Improvement of the Method for Determination of Time-of-Flight of Ultrasound in Ultrasonic TOF CT
Hiroya FUJII, Kazunari ADACHI, Hirotaka YANAGIDA, Tomoki HOSHINO, Tomoya NISHIWAKI
In inspection of structural members of buildings using the ultrasonic time-of-flight computed tomography (TOF CT) system previously developed by the authors, the reconstructed images did not always reflect their internal states appropriately, since no consistent technique for determination of TOF of ultrasonic signals had been clearly established yet. Hence, the authors have proposed the “squared amplitude integral method” for determination of the TOF now. In numerical simulations of wave propagation in circular cross sections of 24 cm in diameter, the TOF values have been obtained with the use of the proposed method, and fine CT images which well reflect the insides have successfully been reconstructed from the data in accordance with the filtered back projection algorithm. To verify the effectiveness of this method experimentally, the authors have tried to reconstruct the cross-sectional image of cylindrical mortal specimens of 25 cm in diameter with their ultrasonic TOF CT system. As the result, the artifacts of low sound-speed region near the circumference have been well suppressed and the size and position of the anomaly have been more precisely represented in the image compared with the previously obtained ones.