Abstract
We report the development of a two-color Fourier domain Pump-Probe Optical Coherence Tomography (PPOCT) system. Tissue phantom experiments to characterize the system performance demonstrated imaging depths in excess of 725 μm, nearly comparable to the base Optical Coherence Tomography system. PPOCT A-line rates were also demonstrated in excess of 1 kHz. The physical origin of the PPOCT signal was investigated with a series of experiments which revealed that the signal is a mixture of short and long lifetime component signals. The short lifetime component was attributed to transient absorption while the long lifetime component may be due to a mixture of transient absorption and thermal effects. Ex vivo images of porcine iris demonstrated the potential for imaging melanin in the eye, where cancer of the melanocytes is the most common form of eye cancer in adults.
Highlights
Optical Coherence Tomography (OCT) [1] is a non-contact imaging modality capable of micron scale resolution at depths of 1-2 mm in living tissue
The imaging depth of the Pump-Probe OCT (PPOCT) system was shown to be nearly comparable to the base OCT system and confirmed to be greater than 725 μm in chicken breast tissue
Similar experiments showed that PPOCT A-line rates up to 2.4 kHz were possible in tissue albeit at reduced signal to noise
Summary
Optical Coherence Tomography (OCT) [1] is a non-contact imaging modality capable of micron scale resolution at depths of 1-2 mm in living tissue. The physical process which leads to the pump induced changes depends in part on the excited state manifold of the molecule of interest. Scheme 3 is similar to scheme 2 except intersystem crossing to a triplet state (Tk) follows pump excitation and the probe drives the Tk-Ti transition. A fourth process not illustrated, but of potential importance is the internal conversion to highly excited vibrational states which leads to local heating and the emission of a pressure (acoustic) wave. We know this is an important mechanism in melanin because of its ubiquitous use as a target chromophore in photoacoustic tomography. The probe beam and the sample arm beam in the OCT interferometer are the same, so in the standard OCT equation for signal to noise ratio, Ppr is equivalent to Ps
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