A 3d Visualization Tool for Landmark Allocation

CurrentCAD/CAM software in prosthesis design is based on various landmark positions on a residual limb, When a user changes the view on one of the sub-windows, the views of the other two sub-windows will also change such as, weight bearing areas: patellar notch, medial and lateral flares of tibia and pressure relief areas: fibular head, distal tibia and fibular. A 3D visualization tool to explore ultrasound data of both external shape and internal tissue and bony structure of a residual limb is developed to aid landmark allocation. This study demonstrates the potential to improve prosthetic CAD/CAM practice using ultrasound. Keyworda: visualization, prosthesis, ultrasoundimage. Introduction The comfort of the prosthesis and its utility in restoring the amputee’s modility are mainly determined by the fit of prosthetic socket. We have previously reported a 3D imaging system for the residual limb using ultrasound [1] [2]. The main advantage of the ultrasound method is its ability to show the limb’s internal structure.The additional information about the limb’s bony and tissue structure can help the prosthetists to accurately locate the weight bearing and pressure relief area in prosthetic socket design. Recently we have developed a 3D-visualization tool to explore the residual limb’s internal structure effective y and to defhe landmarks interactively on its CAD/CAM model. Method 1) System Overview The Wright State 3D Limb scanning system for residual limb using ultrasoundhas been reportedpreviously [1] [2]. It scans the limb using a linear array ultrasound transducer in vertical B-scan mode and horizontal compounding mode and acquires two sets of ultrasound images. A 3D volume image is generated using data alignment and fusion of these two sets of image data that will be reported separately. 2) Limb Visualization and Landmark Allocation A 3D CAD/CAM surface model extracted from vertical mode scanned images, together with a horizontal and a vertical cutting slices of ultrasound image, visualize the 3D volume data of limb. The 3D CAD/CAM model guides the two cutting slices in exploring 3D volume data and landmark identification. The user can view a specific vertical or horizontal slice of the residual limb with respect to the CAD/CAM model. If a particular landmark is identified, the landmark is then annotated on the corresponding 3D CAD/CAM model for prosthetic socket design. The visualization tool is developed using Microsoft Visual C++ and OpenGL library for the Microsoft Win95/NT operating systems. The typical user interface of the visualization tool is shown in Fig. 1. There are three subwindows in the interface, which show the horizontal and vertical slices and 3D surface wireframe simultaneously. 0-7803-5674-8/99/$ 10.00 @ 1999 IEEE 651 accordingly. It gives a user an interactive tool to exploring internal 3D volume data with a direct reference to the corresponding 3D CAD/CAM model. We expect that internal tissue and bony structure can directly aid landmark allocation and make the landmark definition more accurate. Fig. 1: User interface of the visualization tool. Left window shows the 3D CAD/CAM model of the limb, and the other show the horizontal and vertical cross sections respectively. Experiments and Conclusion In current practice, a prosthetist first interrogates the bony structureof the residual limb using palpation and then draws landmarkson the limb surface to identify them. The landmarksare transferredinto CAD/CAM model via plaster casting and digitization. Both system and human errors cause inaccurate landmark allocation. We found that the distant errorson the landmarks from the same patient using the conventional method by the same prosthetist were in the range of 13.9mm to 16.8mm. Using the ultrasounddata and the 3D visualization tool, the prosthetist can consistently allocate all the landmarkswithout any contact to the patient. The distances among the six landmarkson a limb were used for comparison. The difference between two methods ranges from 2.06mm to 19. 17mm. We conclude that the errors are most likely caused by the conventional method although further research is needed.