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Multiple-echo NMR angiography for enhancement of signal-to noise ratio

  • US 5,022,398 A
  • Filed: 03/22/1990
  • Issued: 06/11/1991
  • Est. Priority Date: 02/11/1987
  • Status: Expired due to Fees
First Claim
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1. A method for acquiring at least one 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 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;

    (d) acquiring, responsive 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 a plurality M of response data acquisition time intervals of each of the first and second sequences, and including the substeps of;

    obtaining all M of the response data sets in each sequence for a single common readout second direction; and

    summing the data values for all M response data sets in each sequence to obtain a single summed data set for that common second direction and that sequence;

    (e) subtracting the summed data set from one of the first and second sequences from the summed data set from the other sequence of the sequence pair, to generate the difference data set for that pair; and

    (f) generating, responsive to all difference data sets, each of at least one angiographic projection image, each lying in a plane having a preselected relationship with respect to the first and second directions.

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