Hematocrit Measurement with R2* and Quantitative Susceptibility Mapping in Postmortem Brain

Area of Science:

• Neuroimaging
• Medical Physics
• Radiology

Background:

• Noninvasive venous oxygenation quantification via MR imaging is crucial for understanding neurological diseases.
• Existing MR methods face limitations due to flow sensitivity and hematocrit assumptions.
• Postmortem imaging offers a flow-artifact-free environment for method evaluation and hematocrit calculation.

Purpose of the Study:

• To compare two venous oxygenation quantification methods: transverse relaxation (R2*) mapping and quantitative susceptibility mapping (QSM).
• To evaluate these methods in an in situ postmortem setting.
• To assess the correlation between R2* and QSM for venous oxygenation and hematocrit determination.

Main Methods:

• Performed transverse relaxation (R2*) mapping and quantitative susceptibility mapping (QSM) on a 4.7T MR imaging system.
• Acquired intravenous measurements in major draining intracranial veins of 3 postmortem subjects.
• Applied QSM to 10 healthy control subjects for comparison with reference venous oxygenation values.

Main Results:

• R2* mapping and QSM demonstrated a significant and strong correlation in early postmortem subjects (R² = 0.805–0.836).
• Consistently higher R2* and susceptibility values were observed in gravitationally dependent venous segments.
• Observed hematocrit values ranged from 0.102 to 0.580, with R2* and susceptibility reaching up to 291 s⁻¹ and 1.75 ppm, respectively.

Conclusions:

• R2* mapping and QSM show a high correlation for measuring venous oxygenation in large intracranial draining veins of early postmortem subjects.
• This study validates the use of QSM for evaluating in vivo venous oxygenation.
• QSM is also supported for postmortem hematocrit concentration assessment.