Quantitative susceptibility mapping for investigating subtle susceptibility variations in the human brain

Area of Science:

• Medical Imaging
• Biophysics
• Neuroimaging

Background:

• Quantitative susceptibility mapping (QSM) reconstructs tissue magnetic susceptibility from MRI field perturbation data.
• Reconstructions often require regularization to mitigate streaking artifacts due to the ill-posed nature of the inverse problem.

Purpose of the Study:

• Introduce a novel QSM algorithm, Homogeneity Enabled Incremental Dipole Inversion (HEIDI).
• Utilize regional homogeneity information from gradient echo phase images as a priori data.
• Analyze the impact of erroneous a priori information on susceptibility map accuracy.
• Evaluate HEIDI's performance against existing methods (TKD, MEDI) for subtle susceptibility variations.

Main Methods:

• Developed and implemented the HEIDI algorithm for QSM.
• Tested HEIDI on numerical models and volunteer data.
• Acquired HEIDI susceptibility maps with varying head orientations in the main magnetic field.
• Compared HEIDI results with Thresholded K-space Division (TKD) and Morphology Enabled Dipole Inversion (MEDI).

Main Results:

• HEIDI generated susceptibility maps free of streaking artifacts.
• The algorithm effectively depicted subtle magnetic susceptibility variations.
• Demonstrated significant dependence of apparent human brain tissue magnetic susceptibility on the main magnetic field direction.

Conclusions:

• HEIDI offers improved QSM reconstruction by leveraging regional homogeneity.
• The algorithm accurately captures subtle susceptibility changes, outperforming TKD and MEDI in tested scenarios.
• Findings highlight the orientation-dependent nature of brain magnetic susceptibility measurements.