DEVELOPMENT QF HOLOGRAPHIC CT SYSTEM FOR FIELD WORKS

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In the research, we propose an ultrasonic computed-tomography (CT) system for field works. The main purpose of the system is visualization of the internal structure of historic relics such as the wooden pillars of shrines. Using ultrasonic, we realized a safe and portable measuring system. However, there occur some problems in the application of ultrasonic to CT. The ultrasonic wavelength is considerably longer than X-ray wavelength, and, the propagation speed varies over a wide range. Hence, the ultrasonic wave properties significantly affect the CT images. Furthermore, the visualization process is also affected by outer shapes of objects and available acoustic paths.We have developed an ultrasonic TOP CT system which utilize data obtained by various sensors such as 3D position detector. A trial data acquisition for acoustical transducer array was constructed. The system consists of flexible modules connected each other with a serial buss. A 64ch digital pattern generator and array of switching amplifiers are available. The amplifiers are directly controlled by digital pattern signal. The output range is 2 Vpp to lOOVpp. The switching frequency range is 1KHz to 10MHz. Receivers are constructed with P(VDF-TrFE) copolymer films. A note-book type PC controlls the data acquisition system and a 3D position detector. The system is based on TOF-CT (Time-Of- Flight CT) method with FBP (Filtered Back Projection) algorithm. As an alternative visualization mode, the system can utilize reflected ultrasound echoes using "Hologram-Matrix method". The results of simulation and experiments indicated the availability of the system.