Author(s):
Duckjune Kim -
Korea Institute of Industrial Technology
Kwang-Hee Lee - Korea Institute of Industrial Technology
Dr. Sang-Hoon Ji - Korea Institute of Industrial Technology
A mobile X-ray imaging system that provides both fluoroscopy and 3D computed tomography (CT) image modes can be used in operating rooms (OR) for many orthopedic and neurological surgery applications. Fluoroscopy imaging mode provides real-time images of the internal structure of a patient at various angles. This enables a surgeon to operate more precisely. 3D CT image mode allows the surgeon to check a patient’s status instantly in the OR without moving the patient. Traditionally, the patient’s status is checked in a CT scanning room after finishing the surgery. Therefore, the system can save a lot of time checking surgical results and it can prevent the need for repeat surgery. In addition, 3D CT image mode can operate with the navigation system so that the surgeon can see the exact position of surgical instrumentations with the 3D CT image using a GPS-guided system to make a precise incision.
The mobility of the system helps users save money because it can be used in many ORs instead of having to install a CT or fluoroscopy system in every OR. Also, it helps give more space for the surgical team because it can be moved away from the operating bed after scanning a patient.
Our research team decided to use NI LabVIEW software and NI hardware to develop the mobile X-ray imaging system because of the expandability of the CompactRIO platform. Developing a complicated system requires a variety of sensors, hardware, and controllers. With the CompactRIO system we was able to build the system easily by adding appropriate modules.
Simulation
Developing the mobile X-ray imaging system can be divided into three parts including the Gantry, manipulator, and mobile system. The Gantry system, which includes the x-ray source and detector, weighs about 300 kg, and the manipulator system, which decides the Gantry position for scanning in various angles, weights about 500 kg. Because of its heavyweight, designing and validating motion profiles, control algorithms, and control sequences is burdensome because of the safety and cost. By drawing 3D mechanical structures of the system from Solidworks software and using LabVIEW NI Softmotion Module for Solidworks with Solidworks Motion Simulation, we designed, simulated, and validated control and motion programs safely. Also, the designed codes were implemented in a real system without any revision, which helped us save huge amounts of time.
Figure1. LabVIEW NI Softmotion Module for Solidworks
Mobile X-ray Imaging System
The mobile X-ray imaging system exhibits robotic system traits because the Gantry can be positioned by a multi-axis manipulator in various angles and X-ray modules are rotated by a motor-driven system to acquire 3D CT images.
LabVIEW software, CompactRIO, and NI 9514 C Series servo drive interface are used to control various motion profiles of the mobile X-ray imaging system with high-precision and high-speed communication. The system has seven motors with absolute type encoders so the positions of all the axes are tracked, regardless of the power source.
To collect initial information from the absolute encoder, seven serial converters are required to connect to the motor drivers. However, we used only one NI 9401 high-speed bidirectional I/O module and programmed the LabVIEW FPGA Module to handle seven pieces of serial data simultaneously. Therefore, the robotic system with the absolute type encoder does not need to return to its home position after traveling a certain distance and limit sensors are not necessarily required.
The Gantry system rotates the X-ray module 360◦ in 12 seconds when in 3D CT image mode. It is important to rotate it with a constant speed for high-quality 3D reconstruction of the image. Using the NI 9514 with velocity control mode, we achieved a constant speed motion profile, which enables us to take multiple images using an equal interval. Also, we programmed LabVIEW FPGA to estimate Gantry position with a high sampling rate so the field-programmable gate array (FPGA) can trigger the X-ray module via the NI 9401 to take multiple X-ray images at desired angles accurately.
One of the most notable features of our system is that the Gantry system has a door module so it can be opened and closed for installation convenience next to the OR bed. The door module sequence is controlled via an NI 9472 sourcing digital output module and the Gantry system is monitored by many sensors. Data is sent to the CompactRIO via an NI 9421 sinking digital input module during the opening and closing sequence.
The manipulation system, which positions the Gantry, has five degree of freedom (DoF). Each axis can be manipulated to install the system to the OR bed or to move away from the bed to give enough room for surgical team. We not only developed single axis motion, but we also developed more complex motion profiles to provide various services such as a larger field of view (FOV) or region of interest (ROI) for users. Those functions require multi-axis manipulation of the Gantry system so we defined inverse kinematics in Labview and used the LabVIEW NI Softmotion module, and NI 9514 to generate multi-axis synchronized motion. After running through an experiment, we checked that the system is controlled with acceptable synchronization error.
Figure2. Mobile X-ray Imaging System Robot Platform
The mobile mechanism is designed so the system can be used in many ORs and it is driven by NI 9505 brushed DC servo drive module and the LabVIEW Robotics Module. The LabVIEW Robotics Module helped us sense obstacles easily, avoid collision, and develop user-friendly steering. The CompactRIO system includes dual power supply inputs to offer both reliability and flexibility in power supply configuration so we designed the system to have power supplied from both the wall-mount power and battery power. Therefore, the mobile X-ray imaging system can be moved outside the OR without a wall-mount power supply.
The LabVIEW Touch Panel Module and a 17” Touch Panel LCD are used to provide a user-friendly Human-Machine Interface (HMI). We also developed a remote device because this option is preferred for users to avoid radiation exposure for certain procedures. We used a WLAN module developed by National Instruments Alliance Partner SEA for direct wireless communication between the CompactRIO and remote device and we developed an iPhone/iPad app that can control and monitor the system.
Figure 3. The GUI
Conclusion
Medical devices require high reliability and safety and have strict electrical regulations. Our research team developed a mobile X-ray imaging system using CompactRIO that satisfies those regulations. Graphical programming and a FPGA-based high-performance embedded controller allowed us to develop the system in three months and provided reliability, expandability, and ease of operation. In addition, providing a user-friendly interface and interoperation with commercial 3D CAD design systems let us save on development time and contributed to developing core technologies for the system. NI technology gave us a chance to commercialize this system in a smaller time frame.
Author Information:
Duckjune Kim
Korea Institute of Industrial Technology
South Korea
mike23@kitech.re.kr
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