Scanning darkfield high-resolution microendoscope for label-free microvascular imaging

Characterization of microvascular changes during neoplastic progression has the potential to assist in discriminating precancer and early cancer from benign lesions. Here, we introduce a novel high-resolution microendoscope that leverages scanning darkfield reflectance imaging to characterize angiogenesis without exogenous contrast agents. Scanning darkfield imaging is achieved by coupling programmable illumination with a complementary metal-oxide semiconductor (CMOS) camera rolling shutter, eliminating the need for complex optomechanical components and making the system portable, low-cost (<$5,500) and simple to use. Imaging depth is extended by placing a gradient-index (GRIN) lens at the distal end of the imaging fiber to resolve subepithelial microvasculature. We validated the capability of the scanning darkfield microendoscope to visualize microvasculature at different anatomic sites in vivo by imaging the oral cavity of healthy volunteers. Images of cervical specimens resected for suspected neoplasia reveal distinct microvascular patterns in columnar and squamous epithelium with different grades of precancer, indicating the potential of scanning darkfield microendoscopy to aid in efforts to prevent cervical cancer through early diagnosis.

Rapid skin optical clearing enhancement with salicylic acid for imaging blood vessels in vivo

BACKGROUND

Light penetration in deeper tissue is impeded by the skin scattering properties, which significantly limits the clinical applications of light in medical diagnosis and therapy. To overcome this problem, skin optical clearing methods using different optical clearing agents (OCAs) have been extensively developed to clear the dermis tissue. It is critically important to remove the outmost stratum corneum (SC) before the OCAs were applied for optical clearing, since the SC works as a natural barrier to the OCAs. For this, a controllable approach for the SC disruption through physical or chemical methods is highly required for enhanced skin optical clearing.

METHODS

Salicylic acid (SA) was combined with OCAs as a rapid skin optical clearing method to create a transparent window within 5 min. The clearing efficacy of this method was demonstrated by using dorsal skin model of mice. In addition, the intensity variations of vessel gray images and diffuse reflectance (DR) spectra were used to quantify the optical clearing efficacy, which were acquired by a low-cost self-built white light imaging system and optical fiber spectrometer, respectively.

RESULTS

Within a specific action time of the OCAs to the skin tissue, the enhanced images of the deeper blood vessels were obtained through the removal of the SC. It takes 5 min for the skin to turn transparent and 15 min to visualize the microvascular morphology for naked eyes. Furthermore, the intensity of blood vessel gray images was identified to be an evaluation parameter for quantifying the optical clearing efficacy.

CONCLUSIONS

An efficient and easy-to-handle method for enhanced skin optical clearing was established by combining SA with OCAs, which could boost the clinical applications of light in medical diagnosis and therapy.

FSOCA-induced switchable footpad skin optical clearing window for blood flow and cell imaging in vivo

The mouse footpad for its feature of hairlessness provides an available window for imaging vascular and cellular structure and function in vivo. Unfortunately, the strong scattering of its skin limits the penetration of light and reduces the imaging contrast and depth. Herein, an innovative footpad skin optical clearing agent (FSOCA) was developed to make the footpad skin transparent quickly by topical application. The results demonstrate that FSOCA treatment not only allowed the cutaneous blood vessels and blood flow distribution to be monitored by laser speckle contrast imaging technique with higher contrast, but also permitted the fluorescent cells to be imaged by laser scanning confocal microscopy with higher fluorescence signal intensity and larger imaging depth. In addition, the physiological saline-treatment could make the footpad skin recover to the initial turbid status, and reclearing would not induce any adverse effects on the distributions and morphologies of blood vessels and cells, which demonstrated a safe and switchable window for biomedical imaging. This switchable footpad skin optical clearing window will be significant for studying blood flow dynamics and cellular immune function in vivo in some vascular and immunological diseases. Picture: Repeated cell imaging in vivo before (a) and after (b) FSOCA treatment. (c) Merged images of 4 h (cyan border) or 72 h (magenta border) over 0 h. (d) Zoom of ROI in 4 h (yellow rectangle) or 72 h (red rectangle).

Use of kurtosis for locating deep blood vessels in raw speckle imaging using a homogeneity representation

Visualization of deep blood vessels in speckle images is an important task as it is used to analyze the dynamics of the blood flow and the health status of biological tissue. Laser speckle imaging is a wide-field optical technique to measure relative blood flow speed based on the local speckle contrast analysis. However, it has been reported that this technique is limited to certain deep blood vessels (about ? = 300 ?? ? m ) because of the high scattering of the sample; beyond this depth, the quality of the vessel’s image decreases. The use of a representation based on homogeneity values, computed from the co-occurrence matrix, is proposed as it provides an improved vessel definition and its corresponding diameter. Moreover, a methodology is proposed for automatic blood vessel location based on the kurtosis analysis. Results were obtained from the different skin phantoms, showing that it is possible to identify the vessel region for different morphologies, even up to 900 ?? ? m in depth.

Fabrication of various optical tissue phantoms by the spin-coating method

Although numerous studies have been performed to fabricate various optical tissue phantom (OTP) models, the fabrication of OTPs that simulate skin layers is laborious and time-consuming owing to the intricate characteristics of skin tissue. This study presents various OTP models that optically and structurally simulate the epidermis–dermis skin layer. The spin-coating method was employed to reproduce a uniform thin layer that mimics the epidermis layer, and the fabrication parameters were optimized for epoxy and silicone reference materials. Various OTP models simulating blood vessels and hyperpigmentation lesions were fabricated using the two reference materials to determine their feasibility. The suitability of each of the two reference materials for OTP fabrication was qualitatively evaluated by comparing the quality of the OTP models.

Recent developments in vascular imaging techniques in tissue engineering and regenerative medicine

Adequate vascularisation is key in determining the clinical outcome of stem cells and engineered tissue in regenerative medicine. Numerous imaging modalities have been developed and used for the visualization of vascularisation in tissue engineering. In this review, we briefly discuss the very recent advances aiming at high performance imaging of vasculature. We classify the vascular imaging modalities into three major groups: nonoptical methods (X-ray, magnetic resonance, ultrasound, and positron emission imaging), optical methods (optical coherence, fluorescence, multiphoton, and laser speckle imaging), and hybrid methods (photoacoustic imaging). We then summarize the strengths and challenges of these methods for preclinical and clinical applications.