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Improved gradient‐echo 3D magnetic resonance imaging using compressed sensing and Toeplitz encoding with phase‐scrambled RF excitation
Author(s) -
Wang Haifeng,
Liang Dong,
Su Shi,
King Kevin F.,
Chang Yuchou,
Liu Xin,
Zheng Hairong,
Ying Leslie
Publication year - 2020
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1002/mp.13987
Subject(s) - imaging phantom , encoding (memory) , toeplitz matrix , fourier transform , computer science , signal (programming language) , radio frequency , phase (matter) , pulse sequence , acoustics , nuclear magnetic resonance , materials science , optics , algorithm , physics , mathematics , artificial intelligence , telecommunications , quantum mechanics , pure mathematics , programming language
Purpose To develop a novel three‐dimensional (3D) hybrid‐encoding framework using compressed sensing (CS) and Toeplitz encoding with variable phase‐scrambled radio‐frequency (RF) excitation, which has the following advantages: low power deposition of RF pulses, reduction of the signal dynamic range, no additional hardware requirement, and signal‐to‐noise ratio (SNR) improvement. Methods In light of the actual imaging framework of magnetic resonance imaging (MRI) scanners, we applied specially tailored RF pulses with phase‐scrambled RF excitation to implement a 3D hybrid Fourier‐Toeplitz encoding method based on 3D gradient‐recalled echo pulse (GRASS) sequence. This method exploits Toeplitz encoding along the phase encoding direction, while keeping Fourier encoding along the readout and slice encoding directions. Phantom experiments were conducted to optimize the amplitude of specially tailored RF pulses in the 3D GRASS sequence. In vivo experiments were conducted to validate the feasibility of the proposed method, and simulations were conducted to compare the 3D hybrid‐encoding method with Fourier encoding and other non‐Fourier encoding methods. Results An optimized low RF amplitude was obtained in the phantom experiments. Using the optimized specially tailored RF pulses, both the watermelon and knee experiments demonstrated that the proposed method was able to preserve more image details than the conventional 3D Fourier‐encoded methods at acceleration factors of 3.1 and 2.0. Additionally, SNR was improved because of no additional gradients and 3D volume encoding, when compared with single‐slice scanning without 3D encoding. Simulation results demonstrated that the proposed scheme was superior to the conventional Fourier encoding method, and obtained comparative performance with other non‐Fourier encoding methods in preserving details. Conclusions We developed a practical hybrid‐encoding method for 3D MRI with specially tailored RF pulses of phase‐scrambled RF excitation. The proposed method improves image SNR and detail preservation compared with the conventional Fourier encoding methods. Furthermore, our proposed method exhibits superior performance in terms of detail preservation, compared with the conventional Fourier encoding method.