# Angiography Simulation and Planning Using a Multi-Fluid Approach
## 2 Overview of Simulation Framework  
As shown in Figure 1a, the proposed system consists of three main components: a simulation software system, a syringe device tool, and a haptic device.  
1. The software system components, see Figure 1b, include three simulation modules: the human-computer interaction (HCI) module, the physics simulation module, and the visualization module. * In the HCI module, a virtual guidewire/catheter is steered by a \"Geomagic touch\" haptic device [11], and the syringe tool is to deliver the contrast fluid media. Realistic haptic feedback is modelled by the haptic device, simulating the force feedback via the software simulation module. * The physics simulation module contains a discrete elastic rod model for physically based guidewire simulation [10; 14]. The discrete elastic rod model is capable of real-time realistic simulation of complex dynamic interactions of guidewires within blood vessel geometry [15],which allows efficient computation the haptics effect. Contrast media injection model and its simulation are further integrated into the system.
* The visualization module renders the simulation results generated by the physics and HCI modules in real time using GPU graphics rendering techniques.
2. Figure 2 demonstrates the syringe device tool and the corresponding circuit, which mainly includes a power module, a stepper motor module, a potentiometer, an air pressure sensor, a force sensing resistor, an Advanced RISC Machine (ARM) processor, an air cylinder, a lead screw and a coronary control syringe normally used in the real medical operations. * The analog-to-digital converter (ADC) interface of ARM processor samples the voltage of slide potentiometer and the piston of syringe is fixed with the slide potentiometer for injection together with the same distance. When moving the piston, the voltage of the slide potentiometer changes, thereby using the sampled voltage data to calculate the injection dosage and injection speed of contrast media in real time.  
Figure 1: Overview of the proposed 3D interactive virtual angiography simulator and its key software components. **(a)**: System overview; **(b)**: Software components.  
The force feedback from the syringe is mainly influenced by the cardiac blood pressure. Therefore, the air cylinder is adopted to imitate the condition inside the blood vessel. We employ a stepper motor to control the piston rod of the air cylinder to change its inner air pressure. In this device, the lead screw is adopted to convert the rotary motion of the stepper motor to a linear motion of screw. Then, the stepper motor can push and release the piston of the air cylinder to produce corresponding blood pressures in inner air cylinder to allow the user to feel the pressure force when he/she pushes the piston of the syringe.  
Using the physical devices as shown in Figure 1a, medical trainees can operate virtual guidewires and catheters, and directly inject contrast media using the syringe tool, and the rendering results are displayed on the monitor to complete the whole process of a virtual angiography procedure. Therefore, the system setup is trying to replicate the real operation as closely as possible.