title: Photoacoustic pump-probe tomography of fluorophores in vivo using interleaved image acquisition for motion suppression.
abstract: In fluorophores, the excited state lifetime can be modulated using pump-probe excitation. By generating photoacoustic (PA) signals using simultaneous and time-delayed pump and probe excitation pulses at fluences below the maximum permissible exposure, a modulation of the signal amplitude is observed in fluorophores but not in endogenous chromophores. This provides a highly specific contrast mechanism that can be used to recover the location of the fluorophore using difference imaging. The practical challenges in applying this method to in vivo PA tomography include the typically low concentrations of fluorescent contrast agents, and tissue motion. The former results in smaller PA signal amplitudes compared to those measured in blood, while the latter gives rise to difference image artefacts that compromise the unambiguous and potentially noise-limited detection of fluorescent contrast agents. To address this limitation, a method based on interleaved pump-probe image acquisition was developed. It relies on fast switching between simultaneous and time-delayed pump-probe excitation to acquire PA difference signals in quick succession, and to minimise the effects of tissue motion. The feasibility of this method is demonstrated in tissue phantoms and in initial experiments in vivo.
authors.affiliation: Institut für Optik und Atomare Physik, Technische Universität Berlin, Hardenbergstraße 36A, 10623 Berlin, Germany.
authors.forename: Julia
authors.initials: J
authors.lastname: Märk
authors.affiliation: Medizinische Klinik mit Schwerpunkt Hepatologie und Gastroenterologie, Charité - Universitätsmedizin Berlin, Campus Virchow-Klinikum, Augustenburger Platz 1, 13353 Berlin, Germany.
authors.forename: Asja
authors.initials: A
authors.lastname: Wagener
authors.affiliation: Department of Medical Physics and Biomedical Engineering, University College London, Gower Street, London WC1E 6BT, UK.
authors.forename: Edward
authors.initials: E
authors.lastname: Zhang
authors.affiliation: Institut für Optik und Atomare Physik, Technische Universität Berlin, Hardenbergstraße 36A, 10623 Berlin, Germany.|Institut für Radiologie, Charité - Universitätsmedizin Berlin, Charitéplatz 1, 10117 Berlin, Germany.
authors.forename: Jan
authors.initials: J
authors.lastname: Laufer