GB2079946A - NMR Imaging Method - Google Patents
NMR Imaging Method Download PDFInfo
- Publication number
- GB2079946A GB2079946A GB8107962A GB8107962A GB2079946A GB 2079946 A GB2079946 A GB 2079946A GB 8107962 A GB8107962 A GB 8107962A GB 8107962 A GB8107962 A GB 8107962A GB 2079946 A GB2079946 A GB 2079946A
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- Prior art keywords
- gradient
- magnetic field
- spins
- gradients
- spin
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Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
- G01R33/48—NMR imaging systems
- G01R33/4818—MR characterised by data acquisition along a specific k-space trajectory or by the temporal order of k-space coverage, e.g. centric or segmented coverage of k-space
- G01R33/482—MR characterised by data acquisition along a specific k-space trajectory or by the temporal order of k-space coverage, e.g. centric or segmented coverage of k-space using a Cartesian trajectory
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
- G01R33/48—NMR imaging systems
- G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
- G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
- G01R33/561—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution by reduction of the scanning time, i.e. fast acquiring systems, e.g. using echo-planar pulse sequences
- G01R33/5615—Echo train techniques involving acquiring plural, differently encoded, echo signals after one RF excitation, e.g. using gradient refocusing in echo planar imaging [EPI], RF refocusing in rapid acquisition with relaxation enhancement [RARE] or using both RF and gradient refocusing in gradient and spin echo imaging [GRASE]
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
- G01R33/48—NMR imaging systems
- G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
- G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
- G01R33/561—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution by reduction of the scanning time, i.e. fast acquiring systems, e.g. using echo-planar pulse sequences
- G01R33/5615—Echo train techniques involving acquiring plural, differently encoded, echo signals after one RF excitation, e.g. using gradient refocusing in echo planar imaging [EPI], RF refocusing in rapid acquisition with relaxation enhancement [RARE] or using both RF and gradient refocusing in gradient and spin echo imaging [GRASE]
- G01R33/5616—Echo train techniques involving acquiring plural, differently encoded, echo signals after one RF excitation, e.g. using gradient refocusing in echo planar imaging [EPI], RF refocusing in rapid acquisition with relaxation enhancement [RARE] or using both RF and gradient refocusing in gradient and spin echo imaging [GRASE] using gradient refocusing, e.g. EPI
Abstract
To produce image information from an object it is subjected to a continuous static magnetic field along a Z axis and to sets of sequences of orthogonal magnetic field gradients Gx, Gy and Gz. Spins in a selected plane X-Z are excited by rf pulses and an associated Gy gradient. The selected spins are subjected to all three gradients of which the Gz gradient provides twist or warp to each column of spins extending along the Z axis to phase-encode the columns. The Gx gradient is reversed and held constant whilst spin-echo signals are read out. In each set of sequences a different value of Gz gradient is employed. The Fourier transformed spin-echo signals obtained from each sequence, when arranged in order of increasing Gz gradient and subjected to a second Fourier transform, represent the distribution of spin density in the Z direction, giving a two-dimensional image of the selected Z plane. <IMAGE>
Description
SPECIFICATION
Methods of Producing Image Information From
Objects
The present invention relates to methods of producing image information from objects. It is concerned with producing images of samples containing nuclear or other spins whose spatial distribution of density or relaxation time is detected by magnetic resonance techniques.
More particularly, it describes methods for producing images from free induction decays (FID's) and spin echoes of the sample in the presence of static magnetic fields and switched magnetic field gradients.
In U.S. Patent No. 4,070, 611 there is described a method of producing images by a series of FID's following separate excitations of the sample. During these FID's, magnetic fields in two (or three) orthogonal directions are switched on and off for specific lengths of time to yield two (or three) dimensional images.
One of the problems associated with the above method is that inhomogeneities of the static magnetic field can simulate the effect of the deliberately introduced switched field gradients and mask the effect of these switched field gradients, thereby destroying some of the information contained in the signal.
The masking effect can occur as follows.
Different Fl D's have field gradients of fixed strength switched on for varying times. For any particular combination of gradient pulse lengths during a single FID, spins in different regions of the sample experience varying phase shifts
relative to each other.
These phase shifts allow spatial discrimination and therefore enable an image to be formed. The amount of phase shift between two regions of the sample is proportional to the difference in local magnetic field of the two regions. If inhomogeneities in the static magnetic field
contribute to the local field (in addition to deliberately introduced gradients), the spatial distribution information can be distorted.
Suppose for example that in one of the FID's needed to produce an image, the gradient Gz in the z direction is switched on for time T. Consider a small volume element of a sample at Z=ZO. It experiences a field B(Z)=Bo+ZoGz+åB(ZO), where Bo is the static magnetic field at Z=CI and AB(Zo) is the deviation from the static field at Z0 due to the inhomogeneity in the static field. Then at the end of time T the spins at Z=ZO experience a change in phase AsX relative to spins at Z=0 given by A=y(ZaGz+AB(Zo))T (1) where y is the gyromagnetic ratio.So effectively the gradient appears to be not Gz but G2+AB(Z0)/Z0. A Fourier transform along the Z direction will yield a distorted abd non-linear scale in that direction. Moreover, the extra phase shifts could cause signals from some parts of the sample to appear incorrectly in the wrong part of the image (aliasing).
A numerical example will illustrate the seriousness of this problem.
In order to produce a well-determined NxN image, it is necessary to take N samples from N signals. For whole-body imaging, one would require a region at least 40 cm in diameter and produce a 64x64 element image.
Referring to equation (1), there need to be 64 different values of â0. These are obtained by having 64 different values of time during which the gradient Gz is applies. Ignoring the AB term in equation (1) for the moment, an example of such a series is given by åb,=O A02=A0*=(yZoGz)(T) åsb3=2å0*=(yZOGz)(2T) å04=350*=(yZOGz)(3T) å0N=(N1 )å0*=(yZOGz)[(N1 )TJ
Note that the strength of the gradient is the same for each åXk but the time the gradients are applied varies. There is a condition, however, that across acrossthe sample.Using reasonable parameters based on a whole-body nuclear magnetic resonance imaging reference, the length of the sample can be set to L=40 cm, T=0.5 ms, y/27r=4260 Hz/Gauss, and the condition å0* < 27r gives Gz < 0.012 Gauss/cm. At 20 cm, the maximum distance from the centre of the field, Gz xZ= 24 Gauss. But the inhomogeneity in a four coil, eighth order resistive magnet (which is typical of those used for whole-body imaging) will be about 10-4 at 20 cm, or .1 Gauss for a 1 kGauss magnet, nearly half the contribution of the gradient. This situation is unacceptable since one is trying to resolve those 20 cm into 32 parts, and the distortion introduced by such inhomogeneity would ruin the image making process.
Looked at in a slightly different way, the above difficulty imposes a stringent condition on the homogeneity of the static magnetic field.
The principal object of the present invention is to provide an improved method of gyromagnetic
resonance imaging employing trains of free induction decays.
According to the present invention a method of deriving image information from an object using nuclear magnetic resonance signals comprises subjecting an object to a continuous static magnetic field along one axis and repeatedly carrying out a set of sequential steps each set of steps comprising:
1) selectively exciting nuclear spins in a plane in the presence of a first gradient of the magnetic field which has a gradient direction perpendicular to said plane;
2) reversing the direction of the said first gradient and applying a second gradient and a third gradient of the magnetic field, the direction of the second gradient being orthogonal to the gradient direction of the first gradient, and the third gradient having a gradient direction orthogonal to the gradient directions of both the first and second gradients;;
3) reversing the direction of the second gradient of the magnetic field and holding the said
reversed gradient while reading out the resultant free induction decay signal from the said object; and then successively repeating the above set of steps with different values of gradient of the third gradient, there being a recovery interval between the repetition of successive sets of steps.
Preferably the period of application of the said
third gradient of the magnetic field is equal in
each of the sets of steps.
In carrying out the invention it may be
convenient to apply the first, second and third
gradients of the magnetic field in step 2)
simultaneously.
In order that the invention may be more fully
understood reference will now be made to the
accompanying drawings in which the single figure
shows pulse sequences for an embodiment of the
invention.
For the purpose of the following description
a static magnetic field B0 lies along the Z axis and
the radiofrequency (rf) field lies along the Y axis.
There are coils to produce gradients Gx, Gy and Gz to the magnetic field Bo in the X, Y aud Z directions. The production of a two-dimensional
image of a thin slab perpendicular to the Y axis is
considered. Where the method is applied to human whole body imaging it is convenient to
position the patient horizontally with the Z direction vertical and the Y direction horizontal
along the length of the patient. The X direction is then horizontal across the patient.
The pulse sequence used to form an image from single spin echoes following separate excitations is shown in Figure 1. The time axis is divided into six into six successive intervals repeated cyclically. The fields which are applied in each of these intervals are as follows:
Interval 1.
A 1800 rf pulse is applied simultaneously with a magnetic field gradient G=. This selectively inverts the nuclear spins in a close to the plane Y=YO.The value of Y0can be altered by a change in the frequency of the 1800 pulse. Alternatively, a non-selective 1800 pulse can be applied with no gradients present. Yet again non-selective spin inversion can be obtained by an adiabatic fast passage in which the rf field is swept through a frequency range. y-dimension selection is then done entirely by the events in interval 3.
Interval 2.
The nuclear spin system is allowed to relax by spin-lattice relaxation for a chosen time T. No fields other than B0 are applied during this interval.
Interval 3.
A weak 900 rf pulse is applied simultaneously with a magnetic field gradient G=. This selectively excites nuclear spins in and close to the plane Y=YO. The value of Y0 can be altered by a change in the frequency of the 900 pulse.
Interval 4.
A gradient of the magnetic field having a negative value G-y is applied to rephase the selected nuclear spins along the Y direction.
Simultaneously a negative gradient G-x to the magnetic field is applied to dephase the nuclear spins along the X direction. Simultaneously a gradient Gz of the magnetic field is applied to dephase the spins along Z.
Interval 5.
A smaller positive magnetic field gradient G+x is applied. During this interval, the nuclear spins rephase to form a spin echo, when the free induction signal is a maximum, and then dephase.
It is desirable to keep G+x constant during this interval at which time the nuclear free induction signal is collected.
Interval 6.
System recovery time until the occurrence of interval 1 of the next sequence. This should be long compared with the spin lattice relaxation time T and is of the order of a second in the whole-body imaging apparatus described in reference 4.
The various gradients of the magnetic field described above need not have a square wave time profile but can have a sinusoidal profile of amplitude against time, which makes less demand on the switching circuits for the gradient coils.
Two different kinds of free induction signals, SA and SB are obtained using this pulse sequence, for any one value of the altered high frequency of interval 1 or interval 3 and any one value of j'4dt G in interval 4, where f4dt indicates the integral over interval 4.
SB: The relaxation interval (2) is comparable with the spin-lattice relaxation time being measured. That is T~T1, which is a few hundred milliseconds for human soft tissue at 1.7 MHz.
SA: The events of intervals 1 and 2 are omitted, but the rest of the sequence is identical.
SA contains mainly proton density information, and SB contains both spin-lattice relaxation time (Tt) information and proton density information.
It may be desirable to consider the events in interval 4 in more detail. In that interval all three orthogonal magnetic field gradients are applied simultaneously. At first sight this would appear to make analysis of the spin behaviour rather difficult but since no radio frequency field is present in interval 4 the efflects of the three gradients can be considered separately. The resultant effect of the three gradients although applied simultaneously is the same as if they were applied sequentially and the coincidence in timing is simply a convenience which serves to save time between excitation and signal acquisition in interval 5. The G y gradient serves to rephase the spins across the width of the selected slice and thus it maximises the signal that is eventually obtained.The Gx- gradient serves to dephase the spins along the X direction as a preliminary to the readout step in interval 5 in which a G+ gradient is applied to cause the spins to rephase and produce a kind of gradient-induced spin echo in the middle of the signal acquisition period. The Fourier transform of this spin echo signal is therefore a one-dimensional projection of the spin density within the slice on to the X axis.
The function of the gradient Gz is to provide discrimination in the Z direction. It is introduced in interval 4 to give a known amount of twist or "warp" to each vertical column of spins (Z axis vertical), and thus it phase encodes the signal prior to projection on to the X axis. In fact it maximises the responce to a particular vertical spatial frequency in the column equal to the spatial frequency of the "warp".
The entire set of steps described above is successfully repeated a number of times and in each repetition a different amplitude of gradient
Gz is utilised to cover a range of vertical spatial frequencies from zero up to a maximum. Now suppose that the projected spin density values for any one column (obtained from the Fourier transforms of the spin-echo signals) are arranged in order of increasing Gz pulse size, and subjected to another Fourier transform, then this will represent the distribution of spin density up the column. When this is done for each column a complete two-dimensional image of the selected slice is obtained. Thus, an NxN image can be obtained by taking N projections on to the same axis, a procedure which is obviously impossible in
X-ray or radio-isotope imaging, simply because the basic signal has no phase information in it.
Another view of the action of the phaseencoding gradient Gz is that in each imaging column N projections are collected onto the X axis. The projections are different because spins at different heights are given varying amounts of phase twist by the presence of different values of
Gz (hence the name "spin warp").
The phase information in an NMR signal is preserved by employing two phase-sensitive detectors in quadrature to produce two signals which are then treated as a single complex number. The outcome of the double Fourier transformation is a matrix of complex numbers whose amplitudes represent the required spin densities. Their phases would ideally be identical in a perfect magnetic field; in practice they may vary considerably by many cycles over the image plane, representing as they do the primary effect of main magnetic field inhomogeneity. This is of no consequence, however, since the phase information is abandoned at this stage of the processing.
In order to derive an NxN proton density image, N samples from each of N SA signals must be collected. The N signals have N different distributions of the phase shift along Z and hence
N different values of r4dt Gz. For this purpose a series of waveforms for Gz, namely Gz0, Gz ..., GZ(N-1} are utilized such that, for example GZO=O J4dt Gz2=2J4dt GZ1=2G* C4dt Gz3=3 r4dt Gz1=3 g* C4dt Gz(N-1)=(N-1) J4dt Gzi=(N1 )G* where G*=J4dt Gz1.
In other words, the Z gradient is always applied for the same period of time but changes in strength for different pulse sequences. In fact in each successive sequence Gz has the same shape and length but its amplitude changes by equal steps from zero to a maximum value. There is a maximum condition on the series, namely that if the total length of the sample in the Z direction is
Lz, then YLZG < 27r. If this limit is exceeded, aliasing will occur, and some parts of the sample may contribute to more than one region of the image.
The image is finally obtained by applying a two-dimensional Fourier transformation to the N echo signals consisting of N samples each. If the signals are designated as fm(m), where m are the sampling times and m and n go from 1 to N, an example of such a transformation is given by
where Lx is the length of the sample in the X
direction, Lz is the length of the sample in the Z
direction, P(l,J) is the image element at co
ordinate (I,J), and I and J each go from 1 to N.
An image containing mostly T1 information can be obtained by collecting N SB signals along with
N SA signals, deriving an SA image array and an image array as outlined above, and calculating the
T, values (from these arrays) corresponding to each imaging element. An image containing a mixture of T, information and proton density information can be obtained from a collection of N SB signals alone.
The method described above lessens the effect of inhomogeneities in the static magnetic field.
The effect of an inhomogeneous static field as in equation (1) can be included thus A9i=(yZOJ4dtGz+yAB(zO)TS (4) AB(Z0) is the difference between the static field value at Z0 and the nominal static field value, and
T' is the duration of interval 4. This difference is due to inhomogeneities in the static field.
Equation (4) shows that there is extra phase shift caused by the inhomogeneity, but the extra phase shift is the same for all pulse sequences because T is the same for all pulse sequences. This extra, constant, phase shift for all signals cannot affect the linearity and scale in the Z direction. This conclusion relaxes the stringent condition imposed on the homogeneity of the static magnetic field by the method of U.S. Patent No.
4,070,611.
Claims (9)
1. A method of deriving image information from an object using nuclear magnetic resonance signals comprising subjecting an object to a continuous static magnetic field and carrying out a set of sequential steps which comprise:
1) selectively exciting nuclear spins in a
selected plane in the presence of a first
gradient of the magnetic field which has a
gradient direction perpendicular to said
plane;
2) reversing the direction of the said first
gradient and applying a second gradient and
a third gradient of the magnetic field, the
direction of the second gradient being
orthogonal to the gradient direction of the
first gradient, and the third gradient having a
gradient direction orthogonal to the gradient
directions of both the first and second
gradients;;
3) reversing the direction of the second
gradient of the magnetic field and holding
the said reversed gradient while reading out
the resultant free induction decay signal
from the said object; and then successively repeating the above set of steps with different values of gradient of the third gradient, there being a recovery interval between the repetition of successive sets of steps.
2. The method as claimed in claim 1 in which the period of application of the said third gradient of the magnetic field is equal in each of the sets of steps.
3. The method as claimed in claim 1 or claim 2 in which the said first, second and third gradients of the magnetic field in step 2) are all applied simultaneously.
4. The method as claimed in any one of the preceding claims in which the plane in which nuclear spins are selectively excited lies parallel to the direction of the magnetic field.
5. The method as claimed in any one of the preceding claims in which prior to step 1 ) there is an initial step of inverting the spins followed by an interval approximately equal to the average relaxation time of the spins.
6. The method as claimed in claim 5 in which the said inversion is achieved by an adiabatic fast passage.
7. The method as claimed in any one of the preceding claims in which successive different values of the third gradient differ from each other by equal amounts.
8. The method as claimed in any one of the preceding claims in which the free induction signals are Fourier transformed.
9. A method of deriving image information from an object substantially as described herein with reference to the accompanying drawing.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8107962A GB2079946B (en) | 1980-03-14 | 1981-03-13 | Nmr imaging method |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8008773 | 1980-03-14 | ||
| GB8107962A GB2079946B (en) | 1980-03-14 | 1981-03-13 | Nmr imaging method |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB2079946A true GB2079946A (en) | 1982-01-27 |
| GB2079946B GB2079946B (en) | 1984-11-07 |
Family
ID=26274832
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8107962A Expired GB2079946B (en) | 1980-03-14 | 1981-03-13 | Nmr imaging method |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2079946B (en) |
Cited By (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2526968A1 (en) * | 1982-05-14 | 1983-11-18 | Thomson Csf | METHOD FOR TOMOGRAPHY OF A NUCLEAR MAGNETIC RESONANCE OBJECT |
| EP0096590A1 (en) * | 1982-06-09 | 1983-12-21 | Picker International Limited | Nuclear magnetic resonance method and apparatus |
| EP0103397A2 (en) * | 1982-08-13 | 1984-03-21 | National Research Development Corporation | Nuclear magnetic resonance imaging method |
| EP0122593A2 (en) * | 1983-04-14 | 1984-10-24 | Hitachi, Ltd. | Imaging apparatus and method using nuclear magnetic resonance |
| EP0133532A2 (en) * | 1983-08-01 | 1985-02-27 | Hitachi, Ltd. | NMR imaging method and apparatus |
| EP0133794A2 (en) * | 1983-08-01 | 1985-03-06 | National Research Development Corporation | Methods of producing images by NMR techniques |
| FR2574551A1 (en) * | 1984-12-12 | 1986-06-13 | Commissariat Energie Atomique | METHOD FOR GENERATING AND PROCESSING SIGNALS FOR NUCLEAR MAGNETIC RESONANCE PRODUCTION OF A DISTORTION FREE IMAGE FROM AN INHOMOGENEOUS POLARIZATION FIELD |
| GB2173003A (en) * | 1985-02-15 | 1986-10-01 | Hitachi Ltd | Nuclear magnetic resonance imaging of flow |
| US4706028A (en) * | 1984-10-12 | 1987-11-10 | Mitsubishi Denki Kabushiki Kaisha | NMR imaging method |
| US4841247A (en) * | 1985-10-15 | 1989-06-20 | Mitsubishi Denki Kabushiki Kaisha | Method for interpolative extension of nuclear magnetic resonance image |
| US4868502A (en) * | 1987-02-05 | 1989-09-19 | Mitsubishi Denki Kabushiki Kaisha | Magnetic resonance imaging method and apparatus therefor |
-
1981
- 1981-03-13 GB GB8107962A patent/GB2079946B/en not_active Expired
Cited By (22)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2526968A1 (en) * | 1982-05-14 | 1983-11-18 | Thomson Csf | METHOD FOR TOMOGRAPHY OF A NUCLEAR MAGNETIC RESONANCE OBJECT |
| US4551679A (en) * | 1982-05-14 | 1985-11-05 | Thomson-Csf | Method of tomographic scanning of an object by nuclear magnetic resonance |
| US4563647A (en) * | 1982-06-09 | 1986-01-07 | Picker International Limited | Nuclear magnetic resonance methods and apparatus |
| EP0096590A1 (en) * | 1982-06-09 | 1983-12-21 | Picker International Limited | Nuclear magnetic resonance method and apparatus |
| EP0103397A2 (en) * | 1982-08-13 | 1984-03-21 | National Research Development Corporation | Nuclear magnetic resonance imaging method |
| EP0103397A3 (en) * | 1982-08-13 | 1985-01-16 | National Research Development Corporation | Nuclear magnetic resonance imaging method |
| EP0122593A2 (en) * | 1983-04-14 | 1984-10-24 | Hitachi, Ltd. | Imaging apparatus and method using nuclear magnetic resonance |
| EP0122593A3 (en) * | 1983-04-14 | 1986-03-26 | Hitachi, Ltd. | Imaging apparatus and method using nuclear magnetic resonance |
| EP0133532A3 (en) * | 1983-08-01 | 1986-03-05 | Hitachi, Ltd. | Nmr imaging method and apparatus |
| US4651095A (en) * | 1983-08-01 | 1987-03-17 | National Research Development Corporation | Methods of producing images by NMR techniques |
| EP0133794A2 (en) * | 1983-08-01 | 1985-03-06 | National Research Development Corporation | Methods of producing images by NMR techniques |
| EP0133532A2 (en) * | 1983-08-01 | 1985-02-27 | Hitachi, Ltd. | NMR imaging method and apparatus |
| EP0133794A3 (en) * | 1983-08-01 | 1986-02-05 | National Research Development Corporation | Methods of producing images by nmr techniques |
| US4706028A (en) * | 1984-10-12 | 1987-11-10 | Mitsubishi Denki Kabushiki Kaisha | NMR imaging method |
| FR2574551A1 (en) * | 1984-12-12 | 1986-06-13 | Commissariat Energie Atomique | METHOD FOR GENERATING AND PROCESSING SIGNALS FOR NUCLEAR MAGNETIC RESONANCE PRODUCTION OF A DISTORTION FREE IMAGE FROM AN INHOMOGENEOUS POLARIZATION FIELD |
| US4684890A (en) * | 1984-12-12 | 1987-08-04 | Commissariat A L'energie Atomique | Process for the generation and processing of signals for obtaining by nuclear magnetic resonance a distortion-free image from a heterogeneous polarization field |
| EP0188145A1 (en) * | 1984-12-12 | 1986-07-23 | Commissariat A L'energie Atomique | Method of generating and processing NMR signals for an image which is free from distortions due to field inhomogeneities |
| GB2173003A (en) * | 1985-02-15 | 1986-10-01 | Hitachi Ltd | Nuclear magnetic resonance imaging of flow |
| US4870362A (en) * | 1985-02-15 | 1989-09-26 | Hitachi, Ltd. | Nuclear magnetic resonance imaging method and apparatus |
| GB2173003B (en) * | 1985-02-15 | 1989-11-22 | Hitachi Ltd | A method of nuclear magnetic resonance imaging |
| US4841247A (en) * | 1985-10-15 | 1989-06-20 | Mitsubishi Denki Kabushiki Kaisha | Method for interpolative extension of nuclear magnetic resonance image |
| US4868502A (en) * | 1987-02-05 | 1989-09-19 | Mitsubishi Denki Kabushiki Kaisha | Magnetic resonance imaging method and apparatus therefor |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2079946B (en) | 1984-11-07 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| 732 | Registration of transactions, instruments or events in the register (sect. 32/1977) | ||
| PE20 | Patent expired after termination of 20 years |
Effective date: 20010312 |