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In video-assisted thoracic surgery (VATS), a surgeon cannot easily detect a lung tumor during surgical operation. This paper discusses a noncontact tumor imager capable of detecting a tumor position for application during VATS; this sensor is based on the phase differential technique. The developed sensor comprises an air supply system and an optical-fiber-based displacement sensor adjacent to the air nozzle. For a periodic air pressure, a displacement sensor provides sinusoidal outputs with individual phases. The phase difference varies according to the change in the mechanical impedance parameters of tissues between two points. We confirmed the validity of the sensor for the removed human lung through basic experiments. With regard to clinical applications, both the tumor detection capability and the safety to lung tissues of the developed sensor were confirmed through in vivo animal experiments using pig lungs. Finally, the sensor system was developed for clinical tests and the results of the clinical experiments are shown.