Magnetic resonance acoustography
First Claim
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1. A method for producing an NMR image of a subject which is affected by spin motion, the steps comprising:
- a) applying a polarizing magnetic field to the subject;
b) applying an RF excitation field to the subject to produce transverse magnetization of spins in an excitation column oriented along an excitation axis;
c) applying a magnetic field gradient to the subject to motion sensitize the transverse magnetization, the magnetic field gradient waveform being shaped to contain a range of frequencies that includes a frequency at which the transversely magnetized spins change their direction of motion;
d) acquiring an NMR signal from the excitation column;
e) reconstructing an image by Fourier transforming the acquired NMR signal; and
f) producing a phase image from the reconstructed image.
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Abstract
Magnetic resonance acoustography images are acquired in real time using a one-dimensional magnetic resonance elastography (MRE) pulse sequence in which a column of tissue is excited. A spin-echo MRE pulse sequence and a gradient-echo MRE pulse sequence are described which employ a broadband motion sensitizing gradient that enables an asynchronous transducer to be used to produce the oscillatory stress in the subject tissues.
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Citations
20 Claims
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1. A method for producing an NMR image of a subject which is affected by spin motion, the steps comprising:
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a) applying a polarizing magnetic field to the subject;
b) applying an RF excitation field to the subject to produce transverse magnetization of spins in an excitation column oriented along an excitation axis;
c) applying a magnetic field gradient to the subject to motion sensitize the transverse magnetization, the magnetic field gradient waveform being shaped to contain a range of frequencies that includes a frequency at which the transversely magnetized spins change their direction of motion;
d) acquiring an NMR signal from the excitation column;
e) reconstructing an image by Fourier transforming the acquired NMR signal; and
f) producing a phase image from the reconstructed image. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A method for producing an NMR image of a subject which comprises:
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a) applying a polarizing magnetic field to the subject;
b) applying an RF excitation field to the subject in the presence of a gradient field to produce transverse magnetization of spins in an excitation column oriented along an excitation axis in the subject;
c) applying a motion sensitizing gradient having an amplitude component which oscillates in synchronism with the applied oscillatory stress;
d) reconstructing a one-dimensional image by Fourier transforming the acquired NMR signal;
e) producing a first one-dimensional phase image from the one-dimensional image;
f) repeating steps a)-e) with the phase of the motion sensitizing gradient reversed to produce a second one-dimensional image; and
g) producing a one-dimensional phase difference image by subtracting said first and second one-dimensional phase images. - View Dependent Claims (10, 11, 12, 13, 14)
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15. A method for producing an NMR image of a subject which is affected by spin motion, the steps comprising:
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a) applying a polarizing magnetic field to the subject;
b) applying an RF excitation field to the subject to produce transverse magnetization of spins in an excitation column oriented along an excitation axis;
c) applying a magnetic field gradient to the subject to motion sensitize the transverse magnetization, the magnetic field gradient waveform being shaped to contain a selected frequency;
d) acquiring an NMR signal from the excitation column;
e) reconstructing a reference image by Fourier transforming the acquired NMR signal;
f) producing a reference phase image from the reconstructed reference image;
g) applying an oscillatory stress to the subject to impart motion in the transversely magnetized spins at said selected frequency;
h) repeating steps a)-d) to acquire a second NMR signal;
i) reconstructing an image by Fourier transforming the acquired second NMR signal;
j) producing a phase image from the reconstructed image;
k) producing a phase difference image by calculating the difference between the phase image and the reference phase image. - View Dependent Claims (16, 17, 18, 19, 20)
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Specification