Multiple-echo, multiple-view NMR angiography
First 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 an 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 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;
each of the flow-encoding pulses in the first sequence of each pair having a polarity 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, and varied to be different in each j-th one, where 1≦
j≦
N, of a plurality N of response data acquisition time intervals of a sequence, with the second direction being the same in each like-numbered j-th acquisition interval of both sequences of all sequence pairs, a set of data from the NMR response echo signal evoked, from the same sample portion, in each different one of the plurality N of acquisition time intervals of each of the first and sequences;
generating a dephasing pulse in the readout gradient prior to each of the N acquisition time intervals in each sequence;
generating a rephasing pulse in the readout gradient after each of the first (N-1) acquisition time intervals in each sequence; and
providing each rephasing pulse with substantially the same amplitude as the associated dephasing pulse;
(e) subtracting, for each different j-th one of the N different acquisition time intervals, the data acquired in the j-th acquisition interval of one sequence from the data acquired in the like-numbered j-th acquisition interval of the other sequence of each sequence pair, to generate a j-th one of N different-pair difference sets from which response data obtained from stationary nuclei has been substantially removed; and
(f) generating N different angiographic images, with the j-th image being generated from all of the j-th pair difference sets and with each j-th image lying in a plane having a preselected relationship with respect to the first direction and the different second direction for that j-th image.
1 Assignment
0 Petitions
Accused Products
Abstract
Several sequences of radio-frequency and magnetic field gradients are presented for obtaining from a sample multiple response echo signals from which to obtain a plurality of independent angiograms, which can be combined or separately analyzed to provide more information than an individual angiogram, but in substantially the same amount of time as a single angiogram. For example, a series of angiograms, each with a different projection axis, can be obtained in the time required to obtain a single angiogram using a single echo method. If the view angle of each echo is the same, then the acquired angiograms can be added to enhance the signal-to-noise ratio. Anothe pulse sequence simultaneously obtains two or more angiograms, each sensitive to one of two orthogonal flow components of the overall blood flow, the angiograms are then added to give an angiogram which is sensitive to total flow in all directions. Multiple velocity ranges are accommodated in a fourth sequence form.
-
Citations
13 Claims
-
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 an 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 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;
each of the flow-encoding pulses in the first sequence of each pair having a polarity 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, and varied to be different in each j-th one, where 1≦
j≦
N, of a plurality N of response data acquisition time intervals of a sequence, with the second direction being the same in each like-numbered j-th acquisition interval of both sequences of all sequence pairs, a set of data from the NMR response echo signal evoked, from the same sample portion, in each different one of the plurality N of acquisition time intervals of each of the first and sequences;
generating a dephasing pulse in the readout gradient prior to each of the N acquisition time intervals in each sequence;
generating a rephasing pulse in the readout gradient after each of the first (N-1) acquisition time intervals in each sequence; and
providing each rephasing pulse with substantially the same amplitude as the associated dephasing pulse;(e) subtracting, for each different j-th one of the N different acquisition time intervals, the data acquired in the j-th acquisition interval of one sequence from the data acquired in the like-numbered j-th acquisition interval of the other sequence of each sequence pair, to generate a j-th one of N different-pair difference sets from which response data obtained from stationary nuclei has been substantially removed; and (f) generating N different angiographic images, with the j-th image being generated from all of the j-th pair difference sets and with each j-th image lying in a plane having a preselected relationship with respect to the first direction and the different second direction for that j-th image. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
-
Specification