Method of acquiring NMR angiograms in selected flow component directions
First Claim
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 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;
(c1) applying, prior to a first of a plurality N of response data acquisition time intervals in each sequence, a pair of alternating-polarity flow-encoding signal pulses in a first magnetic field gradient impressed upon the sample in a first one of a pair of flow-encoding directions;
(c2) applying, after the first response interval in each sequence and prior to a second response data acquisition time interval, another pair of alternating-polarity flow-encoding signal pulses which are the inverse of the pulse pair of step (c1) and are in the first magnetic field gradient in the same first one of the flow-encoding directions;
(c3) applying, prior to the second response interval in each sequence, a pair of alternating polarity flow-encoding signal pulses in the remaining one of the flow-encoding directions in a second magnetic field gradient substantially orthogonal to the first magnetic field gradient;
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;
each flow-encoding direction being selective to establish one axis of an associated NMR angiographic projection image in which a resulting NMR response echo signal from the spin of a moving nucleus differs from the NMR response echo signal resulting from the spin of a substantially stationary nucleus;
(d) acquiring, responsive to a readout magnetic field gradient impressed upon the sample in a direction substantially independent of the flow-encoding directions, a set of data from the NMR response echo signal evoked, from at least the sample portion, in each different one of the plurality N of response data acquisition time intervals of each of the first and second sequences;
(e) subtracting the data in each first and second sets of data from the NMR response echo signal evoked in the first sequence, from the data in the like-numbered data set of the second sequence, to generate a respective first one IA and a second one IB of a pair of difference data sets from which response data obtained from stationary nuclei has been substantially removed; and
(f) processing the difference data IA set in the first direction and the difference data IB set in the second direction to obtain a final difference data set It having a value given to It =((IA)2 +(IB)2)1/2, to display a total-flow angiogram.
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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. Another 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.
20 Citations
8 Claims
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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:
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(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; (c1) applying, prior to a first of a plurality N of response data acquisition time intervals in each sequence, a pair of alternating-polarity flow-encoding signal pulses in a first magnetic field gradient impressed upon the sample in a first one of a pair of flow-encoding directions; (c2) applying, after the first response interval in each sequence and prior to a second response data acquisition time interval, another pair of alternating-polarity flow-encoding signal pulses which are the inverse of the pulse pair of step (c1) and are in the first magnetic field gradient in the same first one of the flow-encoding directions; (c3) applying, prior to the second response interval in each sequence, a pair of alternating polarity flow-encoding signal pulses in the remaining one of the flow-encoding directions in a second magnetic field gradient substantially orthogonal to the first magnetic field gradient;
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;
each flow-encoding direction being selective to establish one axis of an associated NMR angiographic projection image in which a resulting NMR response echo signal from the spin of a moving nucleus differs from the NMR response echo signal resulting from the spin of a substantially stationary nucleus;(d) acquiring, responsive to a readout magnetic field gradient impressed upon the sample in a direction substantially independent of the flow-encoding directions, a set of data from the NMR response echo signal evoked, from at least the sample portion, in each different one of the plurality N of response data acquisition time intervals of each of the first and second sequences; (e) subtracting the data in each first and second sets of data from the NMR response echo signal evoked in the first sequence, from the data in the like-numbered data set of the second sequence, to generate a respective first one IA and a second one IB of a pair of difference data sets from which response data obtained from stationary nuclei has been substantially removed; and (f) processing the difference data IA set in the first direction and the difference data IB set in the second direction to obtain a final difference data set It having a value given to It =((IA)2 +(IB)2)1/2, to display a total-flow angiogram. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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Specification