To understand the impact of collagen absorption in a diffuse reflectance measurement on biological tissues, we have calculated the contribution of key tissue constituents on the absorption spectrum of a bone prominence location. The radius distal location was chosen, as it has thin superficial muscle, giving easy access to bone probing in an in vivo measurement.14 Importantly, radius distal is one among the locations considered for bone mineral assessment by DXA scans and is rich of collagen, which can be of interest for diagnosing bone pathologies.34Figure 4 depicts the calculated broadband (500 to 1700 nm) weighted spectra of major tissue constituents, namely oxy-hemoglobin (, ), deoxy-hemoglobin (Hb, ), lipid (), water (), and collagen () for a simulated in vivo measurement on the forearm at radius distal location. The data required for this simulation were derived from in vivo measurements reported in Ref. 35. From Fig. 4, collagen dominates the other constituents around 700 nm, where the absorption of water and lipid is minimal, and also Hb and contributions are small. Still, the flat spectral shape of collagen in this region hampers its robust estimate. Local minima of water and local maxima of collagen around 1050 nm make it a suitable spectral window for collagen detection. However, the competing lipid peak and limited penetration depth of light due to high scattering challenge the detection of deep tissue collagen (bone). Finally, around 1700 nm, the absorption of collagen is 5 times stronger than lipid absorption, compared to only 1.5 times around 1100 nm, and water shows a local minimum. These features could make the spectral range around 1700 nm more specific for in vivo collagen detection from deep tissues, provided that the decrease in penetration depth and signal due to increased absorption is compensated by the penetration depth and signal gained by decrease in scattering at 1700 nm.36 Apart from this specific example, due to its specificity and high absorption, we predict that the detection of collagen peak at 1700 nm may have potential applications in the intraoperative and in vitro study of collagen-rich regions.