Two Aspects of Calibrating a 3D Ultrasonic Computed-Tomography System

Abstract

The paper concerns providing the auxiliary data for image reconstruction in ultrasonic computed tomography (USCT) by calibrating the measuring USCT system. Basically two aspects are considered: calibrating the individual transducers as to their transmitting and receiving properties concerns, and calibrating the geometry of the measuring system, i.e. providing the exact information on the individual transducer deviations from the expected precise positions (including the individual delays in signal processing that act similarly as to the image reconstruction concerns). We will concentrate primarily on the 3D generalization of the principle of individual transducer efficiency and directional characteristics calibration that appeared for 2D case in [3] and complement the information by overview on the other calibration aspects as well. The described methods, based on sc. empty measurements (no measuring phantoms needed) have been tested by both extensive simulations and by first practical applications utilising real measurement data. The tests proved the feasibility of the approach and its robustness under difficult circumstances — i.e. imprecise initial estimates of the calibrated quantities and presence of non-negligible noise in the measurements.