A 50 MHz C-scan imaging system is under construction for fast defect detection. A high-frequency (150-450 MHz) A-scan system is used for host material evaluation, and defect characterization. Several signal processing schemes such as time and space averaging, Wiener filtering, diffraction and propagation loss corrections are used in the process of defect characterization. Further modifications of the exact theory of scattering from spherical inclusions are made to ease the process of defect identification.