Complex sentence: Because terahertz radiation can "see" what visible light and IR cannot see, unique information can be obtained by terahertz tomography except without all the hazardous effects of X-ray.
Split into simpler sentences: Because terahertz radiation can "see" what visible light and IR cannot see, unique information can be obtained by terahertz tomography. This is in a sense similar to X-ray except without all the hazardous effects of X-ray.