Development and Evaluation of a Simulator of

Development and Evaluation of a Simulator of Invasive Procedures in Pediatric Bone Marrow Transplant Liliane dos Santos MACHADO and Marcelo Knõrich ZUFFO Laboratório de Sistemas Integráveis – Escola Politécnica da Universidade de São Paulo Av. Prof Luciano Gualberto, 158 travessa 3 Cidade Universitária São Paulo/SP – BRAZIL 05508-900 {liliane, mkzuffo}@lsi.usp.br Abstract. In the past we proposed the development of a bone marrow harvest simulator to support the learning of this procedure. This work presents some aspects of this development and shows the results and analysis of the simulator after its first evaluation.

Introduction Recently, virtual reality based simulators for pediatric oncology were proposed and developed focusing on bone marrow transplant [1]. This minimally invasive procedure is a treatment approach for hematologic, oncologic and immunologic diseases. It consists of the extraction, treatment and re-infusion of the bone marrow. In children, the procedure is made through many material aspirations, using a thick needle and syringe, from the iliac crest bone marrow from the donator under general anesthesia [2]. This is a blind procedure performed without any visual feedback except the external view of the donor. So, the physician needs to feel the skin and bone levels trespassed by the needle to reach the bone marrow and then start the material aspiration. The system developed has as challenge to provide realistic simulation basically by the union of touch and stereoscopic view senses on a desktop based simulator. The system intends to be used as an alternative method of training and eliminate the use of guinea pigs, being available at any time, and offering reusability. This is the first VR system developed for pediatric medical training and the first one developed in Brazil. It was designed and calibrated to be used for pediatric training in bone marrow harvest. The pediatric approach is necessary due the particularities related to the properties of children’s tissues. 1. Development The simulator is a semi-immersive system that allows the user training and sharing with an expert all three steps of a bone marrow harvest procedure: visualization, palpation and harvest. These steps were used to design the three modules of the system. Because the objective of the system is training and consequently learning, the interactive anatomy study can offer an improvement to the educational process. This can be done in the visualization module where the user can explore the model and observe the tissue layers with transparency. In the second module the user can touch the virtual body

and perform a palpation to determine where is located the iliac crest. The location is done from the touch perception of the skin and the structures below it. After the location of the iliac crest the last module can be activated and the harvest can be performed. For this the user manipulates a virtual needle to perforate the virtual body. During the perforation the tissue layers under the skin can be felt and must be used to determine when the bone marrow layer was reached [3]. The execution of the modules can be observed in figure 1.

Figure 1: The observation, palpation and harvest module of the bone marrow harvest simulator.

The system utilizes different visual and haptic models controlled by independent routines that render three models each one. These three models represent six tissue layers: epidermis, dermis and subcutaneous, periosteum, compact bone, and bone marrow. In spite of the haptic models have been simplified for performance reasons, the total number of polygons rendered by the system is 30977. For the interaction the user manipulates a 6DOF haptic device [4] represented as a finger in the palpation module and represented as a needle in the harvest module. The tactile sensations attributed to the layers were related to their elasticity, stiffness, density and roughness. For this, control routines were defined to allow collision and force applied detection. All the modules offer stereoscopic visualization and parallax adjustments to provide a natural interaction in the 3D space. 2. Calibration In spite of force models [5] and devices to measure in vivo tissue properties [6] have been developed, the numerical values of the properties of the human tissues are still unknown. This fact has special relevance when it is taken into account that the properties of children’s tissues present characteristics different from adults. Because of that, only physicians used to the bone marrow harvest procedure know and could describe the tactile sensations related to the procedure. To collect and register the characteristics of each tissue from the models we developed a calibration system. In this system different cubes were present to an expert physician that choose the one that better match the sensation he experiments when performing a real bone marrow harvest. Initially, the presented properties embraced the scale of forces of the haptic device used and later on they were refined according to the subsequent choices done by the doctor. For each tissue layer of the simulator were calibrated: elasticity, density, roughness and stiffness. 3. Evaluation After the conclusion of the simulator with the calibration of the tactile properties, a first evaluation of the same was made. The goal of the evaluation was to determine the degree of the potential users' satisfaction with the system. For this, aspects related to the virtual

environment, the interaction and the realism, were taken in account to elaborate a questionnaire. Based on evaluation questionnaires of immersive systems and simulators [7] [8], we formulated nine questions tends as answer a discreet scale understood between the extremes very positive (10) and very negative (0), when applicable. Thus, the specialist appreciated the several characteristics of the system, as well as its totality through a brief questionnaire. The formulated questions and respective marks were: “How do you consider your experience in harvest or transplant of bone marrow? (10)”, “Did you feel comfortable and involved with the simulation? (8)”, “Are the haptic/tactile properties appropriated? (6)”, “Is the visual representation adequate to an initial training? (10)”, “How much similar is the visualization in relation to the reality? (8)”, “Do you consider important/valid the previous study of the anatomy as presented in the system? (10)”, “How do you classify the environments in interaction aspects? (10)”, “How much similar is the interaction if compared with the real procedure? (5)”, “How do you classify the system in general? (7)“. 4. Conclusions In this first evaluation the system received seven as global rate and demonstrated potentiality and user motivation when used in the learning process. The presence of a study/observation module was considered important because it complemented the theoretical study and set up the user to start the simulation. The visualization platform, composed by shutter glasses and a 21” monitor, was considered comfortable and natural, besides to allow the visualization for other people. In general, the simulation environment was considered easy to use and comprehend because its simple and intuitive menus. The limitations observed are related to the haptic feedback: a more powerful device should be used to provide and support greater forces. This avoided the attribution of the necessary hardness to the bone layer. Other limitation is related to the torque lack, what makes the manipulation of the needle angularity free during the puncture, what do not happen in the real procedure. Additionally, the use of a haptic glove was mentioned as a solution for a more realistic palpation. Acknowledgements This project is funded by Fundação de Amparo à Pesquisa do Estado de São Paulo, grant # 99/01583-0, with additional support from RECOPE/FINEP – “Visualização na Engenharia”. Thanks to Dr. Vicente Odone Fo and Dr. Andre Nebel de Mello for their support in this work. References [1] Machado, L.S et al., A Virtual Reality Simulator for Bone Marrow Harvest for Pediatric Transplant. Studies in Health Technology and Informatics, vol. 81, pp.293-297. Amsterdam, IOSPress, 2001. [2] Pizzo, P.A.; Poplack, D.G. Principles and Practice of Pediatric Oncology, 3th edition. Lippincott-Raven Publishers, 1997. [3] Machado, L.S. et al., Tactile Modeling, Stereoscopic Visualization e Evaluation Aspects of a Simulator of Bone Marrow Harvest for Transplant (in Portuguese). Proceedings of the 4th SBC Symposium on Virtual Reality, pp. 23-31, Brazil, 2001. [4] Massie, T.; Salisbury, J.K. The PHANTOM Haptic Interface. ASME Proceedings, 1994. [5] Holton, L.H. Force Models for Needle Insertion Created from Measured Needle Puncture Data. Studies in Health Technology and Informatics, vol. 81, pp.180-186. Amsterdam, IOSPress, 2001. [6] Brouwer, I. et al., Measuring In Vivo Animal Soft Tissue Properties for Haptic Modeling in Surgical Simulation. Studies in Health Technology and Informatics, vol. 81, pp.69-74. Amsterdam, IOSPress, 2001. [7] Ijsselsteijn, W. et al., Presence: Concept, Determinants and Measurement. Proceedings of SPIE, Human Vision and Electronic Imaging V, p.3956-3975, 2000. [8] McCarthy, A.; Harley, P.; Smallwood, R. Virtual Arthroscopy Training: Do the “Virtual Skills” Developed Match the Real Skills Required? Studies in Health Technology and Informatics, vol. 62, pp.221227. Amsterdam, IOSPress, 1999.