Nova Patents
USRE35656E

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

Claim Score by NHIP

Read claim 47, the broadest

Abstract

Fast magnetic resonance imaging uses combined gradient echoes and spin echoes. In each of one or more TR intervals, after an initial NMR RF nutation pulse, a sequence of 180 DEG RF nutation pulses is used to refocus the RF response into corresponding string of spin echoes. However, in addition, during the time that such spin echo would normally occur after each such 180 DEG RF nutation pulse, a plurality of alternating polarity read-out magnetic gradient pulses is utilized so as to very rapidly form a sub-sequence of gradient echoes. This fast multi-section MRI sequence utilizes the speed advantages of gradient refocusing while overcoming the image artifacts arising from static field homogeneity and chemical shift. Image contrast is still determined by the T2 contrast in Hahn spin echoes. A novel k-space trajectory temporally modulates signals and demodulates artifacts. The echo responses are selectively phase-encoded and time shifted in occurrence so as to smoothly distribute unwanted phase shift from field inhomogeneity and/or chemical phase shift effects over the entire phase encoded dimension in k-space. The technique can also be extended so as to provide T2-weighted multi-slab three-dimensional volume images.

Term

Term ended

Expired 15 August 2015, 11.1 years ago.

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49 claims: 20 independent, 29 dependent

  1. 1.
    1. A method for generating MRI signals from NMR nuclei within an image volume, said method comprising:PA1 nutating nuclei within a slice-volume to initiate a TR interval;PA1 repetitively applying 180.degree. NMR RF pulses to further nutate nuclei within the same said slice-volume by substantially 180.degree. at subsequent .Iadd.equal time .Iaddend.intervals within the same TR interval .�.and.!..Iadd., each of said equal time intervals being substantially twice the interval between said initial nutating step and the first 180.degree. NMR RF pulse, .Iaddend.thus to generate a train of NMR spin echoes;PA1 .�.between pairs.!. .Iadd.only after each .Iaddend.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 occurring between said 180.degree. NMR RF pulses.
  2. 10.
    10. A method for generating MRI signals, said method comprising:PA1 (a) subjecting NMR nuclei within an image volume to a perturbing NMR RF nutation pulse;PA1 (b) thereafter subjecting said NMR nuclei to PA2 (i) a 180.degree. NMR RF nutation pulse following by PA2 (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 PA2 (iii) repeating steps (i) and (ii) .Iadd.at equal time intervals within the same TR interval, each of said equal intervals being substantially twice the interval between the initial said perturbing pulse and the first 180.degree. NMR RF pulse .Iaddend.to generate a further sequence of gradient echoes .Iadd.without applying alternate polarity read-out magnetic gradient pulses before the first 180.degree. RF nutation pulse.Iaddend..
  3. 16.
    16. A method for generating MRI signals, said method comprising:PA1 (a) subjecting NMR nuclei within an image volume to a perturbing NMR RF nutation pulse;PA1 (b) thereafter subjecting said NMR nuclei to PA2 (i) a 180.degree. NMR RF nutation pulse followed by PA2 (ii) a plurality of alternating polarity magnetic gradient read-out pulses to generate a sequence of gradient echoes, and PA2 (iii) repeating steps (i) and (ii) to generate a further sequence of gradient echoes. PA1 said NMR RF nutation pulses occurring during a slice volume selecting magnetic gradient pulse in a multi-slice sequence, PA1 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 PA2 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.
  4. 2.
    2. A method for generating MRI signals from NMR nuclei within an image volume, said method comprising:PA1 nutating nuclei within a slice-volume to initiate a TR interval;PA1 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;PA1 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 PA1 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.
  5. 20.
    20. A method for generating MRI signals, said method comprising:PA1 (a) subjecting NMR nuclei within an image volume to a perturbing NMR RF nutation pulse;PA1 (b) thereafter subjecting said NMR nuclei to PA2 (i) a 180.degree. NMR RF nutation pulse followed by PA2 (ii) a plurality of alternating polarity magnetic gradient read-out pulses to generate a sequence of gradient echoes, and PA2 (iii) repeating steps (i) and (ii) to generate a further sequence of gradient echoes. PA1 said NMR RF nutation pulses occurring during a slice volume selecting magnetic gradient pulse in a multi-slice sequence, PA1 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 PA1 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.
  6. 21.
    21. A method as in claim .�.19.!. .Iadd.20 .Iaddend.wherein steps (a) and (b) are repeated in each of plural TR intervals to generate additional sequences of gradient echoes.
  7. 22.
    22. Apparatus for generating MRI signals from NMR nuclei within an image volume, said apparatus comprising:PA1 means for nutating nuclei within a slice-volume to initiate a TR interval;PA1 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 .Iadd.equal time .Iaddend.intervals within the same TR interval .�.and.!..Iadd., each of said equal intervals being substantially twice the interval between said initial nutating pulse and the first 180.degree.
  8. 23.
    23. Apparatus for generating MRI signals from NMR nuclei within an image volume, said apparatus comprising:PA1 means for nutating nuclei .Iadd.within .Iaddend.a slice-volume to initiate a TR interval;PA1 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;PA1 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 PA1 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.
  9. 26.
    26. Apparatus for generating MRI signals from NMR nuclei within an image volume, said apparatus comprising:PA1 means for generating a train of NMR spin echoes using a sequence of plural 180.degree. NMR RF nutation pulses;PA1 means for generating a sub-sequence of NMR gradient echoes for each such .�.RF refocused.!. .Iadd.NMR .Iaddend.spin echo by using a sequence of alternating polarity read-out magnetic gradient pulses;PA1 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 or k-space;and PA1 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.
  10. 31.
    31. Apparatus for generating MRI signals, said apparatus comprising:PA1 (a) means for subjecting NMR nuclei within an image volume to a perturbing
  11. 35.
    35. Apparatus for generating MRI signals, said apparatus comprising:PA1 (a) means for subjecting NMR nuclei within an image volume to a perturbing
  12. 39.
    39. Apparatus for generating MRI signals, said apparatus comprising:PA1 (a) means for subjecting NMR nuclei within an image volume to a perturbing
  13. 40.
    40. Apparatus as in claim .�.38.!. .Iadd.39 .Iaddend.wherein means (a) and (b) are repetitively operated to define plural TR intervals generating additional sequences of gradient echoes.
  14. 41.
    41. A method for generating MRI signals from NMR nuclei with an image volume, said method comprising:PA1 nutating nuclei within a slice-volume to initiate a TR interval;PA1 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;PA1 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 PA1 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.
  15. 42.
    42. A method for generating MRI signals from NMR nuclei within an image volume, said method comprising:PA1 nutating nuclei within a slice-volume to initiate a TR interval;PA1 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;PA1 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 PA1 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.
  16. 43.
    43. Apparatus for generating MRI signals from NMR nuclei within an image volume, said apparatus comprising:PA1 means for nutating nuclei within a slice-volume to initiate a TR interval;PA1 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;PA1 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 PA1 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.
  17. 44.
    44. Apparatus for generating MRI signals from NMR nuclei within an image volume, said apparatus comprising:PA1 means for nutating nuclei within a slice-volume to initiate a TR interval;PA1 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;PA1 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 PA1 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.
  18. 45.
    45. A method for generating MRI signals from NMR nuclei within an image volume, said method comprising:PA1 (i) nutating nuclei within a selected volume to initiate a TR interval;PA1 (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 PA1 (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 or 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.
  19. 47.
    �.A method.!. .Iadd.Apparatus .Iaddend.for generating MRI signals from
  20. 5.
    5. A method for generating MRI signals from NMR nuclei within an image volume, said method comprising:PA1 generating a train of NMR spin echoes using a sequence of plural 180.degree. NMR RF nutation pulses;PA1 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;PA1 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 PA1 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.
Independent claims20