Optimal focus evaluated using Monte Carlo simulation in non-invasive neuroimaging in the second near-infrared window

Tatsuto Iida,Hiro Yamato,Takashi Jin,Yasutomo Nomura

doi:10.1016/j.mex.2019.09.010

Tatsuto Iida, Hiro Yamato + Show 2 more

Open Access

https://doi.org/10.1016/j.mex.2019.09.010

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Abstract

Adjusting the focal plane through the intact scalp of mice is crucial in novel angiography of cerebral vasculature using quantum dots emitting second near-infrared light at a wavelength of 1100 nm. Reagents were administered through the caudal vein. When we focused 0.4 mm below the scalp surface, based on the anatomical properties of mice reported previously, the intensity of clear fluorescence images observed transiently under a microscope became very weak within several seconds. The remaining time was extremely short to repeat adjustment of the focal plane. To investigate focus, photons exciting quantum dots at depths of 0.4, 0.8, 1.4, and 2.0 mm and emission photons were tracked in a four-layered Monte Carlo model including the scalp, skull, cerebrospinal fluid, and cortex. Based on the most near-ballistic photons emitted from quantum dots at 0.4 mm depth and specification of the microscope used, including numerical aperture and depth of field, the optimal focus plane was set.•Novel angiography for cerebrovascular structures was proposed using quantum dots with second near-infrared fluorescence.•Anatomical properties reported previously allowed focusing 0.4 mm below the surface of intact scalp before observation under fluorescence.•Clear images of cerebrovascular structures were attributed to many near-ballistic photons emitted from quantum dots at 0.4 mm depth.

Highlights

By focusing at a depth of 0.4 mm below the sculp surface, examination was conducted using Monte Carlo simulation because the photon propagation of excitation and emission was dependent on image quality
Near-axis coaxial fluorescence photons were captured by an image sensor using an optical system of our epifluorescence macro zoom microscope
Considering the mechanism underlying fluorescence, we examined the effect of initial photon weight (0.05–1) on photon propagation of excitation at a wavelength of 785 nm (Fig. S1) and emission at a wavelength of 1100 nm (Fig. S2) in the four-layered Monte Carlo model with QD1100 localized at z = 0.4 mm and r =0 mm

Summary

Introduction

By focusing at a depth of 0.4 mm below the sculp surface, examination was conducted using Monte Carlo simulation because the photon propagation of excitation and emission was dependent on image quality. They became a new light source that emitted isotropic fluorescence depending on the sum of excitation photon weights at a specific depth.

Results

Conclusion