Long-wavelength optical coherence tomography at 17 μm for enhanced imaging depth

Abstract

Multiple scattering in a sample presents a significant limitation to achieve meaningful structural information at deeper penetration depths in optical coherence tomography (OCT). Previous studies suggest that the spectral region around 1.7 µm may exhibit reduced scattering coefficients in biological tissues compared to the widely used wavelengths around 1.3 µm. To investigate this long-wavelength region, we developed a wavelength-swept laser at 1.7 µm wavelength and conducted OCT or optical frequency domain imaging (OFDI) for the first time in this spectral range. The constructed laser is capable of providing a wide tuning range from 1.59 to 1.75 µm over 160 nm. When the laser was operated with a reduced tuning range over 95 nm at a repetition rate of 10.9 kHz and an average output power of 12.3 mW, the OFDI imaging system exhibited a sensitivity of about 100 dB and axial and lateral resolution of 24 µm and 14 µm, respectively. We imaged several phantom and biological samples using 1.3 µm and 1.7 µm OFDI systems and found that the depth-dependent signal decay rate is substantially lower at 1.7 µm wavelength in most, if not all samples. Our results suggest that this imaging window may offer an advantage over shorter wavelengths by increasing the penetration depths as well as enhancing image contrast at deeper penetration depths where otherwise multiple scattered photons dominate over ballistic photons.

Dental Applications of Optical Coherence Tomography (OCT) in Cariology

“…For soft and hard tissues, there are characteristic dependences of wavelength of OCT signal attenuation [36]. Some authors suggested that an imaging window at 1700 nm offers an advantage over shorter wavelengths by increasing penetration depth as well as enhancing the image contrast at deeper penetration depths by reducing multiple scattering [37]. For biological tissues, it is expected an increase in OCT imaging depth at 1600 nm compared to 1300 nm on samples with high scattering power and low water content (enamel) [38].…”

“…For biological tissues, it is expected an increase in OCT imaging depth at 1600 nm compared to 1300 nm on samples with high scattering power and low water content (enamel) [38]. Otherwise at longer wavelengths, absorption increases with greater water content, which has a counterbalancing effect [37]. Also, as in the case of The studies were conducted in accordance with the Declaration of Helsinki, and the protocols were approved by the Ethics Committee of the University of Leipzig.…”

Generic foundry model for InP-based photonics

“…For skin or blood vessel diagnostics wavelengths longer than 1500 nm are better, because there the penetration depth is three times as large due to reduced scattering losses at this wavelength. This provides good opportunities for InP PICs in OCT equipment [29].…”

Optical coherence tomography—current technology and applications in clinical and biomedical research

“…Light at 1300 nm allows for deep penetration into most tissues, like skin or mucosa, because absorption in melanin and scattering decrease with increasing wavelength [49]. Longer wavelengths, e. g. around 1700 nm, may enable even deeper penetration for applications where water absorption has no significant influence [51]. However, these long wavelengths are not suited for probing the posterior eye segment in vivo due to strong signal attenuation in the vitreous which mainly consists of water.…”