Supercontinuum sources in the practice of multimodal imaging

The development of recent imaging modalities and of multimodal imaging may offer new perspectives for biomedical imaging, such as in-vivo cancer detection at early stages. By combining optical coherence tomography (OCT) and photoacoustic microscopy (PAM), complementary information is extracted from tissue: scattering and absorption. Non-invasive cross-sectional images with micrometre resolution are obtained. In this thesis, for the first time, encouraging results using a single SC source for OCT and PAM are obtained. Micrometre axial resolution is achieved using SC sources for OCT. The use of SC sources for PAM allows for multispectral PAM (MPAM) by using several excitation spectral bands. With MPAM, different absorbers are distinguishable and recognisable through their absorption spectra. In addition, for the first time, spectroscopic photoacoustic (sPA) measurements are demonstrated in the visible using a bandwidth narrower than 40 nm. These results were obtained with the first multimodal imaging system that combines sPA, PAM, MPAM and OCT. A single commercially available SC source is used for excitation. Diverse in-vitro and in-vivo samples are imaged to show the capabilities of such a configuration. In addition, the development of a novel fibre-based SC source with both increased energy density and pulse repetition frequency (PRF) is presented. The increased pulse energy allows reduction of excitations bands that leads to more accurate MPAM and sPA measurements, while the access to larger PRFs allows for both noise reduction and faster imaging rates in PAM and OCT. A tapered photonic crystal fibre (PCF) is used to generate the SC by nonlinear spectral broadening. The larger input core of the tapered PCF enables enhanced energy density, where more than 50-100 nJ is achieved with less than 30 nm wide bandwidth, over a broad spectrum extending from 500 nm to 1700 nm. Such a source can be used for in-vivo blood oxygen saturation determination, skin and other superficial organs imaging, which is critical to image tumours and diagnose early stage cancers. Such imaging modalities can also be beneficial during surgery and treatment