## 3 The Use of Supercontinuum Lasers in Biomedical Diffuse Optics
### Novel Instrument Development
This system can be seen in Figure 2 and an example of data in Figure 3. Another approach can be to use spatial frequency domain imaging (SFDI), a wide-field, noncontact, model-based technique that can quantitatively assess absorption and scattering, on a pixel-by-pixel basis by calculating the modulation transfer function of structured light projected onto the tissue. This technique can be hyperspectral if a proper source is used. However, the system developed thus far was based on conventional broadband sources coupled with tunable filters, which limited their acquisition speed and spectral resolution. [PERSON] and colleagues [82] applied this technique using the principles of the single-pixel compressive sensing. They used a commercial SCL coupled with a dispersive prism to achieve a final bandwidth 1000 spectral bands between 580 and 950 nm, which was larger than the previously developed systems. With this system, the authors were able to characterize the optical properties of a beef sample ex-vivo in 2D, and extract physiological information (i.e., hemoglobin content and fat and water content). The authors noted that the wavelength selection technique used was still slow (i.e., 150 s of acquisition time for a 4 cm \(\times\) 6 cm), but that switching to an AOTF solution could greatly improve this speed. Using the same principle of the single-pixel compressive sensing, [PERSON] and colleagues reported a TD-DOT instrument based on time-resolved single pixel camera [83]. Their approach was based on a SCL source filtered at 620 nm coupled with a digital micromirror device (DMD) to generate the spatial pattern. The time domain acquisition was based on TCSPC. [PERSON] and colleagues used a similar approach but expended it to a broadband illumination and detection [84]. The authors reported that their system, aimed at fluorescence molecular tomography, benefitted for the commercial SCL source to perform hyperspectral excitation of the sample which offers a spectral information boost within the same data acquisition time compared to single wavelength excitation situations. Another work aiming at improving the spatial resolution of TD-DOT was to investigate the effect of only considering early photons, which undergo fewer scattering events [85]. In this work, this approach has been tested using a commercial SCL together with a bandpass filter at 670 nm. It worth noting that the commercial version of this laser was modified by the manufacturer so that it had a shortened fibre compared to standard models, which reduced the pulse width to approximately 300 ps. This is important as the benefit of the gating of the early photons is highly dependent on the instrument response function (IRF) of the system. The authors reported that with this technique, and this instrument, a 64 to 84% image resolution could be achieved, which could be a great benefit for preclinical imaging with diffuse optics. Novel algorithms can also be used in combination to TD-DOT instruments to recovers 3D images of the optical properties and physiological parameters. A team in Grenoble has explored the use of the Mellin-Laplace transform to reconstruct 3D images of the chromophores inside phantoms and for the non-invasive assessment of flap viability in rats' models. There instrumentation was based on commercial SCL, coupled with either an AOTF or an interferential filter, for the source and a TCPSC scheme for the detection [86; 87]. TD-DOT has also been explored in humans, in order to reconstruct 2D or 3D maps of the optical properties and hemodynamic parameters. To this end, the UCL team had design MONSTIR II to perform tomographic brain imaging [28]. This system is based on a commercial SCL with an AOTF filtering and has 32 channels based on TCSPC.