Phase-regularized and displacement-regularized compressed sensing for fast magnetic resonance elastography.

Area of Science:

• Medical Imaging
• Biophysics
• Signal Processing

Background:

• Liver magnetic resonance elastography (MRE) is a noninvasive technique for assessing tissue stiffness.
• Accelerated MRE techniques like simultaneous multislice (SMS) and compressed sensing (CS) are crucial for reducing scan times but often apply uniform regularization.
• Existing methods apply a single regularization function to the complex MRE image, potentially overlooking distinct magnitude and phase characteristics.

Purpose of the Study:

• To design and evaluate novel compressed sensing methods for liver MRE that apply separate regularization to image magnitude and phase.
• To exploit the distinct spatiotemporal characteristics of MRE magnitude and phase for improved reconstruction quality.
• To assess the performance of these methods, particularly displacement-regularized compressed sensing (DRCS), in accelerated MRE.

Main Methods:

• Introduced two compressed sensing methods: phase-regularized compressed sensing (PRCS) and displacement-regularized compressed sensing (DRCS).
• PRCS uses 2D total variation on magnitude and 2D wavelet regularization on phase.
• DRCS employs 3D total variation on magnitude and includes a displacement fitting function for wavelet regularization of the displacement phasor, evaluated on in silico, in vitro, and in vivo datasets.

Main Results:

• DRCS demonstrated superior reconstruction quality compared to conventional CS in highly undersampled in silico and in vitro datasets, showing a 24% and 22% increase in displacement SSIM, respectively.
• DRCS achieved the strongest correlation (R=0.95) with full-sampled data for liver stiffness measurements, with the second-lowest mean bias (-0.18 kPa) and lowest coefficient of variation (3.6%) at a compression ratio of 4.
• Quantitative metrics including structural similarity index (SSIM) for magnitude, displacement, and shear modulus confirmed DRCS's improved performance.

Conclusions:

• Separate regularization of MRE magnitude and phase, particularly with the DRCS method, significantly improves reconstruction quality in accelerated scans.
• DRCS shows substantial potential for enhancing the accuracy and reliability of liver stiffness measurements obtained from accelerated MRE.
• The findings suggest DRCS as a promising technique for clinical applications requiring efficient and accurate MRE assessments.