paper_authors: Dimitrios G. Gkotsoulias, Carsten Jäger, Roland Müller, Tobias Gräßle, Karin M. Olofsson, Torsten Møller, Steve Unwin, Catherine Crockford, Roman M. Wittig, Berkin Bilgic, Harald E. Möller
For: The paper aims to investigate the effects of non-ideal sampling and susceptibility anisotropy on the accuracy of quantitative susceptibility mapping (QSM) in the primate brain using the COSMOS method.* Methods: The authors used gradient-recalled echo (GRE) data of an entire fixed chimpanzee brain acquired at 7 T, including ideal COSMOS sampling and realistic rotations in vivo. They compared the results with ideal COSMOS, in-vivo feasible acquisitions with 3-8 orientations, and single-orientation iLSQR QSM.* Results: The authors found that in-vivo feasible and optimal COSMOS yielded high-quality susceptibility maps with increased signal-to-noise ratio (SNR) resulting from averaging multiple acquisitions. However, COSMOS reconstructions from non-ideal rotations about a single axis required additional L2-regularization to mitigate residual streaking artifacts.Here is the same information in Simplified Chinese text:* For: 这篇论文目的是 investigate COSMOS方法在非理想样本和磁矢相变的情况下，量子透镜 mapping (QSM) 在 primate 大脑中的准确性。* Methods: 作者使用了 gradient-recalled echo (GRE) 数据，包括理想的 COSMOS 样本和在 vivo 实际旋转。他们比较了理想的 COSMOS，在 vivo 可行的 3-8 个orientation 和单 orientation iLSQR QSM。* Results: 作者发现，在 vivo 可行和优化的 COSMOS 可以生成高质量的抵抗强度图，并通过多个取样提高信号响应比 (SNR)。然而，在非理想的单轴旋转情况下，需要额外的 L2 正则化来mitigate 剩下的扫描 artifacts。Abstract
Purpose: Field-to-susceptibility inversion in quantitative susceptibility mapping (QSM) is ill-posed and needs numerical stabilization through either regularization or oversampling by acquiring data at three or more object orientations. Calculation Of Susceptibility through Multiple Orientations Sampling (COSMOS) is an established oversampling approach and regarded as QSM gold standard. It achieves a well-conditioned inverse problem, requiring rotations by 0{\deg}, 60{\deg} and 120{\deg} in the yz-plane. However, this is impractical in vivo, where head rotations are typically restricted to a range of +-25{\deg}. Non-ideal sampling degrades the conditioning with residual streaking artifacts whose mitigation needs further regularization. Moreover, susceptibility anisotropy in white matter is not considered in the COSMOS model, which may introduce additional bias. The current work presents a thorough investigation of these effects in primate brain. Methods: Gradient-recalled echo (GRE) data of an entire fixed chimpanzee brain were acquired at 7 T (350 microns resolution, 10 orientations) including ideal COSMOS sampling and realistic rotations in vivo. Comparisons of the results included ideal COSMOS, in-vivo feasible acquisitions with 3-8 orientations and single-orientation iLSQR QSM. Results: In-vivo feasible and optimal COSMOS yielded high-quality susceptibility maps with increased SNR resulting from averaging multiple acquisitions. COSMOS reconstructions from non-ideal rotations about a single axis required additional L2-regularization to mitigate residual streaking artifacts. Conclusion: In view of unconsidered anisotropy effects, added complexity of the reconstruction, and the general challenge of multi-orientation acquisitions, advantages of sub-optimal COSMOS schemes over regularized single-orientation QSM appear limited in in-vivo settings.
摘要
目的：在量化感受mapping（QSM）中，场到感受性的倒置是不稳定的，需要数值稳定化通过Regularization或多样化数据收集。多样化样本收集（COSMOS）是已确立的多样化方法，被视为QSM的金标准。它实现了一个良好的倒置问题，需要在yz平面上进行0°、60°和120°的旋转。然而，这在生物体内不是实际可行的，因为头部旋转通常只能在+/-25°的范围内进行。非理想的抽象会导致倒置的稳定性受损，并需要进一步的Regularization来缓解这些残留的扭曲artefacts。此外，感受性不均匀在白 mater中的影响也没有考虑在COSMOS模型中，可能会引入额外的偏见。本研究对这些效果进行了全面的调查，并使用了7T的扩展echo（GRE）数据，包括理想的COSMOS样本和生物体内实际可行的旋转。方法：使用7T的GRE数据，包括理想的COSMOS样本和生物体内实际可行的旋转，并对比以下方法：理想的COSMOS、生物体内可行的多orientation iLSQR QSM和单orientation iLSQR QSM。结果：生物体内可行的多orientation COSMOS和理想的COSMOS可以提供高质量的感受度图，提高Signal-to-noise ratio（SNR）通过多次抽样。COSMOS重建从非理想旋转中需要额外的L2正则化来缓解剩下的扭曲artefacts。结论：由于不考虑感受性不均匀的影响，加之重建复杂化的问题，以及生物体内多orientation收集的挑战，对于在生物体内设置的情况，优于单orientation QSM的COSMOS方法的优势可能有限。