Estimation of Mechanical and Transport Parameters in Cancers Using Short Time Poroelastography

Abstract

Mechanical and transport properties of cancers such as Young’s modulus (YM), Poisson’s ratio (PR), and vascular permeability (VP) have great clinical importance in cancer diagnosis, prognosis, and treatment. However, non-invasive estimation of these parameters in vivo is challenged by many practical factors. Elasticity imaging methods, such as “poroelastography”, require prolonged data acquisition, which can limit their clinical applicability. In this paper, we investigate a new method to perform poroelastography experiments, which results in shorter temporal acquisition windows. This method is referred to as “short-time poroelastography” (STPE). Finite element (FE) and ultrasound simulations demonstrate that, using STPE, it is possible to accurately estimate YM, PR (within 10% error) using windows of observation (WoOs) of length as short as 1 underlying strain Time Constant (TC). The error was found to be almost negligible (< 3%) when using WoOs longer than 2 strain TCs. In the case of VP estimation, WoOs of at least 2 strain TCs are required to obtain an error < 8% (in simulations). The stricter requirement for the estimation of VP with respect to YM and PR is due its reliance on the transient strain behavior while YM and PR depend on the steady state strain values only. In vivo experimental data are used as a proof-of-principle of the potential applicability of the proposed methodology in vivo . The use of STPE may provide a means to efficiently perform poroelastography experiments without compromising the accuracy of the estimated tissue properties.

Non-invasive imaging of interstitial fluid transport parameters in solid tumors in vivo

“…To estimate YM and PR, we used Eshelby’s theory for elliptical tumors 46 . YM and PR are important indicators for tumor diagnosis and prognosis 52 , 59 . Likewise, poroelastic material properties such as interstitial hydraulic conductivity (IHC), vascular permeability (VP), extracellular volume fraction (EVF), interstitial space fraction (IVF), etc.…”

“…Likewise, poroelastic material properties such as interstitial hydraulic conductivity (IHC), vascular permeability (VP), extracellular volume fraction (EVF), interstitial space fraction (IVF), etc. are important markers of tumor progression and may be used to assess the efficacy of treatments 5 , 25 , 52 , 60 , 61 . These poroelastic properties can have substantial impact on drug delivery to the tumor.…”

“…Elevated IFP and SS inside the tumor could alter the strains experienced by the tumor and, therefore, would affect the estimation of the poroelastic measurements in this study. It is reasonable to expect that elevated IFP and SS may not affect the estimates of the poroelastic parameters as long as they are much smaller than the applied stress in the poroelastography experiment (1–5 kPa 46 , 52 ). However, in cases where IFP and SS are significantly high and/or comparable to the applied poroelastography stress, a correction in the computation of the bulk and shear moduli may be required to obtain accurate estimates of the poroelastic parameters.…”

“…To determine the YM and PR of the tumor and background tissue, we used our Eshelby-based method in 45 . In case of the in vivo experiments, the tumor shape Was approximated with its best fit ellipse using eigen decomposition 46 – 52 . Tumor boundaries were segmented from the axial strain elastograms.…”