## 3 The Use of Supercontinuum Lasers in Biomedical Diffuse Optics
### Novel Instrument Development
Finally, they have produced a system able to cover the entire bandwidth from 600 to 1350 nm using a single SCL coupled with a prism for the wavelength selection, and 2 TCSPC cards couples with 2 detectors covering different bandwidth [23]. They managed to fix the issue of the spectral broadening induced by the prism by refining the optical chain. Additionally, this system was mounted on a 19-inch medical cart, making it easily used in a clinical environment. This system can be seen in Figure 2 and in an example of data in Figure 3. Moreover, by adjusting the detector used, the same instrument can be used to cover an even larger bandwidth, between 500 to 1700 nm [46]. With all these developments, POLIMII has been a major contributor to multispectral TD-NIRS and were able to characterize various tissue over a large bandwidth. They were able to characterize bones [47; 48; 49], thyroid tissues [50], adipose tissues [51], collagen [46; 52], and elastin [53]. This groundwork was crucial in order to investigate the tissue composition of breast for example, which can help for diagnosis of cancerous tissue [54; 55]. Finally, we can report that the latest reported system has also been used to monitor the thermal effect of Radio Frequency (RF) on tissues [56; 57]. The previously reported systems were only composed of one channel, which can be a drawback when an image is required, like for performing mammography. Therefore, parallel to these developments, another system aimed at optical mammography was developed, based on a supercontinuum light generated in PCF and a 32-channel parallel detection [58]. This allowed to acquired image of the breast between 606 and 885 nm, and to extract hemoglobin, tissue saturation, lipid and water content, and scattering parameters of the tissue. All the systems reported above were designed to collect spectral information about tissue, with a first application in breast cancer detection. Therefore, the acquisition time was not limited, and functional contrast was not explored. However, the potential of monitoring real time change in optical properties over a large bandwidth is quite appealing for various application, like brain monitoring [59]. Therefore, other systems were developed in order to achieve that goal. A system was developed at POLIMII based on a supercontinuum source generated in a PCF by a self-locking mode-locked Ti:Sapphire oscillator and a detection scheme based on an imaging spectrometer coupled to a 16-channel multianode PMT connected to a TCSPC board [60]. The fact that all the 16 wavelengths were captured at once enabled a fast acquisition and permitted to track dynamic variations in absorption and scattering spectra following hemodynamic changes [61]. The limitation of the detections scheme constraint the bandwidth of this system between 520 and 850 nm. A similar approach was taken by a group based in Poland [62; 63]. The system was based on a commercial SCL for the source, coupled to a 16-channel multianode PMT connected to a TCSPC board for the detection part. This system was used to follow a contrast agent (Indocyanine green (ICG)), which allows to estimate the cerebral blood perfusion. The same system can be used without ICG to monitor the intrinsic optical contrast [64]. Similarly, the author and colleagues used a TD-NIRS system based on a SCL filtered at 808 nm and on a detection scheme based on a single channel TCSPC to follow ICG bolus [65]. The novelty of this study was the fact that the TD-NIRS was coupled with a diffuse correlation spectroscopy system (DCS) [66]. The coupling of these two techniques allowed to retrieve absolute cerebral blood flow measurement in patients in the intensive care unit, showing that these systems could be used in a particularly difficult clinical environment. Moreover, the possibility to also measure blood perfusion is of great interest and might help in the adoption of the technique in the clinic. Another potential detection scheme in order to collect parallel data is to use an Intensified CCD (ICCD) camera.