Multiple-echo NMR angiography with multiple-velocity images

Claim 1

A method for acquiring a plurality of nuclear magnetic resonance (NMR) angiographic images 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, prior to each of a plurality N of response acquisition time intervals, 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 each of the NMR angiographic projection images, 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; all of the pulse pairs in the flow-encoding signal having the same polarity of first pulses and 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, said first direction being a flow-encoding direction; (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 N 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≦N, 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 N difference data sets from which response data obtained from stationary nuclei has been substantially removed; and (f) generating, responsive to all difference data sets, a plurality of angiographic projection images, each lying in a plane having a preselected relationship with respect to the first and second directions, and displaying from each of the N resulting difference data sets an angiographic image having information about a sample portion fluid flow velocity different from the velocity information displayable from any other one of the remaining difference data sets.

Claim 2

A method for acquiring a plurality of nuclear magnetic resonance (NMR) angiographic images 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, prior to each of a plurality N of response acquisition time intervals, 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 each of the NMR angiographic projection images, 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; all of the pulse pairs in the flow-encoding signal having the same polarity of first pulses and 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, said first direction being a flow-encoding direction; (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 N 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≦N, 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 N difference data sets from which response data obtained from stationary nuclei has been substantially removed; and (f) generating, responsive to all difference data sets, a plurality of angiographic projection images, each lying in a plane having a preselected relationship with respect to the first and second directions, and displaying from each of the N resulting difference data sets an angiographic image having information about a sample portion fluid flow velocity different from the velocity information displayable from any other one of the remaining difference data sets.