Three‐dimensional fluorescence lifetime tomography

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Abstract
Near‐infrared fluorescence tomography using molecularly targeted lifetime‐sensitive, fluorescent contrast agents have applications for early‐stage cancer diagnostics. Yet, although the measurement of fluorescent lifetime imaging microscopy (FLIM) is extensively used in microscopy and spectroscopy applications, demonstration of fluorescence lifetime tomography for medical imaging is limited to two‐dimensional studies. Herein, the feasibility of three‐dimensional fluorescence‐lifetime tomography on clinically relevant phantom volumes is established, using (i) a gain‐modulated intensified charge coupled device (CCD) and modulated laser diode imaging system, (ii) two fluorescent contrast agents, e.g., Indocyanine green and 3‐3’‐Diethylthiatricarbocyanine iodide differing in their fluorescence lifetime by 0.62 ns, and (iii) a two stage approximate extended Kalman filter reconstruction algorithm. Fluorescence measurements of phase and amplitude were acquired on the phantom surface under different target to background fluorescence absorption (70:1, 100:1) and fluorescence lifetime (1:1, 2.1:1) contrasts at target depths of 1.4–2 cm. The Bayesian tomography algorithm was employed to obtain three‐dimensional images of lifetime and absorption owing to the fluorophores.