Effect of off-frequency sampling in magnetic resonance elastography

Area of Science:

• Biomedical Engineering
• Medical Imaging

Background:

• Magnetic Resonance Elastography (MRE) uses shear waves to measure tissue stiffness.
• Brain MRE is susceptible to frequency mismatches between actuation, encoding, and sampling frequencies due to internal and external factors.
• These mismatches can arise from scanner vibrations or head-based damping mechanisms.

Purpose of the Study:

• To investigate the impact of frequency mismatch on MRE shear stiffness measurements in the brain.
• To quantify the effects of off-frequency encoding and sampling on stiffness quantification.
• To determine if frequency mismatch can explain variability in published brain MRE data.

Main Methods:

• Experiments were conducted on a dual-medium agarose gel phantom.
• Numerical simulations were used to compare and quantify the observed effects.
• The study analyzed the impact of off-frequency encoding and sampling on wave amplitude and stiffness estimates.

Main Results:

• Off-frequency encoding alone scales wave amplitude.
• Off-frequency sampling leads to global shear stiffness estimation errors and local variations mimicking stiffer/softer structures.
• Small frequency differences can cause up to 12.5% global stiffness variation and 3.7% local variation.

Conclusions:

• Performing MRE at frequencies deviating from tissue vibration introduces artifacts in stiffness images.
• Frequency mismatch is a potential explanation for reported data scatter and lack of repeatability in brain MRE studies.
• Accurate frequency matching is crucial for reliable and reproducible MRE stiffness measurements.