Abstract

The problem of obtaining the precise localization of a hidden absorber in a highly scattering medium of large dimension has confronted the scientific community for a number of years. Optical methods can also use contrast agents and can identify a line from the tissue surface, including the localized contrast agent and hence the tumor. Localization of absorbers/fluorochromes deep within a highly scattering large body of tissue such as the human breast can be effected most precisely by photon diffusive waves (Yodh, physical Review) that are not only amplitude modulated in the MHz region. If they consist of paired sources or detector, in-phase and anti-phase signal can be obtained to establish a null plane (Ref 1,2,3). Such a null plane is highly sensitive to perturbations by extremely small objects, of the order of the size of 70 microliters volume and containing as little as 20 picamole of an absorber. The null plane afforded by the in phase and out of phase cancellation diffusive wave is extremely narrow, and displacements of the array with respect to the hidden absorber of a fraction of a millimeter can be detected. Previous work has shown that the multiple source array consisting of portion of laser diode modulated at 200Mhz (50Mhz) RF signal 180 degree out of phase with the rest of the array gives a sharp phase transition and amplitude null plane. This plane provides a sensitive way for the detection of heterogeneity, and thereby may be used for the localization of small tumors within the human tissue. In order to enlarge the search field for phased array, the amplitude of the RF(200Mhz or 50 MHz) is modulated' by a second lower frequency signal(60 Hz),the phase transition plane moves back and forth in the certain region at the lower frequency. That is the principle of electronic scanning of the phased array. With this technology, we can make a real-time display of the line sight, which can goide the needle to the tumor in the surgeon's biopsy operation. In this paper, we will present the work for the localization of object in media using the phased array scanning.

© 1996 Optical Society of America