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.
Crisaborole 2% ointment is a non-steroidal treatment for mild-moderate atopic dermatitis (AD) and may have a better safety profile than topical corticosteroids (TCS), which produce pronounced epidermal atrophy. In this study we compared crisaborole to betamethasone valerate (BMV) in terms of changes to dermal collagen, using PS-OCT to quantify dermal birefringence. 37 subjects were enrolled in this study, which involved daily application of BMV & crisaborole. Results showed BMV produced a significant increase in dermal birefringence, whereas crisaborole showed no significant change. PS-OCT may thus have an important role in the safety assessment of non-steroidal alternatives to TCS.
Atopic dermatitis is a chronic, relapsing inflammatory skin disease, which has one of the highest prevalence rates in the world. It is widely believed to be driven by deficiencies in the skin barrier layer, which is provided by the stratum corneum. The stratum corneum thickness determines the absorption rate of topical treatments and may correlate with its barrier function of preventing allergen penetration. Here we demonstrate a free-space, portable Fourier domain visible-light optical coherence tomography (OCT) system to study the stratum corneum thickness (5-15 μm typically) in non-palmar human skin. We use a supercontinuum laser source, optimized for emission in the 500-700 nm range and achieve axial resolution of ~ 1 μm in tissue (for the refractive index n = 1.55 of the stratum corneum). Our system has ~ -85 dB sensitivity at an A-scan rate of 125 kHz and about 1 mW of optical power onto the skin. High-quality B-scans from various human skin sites are obtained, with a clearly resolved stratum corneum layer presenting as a hypoechogenic dark layer, similar to that found in palmar skin with traditional OCT systems.
Undesirable cross-coupling between polarisation-maintaining (PM) fibers can result in detrimental ghost artefacts within polarisation sensitive optical coherence tomography (PS-OCT) images. Such artefacts combine with coherence noise stripes (originating from Fresnel reflections of optical components), complex-conjugate derived mirror-images and further irregular autocorrelation terms originating from the sample. Together, these artefacts can severely degrade the detected images, making quantitative measurements of the tissue birefringence challenging to perform. In this work, we utilize the recently presented wavelet-FFT filter1 to efficiently suppress these imaging artefacts entirely through post-processing. While the original algorithm was designed to suppress one-dimensional stripe artefacts, we extend this methodology to also facilitate removal of artefacts following a duplicate or inverse (mirror) profile to that of the skin surface. This process does not require any hardware modification of the system and can be applied retroactively to previously acquired OCT images. The performance of this methodology is evaluated by processing artefact-corrupted PS-OCT images of skin consisting of simultaneously detected horizontal and vertical polarized light. The resulting images are used to calculate a phase retardance map within the skin, the profile of which is indicative of localized birefringence. Artefacts in the resulting processed PSOCT images were notably attenuated compared to the unprocessed raw-data, with minimal degradation to the underlying phase retardation information. This should improve the reliability of curve-fitting for measurements of depth-resolved birefringence.
Background and Aim: With inflammatory skin conditions such as atopic dermatitis (AD), epidermal thickness is
mediated by both pathological hyperplasia and atrophy such as that resulting from corticosteroid treatment. Such changes
are likely to influence the depth and shape of the underlying microcirculation. Optical coherence tomography (OCT)
provides a non-invasive view into the tissue, however structural measures of epidermal thickness are made challenging
due to the lack of a delineated dermal-epidermal junction in AD patients. Instead, angiographic extensions to OCT may
allow for direct measurement of vascular depth, potentially presenting a more robust method of estimating the degree of
epidermal thickening.
Methods and results: To investigate microcirculatory changes within AD patients, volumes of angiographic OCT data
were collected from 5 healthy volunteers and compared to that of 5 AD patients. Test sites included the cubital and
popliteal fossa, which are commonly affected by AD. Measurements of the capillary loop and superficial arteriolar
plexus (SAP) depth were acquired and used to estimate the lower and upper bounds of the undulating basement
membrane of the dermal-epidermal junction. Furthermore, quantitative parameters such as vessel density and diameter
were derived from each dataset and compared between groups. Capillary loop depth increased slightly for AD patients at
the poplitial fossa and SAP was found to be measurably deeper in AD patients at both sites, likely due to localized
epidermal hyperplasia.
Joseph Boadi, Robert Byers, Jon Fernandes, Shweta Mittar, Vanessa Hearnden, Zenghai Lu, Sheila MacNeil, Martin Thornhill, Craig Murdoch, Keith Hunter, Alasdair McKechnie, Stephen Matcher
OCT has demonstrated great potential to non-invasively detect oral epithelial cancers, potentially guiding biopsy and surgical resection. On non-ophthalmic tissues the preferred illumination wavelength is 1300 nm. Previous studies on skin have shown that useful image data can also be obtained at shorter wavelengths, with systems at 1060 nm and 820 nm offering reduced depth penetration but higher contrast. Here we apply a similar comparison to tissue engineered models of oral cancer and also to human biopsy samples, generally finding a similar trend. 1300 nm multi-beam OCT (Michelson Diagnostics EX1301) visualises stromal structures and surface keratin more clearly, providing useful image contrast down to around 1 mm. This system was compared with an ultra-high resolution home-built system operating at 890 nm (2.5 micron resolution vs 7.5 micron axial resolution for the EX1301). The UHR system reveals epithelial features more clearly, especially in the DOK pre-invasive cell line model and the biopsy samples. The relative effects of center wavelength vs axial resolution in generating the differential, wavelength-dependent contrast are assessed and the OCT biopsy images are compared with contemporary histology.
Bio-mechanical properties of the human skin deformed by external forces at difference skin/material interfaces attract much attention in medical research. For instance, such properties are important design factors when one designs a healthcare device, i.e., the device might be applied directly at skin/device interfaces. In this paper, we investigated the bio-mechanical properties, i.e., surface strain, morphological changes of the skin layers, etc., of the human finger-pad and forearm skin as a function of applied pressure by utilizing two non-invasive techniques, i.e., optical coherence tomography (OCT) and digital image correlation (DIC). Skin deformation results of the human finger-pad and forearm skin were obtained while pressed against a transparent optical glass plate under the action of 0.5-24 N force and stretching naturally from 90° flexion to 180° full extension respectively. The obtained OCT images showed the deformation results beneath the skin surface, however, DIC images gave overall information of strain at the surface.
Background and Aim: Recently developed decorrelative techniques such as speckle-variance optical coherence tomography (svOCT) have demonstrated non-invasive depth-resolved imaging of the microcirculation in-vivo. However, bulk tissue motion (BTM) originating from the subject's breathing or heartbeat remains problematic at low imaging speeds, often resulting in full frame decorrelation and a loss of vascular contrast. The aim of this study was to build upon existing svOCT techniques through utilisation of a commercially available, probe-based VivoSight OCT system running at 20 kHz Axial-scan rate. Methods and results: Custom four-dimensional scanning strategies were developed and utilised in order to maximise the interframe correlation during image acquisition. Volumes of structural OCT data were collected from various anatomical regions and processed using the aforementioned svOCT algorithm to reveal angiographic information. Following data collection, three dimensional image registration and novel filtering algorithms were applied to each volume in order to ensure that BTM artefacts were sufficiently suppressed. This enabled accurate visualisation of the microcirculation within the papillary dermis, to a depth of approximately 2mm. Applications of this technique, including quantitative capillary loop density measurement and visualisation of wound healing are demonstrated and enhanced through widefield mosaicing of the svOCT data. Conclusions: Non-invasive microcirculation imaging using an FDA 510(k) approved OCT scanner such as the VivoSight allows direct clinical utilisation of these techniques, in particular for the pathological analysis of skin diseases. This research was supported by BBSRC Doctoral Training Grant: BB/F016840/1. The authors also gratefully acknowledge the use of equipment funded by MRC grant: MR/L012669/1.
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