conductors on circumferencial direction conductor 2 zones improves.
Figure 17 represents that the part sectional drawing of coil system shown in Figure 7 obtains along the C-M-D line.The parts in Fig. 7 Fig. 8, Figure 17 system also comprises a coupling line 171, and coupling line 171 is arranged in the space between inner shield 51 and the external shield 52, in the outside of the first conductor group 7; By first end 172, the coupling line is linked in the external shield 52; By second end 173, link on the inner wire of coaxial connection lead 170, and the outer conductor of coaxial connection lead is connected in the external shield 52.By coaxial connection lead 170, coil system can receive or export R, F electromagnetic energy, and coupling line 171 is used for energy is delivered to from the inner wire of coaxial connection lead 170 conductor segment 1 of the first conductor group 7.
Magnetic field by the electric current that flows through in coupling line 171 comes coupling , And to power by coaxial connection lead 170.Coupling between coupling line 171 and conductor group 7 can be adjusted by changing surf zone, and this surf zone is limited by coupling line 171 and external shield 52.In order to adjust this surf zone, coupling line 171 comprises a fexible conductor, and And is connected to and regulates on the parts 174, and the distance between coupling line 171 and the external shield 52 can change.This adjusting parts 174 can be installed with screw or other guide rail.
For the resonance frequency of syntonizing coil system well, second end 173 of coupling line 171 is linked in the external shield 52 by tuning capacity 175.Resonance frequency can be adjusted to the error near 2%.
Regulate coupling line 171 by adjustment component 174, not only regulated the coupling degree, and regulated terminal/inductance that coupling line 171 forms on the terminal of coaxial connection lead 170.
Figure 18 represents the perspective view of coupling line 171 mechanical fixation.Magnetic coupling between the coupling line 171 and the first conductor group 7 is a constant.The coupling of terminal inductance is formed by the coupling line, offers coaxial connection lead 170 by a trimmer 181, and trimmer 181 is connected between second end 173 in the inner wire of coaxial connection lead 170 and coupling loop 171.First end, 172 ground connection of coupling line 171 are linked external shield 52, inner shield 51, the crust of coaxial connection lead 21.
In order to increase the magnetic coupling between the coupling line 171 and the first conductor group 7, an auxiliary conductor 180 is included in the conductor group 7.Auxiliary conductor and the coupling line 171 , And that is arranged in parallel links on the link Z3 and 4 of conductor group 7.For symmetry, a same auxiliary conductor 180 is included in conductor group 8 Zhong , And and is receiving on the end Z5 and 6.
Figure 19 represents conductor group 7,8 and the connection layout that is connected lead 20,21.In the figure, first connects lead 20 comprises a component branch line 190, in this zone, forms when potential loop moves under the coil resonance frequency, and branch line 190 receives R, the F electromagnetic energy that connects lead 170.The layout of expression is equally applicable to accept small-signal from testee and connects equipment to receipts in Figure 18 and 19.At branch line 190 with connect the trimmer that to be connected in series between the lead 170, be used to connect lead 170 is connected the characteristic impedance of lead 20 with first coupling or fine setting.
Figure 20 represents a coil system, with Figure 19 roughly the same, connect lead 20,21 and comprise tuning branch line 200 now; In this zone, under the situation of coil system resonance, form potential loop.Connect lead at stub area by tuning capacity 201 bridge joints.Regulate tuning capacity 201, the electrical length and the resonance frequency of the connection lead 20,21 of coil system can change.For symmetry, in order to prevent moving of electric current anti-node location on the conductor segment 1, the electric capacity of tuning capacitor 201 is selected to be equated.This tuning capacity 201 can surpass 10% by mobile resonance frequency.
Replace the tuning capacitor 201 used among Figure 20, also the usefulness one tuning lead 210 that can represent as Figure 21.This lead partly is made up of concentric conductor, and it comprises medium 211.Medium 211 vertically can move.Move media 211, shown in arrow 212, the electrical length of tuning lead just can change, and the electrical length that therefore connects lead 20 or 21 also can change.
The structure of Fig. 7 and a coil system shown in Figure 8, its external shield 52 diameters are 52cm, inner shield 51 diameters are 30cm.The length L of conductor segment 1
1Reach 31cm.Conductor segment is made by brass tube, and the brass tube overall diameter is 4.8mm, wall thickness 0.1mm.To this size, eddy current Shuai Minus time constant is less than 0.1ms.Eddy current induces in the conductor group.So the obvious influence that has on several kilo hertzs the gradient magnetic of frequency is of short duration.Conductor segment 1 is arranged in from the place of inner shield less than 10mm.
In the coil system of being discussed, connect the length L of lead 20,21
0Equal 100cm.With characteristic impedance is 50 ohm, and velocity of wave propagation is made for 82% coaxial electrical rhenium of in a vacuum the light velocity.This size, the characteristic impedance of conductor group approaches 180 ohm, and velocity of wave propagation approaches the light velocity.The resonance frequency of system approaches 66MHZ.The quality factor of coil system are 550 when not having testee, are 163 after introducing human body.On the contrary, resonance frequency moves on to 10KHZ, because R, F electric field have masked from tested human body effectively.
Claims (41)
1, one supplies generation and/or receives to come down to uniform alternating magnetic field at least, especially for the rf coil system in the nuclear magnetic resonance apparatus, said system is columniform detecting around the space by device at one basically, and having comprised at least four in fact is parallel to and detects space longitudinal center axis, and on circumference, be symmetrical at least one with respect to the conductor segment of settling by the plane of longitudinal center's axis, said conductor segment couples together with connecting line, constitute a closed-loop path, it is characterized in that: with respect to detecting conductor segment (1) conductor (2) that is located substantially on the circumferencial direction of detecting the space that space longitudinal center axis (9) feeds electric current (I) with being equal to, conductor group (7,8) with the connecting line of receiving on the conductor (2) that is positioned on the circumferencial direction (20,21; 30,31) be connected to each other connecting line (20,21; 30,31) length (Lo) is selected like this, and the maximum point of the width of cloth appears at the central authorities of each conductor segment (1) when making radio-frequency current, and the smallest point of the width of cloth appears at each root connecting line (20,21 when having a radio-frequency current at least; 30,31) on.
2,, it is characterized in that the characteristic impedance (Z of conductor group (7,8) and connecting line (20,21) according to the coil system of claim 1
0, Z
1) ratio and connecting line length (L
0, L
1) and propagation constant (β
0, β
1) by following relational expression:
Z
0/ Z
1=| tan(β
0* L
0/ 2) * tan(β
1* L
1/ 2) or high slightly.
3,, it is characterized in that the characteristic impedance (Z of conductor group (7,8) and connecting line (30,31) according to the coil system of claim 1
0, Z
1) ratio and connecting line length (L
0, L
1) and propagation constant (β
0, β
1) by following relational expression:
Z
0/ Z
1=| tan(β
1* L
1/ 2)/tan(β
0* L
0/ 2) or high slightly.
4,, it is characterized in that connecting line (20,21 according to the coil system of claim 1,2 or 3; 30,31) include conductive shielding layer.
5, according to the coil system of one or several claim in the above claim, it is characterized in that conductor group (7,8), each comprises two adjacent conductor segment (1).
6, according to the coil system of one or several claim in the above claim, it is characterized in that conductor segment (1) is positioned in two conductor groups (7,8) in, these conductor groups are arranged symmetrically with respect to the plane (53) by longitudinal center's axis (9).
7, according to the coil system of one or several claim in the above claim, per two conductor segment (1) that it is characterized in that feeding same electric current (I) are placed to such an extent that make and be approximately 60 ° at least to detecting the angle of circumference of opening in the space (10).
8, according to the coil system of one or several claim in the above claim, it is characterized in that the screen (51,52) of magnetic that conductor segment (1) is conducted electricity and saturating surrounds, screen is settled to such an extent that insulate with described conductor segment on electric.
9, coil system according to Claim 8 is characterized in that each encirclement of part of screen (51, the 52) sealing of magnetic that conduct electricity and saturating belongs to the conductor segment (1) of a conductor group (7,8).
10, according to Claim 8 or 9 coil system, the screen (51 that it is characterized in that magnetic that conduct electricity and saturating, 52) comprise one towards detecting the space and sentence encloses internal shield (51) and an outer shielding layer (52) outside in this space, internal shield (51) and outer shielding layer (52) composition switch are essentially the part of cylindrical surface sector.
11,, it is characterized in that in conductor segment (1) scope, internal shield (51) comprises the slit (60) of circumferencial direction according to the coil system of claim 10.
12,, it is characterized in that on longitudinal center's axis (9) direction of detecting the space of width in slit (60) that the mind-set two ends reduce (Figure 10) from coil system according to the coil system of claim 11.
13, according to the coil system of claim 11 or 12, it is characterized in that internal shield (51) make with at one by longitudinal center's axis (9), and conductor group (7,8) with respect to it be symmetrical placement the plane area and be positioned at an area at conductor (2) place on the circumferencial direction and seal.
14,, it is characterized in that connecting line (20,21 according to the coil system of one or several claim in the claim 10 to 13; 30,31) total length all is positioned within the enclosed areas of internal shield (51).
15,, it is characterized in that internal shield (51) and outer shielding layer (52) are connected to each other by the conducting strip (72) of the width of cloth to rotation at the place, end of coil system according to the coil system of one or several claim in the claim 10 to 14.
16,, it is characterized in that screen (51,52) is hierarchy at least in part according to the coil system of one or several claim in the claim 10 to 15.
17,, it is characterized in that screen (51,52) is placed in non-conductor supporting (70,71) according to the coil system of one or several claim in the claim 10 to 16.
18,, it is characterized in that screen (51,52) has network structure according to the coil system of one or several claim or claim 17 in the claim 10 to 15.
19,, it is characterized in that screen (51,52) is made up of gauze according to the coil system of claim 18.
20, according to the coil system of claim 16 or 17, the bed thickness that it is characterized in that screen (51,52) is several times of radio-frequency current (I) frequency next part effect penetration depth.
21, according to the coil system of one or several claim in the claim, the conductor (2) that it is characterized in that conductor segment (1) and/or be positioned at circumferencial direction is made the conductor tube of thin-walled.
22,, it is characterized in that it is concentric basically that outer shielding layer (52) and internal shield (51) are placed for detecting space longitudinal center axis according to the coil system of one or several claim in the claim 10 to 20.
23,, it is characterized in that coming down to perpendicular to an ellipse in the plane of longitudinal center's axis (9) by the cross-sectional profiles line of detecting the space that internal shield (51) surrounds according to the coil system of one or several claim in the claim 10 to 20.
24,, it is characterized in that outer shielding layer (52) and internal shield (51) have the radius of curvature that is actually same at least according to the coil system of one or several claim or claim 23 in the claim 10 to 20.
25, according to the coil system of one or several claim in claim 9 to 20 or 22 to 24, it is characterized in that screen (51,52) two parts of being sealed by self are formed, each part constitutes a shielding box (90,91) each comprises a part of internal shield (51) and a part of outer shielding layer (52), and the distance between above-mentioned two parts can be in the direction adjusted perpendicular to longitudinal center's axis (9) of detecting the space.
26,, it is characterized in that on the direction of shielding box (90,91) be transportable according to the coil system of claim 25.
27, according to the coil system of claim 25, it is characterized in that screen (90,91) install to such an extent that can turn round relatively around an axle (130) each other, this axle is parallel to longitudinal center's axis (9) and extends, and be arranged in a plane (53), and conductor group (7,8) it is arranged symmetrically relatively.
28, according to the coil system of one or several claim in the above claim, it is characterized in that connecting line (20,21; 30,31) make soft.
29,, it is characterized in that conductor segment (1) has the bending that is tubbiness detecting on the space longitudinal center axis (9) according to the coil system of one or several claim in the above claim.
30,, it is characterized in that the connection line segment (160,161) that adds linked connecting line (20,21 according to the coil system of one or several claim in the above claim; 30,31) and the binding post (3,4,5,6) that is positioned between the conductor (2) of the circumferencial direction of detecting the space go up as first line end.
31, according to the coil system of claim 30, it is characterized in that adding connection line segment (160,161) and make coaxial line, its second line end is unsettled.
32, according to the coil system of claim 10 to 31, it is characterized in that the coupling line (171) that conducts electricity is placed at least between the internal shield (51) and outer shielding layer (52) of a conductor group (7,8) scope, thereby to conductor segment (1) symmetry.Said line is arranged essentially parallel to longitudinal center's axis (9) of detecting the space, and its first line end (172) is received outer shielding layer (52), and its second line end (173) received RF electromagnetic energy.
33,, it is characterized in that coupling line (171) makes to such an extent that can change shape, so that the surface area that is surrounded by its (171) and outer shielding layer (52) is variable according to the coil system of claim 32.
34, according to the coil system of claim 32 or 33, it is characterized in that auxiliary conductor (180) is parallel to longitudinal center's axis of detecting the space and is placed on the circumference (9), thereby may in fact be parallel to each conductor group (7,8) coupling line (171), said auxiliary conductor are received the conductor (2) that is positioned on the circumferencial direction.
35,, it is characterized in that radio frequency electromagnetic energy passes through on second termination (173) that a variable capacitor (181) is added to coupling line (171) according to the coil system of claim 32,33 or 34.
36,, it is characterized in that connecting line (20,21 according to the coil system of one or several claim in the claim 1 to 31; 30,31) at least one includes power supply branch line (190) in, is added to by connecting line (20,21 through its radio frequency electromagnetic energy; 30,31) and in the loop of conductor (1) composition go.
37,, it is characterized in that radio frequency electromagnetic energy adds through a variable capacitor (181) according to the coil system of claim 36.
38, according to the coil system of one or several claim in the claim 32 to 35, second line end (173) that it is characterized in that coupling line (171) received outer shielding layer (52) through a variable capacitor (175) and got on.
39, the coil system of one or several claim in 38 according to Claim 8 is characterized in that each connecting line (20,21; 30,31) comprise a tuning branch line (200), by it, each time of connecting line received on the screen (51,52) through a variable capacitor (201).
40, the coil system of one or several claim in 38 according to Claim 8 is characterized in that each root connecting line (20,21; 30,31) comprise a tuning branch line (200), each has another line end of a coaxial tuning lead-in wire (210) to receive on the screen (51,52), and its length is variable.
41, according to the coil system of claim 40, it is characterized in that second line end of tuning lead-in wire (210) is unsettled, dielectric (211) is positioned in just can slide within the crust on the wire length direction.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
CN 85101788 CN1009140B (en) | 1985-04-01 | 1985-04-01 | Produce and/or receive the rf coil system of alternating magnetic field |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
CN 85101788 CN1009140B (en) | 1985-04-01 | 1985-04-01 | Produce and/or receive the rf coil system of alternating magnetic field |
Publications (2)
Publication Number | Publication Date |
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CN85101788A true CN85101788A (en) | 1987-01-17 |
CN1009140B CN1009140B (en) | 1990-08-08 |
Family
ID=4792059
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
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CN 85101788 Expired CN1009140B (en) | 1985-04-01 | 1985-04-01 | Produce and/or receive the rf coil system of alternating magnetic field |
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CN (1) | CN1009140B (en) |
Cited By (5)
Publication number | Priority date | Publication date | Assignee | Title |
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CN103959085A (en) * | 2011-10-18 | 2014-07-30 | 皇家飞利浦有限公司 | Mri coil assembly with a radio frequency shield switchable between a blocking state and a transparent state |
CN104280706A (en) * | 2013-07-02 | 2015-01-14 | 西门子公司 | Method and apparatus to acquire magnetic resonance data of a target region including a metal object |
CN108398657A (en) * | 2018-01-12 | 2018-08-14 | 上海东软医疗科技有限公司 | Magnetic resonance transmitting coil |
CN109444780A (en) * | 2018-11-28 | 2019-03-08 | 上海联影医疗科技有限公司 | Emission array unit, body transmitting antenna and magnetic resonance equipment |
CN111383830A (en) * | 2018-12-29 | 2020-07-07 | 台达电子企业管理(上海)有限公司 | Magnetic unit |
-
1985
- 1985-04-01 CN CN 85101788 patent/CN1009140B/en not_active Expired
Cited By (9)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN103959085A (en) * | 2011-10-18 | 2014-07-30 | 皇家飞利浦有限公司 | Mri coil assembly with a radio frequency shield switchable between a blocking state and a transparent state |
CN103959085B (en) * | 2011-10-18 | 2017-03-08 | 皇家飞利浦有限公司 | There is the MRI coil assembly of the radio shielding that can switch between blocked state and pellucidity |
CN104280706A (en) * | 2013-07-02 | 2015-01-14 | 西门子公司 | Method and apparatus to acquire magnetic resonance data of a target region including a metal object |
CN104280706B (en) * | 2013-07-02 | 2017-05-17 | 西门子公司 | Method and apparatus to acquire magnetic resonance data of a target region including a metal object |
US9784807B2 (en) | 2013-07-02 | 2017-10-10 | Siemens Aktiengesellschaft | Method and magnetic resonance apparatus to acquire magnetic resonance data of a target region including a metal object |
CN108398657A (en) * | 2018-01-12 | 2018-08-14 | 上海东软医疗科技有限公司 | Magnetic resonance transmitting coil |
CN109444780A (en) * | 2018-11-28 | 2019-03-08 | 上海联影医疗科技有限公司 | Emission array unit, body transmitting antenna and magnetic resonance equipment |
CN111383830A (en) * | 2018-12-29 | 2020-07-07 | 台达电子企业管理(上海)有限公司 | Magnetic unit |
US11437175B2 (en) | 2018-12-29 | 2022-09-06 | Delta Electronics (Shanghai) Co., Ltd | Magnetic unit |
Also Published As
Publication number | Publication date |
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CN1009140B (en) | 1990-08-08 |
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