Simultaneous magnetic resonance and optical elastography acquisitions: Comparison of displacement images and shear modulus estimations using a single vibration source.

Abstract

The mechanical properties of tissue are sensitive to pathological changes, which is the basis for using dynamic elastography as a diagnostic tool. The purpose of this study is a concurrent cross-modality comparison of two dynamic elastography methods, Magnetic Resonance Elastography (MRE) and Scanning Laser Doppler Vibrometry (SLDV) using a single vibration source method. Cylindrical soft tissue mimicking specimens of Plastisol and Ecoflex are stimulated with 60, 100, 150, and 250 Hz sinusoidal vibration during imaging. Specimen stiffness was also varied by adjusting the softener amount in each material. Displacement fields acquired using the two methods show similarity in wave front geometry at all frequencies. Magnetic Resonance Elastography (MRE) with 3D inversion and Optical Elastography (OE) with averaged 1D curve fitting were used to derive complex shear moduli from each imaging modality. MRE and OE shear storage modulus (n = 3) results were closest at 150 Hz with Plastisol G' (MRE) = 9.03 ± 0.43 kPa and G' (OE) = 8.46 ± 0.14 kPa while Ecoflex was G' (MRE) = 15.71 ± 0.95 kPa and G' (OE) = 13.71 ± 0.03 kPa. Correlation between MRE and OE complex shear moduli related by all 36 coupled scans performed during this study yield a Pearson's correlation of ρ = 0.88 with p < 0.001 for G' (storage modulus) and ρ = 0.85 with p < 0.001 for G" (loss modulus). The simultaneous imaging approach yields stiffness values within the same range and acceptable error margins for MRE and OE.