Early relaxation time assessment for characterization of breast tissue and diagnosis of breast tumors.

During recent years, many efforts have been made to increase the efficiency of the treatment methods by adjusting the treatment with the specification of related tissue. Non-penetrating indentation test is a non-invasive method for characterizing mechanical behavior of the tissue. In this study, characterization of the viscoelastic behavior of breast tissue is investigated by means of the relaxation time. To this end, an in-vivo study is conducted on the breast tissue of 18 female cases by performing a compressive indentation test with controlled rate of deformation. The test is performed in two subsequent stages; at first stage, the tissue is compressed by a specified strain rate and is called the loading procedure. At the second stage, which is the unloading procedure, the load is removed by the same rate and the tissue behavior is studied while it returns to the unloaded position. A generalized Maxwell model with two Maxwell-arms is used to model the tissue's viscoelastic response. Force vs. compression data during the unloading course, are obtained and interpolated by the transfer function of the viscoelastic model and two relaxation times are obtained. The smaller in value is referred to as the early relaxation time and results show that it has variation with the tissue's mechanical structure, which makes it suitable as a characteristic property. This property has insignificant variation over each individual's breast tissue, meanwhile major variation is observed between different cases and also in the presence of a tumor. Results show that existence of tumor in the breast tissue can increase the early relaxation time up to 6 times more than the corresponding value at the healthy tissue. Based on case-dependent character of the early relaxation time, tumor detection procedure based on the elevation of characteristic early relaxation time should be performed individually for each case.