Analysis of a new combined stretch and pressure sensor for internal nodule palpation

In clinical practice doctors routinely palpate the patient's body with the fingers and palm to determine the condition of the parts beneath the skin surface. Detection of indwelling lumps and smaller nodules is an important consequence of such examination by touch. However, clinical palpation is frequently unable to detect the presence of nodules with sufficient clarity. Thus, there is a need for a sensor that can transduce the perception of a nodule with enhanced sensitivity. Deformable force-stretch array (DFSA) is a new sensor form proposed for indwelling nodule detection. The DFSA sensor combines an array of linearly deforming tactels with length change transducing stretch elements connecting the tactel tips. Biomechanical analysis of a human body palpation model comprising of the DFSA pressed upon a homogenous elastic slab containing a hard nodule has been performed. Body elasticity independent parameters strain index (SI) and bulge index (BI) have been formulated. From the SI and BI values, which are obtained from the measured values of tactel strain and stretch element length change, and a nomogram the nodule size and depth are derived. The results show that the sensor enables the identification of relatively small and deep-seated nodules. A variable elasticity body simulator has been used for experimental validation of the theoretical results.