Magnetic resonance acoustography
First Claim
Patent Images
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 a one-dimensional image by Fourier transforming the acquired NMR signal; and
f) producing a one-dimensional phase image from the reconstructed one-dimensional image.
1 Assignment
0 Petitions
Accused Products
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.
-
Citations
20 Claims
-
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 a one-dimensional image by Fourier transforming the acquired NMR signal; and
f) producing a one-dimensional phase image from the reconstructed one-dimensional image. - View Dependent Claims (2, 3, 4, 5, 6, 7)
-
-
8. 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 RE 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;
g) setting the spins in oscillatory motion with a transducer driven by a signal of a desired frequency;
h) repeating steps a)-f) to acquire and reconstruct a second phase image;
i) subtracting the first and second phase images to produce a phase difference image;
j) repeating steps g)-i) to produce a plurality of phase difference images in substantially real time; and
in which each phase difference image is a line which is color coded along its length according to the phase at locations along the excitation axis, and a plurality of the color coded lines are rendered side-by-side to produce a waterfall image.
-
-
9. A method for producing an NMR image of a subject which comprises:
-
a) applying a polarizing magnetic field to the subject;
b) applying an oscillatory stress to the subject to impart motion to spins therein;
c) 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;
d) applying a motion sensitizing gradient having an amplitude component which oscillates in synchronism with the applied oscillatory stress;
e) reconstructing a one-dimensional image by Fourier transforming the acquired NMR signal;
f) producing a first one-dimensional phase image from the one-dimensional image;
g) repeating steps a)-e) with the phase of the motion sensitizing gradient reversed to produce a second one-dimensional image; and
h) 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. A method for producing an NMR image of a subject which comprises:
-
a) applying a polarizing magnetic field to the subject;
b) applying an oscillatory stress to the subject to impart motion to spins therein;
c) 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;
d) applying a motion sensitizing gradient having an amplitude component which oscillates in synchronism with the applied oscillatory stress;
e) reconstructing a one-dimensional image by Fourier transforming the acquired NMR signal;
f) producing a first one-dimensional phase image from the one-dimensional image;
g) repeating steps a)-e) with the phase of the motion sensitizing gradient reversed to produce a second one-dimensional image;
h) producing a one-dimensional phase difference image by subtracting said first and second one-dimensional phase images;
i) repeating steps a)-h) to produce a plurality of one-dimensional phase difference images in substantially real time; and
in which each phase difference image is rendered on a display as a line which is color coded along its length according to the phase at locations along the excitation axis, and a plurality of the color coded lines are rendered side-by-side to produce a waterfall image.
-
-
15. 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 selected frequency;
d) acquiring an NMR signal from the excitation column;
e) reconstructing a one-dimensional reference image by Fourier transforming the acquired NMR signal;
f) producing a one-dimensional reference phase image from the reconstructed one-dimensional 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 a one-dimensional image by Fourier transforming the acquired second NMR signal;
j) producing a one-dimensional phase image from the reconstructed one-dimensional image;
k) producing a one-dimensional phase difference image by calculating the difference between the one-dimensional phase image and the one-dimensional reference phase image. - View Dependent Claims (16, 17)
-
-
18. 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 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;
l) repeating steps a)-k) to acquire and reconstruct additional chase difference images in substantially real time; and
in which each phase difference image is displayed as a line which is color coded according to the phase difference at locations along the excitation axis. - View Dependent Claims (19, 20)
-
Specification