Chaos and COSMOS-Considerations on QSM methods with multiple and single orientations and effects from local...

Area of Science:

• Medical Imaging
• Neuroscience
• Biophysics

Background:

• Quantitative susceptibility mapping (QSM) is crucial for neuroimaging but faces challenges with ill-posed inversion problems.
• The Calculation Of Susceptibility through Multiple Orientations Sampling (COSMOS) method, while a gold standard, requires impractical multi-orientation acquisitions in vivo.
• Susceptibility anisotropy in white matter is not accounted for in standard COSMOS, potentially introducing bias.

Purpose of the Study:

• To investigate the effects of non-ideal sampling and anisotropy on QSM in primate brains.
• To evaluate the performance of in vivo feasible COSMOS acquisitions compared to ideal COSMOS and single-orientation methods.
• To assess the need for regularization in QSM with limited orientation data.

Main Methods:

• Acquisition of gradient-recalled echo (GRE) data from a fixed chimpanzee brain at 7T with 10 orientations.
• Comparison of QSM reconstructions using ideal COSMOS, in vivo feasible COSMOS (3-8 orientations), and single-orientation iLSQR.
• Analysis of streaking artifacts and signal-to-noise ratio (SNR) in susceptibility maps.

Main Results:

• In vivo feasible COSMOS reconstructions produced high-quality susceptibility maps with improved SNR.
• COSMOS reconstructions from non-ideal, single-axis rotations necessitated additional L2-regularization to reduce streaking artifacts.
• Averaging multiple acquisitions in feasible COSMOS improved map quality.

Conclusions:

• The practical advantages of sub-optimal COSMOS over regularized single-orientation QSM appear limited for in vivo applications.
• Challenges include unconsidered anisotropy effects, reconstruction complexity, and difficulties with multi-orientation acquisitions.
• Further research is needed to optimize QSM techniques for in vivo neuroimaging.