Data_Sheet_1_Practical considerations of diffusion-weighted MRS with ultra-strong diffusion gradients.zip

IntroductionDiffusion-weighted magnetic resonance spectroscopy (DW-MRS) offers improved cellular specificity to microstructure—compared to water-based methods alone—but spatial resolution and SNR is severely reduced and slow-diffusing metabolites necessitate higher b-values to accurately characterize their diffusion properties. Ultra-strong gradients allow access to higher b-values per-unit time, higher SNR for a given b-value, and shorter diffusion times, but introduce additional challenges such as eddy-current artefacts, gradient non-uniformity, and mechanical vibrations.MethodsIn this work, we present initial DW-MRS data acquired on a 3T Siemens Connectom scanner equipped with ultra-strong (300 mT/m) gradients. We explore the practical issues associated with this manner of acquisition, the steps that may be taken to mitigate their impact on the data, and the potential benefits of ultra-strong gradients for DW-MRS. An in-house DW-PRESS sequence and data processing pipeline were developed to mitigate the impact of these confounds. The interaction of TE, b-value, and maximum gradient amplitude was investigated using simulations and pilot data, whereby maximum gradient amplitude was restricted. Furthermore, two DW-MRS voxels in grey and white matter were acquired using ultra-strong gradients and high b-values.ResultsSimulations suggest T2-based SNR gains that are experimentally confirmed. Ultra-strong gradient acquisitions exhibit similar artefact profiles to those of lower gradient amplitude, suggesting adequate performance of artefact mitigation strategies. Gradient field non-uniformity influenced ADC estimates by up to 4% when left uncorrected. ADC and Kurtosis estimates for tNAA, tCho, and tCr align with previously published literature.DiscussionIn conclusion, we successfully implemented acquisition and data processing strategies for ultra-strong gradient DW-MRS and results indicate that confounding effects of the strong gradient system can be ameliorated, while achieving shorter diffusion times and improved metabolite SNR.

引言：扩散加权磁共振波谱成像（DW-MRS）相较于单纯的水基方法，在微结构成像方面具有更高的细胞特异性，但空间分辨率和信噪比显著降低，而缓慢扩散的代谢物需要更高的b值以准确表征其扩散特性。超强梯度使得在单位时间内能够达到更高的b值，给定b值下的信噪比更高，以及更短的扩散时间，但同时也引入了诸如涡流伪影、梯度非均匀性和机械振动等额外挑战。方法：在本研究中，我们展示了在配备超强梯度（300 mT/m）的3T西门子Connectom扫描仪上获取的初始DW-MRS数据。我们探讨了这种获取方式所伴随的实践问题，以及可能采取的减轻这些影响的方法，以及超强梯度对DW-MRS的潜在益处。我们开发了一套内部DW-PRESS序列和数据处理流程，以减轻这些干扰的影响。通过模拟和试点数据，我们研究了TE、b值和最大梯度幅度的相互作用，其中最大梯度幅度受到限制。此外，我们还使用超强梯度和高b值在灰质和白质中获取了两个DW-MRS体素。结果：模拟表明，基于T2的信噪比增益得到了实验验证。超强梯度获取的伪影特征与较低梯度幅度的类似，表明伪影减轻策略的性能良好。当未校正时，梯度场非均匀性对ADC估计的影响高达4%。tNAA、tCho和tCr的ADC和峰度估计与先前发表的文献一致。讨论：综上所述，我们成功实施了超强梯度DW-MRS的获取和数据处理策略，结果表明，强梯度系统的干扰效应可以得以改善，同时实现了更短的扩散时间和提高的代谢物信噪比。