CN1131906A - Magnetic resonance imaging method with pulse sequence optimisation and device for such method - Google Patents

Abstract

A method for magnetic resonance imaging features that before RF and gradient pulse sequence are applied to the object or patient to be imaged, the imaging sequence including RF and gradient magnetic field pulses (RF, Gx, Gy and Gz) is optimized relatively to an associated parameter (SAR, S/N ratio, etc.), so reducing the number of different sequences to limited basic sequence, from which operator selects, and allowing application of the sequence in particular image to be obtained.

Description

Optimized MR imaging method of pulse train and device thereof

The present invention relates to a kind of being used for to putting into the method that a static state and basic at least a portion of the human body of main field are uniformly carried out nuclear magnetic resonance.The invention still further relates to the device of realizing this method.

In nuclear magnetic resonance (MRI), apply pulse train to produce the information that magnetic resonance signal also obtains to be used to subsequently reproduce this object images thus to an object (patient).Because it is in the starting developmental stage, so the quantity of using the clinical relevant of MRI very rapidly increases.MRI can be used in almost each part of human body and is used for obtaining the information of relevant many important functions, as blood flow, heart body, cerebral activity and other many functions.All need one group of MR pulse train for every function.A MR pulse train just can be determined the feature of reproduced image fully, as at patient position on one's body and orientation, size, resolution, signal to noise ratio, contrast, autokinesis, other or the like.In order to obtain to have the image about different functions of various one-tenth stack features, need the possible pulse train of a big group and be used for operating a MRI device.The operator must select a particular sequence and be limited to about being fitted to of a specific image more to select one group of numerical value about no more than Several Parameters.

In EP-A-0567794, disclosed a kind of MRI device, wherein selected a kind of basic pulse sequence form from the basic pulse sequence form of many storages.By utilizing the pulse train parameter that produces corresponding to required image-forming condition selected basic pulse sequence form is constantly made amendment.After this, produce a suitable pulse train and under the situation of taking into account system and patient characteristics, simulating.From this simulation that begins to calculate by the Bloch equation, obtain the effect of the pulse train that produces, adjust according to the Simulation result pulse sequence subsequently.

As illustrated among the EP-A-0567794, realize this known method by in the time of a weak point, finishing required calculating by a very strong computer of function, can make the quantity of measurement and adjust the required time minimum of pulse train.But this known method is just adjusted sequence obtaining required image-forming condition, and pulse sequence itself and can not exert an influence by the quality of measuring the data that the magnetic resonance signal that produces obtains.This known method can not make the operator make suitable selection and the careful cognitive image that is obtained by a particular sequence.This known method can not make all variable element the bests, also just can not obtain best possible sequence.

One object of the present invention is exactly that a kind of method and apparatus that is used for nuclear magnetic resonance is provided especially, wherein can make data best in quality of acquisition with regard to one group of predetermined required image-forming condition with the auxiliary of minimum staff.

For this reason, a method according to the present present invention comprises

Select the basic sequence type of a radio frequency (RF) and magnetic field gradient pulse, in an object, to produce magnetic resonance signal;

Select running parameter, these running parameters and selected basic sequence are described required imaging features together;

On the basis of considering machine-limited and said running parameter, determine the work sequence of RF and magnetic field gradient pulse by making said basic sequence optimization;

Said part to human body applies said work sequence, produces magnetic resonance signal in said part thus;

Measure said magnetic resonance signal and from said measured signal, obtain the image of the said part of this human body.

Running parameter is for example visual field, slice thickness, echo or recovery time, location and directed.About a kind of relevant parameter, for example relevant with picture quality parameter realizes optimization.On the other hand, can select with assembly as the contrast in time, instantaneous or spatial resolution, visual field, the image, short echo time, flow information, SAR (special absorptance) or sound noise, other or the like relevant parameter.Can realize by program that has appropriate algorithm of operation in a computer because optimization is handled, so, the staff can attention concentrate on select institute's image that requires need feature on.The operator does not have the technical limitations that notes with about each relevant technical and MRI devices of the many various basic pulse sequences of requirement image condition.

In the method for the invention, selecting step is what to separate on function with the optimization step preferably, and realizes the optimization step in a kind of mode of carrying out with the determining to have nothing to do of work sequence.By the generation of pulse sequence and optimization are separated, can carry out the optimization step with a kind of commonsense method, just can introduce new pulse train so that can repeat optimized algorithm in a large number.

Specifically, in the method for the invention, make the basic sequence optimization determine work sequence by making the cycle maximum, with the signal to noise ratio that is used to measure the magnetic resonance signal of generation or wherein expect.Signal to noise ratio is to determine the important parameter of picture quality.The signal to noise ratio of the sampled data that obtains from magnetic resonance signal increases along with the reinforcement of the time cycle that can obtain each sample.

In an embodiment of method of the present invention, wherein at first from a basic sequence type, determine a kind of overall statement of work sequence, said overall statement comprises the time cycle of RF pulse and the intensity of the magnetic field gradient that applies simultaneously with the RF pulse, and, next realizes optimization, to determine magnetic field gradient waveforms at the interval that does not provide in said overall statement.In these two step process, the RF pulse is to occur on some specific time points, and magnetic gradient field is set up in some specified time intervals.Then, in optimization is handled, in other interval of pulse train, determine particular location, scope and the intensity of magnetic field gradient.

In another embodiment of method of the present invention, wherein at first determine the overall statement of work sequence by a kind of basic sequence type, carry out optimization then to determine cycle, wavelength and the intensity of RF pulse and magnetic field gradient waveforms.In the present embodiment, the feature of RF pulse itself also counts in optimization is handled.These features can be optimized within certain limit, and if for example must the restriction SAR, then preferentially about RF pulse optimization.Square being directly proportional and being inversely proportional to its persistent period of SAR and RF field, simultaneously, the RF field is directly proportional with time integral intensity to magnetized influence.

Present embodiment can have another feature, and promptly magnetic field gradient waveforms is a piecewise linear function.A piecewise linear function comprises some straight edges.Because it is very fast relatively to comprise the calculating of linear function, so optimization procedure can enough medium operational capabilities carry out.For the sectional linear wave of magnetic field gradient allow be any in imaging process a kind of meet the demands approximate of needed gradient waveform.

The invention still further relates to a kind of MRI device that is used to realize a kind of MRI method.A kind of like this MRI device comprises the device that is used to set up main field, be used to produce the device that is superimposed upon the gradient magnetic on the main field, be used for device to the pulse of human body transmitting RF, be used to control the control device of gradient magnetic and the generation of RF signal, be used for device to producing by RF pulse train and receiving and sample by the magnetic resonance signal of gradient magnetic control, with the transcriber that is used for being formed by said sampled signal image, said control device also comprises:

The overall statement of the basic sequence of-limited quantity;

-one operator importation is used to import the running parameter of describing the feature that requires that will obtain image, and is used to select a basic sequence;

-arithmetic unit is used for determining the work sequence of RF and magnetic field gradient pulse on the basis of considering machine-limited and said running parameter by making said basic sequence optimization.

In another embodiment of a kind of like this device, the user control device comprises an output, is used for to the optimized result of operator's transfer sequence and is used to make the operator can adopt additional parameter.If do not find single separating, so, this just makes the operator participate in optimization to a certain extent and handles.The operator can determine use which may exist separates, and meets separating of required setting if perhaps can not find, and so, just can add, changes or limits any parameter.

Referring now to accompanying drawing, illustrate in greater detail these and other aspect of the present invention by way of example.

Shown accompanying drawing has

Fig. 1 is the sketch map that is applicable to a kind of MR imaging apparatus of the inventive method;

What Fig. 2 represented is to have excitation RF pulse, and one focuses on the RF pulse again, and spin echo (SE) sequence of phase code and measurement gradient pulse is selected in section;

What Fig. 3 represented is the magnetic field gradient waveforms with piecewise linear function and non-coincidence node;

What Fig. 4 a and 4b represented is a few gradient waveform that obtains about a SE sequence;

Fig. 5 a and 5b are presented at a functional block diagram that concerns between the different step of the inventive method and the flow chart that optimization procedure is described.

In Fig. 1, schematically shown a kind of MR imaging apparatus 1.Device 1 comprises one group of main magnetic coil 2 and three groups of gradient coils 3,4 and 5 that are used for having in choice direction with one of intensity controlled stack the complementary field of a gradient of being used to produce a kind of static state and uniform main field.Will be by convention, the direction of main field is marked as the z direction, and perpendicular both direction is marked as x and y direction.Gradient coil is by power supply 11 power supplies.Device 1 also comprises radiation emitter 6, and promptly antenna or coil are used for to a human body 7 emission radio-frequency pulses (RF pulse), and radiation emitter and manipulator 8 are coupled and produce the RF pulse and it is modulated being used to.Also provide a receptor to receive the NMR signal, receptor can be same or separate with emitter 6.If emitter is identical antenna or coil with receptor in the physical sense as shown in the figure, a transmission-receiving key 9 then to be set so that the signal that receives is separated with the pulse that will launch.The NMR signal that receives row is inputed to a demodulator 10.The power supply 11 of manipulator 8, emitter 6 and gradient coil 3,4 and 5 is controlled to produce the predetermined sequence of a RF pulse and magnetic field gradient pulse by a control system 12.The such data processing unit 14 of demodulator 10 and for example computer links to each other, and being used for received conversion of signals is become can be at observable image on visual display unit 15 for example.

If MR imaging apparatus 1 is put at human body 7 under the situation in magnetic field and is entered duty, so, the direction that magnetic field is aimed in excessive a little nuclear dipole moment or nuclear spin meeting in the human body.Under poised state, this can make the net magnetisation M in human body 7 materials ₀Be parallel to magnetic field.Then,, this macroscopic magnetization intensity is controlled, made these nuclear polar moments enter foment and make intensity of magnetization M thus by equal the RF pulse of these nuclear Larmor frequencies to human body radiation frequency ₀Reorientation, thus this macroscopic intensity of magnetization M controlled ₀By applying suitable R F pulse, the macroscopic magnetization strength vector is rotated, the angle of rotation is called as the angle of revolution.The variation of introducing intentionally in magnetic field by applying gradient magnetic can influence resonant frequency and local magnetized.After the sequence that applies an appropriate RF pulse of selecting and magnetic field gradient pulse, by human body emission NMR signal, these signals provide relevant certain kind of atom nuclear, as the density of hydrogen nuclei, and the information that wherein produces the material of these signals.Signal by analyzing these emissions and with pictorial form to they represent, just can obtain the information of relevant human body 7 internal structure aspects.In order to illustrate in greater detail nuclear magnetic resonance and MRI device, can be with reference in a large number about the documents of this theme, handbook " Practical NMR Imaging " for example, edited by M.A.Foster and J.M.S.Hutchison, 1987, IRL Press.

Fig. 2 represents is to comprise an excitation RF pulse and so-called spin echo (SE) sequence that focuses on the RF pulse again as an example.Also can adopt and resemble other such sequence of FLASH, RARE, GRASE or EPI-spiral.Fig. 2 represents to have 5 row, be labeled as the occurrence rate of that line display of RF as the RF pulse of time function, Gx, Gy and Gz are illustrated respectively in the occurrence rate of the magnetic gradient field on x, y and the z direction, and MR represents to be caused and the occurrence rate of magnetic resonance signal in human body 7 by RF and gradient pulse.

At time t ₀The place provides excitation RF pulse 21 with angle of revolution α, at later time t ₁The place provides one to focus on RF pulse 22 again with angle of revolution β.The numerical value of α and β is generally elected 90 ° and 180 ° respectively as, but also can adopt other angle of revolution angle.After excitation RF pulse 21, produce the free induction decay shown in the MR (FID) NMR signal 61 of being expert at, when wherein ought make the nuclear-magnetism polar moment forfeiture phase coherence (phase shift) of each precession owing to the localized variation in the magnetic field, signal 61 rapid vanishing.Focusing on RF pulse 22 again puts upside down the direction of these single dipole moments and does not influence local magnetic field.Therefore, phase shift is inverted to phase coincidence, and this is not having under the situation of magnetic field gradient pulse at t ₀One-period 2 (t afterwards ₁-t ₂) echo t constantly _ECan cause a NMR spin echo signal 62.Echo time t _ESelection be to determine by such fact, promptly can cause the different contrast of all kinds tissue in the human body about the different numerical value of echo time.

In order in resulting signal, to provide spatial resolution, will on x, y and z direction, apply gradient magnetic.On the z direction, be synchronized with the RF pulse and apply gradient 51 and 52 feasible only excited nucleus spins in section.Because this gradient produced the phase contrast of the spin that changes on the direction of terrace cut slice, so, apply in the opposite direction compensating field 51 with this gradient '.For the resolution on the x direction, on the x direction, provide a magnetic field 31 prior to focusing on RF pulse 22 again with this gradient, this gradient fields causes the initial phase shift of nuclear spin.By focusing on again after RF pulse 22 makes spin flip conversion, apply a magnetic-field measurement gradient 32, so that to produce a kind of magnetic resonance signal 62 with frequency relevant with the space.Preferably select above-mentioned two x gradients 31 and 32 like this, promptly they are at t ₀And t ₁Between time integral intensity equal at t ₁And t ₂Between time integral intensity, and can be to time t ₂The x gradient at place has clean influence and obtains a maximum spin echo signal.Space about the y direction is selected, and applies a gradient 42 before or after focusing on the RF pulse again before measuring N MR signal, sets up a kind of relation with phase place and NMR signal source at the NMR signal between the position on the y direction.For the spatial resolution of y direction, the measurement that will carry out with different Grad on the y direction combines, shown in vertical arrow 43.General adopt two-dimentional fourier transform to convert an image to obtaining measured value by the x of different time integrals and y gradient.

The amount of measuring the used time with each sampled signal improves the quality of gained data.This is because signal to noise ratio is directly proportional with the square root of the length of total measuring period.So, need existing measuring period long as much as possible, to observe the physics and the technical limitations of gradient simultaneously.The main physical restriction is to avoid gradient to move effect in any net phase of z direction, on the x direction, at the t of gradient ₀And t _EBetween clean Phasing need be zero, and the gradient that on the z direction, needs to apply constant intensity, and do not have other gradient at the RF impulse duration.Technology or mechanical constraint are exactly the gradient intensity and the slope of the machine hardware maximum that can provide.Purpose of the present invention just is to provide a kind of method of obtaining best signal within these restrictions.

It is for example to wish the compensation of flowing that the MRI sequence causes the supplementary features of different restrictions.Can make parameter optimization realize the compensation of flowing not sacrifice, perhaps, if desired, can be that cost is improved the compensation of flowing to sacrifice about the optimum solution that makes parameter optimization.And, in a sequence, about being closely connected correlation time of RF pulse and gradient fields, to reduce the quantity of parameter related in the optimization procedure.

Because in fact the quantity of possible gradient waveform be not restricted in these physics and technical limitations, so, need additional restriction so that limit for the quantity of the parameter that in optimization is handled, can change.These added limitations are not inherent, but can be replaced by other restriction, if perhaps so allow this optimized algorithm can also remove these restrictions.Primary possible added limitations has the regulation of the trapezoidal magnetic field gradient of fixed rising and fall time.Now number of parameters is restricted, and relationship between parameters is linear and has one or two non-linear inequality restriction, and this is should not surpass their possible maximums from gradient change rate and intensity draw.

In seeking first method that the best dissolves, the persistent period of measuring gradient is made as its maximum, promptly focuses on RF pulse 22 again for symmetry and equals 2 (t _E-t ₁-△), wherein △ is half length of RF pulse.Then, seek whether to exist any separating about other gradient coexisting with it.Separate if can not find, the length of then measuring gradient reduces a bit of δ and seeks any once new trial of separating.So repeat up to finding possible separating.In order to finish the change in phase encoding gradient, seek one about two extreme value and separate.Get then to have and measure separating of gradient 32 shortest lengths and be complete solution.

For more complicated sequence, resemble wherein by a gradient fields produce some echoes such sequence, comprise a plurality of multiple RARE that focuses on the RF pulse again of magnetic resonance signal (obtaining fast) or TSE (turbine spin echo) of causing by repeatedly echo, have alternating polarity and measure the EPI (echo-planar imaging) of gradient or have the GRASE (gradient and spin echo) that alternating polarity is measured gradient and repeated to focus on the RF pulse again, can list several groups of similar restrictions and a kind of similar method of seeking to separate can be provided.

This method for solving has some shortcomings.At first, because in the picture quality with raising with reduce constantly developing at the new imaging technique aspect the MRI of acquisition time, so, new physical restriction carried out possibly.For the new restriction of each introducing, must be suitable for this method.Because the probability of restriction is non-linear like this, be difficult to this method is made any tangible adjustment.Secondly, because only change the parameter of limited quantity and only seek single possible separating, so this is separated and needs not to be the optimum solution that adopts more parameter to access.At last, because discontinuous step δ, this optimum must be inaccurate.The method that any δ by the littler value of selection improves precision all can increase operation time.

In second embodiment according to method of the present invention, proposed to form more neatly restriction in groups, be exactly to allow the big and non-linear restriction of permission of number of parameters specifically.A kind of so general expression formula of optimization problem is according to (non-linear) restricted function decision (non-linear) antiderivative minima, and wherein original function is f (x ₁..., x _n), restricted function is: C _j(x ₁... x _n)=0, this is for j=1 ..., m ₁Situation, and for j=m ₁+ 1 ..., m, C _j(x ₁..., x _n)≤0.Separating of a kind of like this system can for example be obtained by order square programming (sequential quadratic programming) method, this method is documented in P.E.Gill et al., " Practical Optimization ", Academic Press, London (1981).This method is with program " E04ucF " ofthe NAG Fortran Library (The NAG Fortran Library ManualMark 15, lst edition (June 1991), The Numerical AlgoritlamGroup Limiteal Oxford) realizes.Also can adopt the ready-made optimization procedure of other standard.

In this embodiment, gradient magnetic is with segmentation straight line waveform, comprises that promptly the form of the continuous function of linear segment provides.To stipulate the bonded node of linear segment, so that be consistent on the time in the gradient waveform on each direction of x, y and z.Especially introduce added limitations and do not need to form again whole pattern than described first embodiment pattern more flexibly though this is one,, resulting limitation is can not find total optimum in some cases.

On principle, the waveform of magnetic field gradient promptly can not have an arbitrary shape when having the transmitting RF pulse or taking place when data are obtained in not needing those intervals of preset value.Just must observe physics and technical limitations.A random waveform in these zones has so potential advantage, promptly can be easy to obtain optimum solution.But, select arbitrary function, for example trigonometric function can cause a large amount of non-linear restrictions in groups in optimization is handled, and therefore, causes being difficult to carry out parametrization and tediously long optimization procedure.

In the 3rd embodiment of the present invention, still describe waveform, but the node in the gradient waveform does not overlap on x, y and z direction with piecewise linear function.Fig. 3 has provided an example of this waveform.In Fig. 3, row Gx, Gy and Gz have represented the magnetic gradient field that exists on x, y and z direction.The standing part of gradient waveform represents that with solid line the part that can change is represented with the dotted line that has node in optimization procedures.The time integral gradient intensity is represented by piecewise linear function, and physical restriction is to represent with the relation between the integration gradient intensity in different interval.These time integral gradient intensity are made up of the summation of each linear segment effect.For example, in the excitation and the interval between the refocusing pulse of a spin-echo sequence, the x direction gradient, the time integral intensity of promptly measuring gradient can be expressed as: ${\∫}_{t_0}^{t_1}{F}_x\left(t\right)\mathrm{dt}=1/2\underset{i=0}{\overset{n-1}{\mathrm{\Σ}}}(G_{\mathrm{xi}+1}+G_{\mathrm{xi}})({\mathrm{\τ}}_{i+1}-{\mathrm{\τ}}_i),$ G wherein _XiAnd τ _iRepresent the gradient intensity and the time of each node.The node of i=0 and i=1 represents to encourage the centre and the afterbody of RF pulse, and i=n-1 and i=n represent to focus on the beginning and the central authorities of RF pulse again.These nodes are fixed about time and gradient intensity.I=2 ..., the node of n-2 is variable about time and gradient intensity.Because the variable intensity and the time of these variable nodes, so all physical restriction causes non-linear relation, promptly the quantity of its quantity and variable node is irrelevant.

Can be the restricted representation to device :-M _Mx≤ G _Xi≤ M _MxWith-S _Mx≤ M wherein _MxRepresent the maximum intensity of gradient, S _MxRepresent the maximum rate of change of gradient.Restriction about rate of change is equivalent to: (G _Xi+1-G _Xi)-S _Mx(τ _I+1-τ _i)≤0 and (G _Xi+1-G _Xi)+S _Mx(τ _I+1-τ _i) 〉=0 is so that each node increases in chronological order: τ _I+1〉=τ _iAdditional restriction is on each direction of three gradient directions, and the preparatory stage must finish in a flash together, and during measuring, stops phase code and section selection gradient.

What Fig. 4 a and 4b represented is possible the separating of selecting and measuring the gradient waveform of gradient about section.Waveform shown in Fig. 4 a has two variable nodes in the both sides that focus on the RF pulse again, and the waveform shown in Fig. 4 b has six variable nodes in both sides.Can see as figure, handle obtaining identical waveform substantially from optimization.The variable node of greater number can not cause better separating, and only can spend more computation time.So it seems that the node of limited quantity be enough.

For fear of unwanted magnetic field gradient waveforms, can introduce a penalty function from technical standpoint.To have separating of desirable characteristics helpful slightly to finding for this penalty function.So, from one group fully the separating of equivalence one of selection have separating of the characteristic that needs most, for example the adjacent node place have separating of equal gradient intensity, perhaps have separating of limited change aspect the rate of change on each node.

In the 4th embodiment, variable node has and is applied to them from one's body regular time relation, makes magnetic field gradient strength become unique independent variable.Consequent advantage be restricted all be linear, therefore, it is very fast that optimization is handled.After having fixed last variable node, other variable node is distributed in the equidistant related interval.In the implementation process of present embodiment, determine the existence of separating by program " E04MBF " of theNAG Fortran Library.If the shortcoming of this method for example can not directly be separated, will obtain optimum solution with the longest measuring period.Separate if can not try to achieve, but can trying to achieve the permission time of enough minimums separate, so, in the present embodiment, carry out binary search to determine there is the maximum measuring time of separating about it with the Measuring Time of maximum.And in this case seemingly the variable node of limited quantity can accept to separate just enough for one.The benefit of using great deal of nodes to obtain is to apply level and smooth gradient waveform, promptly limits the poor of rate of change between neighboring edge.

In the above description, suppose on x, y and z direction, to apply magnetic field gradient.But in fact, can with will adopt every group of orthogonal direction to allow that imaging is carried out in the section with different orientation.Relation between " machine " direction x, y, z and image direction m, p, the s (measuring phase code and section choice direction) is revolved product representation with one and is: $\left[\begin{array}{ccc}{s}_x& m_x& p_x\\ s_y& m_y& p_y\\ s_z& m_z& p_z\end{array}\right]\left[\begin{array}{c}{F}_s\left(t\right)\\ F_m\left(t\right)\\ F_p\left(t\right)\end{array}\right]=\left[\begin{array}{c}{F}_x\left(t\right)\\ F_y\left(t\right)\\ F_z\left(t\right)\end{array}\right].$ (s) system proposes physical restriction for m, p, and (z) system proposes technical limitations for x, y to machine to imaging then.The difference relation between the effective magnetic field gradient that in the gradient that in magnetic resonance device, produced and the human body for the treatment of imaging, exists, treat that the rotation of imaging section can not produce essential difference.But optimization problem can become more complicated and non-linear from being essentially linearity.

What represent in Fig. 5 a is the block diagram of representative functional relationship between the different step of the inventive method, and what Fig. 5 b represented is the flow chart of this method.Function will be provided by control unit shown in Figure 1 12.Afterwards to user interface section 90 initialization (square 100), receive from operator's instruction (square 110) selecting the basic pulse sequence, and the frequently such physics relevant parameter and relevant echo time T of picture frame _EWith repetition time T _R, these relevant parameters of slice thickness and orientation and visual field.What also will select is the criterion of optimality.In square 120, that retrieve or be included in overall statement in the coding of computer program of storage and combine with special parameter in the pulse generation unit 94 and carry out overall physical representation by memorizer 92 with pulse sequence, also comprise the restriction that must apply.This overall physical representation comprises the area and the corresponding time of various gradient fields.If the RF pulse self is to be included in the optimization processing, so, overall physical representation also comprises its time and time integral intensity.The technical limitations that square 130 expressions must apply.In optimization part 96, determine the details of sequence according to optimization procedure (square 140).Transmit its result by user interface (square 170) to the operator then.Then the operator can revise restriction or apply added limitations, repeats optimization procedure after this.If the operator accepts the result of this optimization procedure, so, then these results will be used to through control interface 98 control MRI devices to carry out imaging (square 160).The caption of table 1 Fig. 5 b

100 initialization

110 are entered as picture sequence type, imaging parameters and the criterion of optimality

120 Parameters Transformation become gradient area requirement, RF pulse and corresponding time

The restriction of 130 instruments

140 according to selected criterion optimization

150 check optimization results

160 realize the optimization sequence

170 operators get involved

Method of the present invention allows the detailed description with the MRI sequence of the physical condition of MRI sequence is separated, and the latter is determined in optimization procedure.Because can carry out optimization procedure with general fashion, so, can realize having sequences new or different restrictions at an easy rate.

In fact, the amount of carrying out the optimization procedure required time can be accepted fully.In the optimization flow process about the considerable amount of the 2D of different initial values with parameter and 3D spin-echo sequence, optimization procedures generally carries out having only indivedual exceptions not finish less than 10 seconds in 20 seconds in the HP9000/735 computer.This result's variation and the initial value of parameter relation are very close.Under a few cases, one group of initial value does not bear results, but always has other initial value in groups that bears results for identical sequence and restriction.

Claims (8)

1. be used for being positioned at the method that static and basic at least a portion of the human body of main field is uniformly carried out nuclear magnetic resonance, this method comprises

Select a basic sequence type of radio frequency (RF) and magnetic field gradient pulse, be used for producing magnetic resonance signal at an object;

Selection is explained the running parameter of required imaging features with selected basic sequence;

Under the condition of considering mechanical constraint and said running parameter by making said basic sequence optimization, thereby determine the work sequence of RF and magnetic field gradient pulse;

Said part to human body applies said work sequence, produces magnetic resonance signal thus in said part;

Measure said magnetic resonance signal and from said measured signal, obtain the image of the said part of human body.

2. the MR imaging method that is used for as claimed in claim 1, wherein selecting step and optimization step is what to separate on function, and the optimization step is to realize in a kind of mode that is independent of determining of work sequence and carries out.

3. the method that is used for nuclear magnetic resonance as claimed in claim 1 or 2 wherein by making maximization measuring period make the basic sequence optimization determine work sequence, is used to measure the magnetic resonance signal or the wherein desired signal to noise ratio that are produced.

4. as claim 1, the 2 or 3 described methods that are used for nuclear magnetic resonance, wherein at first determine the overall statement of work sequence from a basic sequence type, said overall statement comprises the time of RF pulse and the intensity of the magnetic field gradient that applies simultaneously with the RF pulse, and next carries out optimization for use in the magnetic field gradient waveforms of determining in the interval that does not offer said overall statement.

5. as claim 1, the 2 or 3 described methods that are used for nuclear magnetic resonance, wherein at first determine the overall statement of work sequence from a basic sequence type, next carries out optimization for use in time, length and the intensity of determining RF pulse and magnetic field gradient waveforms.

6. the method that is used for nuclear magnetic resonance as claimed in claim 5, wherein magnetic field gradient waveforms is a piecewise linear function.

7. be used for according to front any one described method of claim to being arranged in a static state and being the device that the human body (7) of uniform main field carries out nuclear magnetic resonance substantially, this device comprises the device (2) that is used to set up main field, be used to produce the device (3 that is superimposed upon the gradient magnetic on the main field, 4,5), be used for device (6 to human body (7) transmitting RF pulse, 8), be used to control the control device (12) of gradient magnetic and RF pulse generation, be used for device (6 to producing by RF pulse train and receiving and sample by the magnetic resonance signal of gradient magnetic control, 10), with the transcriber that is formed image by said sampled signal, said control device also comprises

The overall statement device of the basic sequence of-limited quantity;

-one operator importation is used to import the running parameter (T of the feature that requires of describing the image that will obtain _R, T _E, the position), and be used to select a basic sequence;

-arithmetic unit is used on the basis of considering mechanical constraint and said running parameter determining a work sequence of RF and magnetic field gradient pulse by said basic sequence is carried out optimization.

8. the device that is used for nuclear magnetic resonance as claimed in claim 7, wherein user control comprises an output, is used for applying additional parameter to operator's transfer sequence optimization result and permission operator.

Images