# An Immersive Virtual Reality Simulator for Echocardiography Examination
## 2 Materials and Methods
### Production of Virtual Space for Echocardiography Examination Practice
The probe model is depicted as being held in either the left- or right-hand model by the trainee, depending on the hand using the HMD controllers or haptics. Through coordinate transformation, the movement and rotation of the probe model are synchronized with the trainee's hand movements. And, upon contact of the probe model with the cardiac region of the patient's 3D model, collision information is incorporated into the probe contact area to generate echocardiographic examination images for the corresponding location. Figure 6 shows the grasp of the 3D probe model by each hand. Figure 5: Three-dimensional hand model with the included skeletal data and the applied animation: (**a**) hand skeletal data and (**b**) hand animation. Figure 6: The 3D probe model and the grasped posture: (**a**) 3D probe model; (**b**) grabbing the probe in the right hand; (**c**) grabbing the probe in the left hand. For the 3D patient models included in the patient model classification, they possess 3D anatomical cardiac models. To achieve realistic representations of 3D patient models, a plug-in utilizing actual facial images was employed to create virtual human models. Additionally, skeletal data and Mesh Deform were utilized for a natural representation of echocardiographic examination positions. The created examination positions include the supine position (lying straight), the lateral position (lying on the side), and the prone position (lying face down with the chest elevated). Keyframes were created for each posture, and keyframe interpolation was utilized to smoothly represent transitions between different positions. Figure 7 shows the postures of the 3D patient model. For the 3D cardiac model, it was created as an anatomical model, realistically represented based on CT volume images. A total of 10 steps (dicom file read \(\rightarrow\) 3D model generation \(\rightarrow\) select segmentation \(\rightarrow\) masking \(\rightarrow\) volume rendering \(\rightarrow\) mesh remove \(\rightarrow\) mesh detach \(\rightarrow\) mesh reconstruction \(\rightarrow\) surface mesh retopology \(\rightarrow\) texture and diffuse map) were followed to produce the basic 3D cardiac model. Next, anatomical information for the basic 3D cardiac model was generated by referencing actual cardiac images and analyzing the internal structure of the cardiac muscle. To achieve a realistic depiction of the 3D anatomical cardiac model, normal map textures and diffuse maps were applied, and animation synchronized with actual cardiac contractions was created using the mesh deformer feature. Figure 8 shows the process for generating the 3D cardiac model, and Figure 9 shows the produced basic 3D anatomical cardiac model. Figure 7: The generated posture of the 3D patient model: (**a**) the supine position; (**b**) the lateral position; (**c**) the prone position. Cardiac diseases arise from factors such as hypertension, atherosclerosis, smoking, hyperlipidemia, diabetes, genetics, and obesity. Depending on the type of disease, cardiac diseases manifest abnormalities in the shape of the cardiac muscle, including damage, expansion, and contraction in the myocardium, ventricles, atria, and valves. Seven cardiac diseases (myocardial infarction, left ventricular hypertrophy, dilated cardiomyopathy, atrial septal defect, mitral valve stenosis, aortic coarctation, and pulmonary atresia) with prominent abnormal cardiac structural forms were selected, and the abnormal structural forms associated with each disease were investigated. Subsequently, based on the investigated shapes, various processes were performed, including texture generation and application, as well as the generation and application of abnormal shapes. These processes were conducted to apply abnormal cardiac forms to the internal or external parts of the normal 3D anatomical cardiac model.