A compact 0.5 T MR elastography device and its application for studying viscoelasticity changes in biological tissues during progressive formalin fixation.
OBJECTIVE
To develop a method of compact tabletop magnetic resonance elastography (MRE) for rheological tests of tissue samples and to measure changes in viscoelastic powerlaw constants of liver and brain tissue during progressive fixation.


METHODS
A 10-mm bore, 0.5-T permanent-magnet-based MRI system was equipped with a gradient-amplifier-controlled piezo-actuator and motion-sensitive spin echo sequence for inducing and measuring harmonic shear vibrations in cylindrical samples. Shear modulus dispersion functions were acquired at 200-5700 Hz in animal tissues at different states of formalin fixation and fitted by the springpot powerlaw model to obtain shear modulus μ and powerlaw exponent α.


RESULTS
In a frequency range of 300-1500 Hz, unfixed liver tissue was softer and less dispersive than brain tissue with μ = 1.68 ± 0.17 kPa and α = 0.51 ± 0.06 versus μ = 2.60 ± 0.68 kPa and α = 0.68 ± 0.03. Twenty-eight hours of formalin fixation yielded a 400-fold increase in liver μ, 25-fold increase in brain μ, and two-fold reduction in α of both tissues.


CONCLUSIONS
Compact 0.5-T MRE facilitates automated measurement of shear modulus dispersion in biological tissue at low costs. Formalin fixation changes the viscoelastic properties of tissues from viscous-soft to elastic-stiff more markedly in liver than brain. Magn Reson Med 79:470-478, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
Institute of Medical Informatics, Charité-Universitätsmedizin Berlin, Berlin, Germany.
Jürgen
J
Braun
Department of Radiology, Charité-Universitätsmedizin Berlin, Berlin, Germany.
Heiko
H
Tzschätzsch
Institute of Medical Informatics, Charité-Universitätsmedizin Berlin, Berlin, Germany.
Clara
C
Körting
Department of Radiology, Charité-Universitätsmedizin Berlin, Berlin, Germany.
Angela
A
Ariza de Schellenberger
Department of Radiology, Charité-Universitätsmedizin Berlin, Berlin, Germany.
Marika
M
Jenderka
Pure Devices, Würzburg, Germany.
Toni
T
Drießle
Pure Devices, Würzburg, Germany.
Michael
M
Ledwig
Department of Radiology, Charité-Universitätsmedizin Berlin, Berlin, Germany.
Ingolf
I
Sack
D000818:Animals; D001921:Brain / Q000000981:diagnostic imaging; D002417:Cattle; D004548:Elasticity; D054459:Elasticity Imaging Techniques; D004867:Equipment Design; D005557:Formaldehyde / Q000737:chemistry*; D005583:Fourier Analysis; D008099:Liver / Q000000981:diagnostic imaging; D008279:Magnetic Resonance Imaging; D012212:Rheology; D033081:Shear Strength; D013314:Stress, Mechanical; D013552:Swine; D016707:Tissue Fixation; D014783:Viscosity
D005557:Formaldehyde
brain; cylinder geometry; liver; magnetic resonance elastography; powerlaw; soft tissue rheology; springpot; vibrations