Optical assessment of tissue mechanical properties

Many disease processes, such as scirrhous carcinoma of the breast and atherosclerosis physically manifest themselves as changes in the mechanical properties of the involved tissue. Optical evaluation of the mechanical properties of biological tissues offers methods that can directly provide information regarding the state of health of both hard and soft tissue. Clinically, this information may be used for diagnostic purposes. Since all biological tissues display viscoelastic behavior and therefore exhibit a time dependence of their mechanical behavior, the important quantities for evaluating the mechanics of tissue under load are those that reflect this rime dependence. For example, by evaluating the retardation (or, alternatively, the relaxation) spectrum of the tissue, the underlying molecular processes that govern the mechanical behavior may be elucidated. Understanding these spectra may provide insight into pathological processes and also provide some guidance for the development of synthetic materials or engineered tissues to replace damaged or pathological tissue. Thus, there is a need for methods that directly assess the time rate of the mechanical response of tissue to an imposed load. Herein, a few such methods will be discussed and applications to biomaterials and medical diagnostics will be discussed.