# An Immersive Virtual Reality Simulator for Echocardiography Examination
## 2 Materials and Methods
### Approaches to Echocardiography Examination Interaction  
In the echocardiography examination simulator, interaction between the 3D models is facilitated through HMD controllers and haptic devices. In the 3D hand model, the left hand is linked with the HMD controller, while the right hand is linked with the haptic device to perform interactions with virtual objects. If the user is left-handed, the interaction devices connected to the left and right hands will be switched. In the case of HMD controllers, the interaction is based on ray casting, involving casting a ray in the direction pointed by the index finger of the hand model and pressing the buttons on the controller. If the projected ray comes into contact with a virtual object for a certain duration, the object is determined to be selected. Through interaction with the HMD controller, it is possible to manipulate UI objects, utilize UI buttons for performing echocardiographic examinations, and select buttons on the echocardiography equipment body. For the haptic device, interaction is based on both ray casting and physical collision techniques, and different functionalities are performed based on each interaction technique. Interaction based on ray casting involves projecting a ray in the direction pointed by the index finger of the hand model when a button on the haptic device is pressed. If the projected ray comes into contact with the probe model for a certain duration, the hand model grasps the corresponding probe model. Then, the probe 3D model is synchronized  
Figure 12: Generated 3D patient models: (**a**) Normal model; (**b**) myocardial infarction-inclusive model; (**c**) left ventricular hypertrophy-inclusive model; (**d**) dilated cardiomyopathy-inclusive model; (**e**) atrial septal defect-inclusive model; (**f**) mitral valve stenosis-inclusive model; (**g**) aortic coarctation-inclusive model; (**h**) pulmonary atresia-inclusive model. with the hand 3D model, which is responsive to the movement of the haptic device through coordinate transformation technology. Interaction based on physical collision techniques involves manipulating the haptic device, and when the haptic device, containing collision information, directly collides with the cardiac region of the patient's 3D model, that area is determined to be selected. If the contacted area corresponds to the actual echocardiography position, the appropriate echocardiographic examination image is displayed in the UI box at the contacted area. Furthermore, by providing tactile feedback through the haptic device when it comes into contact with the patient's 3D model, the sense of immersion in the interaction is enhanced. Figure 13 shows the developed interaction method. Through the manipulation of a virtual probe or the control of the ultrasound equipment panel using interactive methods, adjustments to the echocardiographic images were made. In an actual echocardiogram, the probe is adjusted to examine eight different views. These views include PLAX (parastermal long axis view), PSAX MV (parastermal short axis view-- mitral valve level), PSAX AV (parastermal short axis view--aortic valve level), PSAX PM (parastermal short axis view--papillary muscles level), PSAX Apical (parastermal short axis apical view), A4C (apical 4-chamber view), A3C (apical 3-chamber view), and A2C (apical 2-chamber View). In the echocardiography VR simulator, the echocardiographic image view changes based on the virtual probe's contact position on the patient's 3D model and the orientation of the probe orientation marker. Figure 14 visually depicts the virtual probe positions and the direction of the probe orientation marker for each type of view, while Table 3 shows the virtual probe positions and the direction of the probe orientation marker for each type of echocardiographic image view. The echocardiography examination equipment can change modes for each view. Typically, it supports B-mode (brightness mode), M-mode (motion mode), and color Doppler mode.