Localization of absorbers/fluorochromes deep within a highly scattering large body of tissue such as the human breast can be affected most precisely by photon diffusive waves (yodh, physical Review) that are in and out of phase amplitude modulated sources in the MHz region. The detector of in-phase and anti-phase signal establishes a null plane. Such a null 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 (ICG). In order to enlarge the search field for phased array, the relative amplitude of the rf (200 Mhz or 50 MHz) is modulated by a second lower frequency signal (60 Hz), the phase transition plane moves back and forth at the lower frequency. The phased array system is applied to the detection the blood concentration and its oxygenation/deoxygenation in human breast pendant within a 'breast box' 40 cm X 15 cm X 15 cm, containing a breast matching intralipid and 1 cm3 tumor phantom used as a blood volume, blood oxygenation calibrator. The breast is located by a pair of soft compression plates during the phased array scan. The sensitivity of the system is estimated by the detectable blood concentration and the corresponding oxygenation/deoxygenation of the blood in the 1 cm3 tumor phantom. We have done over 40 experiments for human breast test.
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