Microfabricated Instruments for Fetal Cardiac Surgery: Experiments on Haptic Tissue Recognition Anna Eisinberg, Oliver Tonet * , Paolo Dario CRIM - Scuola Superiore Sant’Anna Giovanna Macr` ı, Maria Chiara Carrozza ARTS Lab - Scuola Superiore Sant’Anna ABSTRACT This paper describes the performance of a microfabricated gripper, equipped with semiconductor strain gauges as force sensors, and teleoperated via a PHANTOM haptic interface. The main objective is to demonstrate that the force sensed by the gripper, when ren- dered to the user by means of a haptic interface, can provide a feel- ing of tissue stiffness that allows the user to successfully discrim- inate among different tissue types during the most delicate opera- tions of minimally invasive surgery, such as in fetal cardiac surgery. Experiments aimed to prove the usefulness of this approach have been carried out: the system allowed unskilled operators to qual- itatively discriminate pieces of pulmonary valve and endocardium (excited from fetal lamb). Haptic response models were created from the measured data and additional experiments were carried out off-line on a PHANTOM interface. User trials on the simu- lated tissue demonstrate the excellent discrimination capability of the system. CR Categories: H.5.2 [Information interfaces and presentation]: User Interfaces—Haptic I/O Keywords: Microgripper, haptic interfaces, fetal surgery 1 I NTRODUCTION Nowadays many research efforts in different technical fields are be- ing devoted to design novel to improve the ability of surgeons to safely perform precision operations. There is an increasing number of surgical procedures that can be now carried out in with mini- mally invasive techniques. Minimally Invasive Surgery (MIS) rep- resents a key example of strong cooperation between medical peo- ple and researchers in engineering and computer science. Actually during MIS a lot of relevant information, useful to help surgeons to safely interact with the intra-operative environment, are less effec- tive, such as visual perception, or even distorted or missing, such as haptic perception, and this results in limited sensory abilities and in a severe reduction of dexterity in manipulation. In this context, it is clear that microengineering and microrobotics can provide very powerful means for the development of a novel generation of re- search instruments. In addition, the development of specific hap- tic interfaces that help surgeons to feel the forces exerted by their microinstruments in a realistic way, is also an important research topic. In the last few years, a wide variety of laboratory apparatuses and microfabricated instruments have been developed and became fundamental tools for minimally invasive diagnostics and surgery. First prototypes of smart instruments, able to provide the opera- tor some sort of haptic feedback during MIS, have been devised in the late 1980’s [3]. Most progresses have been achieved during the 1990’s, both in the field of visual and haptic feedback. Concerning * e-mail: oly@sssup.it the visualization issue, enhancement of current performance in la- paroscopic surgery could be achieved either by higher definition im- ages from the vision system, or by employing different techniques. An example can be found in [11], where an infrared imaging-based system is illustrated. The use of stereoscopic head mounted dis- plays (HMDs) is also considered to be helpful for improving the surgeons’ sense of immersion during task execution [7]. On the other hand, HMDs can cause serious real world occlusion prob- lems [16]. Anyway, most research efforts have been focused on the introduction of haptic feedback, intended as tactile- and/or force- feedback, and many papers have been devoted to the distinction between haptic, tactile and force feedback [8]. Kitagawa et al. pro- vide a clear classification in [9] and then investigate differences in forces applied while performing knot tying exercises. Other studies focused on the evaluation of surgeon performance during the inter- action with stiff objects [17]. Nevertheless, up to now, few studies have been focused on the role of force feedback in the manipula- tion of soft tissues. One of these was done by Wagner et al. in [19]. He observed that, in blunt dissection, the absence of force feedback increased the magnitude of forces applied to the tissue and also the number of errors that could damage the tissue. Our approach is as well focused on force feedback: prelimi- nary work on force sensing micro instruments is presented in [14] and [13]. Because of size and limited spatial resolution of tactile sensors, tactile feedback has, as a matter of fact, severe limita- tions, mainly imposed by technological constraints [10]. Moreover, applications in MIS require small overall size of the sensorized tools. The main goal of recent systems for MIS (but also for macro and open surgery) is, in most cases, to implement teleoperation schemes. Such systems typically consist in two slave manipula- tors in the operating subsystem, and a complete remote workstation with master manipulators, including visual, auditory and force re- flection capabilities. This tele-surgery concept has been enhanced and brought to a commercial stage, e.g. da Vinci system by Intuitive Surgical, Inc. [6]. Besides “traditional” MIS (laparoscopy, arthroscopy), an emerg- ing and interesting field of application can be found in prenatal surgery. In a prenatal surgery scenario, characteristic forces and dimensional ranges scale down to really small values, compared to those common in open field surgery, and surgeons often need some augmenting mechanisms to be aware of how strongly they are inter- acting with the most delicate structures of the fetus. For the stated above reasons, fetal surgery can be considered as one of the new frontiers of MIS. In the last few years, diagnostics of congenital pathologies in fetus is becoming established, but there are how- ever a very few specialized centers worldwide where fetal surgical procedures are performed. These interventions concern mostly spe- cific pathologies, such as spina bifida and, although these are very important from the scientific point of view in terms of future per- spectives, to date, fetal surgery for the neural tube does not give any chance of well-assessed clinical results. These types of intervention are considered at high risk of abortion, and the solution, by now, is to operate just after the birth, in the first 24 hours. As regards congenital heart diseases, therapeutic treatments are even less ad- vanced. Ultrasound and Doppler sonography, beginning from week 18, with final diagnosis on week 20-22, allow detecting patholo- 273 Symposium on Haptic Interfaces for Virtual Environment and Teleoperator Systems 2006 March 25 - 26, Alexandria, Virginia, USA 1-4244-0226-3/06/$20.00 ©2006 IEEE