CA1247699A - Fast method and device for determining an nmr distribution in a region of a body - Google Patents
Fast method and device for determining an nmr distribution in a region of a bodyInfo
- Publication number
- CA1247699A CA1247699A CA000491593A CA491593A CA1247699A CA 1247699 A CA1247699 A CA 1247699A CA 000491593 A CA000491593 A CA 000491593A CA 491593 A CA491593 A CA 491593A CA 1247699 A CA1247699 A CA 1247699A
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- Canada
- Prior art keywords
- gradient magnetic
- period
- alternating
- magnetic field
- generating
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- 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]
- G01R33/446—Multifrequency selective RF pulses, e.g. multinuclear acquisition mode
-
- 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
- G01R33/4822—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 in three dimensions
-
- 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
Abstract
ABSTRACT:
"Fast method and device for determining an NMR distribution in a region of a body"
The invention relates to a method of making NMR images (density distributions, location-dependent spectroscopy) utilizing two alternating gradient fields whose gradient directions are mutually perpendicular. Thus, a two-dimensional "plane" in the 3-D
image frequency space can be filled with a uniform density of measurement points. Per FID signal more signal samples can be taken, resulting in a substantial reduction of the entire measure-ment procedure for a 3-D image. This method is very well suitable for the imaging of 3-D density distributions, 2-D or 3-D spectro-scopy etc. The periods and the amplitudes of the alternating gra-dient fields are preferably the same; however, these fields are preferably phase-shifted 90° with respect to one another.
"Fast method and device for determining an NMR distribution in a region of a body"
The invention relates to a method of making NMR images (density distributions, location-dependent spectroscopy) utilizing two alternating gradient fields whose gradient directions are mutually perpendicular. Thus, a two-dimensional "plane" in the 3-D
image frequency space can be filled with a uniform density of measurement points. Per FID signal more signal samples can be taken, resulting in a substantial reduction of the entire measure-ment procedure for a 3-D image. This method is very well suitable for the imaging of 3-D density distributions, 2-D or 3-D spectro-scopy etc. The periods and the amplitudes of the alternating gra-dient fields are preferably the same; however, these fields are preferably phase-shifted 90° with respect to one another.
Description
P~ 147 1 25.6.1985 "~ast method and device for determining an ~MR distribution in a region of a body"
~he invention relates to a method of determining an NMR
distribution in a region of a body which is situated in a generated steady, uniform magnetic field, including the steps of a) generating an r.f. electromagnetic pulse in order to cause a precessional motion of the magnetization of the nuclei in the body, thus generating a resonance signal, b) then generating, after a preparation period, a steady gradient magnetic field and an alternating, periodic gradient magnetic field during a measurement period of several measurement periods, said measurement period (periods) being divided into a number of sampling intervals for taking a number of signal s~mples of the resonance signal, c) then repeating, each time after a waiting period, the steps a) ~and b) a mlmber of times, the dura-tion of the preparation period lS ~d/or the integral over the preparation period of at least one ~radient magnetic field applied during the preparation period each time having a different value in order to obtain a group of signal samples from which, after signal transformation there-o~`, an image of a nuclear magnetization is determined.
2d ~he invention also relates to a device for determining ~n NMR distribution in a region of a body, comprising:
~) means for generating a steady, uniform magnetic field, b) means for generating r.f. electromagnetic radiation, c~ means for generating a steady gradient magnetic field, d) means for generating an alternating, periodic gradient magnetic field, e) sampling means for taking signal samples of a resonance signal generated by the means specified in the paragraphs a) and b) in the presence of a steady gradient magnetic field and of an alternating gradient magnetic field generated by the means specified in paragraphs c) and d), f) processing means for the processing of the signal samples in order to obtain an ~MR distxibution, and 76~
PHN. 11.147 2 g) control means for controlling at least the means specified in the paragraphs b) to f) for generating, conditioning, and sampling a number of resonance signals and for processing the signal samples.
According to a known method, a periodic alternating ~r~ t magnetic field is generated during the measurement period, ~e ~riod of said gradient field being equal to the sampling inter-val, at least one additional signal sample being taken in each s.~mpling interval.
The use of the alternating gradient magnetic field and the t~king of the additional signal samples ensure that at least two r~ws of a (t~-din~nsional) image fre~uency matrix will have been filled after the sampling of a resonance signal (FID or spin echo si~ l). Thus~ the duration of a measurement cycle is reduced to ~1~ half (onc third, one quarter) when one ~two, three) additional si~al samples are taken, respectively. Beaause the duration of ~ resonance signal amounts to only some tens of milliseconds, the taking of 128 or 256 signal samples (in a row in the image fre-g~lelcy matrix) will require a sampling interval in the order of
~he invention relates to a method of determining an NMR
distribution in a region of a body which is situated in a generated steady, uniform magnetic field, including the steps of a) generating an r.f. electromagnetic pulse in order to cause a precessional motion of the magnetization of the nuclei in the body, thus generating a resonance signal, b) then generating, after a preparation period, a steady gradient magnetic field and an alternating, periodic gradient magnetic field during a measurement period of several measurement periods, said measurement period (periods) being divided into a number of sampling intervals for taking a number of signal s~mples of the resonance signal, c) then repeating, each time after a waiting period, the steps a) ~and b) a mlmber of times, the dura-tion of the preparation period lS ~d/or the integral over the preparation period of at least one ~radient magnetic field applied during the preparation period each time having a different value in order to obtain a group of signal samples from which, after signal transformation there-o~`, an image of a nuclear magnetization is determined.
2d ~he invention also relates to a device for determining ~n NMR distribution in a region of a body, comprising:
~) means for generating a steady, uniform magnetic field, b) means for generating r.f. electromagnetic radiation, c~ means for generating a steady gradient magnetic field, d) means for generating an alternating, periodic gradient magnetic field, e) sampling means for taking signal samples of a resonance signal generated by the means specified in the paragraphs a) and b) in the presence of a steady gradient magnetic field and of an alternating gradient magnetic field generated by the means specified in paragraphs c) and d), f) processing means for the processing of the signal samples in order to obtain an ~MR distxibution, and 76~
PHN. 11.147 2 g) control means for controlling at least the means specified in the paragraphs b) to f) for generating, conditioning, and sampling a number of resonance signals and for processing the signal samples.
According to a known method, a periodic alternating ~r~ t magnetic field is generated during the measurement period, ~e ~riod of said gradient field being equal to the sampling inter-val, at least one additional signal sample being taken in each s.~mpling interval.
The use of the alternating gradient magnetic field and the t~king of the additional signal samples ensure that at least two r~ws of a (t~-din~nsional) image fre~uency matrix will have been filled after the sampling of a resonance signal (FID or spin echo si~ l). Thus~ the duration of a measurement cycle is reduced to ~1~ half (onc third, one quarter) when one ~two, three) additional si~al samples are taken, respectively. Beaause the duration of ~ resonance signal amounts to only some tens of milliseconds, the taking of 128 or 256 signal samples (in a row in the image fre-g~lelcy matrix) will require a sampling interval in the order of
2~ n~a~nit~e of 100 /~n, which means that the frequency of the addi-tional gradient magnetic fie]d must amount to 10 kHz. This com-p~r~tiv~ly high frequency of the alternating gradient magnetic field limits the mclximum number of rows of the image freq~lency n~atrix which can be filled by the sampling of a single resonance ~5 signal. The maximum distance ~k between two rows filled by the sall~ling of a resonance signal amounts to:
~tm ~k = ~ ~.G(1~) . d o in which ~tm is the first half period of the periodic, alter-nating gradient magnetic field, ~is the gyr~nagnetic ratio, and G( ~) is the alternating gradient magnetic field. m e maximum distance Qk determines the ~ximum n~nber of rows in the image frequency matrix filled after the sampling of a resonance signal P~N.11.1~7 3 25.6.1985 and is proportional to the amplitude of the applied alternating gradient magnetic field. ~he amplitude of the alternating gradient magnetic field cannot be increased at random, because the rate of change dG/dt of the aiternating gradient magnetic field must remain within health safety limits imposed. ~his rate of change dG/dt is proportional to the product of the amplitude and the frequency of the alternatin~ gradient magnetic field ~ecause the frequency ~1~ kHz) is comparatively high, a maximum permissible amplitude t~ill be quickly reached. If the period of time required for col-lecting all signal samples were to be reduced to one quarter, the amplitude of the alternating field would have to be increased by a factor 4.
It is the object of the invention to provide a method and a device in which, utilizing compa~atively weaker alter-1~ nating gradient magnetic fields~ the time required tc form anima~e having a resolution which at least equals that when use is ma~e of the prior art method and device is substantially reduced when three-dimensional images of ~MR-distributions are made.
~ o achieve this, the method in accordance with the in-vention is characterized in that during the measurement period there is applied a second periodic alternating gradient magnetic field whose æradient direction extends perpendicularly to the gra-dient direction of the first-mentioned alternating gradient mag-netio field. According to the method in accordance with the in-vention, durin~ a single FID-signal the signal samples are measured not only along an image frequency line or in a flat image fre-quency plane, but in a ~-D part of the image frequency space which can now be covered due to the additional degree of freedom offered by the second alternating gradient magnetic field.
A preferred version of the method in accordance with the invention is characterized in that the two periodic alter-nating gradient magnetic fields have the same period and are phase-shifted 90 with respect to one another. In the preferred version of the method in accordance with the invention, the image frequency space (or image frequency time domain in the case of location~
dependent spectroscopy) is covered via a helical path. Thus, per period four signal samples can be taken which are situated at the Gorners of a square circumscribed by the projected helix. Conse-i9~
PE~.11.147 4 25.6.1985 quently, the overall measuremen-t period will be reduced by a factor four; however, two alternating gradient fields will then be re-quired which effectively produce a gradient field which is a factor ~ stronger than a single gradient field in accordance with the present state of the art (with the same frequency) which reduces the overall measurement period only to one half.
A further inventive method of determining an NMR
Aistribution in a region of a body which is situated in a generated steady, uniform magnetic field, including the steps of:
lo a3 generating an r.f. electromagnetic pulse in order to cause a precessional motion of the magnetization of the nuclei in the body, thus generating a resonance signal, b) then generating, after a preparation period, an alternating, periodic g~adient magnetic field during a measurement period or several measurement periods ? said measurement period (periods) being divided into a number of sampling intervals for taking a number of signal samples of the resonance signal, c) then repeating, each time after a ~ting period, the steps a) ~nd b) a number of times, the integral over the preparation period of at least one gradient magnetic field applied during the preparation period each time having a different value in order to obtain a group of signal samples from which, after signal transformation thereof, an image of a nuclear magnetization is determined, characterized in that during the measwrement period there is applied second periodic alternating gradient magnetic field whose gra-dient direction e~tends perpendicularly to the gradi~nt direction of the first-mentioned alternating gradient magnetic field.
A device in accordance with the invention is character-ized in that it comprises means for generating two alternating~radient magnetic fields whose gradient directions are mutually perpendicular.
A preferred embodimen-t of a device in accordance with the invention is characterized in that the periods of the alter-nating gradient fields are the same and 9O out of phase.
Embodiments in accordance with the invention will bedescribed in detail hereinafter wi-th reference to the drawing;
therein PXN.11.l47 5 25.6.1985 Fig. 1 diagrammatically shows a coil sys-tem of a device for performing a method in accordance with the invention, ~ig. 2 shows a block diagram of a device for performing the method in accordance with the invention, S~igs. 3a ana 3b show simple embodiments and methods in acco~dance with the invention, Figs. 4a and 4b show a preferred version of a method in accordance with the invention, ~igs. 5a and 5b illustrate the method shown in the l~ ~igs. 4a and 4b, and ~ ig. 6 shows a part of a device for performing the method in accordance with the invention.
~ ig. 1 shows a coil system 10 which forms part of a device 15 (~ig. 2) used for determining an NMR distribution in a lS region of a body 20. The region has a thickness of, for example ~z ~nd is situated in the x-y-plane of the x-y z-coordinate sy-stem shown The y-axis of the system extends upwards perpendicularly to the plane of drawing. ~he coil system 10 generates a steady, uniform magnetic field ~o having a field direction parallel to the Z-~YiS, three gradient magnetic fields Gx, Gy, Gz having a field direction parallel to the z-axis and a gradient direction parallel to the x, y and z-axis, respectively, and an r.f. magnetic field.
To achieve this, the coil system 10 comprises a set of main coils l for generating the steady, uniform magnetic field ~o. The main coils l may be arranged, for example on the surface of a sphere 2 osa centre is situated at the origin 0 of the cartesian coor-dinate system x, y, z shown, the axes of the main coils 1 being coincident with the z-axis.
The coil system 10 also comprises four coils 3a, 3b for senerating the gradient magnetic field Gz. To achieve this, a first set 3a is excited by current in the opposite sense with respect to the current direction in the second set 3b; this is denoted by ~ and ~ in the ~igure. Therein, ~3 means a current entering the ~ection of the coil 3 and ~ means a current leaving the section of the coil.
The coil system 10 furthermore comprises four rectangular coils 5 (only two of which are shown) or four other coils such as, for example "Golay coils", for generating the gradient magnetic PH~.11.147 6 25.6.1985 field Gy. In order to generate the gradient magnetic field Gx, use is made of four coils 7 which have the same shape as the coils 5 and which have been rotated through an angle of 90 about the z-axis with respect to the coils 5~ Fig. 1 also shows a coil 11 for generating and detecting an r.f. electromagnetic field.
Fig. 2 shows a device ~ for performing a method in accordance with the invention. The device 15 comprises coils 1, 3, 5, 7 and 11 which have already been described with reference to Fig. 1, current generators 17, 19, 21 and 23 for energizing the 10 coils 1, 3, 5 and 71 respectively, and an r.f. signal generator 25 for energizing the coil 11. The device 15 also comprises an r.f.
signal detector 27, a demodulator 28, a sampling circuit 29~ pro-cessing means such as an analog-to-digital converter 31, a memory 33 and an arithmetic circuit 35 for performing a Fourier trans-formation, a control unit 37 for controlling the sampling instants, and also a display device 43 and central control means 45 whose functions and relationships will be described in detail herein-after.
~ he described device 15 performs a method of determining the ~ distribution in a region of a body 20 as will be described hereinafter. ~he method involves the frequent repetition of a mea-surement cycle which itself can be divided into several steps.
During a measurement cycle, a part of the nuclear spins present in the body is resonantly excited. For resonant excitation of the l~ nuclear spins, the current generator 17 is switched on by the central control lmit 45, so that the coil 1 is energized and re-mnins energized for a desired number of measurement cycles. ~hus, a steady and uniform magnetic field Bo is generated. Furthermore, the r.f. generator 25 is switched on for a short period of time, so that the coil 11 generates an r.f. electromagnetic field. The nuclear spins in the body 20 can be excited by the applied magnetic fields and the excited nuclear magnetization takes up a given angle, for example 90 ~90 r.f. pulse) with respect to the direct-ion of the uniform magnetic field Bo. ~he location where and which nuclear spins will be excited depends inter al1a on the intensity of the field Bo, on any gradient magnetic field to be applied, and on the angular frequency t~o f the r.f. electromagnetic field, because the equation ~O = r . Bo (1) must be satisfied, in which ~L~L/~ 7~
P~N.11.1~7 7 25.6.1985 r is the gyromagnetic ratio (for free protons, for example ~2 protons, ~/2 1~ = 42.576 MHz/~). After an excitation period, the r.f. generator 25 is switched off by the central control means 45.
~he resonant excitation is always performed at the beginning of each measurement cycle. For some versions r.f. pulses are gene-rated also during the measurement cycle. These r.f. pulses are then, for example a series composed of 180 r.f. pulses which are periodically generatsd. ~he latter is referred to as "spin echo".
Spil1 echo is inter alia described in the article by I.~. Pykett ld "N~m in Medicine", published in Scientific American, May 1982.
During a next step signal samples are collected. ~or this purpose use can be made of the gradient fields which are gene-rated by the generators 19, 21 and 23, respectively, under the control of the central control means 45. ~he detection of the resonance signal (referred to as FID signal) is performed by switch-ing on the r.f. detector 27, the demodulator 28, the sampling cir-ouit ~9, the analog-to-digital converter 31 and the control unit 37. This FID signal appears as a result of the precessional motion of the nuclear magnetizations about the field direction of the mag-netic field ~o due to the r.f. excitation pulse. This nuclear mag-netization induces an induction vol-tage in the detection coil whose amplitude is a measure of the nuclear magnetization.
~ he analog sampled FID signals originating from the sampling circuit 29 are digitized (converter 31) and stored in a memory 33. After a final signal sample has been taken during a meAsurement period ~Mr the central control means 45 deactivate the generators 19, 21 and 23, the sampling circuit 29, the control unit 37 and the analog-to-digital converter 3~.
The sampled FID signal is and remains stored in the
~tm ~k = ~ ~.G(1~) . d o in which ~tm is the first half period of the periodic, alter-nating gradient magnetic field, ~is the gyr~nagnetic ratio, and G( ~) is the alternating gradient magnetic field. m e maximum distance Qk determines the ~ximum n~nber of rows in the image frequency matrix filled after the sampling of a resonance signal P~N.11.1~7 3 25.6.1985 and is proportional to the amplitude of the applied alternating gradient magnetic field. ~he amplitude of the alternating gradient magnetic field cannot be increased at random, because the rate of change dG/dt of the aiternating gradient magnetic field must remain within health safety limits imposed. ~his rate of change dG/dt is proportional to the product of the amplitude and the frequency of the alternatin~ gradient magnetic field ~ecause the frequency ~1~ kHz) is comparatively high, a maximum permissible amplitude t~ill be quickly reached. If the period of time required for col-lecting all signal samples were to be reduced to one quarter, the amplitude of the alternating field would have to be increased by a factor 4.
It is the object of the invention to provide a method and a device in which, utilizing compa~atively weaker alter-1~ nating gradient magnetic fields~ the time required tc form anima~e having a resolution which at least equals that when use is ma~e of the prior art method and device is substantially reduced when three-dimensional images of ~MR-distributions are made.
~ o achieve this, the method in accordance with the in-vention is characterized in that during the measurement period there is applied a second periodic alternating gradient magnetic field whose æradient direction extends perpendicularly to the gra-dient direction of the first-mentioned alternating gradient mag-netio field. According to the method in accordance with the in-vention, durin~ a single FID-signal the signal samples are measured not only along an image frequency line or in a flat image fre-quency plane, but in a ~-D part of the image frequency space which can now be covered due to the additional degree of freedom offered by the second alternating gradient magnetic field.
A preferred version of the method in accordance with the invention is characterized in that the two periodic alter-nating gradient magnetic fields have the same period and are phase-shifted 90 with respect to one another. In the preferred version of the method in accordance with the invention, the image frequency space (or image frequency time domain in the case of location~
dependent spectroscopy) is covered via a helical path. Thus, per period four signal samples can be taken which are situated at the Gorners of a square circumscribed by the projected helix. Conse-i9~
PE~.11.147 4 25.6.1985 quently, the overall measuremen-t period will be reduced by a factor four; however, two alternating gradient fields will then be re-quired which effectively produce a gradient field which is a factor ~ stronger than a single gradient field in accordance with the present state of the art (with the same frequency) which reduces the overall measurement period only to one half.
A further inventive method of determining an NMR
Aistribution in a region of a body which is situated in a generated steady, uniform magnetic field, including the steps of:
lo a3 generating an r.f. electromagnetic pulse in order to cause a precessional motion of the magnetization of the nuclei in the body, thus generating a resonance signal, b) then generating, after a preparation period, an alternating, periodic g~adient magnetic field during a measurement period or several measurement periods ? said measurement period (periods) being divided into a number of sampling intervals for taking a number of signal samples of the resonance signal, c) then repeating, each time after a ~ting period, the steps a) ~nd b) a number of times, the integral over the preparation period of at least one gradient magnetic field applied during the preparation period each time having a different value in order to obtain a group of signal samples from which, after signal transformation thereof, an image of a nuclear magnetization is determined, characterized in that during the measwrement period there is applied second periodic alternating gradient magnetic field whose gra-dient direction e~tends perpendicularly to the gradi~nt direction of the first-mentioned alternating gradient magnetic field.
A device in accordance with the invention is character-ized in that it comprises means for generating two alternating~radient magnetic fields whose gradient directions are mutually perpendicular.
A preferred embodimen-t of a device in accordance with the invention is characterized in that the periods of the alter-nating gradient fields are the same and 9O out of phase.
Embodiments in accordance with the invention will bedescribed in detail hereinafter wi-th reference to the drawing;
therein PXN.11.l47 5 25.6.1985 Fig. 1 diagrammatically shows a coil sys-tem of a device for performing a method in accordance with the invention, ~ig. 2 shows a block diagram of a device for performing the method in accordance with the invention, S~igs. 3a ana 3b show simple embodiments and methods in acco~dance with the invention, Figs. 4a and 4b show a preferred version of a method in accordance with the invention, ~igs. 5a and 5b illustrate the method shown in the l~ ~igs. 4a and 4b, and ~ ig. 6 shows a part of a device for performing the method in accordance with the invention.
~ ig. 1 shows a coil system 10 which forms part of a device 15 (~ig. 2) used for determining an NMR distribution in a lS region of a body 20. The region has a thickness of, for example ~z ~nd is situated in the x-y-plane of the x-y z-coordinate sy-stem shown The y-axis of the system extends upwards perpendicularly to the plane of drawing. ~he coil system 10 generates a steady, uniform magnetic field ~o having a field direction parallel to the Z-~YiS, three gradient magnetic fields Gx, Gy, Gz having a field direction parallel to the z-axis and a gradient direction parallel to the x, y and z-axis, respectively, and an r.f. magnetic field.
To achieve this, the coil system 10 comprises a set of main coils l for generating the steady, uniform magnetic field ~o. The main coils l may be arranged, for example on the surface of a sphere 2 osa centre is situated at the origin 0 of the cartesian coor-dinate system x, y, z shown, the axes of the main coils 1 being coincident with the z-axis.
The coil system 10 also comprises four coils 3a, 3b for senerating the gradient magnetic field Gz. To achieve this, a first set 3a is excited by current in the opposite sense with respect to the current direction in the second set 3b; this is denoted by ~ and ~ in the ~igure. Therein, ~3 means a current entering the ~ection of the coil 3 and ~ means a current leaving the section of the coil.
The coil system 10 furthermore comprises four rectangular coils 5 (only two of which are shown) or four other coils such as, for example "Golay coils", for generating the gradient magnetic PH~.11.147 6 25.6.1985 field Gy. In order to generate the gradient magnetic field Gx, use is made of four coils 7 which have the same shape as the coils 5 and which have been rotated through an angle of 90 about the z-axis with respect to the coils 5~ Fig. 1 also shows a coil 11 for generating and detecting an r.f. electromagnetic field.
Fig. 2 shows a device ~ for performing a method in accordance with the invention. The device 15 comprises coils 1, 3, 5, 7 and 11 which have already been described with reference to Fig. 1, current generators 17, 19, 21 and 23 for energizing the 10 coils 1, 3, 5 and 71 respectively, and an r.f. signal generator 25 for energizing the coil 11. The device 15 also comprises an r.f.
signal detector 27, a demodulator 28, a sampling circuit 29~ pro-cessing means such as an analog-to-digital converter 31, a memory 33 and an arithmetic circuit 35 for performing a Fourier trans-formation, a control unit 37 for controlling the sampling instants, and also a display device 43 and central control means 45 whose functions and relationships will be described in detail herein-after.
~ he described device 15 performs a method of determining the ~ distribution in a region of a body 20 as will be described hereinafter. ~he method involves the frequent repetition of a mea-surement cycle which itself can be divided into several steps.
During a measurement cycle, a part of the nuclear spins present in the body is resonantly excited. For resonant excitation of the l~ nuclear spins, the current generator 17 is switched on by the central control lmit 45, so that the coil 1 is energized and re-mnins energized for a desired number of measurement cycles. ~hus, a steady and uniform magnetic field Bo is generated. Furthermore, the r.f. generator 25 is switched on for a short period of time, so that the coil 11 generates an r.f. electromagnetic field. The nuclear spins in the body 20 can be excited by the applied magnetic fields and the excited nuclear magnetization takes up a given angle, for example 90 ~90 r.f. pulse) with respect to the direct-ion of the uniform magnetic field Bo. ~he location where and which nuclear spins will be excited depends inter al1a on the intensity of the field Bo, on any gradient magnetic field to be applied, and on the angular frequency t~o f the r.f. electromagnetic field, because the equation ~O = r . Bo (1) must be satisfied, in which ~L~L/~ 7~
P~N.11.1~7 7 25.6.1985 r is the gyromagnetic ratio (for free protons, for example ~2 protons, ~/2 1~ = 42.576 MHz/~). After an excitation period, the r.f. generator 25 is switched off by the central control means 45.
~he resonant excitation is always performed at the beginning of each measurement cycle. For some versions r.f. pulses are gene-rated also during the measurement cycle. These r.f. pulses are then, for example a series composed of 180 r.f. pulses which are periodically generatsd. ~he latter is referred to as "spin echo".
Spil1 echo is inter alia described in the article by I.~. Pykett ld "N~m in Medicine", published in Scientific American, May 1982.
During a next step signal samples are collected. ~or this purpose use can be made of the gradient fields which are gene-rated by the generators 19, 21 and 23, respectively, under the control of the central control means 45. ~he detection of the resonance signal (referred to as FID signal) is performed by switch-ing on the r.f. detector 27, the demodulator 28, the sampling cir-ouit ~9, the analog-to-digital converter 31 and the control unit 37. This FID signal appears as a result of the precessional motion of the nuclear magnetizations about the field direction of the mag-netic field ~o due to the r.f. excitation pulse. This nuclear mag-netization induces an induction vol-tage in the detection coil whose amplitude is a measure of the nuclear magnetization.
~ he analog sampled FID signals originating from the sampling circuit 29 are digitized (converter 31) and stored in a memory 33. After a final signal sample has been taken during a meAsurement period ~Mr the central control means 45 deactivate the generators 19, 21 and 23, the sampling circuit 29, the control unit 37 and the analog-to-digital converter 3~.
The sampled FID signal is and remains stored in the
3~ memory 33. Subsequently, a next measurement cycle is performed during which an FID signal is generated, sampled and stored in the memory 33. When a sufficient number of FID signals has been measured (the number of FID signals to ba measured depends9 for example on the desired resolution), an NMR-image can be determined via a 2-D or 3-D Fourier transformation (this depends on the use of the gradient magnetic fields under whose effect the ~ID signals are generated and sampled). Fig. 3a shows an example of a measure-ment cycle in accordance with the inven-tion which will be illu-~2~
pH~ 47 8 25.6.1985 strated with reference to the device 15 shown in Fig. 2. Usingthe r.f. coil 1 1, a 90 pulse P1 is generated after the switching-on of the main coils 1 which generate a steady, uniform magnetic field ~o. The resonance signal ~1 which results is allowed to decay when using the spin echo technique and after a period of ti~e tV1 a 180 pulse P2 is generated by the r.f. coil 11. During a part of the period t 1 gradient fields G and G (denoted by curves ~l and G3) are generated for reasons to be described here-inafter. After a period of time tV2 which is equal to tV1, an echo lD l~esonance signal F2 produced by the 180 pulse P2 will reach a peak value. ~he use of the so-called spin echo technique (180 pulse P2) prevents the occurrence of phase errors in the resonance signals produced by nuclear spins; such phase errors are caused by inhomo-geneities in the steady magnetic field ~o. The echo resonance signal is sampled each time after a sampling interval tm (not shown in the Figure) in the presence of alternating gradient fields Gx and Gy which are denoted by curves G2 and G4, respectively.
It is known that the phase angle of a magnetization at a point z in a gradient magnetic field Gz is determined by t ~ ~. Gz . z . d1r Thus, an image frequency kz can be defined as:
~t ~hus, after each sampling period tm a respective signal sample is determined which is associated with a differen-t image frequency kz.
The sllccessive image frequencies exhibit an image frequency dif-ference t m It will be apparent that when an alternating gradient field Gx isapplied, signal samples are obtained which are associated with image frequencies kx which will be situated between two extreme values kXi and ~- 2 L~
PE~.11.147 9 25.6~1985 ~- J G2 d ~ + k~i.
t~/2 The quickly alternating G gradient field G2 is now superposed on a slowly alternating G gradient field G4. If this Gy gradient field G~ were present and also a constant G gradient field (not shot~l)~ the successive signal samples to be taken would be as-sociated with the image f~equencies (k , k ), k then varying be-tween two extreme values as denoted by the line 1 in Fig. 3b.When the alternating G gradient magnetic field as well as the alternating Gx gradient field and a constant G gradient field are applied, the path S on which the signal samples to be taken during the measurement period ~ are situated will form as i~ it were a band-shaped plane L which passes throuæh the line 1 and which has a width which is determined by the two extreme values ( xi and kxi ~ r J . G2 . d ~) ~tx of k~. ~ecause sampling takes place with three degrees of freedom Au-~ing an FID signal in accordance with the present method {(kx, ky, kz) or, for example k , k , t) for spectroscopy3, more signal ~mples oan be derived per FID signal, so that the overall measure-ment period for the filling of a 3-D (or 4-D) matrix with signal samples is drastically reduced. ~y application of Gx and/or Gy preparation gradient magnetic fields G1 and/or G3 during the pre-paration period tV1, the band-shaped plane L can be shifted in the tkX~ k~" kz) or (kx, ky, t) space in the kx and/or the ky-direct-ion, so that a regular filling of said image frequency domain orima~e frequency-time domain is obtained. In order to counteract the effect of '~2 relaxation times and field inhomogeneities which cause æhost images and blurring, it is advantageous to take a siænal sample associated with, for example the frequency plane k~
3~ always at the same relative instant after the excitation pulse P1 (or echo pulse P2). In the present example this can be achieved by ohoosing for each different presetting of the Gy gradient field G3 (aotually the time integral thereover) an adapted instant ~D for pHN.1~.~47 1~ 25.6.1985 the switching-on of the alternating G and Gy gradient fields G2 ana G4, the G2 gradient magnetic field and the measurement period not being shifted in the "time domain".
Figs. 4a and 4b illustrate the principle of a preferred ver3ion of a method in accordance with the invention. According to this method, the applied G gradient magnetic field Gy4 deviates from the G ~radient field G4 shown in ~ig. 3a. The gradient field l.y4 has the same period ty, tx as the gradient field Gx4. The gra-dient fields G 4 and G 4 exhibit a phase difference of preferably 9~ . It can be deduoed that in the case of two alternating gra-(~ient fields thus applied, the image frequenoies at which signal s~mples are taken are situated on an ellipse (a circle when the smplitudes Gx4 and Gy4 are equal) in the kX-ky image frequency plane. l~hen a constant gradient field G~ is switched on simulta-neously with the alternating gradient fields Gx4 and Gy4 (only during the measurement period ~ ), the signal samples taken will be associated with image frequency triplets (k , k , k ) which are sitllated on a halix 1' which is wound about the elliptical cylinder C (circular cylinder if G 4 = Gy4) with a constant pitch. ~y shift-in the phases of the Gx and the Gy gradient fields Gx4 and Gy4 with respect to the starting instant ts of the measurement period , the helix can be rotated about the cylinders (in order to acllieve a more uniform coverage of the cylinder surface, if neces~
sary). ~he cylinder C itself can be shifted in the kx and/or ky~
direction by varying the preparation gradient fields GVx and/or Gvy (the shaded surfaoes) as regards amplitude and/or time, so that a uniform filling of the (kx, ky, kz) space or (kx~ ky, t) space can be realized (the starting instant ts is then fixed in time ~ith respect to the pulse P1 (or P2) before the s-tart of each measurement period).
~ ig. 5a is a projection perpendicu~lyto the kX-k plane of all measurement points obtained along three helices. As appears from ~ig. 5a, when four signal samples are taken per turn of the helix, a uniform filling on cartesian coordinates kx, ky is possible. When the amplitude of the gradient fields Gx4 and Gy4 is increased whilst their frequency is decreased, an equal number of signal samples oan be taken with less energy and a lower dG/dt in the same period of time, whilst a "cartesian" filling in the k 5~
PHN.11.147 11 25.6.1985 and k direction is still feasible. Instead of four signal samples, eight signal samples are now taken per turn of the helix 1' (see Fig. 4b) (however, the sampling is no longer equidistant in time)~
said samples being situated at the corners of octagons which are denoted by 0, ~ , x, ~ and . in ~ig. 5b. ~y allowing the "cylin-ders" to overlap, a cartesian filling of the k -ky plane is achieved (see, for exampie Q, o, x). A phase correction is re-quired only in the k -direction, said correction being different fol~ seven si~nal samples successively situated on a helix (assuming n that one of the eight is "correctly" situated on the kz grid);
this is also applicable to three of the four signal samples measured accordin6 to ~ig. 5a. ~he phase correction to be used is already known from ~etherlands Patent Application NL-A-82.03519. Further~
more, it is necessary to fill the holes MS1 and MS2 occurring at the edge of the kX-ky space to be filled with missing signal samples.
3ecause each time two adjacent signal samples are concerned (kx =
constant), said holes MS1 and MS2 can be successively filled by me~ s of the method described in said ~etherlands Patent Application ~L-A-~.03519 (Gz = constant, Gy is modulated).
~0 The methods described with reference to the Figs. 4a, b and 5a, b are also very suitable for ~MR spectroscopy; to this end, for e2ample it is not necessary to apply a gradient field duxing the measurement period M~; it is merely necessary to rea~ize n presetting k3 with a gradient field Gz during the preparation ~S period (for e2ample during tV1 or after P2 and before ts).
For the selection/adjustment of a given pulse sequence, time lntervals and assooiated æradient magnetic fields for a measurement oycle, use is made of programmed oomputer means. In an embodiment of the devioe 15 (Fig. 2) the central oontrol means ~ comprise a programmed computer (VAX 11/730) which comprises an input/output station 52 for control data and an interfaoe 53 (see Fiæ. 6). Outputs 55 of the interface 53 are connected, via the bus (see Fig. 2), to the current generators 19, 21, 23 and 25 to be oontrolled as well as to the oontrol inputs of the receiver 27, the demodulator 28 and the sampling circuit 29.
pH~ 47 8 25.6.1985 strated with reference to the device 15 shown in Fig. 2. Usingthe r.f. coil 1 1, a 90 pulse P1 is generated after the switching-on of the main coils 1 which generate a steady, uniform magnetic field ~o. The resonance signal ~1 which results is allowed to decay when using the spin echo technique and after a period of ti~e tV1 a 180 pulse P2 is generated by the r.f. coil 11. During a part of the period t 1 gradient fields G and G (denoted by curves ~l and G3) are generated for reasons to be described here-inafter. After a period of time tV2 which is equal to tV1, an echo lD l~esonance signal F2 produced by the 180 pulse P2 will reach a peak value. ~he use of the so-called spin echo technique (180 pulse P2) prevents the occurrence of phase errors in the resonance signals produced by nuclear spins; such phase errors are caused by inhomo-geneities in the steady magnetic field ~o. The echo resonance signal is sampled each time after a sampling interval tm (not shown in the Figure) in the presence of alternating gradient fields Gx and Gy which are denoted by curves G2 and G4, respectively.
It is known that the phase angle of a magnetization at a point z in a gradient magnetic field Gz is determined by t ~ ~. Gz . z . d1r Thus, an image frequency kz can be defined as:
~t ~hus, after each sampling period tm a respective signal sample is determined which is associated with a differen-t image frequency kz.
The sllccessive image frequencies exhibit an image frequency dif-ference t m It will be apparent that when an alternating gradient field Gx isapplied, signal samples are obtained which are associated with image frequencies kx which will be situated between two extreme values kXi and ~- 2 L~
PE~.11.147 9 25.6~1985 ~- J G2 d ~ + k~i.
t~/2 The quickly alternating G gradient field G2 is now superposed on a slowly alternating G gradient field G4. If this Gy gradient field G~ were present and also a constant G gradient field (not shot~l)~ the successive signal samples to be taken would be as-sociated with the image f~equencies (k , k ), k then varying be-tween two extreme values as denoted by the line 1 in Fig. 3b.When the alternating G gradient magnetic field as well as the alternating Gx gradient field and a constant G gradient field are applied, the path S on which the signal samples to be taken during the measurement period ~ are situated will form as i~ it were a band-shaped plane L which passes throuæh the line 1 and which has a width which is determined by the two extreme values ( xi and kxi ~ r J . G2 . d ~) ~tx of k~. ~ecause sampling takes place with three degrees of freedom Au-~ing an FID signal in accordance with the present method {(kx, ky, kz) or, for example k , k , t) for spectroscopy3, more signal ~mples oan be derived per FID signal, so that the overall measure-ment period for the filling of a 3-D (or 4-D) matrix with signal samples is drastically reduced. ~y application of Gx and/or Gy preparation gradient magnetic fields G1 and/or G3 during the pre-paration period tV1, the band-shaped plane L can be shifted in the tkX~ k~" kz) or (kx, ky, t) space in the kx and/or the ky-direct-ion, so that a regular filling of said image frequency domain orima~e frequency-time domain is obtained. In order to counteract the effect of '~2 relaxation times and field inhomogeneities which cause æhost images and blurring, it is advantageous to take a siænal sample associated with, for example the frequency plane k~
3~ always at the same relative instant after the excitation pulse P1 (or echo pulse P2). In the present example this can be achieved by ohoosing for each different presetting of the Gy gradient field G3 (aotually the time integral thereover) an adapted instant ~D for pHN.1~.~47 1~ 25.6.1985 the switching-on of the alternating G and Gy gradient fields G2 ana G4, the G2 gradient magnetic field and the measurement period not being shifted in the "time domain".
Figs. 4a and 4b illustrate the principle of a preferred ver3ion of a method in accordance with the invention. According to this method, the applied G gradient magnetic field Gy4 deviates from the G ~radient field G4 shown in ~ig. 3a. The gradient field l.y4 has the same period ty, tx as the gradient field Gx4. The gra-dient fields G 4 and G 4 exhibit a phase difference of preferably 9~ . It can be deduoed that in the case of two alternating gra-(~ient fields thus applied, the image frequenoies at which signal s~mples are taken are situated on an ellipse (a circle when the smplitudes Gx4 and Gy4 are equal) in the kX-ky image frequency plane. l~hen a constant gradient field G~ is switched on simulta-neously with the alternating gradient fields Gx4 and Gy4 (only during the measurement period ~ ), the signal samples taken will be associated with image frequency triplets (k , k , k ) which are sitllated on a halix 1' which is wound about the elliptical cylinder C (circular cylinder if G 4 = Gy4) with a constant pitch. ~y shift-in the phases of the Gx and the Gy gradient fields Gx4 and Gy4 with respect to the starting instant ts of the measurement period , the helix can be rotated about the cylinders (in order to acllieve a more uniform coverage of the cylinder surface, if neces~
sary). ~he cylinder C itself can be shifted in the kx and/or ky~
direction by varying the preparation gradient fields GVx and/or Gvy (the shaded surfaoes) as regards amplitude and/or time, so that a uniform filling of the (kx, ky, kz) space or (kx~ ky, t) space can be realized (the starting instant ts is then fixed in time ~ith respect to the pulse P1 (or P2) before the s-tart of each measurement period).
~ ig. 5a is a projection perpendicu~lyto the kX-k plane of all measurement points obtained along three helices. As appears from ~ig. 5a, when four signal samples are taken per turn of the helix, a uniform filling on cartesian coordinates kx, ky is possible. When the amplitude of the gradient fields Gx4 and Gy4 is increased whilst their frequency is decreased, an equal number of signal samples oan be taken with less energy and a lower dG/dt in the same period of time, whilst a "cartesian" filling in the k 5~
PHN.11.147 11 25.6.1985 and k direction is still feasible. Instead of four signal samples, eight signal samples are now taken per turn of the helix 1' (see Fig. 4b) (however, the sampling is no longer equidistant in time)~
said samples being situated at the corners of octagons which are denoted by 0, ~ , x, ~ and . in ~ig. 5b. ~y allowing the "cylin-ders" to overlap, a cartesian filling of the k -ky plane is achieved (see, for exampie Q, o, x). A phase correction is re-quired only in the k -direction, said correction being different fol~ seven si~nal samples successively situated on a helix (assuming n that one of the eight is "correctly" situated on the kz grid);
this is also applicable to three of the four signal samples measured accordin6 to ~ig. 5a. ~he phase correction to be used is already known from ~etherlands Patent Application NL-A-82.03519. Further~
more, it is necessary to fill the holes MS1 and MS2 occurring at the edge of the kX-ky space to be filled with missing signal samples.
3ecause each time two adjacent signal samples are concerned (kx =
constant), said holes MS1 and MS2 can be successively filled by me~ s of the method described in said ~etherlands Patent Application ~L-A-~.03519 (Gz = constant, Gy is modulated).
~0 The methods described with reference to the Figs. 4a, b and 5a, b are also very suitable for ~MR spectroscopy; to this end, for e2ample it is not necessary to apply a gradient field duxing the measurement period M~; it is merely necessary to rea~ize n presetting k3 with a gradient field Gz during the preparation ~S period (for e2ample during tV1 or after P2 and before ts).
For the selection/adjustment of a given pulse sequence, time lntervals and assooiated æradient magnetic fields for a measurement oycle, use is made of programmed oomputer means. In an embodiment of the devioe 15 (Fig. 2) the central oontrol means ~ comprise a programmed computer (VAX 11/730) which comprises an input/output station 52 for control data and an interfaoe 53 (see Fiæ. 6). Outputs 55 of the interface 53 are connected, via the bus (see Fig. 2), to the current generators 19, 21, 23 and 25 to be oontrolled as well as to the oontrol inputs of the receiver 27, the demodulator 28 and the sampling circuit 29.
Claims (15)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of determining an NMR distribution in a region of a body which is situated in a generated steady, uniform mag-netic field, including the steps of:
a) generating an r.f. electromagnetic pulse in order to cause a precessional motion of the magnetization of the nuclei in the body thus generating a resonance signal, b) then generating, after a preparation period, a steady gradient magnetic field and an alternating, periodic gradient magnetic field during a measurement period or several measurement periods, said measurement period (periods) being divided into a number of sampling intervals for taking a number of signal samples of the resonance signal, c) then repeating, each time after a waiting period, the steps a) and b) a number of times, the duration of the preparation period and/or the integral over the preparation period of at least one gradient magnetic field applied during the preparation period each time having a different value in order to obtain a group of signal samples from which, after signal transformation there-of, an image of a nuclear magnetization is determined, characterized in that during the measurement period there is applied a second periodic alternating gradient magnetic field whose gra-dient direction extends perpendicularly to the gradient direction of the first-mentioned alternating gradient magnetic field.
a) generating an r.f. electromagnetic pulse in order to cause a precessional motion of the magnetization of the nuclei in the body thus generating a resonance signal, b) then generating, after a preparation period, a steady gradient magnetic field and an alternating, periodic gradient magnetic field during a measurement period or several measurement periods, said measurement period (periods) being divided into a number of sampling intervals for taking a number of signal samples of the resonance signal, c) then repeating, each time after a waiting period, the steps a) and b) a number of times, the duration of the preparation period and/or the integral over the preparation period of at least one gradient magnetic field applied during the preparation period each time having a different value in order to obtain a group of signal samples from which, after signal transformation there-of, an image of a nuclear magnetization is determined, characterized in that during the measurement period there is applied a second periodic alternating gradient magnetic field whose gra-dient direction extends perpendicularly to the gradient direction of the first-mentioned alternating gradient magnetic field.
2. A method of determining an NMR distribution in a region of a body which is situated in a generated steady, uniform mag-netic field, including the steps of:
a) generating an r.f. electromagnetic pulse in order to cause a precessional motion of the magnetization of the nuclei in the body, thus generating a resonance signal, b) then generating, after a preparation period, an alternating, periodic gradient magnetic field during a measurement period or several measurement periods, said measurement period (periods) being divided into a number of sampling intervals for taking a number of signal samples of the resonance signal, c) then repeating, each time after a waiting period, the steps a) and b) a number of times, the integral over the preparation period of at least one gradient magnetic field applied during the preparation period each time having a different value in order to obtain a group of signal samples from which, after signal transformation thereof, an image of a nuclear magnetization is determined, characterized in that during the measurement period there is applied a second periodic alternating gradient magnetic field whose gra-dient direction extends perpendicularly to the gradient direction of the first-mentioned alternating gradient magnetic field.
a) generating an r.f. electromagnetic pulse in order to cause a precessional motion of the magnetization of the nuclei in the body, thus generating a resonance signal, b) then generating, after a preparation period, an alternating, periodic gradient magnetic field during a measurement period or several measurement periods, said measurement period (periods) being divided into a number of sampling intervals for taking a number of signal samples of the resonance signal, c) then repeating, each time after a waiting period, the steps a) and b) a number of times, the integral over the preparation period of at least one gradient magnetic field applied during the preparation period each time having a different value in order to obtain a group of signal samples from which, after signal transformation thereof, an image of a nuclear magnetization is determined, characterized in that during the measurement period there is applied a second periodic alternating gradient magnetic field whose gra-dient direction extends perpendicularly to the gradient direction of the first-mentioned alternating gradient magnetic field.
3. A method as claimed in Claim 1 or 2, characterized in that the two periodic, alternating gradient magnetic fields have the same period and are phase-shifted with respect to one another.
4. A method as claimed in Claim 1 or 2, characterized in that the two alternating gradient magnetic fields have the same period and are 90° out of phase.
5. A method as claimed in Claim 1 or 2, characterized in that per period of an alternating gradient magnetic field a signal sample is taken at least four times.
6. A method as claimed in Claim 1 or 2, characterized in that the starting instant of one of the alternating gradient magnetic fields coincides with the end of the preparation period, the instant at which a first signal sample is taken always commencing the same time interval after the r.f. electromagnetic pulse.
7. A method as claimed in Claim 1 or 2, characterized in that during the successive measurement periods the amplitudes of the alternating gradient magnetic fields are the same.
8. A method as claimed in Claim 1 or 2, characterized in that during the preparation period there are applied at least two pre-paration gradient magnetic fields, the integral over the period of at least one preparation gradient magnetic field having a different value in two successive measurement cycles.
9. A method as claimed in Claim 1, characterized in that eight signal samples are taken per period of an alternating gradient magnetic field.
10. A method as claimed in Claim 9, characterized in that the gradient directions of the two respective preparation gradient mag-netic fields are the same as the gradient directions of the two respective alternating gradient magnetic fields.
11. A method as claimed in Claim 1, 2 or 10, characterized in that alternating gradient magnetic fields are applied during successive measurement cycles, the periods of said alternating fields being different and the ratio of the maximum field intensity of the total generated alternating gradient magnetic field and the period always being smaller than or equal to a predetermined, fixed value.
12. A device for determining an NMR distribution in a region of a body, comprising a) means for generating a steady, uniform magnetic field, b) means for generating r.f. electromagnetic radiation, c) means for generating a steady, gradient magnetic field, d) means for generating an alternating, periodic gradient magnetic field, e) sampling means for taking signal samples of a resonance signal generated by the means specified in the paragraphs a) and b) in the presence of an alternating gradient magnetic field generated by the means specified in paragraph d), f) processing means for the processing of the signal samples in order to obtain an NMR distribution, and g) control means for controlling at least the means specified in the paragraphs b) to f) for generating, conditioning and sampling a number of resonance signals and for processing the signal samples, characterized in that the device comprises means for generating two alternating gradient magnetic fields whose gradient directions are mutually perpendicular.
13. A device as claimed in Claim 12, characterized in that the periods of the alternating gradient magnetic fields are the same and 90° out of phase.
14. A device as claimed in Claim 12 or 13, characterized in that the period of the alternating gradient magnetic fields is adjustable.
15. A device as claimed in Claim 12 or 13, characterized in that the intensity of the alternating gradient magnetic fields is adjustable.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NL8402959A NL8402959A (en) | 1984-09-28 | 1984-09-28 | QUICK METHOD AND APPARATUS FOR DETERMINING A NUCLEAR MAGNETIZATION DISTRIBUTION IN PART OF A BODY. |
| NL8402959 | 1984-09-28 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1247699A true CA1247699A (en) | 1988-12-28 |
Family
ID=19844530
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000491593A Expired CA1247699A (en) | 1984-09-28 | 1985-09-26 | Fast method and device for determining an nmr distribution in a region of a body |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US4812762A (en) |
| EP (1) | EP0181015B1 (en) |
| JP (1) | JPS6186641A (en) |
| CA (1) | CA1247699A (en) |
| DE (1) | DE3574620D1 (en) |
| IL (1) | IL76522A (en) |
| NL (1) | NL8402959A (en) |
Families Citing this family (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4678996A (en) * | 1985-05-07 | 1987-07-07 | Picker International, Inc. | Magnetic resonance imaging method |
| DE3604280A1 (en) * | 1986-02-12 | 1987-08-13 | Philips Patentverwaltung | METHOD FOR DETERMINING THE SPATIAL AND SPECTRAL DISTRIBUTION OF CORE MAGNETIZATION IN AN EXAMINATION AREA AND ARRANGEMENT FOR IMPLEMENTING THE METHOD |
| JPH0763455B2 (en) * | 1986-03-31 | 1995-07-12 | 株式会社東芝 | Magnetic resonance imager |
| US4748410A (en) * | 1986-08-06 | 1988-05-31 | Stanford University | Rapid NMR imaging system |
| GB8719244D0 (en) * | 1987-08-14 | 1987-09-23 | Mansfield P | Nmr imaging |
| JPH02140145A (en) * | 1988-11-21 | 1990-05-29 | Toshiba Corp | Data collecting and processing system for mri device |
| JPH0312130A (en) * | 1989-06-09 | 1991-01-21 | Fuji Electric Co Ltd | Magnetic resonance imaging device |
| US5192909A (en) * | 1991-01-07 | 1993-03-09 | General Electric Company | Spectroscopic localization using pinwheel nmr excitation pulses |
| GB9200606D0 (en) * | 1992-01-13 | 1992-03-11 | British Tech Group | Method of and apparatus for obtaining spatial nmr information |
| DE4343022C1 (en) * | 1993-12-16 | 1995-03-30 | Bruker Medizintech | Magnetic-resonance imaging with combined single-point and back-projection imaging methods |
| US6476607B1 (en) * | 2000-12-08 | 2002-11-05 | Koninklijke Philips Electronics N.V. | MRI method and apparatus for rapid acquisition of multiple views through a volume |
Family Cites Families (13)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1596160A (en) * | 1976-12-15 | 1981-08-19 | Nat Res Dev | Nuclear magnetic resonance apparatus and methods |
| US4333053A (en) * | 1979-03-13 | 1982-06-01 | Emi Limited | Imaging systems |
| GB2056078B (en) * | 1979-08-03 | 1984-02-29 | Emi Ltd | Nuclear magnetic resonance systems |
| US4319190A (en) * | 1980-03-06 | 1982-03-09 | Bell Telephone Laboratories, Incorporated | Nuclear magnetic resonance imaging in space and frequency coordinates |
| GB2091884B (en) * | 1981-01-26 | 1984-07-18 | Hinsaw Waldo Stephen | Investigation of samples by nmr techniques |
| EP0076054B1 (en) * | 1981-09-21 | 1986-06-04 | Peter Mansfield | Nuclear magnetic resonance methods |
| US4607223A (en) * | 1982-08-13 | 1986-08-19 | National Research Development Corporation | Nuclear magnetic resonance imaging method |
| NL8203519A (en) * | 1982-09-10 | 1984-04-02 | Philips Nv | METHOD AND APPARATUS FOR DETERMINING A NUCLEAR MAGNETIZATION DISTRIBUTION IN PART OF A BODY. |
| US4551680A (en) * | 1983-04-21 | 1985-11-05 | Albert Macovski | Selective region NMR projection imaging system |
| US4570120A (en) * | 1983-04-25 | 1986-02-11 | The University Of British Columbia | N.M.R. Imaging |
| US4639671A (en) * | 1983-05-31 | 1987-01-27 | General Electric Company | Simultaneous NMR imaging system |
| US4651096A (en) * | 1985-02-19 | 1987-03-17 | Resonex | Imaging method for nuclear magnetic resonance utilizing balanced gradient fields |
| US4678996A (en) * | 1985-05-07 | 1987-07-07 | Picker International, Inc. | Magnetic resonance imaging method |
-
1984
- 1984-09-28 NL NL8402959A patent/NL8402959A/en not_active Application Discontinuation
-
1985
- 1985-09-18 DE DE8585201493T patent/DE3574620D1/en not_active Expired - Lifetime
- 1985-09-18 EP EP85201493A patent/EP0181015B1/en not_active Expired
- 1985-09-26 CA CA000491593A patent/CA1247699A/en not_active Expired
- 1985-09-27 IL IL76522A patent/IL76522A/en unknown
- 1985-09-28 JP JP60213698A patent/JPS6186641A/en active Pending
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1987
- 1987-12-22 US US07/136,515 patent/US4812762A/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| IL76522A (en) | 1989-07-31 |
| DE3574620D1 (en) | 1990-01-11 |
| JPS6186641A (en) | 1986-05-02 |
| US4812762A (en) | 1989-03-14 |
| EP0181015B1 (en) | 1989-12-06 |
| EP0181015A1 (en) | 1986-05-14 |
| NL8402959A (en) | 1986-04-16 |
| IL76522A0 (en) | 1986-01-31 |
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