Ultra-fast multi-section MRI using gradient and spin echo (grase) imaging

A method for generating MRI signals from NMR nuclei within an image volume, said method comprising:

• nutating nuclei within a slice-volume to initiate a TR interval;
• repetitively applying 180.degree. NMR RF pulses to further nutate nuclei within the same said slice-volume by substantially 180.degree. at subsequent intervals within the same TR interval and thus to generate a train of NMR spin echoes;
• between pairs of said 180.degree. NMR RF pulses, applying a plurality of alternate polarity read-out magnetic gradient pulses to produce sub-sequences of plural gradient echoes, and
• phase-encoding each said gradient echo within each sub-sequence to traverse a discontinuous trajectory in k-space which is interleaved with the trajectories of other sub-sequence to traverse a discontinuous trajectory in k-space which is interleaved with the trajectories of other sub-sequences so as to more evenly distribute field inhomogeneity and/or chemical phase shift effects over the phase-encoded dimension of k-space.

A method for generating MRI signals from NMR nuclei within an image volume, said method comprising:

• generating a train of NMR spin echoes using a sequence of plural 180.degree. NMR RF nutation pulses;
• for each such RF refocused spin echo, generating a sub-sequence of NMR gradient echoes by using a sequence of alternating polarity read-out magnetic gradient pulses;
• phase-encoding each such gradient echo to trace different trajectories in k-space, the phase-encoding being modulated to cause gradient echoes of each said sub-sequence to have k-space trajectories which are interleaved with those of other such sub-sequences so as to more evenly distribute T2* and/or chemical phase shift effects over the phase-encoded dimension of k-space;
• and
• after each said sub-sequence of gradient echoes, applying a phase-decoding magnetic gradient pulse to return nuclei phase encoding to the same point in the k-space prior to generation of the next NMR spin echo.

A method for generating MRI signals, said method comprising:

• (a) subjecting NMR nuclei within an image volume to a perturbing NMR RF nutation pulse;
• (b) thereafter subjecting said NMR nuclei to
• (i) a 180.degree. NMR RF nutation pulse followed by
• (ii) a plurality of alternating polarity magnetic gradient read-out pulses to generate a sequence of plural gradient echoes occurring after said 180.degree. NMR RF nutation pulse and before application of another 180.degree. NMR RF nutation pulse, and
• (iii) repeating steps (i) and (ii) to generate a further sequence of gradient echoes.

A method for generating MRI signals, said method comprising:

• (a) subjecting NMR nuclei within an image volume to a perturbing NMR RF nutation pulse;
• (b) thereafter subjecting said NMR nuclei to
• (i) a 180.degree. NMR RF nutation pulse followed by
• (ii) a plurality of alternating polarity magnetic gradient read-out pulses to generate a sequence of gradient echoes, and
• (iii) repeating steps (i) and (ii) to generate a further sequence of gradient echoes.
• said NMR RF nutation pulses occurring during a slice volume selecting magnetic gradient pulse in a multi-slice sequence,
• each magnetic gradient read-out pulse being preceded by a phase-encoding magnetic gradient pulse of predetermined magnitude, different from the magnitude of other such phase-encoding pulses, and
• wherein the magnitude of phase-encoding magnetic gradient pulses with each repetition of steps (i) and (ii) generate MRI gradient echoes respectively corresponding to non-contiguous trajectories in k-space, the MRI gradient echoes generated from other repetitions of steps (i) and (ii) respectively filling in the remaining contiguous trajectories in k-space in an interleaved fashion.

A method for generating MRI signals, said method comprising:

• (a) subjecting NMR nuclei within an image volume to a perturbing NMR RF nutation pulse;
• (b) thereafter subjecting said NMR nuclei to
• (i) a 180.degree. NMR RF nutation pulse followed by
• (ii) a plurality of alternating polarity magnetic gradient read-out pulses to generate a sequence of gradient echoes, and
• (iii) repeating steps (i) and (ii) to generate a further sequence of gradient echoes.
• said NMR RF nutation pulses occurring during a slice volume selecting magnetic gradient pulse in a multi-slice sequence,
• each magnetic gradient read-out pulse being preceded by a phase-encoding magnetic gradient pulse of predetermined magnitude, different from the magnitude of other such phase-encoding pulses, and
• wherein prior to each repetition of steps (i) and (ii), a phase-return magnetic gradient pulse is applied to said NMR nuclei having polarity and magnitude for substantially cancelling all prior phase-encoding magnetic gradient pulses and thus momentarily returning the NMR nuclei to the origin of k-space.

Apparatus for generating MRI signals from NMR nuclei within an image volume, said apparatus comprising:

• means for nutating nuclei a slice-volume to initiate a TR interval;
• means for repetitively applying 180.degree. NMR RF pulses to further nutate nuclei within the same said slice-volume by substantially 180.degree. at subsequent intervals within the same TR interval and thus to generate a train of NMR spin echoes;
• means for applying a plurality of alternate polarity read-out magnetic gradient pulses between pairs of said 180.degree. NMR RF pulses to produce sub-sequences of plural gradient echoes;
• and
• means for phase-encoding each said gradient echo within each sub-sequence to traverse a discontinuous trajectory in k-space which is interleaved with the trajectories of other sub-sequences so as to more evenly distribute field inhomogeneity and/or chemical phase shift effects over the phase-encoded dimension of k-space.

Apparatus for generating MRI signals from NMR nuclei within an image volume, said apparatus comprising:

• means for generating a train of NMR spin echoes using a sequence of plural 180.degree. NMR RF nutation pulses;
• means for generating a sub-sequence of NMR gradient echoes for each such RF refocused spin echo by using a sequence of alternating polarity read-out magnetic gradient pulses;
• means for phase-encoding each such gradient echo to trace different trajectories in k-space, the phase-encoding being modulated to cause gradient echoes of each said sub-sequence to have k-space trajectories which are interleaved with those of other such sub-sequences so as to more evenly distribute field inhomogeneity and/or chemical phase shift effects over the phase-encoded dimension of k-space;
• and
• means for applying a phase-decoding magnetic gradient pulse after each said sub-sequence of gradient echoes to return nuclei phase encoding to the origin of k-space prior to generation of the next NMR spin echo.

Apparatus for generating MRI signals, said apparatus comprising:

• (a) means for subjecting NMR nuclei within an image volume to a perturbing NMR RF nutation pulse;
• (b) means for thereafter subjecting said NMR nuclei to
• (ii) a plurality of alternating polarity magnetic gradient read-out pulses to generate a sequence of gradient echoes, and
• (iii) repeating steps (i) and (ii) to generate a further sequence of plural gradient echoes occurring after said 180.degree. NMR RF nutation pulse and before application of another 180.degree. NMR RF nutation pulse.

Apparatus for generating MRI signals, said apparatus comprising:

• (a) means for subjecting NMR nuclei within an image volume to a perturbing NMR RF nutation pulse;
• (b) means for thereafter subjecting said NMR nuclei to
• (i) a 180.degree.60 NMR RF nutation pulse followed by
• (ii) a plurality of alternating polarity magnetic gradient read-out pulses to generate a sequence of gradient echoes, and
• (iii) repeating steps (i) and (ii) to generate a further sequence of gradient echoes,
• said means (a) and means (b) including means for generating said NMR RF nutation pulses during a slice volume selecting magnetic gradient pulse in a multi-slice sequence;
• said means (b) includes means for generating a phase-encoding magnetic gradient pulse of predetermined magnitude, different from the magnitude of other such phase-encoding pulses prior to each magnetic gradient read-out pulse;
• and
• wherein means (b) includes means for causing the magnitude of phase-encoding magnetic gradient pulses within each repetition to generate MRI gradient echoes respectively corresponding to non-contiguous trajectories in k-space, the MRI gradient echoes generated from other repetitions of respectively filling in the remaining contiguous trajectories in k-space in an interleaved fashion.

Apparatus for generating MRI signals, said apparatus comprising:

• (a) means for subjecting NMR nuclei within an image volume to a perturbing NMR RF nutation pulse;
• (b) means for thereafter subjecting said NMR nuclei to
• (i) a 180.degree.60 NMR RF nutation pulse followed by
• (ii) a plurality of alternating polarity magnetic gradient read-out pulses to generate a sequence of gradient echoes, and
• (iii) repeating steps (i) and (ii) to generate a further sequence of gradient echoes,
• said means (a) and means (b) including means for generating said NMR RF nutation pulses during a slice volume selecting magnetic gradient pulse in a multi-slice sequence;
• said means (b) includes means for generating a phase-encoding magnetic gradient pulse of predetermined magnitude, different from the magnitude of other such phase-encoding pulses prior to each magnetic gradient read-out pulse;
• and
• means for generating a phase-return magnetic gradient pulse applied to said NMR nuclei having polarity and magnitude for substantially cancelling all prior phase-encoding magnetic gradient pulses and thus momentarily returning the NMR nuclei to the same point in k-space prior to each repetition of a 180.degree. RF pulse.

A method for generating MRI signals from NMR nuclei with an image volume, said method comprising:

• nutating nuclei within a slice-volume to initiate a TR interval;
• repetitively applying 180.degree. NMR RF pulses to further nutate nuclei within the same said slice-volume by substantially 180.degree. at subsequent intervals within the same TR interval and thus to generate a train of NMR spin echoes;
• between pairs of said 180.degree. NMR RF pulses, applying a plurality of alternate polarity read-out magnetic gradient pulses to produce sub-sequences of gradient echoes;
• and
• wherein the time occurrences of gradient echoes within different said sub-sequences are relatively shifted so as to more evenly distribute field inhomogeneity and/or chemical phase shift effects over the phase-encoded dimension if k-space.

A method for generating MRI signals from NMR nuclei within an image volume, said method comprising:

• nutating nuclei within a slice-volume to initiate a TR interval;
• repetitively applying 180.degree. NMR RF pulses to further nutate nuclei within the same said slice-volume by substantially 180.degree. at subsequent intervals within the same TR interval and thus to generate a train of NMR spin echoes;
• between pairs of said 180.degree. NMR RF pulses, applying a plurality of alternate polarity read-out magnetic gradient pulses to produce sub-sequences of gradient echoes;
• and
• at the conclusion of each said subsequence, applying a phase-decoding magnetic gradient pulse to return nuclei phase encoding to the same point in k-space prior to application of the next 180.degree. NMR RF nutation pulse.

Apparatus for generating MRI signals from NMR nuclei within an image volume, said apparatus comprising:

• means for nutating nuclei within a slice-volume to initiate a TR interval;
• means for repetitively applying 180.degree. NMR RF pulses to further nutate nuclei within the same said slice-volume by substantially 180.degree. at subsequent intervals within the same TR interval and thus to generate a train of NMR spin echoes;
• means for applying a plurality of alternate polarity read-out magnetic gradient pulses between pairs of said 180.degree. NMR RF pulses to produce sub-sequences of gradient echoes;
• and
• means for shifting the time occurrences of gradient echoes within different said sub-sequences so as to more evenly distribute field inhomogeneity and/or chemical phase shift effects over the phase-encoded dimension of k-space.

Apparatus for generating MRI signals from NMR nuclei within an image volume, said apparatus comprising:

• means for nutating nuclei within a slice-volume to initiate a TR interval;
• means for repetitively applying 180.degree. NMR RF pulses to further nutate nuclei within the same said slice-volume by substantially 180.degree. at subsequent intervals within the same TR interval and thus to generate a train of NMR spin echoes;
• means for applying a plurality of alternate polarity read-out magnetic gradient pulses between pairs of said 180.degree. NMR RF pulses to produce sub-sequences of gradient echoes;
• and
• means for applying a phase-decoding magnetic gradient pulse at the conclusion of each said subsequence to return nuclei phase encoding to the origin of k-space prior to application of the next 180.degree. NMR RF nutation pulse.

A method for generating MRI signals from NMR nuclei within an image volume, said method comprising:

• (i) nutating nuclei within a selected volume to initiate a TR interval;
• (ii) applying a 180.degree. NMR RF pulse to further nutate nuclei within said volume by substantially 180.degree. at a subsequent interval to generate a NMR spin echo RF response;
• and
• (iii) applying a plurality of phase-encoding magnetic and gradient pulses and alternate polarity read-out magnetic gradient pulses to produce a sequence of plural gradient echoes wherein the time domain positions of at least some of said gradient echoes is shifted as a result of shifted time domain positions for the phase-encoding magnetic gradient pulses and alternate polarity read-out magnetic gradient pulses from the nominally expected respective Hahn spin echo times to provide controlled increments of undesired phase shifts in contiguous k-space MRI data.

A method for generating MRI signals from NMR nuclei within an image volume, said method comprising:

• (i) nutating nuclei within a selected volume to initiate a TR interval;
• (ii) applying a 180.degree. NMR RF pulse to further nutate nuclei within said volume by substantially 180.degree. at a subsequent interval to generate a NMR spin echo RF response;
• and
• (iii) means for applying a plurality of phase-encoding magnetic and gradient pulses and alternate polarity read-out magnetic gradient pulses to produce a sequence of plural gradient echoes wherein the time domain positions of at least some of said gradient echoes is shifted as a result of shifted time domain positions for the phase-encoding magnetic gradient pulses and alternate polarity read-out magnetic gradient pulses from the nominally expected respective Hahn spin echo times to provide controlled increments of undesired phase shifts in contiguous k-space MRI data.