## 3 The Use of Supercontinuum Lasers in Biomedical Diffuse Optics
### Methodology
This has been tested recently, especially with blood phantoms and compared to the results of a TD-NIRS instrument based on a SCL source [121]. The large amount of data collected by TD-NIRS also enables different data processing scheme to extract the relevant information. Therefore, there is a need to properly compare all the available methods in order to evaluate their strength and weaknesses. This work has recently been undertaken in order to compare the moment and time windowing techniques [122, 123]. Having a deep understanding of all the data processing method is also crucial so the proper technique can be used depending on the application. Several multi-centre initiatives have recently promoted this standardisation effort to compare instruments and algorithms. To that end, partners from the BitMap network ([[http://www.bitmap-itn.eu/](http://www.bitmap-itn.eu/)]([http://www.bitmap-itn.eu/](http://www.bitmap-itn.eu/)), accessed date: 1 February 2021) have started comparing instruments from different institutions all over Europe, by using the same sets of solid phantoms from the 3 main protocols [124, 125]. Moreover, several centres in Europe have used their instruments (several based on SCL) on 9 subjects, to study the inter-subject variability of the optical properties of the human head measured by several instruments [126]. They could show that the inter-subject variability was significant, with a big effect of the technique used (either CW or TD) because of their different depth sensitivity, which in turn affects the averaged optical properties retrieved. Therefore, it is evident that all the efforts to precisely characterized instruments and methods will have a huge impact on the precision of the optical measurement of tissue parameters. Finally, the use of SCL can help to explore new avenues in diffuse optics. The main one is to go above the \"therapeutical window\" in the second (1100 nm to 1350 nm) and the third (1600 to 1870 nm) near-infrared optical window. On top of the previously reported works that expand the bandwidth of TD-NIRS systems up to 1700 nm, [PERSON] and colleagues reported the use of a commercial SCL source, filtered with a bandpass and long pass filters to target the second and third NIR windows, coupled with an IR-CCD camera, to acquire transmission images of 3 targets embedded in chicken tissue of various thickness [127]. They were able to distinguish the targets up to a depth of 10 mm, which was not possible when using the same setup but with a traditional lamp source. These results are promising in order to implement transmission measurement, especially for preclinical imaging. As we have seen previously, the use of these long NIR wavelength is useful to resolve more chromophores like collagen. It is also promising to resolve glucose, which could be a true benefit for several clinical applications like monitoring diabetes [128], or monitoring brain injuries [129] or neonatal encephalopathy [130]. Once again, in this wavelength range, the power delivered by SCL has proved efficient to monitor the glucose contrast in the NIR [131; 132]. Finally, a tentative to non-invasively probe the lungs with a TD-NIRS system based on SCL source was reported [133]. The measurements were performed on three subjects, and spectra from 600 to 1100 nm could be acquired. Here, the depth sensitivity of a TD-NIRS is essential and this application shows that instruments based on that technology could be used to non-invasively probes tissues previously thought out of reach.