Method of three-dimensional NMR imaging using selective excitation

Claim 1

A method of three-dimensional NMR imaging in which selective excitation is used to excite a thick planar slab of nuclear spins in an imaging sample situated in a static magnetic field and in which the necessary imaging information for constructing a series of tomographic section images of said thick planar slab is collected simultaneously from throughout said thick planar slab, said method comprising the steps of: a. applying for a first predetermined time interval a magnetic field gradient along a first axis of said imaging sample; b. irradiating said imaging sample, during said first time interval, with a frequency selective RF pulse so as to excite a plurality of nuclear spins in said thick planar slab of said imaging sample such that saic thick planar slab is selected to be situated within the region over which the receiver coil for detecting NMR signals is sensitive; c. applying during a second predetermined time interval, subsequent to said first time interval: (1) a first magnetic field gradient directed along said first axis for phase encoding nuclear spin spatial distribution information along said first axis, said first magnetic field gradient having a predetermined amplitude selected from n different amplitudes, wherein n is equal to the number of said tomographic section images, (2) a second magnetic field gradient directed along a second axis of said imaging sample for dephasing said excited nuclear spins, and (3) a third magnetic field gradient directed along a third axis of said imaging sample, said third axis being orthogonal to said second axis, for phase encoding nuclear spin spatial information along said third axis, said third magnetic field gradient having a predetermined amplitude selected from n y different amplitudes, wherein n y is equal to the number of pixels in one of said tomographic section images along said third axis; d. applying, during a third predetermined time interval, subsequent to said second time interval, a rephasing magnetic field gradient having the same direction as said second magnetic field gradient, so as to rephase said nuclear spins dephased during said second time interval to produce a spin echo signal, the Fourier transform of which is a projection of nuclear spin spatial distribution information from throughout said thick planar slab onto said second axis; e. sampling said spin echo signal n times in the presence of said rephasing magnetic field gradient, wherein n is equal to the number of pixels in one of said tomographic section images along said second axis; f. repeating the preceding steps for n different amplitudes of said third magnetic field gradient; and g. repeating the preceding steps for n different amplitudes of said first magnetic field gradient.

Claim 2

A method of three-dimensional NMR imaging in which selective excitation is used to excite a thick planar slab of nuclear spins in an imaging sample situated in a static magnetic field and in which the necessary imaging information for constructing a series of tomographic section images of said thick planar slab is collected simultaneously from throughout said thick planar slab, said method comprising the steps of: a. applying for a first predetermined time interval a magnetic field gradient along a first axis of said imaging sample; b. irradiating said imaging sample, during said first time interval, with a frequency selective RF pulse so as to excite a plurality of nuclear spins in said thick planar slab of said imaging sample such that saic thick planar slab is selected to be situated within the region over which the receiver coil for detecting NMR signals is sensitive; c. applying during a second predetermined time interval, subsequent to said first time interval: (1) a first magnetic field gradient directed along said first axis for phase encoding nuclear spin spatial distribution information along said first axis, said first magnetic field gradient having a predetermined amplitude selected from n different amplitudes, wherein n is equal to the number of said tomographic section images, (2) a second magnetic field gradient directed along a second axis of said imaging sample for dephasing said excited nuclear spins, and (3) a third magnetic field gradient directed along a third axis of said imaging sample, said third axis being orthogonal to said second axis, for phase encoding nuclear spin spatial information along said third axis, said third magnetic field gradient having a predetermined amplitude selected from n y different amplitudes, wherein n y is equal to the number of pixels in one of said tomographic section images along said third axis; d. applying, during a third predetermined time interval, subsequent to said second time interval, a rephasing magnetic field gradient having the same direction as said second magnetic field gradient, so as to rephase said nuclear spins dephased during said second time interval to produce a spin echo signal, the Fourier transform of which is a projection of nuclear spin spatial distribution information from throughout said thick planar slab onto said second axis; e. sampling said spin echo signal n times in the presence of said rephasing magnetic field gradient, wherein n is equal to the number of pixels in one of said tomographic section images along said second axis; f. repeating the preceding steps for n different amplitudes of said third magnetic field gradient; and g. repeating the preceding steps for n different amplitudes of said first magnetic field gradient.

Claim 12

A method for three-dimensional NMR image formation which overcomes the effects of inherent static magnetic field inhomogeneity on nuclear spin echo formation and in which the necessary imaging information for constructing a series of tomographic section images of a thick planar slab of an imaging sample is collected simultaneously from throughout the thick planar slab, said method comprising the steps of: a. maintaining a static magnetic field along a first axis of said imaging sample; b. applying for a first predetermined time interval a magnetic field gradient along said first axis of said imaging sample; c. irradiating said imaging sample, during said first time interval, with a frequency selective RF pulse so as to excite a plurality of nuclear spins in said thick planar slab of said imaging sample such that said thick planar slab is selected to be situated within the region over which the receiver coil for detecting NMR signals is sensitive; d. applying during a second predetermined time interval, subsequent to said first time interval: (1) a first magnetic field gradient directed along said first axis for phase encoding nuclear spin spatial distribution information along said first axis, said first magnetic field gradient having a predetermined amplitude selected from n different amplitudes, wherein n z is equal to the number of said tomographic section images, (2) a second magnetic field gradient directed along a second axis of said imaging sample for dephasing said excited nuclear spins, said dephasing being in addition to nuclear spin dephasing induced by inherent inhomogeneities in said static magnetic field, and (3) a third magnetic field gradient directed along a third axis of said imaging sample, said third axis being orthogonal to said second axis, for phase encoding nuclear spin spatial distribution information along said third axis, said third magnetic field gradient having a predetermined amplitude selected from ny different amplitudes, werein n y is equal to the number of pixels in one of said tomographic section images along said third axis; e. irradiating said image sample, after a time interval τ a subsequent to the mean occurrence of said frequency selective RF pulse, with a first 180° RF pulse so as to initiate the rephasing of said excited nuclear spins; f. applying during a third predetermined time interval, subsequent to said second time interval, a rephasing magnetic field gradient having the same direction as said second magnetic field gradient such that, after a time interval τ a following said 180° RF pulse, the nuclear spin echo caused by rephasing of the nuclear spins dephased by said second magnetic field gradient coincides with the occurrence of the nuclear spin echo derived from the rephasing of the nuclear spins dephased by the inherent inhomogeneities in said static magnetic field, said nuclear spin echoes producing a composite NMR signal, the Fourier transform of which is a projection of nuclear spin spatial distribution information from throughout said thick planar slab onto said second axis;

Claim 13

A method for three-dimensional NMR image formation which overcomes the effects of inherent static magnetic field inhomogeneity on nuclear spin echo formation and in which the necessary imaging information for constructing a series of tomographic section images of a thick planar slab of an imaging sample is collected simultaneously from throughout the thick planar slab, said method comprising the steps of: a. maintaining a static magnetic field along a first axis of said imaging sample; b. applying for a first predetermined time interval a magnetic field gradient along said first axis of said imaging sample; c. irradiating said imaging sample, during said first time interval, with a frequency selective RF pulse so as to excite a plurality of nuclear spins in said thick planar slab of said imaging sample such that said thick planar slab is selected to be situated within the region over which the receiver coil for detecting NMR signals is sensitive; d. applying during a second predetermined time interval, subsequent to said first time interval: (1) a first magnetic field gradient directed along said first axis for phase encoding nuclear spin spatial distribution information along said first axis, said first magnetic field gradient having a predetermined amplitude selected from n different amplitudes, wherein n z is equal to the number of said tomographic section images, (2) a second magnetic field gradient directed along a second axis of said imaging sample for dephasing said excited nuclear spins, said dephasing being in addition to nuclear spin dephasing induced by inherent inhomogeneities in said static magnetic field, and (3) a third magnetic field gradient directed along a third axis of said imaging sample, said third axis being orthogonal to said second axis, for phase encoding nuclear spin spatial distribution information along said third axis, said third magnetic field gradient having a predetermined amplitude selected from ny different amplitudes, werein n y is equal to the number of pixels in one of said tomographic section images along said third axis; e. irradiating said image sample, after a time interval τ a subsequent to the mean occurrence of said frequency selective RF pulse, with a first 180° RF pulse so as to initiate the rephasing of said excited nuclear spins; f. applying during a third predetermined time interval, subsequent to said second time interval, a rephasing magnetic field gradient having the same direction as said second magnetic field gradient such that, after a time interval τ a following said 180° RF pulse, the nuclear spin echo caused by rephasing of the nuclear spins dephased by said second magnetic field gradient coincides with the occurrence of the nuclear spin echo derived from the rephasing of the nuclear spins dephased by the inherent inhomogeneities in said static magnetic field, said nuclear spin echoes producing a composite NMR signal, the Fourier transform of which is a projection of nuclear spin spatial distribution information from throughout said thick planar slab onto said second axis;

Claim 30

A method of three-dimensional NMR imaging in which selective excitation is used to excite a thick planar slab of nuclear spins in an imaqinq sample situated in a static magnetic field and in which the necessary iamging information for constructing a series of tomographic section images of said thick planar slab is collected simultaneously from throughout said thick planar slab, said method comprising the steps of: a. applying for a first predetermined time interval a magnetic field gradient along a first axis, corresponding to the Z-axis of a Cartesian coordinate system, of said imaging sample; b. irradiating said imaging sample, during said first time interval, with a frequency selective RF pulse so as to excite a plurality of nuclear spins in said thick planar slab of said imaging sample, such that said thick planar slab is selected to be situated within the region over which the receiver coil for detecting NMR signals is sesnitive; c. applying during a second predetermined time interval, subsequent to said first time interval: (1) a first magnetic field gradient directed along said first axis for phase encoding nuclear spin spatial distribution information along said first axis, said first magnetic field gradient having a predetermined amplitude selected from n different amplitudes, wherein n is equal to the number of said tomographic section images, (2) a second magnetic field gradient directed along a second axis of said imaging sample, corresponding to the X-axis of the Cartesian coordinate system, for dephasing said excited nuclear spins, and (3) a third magnetic field gradient directed along a third axis of said imaging sample, corresponding to the Y-axis of the Cartesian coordinate system, for phase encoding nuclear spin spatial distribution information along said third axis, said third magnetic field gradient having a predetermined amplitude selected from n y different amplitudes, wherein n y is equal to the number of pixels in one of said tomographic section images along said third axis; d. applying, during a third predetermined time interval, subsequent to said second time interval, a rephasing magnetic field gradient, having the same direction as said second magnetic field gradient, so as to rephase said nuclear spins dephased during said second time interval to produce a spin echo signal which is a projection of nuclear spin spatial distribution information from throughout said thick planar slab onto said second axis; and e. sampling said spin echo signal n times in the presence of said rephasing magnetic field gradient, wherein n is equal to the number of pixels in one of said tomographic section images along said second axis; wherein said first, third, and rephasing magnetic field gradients are selected so as to produce (n y ).(n z ) NMR signals which upon Fourier analysis yield (n x )·(n y )·(n z ) pixels, each of said NMR signals corresponding to a unique pair of integers, k y and k z , selected such that and wherein the NMR signal S(x,y,z,k y ,k z ,t originating from said thick planar slab at point (x,y,z) is defined by wherein φ y and φ z are the phase shifts of each NMR signal in the Y- and Z-axis directions, respectively, and are defined by where i = , t is time, and Land L 2 are the lengths of the imaging aperture in the direction of the Y- and Z-axis, respectively.

Claim 31

A method of three-dimensional NMR imaging in which selective excitation is used to excite a thick planar slab of nuclear spins in an imaqinq sample situated in a static magnetic field and in which the necessary iamging information for constructing a series of tomographic section images of said thick planar slab is collected simultaneously from throughout said thick planar slab, said method comprising the steps of: a. applying for a first predetermined time interval a magnetic field gradient along a first axis, corresponding to the Z-axis of a Cartesian coordinate system, of said imaging sample; b. irradiating said imaging sample, during said first time interval, with a frequency selective RF pulse so as to excite a plurality of nuclear spins in said thick planar slab of said imaging sample, such that said thick planar slab is selected to be situated within the region over which the receiver coil for detecting NMR signals is sesnitive; c. applying during a second predetermined time interval, subsequent to said first time interval: (1) a first magnetic field gradient directed along said first axis for phase encoding nuclear spin spatial distribution information along said first axis, said first magnetic field gradient having a predetermined amplitude selected from n different amplitudes, wherein n is equal to the number of said tomographic section images, (2) a second magnetic field gradient directed along a second axis of said imaging sample, corresponding to the X-axis of the Cartesian coordinate system, for dephasing said excited nuclear spins, and (3) a third magnetic field gradient directed along a third axis of said imaging sample, corresponding to the Y-axis of the Cartesian coordinate system, for phase encoding nuclear spin spatial distribution information along said third axis, said third magnetic field gradient having a predetermined amplitude selected from n y different amplitudes, wherein n y is equal to the number of pixels in one of said tomographic section images along said third axis; d. applying, during a third predetermined time interval, subsequent to said second time interval, a rephasing magnetic field gradient, having the same direction as said second magnetic field gradient, so as to rephase said nuclear spins dephased during said second time interval to produce a spin echo signal which is a projection of nuclear spin spatial distribution information from throughout said thick planar slab onto said second axis; and e. sampling said spin echo signal n times in the presence of said rephasing magnetic field gradient, wherein n is equal to the number of pixels in one of said tomographic section images along said second axis; wherein said first, third, and rephasing magnetic field gradients are selected so as to produce (n y ).(n z ) NMR signals which upon Fourier analysis yield (n x )·(n y )·(n z ) pixels, each of said NMR signals corresponding to a unique pair of integers, k y and k z , selected such that and wherein the NMR signal S(x,y,z,k y ,k z ,t originating from said thick planar slab at point (x,y,z) is defined by wherein φ y and φ z are the phase shifts of each NMR signal in the Y- and Z-axis directions, respectively, and are defined by where i = , t is time, and Land L 2 are the lengths of the imaging aperture in the direction of the Y- and Z-axis, respectively.