Atopic dermatitis, characterized by itchiness and inflammation, often results in increased skin thickness. Traditional treatments with topical corticosteroids may compound this effect. Addressing the need for accurate epidermal measurement and the slow acquisition times of previous methods, we have developed a high-speed OCT system utilizing a 1.67 MHz Fourier-domain Mode-locked (FDML) and a MEMS scanner, providing a 3 kHz frame rate. The measured axial and lateral resolutions are 13-14 μm and 35 μm in air, respectively. We have tested our system on the dorsal skin of human hands in vivo, targeting a volume scan of 2.8 x 2.8 x 5 mm3. The acquisition from the digitizer to PC memory only takes 0.1 seconds. To assess the epidermal thickness, we have developed an automatic segmentation algorithm for the detection of the skin surface and epidermal-dermal junction. The results indicate that the epidermal thickness is mostly between 110 to 150 μm on healthy dorsal hand skin. Additionally, we have generated an epidermal thickness map overlaying the enface skin image, providing a comprehensive view of the skin's structural integrity.
Atopic dermatitis (AD) often induces vasodilation, potentially impacting the velocity of blood flow within capillaries and vessels. To quantify the velocity change, we have developed and tested a 1.67 MHz 1310 nm Fourier-domain mode-locked (FDML) OCT system for measuring the decorrelation coefficient in blood vessels. This system provides an inter-frame time of 0.33 milliseconds and an A-scan spacing of 10 microns. A flow phantom, comprising a glass capillary tube of 80 μm inner diameter infused with unhomogenized milk by a syringe pump, was designed to test our OCT system mimicking the blood vessel. We collected 280 sequential B-scans at the same Y position of the phantom for a number of the velocity values. Based on variable interscan time analysis (VISTA) processing, we observed a strong correlation between the calculated decorrelation coefficients and the predetermined flow velocities, spanning a range from 0.16 mm/s to 30 mm/s. These findings enable us to explore our clinical hypotheses with in vivo tests.
The leading global cause of death in children under the age of five is due to complications arising from Preterm Birth (PTB). Although it is not fully understood why PTB can happen spontaneously, it is known that the cervix’s collagen rich extracellular matrix remodels prior to both term and preterm labor. In vitro Polarization-Sensitive Optical Coherence Tomography (PS-OCT) has successfully imaged the distribution and 3D alignment of collagen in the cervix, as well as determined birefringence and measured cervical tissue depolarization in healthy tissue samples. The present investigation aims to expand on this research, by implementing in silico design, optimization, and simulation techniques for a PS-OCT probe to be used for human in vivo cervical scanning. The design considers patient comfort and clinical access as key parameters; ensuring the components are suitable for a colposcope-like probe and commercially available for quick and cost-effective manufacturing. To achieve these aims, the design benefits from using as few components as possible and limiting optical surface reflections. In this paper we demonstrate that with the use of a cemented Gradient Index (GRIN) relay system, a Field of View (FOV) of up to 6 mm can be achieved, with a back-coupling efficiency of over 73%, on-axis and at up to a 2° scanning angle. Although Huygens Point Spread Function (PSF) lateral resolution reached 81 μm, this paper demonstrates that manual adjustment and optimization of the components can increase this resolution to 12 μm, although at the expense of FOV width reduction. The simulated probe design was verified in preliminary experiments using an in-house built fiber-based OCT engine where high-quality OCT images with wide FOV were obtained from various samples, including healthy human skin.
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