Abstract:Electrical Impedance Tomography (EIT) is a safe medical imaging technology, requiring no ionizing or heating radiation, as opposed to most other imaging modalities. This has led to a clinical interest in its use for long-term monitoring, possibly at the bedside, for ventilation monitoring, bleeding detection, gastric emptying and epilepsy foci diagnosis. These long-term applications demand auto-calibration and high stability over long time periods. To address this need we have developed a new multi-frequency E… Show more
“…We, therefore, adopted the star network topology with a dedicated FIFO-based synchronous serial communication channel to each IMM, which is denoted as TxRxD . To implement the pipelined operation for a maximum frame rate of 100 frames/sec [18], we used the double-buffered memory structure in each serial communication channel to transmit previous data and store new data simultaneously.…”
Section: Methodsmentioning
confidence: 99%
“…It receives the synchronization signal SyncOut from the intra-network controller and exchanges commands and data via the dedicated serial communication channel TxRxD . Each IMM FPGA operates independently for current injection and voltage measurement regardless of the behavior of other IMMs [18]. Figure 3
Functional block diagram of the IMM FPGA.…”
Section: Methodsmentioning
confidence: 99%
“…For example, high-quality fast data collections in EIT require careful digital controls of timing signals, switches, and digital potentiometers, which are used together with analog circuits for current sources and voltage amplifiers [8, 17, 18]. These are especially important in a parallel EIT system to remove systematic artifacts and maximize performance since multiple current sources and voltmeters must be operating synchronously.…”
Section: Introductionmentioning
confidence: 99%
“…Lately, we have developed a fully parallel multi-frequency EIT system called the KHU Mark2.5 with various functions such as the automatic calibration, pipelining, and long-term stability [18]. Since its digital design was based on FPGAs, we could add new functions such as bio-signal gating and fast multi-frequency imaging using frequency multiplexing by changing only the FPGAs.…”
Section: Introductionmentioning
confidence: 99%
“…Since its digital design was based on FPGAs, we could add new functions such as bio-signal gating and fast multi-frequency imaging using frequency multiplexing by changing only the FPGAs. Though Wi et al described the development of the KHU Mark2.5 EIT system [18], they focused on its overall structure and performance evaluation rather that providing technical details of the FPGAs.…”
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.
“…We, therefore, adopted the star network topology with a dedicated FIFO-based synchronous serial communication channel to each IMM, which is denoted as TxRxD . To implement the pipelined operation for a maximum frame rate of 100 frames/sec [18], we used the double-buffered memory structure in each serial communication channel to transmit previous data and store new data simultaneously.…”
Section: Methodsmentioning
confidence: 99%
“…It receives the synchronization signal SyncOut from the intra-network controller and exchanges commands and data via the dedicated serial communication channel TxRxD . Each IMM FPGA operates independently for current injection and voltage measurement regardless of the behavior of other IMMs [18]. Figure 3
Functional block diagram of the IMM FPGA.…”
Section: Methodsmentioning
confidence: 99%
“…For example, high-quality fast data collections in EIT require careful digital controls of timing signals, switches, and digital potentiometers, which are used together with analog circuits for current sources and voltage amplifiers [8, 17, 18]. These are especially important in a parallel EIT system to remove systematic artifacts and maximize performance since multiple current sources and voltmeters must be operating synchronously.…”
Section: Introductionmentioning
confidence: 99%
“…Lately, we have developed a fully parallel multi-frequency EIT system called the KHU Mark2.5 with various functions such as the automatic calibration, pipelining, and long-term stability [18]. Since its digital design was based on FPGAs, we could add new functions such as bio-signal gating and fast multi-frequency imaging using frequency multiplexing by changing only the FPGAs.…”
Section: Introductionmentioning
confidence: 99%
“…Since its digital design was based on FPGAs, we could add new functions such as bio-signal gating and fast multi-frequency imaging using frequency multiplexing by changing only the FPGAs. Though Wi et al described the development of the KHU Mark2.5 EIT system [18], they focused on its overall structure and performance evaluation rather that providing technical details of the FPGAs.…”
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.
We demonstrated the feasibility of time difference and weighted frequency difference conductivity imaging for real-time monitoring of temperature distribution and ablation region estimation during radiofrequency (RF) ablation. The electrical conductivity spectrum of biological tissue reflects mobility of ions in intra- and extra-cellular fluids and changes in cellular morphology induced by heating. The time series conductivity spectra were measured in an ex vivo bovine liver by a high-speed electrical impedance tomography (EIT) system. The EIT system was protected by filters to suppress RF energy and allow interleaved real-time imaging. We recorded time and weighted frequency-difference conductivity images and direct temperature variations at the ablation region and control region during 8 min ablation and for the following 66 min of cooling. Conductivity variation in regions of interest was compared with temperature recordings. Contours of conductivity change were visualized and compared to estimate the ablation area. EIT images confirmed increase of conductivity at all frequencies and loss of frequency conductivity change associated with loss of cellular structure. Time difference conductivity images showed changes due to both heating during ablation and heat dissipation following ablation together with tissue property changes. Weighted frequency-difference images presented persistent changes following heating due to the morphological change in the ablation zone.
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