Viscoelastic Properties NMR vs Ultrasound

Since NMR is at present an emerging method for the characterization of mechanical waves, it cannot as yet be considered as a gold standard in elastography. In the same way the use of ultrasounds (US) for characterizing crystalline, amorphous or biological materials is also an emerging research 

Surprisingly the first attempts to measure displacements originating from genuine periodic or quasi-periodic perturbations were carried out in vivo. Those studies took advantage of the internal pulsatile motions provided by heart beating. As soon as 1982 small displacements from aortic pulsations were visualized in liver on M-mode scans.69 It was shown that such displacements could be calculated from correlated successive A-scans,70 with an application on liver.71,72 Correlation techniques were also applied on M-mode images to quantitatively estimate motions and deformations of fetal lung.73,74 

400-600 Hz. In this study, it was shown both theoretically and experimentally the presence of a shear wave focal zone that made possible a clear detection of the tumour-like inclusion of the phantom. Elastograms were computed from Doppler spectral variance and space resolution of elastography images was in the millimetre scale. 

Until now matter displacements as small as several micrometres were observed using sonoelasticity.87 More developments are needed to visualize periodic motions in the range of 100 nm as assessed in a few MRE studies.17,29,30 Less anecdotic is the capability of MRE to obtain 3D images of 

3D motion vectors. This allows complete determination of the strain at any coordinate of the investigated object, a significant advantage of NMR over challenging methods. 

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