arXiv subjects

Lijing Xin

Publications and source records attributed to Lijing Xin.

5 recordsLinked to original sources

arXiv2026

Synthetic Data in MR Spectroscopy: Current Practices, Applications, and Considerations

The use of synthetic data has emerged as an essential tool in Magnetic Resonance Spectroscopy (MRS) research and applications, providing advantages for optimization of acquisition, software validation, deep learning applications, and enhanced reproducibility. Importantly, synthetic data addresses challenges of limited training data availability, particularly for clinical populations, and offers controlled solutions for investigating uncertainties and unexplained variance with in vivo data. This work provides a review and evaluation of current practices in the use and generation of synthetic data within the MRS field. Conducted by the MRS Synthetic Data Working Group under the Code & Data Sharing Committee of the MRS Study Group of the International Society for Magnetic Resonance in Medicine (ISMRM), this manuscript encompasses existing literature, supplemented by collective experience and in-house methodologies.

physics.med-ph↗

arXiv2024

Rosette spectroscopic imaging for whole-brain metabolite mapping at 7T: acceleration potential and reproducibility

Whole-brain proton magnetic resonance spectroscopic imaging (1H-MRSI) is a non-invasive technique for assessing neurochemical distribution in the brain, offering valuable insights into brain functions and neural diseases. It greatly benefits from the improved SNR at ultrahigh field strengths ($\geq$7T). However, 1H-MRSI still faces several challenges, such as long acquisition time and severe signal contaminations from water and lipids. In this study, 2D and 3D short TR/TE 1H-FID-MRSI sequences using rosette trajectories were developed with spatial resolutions of 4.48$\times$4.48 mm$^2$ and 4.48$\times$4.48$\times$4.50 mm$^3$, respectively. Water signals were suppressed using an optimized Five-variable-Angle-gaussian-pulses-with-ShorT-total-duration of 76 ms (FAST) water suppression scheme, and lipid signals were removed using the L2 regularization method. Metabolic maps of major 1H metabolites were obtained within 5:40 min with 16 averages and 1 average for the 2D and 3D acquisitions, respectively. Excellent inter-session reproducibility was shown, with the coefficients of variance (CV) being lower than 6% for N-Acetyle-L-aspartic acid (NAA), Glutamate (Glu), Choline Chloride and glycerophosphocholine (tCho), Creatine and Phosphocreatine (tCr), and Glycine and Myo-inositol (Gly+Ins). To explore the potential of further accelerating the acquisition, compressed sensing was applied retrospectively to the 3D datasets. The structural similarity index (SSIM) remained above 0.85 and 0.8 until $R = 2$ and $R = 3$ for the metabolite maps of Glu, NAA, tCr, and tCho, indicating the possibility for further reduction of acquisition time to around 2min.

physics.med-ph↗

arXiv2024

A Toolbox for Optimization of Reconstruction and Post-processing Pipelines in In Vivo $^{31}$P MR Imaging

Background: X-nuclei imaging (e.g. 31P MRI) suffers low SNR due to lower gyromagnetic ratios and tissue concentrations than 1H MRI. Enhancing SNR requires high fields, advanced coils, optimized sequences, and sophisticated reconstruction methods. An optimized pipeline is essential for maximizing SNR in X-nuclei imaging. Purpose: To develop a toolbox of reconstruction and processing methods for fast 31P MR imaging, evaluating optimal pipelines for two data types: 31P-GRE and bSSFP-like MRF imaging. Methods: The toolbox includes coil combination (adaptive and whitened-SVD), k-space filtering, reconstruction (Kaiser-Bessel regridding with FFT and NUFFT), and denoising (compressed sensing and MP-PCA). 31P MR datasets were acquired at 7T using spiral encoding with a double-tuned birdcage coil and a 32-channel phased array. GRE parameters: readout 18.62ms, flip angle 59deg, TR 5400ms, TE 0.3ms. MRF used a bSSFP-like scheme: readout 9.12ms, TR 19.8ms, TE 0.3ms. Results: For GRE data, adaptive coil combination with Kaiser-Bessel regridding (AC-KB) achieved highest mean SNRs: 38 (phantom) and 3.4 (in vivo), outperforming others. For MRF data, whitened-SVD with Kaiser-Bessel regridding yielded an SNR of 18, surpassing AC-KB's 16. MP-PCA denoised GRE effectively; compressed sensing suited MRF data. Conclusion: We demonstrated a toolbox for optimizing fast 31P MR imaging pipelines. Optimal methods depend on acquisition and data. Kaiser-Bessel regridding outperforms NUFFT. Adaptive coil combination and MP-PCA denoising are preferred for GRE data; whitened-SVD and compressed sensing are superior for MRF data. Careful selection of processing methods is crucial, as conventional 1H MRI techniques may not suffice. The toolbox facilitates future investigation for other X-nuclei datasets.

physics.med-ph↗

arXiv2024

Fast 3D 31P B1+ mapping with a weighted stack of spiral trajectory at 7 Tesla

Purpose: Phosphorus Magnetic Resonance Spectroscopy (31P MRS) enables non-invasive assessment of energy metabolism, yet its application is hindered by sensitivity limitations. To overcome this, often high magnetic fields are used, leading to challenges such as spatial B_1^+ inhomogeneity and therefore the need for accurate flip angle determination in accelerated acquisitions with short repetition times (T_R). In response to these challenges, we propose a novel short T_R and look-up table-based Double-Angle Method for fast 3D 31P B_1^+ mapping (fDAM). Methods: Our method incorporates 3D weighted stack of spiral gradient echo acquisitions and a frequency-selective pulse to enable efficient B_1^+ mapping based on the phosphocreatine signal at 7T. Protocols were optimised using simulations and validated through phantom experiments. The method was validated in phantom experiments and skeletal muscle applications using a birdcage 1H/31P volume coil. Results: The results of fDAM were compared to the classical DAM (cDAM). A good correlation (r=0.94) was obtained between the two B_1^+ maps. A 3D 31P B_1^+ mapping in the human calf muscle was achieved in about 10 min using a birdcage volume coil, with a 20% extended coverage relative to that of the cDAM (24 min). fDAM also enabled the first full brain coverage 31P 3D B_1^+ mapping in approx. 10 min using a 1 Tx/ 32 Rx coil. Conclusion: fDAM is an efficient method for 31P 3D B_1^+ mapping, showing promise for future applications in rapid 31P MRSI.

physics.med-ph↗

arXiv2023

Twisted Pair Transmission Line Coil -- A Flexible, Self-Decoupled and Extremely Robust Element for 7T MRI

This study evaluates the performance of a twisted pair transmission line coil as a transceive element for 7T MRI in terms of physical flexibility, robustness to shape deformations, and interelement decoupling. Each coil element was created by shaping a twisted pair of wires into a circle. One wire was interrupted at the top, while the other was interrupted at the bottom, and connected to the matching circuit. Electromagnetic simulations were conducted to determine the optimal number of twists per length (in terms of B$_1^+$ field efficiency, SAR efficiency, sensitivity to elongation and interelement decoupling properties) and for investigating the fundamental operational principle of the coil through fields streamline visualization. A comparison between the twisted pair coil and a conventional loop coil in terms of B$_1^+$ fields, maxSAR10g, and stability of $S_{11}$ when the coil was deformed, was performed. Experimentally measured interelement coupling between individual elements of multichannel arrays was also investigated. Increasing the number of twists per length resulted in a more physically robust coil. Poynting vector streamline visualization showed that the twisted pair coil concentrated most of the energy in the near field. The twisted pair coil exhibited comparable B$_1^+$ fields and improved maxSAR10g to the conventional coil but demonstrated exceptional stability with respect to coil deformation and a strong self-decoupling nature when placed in an array configuration. The findings highlight the robustness of the twisted pair coil, showcasing its stability under shape variations. This coil holds great potential as a flexible RF coil for various imaging applications using multiple-element arrays, benefiting from its inherent decoupling.

physics.med-ph↗