Noninvasive assessment of the rheological behavior of human organs using multifrequency MR elastography: a study of brain and liver viscoelasticity

Abstract

MR elastography (MRE) enables the noninvasive determination of the viscoelastic behavior of human internal organs based on their response to oscillatory shear stress. An experiment was developed that combines multifrequency shear wave actuation with broad-band motion sensitization to extend the dynamic range of a single MRE examination. With this strategy, multiple wave images corresponding to different driving frequencies are simultaneously received and can be analyzed by evaluating the dispersion of the complex modulus over frequency. The technique was applied on the brain and liver of five healthy volunteers. Its repeatability was tested by four follow-up studies in each volunteer. Five standard rheological models (Maxwell, Voigt, Zener, Jeffreys and fractional Zener model) were assessed for their ability to reproduce the observed dispersion curves. The three-parameter Zener model was found to yield the most consistent results with two shear moduli mu(1) = 0.84 +/- 0.22 (1.36 +/- 0.31) kPa, mu(2) = 2.03 +/- 0.19 (1.86 +/- 0.34) kPa and one shear viscosity of eta = 6.7 +/- 1.3 (5.5 +/- 1.6) Pa s (interindividual mean +/- SD) in brain (liver) experiments. Significant differences between the rheological parameters of brain and liver were found for mu(1) and eta (P < 0.05), indicating that human brain is softer and possesses a higher viscosity than liver.

A comprehensive computational model of sound transmission through the porcine lung

“…Previously MRE has been successfully applied to the study of the mechanical properties of a variety of other organs and soft tissue regions in vivo, including the breast, brain, kidney, prostate, liver, and muscle. [16][17][18][19][20] Application to the lungs has proven more challenging given the poor signal-to-noise available in imaging due to a lower presence of hydrogen in air than in soft tissue (containing water) and the complex nature of vibratory wave propagation found in the lungs. A better understanding of mechanical wave motion in the lungs would aid in the interpretation of the wave images that are acquired using MRE to reconstruct a quantitative map of variation in mechanical properties that can correlate with injury, the progression of disease, and/or the response to therapy.…”

MR elastography measurement of the effect of passive warmup prior to eccentric exercise on thigh muscle mechanical properties

“…These assumptions allow calculation of the complex modulus G* from the temporally Fourier‐transformed 3D displacement field U using the Helmholtz‐type equation48: $G^{\ast }=-\rho {\omega }^2\frac{U}{\Delta U}$ …”

Finite element analysis to investigate variability of MR elastography in the human thigh

“…[22] calculated storage and loss modulus values at multiple frequencies for the grouped quadricep muscles (rectus femoris, vastus medialis, vastus intermedius and vastus lateralis). Parameters for the Zener model based on these measurements were calculated by minimising the cost function in the same manner as previous studies [24,23]:…”