Method for measuring relaxation time of ultrashort echo time magnetic resonance fingerprinting

Patent metadata

Field	Value
Publication number	US-11353531-B2
Application number	US-202017263549-A
Country	US
Kind code	B2
Filing date	May 9, 2020
Priority date	May 10, 2019
Publication date	Jun 7, 2022
Grant date	Jun 7, 2022

Abstract

The present disclosure discloses a method for measuring relaxation time of ultrashort echo time magnetic resonance fingerprinting. In the method, semi-pulse excitation and semi-projection readout are adopted to shorten echo time (TE) to achieve acquisition of an ultrashort T2 time signal; and image acquisition and reconstruction are based on magnetic resonance fingerprint imaging technology. A TE change mode of sinusoidal fluctuation is introduced, so that distinguishing capability of a magnetic resonance fingerprint signal to short T2 and ultrashort T2 tissues is improved, and multi-parameter quantitative imaging of the short T2 and ultrashort T2 tissues and long T2 tissues is realized. Non-uniformity of a magnetic field is modulated into phase information of the fingerprint signal through the TE of the sinusoidal fluctuation; a B0 graph is directly reconstructed according to an amplitude-modulated signal demodulation principle; and the phase change caused by a B0 field is compensated in the fingerprint signal.

First claim

What is claimed is:

1. A method for measuring relaxation time of ultrashort echo time magnetic resonance fingerprinting, comprising steps of:
S1, establishing design and implementation of an echo magnetic resonance fingerprint imaging sequence, comprising optimization of sinusoidal fluctuation echo time parameters;
S2, scanning a subject through a magnetic resonance scanner by utilizing the echo magnetic resonance fingerprint imaging sequence established in S1, so as to obtain original k-space data;
S3, reconstructing the original k-space data obtained in S2 into a series of down-sampled images; and
S4, phases of the series of down-sampled images in S3 being results of echo time TE of sinusoidal fluctuation modulated with non-uniformity of a B0 field: Phase=2pi·B off ·(α sin(ωτ)+β)+n,
where, B off is a frequency shift caused by field non-uniformity and chemical shift and has a unit of Hz, α, β and ω are sampling parameters of the TE, α=(TE max −TE min )/2, β=(TE max +TE min )/2, TE max and TE min are respectively maximum TE and minimum TE; ω is a frequency of a sinusoidal wave; τ is a time vector [1, 2, . . . , F] T , and the time unit is a repetition time TR; n represents a noise term, and demodulation of B off is realized by multiplying a carrier sin(ωτ) followed by low-pass filtering;
S5, moving-averaging a fingerprint signal by sliding window technology, and then performing amplitude demodulation on S4, that is, calculating B off :

B

o
⁢
f
⁢
f

=

2

2
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π
·
α
·
mT

·

∑
0
mT

⁢

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(

S
·
dPhase

)

by multiplying by the carrier sin(ωτ) followed by low-pass filtering;
where, dPhase is a phase signal multiplied by sin(ωτ) in S4, mT is a phase integral period, m is a number of cycles, π is PI, T=2π/ω, S is a matrix of F×F, an element contained is either 0 or 1, each row of S represents a window; if and only if the signal is in the window, a value of the element is 1, otherwise the value of the element is 0; and from the first row to the last row in the matrix S, the window moves from left to right;
S6, compensating B off calculated in S5 into the fingerprint signal processed by sliding window; then, reconstructing a multi-parameter quantitative graph from the collected fingerprint signal by a dictionary recognition method in the magnetic resonance fingerprint imaging technology; and
S7, according to tissue relaxation time reconstructed in S6, looking up in a dictionary to obtain a corresponding longitudinal magnetization vector change curve, selecting an image with a highest contrast of a bone tissue as a bone enhancement image, which is recorded as Mz, and using Mz/T1 as output of the bone enhancement image, so as to suppress a long T1 tissue, where T1 is a quantitative result of the longitudinal relaxation time outputted in S6.

2. The method for measuring relaxation time of ultrashort echo time magnetic resonance fingerprinting according to claim 1 , wherein the optimization of parameters in S1 is implemented by selecting echo time parameters with the highest measurement accuracy by a MATLAB simulation method, and the echo time parameters comprises the minimum echo time, the maximum echo time and a sinusoidal fluctuation period.

3. The method for measuring relaxation time of ultrashort echo time magnetic resonance fingerprinting according to claim 1 , wherein in S3, the original k-space data in S2 is reconstructed into the series of down-sampled images by a non-uniform fast Fourier transform reconstruction algorithm.

4. The method for measuring relaxation time of ultrashort echo time magnetic resonance fingerprinting according to claim 1 , wherein in S5, when a width of the sliding window is 4, S is written as:

S
=

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1
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1
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0
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…
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Assignees

• Univ Zhejiang

Inventors

• He Hongjian
• Li Qing
• Ye Huihui
• Cao Xiaozhi
• Zhong Jianhui
• Ding Qiuping

Classifications

• G01R33/50 Primary

  based on the determination of relaxation times {, e.g. T1 measurement by IR sequences; T2 measurement by multiple-echo sequences} · CPC title

• G01R33/56563

  caused by a distortion of the main magnetic field B0, e.g. temporal variation of the magnitude or spatial inhomogeneity of B0 (G01R33/56509, G01R33/56518, G01R33/56536 take precedence) · CPC title

• G01R33/561

  by reduction of the scanning time, i.e. fast acquiring systems, e.g. using echo-planar pulse sequences · CPC title

• G01R33/4816 Primary

  NMR imaging of samples with ultrashort relaxation times such as solid samples, e.g. MRI using ultrashort TE [UTE], single point imaging, constant time imaging · CPC title

• G01R33/4641

  Sequences for NMR spectroscopy of samples with ultrashort relaxation times such as solid samples · CPC title