Near-infrared phase cancellation instrument for fast and accurate localization of fluorescent heterogeneity

Near-infrared (NIR) diffuse optical imaging has become a promising method for noninvasive in vivo detection of breast cancer with intrinsic chromophores. Recent developments in molecular specific targeting fluorescent contrast agents offer high tumor to normal tissue contrast, and are capable of selectively labeling various precancer/cancer signatures, thus enhancing both the sensitivity and specificity of cancer detection. To detect a subsurface tumor labeled by fluorescent contrast agents, we have developed a phase cancellation imaging system for fast localization of fluorescent object embedded several centimeters deep inside the turbid media. The instrument is a frequency domain (50 MHz) phase modulation system with dual out-of-phase sources. The excitation wavelength is 780 nm and the fluorescence photons are collected through an 830+/-10 nm band-pass filter. Localization of fluorescent objects inside the scattering media is accurate using a phase cancellation device. The localization error for a 5 mm diameter sphere filled with 1 nanomole fluorescent dye and 3 cm deep inside the turbid media is about 2 mm. The accuracy of the localization suggests that this system could be helpful in guiding clinical fine-needle biopsy, and would benefit the early detection of breast tumors. (C) 2003 American Institute of Physics.