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Towards in-vivo assessment of fluorescence lifetime: imaging using time-gated intensified CCD camera

Sawosz P., Wojtkiewicz S., Kacprzak M., Zieminska E., Morawiec M., Maniewski R., Liebert A.

Biocybernetics and Biomedical Engineering

2018

Vol. 38, no. 4

966--974

A novel technique for imaging of a small animal with application of time-gated intensified CCD camera was proposed. The time-resolved method based on emission of picosecond light pulses and detection of the light penetrating in tissues was applied. In this technique, the fluorescence photons, excited in the dye circulating in the tissue, that diffusely penetrate in the optically turbid medium are detected. The data acquired during measurements carried out on a rat was analyzed in order to estimate fluorescence life time which depends strongly on the environment in which the dye is distributed. In the life time estimation a special emphasis was put on compensation of influence of the instrumental response function of the setup on the measured quantity. The proposed optical system was validated in series of phantom experiments, in which estimates of fluorescence lifetime of inclusions containing indocyanine green (ICG) were obtained. ICG is a dye revealing florescence properties in near-infrared wavelength region. Images of the estimate of fluorescence lifetime of the ICG accumulated in tissues of a rat were successfully acquired around six circular spots of illumination of the diameter of 6mm. Larger lifetime values were observed in lung/heart region of the animal. Aspect of sampling rate of the fluorescence lifetime images optimization was finally discussed.

Cerebral perfusion in acute stroke monitored by time-domain near-infrared reflectometry

Steinkellner O., Wabnitz H., Jelzow A., Macdonald R., Gruber C., Steinbrink J., Obrig H.

Biocybernetics and Biomedical Engineering

2012

Vol. 32, no. 1

3-16

Though potentially relevant for monitoring of acute stroke, even specialized stroke units do not provide continuous methods to determine cerebral perfusion at the bedside. We present patient measurements on cerebral perfusion in ischemic stroke applying optical bolus tracking. To this end, our portable time-domain near-infrared reflectometer has been optimized and technically approved for clinical studies by a notified body. We used data analysis based on statistical moments of measured time-of-flight distributions of photons. Selective sensitivity to deep absorption changes and a suitable representation of cerebral signals is associated with the suppression of movement artifacts in severely affected patients. The proposed technique offers a unique possibility for a frequently repeatable monitoring of cerebral blood flow during acute and subacute cerebral ischemia directly at the bedside.