Three-dimensional electrical capacitance tomography
Three-dimensional electrical capacitance tomography (3D ECT) also known as electrical capacitance volume tomography (ECVT) is a non-invasive 3D imaging technology applied primarily to multiphase flows. It was introduced in the early 2000s as an extension of the conventional two-dimensional ECT. In conventional electrical capacitance tomography, sensor plates are distributed around a surface of interest.
Source: Wikipedia — Three-dimensional electrical capacitance tomography (CC BY-SA 4.0)