Continuously increasing demand for biomedical diagnostics requires advanced imaging techniques. Time-gated imaging (TGI) of photoluminent bioprobes has a number of unique features, such as possibility to cut-off the excitation and autofluorescence and provide photoluminescence (PL) lifetime information in every pixel. However, as the other bioimaging techniques, TGI itself is not able to overcome the problem of high attenuation of light in the biological tissues. In recent years, imaging in the biological windows of optical transparency in near-infrared (NIR) and short wave infrared (SWIR) spectral ranges is being actively developed, providing an opportunity for the excitation and detection of PL signal in deeper biological tissues with higher resolution. In order to combine both advantages of NIR-SWIR imaging and TGI, we have built a time-gated imaging system performing in NIR-SWIR (900-1700nm) spectral range. Synchronizing setup has been developed in order to control delay between pulsed excitation source and NIR-SWIR camera. Through manipulation of the delay between the PL excitation source and imaging camera, stack of time-resolved PL images is obtained, which can be processed by the unmixing software. In summary, the developed technique allows us to distinguish and map regions of different NIR-SWIR PL lifetimes. An application of this method for spatial discrimination of rareearth ion doped nanoparticles emitting in NIR-SWIR range has been demonstrated.
Comparing to other optical imaging techniques, hyperspectral imaging (HSI) possesses a unique feature, being capable of not only obtaining a spatial information about a specimen, but also providing a spectral information in every image pixel. Being employed in biomedical applications, similarly to other optical bioimaging techniques, HSI struggles with limited light penetration depth, caused by high absorption and scattering of light by biological tissues. Overcoming the limitations of imaging in visible spectral range, optical bioimaging in near-infrared (NIR) and short wave infrared (SWIR) spectral ranges (~700 –1700 nm) has being actively advanced in recent years, as due to the strongly reduced tissue absorption and scattering, NIR-SWIR imaging systems can achieve deeper tissue imaging with higher resolution. With the aim to combine both the advantages of SWIR imaging and HSI, we have built a hyperspectral imaging system operating in NIR-SWIR spectral region (900 – 1700 nm). The constructed HSI system is based on a wavelengths scanning method, with a liquid crystal tunable filter (LCTF) as a dispersion element. The spectral unmixing software has been developed to map the regions of the specified spectral features. Finally, an application of the developed method towards spatial differentiation of rare-earth doped nanoparticles emitting in NIR-SWIR range has been demonstrated.
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