Rapid-scan NMR angiography

Claim 1

A method for rapidly acquiring at least one nuclear magnetic resonance (NMR) angiographic projection image of flowing material in at least a selected portion of a living organism sample having a cardiac cycle occuring at a cardiac rate, comprising the steps of: (a) immersing the sample in a main static magnetic field; (b) nutating by an angle α which is less than 90°, 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 phase-encoding amplitudes operating upon said selected sample portion, the spins of all nuclei of a selected species and with a repetition time interval T R between sequential nutations being less than the reciprocal of the cardiac rate; (c) applying, after each nutation, a flow-encoding subsequence comprising a pair of alternating-polarity signal pulses in a first magnetic field gradient impressed upon the sample, in a first direction selected to cause a resulting NMR response echo signal from the spin of a moving nucleus to different 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) then acquiring, responsive to an imaging subsequence evoking an NMR response echo signal from at least the sample portion, a set of data in a response data acquisition time interval of each of the first and second sequences; (e) subtracting the data in each of the NMR response signal data sets acquired in a selected one of the first and second sequences from the data in the data set of the remaining one of the first and second sequences, to generate a difference data set from which response data obtained from stationary nuclei has been substantially removed; (f) repeating steps (b)-(e) a plurality N times, with N set approximately equal to 60(M)/(2T R (PR)), where M is a positive number and PR is the cardiac rate, to generate a plurality N of difference data sets for each of the different S amplitudes; (g) averaging all N difference data sets for each of the S amplitudes, to obtain a single average data set for each of the S amplitudes; and (h) generating, responsive to all S average data sets, each of at least one angiographic projection image, each lying in a plane having a preselected relationship with respect to the first direction.

Claim 2

A method for rapidly acquiring at least one nuclear magnetic resonance (NMR) angiographic projection image of flowing material in at least a selected portion of a living organism sample having a cardiac cycle occuring at a cardiac rate, comprising the steps of: (a) immersing the sample in a main static magnetic field; (b) nutating by an angle α which is less than 90°, 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 phase-encoding amplitudes operating upon said selected sample portion, the spins of all nuclei of a selected species and with a repetition time interval T R between sequential nutations being less than the reciprocal of the cardiac rate; (c) applying, after each nutation, a flow-encoding subsequence comprising a pair of alternating-polarity signal pulses in a first magnetic field gradient impressed upon the sample, in a first direction selected to cause a resulting NMR response echo signal from the spin of a moving nucleus to different 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) then acquiring, responsive to an imaging subsequence evoking an NMR response echo signal from at least the sample portion, a set of data in a response data acquisition time interval of each of the first and second sequences; (e) subtracting the data in each of the NMR response signal data sets acquired in a selected one of the first and second sequences from the data in the data set of the remaining one of the first and second sequences, to generate a difference data set from which response data obtained from stationary nuclei has been substantially removed; (f) repeating steps (b)-(e) a plurality N times, with N set approximately equal to 60(M)/(2T R (PR)), where M is a positive number and PR is the cardiac rate, to generate a plurality N of difference data sets for each of the different S amplitudes; (g) averaging all N difference data sets for each of the S amplitudes, to obtain a single average data set for each of the S amplitudes; and (h) generating, responsive to all S average data sets, each of at least one angiographic projection image, each lying in a plane having a preselected relationship with respect to the first direction.