# An Immersive Virtual Reality Simulator for Echocardiography Examination
## 2 Materials and Methods
### Production of Virtual Space for Echocardiography Examination Practice  
Information about the actual environment where echocardiography examinations take place was collected. We visited medical facilities outside of clinic hours to directly observe the echocardiography examination space. We collected information about the actual environment where echocardiography examinations take place by seeking advice from specialists in cardiology. The gathered information includes the layout of the echocardiography examination space, the procedures involved, the types of equipment used, and the methods of interaction related to echocardiography examinations. Based on this information, we created 3D models of the space where echocardiography examinations are performed, the equipment used for echocardiography examination, and the 3D models of normal and abnormal anatomical cardiac muscle. These models were developed using Universal Render Pipeline (URP) shaders and 3D CAD software (3 Ds Max 2022.3 and Cinema4D R23.110). The 3D models include geometric shapes, color, and material information and are saved in formats such as DXF, OBJ, and FBX that are compatible with virtual environment creation software like Unity (Unity, San Francisco, CA, USA). Subsequently, to mitigate resource consumption during rendering, we utilized Unity's Light Mapping feature. Figure 2 shows the configured virtual space for echocardiography practice. Figure 1: Schematic diagram of the development of an immersive simulator for echocardiography examination. Figure 2: Virtual space for the echocardiography examination learning. The 3D models constituting the virtual space are categorized into environmental models representing the space where echocardiography examination is performed, models interacting with the HMD controller (Oculus Quest 2, Meta Platforms, Inc., Menlo Park, CA, USA) or haptic device (Touch, 3D systems, Rock Hill, SC, USA) manipulation, and patient models incorporating anatomical 3D models of the cardiac muscle. Table 1 shows the classification of the 3D models according to the utilization plan. The 3D models categorized under the environmental model, such as ward and medical beds, were meticulously designed to closely resemble real environmental information for an enhanced sense of immersion. These 3D models are fixed in the virtual space, and each model interacts with models belonging to different categories. The ward 3D model represents a space where the trainee wearing the HMD can perform activities and learn, while the 3D medical bed model represents the place where the posture of the 3D patient model is portrayed and changes. When directly utilized in the virtual environment, the ward and medical bed models created in 3D CAD software (3 Ds Max 2022.3 and Cinema4D R23.110) can lead to various issues. Problems such as the trainee passing through ward walls during activities and learning in the ward model and the medical bed model experiencing overlap or pose changes when the 3D patient model passes through or changes posture could occur. To prevent these issues, rigid body properties were assigned to the ward and medical bed models. Rigid body properties provide physical information (shape invariance, volume, mass, constraints on external forces, etc.) to the models, allowing 3D models in the virtual space to exhibit realistic movements. To ensure the stability and invariance of the hospital and medical bed models, mass and constraint information were assigned as rigid body properties. Figure 3 shows the ward and medical bed models. Furthermore, the echocardiography equipment model was created based on the actual echocardiography examination equipment (RS85, Samsung, Suwon, Gyeonggi, KR) used in clinical settings to enhance the immersion of the VR simulator. Separate 3D models were generated for the probe, monitor, panel, and main body, mimicking the real echocardiography examination equipment. These models were then assembled, and rigid body