The clinical applications of Impedance Tomography are expanding rapidly. Brown et al. (1994a) used a 16-electrode thorax measurement and computed impedance parameters using a three-component electrical model. They then adapted the measured data to the Cole impedance equation.
Adaptive current tomography (ACT)
Adaptive current tomography is a method of imaging the body using currents. It uses electrodes placed on the outside of the body and applies current to them simultaneously. The voltages at the electrodes are then measured to create an impedance image. The electrodes can be placed in a single plane or multiple layers. The third generation of ACT systems uses a network of 32 or 64 electrodes. They measure the lossy and reactive components of the impedance and can capture 20 images per second.
This method has several advantages over other methods of imaging the body. One of the major advantages is the fact that it does not involve any invasive procedures, and it can be used to measure deep-seated cancers. Adaptive current tomography is a technique which is considered a promising alternative to conventional thermography.
Single-pass versus iterative processes
Electrical impedance tomography (EIT) is a form of imaging in which electrical signals are applied at different frequencies to produce cross-sectional images of the internal distribution of impedance. These images can be obtained on a continuous basis at the bedside. However, there are disadvantages to single-pass EIT, including a lower spatial resolution and a tendency for the solution to be unstable.
Single-pass reconstruction methods rely on low-pass filtering to stabilize the process and deal with the effects of noise. The drawbacks of this method include a loss of sharpness and a need to model the shape of the boundary. Iterative processes rely on the use of complex mathematical models to deal with uncertainties.
Frequency dependence
Impedance tomography is a noninvasive method for evaluating the brain’s electrical activity, using electrical signals to measure the brain’s electrical impedance. In studies of normal and ischaemic brains, it has been shown that impedance decreases in both healthy and injured brain tissue over a range of frequencies.
Several different methods are available for performing impedance tomography. In this technique, electrodes are used to measure current and voltage in a region of interest (ROI). The impedance values will vary according to the distribution of materials in the ROI. Different materials will present different electrical properties, making this problem ill-posed. The problem is well-posed when it has a single unique solution, and the number of electrodes is relevant.
Clinical applications
Impedance tomography (EIT) is a technique that uses electrical signals to map the cardiovascular system. It is useful in monitoring the heart and lungs, and has a high sensitivity. However, it is not as accurate as magnetic resonance or computed tomography. Further studies on larger patient groups are needed to evaluate EIT’s potential.
A recent review found that 51 articles have reported clinical applications of impedance spectroscopy in the diagnosis of cancer. Of these, 30 were published between 2010 and 2015 and covered 7035 patient specimens. Of these, 4 multicentre studies were conducted in cutaneous melanoma and one breast study, while 45 were single-site studies. Among these, four of the studies were from the same institution, while 12 were from different countries.
