Uniqueness of poroelastic and viscoelastic nonlinear inversion MR elastography at low frequencies. (27th March 2019)

• Record Type: Journal Article
• Authors: McGarry, Matthew; Van Houten, Elijah; Solamen, Ligin; Gordon-Wylie, Scott; Weaver, John; Paulsen, Keith
• Is Part Of: Physics in medicine & biology. Volume 64:Number 7(2019:Apr.)
• Publication Date: 2019-03-27
• Subjects: elastography -- poroelastic -- viscoelastic -- simulation -- phantom; Biophysics -- Periodicals; Medical physics -- Periodicals; 610.153
• DOI: 10.1088/1361-6560/ab0a7d
• Languages: English
• ISSNs: 0031-9155

Abstract

Abstract: Intrinsic actuation MR elastography (IA-MRE) exploits natural pulsations of the brain as a motion source to estimate mechanical property maps. The low frequency motion of IA-MRE introduces new considerations for inversion algorithms relative to traditional external actuation MRE. Specifically, inertial forces become very small, which leaves low frequency viscoelastic inversions with a non-unique scalar multiplier. Biphasic poroelastic inversions include additional fluid–solid interaction forces to balance the elastic forces, which avoids the non-uniqueness. Analyzing the convergence behavior from different starting values using 1 Hz simulated data, IA-MRE data from a gelatin phantom and in vivo brain IA-MRE data reveal that higher frequency (50 Hz) viscoelastic inversion reaches the correct, unique solution regardless of initial property estimate; whereas, low frequency viscoelastic inversion recovers relative values of shear modulus. In the presence of measurement noise, the non-unique scalar multiplier is determined by the softest material reaching the prescribed lower bound on shear modulus. Poroelastic inversion produces a unique solution at both 50 Hz and 1 Hz; however, hydraulic conductivity must be known or accurately estimated in order to recover quantitatively accurate shear modulus maps at low frequency.