Remote Ultrasound Palpation for Robotic Interventions Using Absolute Elastography Caitlin Schneider 1 , Ali Baghani 1 , Robert Rohling 1,2 , and Septimiu Salcudean 1 1 Department of Electrical and Computer Engineering, University of British Columbia, Vancouver, BC, Canada 2 Department of Mechanical Engineering, University of British Columbia, Vancouver, BC, Canada Abstract. Although robotic surgery has addressed many of the chal- lenges presented by minimally invasive surgery, haptic feedback and the lack of knowledge of tissue stiffness is an unsolved problem. This pa- per presents a system for finding the absolute elastic properties of tissue using a freehand ultrasound scanning technique, which utilizes the da Vinci Surgical robot and a custom 2D ultrasound transducer for intra- operative use. An external exciter creates shear waves in the tissue, and a local frequency estimation method computes the shear modulus. Re- sults are reported for both phantom and in vivo models. This system can be extended to any 6 degree-of-freedom tracking method and any 2D transducer to provide real-time absolute elastic properties of tissue. Keywords: Ultrasound, Absolute Elastography, Robotic Surgery. 1 Introduction During laparoscopic procedures, surgeons face challenges such as limited vision of the surgical site and lack of dexterity and haptic feedback. In this type of surgery, the organs are only touched with the distal ends of long surgical instru- ments that must pass through the patient’s abdominal wall. While the da Vinci Surgical System (Intuitive Surgical, Sunnyvale, CA) has overcome with some of the issues that make laparoscopic surgery difficult, including stereoscopic vision and improved tool dexterity [7], the issue of haptic feedback remains unsolved. Ultrasound elastography has the potential to offer an alternative to providing haptic feedback by instead providing a full image of tissue stiffness and viscosity - the very properties that surgeons try to measure during manual palpation. Ul- trasound imaging is relatively inexpensive, non-ionizing and real-time, making it an advantageous imaging modality for intra-operative navigation. Conventional ultrasound has been integrated previously into the da Vinci Surgical System using multiple types of ultrasound transducers [14,15]. Previous ultrasound elastography has been primarily based on strain imaging. Ultrasound strain imaging, which provides images of relative tissue deformation in response to various compression levels applied by the ultrasound transducer N. Ayache et al. (Eds.): MICCAI 2012, Part I, LNCS 7510, pp. 42–49, 2012. c  Springer-Verlag Berlin Heidelberg 2012