Recently, we have succeeded in the development of high power and high sensitivity THz wave spectral imaging system using injection-seeded THz parametric generation (is-TPG) and detection. A dynamic range of 100 dB has been obtained, and the peak output power of is-TPG approached 50 kW by introducing a microchip YAG laser with shorter pulse width of 420ps. Now we can detect drugs under much thicker obstacles than before using is-TPG spectroscopic imaging system