Balanced multipoint displacement encoding for DENSE MRI.

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Quantitative Imaging
• Biomedical Engineering

Background:

• Displacement encoding with stimulated echoes (DENSE) is a quantitative MRI technique encoding tissue displacement in signal phase.
• Existing DENSE sequences often use simple multipoint methods similar to phase contrast (PC) MRI.
• These simple methods can introduce phase noise and directional bias, potentially affecting image accuracy.

Purpose of the Study:

• To develop and evaluate general n-dimension balanced multipoint encoding for DENSE MRI.
• To assess the impact of balanced encoding on phase noise variance and covariance.
• To determine if balanced encoding improves displacement and strain mapping accuracy compared to simple methods.

Main Methods:

• Developed general n-dimension balanced multipoint encoding sequences for DENSE MRI.
• Experimentally measured phase noise variance and covariance using the new balanced methods.
• Compared performance metrics (phase noise, direction bias) against traditional simple multipoint encoding methods.
• Visualized displacement and strain maps in phantom and volunteer images.

Main Results:

• Phase noise variance decreased significantly: 73.7% (1D), 65.6% (2D), and 61.9% (3D) experimentally, matching theoretical predictions.
• Phase noise covariance decreased dramatically by 99.2% (2D) and 99.3% (3D).
• Inherent direction bias of simple methods was reduced to near zero with balanced encoding.
• Improved displacement and strain maps were visually observed in phantoms and volunteers.

Conclusions:

• General n-dimension balanced multipoint encoding offers substantial improvements in DENSE MRI quantitative accuracy.
• The method significantly reduces phase noise and direction bias, leading to clearer displacement and strain maps.
• Balanced multipoint encoding is a valuable advancement for DENSE MRI and is applicable to PC MRI as well.