Molecular contrast optical coherence tomography: a pump-probe scheme using indocyanine green as a contrast agent

Abstract

Abstract. The use of indocyanine green ͑ICG͒, a U.S. Food and Drug Administration approved dye, in a pump-probe scheme for molecular contrast optical coherence tomography ͑MCOCT͒ is proposed and demonstrated for the first time. In the proposed pump-probe scheme, an optical coherence tomography ͑OCT͒ scan of the sample containing ICG is first acquired. High fluence illumination ͑ϳ190 kJ/ cm 2 ͒ 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, 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 B,cum decreases with fluence as well as with increasing dye concentration. The quantity B,cum is useful for estimating the extent of photobleaching in an ICG sample ͑MCOCT contrast͒ 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.

Control of reaction efficiency by two-color two-pulse excitation: Photoisomerization of indocyanine green in condensed phase

“…On the ground state potential, molecules either relax back to the trans configuration or form a cis isomer [8,9]. In our previous study, we irradiated two near-infrared (NIR) ultrashort pulses on indocyanine green (ICG), a widely used and investigated dye [10][11][12][13][14][15][16][17], and measured transient absorption by photo-produced cis-isomers as a function of pump-pump interval, in other words two-pulse correlation (2PC) trace [7]. We found that the transient absorption shows clear dependence on pumppump interval and increases with decrease of the interval.…”

Spectral fractionation detection of gold nanorod contrast agents using optical coherence tomography

“…This differed from previous methods that enhanced contrast by means of characteristic spectral OCT signal shift due to absorption effects from indocyanine green dye [5] or nanoparticles [6][7][8]. The reasoning was that absorption effects would be too small for small clusters of GNR in a sparse concentration of cells to produce useful contrast.…”

Nanotechnology Approaches to Contrast Enhancement in Optical Imaging and Disease‐Targeted Therapy

“…Polarization-sensitive OCT is used to measure phase retardation in birefringent tissue which has application in retinal imaging [110], burn-depth determination [111], atherosclerosis imaging [112], muscular dystrophy [113], and detection of basal cell carcinomas [114]. Pump-probe OCT [115,116] and nonlinear interferometric vibrational imaging [117] are also promising methods to sense endogenous biomolecules based on their nonlinear optical susceptibilities. Although these endogenous methods are attractive as they do not require the addition of exogenous agents for contrast, they may be limited in scope because many diagnostic markers do not exhibit a detectible optical signal.…”

“…11 OCT images of tissue phantoms with varying concentrations of plasmon-resonant nanorods, as described in[115,119]. Left and right columns are the structural OCT and their associated spectroscopically contrasted nanorod OCT images, respectively.…”