Piezoelectric Tactile Sensor using Multisine Excitation for Differentiation of Biological Tissues and Phantom

Brain tumor surgery is a complex task that relies critically on a correct identification of tumor boundaries based on visual and tactile impressions performed by neurosurgeons. The information of the pre-operative 3D coordinates of the tumor provided by imaging techniques (e.g. Magnetic Resonance Imaging) will differ from the real position at the moment the skull is opened due to brain shift phenomenon. Thus, the development of assisting tools for intra-operative tumor delineation and tumor resection in neurosurgery is vital to increase the safety and accuracy of this procedure. In this contribution we report our efforts developing a piezoelectric tactile sensor using a piezoelectric bimorph where results of experiments carried out on tissue gelatin phantoms (with slightly differences in their mechanical properties) shown that is feasible to differentiate them by the evaluation of the frequency response function. Moreover, the use of broadband multisine excitations instead of standard frequency sweep has led to an important improvement in measurement time. In addition, it is discussed the design and selection of optimal excitation signals based on multisine that provide useful information to construct a valid model capable to estimate the mechanical parameters of biological tissues and soft materials. In practice, all biological tissues, including gelatin phantoms behave as a nonlinear viscoelastic material. Experiments using several contact forces were carried out to determine the influence of the contact force on the differentiation process. Measurements results showed that nonlinear distortions are present but still a linear model can be used to differentiate phantoms with high accuracy.