2479

Non-Water suppressed High-Resolution 1H-MRSI of the Brain Using Short-TE SPICE with semi-LASER Concentric Ring Trajectory Acquisition
Uzay Emir1,2, Pingyu Xia1, Ulrike Dydak1,3, Xiaopeng Zhou1, Albert Thomas4, Mark Chiew5, Rong Guo6,7, Yudu Li6,7, Yibo Zhao6,7, and Zhi-Pei Liang6,7

1School of Health Sciences, Purdue University, West Lafayette, IN, United States, 2Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN, United States, 3Department of Radiology and Imaging Sciences, Indiana University School of Medicine, Indianapolis, IN, United States, 4Department of Radiology, University of California Los Angeles, Los Angeles, CA, United States, 56Wellcome Centre for Integrative Neuroimaging, University of Oxford, Oxford, United Kingdom, 6Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Illinois 2Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Illinois Beckman Institute for Advanced Science and Technology, University of Illinois, Urbana-Champaign, IL, United States, 7Department of Electrical and Computer Engineering, University of Illinois, Urbana-Champaign, IL, United States

Synopsis

Magnetic resonance spectroscopic imaging (MRSI) is an appealing technique in both research and clinical settings. However, the utility of MRSI has been hampered by long acquisition times and artifacts caused by lipid contamination and poor water suppression. Recent advances in MRSI acquisition and preprocessing, like concentric rings (CRT) trajectories and SPICE (SPectroscopic Imaging by exploiting spatiospectral CorrElation) (REF3), have overcome some of these issues. This work reports our success in integrating SPICE with CRT acquisitions to address the challenges of sensitivity, spectral quality, speed, and spatial resolution.

Introduction

Proton (1H) MRSI allows for the observation, identification, and quantification of a large number of biologically important molecules (neurotransmitters and metabolites) and provides a unique capability to study brain metabolism and neurodegenerative diseases. Since the pioneering work on chemical shift imaging (CSI) in 1982, a lot of outstanding work has been done over the last three decades, resulting in significant advances in MRSI data acquisition, pulse sequences, data processing, and image reconstruction. However, the utility of MRSI is still rather limited due to long acquisition times and artifacts caused by lipid contamination and poor water suppression [1]. Recent advances in MRSI acquisition and preprocessing, like concentric rings trajectories(CRT) [2] and SPICE (SPectroscopic Imaging by exploiting spatiospectral CorrElation) [3], have overcome some of these issues. This work reports our success in integrating SPICE with CRT acquisitions to address the challenges of sensitivity, spectral quality, speed, and spatial resolution.

Methods

A healthy volunteer was scanned in this study. Data were collected using a whole-body 3T Prisma MR system (Siemens, Erlangen) with a 64-channel head coil. GRESHIM was used for B0 shimming [4]. Two asymmetric narrow transition-band adiabatic RF pulses with mirrored inversion profiles were applied in alternate scans to acquire the upfield and downfield (relative to water) spectral resonances before the semi-LASER localization [5]. For metabolite-cycling, an 80 Hz transition bandwidth (-0.95 < Mz/M0 < 0.95) and 820 Hz inversion bandwidth (-1 < Mz/M0 < -0.95), 70 to -750 Hz) downfield/upfield from the carrier frequency (carrier frequency offset=+60 Hz and -60 Hz for downfield and upfield). CRT was prescribed using the following parameters: points-per-ring=64, temporal samples=512, resolution=5x5x10 mm3, Rings=48, FOV=240x240x10 mm, TR=1350 ms, TE=32 ms, averages=6, spectral bandwidth =893 Hz, timeacquire~13 min. Only one of the water scan of metabolite-cycling acquisition was used. Data processing is done using a SPICE subspace model-based method. The water and residual lipid signals are first removed using a union-of-subspaces model [3]. Then, the desired spatiospectral function is reconstructed using a subspace model that incorporates pre-trained spectral basis functions and spatial prior information. After the reconstruction, spectral quantification was done using LCModel [6].

Results

Figure 1 shows results from a resolution phantom using the non‐water‐suppressed metabolite‐cycling MRSI technique. Although the final resolution of the image generated from the first time point of the FID was poorer than the MP‐RAGE image (0.0625 mL versus 0.0045 mL), the non‐water‐suppressed metabolite‐cycling MRSI and its reconstruction generated a spectroscopic image with structural information similar to that of the MPRAGE. The in vivo results for the non‐water‐suppressed metabolite‐cycling MRSI technique is shown in Figure 2. Similar to the resolution phantom experiment, the non‐water‐suppressed metabolite‐cycling MRSI and its reconstruction generated a spectroscopic image resembling the anatomical features of the MP-RAGE image. Figure 3 shows representative spectra of nuisance signal removal results of a short-TE SPICE using CRT-Semi-LASER dataset. This further demonstrates that the proposed method was able to effectively remove the dominant water and lipid signals. Due to the high spectral quality provided by short-TE SPICE using CRT-Semi-LASER dataset, three important brain metabolites (total NAA (tNAA), total Choline (tCho) and Glutamate+Glutamine (Glu+Gln)) could be mapped with CRLBs less than 10%.

Discussion

We demonstrated that a short-TE SPICE using CRT-semi-LASER technique enables high-resolution metabolite maps (with an in-plane resolution of 2.5 mm x 2.5 mm) deliverable at 3T in a clinically viable acquisition time. Future work would extend towards a whole brain coverage.

Acknowledgements

No acknowledgement found.

References

1. Zhu, H. and P.B. Barker, MR spectroscopy and spectroscopic imaging of the brain. Methods Mol Biol, 2011. 711: p. 203-26.

2. Emir UE, Burns B, Chiew M, Jezzard P, Thomas MA. Non‐water‐suppressed short‐echo‐time magnetic resonance spectroscopic imaging using a concentric ring k‐space trajectory. NMR in Biomedicine. 2017;30:e3714.

3. Ma C , Lam F, Ning Q, Johnson CL, Liang Z. High‐resolution 1H‐MRSI of the brain using short‐TE SPICE. Magn. Reson. Med..2017; 77: 467.

4. Shah, S., et al., Rapid Fieldmap Estimation for Cardiac Shimming, in Proceedings 17th Scientific Meeting, International Society for Magnetic Resonance in Medicine. 2009: Honolulu p. 565.

5. Steel A, Chiew M, Jezzard P, Voets NL, Plaha P, Thomas MA, Stagg CJ, Emir UE. Metabolite-Cycled Density-Weighted Concentric Rings k-Space Trajectory (DW-CRT) Enables High-Resolution 1 H Magnetic Resonance Spectroscopic Imaging at 3-Tesla. Scientific Reports 2018; 8: 7792.

6. Provencher, S.W., Automatic quantitation of localized in vivo 1H spectra with LCModel. NMR in Biomedicine. 2001;14(4): 260.

Figures

Figure 1 Resolution phantom: High‐resolution T1‐weighted MP-RAGE image of the slice studied and the water image with a final grid of 96 × 96 (2.5 mm × 2.5 mm) obtained using the first time point of the water FID.

Figure 2 In vivo: High‐resolution T 1‐weighted MP-RAGE image of the slice studied and the water image with a final grid of 96 × 96 (2.5 mm × 2.5 mm) obtained using the first time point of the water FID.

Figure 3 Reconstructed spectra from localized 3 × 3 voxels using short-TE SPICE with CRT-semi-LASER acquisition.

Figure 4 Quantification with LCModel: Due to the high spectral quality provided by both techniques, three important brain metabolites could be mapped with CRLBs less than 10%.

Proc. Intl. Soc. Mag. Reson. Med. 27 (2019)
2479