Wide dynamic range MR elastography of liver

Introduction: The dynamics of the complex shear modulus of biological tissue is determined by rigidity and connectivity of cells. Thus, measuring the frequency dispersion of G* of an organ can provide a macroscopic parameter which is related to the mechanical microstructure and therewith to the state of health of tissue. Magnetic Resonance Elastography (MRE) is capable of determining G* in vivo [1]. Therefore shear waves are excited and measured by motion-sensitive sequences. Multifrequency MRE has been proposed for measuring the dynamics of G* in liver, muscle and brain in vivo [2,3]. Problem: Structure information about the mechanical network of tissue is accessible by fitting the dispersion relation of G* in a wide dynamic range. The dynamic range of MRE is intrinsically limited e.g. due to constraints in spatial resolution, in encoding-gradient power and wave inversion artifacts. For these reasons MRE investigations of biological samples have been limited to a frequency range below 2.5 octaves [4,5]. Objective: Wide-dynamic range MRE is performed on tissue samples of bovine liver using a 1.5T human MRI system and a 7T animal scanner. The dynamics of G* is measured over more than 4.5 octaves (25 Hz–600 Hz) and analyzed employing the springpot model [3].