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Frequency-division multiplexing for electrical impedance tomography in biomedical applications.

Granot Y, Ivorra A, Rubinsky B - Int J Biomed Imaging (2007)

Bottom Line: This is achieved by injecting current through all of the current injecting electrodes simultaneously, and measuring all of the resulting voltages at once.In biomedical applications, using different frequencies has important implications due to dispersions as the tissue's electrical properties change with frequency.Another significant issue arises when we are recording data in a dynamic environment where the properties change very fast.

View Article: PubMed Central - PubMed

Affiliation: School of Computer Science and Engineering, Hebrew University of Jerusalem, 78b Ross Building, Jerusalem 91904, Israel.

ABSTRACT
Electrical impedance tomography (EIT) produces an image of the electrical impedance distribution of tissues in the body, using electrodes that are placed on the periphery of the imaged area. These electrodes inject currents and measure voltages and from these data, the impedance can be computed. Traditional EIT systems usually inject current patterns in a serial manner which means that the impedance is computed from data collected at slightly different times. It is usually also a time-consuming process. In this paper, we propose a method for collecting data concurrently from all of the current patterns in biomedical applications of EIT. This is achieved by injecting current through all of the current injecting electrodes simultaneously, and measuring all of the resulting voltages at once. The signals from various current injecting electrodes are separated by injecting different frequencies through each electrode. This is called frequency-division multiplexing (FDM). At the voltage measurement electrodes, the voltage related to each current injecting electrode is isolated by using Fourier decomposition. In biomedical applications, using different frequencies has important implications due to dispersions as the tissue's electrical properties change with frequency. Another significant issue arises when we are recording data in a dynamic environment where the properties change very fast. This method allows simultaneous measurements of all the current patterns, which may be important in applications where the tissue changes occur in the same time scale as the measurement. We discuss the FDM EIT method from the biomedical point of view and show results obtained with a simple experimental system.

No MeSH data available.


Implementation of a possible FDM EIT system with 16 electrodes. AC currents at different frequencies are injected simultaneously into the sample and are collected by a single electrode (0). Differential voltage at electrode pairs are amplified and processed by demodulators (D).
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fig2: Implementation of a possible FDM EIT system with 16 electrodes. AC currents at different frequencies are injected simultaneously into the sample and are collected by a single electrode (0). Differential voltage at electrode pairs are amplified and processed by demodulators (D).

Mentions: Figure 2 illustrates the concept of the FDM EIT technique. The figure shows an ideal implementation of a possible FDM EIT system with 16 electrodes. As an example, even-numbered electrodes are used to inject currents into the sample whereas odd-numbered electrodes are employed to measure the resulting voltage differences. Using only half of the available electrodes for each task affects the reconstruction quality, but this is not specific for FDM, and the consequences are identical to traditional systems that apply two sets of electrodes [22]. The currents are simultaneously injected from the current electrodes to a single sink electrode (electrode number 0). Each AC current source has a specific frequency and the voltage differences are demodulated for these frequencies. That is, demodulators (referred to as ā€œDā€ in Figure 2) have multiple outputs: one for each injected frequency. Therefore, the contribution from each current source at each electrode pair can be isolated. Time is only consumed for the demodulation process but not for multiplexing. As it will be explained later, demodulation time will depend on the spectral separation between the injected currents.


Frequency-division multiplexing for electrical impedance tomography in biomedical applications.

Granot Y, Ivorra A, Rubinsky B - Int J Biomed Imaging (2007)

Implementation of a possible FDM EIT system with 16 electrodes. AC currents at different frequencies are injected simultaneously into the sample and are collected by a single electrode (0). Differential voltage at electrode pairs are amplified and processed by demodulators (D).
© Copyright Policy - open-access
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2211417&req=5

fig2: Implementation of a possible FDM EIT system with 16 electrodes. AC currents at different frequencies are injected simultaneously into the sample and are collected by a single electrode (0). Differential voltage at electrode pairs are amplified and processed by demodulators (D).
Mentions: Figure 2 illustrates the concept of the FDM EIT technique. The figure shows an ideal implementation of a possible FDM EIT system with 16 electrodes. As an example, even-numbered electrodes are used to inject currents into the sample whereas odd-numbered electrodes are employed to measure the resulting voltage differences. Using only half of the available electrodes for each task affects the reconstruction quality, but this is not specific for FDM, and the consequences are identical to traditional systems that apply two sets of electrodes [22]. The currents are simultaneously injected from the current electrodes to a single sink electrode (electrode number 0). Each AC current source has a specific frequency and the voltage differences are demodulated for these frequencies. That is, demodulators (referred to as ā€œDā€ in Figure 2) have multiple outputs: one for each injected frequency. Therefore, the contribution from each current source at each electrode pair can be isolated. Time is only consumed for the demodulation process but not for multiplexing. As it will be explained later, demodulation time will depend on the spectral separation between the injected currents.

Bottom Line: This is achieved by injecting current through all of the current injecting electrodes simultaneously, and measuring all of the resulting voltages at once.In biomedical applications, using different frequencies has important implications due to dispersions as the tissue's electrical properties change with frequency.Another significant issue arises when we are recording data in a dynamic environment where the properties change very fast.

View Article: PubMed Central - PubMed

Affiliation: School of Computer Science and Engineering, Hebrew University of Jerusalem, 78b Ross Building, Jerusalem 91904, Israel.

ABSTRACT
Electrical impedance tomography (EIT) produces an image of the electrical impedance distribution of tissues in the body, using electrodes that are placed on the periphery of the imaged area. These electrodes inject currents and measure voltages and from these data, the impedance can be computed. Traditional EIT systems usually inject current patterns in a serial manner which means that the impedance is computed from data collected at slightly different times. It is usually also a time-consuming process. In this paper, we propose a method for collecting data concurrently from all of the current patterns in biomedical applications of EIT. This is achieved by injecting current through all of the current injecting electrodes simultaneously, and measuring all of the resulting voltages at once. The signals from various current injecting electrodes are separated by injecting different frequencies through each electrode. This is called frequency-division multiplexing (FDM). At the voltage measurement electrodes, the voltage related to each current injecting electrode is isolated by using Fourier decomposition. In biomedical applications, using different frequencies has important implications due to dispersions as the tissue's electrical properties change with frequency. Another significant issue arises when we are recording data in a dynamic environment where the properties change very fast. This method allows simultaneous measurements of all the current patterns, which may be important in applications where the tissue changes occur in the same time scale as the measurement. We discuss the FDM EIT method from the biomedical point of view and show results obtained with a simple experimental system.

No MeSH data available.