Developing formalin-based fixative agents for post mortem brain MRI at 9.4 T

Area of Science:

• Neuroimaging
• Biophysics
• Materials Science

Background:

• High-field MRI requires specialized fixatives for brain tissue preservation.
• Standard formalin fixation can alter dielectric and magnetic resonance properties.

Purpose of the Study:

• Develop novel fixative agents for high-field MRI with optimized dielectric properties.
• Assess magnetic resonance (MR) properties in immersion-fixed brain tissue.

Main Methods:

• Formulated formalin-based agents with varying polyvinylpyrrolidone (PVP) and salt concentrations.
• Measured dielectric properties (100 MHz-4.5 GHz) and MR parameters (T1, T2, QSM) in pig brain tissue over 35 days.
• Estimated fixative penetration using Medawar coefficients derived from T2* kinetics.

Main Results:

• Fixatives with 5% PVP and 0.04% NaCl achieved in vivo-like B1 fields.
• PVP addition resulted in lower T1, higher T2*, and more paramagnetic QSM values.
• Fixative penetration kinetics (Medawar coefficient) were lower with PVP (0.9) compared to without (1.5).

Conclusions:

• Optimized formalin fixatives using PVP and low salt concentration enable in vivo-like B1 fields for high-field MRI.
• These fixatives improve MR property measurements, including magnetic susceptibility (QSM).
• The study provides a method to estimate fixative penetration kinetics in brain tissue.