0007
Fast 2D J-resolved MRSI combining echo planar imaging acquisition and turbo spin echo train evolution1School of Biomedical Engineering, Shanghai, China, 2Wuhan United Imaging Life Science Instruments Co., Ltd, Wuhan, China, Wuhan, China, 3Department of Chemical and Biological Physics, Weizmann Institute of Science, Rehovot, Israel
Synopsis
J-resolved MRSI is a powerful tool for separating overlapping resonances and detecting coupled species such as GABA and glutamate, which are of great interest to brain studies. However, a major practical limitation of J-resolved MRSI lies in its long data acquisition time. In this work, we present a novel fast fully sampled 2D J-resolved MRSI, termed as J-resolved xSPEN spectroscopy, combining echo planar imaging acquisition and turbo spin echo train evolution. Our preliminary phantom results demonstrate the proposed method can achieve highly efficient fully sampled 2D J-resolved MRSI with increasing chemical shift separation and detection of coupled species.
Introduction
Magnetic resonance spectroscopic imaging (MRSI) is an important technique for assessing the spatial variation of metabolites1. However, one common feature of the MR spectrum is the appearance of multiplets, arising because of spin–spin coupling, or J-coupling, whereby the field experienced by a spin is affected by adjacent spins within the molecule2. 2D J-resolved MRSI techniques enable highly selective mappings of multiplets while requiring multistep TE encodings, which further prolongs the acquisition time3. Many approaches have been proposed to accelerate 2D J-resolved MRSI, including EPSI and spiral trajectories, compressed sensing and subspace -based approaches3-6. In this work, we propose a novel fast fully sampled 2D J-resolved MRSI, termed as J-resolved xSPEN spectroscopy, combining echo planar imaging acquisition and turbo spin echo train evolution. Differ from conventional EPSI, its chemical shift encoding is obtained along the echo-planar gradient oscillation dimension and the spatial encoding is carried out in a multistep encoding. The proposed method introduces a time increasing t1 evolution as chemical shift encoding to the xSPEN imaging acquisition7. The distortion-free echo planar imaging acquisition is repeated in a turbo spin echo train evolution, endowing multiple TE encodings in the same shot. We present phantom results demonstrating the highly efficient fully sampled 2D J-resolved MRSI with increasing chemical shift separation and detection of coupled species.Methods
The J-resolved xSPEN spectroscopy sequence is shown in Fig. 1a by performing multiple scans with increasing time (t1) evolution to achieve the chemical shift dimension, while the J couplings are obtained by repeating the distortion-free echo-planar imaging-based acquisition of xSPEN in a turbo spin echo train evolution way. By splitting the t1 evolution into τ-t1/2 and t1/2 on two sides of π pulse, it results a constant-τ J coupling evolution along the chemical shift encoding dimension bringing a J-decoupled spectrum as shown in Fig.1b. The acquired chemical shifts, J couplings and spatial information can be indicated in Fig.1 on the right side of the figure, please noting that the J-decoupled spectrum can be obtained by Fig.1b. Studies were conducted with a 3.0T United Imaging uMR790 system (Shanghai, China). To demonstrate the concept, a phantom of ethanol/water solution with a volume ratio of 1:10 was used. Parameters for the J-resolved xSPEN MRSI include, TR =2 s, 200×200 mm2 FOV, 10 mm slice thickness, 32×32 image matrix size, a total of 128 t1 encodings with a bandwidth of 1000 Hz. A turbo spin echo train length is 64 with an increasing TE step of 15 ms. The constant J coupling evolution τ=120 ms is used for obtaining J-decoupled spectrum. Total scan time for the fully sampled 2D J-resolved MRSI is 4.2 min.Results and Discussion
The representative J-resolved spectra obtained from the phantom (from the spatial location marked by the red dot) are shown in Fig. 2. As can be seen, J splits can be clearly obtained along the turbo spin echo train dimension. With the J-decoupled evolution option (Fig.2b), singlets can be projected along the chemical shift encoding dimension with increasing signal height and higher spectral resolution. Only half of the encodings along multiple TEs evolution dimension was used to extract the J splittings by Fourier transformation, a restriction of bandwidth along this J-resolved dimension may limit the observation of numerous splittings. However, combination of all the encodings and interleaving with small TE increment can be further extended to allow higher bandwidth along the J-resolved dimension.Conclusions
We propose a novel fast fully sampled 2D J-resolved MRSI, termed as J-resolved xSPEN MRSI, combining echo planar imaging acquisition and turbo spin echo train evolution. With further development, the proposed method is expected to provide an alternative powerful tool for separating overlapping resonances and J-resolved MRSI.Acknowledgements
This work is supported by National Science Foundation of China (No. 62001290) and sponsored by Shanghai Sailing Program (20YF1420900).References
1. Wilson M, Andronesi O, Barker PB, Bartha R, Bizzi A, Bolan PJ, Brindle KM, Choi I-Y, Cudalbu C, Dydak U, Emir UE, Gonzalez RG, Gruber S, Gruetter R, Gupta RK, Heerschap A, Henning A, Hetherington HP, Huppi PS, Hurd RE, Kantarci K, Kauppinen RA, Klomp DWJ, Kreis R, Kruiskamp MJ, Leach MO, Lin AP, Luijten PR, Marjańska M, Maudsley AA, Meyerhoff DJ, Mountford CE, Mullins PG, Murdoch JB, Nelson SJ, Noeske R, Öz G, Pan JW, Peet AC, Poptani H, Posse S, Ratai E-M, Salibi N, Scheenen TWJ, Smith ICP, Soher BJ, Tkáč I, Vigneron DB, Howe FA. Methodological consensus on clinical proton MRS of the brain: Review and recommendations. Magn Reson Med 2019;82(2):527-550.
2. Puts NA, Edden RA. In vivo magnetic resonance spectroscopy of GABA: a methodological review. Prog Nucl Magn Reson Spectrosc 2012;60:29-41.
3. Tang L, Zhao Y, Li Y, Guo R, Clifford B, El Fakhri G, Ma C, Liang Z-P, Luo J. Accelerated J-resolved 1H-MRSI with limited and sparse sampling of (-space. Magn Reson Med 2021;85(1):30-41.
4. Vidya Shankar R, Chang JC, Hu HH, Kodibagkar VD. Fast data acquisition techniques in magnetic resonance spectroscopic imaging. NMR Biomed 2019;32(3):e4046.
5. Sarma MK, Nagarajan R, Macey PM, et al. Accelerated echo‐planar J‐resolved spectroscopic imaging in the human brain using compressed sensing: a pilot validation in obstructive sleep apnea. Am J Neuroradiol. 2014;35(Suppl 6):S81‐S89.
6. Wilson NE, Iqbal Z, Burns BL, Keller M, Thomas MA. Accelerated five‐dimensional echo planar J‐resolved spectroscopic imaging: implementation and pilot validation in human brain. Magn Reson Med. 2016;75(1):42‐51.
7. Zhang Z, Seginer A, Frydman L. Single-scan MRI with exceptional resilience to field heterogeneities. Magn Reson Med 2017;77(2):623-634.
Figures
