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Multiple gradient echo pulse sequence for acquisition of NMR angiograms

  • US 5,038,783 A
  • Filed: 03/22/1990
  • Issued: 08/13/1991
  • Est. Priority Date: 02/11/1987
  • Status: Expired due to Fees
First Claim
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1. A method for acquiring a nuclear magnetic resonance (NMR) angiographic image of flowing material in at least a selected portion of a sample, comprising the steps of:

  • (a) immersing the sample in a main static magnetic field;

    (b) nutating, in the initial part of each of a first sequence and a second sequence of a sequential pair of imaging sequences for each of a multiplicity S of regions of said selected sample portion, the spins of all nuclei of a selected species;

    (c) applying a pair of alternating-polarity flow-encoding signal pulses in a first magnetic field gradient impressed upon the sample, in a first direction selected to establish one axis of the NMR angiographic projection image, to cause a resulting NMR response echo signal from the spin of a moving nucleus to differ from the NMR response echo signal resulting from the spin of a substantially stationary nucleus, each of the flow-encoding pulses in the first sequence of each pair having a polarity opposite to the polarity of the like-positioned flow-encoding pulse in the second sequence of each pair, and wherein this step (c) comprises the steps of;

    (c1) applying no flow-encoding signal pulses prior to a first response data acquisition time interval in each sequence;

    (c2) applying, after the first response interval in each sequence and prior to a second response data acquisition time interval, a pair of alternating-polarity flow-encoding signal pulses in a first magnetic field gradient in a first flow-encoding gradient direction; and

    (c3) repeating steps (c1) and (c2) in the second sequence of each pair;

    (d) acquiring, response to a readout magnetic field gradient impressed upon the sample in a second direction, substantially orthogonal to the first direction, a set of data from the NMR response echo signal evoked, from at least the sample portion, in each different one of two response data acquisition time intervals of each of the first and second sequences;

    (e) subtracting the data in each j-th one, where 1≦

    j≦

    2, of the NMR response signal data sets acquired in a selected one of the first and second sequences, from the data in the like-numbered j-th data set of the remaining one of the first and second sequences, to generate a j-th one of two difference data sets from which response data obtained from stationary nuclei has been substantially removed, and wherein this step (e) comprises the steps of;

    (e1) subtracting a data set S12, from the second response acquisition interval in the first sequence, from a data set S11 from the first response acquisition interval in the first sequence, to form a data set S1 ;

    (e2) subtracting a data set S22, from the second response acquisition interval in the second sequence, from a data set S21, from the first response acquisition interval in the second sequence, to form a data set S2 ; and

    (e3) subtracting the data set S2 from the data set S1 to obtain a difference data set; and

    (f) generating, responsive to all difference data sets, an angiographic projection image lying in a plane having a preselected relationship with respect to the first and second directions, wherein this step (f) includes the step of displaying an angiographic image having increased suppression of motion artifacts.

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