  Different clinical elastography devices show different liver-stiffness values
in the same subject, hindering comparison of values and establishment of
system-independent thresholds for disease detection. Therefore, authorities
request standardized phantoms that address the viscosity-related dispersion of
stiffness over frequency. A linear polymerized polyacrylamide phantom (PAAm)
was calibrated to the viscoelastic properties of healthy human liver in vivo.
Shear-wave speed as a surrogate of stiffness was quantified between 5 Hz and
3000 Hz frequency-range by shear rheometry, ultrasound-based time-harmonic
elastography, clinical MR elastography (MRE), and tabletop MRE. Imaging
parameters for ultrasound were close to those of liver in vivo.
Reproducibility, aging behavior and temperature dependency were assessed and
fulfilled requirements for quantitative elastography. In addition, the phantom
was used to characterize the frequency bandwidth of shear-wave speed of several
clinical elastography methods. The liquid-liver phantom has favorable
properties for standardization and development of liver elastography: first, it
can be used across clinical and experimental elastography devices in ultrasound
and MRI. Second, being a liquid, it can easily be adapted in size and shape to
specific technical requirements, and by adding inclusions and scatterers.
Finally, since the phantom is based on non-crosslinked linear PAA constituents,
it is easy to produce, indicating potential widespread use among researchers
and vendors to standardize liver-stiffness measurements.
