CA1250891A - Method and device for determining an nmr distribution in a region of a body - Google Patents
Method and device for determining an nmr distribution in a region of a bodyInfo
- Publication number
- CA1250891A CA1250891A CA000496409A CA496409A CA1250891A CA 1250891 A CA1250891 A CA 1250891A CA 000496409 A CA000496409 A CA 000496409A CA 496409 A CA496409 A CA 496409A CA 1250891 A CA1250891 A CA 1250891A
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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
- G01R33/54—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
- G01R33/567—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution gated by physiological signals, i.e. synchronization of acquired MR data with periodical motion of an object of interest, e.g. monitoring or triggering system for cardiac or respiratory gating
- G01R33/5676—Gating or triggering based on an MR signal, e.g. involving one or more navigator echoes for motion monitoring and correction
-
- 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
- G01R33/58—Calibration of imaging systems, e.g. using test probes, Phantoms; Calibration objects or fiducial markers such as active or passive RF coils surrounding an MR active material
Abstract
ABSTRACT:
"Method and device for determining an NMR distribution in a region of a body."
The method and the device for making NMR images in accor-dance with the invention utilize additional measurements and addi-tional calculations in order to achieve a substantial reduction of image artefacts caused by (respiratory) motion of the body. The additional measurements involve the sampling of the non-conditioned FID or spin echo signal which can (but need not) be performed during each measurement cycle without consuming a substantial amount of additional measurement time. The non-conditioned signal samples are used to derive a reference frequency spectrum which is a measure of the size of the object. By comparing this reference with the fre-quency spectra of the various measurement cycles, standardization is obtained so that image signals produce an unambiguous image even though they have been derived from signal samples taken from measure-ment cycles performed in different states of motion (different object size).
"Method and device for determining an NMR distribution in a region of a body."
The method and the device for making NMR images in accor-dance with the invention utilize additional measurements and addi-tional calculations in order to achieve a substantial reduction of image artefacts caused by (respiratory) motion of the body. The additional measurements involve the sampling of the non-conditioned FID or spin echo signal which can (but need not) be performed during each measurement cycle without consuming a substantial amount of additional measurement time. The non-conditioned signal samples are used to derive a reference frequency spectrum which is a measure of the size of the object. By comparing this reference with the fre-quency spectra of the various measurement cycles, standardization is obtained so that image signals produce an unambiguous image even though they have been derived from signal samples taken from measure-ment cycles performed in different states of motion (different object size).
Description
PHN. 11.232 m e invention relates to a method of determining an NMR
distribution in a region of a kody in whichr in the presence of a steady uniform magnetic field, a nuclear spin resonance signal is generated during a plurality of successive measurement cycles by rneans of an r.f. electromagnetic pulse, which resonance signal is aonditioned during a preparation period and sampled during a subse-quent measurement pericd in order to provide a set of signal samples fr~n which after -transfarmation, an image of an NMR distribution is determined.
The invention also relates -to a device Eor determining an NMR distribution in a region of a kcdy, comprising:
a) rreans for generating a steady, uniform magnetic field, bl means for genera-ting an r.f. electromagnetic radiation, c) means for generating a gradient magnetic field, d) sampling means for taking signal samples of a resonance signal generated by the means specified in the para-graphs a) and b), e) processing means for processing the signal samples in order to compute an NMR distribution, and f) control means for controlling at least the means speci-fied in the paragraphs b) to e) for generating, con-ditioning and sampling a nu~ber of resonance signals and for processing the signal s~mples.
Such a method and device are known from U.S. Patent 25 4,070,611 which issued on January 24, 1978 to Varian Associates, Inc.
According to the method described therein, one row of a two- (or three-) dimensional image freql~ncy matrix is filled with signal sam-ples during each measurement cycle. After the entire matrix has been filled, an image of the nuclear magnetization can ke provided by means of a-tw~- (or three-) dimensional Fourier transforrnation. When an irnage having a reasonable resolution is desired (for example, 128 x 128 pixels), a rneasurement period of a few minutes will be required.
When a body to ke examined moves or is moved, defects or unsharpness will occur in the image. When measurements are performed on a human torso, image defects due to respiratory (and cardiac) motion will be :`
~L'~ 3~L
PHN. 11.232 -2-unavoidable.
m e foreyoing defects canno-t be avoided by means of a method or device as disclosed in our Canadian Patent 1,194,107 which issued on September 24, 1985, even though the total measurement period can thus be reduced by a factor of 2 or more.
It is an object of the invention to provide a method and a device in which the defects caused by movement of the body beiny measured are at leas-t reduced.
To achieve -this, a method in accordance with the invention is characterized in that a non-conditioned nuclear spin resonance signal is generated and sampled at least during a numker of measure-ment cycles each time in the presence of the same gradient magnetic field in order to obtain reference signal samples, the gradient direc-tion being coincident wi-th a direction of motion of the body, after which the reference signal samples are used during the signal trans formation of the signal samples taken in order to reduoe the ef-fects of body movement.
A device in accordance with the invention is characterized in that the processing means comprise: signal transformation means Eor determining frequency spectra from the reference signal samples, storage means Eor storing at least one of the frequency spectra, and comparison means Eor comparing a frequency spectrum -thus determined with the frequency spectrum stored in the storage means, said com~
parison means supplying correction factors for correcting values to be derived from the signal samples associated with said frequency spectrum.
E~bodiments in accordance with the invention will be des-cribed in detail hereinafter with reference to the accompanying drawing, wherein:
Figure 1 shows a measurement cycle of a method in accordance with the invention, Figure 2 shows two states of motion of a bc~y being measured, Figwres 3a and b show frecluency spectra of-the body in the two sta-tes of motion, Fig~re 4 shows a coordinate relation of images of the two states of motion of the body, and Figure 5 shows an embcdiment of the processing means of a device in accordance with -the invention.
r3 ~
PHN. 11.232 -3-Figure 1 shows a measurement cycle of a method in accordance with tne invention. Using an r.f. 90 pulse Pl, magnetic moments of spin nuclei in a bo~y in a steady uniform magnetic field are made to perform a precessional motion about the direction of said field, thus generating a resonance signal Fl (FID signal). During a prepara-tion period tv subsequent to the pulse Pl, a nuclear spin echo signal F2 which is to be generated by the application of an r.f. 180 pulse P2, is conditioned by means of a gradient magnetic field Gl (in -the x, y or z- direction) which has a different intensity during each measure-men-t cycle. The echo signal F2 thus genera-ted is sampled during a measuremen-t period tm subsequent to ~he preparation period tv. A con-stant Gx gradient magnetic field G2 is applied during the measurement period tm. Tne signal samples taken during tm are s-tored in storage means forming part of a de~ice in accordance with the invention whicln is yet -to be clescrihed. After expiry of the measurement period -tm, a second nuclear spin echo signal F2' is generated by means of a second r.f. 180 pulse P2', which seco~ld spin echo signal is brought into a non-conditioned state by applying, after the 180 pulse P2', a gradient field G2', whose effect is the opposite of that of the conditioning gradient field Gl applied for the first 180 pulse P2. During an additional measurement period -tm', reference signal sa~ples are taken from -the Non-conditioned echo signal F2' in the presence of a con-stant gradient field GR (in -this example a Gx gradien-t field as will be explained hereinafter).
It will be apparent tha-t, in addition to -the described way of obtaining non~condi-tioned signal samples, the signal Fl can also be sampled during the preparation period tv before -the gradient field Gl is applied. Conditioning can also be achieved by using different values for the preparation period tv during successive measuremen-t cycles.
Fig~re 2 shows a body 3 which is positioned on a -table 1 as is customarily done in known devices (for example, as described in the previously mentioned U.S. Patent 4,070,611 aNd Canadian Pate~t 1,194,107). When measurements are per-Eormed, for example on a human torso, the body 3 will move, for example due to respiration. The reference numeral 3 represents the state of mo-tion of the body after exhalation and the reference numeral 3' (denoted by a broken line) represents -the state af-ter il~lalation.
PHN 11 232 ~ 1985 As i~s shown, the motion occurs mainly in the x-direction. When signal samples are taken during successive measurement cycles (during the measurement periods tm) and simply processed so as to form an image, such an image will be affected by defects and unsharpness due to the described motion. When a non-conditioned nuclear spin echo signal is sampled in the presence of a Gx gradient magnetic field, for example in the exhalted state (of motion), a transformation (generally a Fourier transformation) will produce a frequency spectrum as shown in Fi~ure 3a. Because the nuclear spin echo signal has been measured in the presence of a Gx gradient fie:Ld, a one-dimensional frequency spectrum will be obtained after 1-D Fourier transformation of the reference signal samples taken, the bandwidth of said frequency spec-trum being a measure of the object dimension in the x-direc-tion.
Assuming that the intensity of the Gx gradient field increases in the '5 positive x-direction, the lowest frequency fO in the spectrum will be associated with the position x = xo in which the body 3 rests on the table 1 (see Figures 2 and 3a3. The highest frequency will be asso-ciated with the surface of the body 3 which is remote from the tableO
It will be understood that in the inhaled state of the body 3' (Figure 2) the frequency band will be wider as is shown diagrammatically in Fig~re 3b. In order to obtain a suitably defined limit at the upE~er end of the frequency band shown in the Figures 3a and 3b, and object 5 (for example, a container filled with water) which supplies a strong resonance signal, is positioned on the body 3, 3'. Comparison of the frequency bandwidth will reveal the extent to which the moving outer surface of the body 3 is displaced; the amount of displacement of the layers present between the outer surface and the surface in contact with the table can be established by comparing some of the significant (recognizable) peaks in both spectra (Figures 3a and 3b), this is diagram~atically denoted by arrows between the Figures 3a and 3b. From the foregoing comparison a relationship can be esta-blished (for exampler by extrapolation) between the E~ositions x' of dif-ferent layers in the body 3' (exhaled state). Figure 4 shows an example of such a relation. For the purpose of comparison Figure ~ also shows the straight line x = x' which is denoted by a broken line. The data concerning the motion of the bcdy 3 which are contained in the fre-quency spectra can be utilized in various ways. According to one method reference signal samples are taken during each measurement ~ 3~
PHN 11 232 -5~ 1985 cycle, which samples are converted into a frequency spectrum. From these spectra it can ke deduced whether the signal sa~ples taken during the measurement cycle are associated with an inhaled or an exhaled state of motion (or with a third, "intermediate" state). On the basis of the spectra determined, the signal samples can ke classi-fied in sub-groups from which suk-images are formed by means of one of the known methcds. One of the sub-images is declared to ke the "stan-dard" and the other suk-~nages are stretched (from x to xl) or ccmr pressed (from x' to x), utilizing correc-tion factors derived from the frequency spectra associated with the sub-groups and the spectrum associated with the "standard", depending on whether the inhaled or the exhaled state is chosen as the "standard". Such stretching and compression can ke performed in various ways, for example linearly across the entire image, or leaving one image half (in the x~direc-tion) undisturbed and performung -the operation linearly across the other image half, or via a non-linear distortion utilizing a curve to be determined as shown in Fig~re ~. It will be apparent that it is alternatively possible to take reference signal samples during only a few measurement cycles when a given state of motion is reached (exhaled or inhaled) which state of motion is detected by a (mecha-nical) detector. This is because, after said (two) states of motion ^have been reached, the state remains stationary for some time so that all signal samples taken during this period are associated with a given sub-group which can ke corrected by means of correction factors which need ke determined only once.
Figure 5 shows the processing means of a device in accordance with the invention. A de~odulated nuclear spin echo signal is applied to an analog-to-digital converter 11 which applies the digitized signal samples to an input gate 13. The P~D converter 11 and the input 3D gate 13 both receive control signals frcm a central control Ul1it 15 via a control bus 16. rrhe digital signal samples are transferred from the input gate 13, via the data bus 19, to a memory 17 under the control of the control unit 15 via the control bus 16. It will be apparent that the reference signal samples follow the same route. The 3s reference signal samples stored in the memory 17 are fetched by the control unit 15 in order to be applied to an arithmetic unit 21 in which the reference signal samples of a measurement cycle are sub-jected to a 1-D Fourier transformation. The resultant frequency spectrum P~ 11 232 ~6~ 11-1985 is stored in a section 17' of the memory 17. The frequency spectra thus determined are used by a comparison and arithmetic unit 23 in order to form sub-groups from the signal samples stored in the memory 17, which sub-groups are associated with the same phase of motion. A
1-D Fourier transformation is performed twice (or three times) on the sub-groups by the arithmetic unit 21 in order to obtain a two- ~or three-) dimensional sub-image per sub-group, at least the first sub-image formed being stored in the memory 17 in order to serve as a basis for the ultimate total image. Because the sub-images are formed row-wise or column-wise, the last 1-D Fourier transEormation oE the further sub-images is preferably performed in the "x-direction", after which the comparison and arithmetic unit 23 performs an x coordinate cor-rection by means of the frequency spectra stored in the memory sec-tion 17' on the row of values ob-tained, which values have an x-coordinate dependency. After correction, the corrected row of valuesis added to the values of the corresponding row of the first "standard"
sub-image determined, which values are fetched from the memory 17. The new values thus obtained are stored again in the same location in the memory 170 Upon completion of an image, i.e. after combining the first sub~image and the standardized sub-image (sub-images), it can be displayed on a display device 25.
It is to be noted that although in the embodiment shown in Figures 1 90 r.f. pulses and 180 r.f. pulses are used, the use of other pulses (e.g. smaller than 90 r.f. pulse) can be used also.
It will be clear too that although in Figure 1 a so-called spin echo technique has been shown the method in accordance with the invention is not restricted to the spin echo technique and can be used in the various different methods of measurement, which are well known within the field of nuclear magnetic resonance imaging~
distribution in a region of a kody in whichr in the presence of a steady uniform magnetic field, a nuclear spin resonance signal is generated during a plurality of successive measurement cycles by rneans of an r.f. electromagnetic pulse, which resonance signal is aonditioned during a preparation period and sampled during a subse-quent measurement pericd in order to provide a set of signal samples fr~n which after -transfarmation, an image of an NMR distribution is determined.
The invention also relates -to a device Eor determining an NMR distribution in a region of a kcdy, comprising:
a) rreans for generating a steady, uniform magnetic field, bl means for genera-ting an r.f. electromagnetic radiation, c) means for generating a gradient magnetic field, d) sampling means for taking signal samples of a resonance signal generated by the means specified in the para-graphs a) and b), e) processing means for processing the signal samples in order to compute an NMR distribution, and f) control means for controlling at least the means speci-fied in the paragraphs b) to e) for generating, con-ditioning and sampling a nu~ber of resonance signals and for processing the signal s~mples.
Such a method and device are known from U.S. Patent 25 4,070,611 which issued on January 24, 1978 to Varian Associates, Inc.
According to the method described therein, one row of a two- (or three-) dimensional image freql~ncy matrix is filled with signal sam-ples during each measurement cycle. After the entire matrix has been filled, an image of the nuclear magnetization can ke provided by means of a-tw~- (or three-) dimensional Fourier transforrnation. When an irnage having a reasonable resolution is desired (for example, 128 x 128 pixels), a rneasurement period of a few minutes will be required.
When a body to ke examined moves or is moved, defects or unsharpness will occur in the image. When measurements are performed on a human torso, image defects due to respiratory (and cardiac) motion will be :`
~L'~ 3~L
PHN. 11.232 -2-unavoidable.
m e foreyoing defects canno-t be avoided by means of a method or device as disclosed in our Canadian Patent 1,194,107 which issued on September 24, 1985, even though the total measurement period can thus be reduced by a factor of 2 or more.
It is an object of the invention to provide a method and a device in which the defects caused by movement of the body beiny measured are at leas-t reduced.
To achieve -this, a method in accordance with the invention is characterized in that a non-conditioned nuclear spin resonance signal is generated and sampled at least during a numker of measure-ment cycles each time in the presence of the same gradient magnetic field in order to obtain reference signal samples, the gradient direc-tion being coincident wi-th a direction of motion of the body, after which the reference signal samples are used during the signal trans formation of the signal samples taken in order to reduoe the ef-fects of body movement.
A device in accordance with the invention is characterized in that the processing means comprise: signal transformation means Eor determining frequency spectra from the reference signal samples, storage means Eor storing at least one of the frequency spectra, and comparison means Eor comparing a frequency spectrum -thus determined with the frequency spectrum stored in the storage means, said com~
parison means supplying correction factors for correcting values to be derived from the signal samples associated with said frequency spectrum.
E~bodiments in accordance with the invention will be des-cribed in detail hereinafter with reference to the accompanying drawing, wherein:
Figure 1 shows a measurement cycle of a method in accordance with the invention, Figure 2 shows two states of motion of a bc~y being measured, Figwres 3a and b show frecluency spectra of-the body in the two sta-tes of motion, Fig~re 4 shows a coordinate relation of images of the two states of motion of the body, and Figure 5 shows an embcdiment of the processing means of a device in accordance with -the invention.
r3 ~
PHN. 11.232 -3-Figure 1 shows a measurement cycle of a method in accordance with tne invention. Using an r.f. 90 pulse Pl, magnetic moments of spin nuclei in a bo~y in a steady uniform magnetic field are made to perform a precessional motion about the direction of said field, thus generating a resonance signal Fl (FID signal). During a prepara-tion period tv subsequent to the pulse Pl, a nuclear spin echo signal F2 which is to be generated by the application of an r.f. 180 pulse P2, is conditioned by means of a gradient magnetic field Gl (in -the x, y or z- direction) which has a different intensity during each measure-men-t cycle. The echo signal F2 thus genera-ted is sampled during a measuremen-t period tm subsequent to ~he preparation period tv. A con-stant Gx gradient magnetic field G2 is applied during the measurement period tm. Tne signal samples taken during tm are s-tored in storage means forming part of a de~ice in accordance with the invention whicln is yet -to be clescrihed. After expiry of the measurement period -tm, a second nuclear spin echo signal F2' is generated by means of a second r.f. 180 pulse P2', which seco~ld spin echo signal is brought into a non-conditioned state by applying, after the 180 pulse P2', a gradient field G2', whose effect is the opposite of that of the conditioning gradient field Gl applied for the first 180 pulse P2. During an additional measurement period -tm', reference signal sa~ples are taken from -the Non-conditioned echo signal F2' in the presence of a con-stant gradient field GR (in -this example a Gx gradien-t field as will be explained hereinafter).
It will be apparent tha-t, in addition to -the described way of obtaining non~condi-tioned signal samples, the signal Fl can also be sampled during the preparation period tv before -the gradient field Gl is applied. Conditioning can also be achieved by using different values for the preparation period tv during successive measuremen-t cycles.
Fig~re 2 shows a body 3 which is positioned on a -table 1 as is customarily done in known devices (for example, as described in the previously mentioned U.S. Patent 4,070,611 aNd Canadian Pate~t 1,194,107). When measurements are per-Eormed, for example on a human torso, the body 3 will move, for example due to respiration. The reference numeral 3 represents the state of mo-tion of the body after exhalation and the reference numeral 3' (denoted by a broken line) represents -the state af-ter il~lalation.
PHN 11 232 ~ 1985 As i~s shown, the motion occurs mainly in the x-direction. When signal samples are taken during successive measurement cycles (during the measurement periods tm) and simply processed so as to form an image, such an image will be affected by defects and unsharpness due to the described motion. When a non-conditioned nuclear spin echo signal is sampled in the presence of a Gx gradient magnetic field, for example in the exhalted state (of motion), a transformation (generally a Fourier transformation) will produce a frequency spectrum as shown in Fi~ure 3a. Because the nuclear spin echo signal has been measured in the presence of a Gx gradient fie:Ld, a one-dimensional frequency spectrum will be obtained after 1-D Fourier transformation of the reference signal samples taken, the bandwidth of said frequency spec-trum being a measure of the object dimension in the x-direc-tion.
Assuming that the intensity of the Gx gradient field increases in the '5 positive x-direction, the lowest frequency fO in the spectrum will be associated with the position x = xo in which the body 3 rests on the table 1 (see Figures 2 and 3a3. The highest frequency will be asso-ciated with the surface of the body 3 which is remote from the tableO
It will be understood that in the inhaled state of the body 3' (Figure 2) the frequency band will be wider as is shown diagrammatically in Fig~re 3b. In order to obtain a suitably defined limit at the upE~er end of the frequency band shown in the Figures 3a and 3b, and object 5 (for example, a container filled with water) which supplies a strong resonance signal, is positioned on the body 3, 3'. Comparison of the frequency bandwidth will reveal the extent to which the moving outer surface of the body 3 is displaced; the amount of displacement of the layers present between the outer surface and the surface in contact with the table can be established by comparing some of the significant (recognizable) peaks in both spectra (Figures 3a and 3b), this is diagram~atically denoted by arrows between the Figures 3a and 3b. From the foregoing comparison a relationship can be esta-blished (for exampler by extrapolation) between the E~ositions x' of dif-ferent layers in the body 3' (exhaled state). Figure 4 shows an example of such a relation. For the purpose of comparison Figure ~ also shows the straight line x = x' which is denoted by a broken line. The data concerning the motion of the bcdy 3 which are contained in the fre-quency spectra can be utilized in various ways. According to one method reference signal samples are taken during each measurement ~ 3~
PHN 11 232 -5~ 1985 cycle, which samples are converted into a frequency spectrum. From these spectra it can ke deduced whether the signal sa~ples taken during the measurement cycle are associated with an inhaled or an exhaled state of motion (or with a third, "intermediate" state). On the basis of the spectra determined, the signal samples can ke classi-fied in sub-groups from which suk-images are formed by means of one of the known methcds. One of the sub-images is declared to ke the "stan-dard" and the other suk-~nages are stretched (from x to xl) or ccmr pressed (from x' to x), utilizing correc-tion factors derived from the frequency spectra associated with the sub-groups and the spectrum associated with the "standard", depending on whether the inhaled or the exhaled state is chosen as the "standard". Such stretching and compression can ke performed in various ways, for example linearly across the entire image, or leaving one image half (in the x~direc-tion) undisturbed and performung -the operation linearly across the other image half, or via a non-linear distortion utilizing a curve to be determined as shown in Fig~re ~. It will be apparent that it is alternatively possible to take reference signal samples during only a few measurement cycles when a given state of motion is reached (exhaled or inhaled) which state of motion is detected by a (mecha-nical) detector. This is because, after said (two) states of motion ^have been reached, the state remains stationary for some time so that all signal samples taken during this period are associated with a given sub-group which can ke corrected by means of correction factors which need ke determined only once.
Figure 5 shows the processing means of a device in accordance with the invention. A de~odulated nuclear spin echo signal is applied to an analog-to-digital converter 11 which applies the digitized signal samples to an input gate 13. The P~D converter 11 and the input 3D gate 13 both receive control signals frcm a central control Ul1it 15 via a control bus 16. rrhe digital signal samples are transferred from the input gate 13, via the data bus 19, to a memory 17 under the control of the control unit 15 via the control bus 16. It will be apparent that the reference signal samples follow the same route. The 3s reference signal samples stored in the memory 17 are fetched by the control unit 15 in order to be applied to an arithmetic unit 21 in which the reference signal samples of a measurement cycle are sub-jected to a 1-D Fourier transformation. The resultant frequency spectrum P~ 11 232 ~6~ 11-1985 is stored in a section 17' of the memory 17. The frequency spectra thus determined are used by a comparison and arithmetic unit 23 in order to form sub-groups from the signal samples stored in the memory 17, which sub-groups are associated with the same phase of motion. A
1-D Fourier transformation is performed twice (or three times) on the sub-groups by the arithmetic unit 21 in order to obtain a two- ~or three-) dimensional sub-image per sub-group, at least the first sub-image formed being stored in the memory 17 in order to serve as a basis for the ultimate total image. Because the sub-images are formed row-wise or column-wise, the last 1-D Fourier transEormation oE the further sub-images is preferably performed in the "x-direction", after which the comparison and arithmetic unit 23 performs an x coordinate cor-rection by means of the frequency spectra stored in the memory sec-tion 17' on the row of values ob-tained, which values have an x-coordinate dependency. After correction, the corrected row of valuesis added to the values of the corresponding row of the first "standard"
sub-image determined, which values are fetched from the memory 17. The new values thus obtained are stored again in the same location in the memory 170 Upon completion of an image, i.e. after combining the first sub~image and the standardized sub-image (sub-images), it can be displayed on a display device 25.
It is to be noted that although in the embodiment shown in Figures 1 90 r.f. pulses and 180 r.f. pulses are used, the use of other pulses (e.g. smaller than 90 r.f. pulse) can be used also.
It will be clear too that although in Figure 1 a so-called spin echo technique has been shown the method in accordance with the invention is not restricted to the spin echo technique and can be used in the various different methods of measurement, which are well known within the field of nuclear magnetic resonance imaging~
Claims (10)
1. A method of determining an NMR distribution in a region of a body in which, in the presence of a steady uniform magnetic field, a nuclear spin echo signal is generated during a plurality of successive measurement cycles by means of an r.f. electromagnetic pulse, which resonance signal is conditioned during a preparation period and sampled during a subsequent measurement period in order to provide a set of signal samples from which after trans-formation, an image of an NMR distribution is determined, characterized in that a non-conditioned nuclear spin reson-ance signal is generated and sampled at least during a plurality of measurement cycles each time in the presence of the same gradient magnetic field in order to obtain reference signal samples, the gradient direction being coincident with a direction of motion of the body, after which the reference signal samples are used during the transformation of the signal samples taken in order to reduce the effects of body movement.
2. A method as claimed in Claim 1, characterized in that a non-conditioned nuclear spin resonance signal is generated and sampled during each measurement cycle.
3. A method as claimed in Claim 2, characterized in that the reference signal samples taken during a measurement cycle are used to standardize the signal samples of the same measurement cycle, after which an image of an NMR distribu-tion is determined from the standardized values derived from the signal samples.
4. A method as claimed in Claim 1, 2 or 3, charac-terized in that while the signal samples are being taken, a measurement gradient field is applied whose gradient direction is the same as that of the gradient field applied while taking the reference signal samples.
5. A method as claimed in Claim 1, 2 or 3, charac-terized in that while the signal samples are being taken, a measurement gradient field is applied whose gradient direc-tion extends at right angles to that of the gradient field applied while taking the reference signal samples.
6. A method as claimed in Claim 2, characterized in that the reference signal samples are used to group the signal samples of all measurement cycles into at least two sub-groups of measurement cycles each relating to a respec-tive given state of motion of the body, after which a sub-image is formed from each sub-group of signal samples, which sub-image is standardized by means of the reference signal samples of a measurement cycle associated with the sub-image, after which the standardized sub-images are combined so as to form a single image.
7. A method as claimed in Claim 1, 2 or 3, charac-terized in that the reference signal samples are taken after excitation and before conditioning during the preparation period of the resonance signal.
8. A method as claimed in Claim 1, 2 or 3, charac-terized in that the reference signal samples are taken from a nuclear spin echo signal formed by means of a 1.0° r.f.
pulse, after compensation for the conditioning performed dur-ing the preparation period.
pulse, after compensation for the conditioning performed dur-ing the preparation period.
9. A method as claimed in Claim 1, characterized in that during a measurement cycle reference signal samples are taken when one of at least two predetermined detectable states of motion of the body is reached, after which at least two sub-groups which are associated with the predeter-mined detectable states of motion are formed from the signal samples of the measurement cycles, which sub-groups are used to form sub-images which are standardized by means of the reference signal samples from the measurement cycle associated with the relevant state of motion, after which the sub-images are combined so as to form a single image.
10. 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 an r.f. electromagnetic radiation, c) means for generating a gradient magnetic field, d) sampling means for taking signal samples of a resonance signal generated by the means specified in the paragraph a) and b), e) processing means for processing the signal sam-ples in order to compute an NMR distribution, and f) control means for controlling at least the means specified in the paragraphs b) and e) for gener-ating, conditioning and sampling a number of resonance signals and for processing the signal samples, characterized in that the processing means comprise: signal transformation means for determining frequency spectra from the reference signal samples, storage means for storing at least one of the frequency spectra, and comparison means for comparing a frequency spectrum thus determined with the fre-quency spectrum stored in the storage means, said comparison means supplying correction factors for correcting values to be derived from the signal samples associated with said frequency spectrum.
a) means for generating a steady, uniform magnetic field, b) means for generating an r.f. electromagnetic radiation, c) means for generating a gradient magnetic field, d) sampling means for taking signal samples of a resonance signal generated by the means specified in the paragraph a) and b), e) processing means for processing the signal sam-ples in order to compute an NMR distribution, and f) control means for controlling at least the means specified in the paragraphs b) and e) for gener-ating, conditioning and sampling a number of resonance signals and for processing the signal samples, characterized in that the processing means comprise: signal transformation means for determining frequency spectra from the reference signal samples, storage means for storing at least one of the frequency spectra, and comparison means for comparing a frequency spectrum thus determined with the fre-quency spectrum stored in the storage means, said comparison means supplying correction factors for correcting values to be derived from the signal samples associated with said frequency spectrum.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NL8403627A NL8403627A (en) | 1984-11-29 | 1984-11-29 | METHOD AND APPARATUS FOR DETERMINING A NUCLEAR MAGNETIZATION DISTRIBUTION IN PART OF A BODY. |
| NL8403627 | 1984-11-29 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1250891A true CA1250891A (en) | 1989-03-07 |
Family
ID=19844829
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000496409A Expired CA1250891A (en) | 1984-11-29 | 1985-11-28 | Method and device for determining an nmr distribution in a region of a body |
Country Status (8)
| Country | Link |
|---|---|
| US (1) | US4682109A (en) |
| EP (1) | EP0184249B1 (en) |
| JP (1) | JPH0628651B2 (en) |
| CN (1) | CN85109320A (en) |
| CA (1) | CA1250891A (en) |
| DE (1) | DE3577140D1 (en) |
| IL (1) | IL77155A (en) |
| NL (1) | NL8403627A (en) |
Families Citing this family (16)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4614195A (en) * | 1984-12-18 | 1986-09-30 | General Electric Company | Method for reduction of motion artifacts in Fourier transform NMR imaging techniques |
| US4728890A (en) * | 1985-08-16 | 1988-03-01 | Picker International, Inc. | Motion artifact suppression technique of magnetic resonance imaging |
| JPS63164943A (en) * | 1986-09-03 | 1988-07-08 | 株式会社日立製作所 | Nmr imaging system |
| US4855910A (en) * | 1986-10-22 | 1989-08-08 | North American Philips Corporation | Time-clustered cardio-respiratory encoder and method for clustering cardio-respiratory signals |
| JPS63183047A (en) * | 1987-01-26 | 1988-07-28 | 株式会社東芝 | Magnetic resonance imaging apparatus |
| FR2616936B1 (en) * | 1987-06-19 | 1989-10-13 | Thomson Cgr | METHOD FOR TAKING INTO ACCOUNT, IN AN IMAGE, THE MOVEMENTS OF AN OBJECT |
| JPH064066B2 (en) * | 1987-10-15 | 1994-01-19 | 株式会社東芝 | Magnetic resonance imaging equipment |
| IL85259A0 (en) * | 1988-01-29 | 1988-07-31 | Elscint Ltd | Motion insensitive imaging using magnetic resonance systems |
| US4937526A (en) * | 1988-11-23 | 1990-06-26 | Mayo Foundation For Medical Education And Research | Adaptive method for reducing motion and flow artifacts in NMR images |
| US4885549A (en) * | 1988-11-30 | 1989-12-05 | General Electric Company | Method of phase and amplitude correction of NMR signals using a reference marker |
| EP0415682A3 (en) * | 1989-08-31 | 1991-07-31 | General Electric Company | Nmr system |
| EP0415683A3 (en) * | 1989-08-31 | 1991-07-31 | General Electric Company | Nmr system |
| JPH05505224A (en) * | 1990-01-20 | 1993-08-05 | ザベート フッシャング | Rotary piston internal combustion engine |
| US5251128A (en) * | 1990-11-19 | 1993-10-05 | General Electric Company | Motion artifact reduction in projection imaging |
| JPH07163537A (en) * | 1994-09-01 | 1995-06-27 | Hitachi Ltd | Nmr imaging method |
| US6566874B1 (en) * | 1998-07-30 | 2003-05-20 | Schlumberger Technology Corporation | Detecting tool motion effects on nuclear magnetic resonance measurements |
Family Cites Families (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA1052861A (en) * | 1975-03-18 | 1979-04-17 | Varian Associates | Gyromagnetic resonance fourier transform zeugmatography |
| GB2037999B (en) * | 1978-12-13 | 1983-01-06 | Emi Ltd | Imaging systems |
| US4599565A (en) * | 1981-12-15 | 1986-07-08 | The Regents Of The University Of Calif. | Method and apparatus for rapid NMR imaging using multi-dimensional reconstruction techniques |
| DE3372907D1 (en) * | 1982-06-09 | 1987-09-17 | Picker Int Ltd | Method and apparatus for monitoring movement of a body under nmr examination |
| NL8203519A (en) * | 1982-09-10 | 1984-04-02 | Philips Nv | METHOD AND APPARATUS FOR DETERMINING A NUCLEAR MAGNETIZATION DISTRIBUTION IN PART OF A BODY. |
| US4579121A (en) * | 1983-02-18 | 1986-04-01 | Albert Macovski | High speed NMR imaging system |
| JPS59155239A (en) * | 1983-02-23 | 1984-09-04 | 株式会社東芝 | Diagnostic nuclear magnetic resonance apparatus |
| JPS6120541A (en) * | 1984-07-05 | 1986-01-29 | 株式会社島津製作所 | Correction of strain of nuclear magnetic resonance image by breathing quickening |
| US4567893A (en) * | 1984-11-21 | 1986-02-04 | General Electric Company | Method of eliminating breathing artifacts in NMR imaging |
-
1984
- 1984-11-29 NL NL8403627A patent/NL8403627A/en not_active Application Discontinuation
-
1985
- 1985-10-11 US US06/786,557 patent/US4682109A/en not_active Expired - Lifetime
- 1985-11-19 DE DE8585201895T patent/DE3577140D1/en not_active Expired - Lifetime
- 1985-11-19 EP EP85201895A patent/EP0184249B1/en not_active Expired
- 1985-11-26 CN CN198585109320A patent/CN85109320A/en active Pending
- 1985-11-26 IL IL77155A patent/IL77155A/en unknown
- 1985-11-28 JP JP60266264A patent/JPH0628651B2/en not_active Expired - Lifetime
- 1985-11-28 CA CA000496409A patent/CA1250891A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| EP0184249A1 (en) | 1986-06-11 |
| DE3577140D1 (en) | 1990-05-17 |
| NL8403627A (en) | 1986-06-16 |
| IL77155A (en) | 1989-12-15 |
| JPH0628651B2 (en) | 1994-04-20 |
| US4682109A (en) | 1987-07-21 |
| CN85109320A (en) | 1986-12-03 |
| EP0184249B1 (en) | 1990-04-11 |
| IL77155A0 (en) | 1986-04-29 |
| JPS61133850A (en) | 1986-06-21 |
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