A REAL-TIME ELECTRICAL-IMPEDANCE TOMOGRAPH

Electrical properties of tissues in the human body can be imaged using a technology known as Electrical Impedance Tomography, In this modali ty, sinusoidal electrical currents are applied to the body using elect rodes attached to the skin, and voltages that are developed on the ele ctrodes are measured, Using these data, a reconstruction algorithm com putes the conductivity and permittivity distributions within the body, This paper describes the reconstruction algorithm, image display algo rithm, and hardware of a real-time Electrical Impedance Tomograph know n as the Real-Time Imaging System, The reconstruction algorithm, execu ted by a commercially available coprocessor board that resides in a 38 6-based personal computer, is a modification of the Newton's One Step Error Reconstructor (NOSER) that minimizes algorithm execution time by precomputing many quantities. The image display algorithm, also execu ted by the coprocessor board, maps the output of the reconstruction al gorithm into an image which is displayed using a video graphics board, The architecture of the system and execution times of algorithms impl emented by the system are discussed, Using the continuous data acquisi tion mode of the Real-Time Imaging System, data from the thorax of a n ormal human subject were collected, Admittivity changes in the chest, as a result of respiration and the cardiac cycle, are presented, Data that were collected from the leg of a normal subject are shown which d emonstrate capabilities of the triggered data acquisition mode of the system, allowing data acquisition synchronization with an electrocardi ogram.