  Interstitial fluid pressure (IFP), interstitial fluid velocity (IFV),
interstitial permeability (IP) and vascular permeability (VP) are cancer
mechanopathological parameters of great clinical significance. To date, there
is a lack of non-invasive techniques that can be used to estimate these
parameters in vivo. In this study, we designed and tested new ultrasound
poroelastography methods capable of estimating the magnitude and spatial
distribution of fluid pressure, fluid velocity and fluid flow inside tumors. We
theoretically proved that fluid pressure, velocity and flow estimated using
poroelastography from a tumor under creep compression are directly related to
the underlying IFP, IFV and fluid flow, respectively, differing only in peak
values. We also proved that, from the spatial distribution of the fluid
pressure estimated using poroelastography, it is possible to derive: the
parameter alpha, which quantifies the spatial distribution of the IFP; the
ratio between VP and IP and the ratio between the peak IFP and effective
vascular pressure in the tumor. Finally, we demonstrated that axial strain time
constant (TC) elastograms are directly related to VP and IP in tumors. Our
techniques were validated using finite element and ultrasound simulations,
while experiments on a human breast cancer animal model were used to show the
feasibility of these methods in vivo.
