title: Molecular contrast optical coherence tomography: A pump-probe scheme using indocyanine green as a contrast agent.
abstract: The use of indocyanine green (ICG), a U.S. Food and Drug Administration approved dye, in a pump-probe scheme for molecular contrast optical coherence tomography (MCOCT) is proposed and demonstrated for the first time. In the proposed pump-probe scheme, an optical coherence tomography (OCT) scan of the sample containing ICG is first acquired. High fluence illumination (approximately 190 kJ/cm2) is then used to permanently photobleach the ICG molecules--resulting in a permanent alteration of the overall absorption of the ICG. A second OCT scan is next acquired. The difference of the two OCT scans is used to determine the depth resolved distribution of ICG within a sample. To characterize the extent of photobleaching in different ICG solutions, we determine the cumulative probability of photobleaching, phi(B,cum), defined as the ratio of the total photobleached ICG molecules to the total photons absorbed by the ground state molecules. An empirical study of ICG photobleaching dynamics shows that phi(B,cum) decreases with fluence as well as with increasing dye concentration. The quantity phi(B,cum) is useful for estimating the extent of photobleaching in an ICG sample (MCOCT contrast) for a given fluence of the pump illumination. The paper also demonstrates ICG-based MCOCT imaging in tissue phantoms as well as within stage 54 Xenopus laevis.
authors.affiliation: California Institute of Technology, Department of Electrical Engineering, Biophotonics Laboratory, 4 Moore Building, M/C 136-93, 1200 E. California Blvd., Pasadena, California 91125, USA. zyaqoob@caltech.edu
authors.forename: Zahid
authors.initials: Z
authors.lastname: Yaqoob
authors.forename: Emily
authors.initials: E
authors.lastname: McDowell
authors.forename: Jigang
authors.initials: J
authors.lastname: Wu
authors.forename: Xin
authors.initials: X
authors.lastname: Heng
authors.forename: Jeff
authors.initials: J
authors.lastname: Fingler
authors.forename: Changhuei
authors.initials: C
authors.lastname: Yang
mesh_terms: D000818:Animals; D003287:Contrast Media; D036681:Fluorescence Recovery After Photobleaching / Q000379:methods*; D007089:Image Enhancement / Q000379:methods*; D007208:Indocyanine Green; D015336:Molecular Probe Techniques; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D041623:Tomography, Optical Coherence / Q000379:methods*; D014982:Xenopus laevis / Q000002:abnormalities* / Q000196:embryology
chemical_list: D003287:Contrast Media; D007208:Indocyanine Green