螺旋磁共振波谱成像中的时间交织伪影：表征与回顾性校正
Temporal interleaving artifacts in spiral MRSI: characterization and retrospective correction
AI总结：
该研究针对螺旋MRSI中时间交织产生的伪影问题，提出数学描述及后处理解决方案。通过特定序列采集数据描述伪影，建立模型并推导校正方法，经体模和志愿者实验验证，显著减少伪影，确保光谱定量准确，还给出控制伪影频率定位的方法。
AI中文摘要：
目的：在螺旋磁共振波谱成像（MRSI）中，实现合适的时空分辨率需要进行交织。时间交织信号之间出现的采样不一致，无论是由于时间交织的模数转换器还是激发和解调阶段的相位/频率失配，都会在重组数据中产生伪影。本文提出了对这些不可避免伪影的数学描述以及一种后处理解决方案，以规避和减轻这些问题。方法：该研究使用在梯度关闭的情况下通过MRSI交织序列以及标准交织FID序列采集的数据，对这些伪影进行了详细描述和解释。交织之间的随机信号失配被描述为每个时间交织处的额外伪影信号ψ(t)。还进一步提出了一个模型，以将采集到的信号与理想的无伪影信号进行匹配。考虑到M个交织，通过最小化一个多变量代价函数，推导出一种校正方法，该方法依赖于为每个交织估计ψ(t)模型中的4个参数。这种校正方法在从体模获取的光谱以及在健康志愿者身上进行的体内采集上进行了评估。结果：所提出的校正方法在体模中显著将伪影减少了4倍，在健康志愿者中减少了1.8倍。这种校正确保了在伪影与感兴趣内容重叠的区域，如皮下脂肪中的脂质，能够进行准确的光谱定量。此外，还证明了适当选择时间交织的数量可以利用观察到的伪影的周期性和有限频率跨度，将伪影从感兴趣的频率移开。结论：在螺旋MRSI中，时间交织虽然增强了光谱带宽，但引入了具有独特共振频率以及不可重复幅度和相位的虚假内容。该研究提出了两种解决方案：操纵交织数量以控制伪影频率定位，或使用回顾性校正方法来近似和减轻伪影。
英文摘要：
Purpose: In Spiral Magnetic Resonance Spectroscopic Imaging (MRSI), achieving suitable spatio-temporal resolutions requires interleaving. Sampling inconsistencies occurring between temporally interleaved signals, -whether due to time-interleaved ADCs or phase/frequency mismatches in the excitation and demodulation stages-, result in artifacts in the recombined data. This paper proposes a mathematical description of these unavoidable artifacts and a postprocessing solution to circumvent the issues and mitigate them. Methods: The study proposed a detailed description and explanation of these artifacts using data acquired with MRSI interleaved sequence with gradients off, as well as standard interleaved FID sequence. The random signal mismatch between the interleaves was described as additional artifactual signals $ψ$(t) at each temporal interleave. A model was further proposed to match the acquired signal in relation to the ideal, artifact-free signal. Considering M interleaves, a correction method was derived relying on estimating 4 parameters in the $ψ$(t) model for each interleave by minimizing a multivariable cost function. This correction method was evaluated on spectra acquired from phantoms and in vivo acquisitions obtained in healthy volunteers. Results: The proposed correction method significantly reduced artifacts by a factor of 4 in the phantom and 1.8 in the healthy volunteers. This correction ensured accurate spectral quantification in regions where artifacts overlapped with the content of interest, such as lipids in subcutaneous fat. Additionally, it was demonstrated that appropriately selecting the number of temporal interleaves can shift the artifact away from the frequency of interest, leveraging the periodic and limited frequency span of the observed artifacts. Conclusion: In spiral-MRSI, temporal interleaves, while enhancing spectral bandwidth, introduced spurious content characterized by distinctive resonance frequencies and nonreproducible amplitudes and phases. The study proposes two solutions: manipulating the number of interleaves to control artifact frequency localization or using a retrospective correction method to approximate and attenuate artifacts.
