US 2011/0210733 A1Published application

B1-robust and t1-robust species suppression in mri

AssigneesKabushiki Kaisha Toshiba, Toshiba Medical Systems Corporation

InventorsAndrew J. WHEATON, James B. MURDOCH

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Abstract

An MRI multi-echo data acquisition sequence (REFUSAL=REFocusing Used to Selectively Attenuate Lipids) includes a spectrally-selective re-focusing RF pulse. The REFUSAL pulse can be non-spatially selective or spatially-selective. The REFUSAL pulse selectively refocuses water spins and avoids refocusing lipid spins. The REFUSAL pulse ideally maximizes refocusing for water and minimizes any lipid refocusing, with built-in robustness to B0-inhomogeneity and B1-inhomogeneity. Following the REFUSAL pulse, the remainder of the echo train continues in a conventional fashion. Only those spins that were refocused with the spectrally selective REFUSAL pulse continue to evolve coherently and generate a train of echoes. Those spins that were minimally refocused are spoiled and thus do not contribute signal to the final image. To incorporate a longer duration REFUSAL pulse, the echo spacing can be made non-uniform such that the first echo spacing is longer than the remainder of the echo spacings in the echo train.

Claims26

Dependent claims

An MRI method comprising using an MRI system that has been configured to:

apply, to an object to be imaged, an initial NMR RF nutation pulse which nutates by approximately equal degrees both a first and a second species of NMR nuclei in at least a portion of the object to be imaged;
thereafter apply a spectrally-selective 180° RF nutation pulse to selectively nutate said first species of NMR nuclei by substantially 180° while substantially avoiding nutation of said second different species of nuclei, thereby selectively causing subsequent NMR refocusing of said first species but not of said second species;
thereafter apply a time-spaced sequence of 180° NMR RE refocusing pulses which nutate both said first and second species by approximately equal degrees to successively refocus said first species of NMR nuclei but not said second species, said sequence of refocusing pulses also being associated with phase-encoding magnetic gradient pulses to produce a respectively corresponding train of phase-encoded NMR RE spin echo responses emanating from said first species of NMR nuclei;
and
acquire said train of RE spin echo responses as MRI data and to store data representing same in computer-readable memory and/or using said MRI data to produce an image of said first species of nuclei.

2 more elements

An MRI apparatus comprising:

an RF transmitter configured to apply, to an object to be imaged, an initial NMR RF nutation pulse which nutates by approximately equal degrees both a first and a second species of NMR nuclei in at least a portion of the object to be imaged;
said RF transmitter also being configured to thereafter apply a spectrally-selective 180° RF nutation pulse to selectively nutate said first species of NMR nuclei by substantially 180° while substantially avoiding nutation of said second different species of nuclei, thereby causing subsequent NMR refocusing of said first species but not of said second species;
said RF transmitter also being configured to thereafter apply a time-spaced sequence of 180° RF refocusing pulses which nutate both said first and second species by approximately equal degrees to successively refocus said first species of NMR nuclei but not said second species, said sequence of refocusing pulses also being associated with phase-encoding magnetic gradient pulses to produce a respectively corresponding train of phase-encoded NMR RE spin echo responses emanating from said first species of NMR nuclei;
and
an RF receiver configured to acquire said train of RF spin echo responses as MRI data and to store data representing same in computer-readable memory and/or using said MRI data to produce an image of said first species of nuclei.

2 more elements

Apparatus for designing an MRI echo train that is spectrally-selective, B1-robust and T1-robust, said apparatus comprising a programmed computer system configured to:

(a) accept input design specification data effectively defining an NMR refocusing bandwidth for a first NMR species and an NMR rejection bandwidth for a second NMR species;
(b) calculate a spectrally-selective 180° NMR RF nutation pulse design for selectively nutating said first species of NMR nuclei by substantially 180° while substantially avoiding nutation of said second different species of nuclei, thereby causing NMR refocusing of said first species but not of said second species;
(c) define a complete MRI data acquisition sequence using said calculated spectrally-selective RE nutation pulse, which is to be applied without any concurrently applied magnetic gradient, followed by a time-spaced sequence of 180° RF refocusing pulses and phase-encoding magnetic gradient pulses to successively refocus said first species of NMR nuclei and to produce a respectively corresponding train of phase-encoded NMR RE spin echo responses emanating from said first species of NMR nuclei;
and
(d) output to computer-readable memory said defined MRI data acquisition sequence for use in a diagnostic MRI scan.

2 more elements

Dependencies are inferred from the claim text.