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SC light source

Feature: Advantage of 1700 nm | Supercontinuum light source

 

Advantage of 1700 nm

Hamamatsu’s supercontinuum light source has a broadband spectrum mainly in the 1700 nm band. Therefore, it is suitable for OCT (optical coherence tomography) measurements of biological samples using the 3rd optical window(1600 - 1800 nm), and enables high-resolution deep imaging of highly scattered biological tissues.
In general, biological tissues imaging selects a wavelength band called the optical window, which is weakly absorbed by water and hemoglobin [1]. In particular, the wavelength bands where the absorption of water decreases are known as the 1st optical window (800 - 900 nm), the 2nd optical window (1100 - 1300 nm), and the 3rd optical window (1600 - 1800 nm), respectively. Among them, the 3rd optical window is the most suitable for deep imaging because it is less affected by light scattering from biological tissues.
As shown below, in the 1st and 2nd optical windows(0.8 μm, 1.1 μm, 1.3 μm), the penetration depth decreases as the scattering by biological tissue increases(Lipid %), but in the 3rd optical window(1.7 μm), the penetration depth is maintained even as the scattering increases [2].

Wavelength characteristics of light absorption and light scattering by biological tissues [1]

Penetration depth at each wavelength [2]

In addition, when applied to SD-OCT (spectral domain - optical coherence tomography), it is confirmed that the S/N ratio decreases as the penetration depth increases in the 1300 nm band, but the S/N ratio is maintained in the 1700 nm band even as the penetration depth increases [3].

Measurement system

S/N ratio

Provided by Nagoya University, Graduate School of Engineering, Department of Electrical Engineering, Nishizawa Research Laboratory

High axial resolution

One of the factors that determine the axial resolution (ΔZ) in OCT is the FWHM (Δλ) of the light source. The formula for determining the axial resolution is given below.

Since the FWHM (Δλ) is affected by the reciprocal, a wide FWHM is required for high-resolution measurements. In addition, when using a light source in the 1700 nm band for deep imaging compared to a light source in the 1300 nm band or lower, which is generally used for OCT, the FWHM (Δλ) needs to be wider because the center wavelength (λ0) affects the axial resolution by the square [4].
Hamamatsu’s supercontinuum light source has a FWHM (Δλ) of more than ±300 nm centered in the 1700 nm band. This allows for high axial resolution even in deep imaging.

Axial resolution at 1700 nm center wavelength

Provided by Nagoya University, Graduate School of Engineering, Department of Electrical Engineering, Nishizawa Research Laboratory

Low noise level

Hamamatsu’s supercontinuum light source is equipped with a unique and highly stable supercontinuum light generation system developed in collaboration with Nishizawa Laboratory, Nagoya University. Compared to supercontinuum light sources made by other companies, the noise characteristics is about 1/10, which enables highly sensitive measurements [5] [6].

Excess noise

Noise model of the OCT system [7]

Provided by Jun Zhu and Vivek J. Srinivasan (University of California Davis)

References

No.
Authors
Title
Source
[1]
M. S. Patterson, et al. The Propagation of Optical Radiation in Tissue. 2 : Optical Properties of Tissues and Resulting Fluence Distributions Lasers in Medical Science, Vol.6, pp. 379-390 (1991)
[2]
N.Nishizawa, H.Kawagoe, M.Yamanaka, M.Matsushima, K.Mori and T.Kawabe Wavelength Dependence of Ultrahigh-Resolution Optical Coherence Tomography Using Supercontinuum for Biomedical Imaging IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 25, NO. 1, JANUARY/FEBRUARY 2019
[3]
M.Yamanaka, N.Hayakawa and N.Nishizawa Signal-to-background ratio and lateral resolution in deep tissue imaging by optical coherence microscopy in the 1700 nm spectral band Scientific Reports volume 9, Article number: 16041 (2019)
[4]
S. Ishida and N. Nishizawa Quantitative comparison of contrast and imaging depth of ultrahigh-resolution optical coherence tomography images in 800-1700 nm wavelength region Biomed. Opt. Express, vol. 3, p. 282, 2012.
[5]
Jun Zhu and Vivek J. Srinivasan In vivo mouse brain imaging through the thinned skull with 1700 nm optical coherence microscopy (Conference Presentation) Proc. SPIE 11228, Optical Coherence Tomography and Coherence Domain Optical Methods in Biomedicine XXIV, 112280P (9 March 2020)
[6]
Jun Zhu, Hercules Rezende Freitas, Izumi Maezawa, Lee-way Jin and Vivek J. Srinivasan 1700 nm optical coherence microscopy enables minimally invasive, label-free, in vivo optical biopsy deep in the mouse brain Light: Science & Applications volume 10, Article number: 145 (2021)
[7]
Shau Poh Chong, Marcel Bernucci, Harsha Radhakrishnan, and Vivek J. Srinivasan Structural and functional human retinal imaging with a fiber-based visible light OCT ophthalmoscope Biomed. Opt. Express, Vol. 8, Issue 1, pp. 323-337, 2017

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