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

Using a single supercontinuum source for visible multispectral photoacoustic microscopy and 1300 nm optical coherence tomography

We present a bimodal system driven by a supercontinuum source to perform photoacoustic-based spectral selective absorption measurements from 500 nm to 800 nm and structural optical coherence tomography imaging at 1300 nm. An energy of 5 to 40 nJ is achieved on sample within a 50 nm bandwidth in the visible range in the photoacoustic channel. Also, a few mW power is also achieved on the sample in the optical coherence tomography channel

Developments on Using Supercontinuum Sources for High Resolution Multi-Imaging Instruments for Biomedical Applications

We report on further progress made on enhancing the capabilities of a multi-imaging modality instrument capable of producing high resolution images of biological tissues. At the core of the instrument is a supercontinuum (SC) source. Two SC sources commercialized by NKT Photonics were employed for our experiments: SuperK COMPACT and SuperK Extreme (EXR9). Using these two sources, we assembled an instrument capable to simultaneously provide in real-time cross-section high-resolution Optical Coherence Tomography (OCT) and Photo-acoustic (PA) images in various spectral ranges. Currently, the OCT channel is operating in the IR range around 1300 nm to allow better penetration into the tissue using either the COMPACT or the EXR9. The measured optical power on the sample is in both cases above 9.5 mW. An in-house spectrometer equipped with a sensitive InGaAs camera capable of operating at 47 kHz and sampling data over a spectral range from 1205 to 1395 nm was developed. A constant axial resolution provided by the instrument in the OCT channel over a range of 1.5 mm was experimentally measured (4.96 µm), matching the theoretical prediction. The spectral range 500-800 nm was used for PA channel. The COMPACT, used in the PA channel, can select the central wavelength and the spectral bandwidth of operations. Typically, the optical energy per pulse on the sample is superior to 60 nJ when a bandwidth superior to 50 nm is employed. This make the instrument usable for PA imaging of tissues

Two octaves spanning photoacoustic microscopy

In this study, for the first time, a Photoacoustic Microscopy instrument driven by a single optical source operating over a wide spectral range (475–2400 nm), covering slightly more than two octaves is demonstrated. Xenopus laevis tadpoles were imaged in vivo using the whole spectral range of 2000 nm of a supercontinuum optical source, and a novel technique of mapping absorbers is also demonstrated, based on the supposition that only one chromophore contributes to the photoacoustic signal of each individual voxel in the 3D photoacoustic image. By using a narrow spectral window (of 25 nm bandwidth) within the broad spectrum of the supercontinuum source at a time, in vivo hyper-spectral Photoacoustic images of tadpoles are obtained. By post-processing pairs of images obtained using different spectral windows, maps of five endogenous contrast agents (hemoglobin, melanin, collagen, glucose and lipids) are produced

Supercontinuum applications in high resolution non invasive optical imaging

Progress will be presented in adapting supercontinuum sources to a variety of applications with emphasis on signal processing procedures. These are customised to alleviate noise and take full advantage of the large bandwidth and large power spectral density of modern supercontinuum sources

Single all-fiber-based nanosecond-pulsed supercontinuum source for multispectral photoacoustic microscopy and optical coherence tomography

We report the usefulness of a single all-fiber-based supercontinuum (SC) source for combined photoacoustic microscopy (PAM) and optical coherence tomography(OCT). The SC light is generated by a tapered photonic crystal fiber pumped by a nanosecond pulsed master oscillator power amplifier at 1064 nm. The spectrum is split into a shorter wavelength band (500–800 nm) for single/multispectral PAM and a longer wavelength band (800–900 nm) band for OCT. In vivo mouse ear imaging was achieved with an integrated dual-modality system. We further demonstrated its potential for spectroscopic photoacoustic imaging by doing multispectral measurements on retinal pigment epithelium and blood samples with 15-nm linewidth