Electrical impedance imaging system using FPGAs for flexibility and interoperability

Abstract

BackgroundModern EIT systems require simultaneously operating multiple functions for flexibility, interoperability, and clinical applicability. To implement versatile functions, expandable design and implementation tools are needed. On the other hand, it is necessary to develop an ASIC-based EIT system to maximize its performance. Since the ASIC design is expensive and unchangeable, we can use FPGAs as a prior step to the digital ASIC design and carefully classify which functions should be included in the ASIC. In this paper, we describe the details of the FPGA design adopted in the KHU Mark2.5 EIT system.MethodsWe classified all functions of the KHU Mark2.5 EIT system into two categories. One is the control and processing of current injection and voltage measurement. The other includes the collection and management of the multi-channel data with timing controls for internal and external interconnections. We describe the implementation of these functions in two kinds of FPGAs called the impedance measurement module (IMM) FPGA and the intra-network controller FPGA.ResultsWe present functional and timing simulations of the key functions in the FPGAs. From phantom and animal imaging experiments, we show that multiple functions of the system are successfully implemented in the FPGAs. As examples, we demonstrate fast multi-frequency imaging and ECG-gated imaging.ConclusionGiven an analog design of a parallel EIT system, it is important to optimize its digital design to minimize systematic artifacts and maximize performance. This paper described technical details of the FPGA-based fully parallel EIT system called the KHU Mark2.5 with numerous functions needed for clinical applications. Two kinds of FPGAs described in this paper can be used as a basis for future EIT digital ASIC designs for better application-specific human interface as well as hardware performance.

Electronic hardware design of electrical capacitance tomography systems

“…The use of FPGA instead of DSP processors has become more popular because FPGAs can host a good set of control or data flow of the reconstruction algorithm without the need for a series of sequential memory access [7]. A recent FPGA-based electrical impedance tomography (EIT) system was discussed in [20]. The system is composed of several FPGA-based impedance measurement modules (IMMs) comprising independent current sources and voltmeters that communicate with each other through a reconfigurable FPGA-based controller [7].…”

“…However, since the IMMs are mainly involved with data acquisition and electric current generation for electrodes, rather than in image reconstruction, the system is found to have a relatively low performance. Another similar FPGAbased ECT system was discussed in [20] where the device digitally modulates the amplitude and phase of AC signals with various carrier frequencies and allows the receivers to band-pass filter the transmitted signal to their allocated carrier frequency ( figure 14). As a result, this allows for simultaneous data acquisition and avoids using CMOS analogue switches [7].…”

FPGA Implementation of ECT Digital System for Imaging Conductive Materials

“…The usage of the FPGA speeds up the reconstruction process by reducing the sequential access of the memory. In [16], an Electrical Impedance Tomography (EIT) system generating 100 f/s and consisting of some impedance measurement FPGA modules is developed. Each FPGA module has its particular current source and voltmeter connected through Intra-network FPGA controller.…”

“…Other tomography techniques such as Computed Tomography (CT) [18], Electrical Impedance Tomography (EIT) [16], and Positron Emission Tomography (PET) [19] also implemented their image reconstruction algorithms on the FPGA. Superior performance was achieved in [20] when the algorithm uses the intrinsic fine parallelism ability of the FPGA.…”

A New Parallel VLSI Architecture for Real-Time Electrical Capacitance Tomography

“…The usage of FPGA instead of DSP processors by other researchers was motivated by the fact that FPGA can host a good portion of the control/data flow of the reconstruction algorithm, without the need of series of sequential memory accesses. Hence, recently, an FPGA-based Electrical Impendence Tomography (EIT) system was disclosed in [7]. The system comprises several FPGA-based Impedance Measurement Modules (IMM) comprising independent current sources and voltmeters intercommunicating through a reconfigurable FPGA-based Intra-network controller.…”