System and method for tissue characterization using fast quantitative spin-lock magnetization transfer imaging

Patent metadata

Field	Value
Publication number	US-12392853-B2
Application number	US-202318101088-A
Country	US
Kind code	B2
Filing date	Jan 24, 2023
Priority date	Jan 25, 2022
Publication date	Aug 19, 2025
Grant date	Aug 19, 2025

Abstract

Systems and methods for fast and robust quantification of magnetization transfer (MT) use off-resonance spin-lock MRI with as few as two or three image acquisitions. Each image acquisition can be performed using an off-resonance spin-lock pulse having a different RF amplitude and frequency offset. A parameter representing the difference of the relaxation rate in the rotating frame between the acquisitions can be computed. This parameter can be used to compute other parameters of magnetization transfer.

First claim

What is claimed is:

1. A method for quantifying magnetization transfer using a magnetic resonance imaging (MRI) apparatus, the method comprising:
performing a first image acquisition process to produce a first MR image, wherein the first image acquisition process includes applying a first off-resonance spin-lock pulse having a first RF amplitude (ω 1 (1) ), a first frequency offset (Δω (1) ), and a first time of spin-lock (TSL (1) );
performing a second image acquisition process to produce a second MR image, wherein the second image acquisition process includes applying a second off-resonance spin-lock pulse having a second RF amplitude (ω 1 (2) ), a second frequency offset (Δω (2) ), and a second time of spin-lock (TSL (2) ), wherein the first time of spin-lock TSL (1) and the second time of spin-lock TSL (2) are equal to the same time of spin-lock (TSL),
wherein the first RF amplitude ω 1 (1) , the first frequency offset Δω (1) , the second, RF amplitude (ω 1 (2) ), and the second frequency offset (Δω (2) ) are chosen such that Δω (1) /ω 1 (1) =Δω (2) /ω 1 (2) and wherein one or both of the following conditions is satisfied:
(a) R 1ρ (ω 1 , Δω)TSL<<1 for each of the first spin-lock pulse and the second spin-lock pulse, wherein R 1ρ (ω 1 , Δω) is a relaxation rate in the rotating frame for a given RF amplitude ω 1 and frequency offset Δω; or
(b) each of the first and second image acquisition processes includes a magnetization reset RF pulse prior to the off-resonance spin-lock pulse and a recovery time (T rec ) between the magnetization reset RF pulse and the beginning of the off-resonance spin-lock pulse is greater than a longitudinal relaxation time (T 1 ) of water protons; and

computing, based on the first and second MR images, one or more parameters of magnetization transfer, wherein the one or more parameters of magnetization transfer include a parameter R mts1 defined as R mts1 =R 1ρ (2) −R 1ρ (1) , wherein:
R 1ρ (1) is a first relaxation rate in the rotating frame responsive to a spin-lock pulse having the first RF amplitude ω 1 (1) and the first frequency offset Δω (1) ; and
R 1ρ (2) is a second relaxation rate in the rotating frame responsive to a spin-lock pulse having the second RF amplitude ω 1 (2) and the second frequency offset Δω (2) ,

wherein computing the parameter R mts1 includes computing:

R
mtsl

=

-
log

⁢

M

(
2
)

M

(
1
)

/
TSL

,

wherein M (1) corresponds to the first image and M (2) corresponds to the second image.

2. The method of claim 1 further comprising:
computing one or more additional parameters of magnetization transfer based on the parameter R mts1 , wherein the one or more additional parameters of magnetization transfer include a macromolecular proton fraction (MPF) indicating a fraction of protons that are bound to semi-solid macromolecules.

3. The method of claim 1 wherein computing the parameter R mts1 includes using machine-learning based methods based on a magnetization model of each image acquisition.

4. The method of claim 1 wherein each instance of applying an off-resonance spin-lock pulse includes applying an off-resonance spin-lock RF pulse cluster that includes a hard RF pulse or an adiabatic RF pulse.

5. The method of claim 1 wherein each instance of applying an off-resonance spin-lock pulse includes applying a saturation RF pulse.

6. The method of claim 1 wherein performing each of the first and second image acquisition processes includes applying at least one preparatory pulse sequence before or after applying the spin-lock pulse and prior to acquiring data.

7. The method of claim 1 further comprising, prior to computing the one or more parameters of magnetization transfer:
determining a phase difference between corresponding pixels of the first MR image and the second MR image; and
discarding pixels of the first MR image and the second MR image for which the phase difference exceeds a threshold.

8. The method of claim 1 further comprising:
performing multiple instances of the first and second image acquisition processes, wherein each instance uses a different selection of RF amplitudes and frequency offsets;
separately computing a measurement of the parameter R mts1 from each instance of the first and second image acquisition processes; and
using the separately computed measurements of the parameter R mts1 to compute one or more of a macromolecular proton fraction (MPF), a magnetization exchange rate between a free-water pool and the bound pool (k ba ), or a transverse relaxation time of the bound pool (T 2b ).

9. The method of claim 1 wherein the first MR image and the second MR image are images of a region of interest that comprises a tissue of a patient.

10. A method for quantifying magnetization transfer using a magnetic resonance imaging (MRI) apparatus, the method comprising:
performing a first image acquisition process to produce a first MR image, wherein the first image acquisition process includes applying a first off-resonance spin-lock pulse having a first RF amplitude (ω 1 (1) ), a first frequency offset (Δω (1) ), and a first time of spin-lock (TSL (1) ), wherein the first image acquisition process is used to determine a first measured magnetization M (1) that depends on a first relaxation rate in the rotating frame R 1ρ (1) ;
performing a second image acquisition process to produce a second MR image, wherein the second image acquisition process includes applying a second off-resonance spin-lock pulse having a second RF amplitude (ω 1 (2) ), a second frequency offset (Δω (2) ), and a second time of spin-lock (TSL (2) ), wherein the second image acquisition process is used to determine a second measured magnetization M (2) that depends on a second relaxation rate in the rotating frame R 1ρ (2) and wherein one or both of the following conditions is satisfied:
(a) R 1ρ (ω 1 , Δω)TSL<<1 for each of the first spin-lock pulse and the second spin-lock pulse, wherein R 1ρ (ω 1 , Δω) is a relaxation rate in the rotating frame for a given RF amplitude ω 1 and frequency offset Δω; or
(b) each of the first and second image acquisition processes includes a magnetization reset RF pulse prior to the off-resonance spin-lock pulse and a recovery time (T rec ) between the magnetization reset RF pulse and the beginning of the off-resonance spin-lock pulse is greater than a longitudinal relaxation time (T 1 ) of water protons;

performing a third image acquisition process to produce a third MR image, wherein the third image acquisition process includes applying a third off-resonance spin-lock pulse having a third RF amplitude (ω 1 (3) ), a third frequency offset (Δω (3) ), and a third time of spin-lock (TSL (3) ) that is equal to zero, wherein the third image acquisition process is used to determine a third measured magnetization M ini that represents the initial magnetizatio

Assignees

• Univ Hong Kong Chinese

Inventors

• Hou Jian
• Chen Weitian

Classifications

• G01R33/5608

  Data processing and visualization specially adapted for MR, e.g. for feature analysis and pattern recognition on the basis of measured MR data, segmentation of measured MR data, edge contour detection on the basis of measured MR data, for enhancing measured MR data in terms of signal-to-noise ratio by means of noise filtering or apodization, for enhancing measured MR data in terms of resolution by means for deblurring, windowing, zero filling, or generation of gray-scaled images, colour-coded images or images displaying vectors instead of pixels (image data processing or generation, in general G06T) · CPC title

• G01R33/446

  Multifrequency selective RF pulses, e.g. multinuclear acquisition mode (spatially selective RF pulses G01R33/4833) · CPC title

• A61B5/055

  involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging · CPC title

• G01R33/5605 Primary

  by transferring coherence or polarization from a spin species to another, e.g. creating magnetization transfer contrast [MTC], polarization transfer using nuclear Overhauser enhancement [NOE] · CPC title