MRI compensated for spurious rapid variations in static magnetic field during a single MRI sequence

Claim 2

A magnetic resonance imaging (MRI) method providing compensation for variations of a nominally static B o field in an imaged volume during an MRI sequence, said method comprising the steps of: (a) generating and recording MRI image data which is phase-encoded by magnetic gradient pulses during a sequence of plural successive TR intervals to yield an image of nuclear magnetic resonant (NMR) nuclei populations within said image volume after multi-dimensional transformation; (b) during each said Tr interval, additionally generating and recording B o field calibration data by omitting at least one of said magnetic gradient pulses during recordation of NMR responses; (c) processing said calibration data to generate correction data required to compensate MRI image data taken during each TR interval for B o magnetic field variations in the nominally static B o field; (d) phase/frequency shifting said MRI image data for each TR interval in accordance with said correction data; and (e) multi-dimensionally transforming the corrected MRI image data resulting from step (d) to produce an image having reduced artifacts caused by variations in the nominally static B o field during said MRI sequence.

Claim 3

A magnetic resonance imaging method as in claim 1 wherein: (i) as a part of step (a), during each TR interval NMR responses are selectively elicited from M plural successive slice volumes for a given φ phase encoding value of a first-dimension magnetic gradient pulse, a second-dimension phase encoding magnetic gradient pulse being present during said NMR responses; and (ii) as a part of step (b), during each TR interval, a further NMR response is selectively elicited from at least one further M+1 slice volume but without said magnetic gradient pulses being present during said further NMR response.

Claim 4

A magnetic resonance imaging method as in claim 1 wherein: (i) as part of step (a), during each TR interval NMR responses are selectively elicited from plural first slice volumes for a given φ phase encoding value of a first-dimension magnetic gradient pulse, a second-dimension phase encoding magnetic gradient pulse being present during said NMR responses; and (ii) as a part of step (b), during each TR interval further NMR responses are selectively elicited from further plural second slice volumes but without said second-dimension magnetic gradient pulse being present during said further NMR responses; said second slice volumes being interleaved with said first slice volumes.

Claim 5

A magnetic resonance imaging method as in claim 1 wherein: (i) as part of step (a), during each TR interval NMR responses are selectively elicited from M plural successive slice volumes for a given φ phase encoding value of a first-dimension magnetic gradient pulse, a second-dimension phase encoding magnetic gradient pulse being present during said NMR responses; (ii) as part of step (b), during each TR interval, further NMR responses are selectively elicited from at least one further M+1 slice volume but without said magnetic gradient pulses being present during said further NMR responses; and (iii) said step (ii) being repeatedly performed within each TR interval and interleaved with elicitation of NMR responses from said M plural successive slice volumes in step (i).

Claim 6

A magnetic resonance imaging method as in claim 1 wherein: (i) as a part of step (a), during each TR interval NMR responses are selectively elicited from M plural successive slice volumes for a given φ phase encoding value of a first-dimension magnetic gradient pulse, a second-dimension phase encoding magnetic gradient pulse being present during said NMR responses; and (ii) as a part of step (b), during each TR interval immediately after eliciting each NMR response in step (i), removing residual phase encoding effects and eliciting a further NMR response from the same slice volume but without said magnetic gradient pulses being present during said further NMR response.

Claim 7

A magnetic resonance imaging method as in claim 2, 3, 4 or 5 wherein only a substantially truncated portion of said further NMR response is recorded as compared with the recorded NMR responses for step (a).

Claim 8

A magnetic resonance imaging method as in claim 6 wherein the duration of NMR responses recorded as part of step (b) are truncated to less than 10% of the duration NMR responses recorded as a art of step (a).

Claim 9

A magnetic resonance imaging method a in claim 1 wherein NMR responses are recorded in step (b) truncated to a substantially decreased duration compared to NMR responses recorded in step (a).

Claim 10

A magnetic resonance imaging method as in claim 8 wherein the duration of NMR responses recorded as part of step (b) are truncated to less than 10% of the duration of NMR responses recorded as a part of step (a).

Claim 11

A magnetic resonance imaging method as in claim 1 wherein step (a) includes eliciting NMR responses simultaneously from an entire imaged volume using a sequence having three dimensions of spatial-domain phase encoding obtained by varying magnetic gradient pulses.

Claim 12

Magnetic resonance imaging (MRI) apparatus providing compensation for variations of a nominally static B o field in an imaged volume during an MRI sequence, said apparatus comprising: (a) means for generating and recording MRI image data which is phase-encoded by magnetic gradient pulses during a sequence of plural successive TR intervals to yield an image of nuclear magnetic resonant (NMR) nuclei populations within said image volume after multi-dimensional transformation; (b) means for, during each said TR interval, additionally generating and recording B o field calibration data by omitting at least one of said magnetic gradient pulses during recordation of NMR responses; (c) means for processing said calibration data to generate phase/frequency correction data required to compensate MRI image data taken during each TR interval for B o magnetic field variations in the nominally static B o field; (d) means for phase/frequency shifting said MRI image data for each TR interval in accordance with said phase/frequency correction data; and (e) means for multi-dimensionally transforming the corrected MRI image data to produce an image having reduced artifacts caused by variations in the nominally static B o field during said MRI sequence.

Claim 13

Magnetic resonance imaging (MRI) apparatus providing compensation for variations of a nominally static B o field in an imaged volume during an MRI sequence, said apparatus comprising: (a) means for generating and recording MRI image data which is phase-encoded by magnetic gradient pulses during a sequence of plural successive TR intervals to yield an image of nuclear magnetic resonant (NMR) nuclei populations within said image volume after multi-dimensional transformation; (b) means for, during each said TR interval, additionally generating and recording B o field calibration data by omitting at least one of said magnetic gradient pulses during recordation of NMR responses; (c) means for processing said calibration data to generate phase/frequency correction data required to compensate MRI image data taken during each TR interval for B o magnetic field variations in the nominally static B o field; (d) means for phase/frequency shifting said MRI image data for each TR interval in accordance with said phase/frequency correction data; and (e) means for multi-dimensionally transforming the corrected MRI image data to produce an image having reduced artifacts caused by variations in the nominally static B o field during said MRI sequence.

Claim 14

Magnetic resonance imaging apparatus as in claim 11 wherein: (i) as a part of means (a), means are provided for selectively eliciting NMR responses during each TR interval from M plural successive slice volumes for a given φ phase encoding value of a first-dimension magnetic gradient pulse, a second-dimension phase encoding magnetic gradient pulse being present during said NMR responses; and (ii) as a part of means (b), means are provided for selectively eliciting a further NMR response during each TR interval from at least one further M+1 slice volume but without said magnetic gradient pulses being present during said further NMR response.

Claim 15

Magnetic resonance imaging apparatus as in claim 11 wherein: (i) as part of means (a), means are provided for selectively eliciting NMR response during each TR interval from plural first slice volumes for a given φ phase encoding value of a first-dimension magnetic gradient pulse, a second-dimension phase encoding magnetic gradient pulse being present during said NMR responses; and (ii) as a part of means (b), means are provided for selectively eliciting further NMR responses during each TR interval from further plural second slice volumes but without said magnetic gradient pulses being present during said further NMR responses. said second slice volumes being interleaved with said first slice volumes.

Claim 16

Magnetic resonance imaging apparatus as in claim 11 wherein: (i) as part of means (a), means are provided for selectively eliciting NMR responses during each TR interval from M plural successive slice volumes for a given φ phase encoding value of a first-dimension magnetic gradient pulse, a second-dimension phase encoding magnetic gradient pulse being present during said NMR responses; (ii) as part of means (b), means are provided for selectively eliciting further NMR responses during each TR interval from at least one further M+1 slice volume but without said magnetic gradient pulses being present during said further NMR responses; and (iii) said eliciting of further NMR responses being repeatedly performed within each TR interval and interleaved with elicitation of NMR responses from said M plural successive slice volumes.

Claim 17

Magnetic resonance imaging apparatus as in claim 11 wherein: (i) as a part of means (a), means are provided for selectively eliciting first NMR responses during each TR interval from M plural successive slice volumes for a given φ phase encoding value of a first-dimension magnetic gradient pulse, a second-dimension phase encoding magnetic gradient pulse being present during said NMR responses; and (ii) as a part of means (b), means are provided for selectively eliciting a further NMR response during each TR interval immediately after eliciting each first NMR response from the same slice volume but without said magnetic gradient pulses being present during said further NMR response and after removing residual phase encoding effects.

Claim 18

Magnetic resonance imaging apparatus as in claim 12, 13, 14 or 15 wherein the means for recording said further NMR responses records only a substantially truncated portion of said further NMR response as compared with the recorded NMR responses used for image reconstruction.

Claim 19

Magnetic resonance imaging apparatus as in claim 16 wherein the duration of truncated recorded NMR responses are truncated to less than 10% of the duration NMR responses recorded for imaging purposes.

Claim 20

Magnetic resonance imaging apparatus as in claim 11 wherein truncated recorded NMR responses truncated to a substantially decreased duration compared to NMR responses recorded for imaging purposes.

Claim 21

Magnetic resonance imaging apparatus as in claim 18 wherein the duration of truncated recorded NMR responses are truncated to less than 10% of the duration of NMR responses recorded for imaging purposes.

Claim 22

Magnetic resonance imaging apparatus as in claim 11 wherein means (a) includes means for eliciting NMR responses simultaneously from an entire imaged volume using a sequence having three dimensions of spatial-domain phase encoding obtained by varying magnetic gradient pulses.

Claim 23

A magnetic resonance imaging method as in claim 1 wherein step (b) is performed at times and volume locations as depicted in at least one of FIGS. 13A through 13G.

Claim 24

A magnetic resonance imaging method as in claim 21 wherein step (a) comprises acquisition of image data using at least one of the following types of NMR RF responses: (a) spin-echo (SE), (b) gradient reversal echo (GRE), (c) free induction decay (FID).

Claim 25

A magnetic resonance imaging method as in claim 21 or 22 wherein step (b) comprises acquisition of calibration data using at least one of the following types of NMR RF responses: (a) spin echo (SE), (b) free induction decay (FID).

Claim 26

A magnetic resonance imaging method as in claim 1 wherein step (c) comprises processing of calibration data using at least one of the following types of processes: (a) Fourier Transformation; (b) determining slope of the phase of the NMR RF response; (c) determining only the fundamental frequency of the NMR RF response.

Claim 27

Magnetic resonance imaging apparatus as in claim 11 wherein means (b) is active at times and volume locations as depicted in at least one of FIGS. 13A through 13G.

Claim 28

Magnetic resonance imaging apparatus as in claim 25 wherein means (a) comprises means for acquiring image data using at least one of the following types of NMR RF responses: (a) spin-echo (SE), (b) gradient reversal echo (GRE), (c) free induction decay (FID).

Claim 29

Magnetic resonance imaging apparatus as in claim 25 or 26 wherein means (b) comprises means for acquiring calibration data using at least one of the following types of NMR RF responses: (a) spin echo (SE), (b) free induction decay (FID).

Claim 30

Magnetic resonance imaging apparatus as in claim 11 wherein means (c) comprises means for processing of calibration data using at least one of the following types of processes: (a) Fourier Transformation; (b) determining slope of the phase of the NMR RF response; (c) determining only the fundamental frequency of the NMR RF response.