Electrical impedance imaging at multiple frequencies in phantoms

Abstract

We have recently built and tested a 32 channel, multi-frequency (1 kHz to 1 MHz) voltage mode system to investigate electrical impedance spectroscopy (EIS) imaging. We completed a series of phantom experiments to define the baseline imaging performance of our system. Our phantom consisted of a plastic circular tank (20 cm diameter) filled with 0.9% aqueous NaCl solution. Conductors and nonconductors of decreasing width (W5: 3.4 cm, W4: 2.54 cm, W3: 0.95 cm, W2: 0.64 cm and WI: 0.32 cm) were positioned at various distances from the tank edge (1 cm, 2 cm, 4 cm and 8 cm). The results suggest that the detection of objects less than 1 cm in width is limited to the first 1 to 2 cm from the tank edge for absolute images, but this depth can extend to 8 cm in difference images. Larger 3.4 cm wide objects can be detected in absolute images at depths up to 8 cm from the tank edge. Generally, conductor images were clearer than their nonconductor counterparts. Not only did electrode artefacts lessen as the frequency increased, but the system's maximum resolution was attained at the highest operating frequencies. Although the system recovered the value of the electrical conductivity at the correct order of magnitude, it tended to smooth out large property discontinuities. The calculated electrical permittivity in these phantom studies was inconclusive due to the presence of electrode artefacts.

Electromagnetic Breast Imaging: Average Tissue Property Values in Women with Negative Clinical Findings

“…In this section, we summarize salient features of each technique's clinical operation and its expected performance on the basis of results of previous phantom studies (17)(18)(19)(20). The total time involved in performing the bilateral multimodality examinations was typically 90 minutes.…”

“…Results of phantom experiments have shown (18,20) that EI spectroscopic imaging performance is also depth dependent. Study results confirm that highcontrast objects are visible 5 cm below the surface if they are 2 cm or larger.…”

A LabVIEW Based Data Acquisition System for Electrical Impedance Tomography (EIT)

“…In the present study with the sixteen electrode EIT system, each of the sixteen current projections (Fig. 4c) yields sixteen boundary potential date (V 1 , V 2 , V 3 , V 4 , V 5 , V 6 , V 7 , V 8 , V 9 , V 10 , V 11 , V 12 , V 13 , V 14 , V 15 and V 16 ) and hence the complete scan yields 256 boundary potential data (Fig. 4c).…”

“…EIT is a non linear inverse problem [12][13][14] which reconstructs the spatial distribution of the conductivity of the DUT from the voltage current data using the image reconstruction algorithm [12][13][14] which a computer program and developed with forward solver [12][13][14] and inverse solver [12][13][14]. An EIT system injects a constant current signal to the DUT such as a practical phantom [15][16][17][18][19][20][21][22][23][24][25][26][27][28] or human subject through electrodes or EIT sensors [1,11,25] using an EIT instrumentation [26][27][28][29][30][31][32][33] consisting of a current injecting device such as constant current source [34][35][36][37][38][39] and a voltage measuring device which may be a volt meter or other electronic voltage data measuring circuit (Fig. 1).…”

Modelling of an Oesophageal Electrode for Cardiac Function Tomography

“…In their study, the pattern of variability with electrode position was not consistent among subjects [12]. The sensitivity of impedance imaging systems to changes in tissue impedance decreases with distance from the nearest electrode (in reality the resolution is best on the periphery and worst at the center) [13]. In a circular array configuration, this means that the central portion of the imaged plane has the least sensitivity.…”