Mechanical properties of the haptic signals indicative of a breast cancer tumor

A clinical breast exam (CBE), in which a nurse or doctor palpates a patient's breast tissue searching for hard lumps, is a recommended annual breast cancer diagnostic for women over 40. Recent advances in training technology have suggested that the sensitivity of this exam can be improved and that clinicians are interested in improving training approaches. Currently researchers have an incomplete understanding of which features of the force pattern an observer must perceive in order to recognize the presence of a tumor. This limitation in our knowledge limits our ability to build more effective simulators that emphasize the specific characteristics of the signal that clinicians must perceive. Three experiments were performed using tissue analogs made from silicone rubber embedded with hard spheres. The size of the balls, their depth and the stiffness of the silicone were varied. The force exerted on a probe indented at regular intervals along the samples revealed the general force profile that a clinician may experience on his or her finger pad when searching for a tumor. Several measures of the force profiles were compared to the salience of the ball within the silicone: the ratio of the response force directly above the sphere to the force response far from the sphere, the rate of change of the force response near the sphere, and difference between the force above and to the side divided by the force to the side. These measures correlated with salience when the ball size and ball depth was varied, but not when the silicone stiffness varied. The results suggest that the relationship between the force profile and the salience of the stimulus is more complex that expected. Once this relationship is more fully understood, new training tools and procedures can be developed to trains clinicians and improve the sensitivity of clinical breast exams.