Brain mechanical property measurement using MRE with intrinsic activation

Area of Science:

• Biophysics
• Medical Imaging
• Materials Science

Background:

• Pathologies alter tissue mechanical properties, necessitating noninvasive characterization methods.
• Magnetic Resonance Elastography (MRE) quantifies tissue mechanics in vivo using induced vibrations and displacement measurements.
• External vibrations in MRE face challenges penetrating the cranium and meninges, limiting deep brain tissue assessment.

Purpose of the Study:

• To develop and validate a novel MRE method, 'intrinsic activation', that utilizes endogenous motion from blood vessel pulsation.
• To overcome the limitations of external vibration delivery in MRE for brain tissue analysis.
• To reconstruct and analyze brain tissue mechanical properties using intrinsic activation.

Main Methods:

• Employed a retrospectively gated phase contrast MR angiography sequence to capture tissue velocity at eight cardiac cycle phases.
• Numerically integrated velocities using Fourier transform to derive harmonic displacements.
• Reconstructed shear modulus images using linear elastic and poroelastic models.

Main Results:

• Achieved reproducible measurements of brain tissue mechanical properties (mean shear modulus: 8.1 kPa linear, 2.4 kPa poroelastic).
• Poroelastic reconstructions provided better visualization of gross brain structures compared to linear elastic models.
• Demonstrated significantly lower intra-subject variability than inter-subject variability, with greater changes observed over time.

Conclusions:

• Intrinsic activation effectively uses cardiac pulsation for MRE, eliminating the need for external mechanical actuators.
• The poroelastic model is more suitable for characterizing low-frequency brain tissue mechanics than the linear elastic model.
• Intrinsic activation offers a patient-friendly MRE approach without noticeable procedural differences for the patient.