Application of DENSE-MR-elastography to the human heart

Area of Science:

• Biomedical Engineering
• Medical Imaging
• Cardiovascular Research

Background:

• Conventional Magnetic Resonance Elastography (MRE) faces challenges with short T(2) tissues, like the heart, due to long echo times.
• Existing fast MRE techniques, such as fractional encoding of harmonic motions, exhibit reduced motion sensitivity, especially at low frequencies.
• The need for sensitive and spectrally specific MRE techniques for cardiac applications is critical for accurate mechanical property assessment.

Purpose of the Study:

• To introduce and validate a novel MRE sequence based on displacement encoding with stimulated echoes (DENSE) for improved cardiac motion encoding.
• To enhance motion sensitivity compared to fractional encoding methods while maintaining spectral specificity similar to conventional MRE.
• To assess the feasibility and performance of DENSE-MRE in phantoms, ex vivo heart tissue, and in vivo human subjects.

Main Methods:

• A new MRE sequence was derived from the displacement encoding with stimulated echoes (DENSE) sequence.
• Theoretical spectral properties of the DENSE-MRE technique were analyzed.
• Validation was performed using phantom experiments, excised pork heart specimens, and in vivo imaging of a healthy volunteer.

Main Results:

• The DENSE-MRE sequence demonstrated significantly higher displacement sensitivity than fractional encoding of harmonic motions.
• Excellent agreement (8% maximum difference) was observed between DENSE-MRE and conventional MRE for displacement field measurements in phantoms and ex vivo hearts.
• Initial in vivo imaging successfully visualized propagating shear waves at 50 Hz in a healthy volunteer.

Conclusions:

• Displacement encoding with stimulated echoes MRE (DENSE-MRE) is a promising advancement for motion encoding in tissues with short T(2)* values.
• This novel technique offers superior motion sensitivity and spectral specificity, addressing limitations of current fast MRE methods for cardiac applications.
• DENSE-MRE shows potential for accurate, non-invasive assessment of cardiac tissue mechanics.