Quantification of linear and nonlinear elasticity by compression optical coherence elastography for determining lymph node status in breast cancer

We report the first application of compression optical coherence elastography (C-OCE) to evaluate both linear and nonlinear elastic properties of lymph nodes (LNs) for assessing their status, which is an important factor for detecting metastasis and staging breast cancer. The reported study involved 27 excised sentinel and axillary LNs from 24 patients with breast cancer, including normal LNs (n = 6), reactive LNs with follicular hyperplasia (n = 7) and sinus histiocytosis (n = 8), and metastatic LNs (n = 6). C-OCE data were compared with co-registered gold-standard histopathology and demonstrated a significantly higher contrast in differentiation of LNs as compared to structural optical coherence tomography imaging. Normal LNs are characterized by low stiffness values in the areas of LN cortex (<200 kPa). C-OCE revealed that abnormal reactive LNs with follicular hyperplasia exhibit moderately increased stiffness (200-300 kPa) in the cortex areas and more pronounced stiffness increase (400-600 kPa) in the areas of sinus histiocytosis. LNs with total metastasis exhibit fairly uniformly distributed highest stiffness values (>600 kPa). Since in terms of the tangent Young's modulus there remained an appreciable overlap among these types of LNs, we also evaluated their elastic nonlinearity parameters. Complementary usage of both linear and nonlinear elastic parameters enabled very clear differentiation of all four main states of LNs. Thus, C-OCE imaging demonstrates high potential for future intraoperative usage to rapidly determine the LN status during breast-conserving surgery and to assess the extent of the cancer cells propagation in regional lymphatic collectors for preserving benign LNs. This is important for reducing the associated risks and complications (such as lymphedema) from excessive surgical removal of lymphoid structures.