Fig. 1. (A) Sketch showing approximate location on arm of the excised tissues studied. (B–D) Distribution of BLS frequency shift (ν_B) and linewidth (Γ_B) for the different tissue samples obtained from large-area confocal grid scans. Distributions are each fitted with a Gaussian distribution (dashed lines) and results are collated in Table 1.

Fig. 2. (A) Schematic of the hand-held BLS probe (PBS = Polarizing Beam Splitter; λ/4 = quarter waveplate; λ/2 = half waveplate; IP = intermediate image plane; L1 & L2 relay lenses; L3 focusing lens; q = predominant phonon-scattering wavevector probed in the sample). Inset shows a sketch of the multimode fiber bundle cross section used for coupling light into and out of the probe, and the excitation pattern projected onto sample (green dots). Scale bar = 1 mm. (B) Photograph of hand-held probe. (C) Example of BLS-spectra showing Stokes (S) and Anti-Stokes (AS) BLS scattering peaks shifted by frequencies ±ν_B relative to the probing laser frequency ν₀. Also shown is an example of a raw spectral projection measured with the BLS imaging spectrometer using the hand-held probe (dashed line = dispersion axis). (D) BLS measurements on the same samples as in Figure 1 using the hand-held probe (x). Also shown are mean values (□) and the standard deviation of the mean (grey bars) of the confocal scan measurements (viz.Fig. 1 and Table 1). Inset: Mean ν_B obtained from confocal scan measurements versus that obtained using the hand-held probe (later is average of 5 measurements). Statistical differences are for ν_B of the different tissues measured using the hand-held probe, and were performed using unpaired t-test’s with Welch’s correction (*p < 0.05, ****p < 0.0001). Sample acronyms are as defined in Table 1.

Fig. 3.

(A) Sketch showing approximate locations along the arm of the excised tissues studied. (B and D) Collated results of independent measurements of ν_B (x) using the hand-held probe at different positions of the Brachial/Radial artery (BA/RA) and Median nerve (MN) as indicated in “A” ( = mean of 5 measurements). (C and E) Corresponding plots of Γ_B versus ν_B. (Solid symbols = individual measurements; open symbols = mean; dashed line = trend line of mean). In (C) the Pearson correlation coefficient for the individual measurements is 0.46, whereas for (E) it is −0.53. (F and G) Expected frequency dispersion of the complex modulus M = M′ + iM″ when probing (F) a heterogeneous sample with different relaxation times (τ) in the vicinity of τ∼νB-1, and (G) the effect of different strengths of a relaxation process with τ>νB-1 as may occur for different solid fractions. (H) Sketch of the expected scaling of Γ_B with respect to ν_B for the two scenarios. Statistics performed using unpaired t-test with Welch’s correction (*p < 0.05, **p < 0.01).