Quantitative susceptibility mapping (QSM) as a means to measure brain iron? A post mortem validation study

Area of Science:

• Neuroimaging
• Biomarkers
• Magnetic Resonance Imaging

Background:

• Quantitative susceptibility mapping (QSM) infers tissue magnetic susceptibility from MRI phase images.
• Previous studies correlated QSM with brain iron but relied on historical iron concentration data.
• The reliability of QSM for assessing in vivo brain iron levels requires direct validation.

Purpose of the Study:

• To directly investigate the relationship between magnetic susceptibility and iron concentration in post mortem human brains.
• To determine the accuracy of QSM in quantifying iron in different brain tissues.
• To validate QSM as a reliable method for assessing brain iron.

Main Methods:

• Utilized unfixed post mortem brains from 13 subjects.
• Acquired MRI data for quantitative susceptibility mapping (QSM).
• Measured iron concentration using inductively coupled plasma mass spectrometry (ICP-MS).

Main Results:

• A strong linear correlation (r=0.84, p<0.001) was observed between QSM and iron concentration in gray matter.
• A weaker correlation (r=0.27, p<0.001) was found in white matter.
• The findings support iron, primarily bound to ferritin, as the main source of susceptibility in deep gray matter.

Conclusions:

• Iron is the dominant source of magnetic susceptibility in deep gray matter, quantifiable with QSM.
• QSM provides a reliable method for assessing iron in gray matter.
• Iron quantification in white matter using QSM is less accurate due to confounding diamagnetic signals from myelin.