Brain cells (also known as "glia" or "neuroglia") come in several types, and perform a number of critical functions, including structural support, metabolic support, insulation, and guidance of development. Neurons, however, are usually considered the most important cells in the brain. The property that makes neurons unique is their ability to send signals to specific target cells over long distances. They send these signals by means of an axon, which is a thin protoplasmic fiber that extends from the cell body and projects, usually with numerous branches, to other areas, sometimes nearby, sometimes in distant parts of the brain or body.
Process tomography imaging methods are used in process tomography, e.g. ultrasonic imaging, positron emission tomography (PET), electrical resistance tomography (ERT) and electrical impedance tomography (EIT), electrical capacitance tomography (ECT), magnetic induction tomography (MIT). In all cases external sensors are used to detect signals from boundary of the object, and the three-dimensional material distribution or the velocity field is computed using the measured data. Process tomography is an area of rapid growth both in terms of research and applications. There are number of challenges remaining in this area including data processing an image reconstruction, and application of imaging modalities in a real applications.