Electrical Impedance Tomography

Impedance tomography is a non-invasive medical imaging technique that measures the electrical properties of tissues. The theory behind impedance tomography is that by applying a constant current across a material, the voltage distribution resulting on the surface will reflect the internal resistivity distribution. There are three types of impedance tomography: conventional EIT, dual frequency, and multi-frequency EIT. Conventional EIT uses a single frequency, most often 50 kHz, and images are constructed from two measurements at two different times to observe the change in conductivity. The images obtained, representing a change in conductivity in the time domain, are called differential images. The main purpose of measuring tissue electrical impedance is to differentiate normal and cancerous tissues in a variety of organs, including breast, cervix, skin, bladder, and prostate. Tissue electrical impedance is a function of its structure, and it can be used to distinguish between normal and suspected abnormal tissue within the same organ.

Tissue impedance is determined by the electrical properties of its components, which include the cell membrane and cytoplasm. At high frequencies, the electrode-tissue interface is the main contributor to tissue impedance. The cell membrane acts as a low-pass filter, restricting the flow of current across it; thus, the higher the frequency, the less current will be able to pass through the cell membrane. The cytoplasm acts as a resistor, producing an impedance that is inversely proportional to the frequency of the applied signal.

High concentrations of electrolytes, extracellular water content, large cells, and the number of cell connections by gap junctions present in blood and muscles reduce impedance. Impedance tomography has several applications, including imaging of lung function, diagnosis of pulmonary embolism, detection of tumors in the chest area, and diagnosis and distinction of ischemic and hemorrhagic stroke. Impedance tomography is also a monitoring tool that allows one to evaluate at the bedside the distribution of pulmonary ventilation continuously, in real-time, and which has proven to be useful in optimizing mechanical ventilation parameters in critically ill patients. The distribution of pulmonary ventilation is continuously monitored in real-time, and this information is used to optimize mechanical ventilation parameters in critically ill patients. In conclusion, impedance tomography is a promising imaging approach with a strong potential that has a large margin of progression before reaching the maturity phase. It is a non-invasive and low-cost imaging method that can provide valuable information about the electrical properties of tissues.

By measuring the electrical properties of tissues, impedance tomography can help diagnose various diseases and conditions, and it can also be used to monitor patients in real-time. The distribution of pulmonary ventilation is continuously monitored in real-time, and this information is used to optimize mechanical ventilation parameters in critically ill patients.