Fig. 2
From: Label-free nanoscale optical metrology on myelinated axons in vivo
Theoretical background on SpeRe. a Scheme of optic simulation for SpeRe. Structural variables of interest in myelinated axons are annotated. Absolute reflectance (%) for each wavelength is simulated by applying the theory of electromagnetic waves. b Simulated reflectance spectra with variable myelin layers. The axon size is set to 0.5 μm. c Fold increase in visible reflectance (400–700 nm) relative to unmyelinated condition. d Simulated reflectance spectra with varying axon size. Horizontal axis shows the wavenumber, \(\tilde \nu\) (inverse of wavelength). The g-ratio (i.e., the ratio of inner axonal diameter to the total outer diameter) is set to 0.7. e Relationship between wavenumber period \(\left( {\tilde \nu _{\rm p}} \right)\) and axon diameter (d). Dotted line indicates fitted curve to hyperbola (R 2 = 0.99), and the best-fit equation is shown. f Simulated reflectance spectra with a varying swelling ratio of the extracellular space between the myelin layers. The axon size and g-ratio at the isosmotic condition are set to 0.5 μm and 0.7 (i.e., 6 myelin layers), respectively. g The relationship between spectral shift (Δλ) and swelling ratio (r s). The equation is the best fit to linear regression (R 2 = 0.98)
