Simultaneous imaging of multiple spectroscopic components with magnetic resonance

• US 5,446,384 A
• Filed: 12/27/1993
• Issued: 08/29/1995
• Est. Priority Date: 12/27/1993
• Status: Expired due to Fees

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Dumoulin, Charles L.
• Primary Examiner(s): O'Shea, Sandra L.
• Assistant Examiner(s): MAH, RAYMOND
• Application Number:
  US08/173,021
• Time in Patent Office: 610 Days
• Field of Search: 324/300, 324/307, 324/309, 324/314, 324/311, 324/310
• US Class Current: 324/307
• CPC Class Codes: G01R 33/4828 Resolving the MR signals of different chemical species, e.g. water-fat imaging
• CPC Class Codes: G01R 33/485 based on chemical shift information [CSI] or spectroscopic imaging, e.g. to acquire the spatial distributions of metabolites
• CPC Class Codes: G01R 33/56527 due to chemical shift effects

Abstract

Magnetic resonance images of selected chemical species are generated by the application of a multi-band radio-frequency excitation pulse. The radio-frequency pulse excites an arbitrary number of spectral bands. As the imaging phase encoding gradient pulse is advanced, the phase of each excitation band is advanced by a unique amount. This causes the signals from the spins in a particular band to appear at a position in the phase encoding direction which is the stem of the spin position and an offset arising from the phase increment given to that excitation band. Additional selectivity of selected chemical species can be accomplished by combining the multi-band excitation with chemical shift selective saturation radio-frequency pulses and echo-time modulation.

Claims

1. A method for obtaining a magnetic resonance (MR) image of a plurality of chemical species of a subject, comprising the steps of:

a) placing a subject in a substantially homogeneous magnetic field;

b) applying a multi-band radio-frequency (RF) pulse having a plurality of bands of selected amplitudes at frequencies which correspond to resonant frequency peaks of chemical species desired to be imaged to said subject, each band having a phase φ

;

c) applying a phase-encoding magnetic field gradient pulse in a phase encoding direction of an amplitude A to said subject;

d) applying a readout magnetic field gradient pulse in a readout direction to said subject;

e) collecting an MR response signal from said subject simultaneously with the application of the readout magnetic field gradient pulse;

f) calculating the Fourier transform of the collected MR response signal with respect to the readout direction to create a processed data set for amplitude A;

g) repeating steps `b` `through` f for N repetitions, each with a unique phase encoding magnetic field gradient amplitude A, and a unique phase offset φ

for at least one band of the multi-band RF pulse; and

h) calculating the Fourier transform of the processed data sets with respect to the phase encoding direction to create an MR image of the desired chemical species.

2. A method for obtaining magnetic resonance (MR) images of a plurality of chemical species of a subject, comprising the steps of:

a) placing a subject in a substantially homogeneous magnetic field;

b) applying a multi-band radio-frequency (RF) pulse having a plurality of bands of selected amplitudes at frequencies which correspond to resonant frequency peaks of chemical species desired to be imaged to said subject, each band having a phase φ

;

c) applying a first phase-encoding magnetic field gradient pulse in a phase encoding direction of an amplitude A₁ to said subject;

d) applying a second phase-encoding magnetic field gradient pulse in a please encoding direction of an amplitude A₂ to said subject;

e) applying a readout magnetic field gradient pulse in a readout direction to said subject;

f) collecting an MR response signal after a time delay TE after the application of the multi-band RF pulse from said subject simultaneously with the application of the readout magnetic field gradient pulse;

g) calculating the Fourier transform of the collected MR response signal with respect to the readout direction to create a processed data set for amplitude A₁ ;

h) repeating steps `b` through `g` for N repetitions, each with a unique phase encoding magnetic field gradient amplitude A₁, and a unique phase offset φ

for at least one band of the multi-band RF pulse; and

i) calculating the Fourier transform of the processed data sets with respect to the first phase encoding direction to create a second processed data set

j) repeating steps `b` through `i` for M repetitions, each with a unique phase encoding magnetic field gradient amplitude A₂, and a unique phase offset φ

for at least one band of the multi-band RF pulse; and

k) calculating the Fourier transform of the second processed data sets with respect to the second phase encoding direction to create M MR images of the desired chemical species.

3. The method of claim 2 in which the phase of selected bands in said multi-band radio-frequency pulse is incremented by a selected amount for each of the N repetitions to result in an image of a plurality of chemical species with each chemical species appearing in a different region of the image.

4. A method for obtaining magnetic resonance (MR) images of a selected chemical species of a subject, comprising the steps of:

a) placing a subject in a substantially homogeneous magnetic field;

b) applying a multi-band radio-frequency (RF) pulse having a plurality of bands of selected amplitudes at frequencies which correspond to resonant frequency peaks of chemical species desired to be imaged to said subject, each band having a phase φ

;

c) applying a first phase-encoding magnetic field gradient pulse in a phase encoding direction of an amplitude A₁ to said subject;

d) applying a second phase-encoding magnetic field gradient pulse in a phase encoding direction of an amplitude A₂ to said subject;

e) applying a readout magnetic field gradient pulse in a readout direction to said subject;

f) collecting an MR response signal from said subject simultaneously with the application of the readout magnetic field gradient pulse;

g) calculating the Fourier transform of the collected MR response signal with respect to the readout direction to create a processed data set for amplitude A₁ ;

h), repeating steps `b` through `g` for N repetitions, each with a unique phase encoding magnetic field gradient amplitude A₁, and a unique phase offset φ

for at least one band of the multi-band RF pulse; and

i) calculating the Fourier transform of the processed data sets with respect to the first phase encoding direction to create a second processed data set

j) repeating steps `b` through `i` for M repetitions, each with a unique phase encoding magnetic field gradient amplitude A₂, and a unique phase offset φ

for at least one band of the multi-band RF pulse;

k) calculating the Fourier transform of the second processed data sets with respect to the second phase encoding direction to create a first set of M MR images of chemical species;

l) repeating steps `b`-`k` with a selected phase offset φ

+π

to create a second set of M MR images of chemical species;

m) computing the difference between corresponding images from the first and second sets of MR images to obtain a third set of MR images having only information from one selected chemical species.

5. A method for obtaining magnetic resonance (MR) images of a selected chemical species of a subject, comprising the steps of:

a) placing a subject in a substantially homogeneous magnetic field;

b) applying a multi-band radio-frequency (RF) pulse having a plurality of bands of selected amplitudes at frequencies which correspond to resonant frequency peaks of chemical species desired to be imaged to said subject, each band having a phase φ

;

c) applying a first phase-encoding magnetic field gradient pulse in a phase encoding direction of an amplitude A₁ to said subject;

d) applying a second phase-encoding magnetic field gradient pulse in a phase encoding direction of an amplitude A₂ to said subject;

e) applying a readout magnetic field gradient pulse in a readout direction to said subject;

f) collecting an MR response signal from said subject simultaneously with the application of the readout magnetic field gradient pulse;

g) calculating the Fourier transform of the collected MR response signal with respect to the readout direction to create a processed data set for amplitude A₁ ;

h) repeating steps `b` through `g` for N repetitions, each with a unique phase encoding magnetic field gradient amplitude A₁, and a unique phase offset φ

for all least one band of the multi-band RF pulse; and

i) calculating the Fourier transform of the processed data sets with respect to the first phase encoding direction to create a second processed data set

j) repeating steps `b` through `i` for M repetitions, each with a unique phase encoding magnetic field gradient amplitude A₂, and a unique phase offset φ

for at least one band of the multi-band RF pulse;

k) calculating the Fourier transform of the second processed data sets with respect to the second phase encoding direction to create a first set of M MR images of chemical species;

l) repeating steps `b`-`k` with a selected time delay TE+Δ

TE, where Δ

TE is chosen to produce a φ

phase shift in the MR response signal of said selected chemical species, to create a second set of M MR images of chemical species;

m) computing the difference between corresponding images from the first and second sets of MR images to obtain a third set of MR images having only information from one selected chemical species.