Optical clearing of melanomain vivo: characterization by diffuse reflectance spectroscopy and optical coherence tomography

Abstract

Melanoma is the most aggressive type of skin cancer, with significant risk of fatality. Due to its pigmentation, light-based imaging and treatment techniques are limited to near the tumor surface, which is inadequate, for example, to evaluate the microvascular density that is associated with prognosis. White-light diffuse reflectance spectroscopy (DRS) and near-infrared optical coherence tomography (OCT) were used to evaluate the effect of a topically applied optical clearing agent (OCA) in melanoma in vivo and to image the microvascular network. DRS was performed using a contact fiber optic probe in the range from 450 to 650 nm. OCT imaging was performed using a swept-source system at 1310 nm. The OCT image data were processed using speckle variance and depth-encoded algorithms. Diffuse reflectance signals decreased with clearing, dropping by ∼ 90% after 45 min. OCT was able to image the microvasculature in the pigmented melanoma tissue with good spatial resolution up to a depth of ∼ 300 μm without the use of OCA; improved contrast resolution was achieved with optical clearing to a depth of ∼ 750 μm in tumor. These findings are relevant to potential clinical applications in melanoma, such as assessing prognosis and treatment responses. Optical clearing may also facilitate the use of light-based treatments such as photodynamic therapy.

Preclinical quantitative in-vivo assessment of skin tissue vascularity in radiation-induced fibrosis with optical coherence tomography

“…[52][53][54] Further, skin is indeed a very important target of such RT imaging studies, given its clinical importance as a dose-limiting organ and thus common occurrence of RIF. However, its thicker structures in humans compared to mice may somewhat limit clinical utility, as OCT can only detect important RIF changes within ∼1 mm of the skin surface (unless optical clearing is used, a promising practical solution to this obstacle), 55 thus its application should be driven by relevant tissue changes within this depth range.…”

Optical strategies for diagnosis and treatment of melanoma

“…Also, the use of OCA improved OCT imaging of pigmented melanoma vascular network, that is related to tumor staging and prognosis. To our knowledge, that was the first report of a non-invasive in vivo optical technique that can image melanoma microvessel network (83) and might represent an improvement in tumor staging and patient prognosis. Moreover, microvasculature imaging can also be used to monitor tumor response to different treatments.…”

“…The α/β ratio represents the average signal brightness in each ROI. (83) Comparing an area in the B-scan before and after OCA application for both, superficial normal skin and melanoma; one can see a decrease in the α/β ratio (Figure 3.8-A). In the beginning, the signal acquired comes mainly from the skin surface, then the OCA is applied, and the signal decreased, that is, the skin becomes transparent.…”

“…The software SPCImage (Becker and Hickl, Berlin, Germany) was used to process the raw data of the time-resolution photon counting as described by Pires et al (2016). (83) In summary, from the first derivative of the increasing part of the fluorescence lifetime spectrum, the software estimates the IRF followed convolution and exponential decay fitting. So, the decay curve of the model function was fitted by a bi-exponential function: 1 and 2 , respectively.…”

“…The OCT B-scans were processed as described by Pires et al (83) Briefly, the noise and artifact due to respiration movements were removed; a surface mask was used to correct the depth encoding and preserve the vessels structures; application of the Otsu's threshold method to retain the deep-vessel information and skin surface mask to flatten the surface. The obtained images were then compared before and after OCA topical application, and the effect of the OCA was quantified.…”