Impedance Tomography uses electrical signals to measure the body’s electrical resistance. It has been used for a variety of medical applications. This article will explore the principles of electrical resistivity tomography and end-expiratory lung impedance. You’ll also learn about its limitations and advantages.
Adaptive current tomography
Adaptive current tomography is a diagnostic imaging technique that creates a cross-sectional image of the body’s electrical conductivity. The device works by applying current simultaneously to multiple electrodes, which are placed on different parts of the body. The electrodes measure their voltages, which are then used to reconstruct the image. The electrodes can be placed in single planes or multiple layers. A third-generation ACT system can record up to 20 images per second.
The technique uses a 72-electrode system that can image at seven different frequencies from 3.3 kHz to 1 MHz. The images are acquired in 6 s, and an off-line analysis can differentiate between normal and malignant tissue.
Electrical resistivity tomography
Electrical resistivity tomography is an imaging technique that uses electric currents to measure the subsurface of a body. The process can yield two or three-dimensional images of the body, depending on the electrodes used. For example, electrodes deployed in a line will gather data for a 2D slice of the subsurface. Alternatively, electrodes arranged in a grid can produce a three-dimensional cube of the earth’s subsurface, similar to a 3D MRI scan of the body. The method has also been used to map variations in overburden thickness.
Another advantage of this technique is the rapidity with which it can collect data. It can gather nine hundred and sixty-seven data points within 30 minutes, or 3,354 unique measurements in one hour and forty-four minutes. Moreover, the process of conducting an electrical resistivity survey is completely safe, since the cables used are buried or attached to non-conductive boreholes.
End-expiratory lung impedance
End-expiratory lung impedance (EELI) on Impedance Tomography is a measurement of the lung’s resistance to air flow. It is measured in the lower lobes and is used in the assessment of respiratory function. A positive EEP (PEEP) level improves patient survival. However, too much PEEP can result in alveolar overdistention and collapse, reducing survival and increasing the risk of complications. Electrical impedance tomography may help doctors determine whether the patient is undergoing excessive PEEP and the reason.
The images on EIT display the impedance of the lung at various pressure levels. High and low impedance changes were identified on the electrical impedance tomography images. The changes in the electrical impedance were quantified using the GREIT algorithm. The subject was asked to breathe silently for 30 s. Then, he or she was instructed to hold breath for 20 s after tidal inspiration and take three deep breaths. The EIT waveforms are representative of global and regional impedance.
