Nonlinear Elasticity Assessment with Optical Coherence Elastography for High-Selectivity Differentiation of Breast Cancer Tissues

Abstract

Soft biological tissues, breast cancer tissues in particular, often manifest pronounced nonlinear elasticity, i.e., strong dependence of their Young’s modulus on the applied stress. We showed that compression optical coherence elastography (C-OCE) is a promising tool enabling the evaluation of nonlinear properties in addition to the conventionally discussed Young’s modulus in order to improve diagnostic accuracy of elastographic examination of tumorous tissues. The aim of this study was to reveal and quantify variations in stiffness for various breast tissue components depending on the applied pressure. We discussed nonlinear elastic properties of different breast cancer samples excised from 50 patients during breast-conserving surgery. Significant differences were found among various subtypes of tumorous and nontumorous breast tissues in terms of the initial Young’s modulus (estimated for stress < 1 kPa) and the nonlinearity parameter determining the rate of stiffness increase with increasing stress. However, Young’s modulus alone or the nonlinearity parameter alone may be insufficient to differentiate some malignant breast tissue subtypes from benign. For instance, benign fibrous stroma and fibrous stroma with isolated individual cancer cells or small agglomerates of cancer cells do not yet exhibit significant difference in the Young’s modulus. Nevertheless, they can be clearly singled out by their nonlinearity parameter, which is the main novelty of the proposed OCE-based discrimination of various breast tissue subtypes. This ability of OCE is very important for finding a clean resection boundary. Overall, morphological segmentation of OCE images accounting for both linear and nonlinear elastic parameters strongly enhances the correspondence with the histological slices and radically improves the diagnostic possibilities of C-OCE for a reliable clinical outcome.

Mapping Large Strains in Phase-Sensitive OCT: Key Role of Supra-Pixel Displacement Tracking in Incremental Strain Evaluation

“…wavelength of 1300 nm (and spectral width 90-100 nm) similar to those used in previous works [22,25,26].…”

“…However, those papers discussed fairly homogeneous tissues and moderately large strains (usually essentially below 10%), for which tracking of a particular tissue portion was not very critical in contrast to strongly heterogeneous tissues (such as cancerous ones discussed in Ref. [22]), for which the procedures of correct particle tracking deserve a special detailed discussion.…”

“…Examples of application of these procedures to particular biomedical problems can be found in Refs. [22,25] (morphological segmentation of human breast-cancer samples) and Ref. [26] (monitoring of morphological changes of animal-model tumors).…”

“…( 16), in the vicinity of point σ0 the current Young's modulus can be represented as: so that the quadratic nonlinearity parameter β near the stress point σ0 can be found as (19) The initial stress can be chosen zero (corresponding to the very beginning of tissue compression) or some non-zero value may be chosen. Preliminary studies demonstrated that various tissue components (for example, morphological component of breast cancer) can exhibit very similar values of the Young's modulus, but at the same time the very same components may demonstrate clearly differing values of the nonlinear parameter β [22]. This fact opens the possibility to differentiate various tissue types using in combination the characteristic values of both the Young's modulus and the nonlinearity parameter.…”

“…However, larger strains that cause essentially suprapixel displacements are also of great interest for various applications (e.g., for studying thermo-mechanical deformations, drying, osmotic deformations [14][15][16][17][18][19]), as well as for studying stress-strain dependences beyond the linear Hooke's law. The latter, for many tissues, may be essentially violated for strains on the order of several tens of percent [8,[20][21][22].…”