The value of ultrahigh resolution OCT in dermatology - delineating the dermo-epidermal junction, capillaries in the dermal papillae and vellus hairs

Abstract

Optical coherence tomography (OCT) imaging of the skin is gaining recognition and is increasingly applied to dermatological research. A key dermatological parameter inferred from an OCT image is the epidermal (Ep) thickness as a thickened Ep can be an indicator of a skin disease. Agreement in the literature on the signal characters of Ep and the subjacent skin layer, the dermis (D), is evident. Ambiguities of the OCT signal interpretation in the literature is however seen for the transition region between the Ep and D, which from histology is known as the dermo-epidermal junction (DEJ); a distinct junction comprised of the lower surface of a single cell layer in epidermis (the stratum basale) connected to an even thinner membrane (the basement membrane). The basement membrane is attached to the underlying dermis. In this work we investigate the impact of an improved axial and lateral resolution on the applicability of OCT for imaging of the skin. To this goal, OCT images are compared produced by a commercial OCT system (Vivosight from Michaelson Diagnostics) and by an in-house built ultrahigh resolution (UHR-) OCT system for dermatology. In 11 healthy volunteers, we investigate the DEJ signal characteristics. We perform a detailed analysis of the dark (low) signal band clearly seen for UHR-OCT in the DEJ region where we, by using a transition function, find the signal transition of axial sub-resolution character, which can be directly attributed to the exact location of DEJ, both in normal (thin/hairy) and glabrous (thick) skin. To our knowledge no detailed delineating of the DEJ in the UHR-OCT image has previously been reported, despite many publications within this field. For selected healthy volunteers, we investigate the dermal papillae and the vellus hairs and identify distinct features that only UHR-OCT can resolve. Differences are seen in tracing hairs of diameter below 20 μm, and in imaging the dermal papillae where, when utilising the UHR-OCT, capillary structures are identified in the hand palm, not previously reported in OCT studies and specifically for glabrous skin not reported in any other in vivo optical imaging studies.

Keywords: (110.4500) Optical coherence tomography; (170.0110) Imaging systems; (170.1870) Dermatology; (170.4500) Optical coherence tomography.

Conflict of interest statement

The authors declare that there are no conflicts of interest related to this article.

Figures

Fig. 1

Photographs of the C-OCT (a) and the UHR-OCT system (b) applied for the comparative study. (c) depicts the home-built handheld probe of the UHR-OCT system.

Fig. 2

(a): OCT images from HP 5 of the cheek generated with the C-OCT and the UHR-OCT system with the green delineations marking the surface tracing performed and representing the axial positions zS. (b) Image signal average along ’x’ relative to the surface trace. The horisontal dashed lines mark the signal readings of Ep and D utilised for computing the Ed-D contrast. (c) presents the Ep-D contrasts calculated for central B-scans each associated with a HP volume scan. HP 1 is excluded due to crucial artefacts in the scans.

Fig. 3

UHR-OCT system: DEJ evaluation for central B-scan of the cheek of HP 2 (top image), scale bar representing 100 μm. A ROI is selected (dashed rectangle) of which a zoom-in is presented (bottom image). Within the zoom-in three subsets (A1, A2 and A3) are emphasised (green vertical lines) and a guide to the eye of the DB propagation through the skin (purple dashed) is given. The subsets, comprising each ten A-scans and representing regions of constant axial DEJ position, are averaged laterally (horizontally in image) to accentuate the DEJ from the speckle noise providing three graphs with means and stds (top graphs). A double sigmoid fitting (bottom graphs) is performed for each average to extract DEJ information.

Fig. 4

C-OCT system: DEJ evaluation for central B-scan of the cheek of HP 2 (top image), scale bar representing 100 μm. A ROI is selected (dashed rectangle) of which a zoom-in is presented (bottom image). Within the zoom-in three subsets (K1, K2 and K3) are emphasised (green vertical lines) and a guide to the eye of the DB propagation through the skin (purple dashed) is given. The subsets, comprising each ten A-scans and representing regions of constant axial DEJ position, are averaged laterally (horizontally in image) to accentuate the DEJ from the speckle noise providing three graphs with means and stds (top graphs). A double sigmoid fitting (bottom graphs) is performed for each average to extract DEJ information.

Fig. 5

The cheek: Ep thickness values and DEJ edge sharpness values found from the double sigmoid fitting procedure for both C-OCT and UHR-OCT system central B-scans for the cheek. A, B and C (K, L and M) denote the three subsets of each of the three high-contrast B-scans denoted 1, 2 and 3 (HP2, HP4 and HP9).

Fig. 6

(a): OCT images from HP 7 of the hand palm generated with the C-OCT and the UHR-OCT system with the green delineations marking the surface tracing performed. (b) Image signal average along ’x’ relative to the surface trace. The horisontal dashed lines mark the signal readings of Ep, DEJ and D utilised for computing the Ed-D contrast. (c) presents the Ep-D contrasts calculated for central B-scans each associated with a HP volume scan. HP 2, HP 6 and HP 9 are excluded due to significant deviations in the DEJ relative position in the scans caused by special skin features.

Fig. 7

UHR-OCT system: DEJ evaluation for central B-scan of the hand palm of HP 3 (top image), scale bar representing 100 μm. A ROI is selected (dashed rectangle) of which a zoom-in is presented (bottom image). Within the zoom-in three subsets (A1, A2 and A3) are emphasised (green vertical lines) and a guide to the eye of the DB propagation through the skin (purple dashed) is given. The subsets, comprising each ten A-scans and representing regions of constant axial DEJ position, are averaged laterally (horizontally in image) to accentuate the DEJ from the speckle noise providing three graphs with means and stds (top graphs). A double sigmoid fitting (bottom graphs) is performed for each average to extract DEJ information.

Fig. 8

C-OCT system: DEJ evaluation for central B-scan of the hand palm of HP 3 (top image), scale bar representing 100 μm. A ROI is selected (dashed rectangle) of which a zoom-in is presented (bottom image). Within the zoom-in three subsets (K1, K2 and K3) are emphasised (green vertical lines) and a guide to the eye of the DB propagation through the skin (purple dashed) is given. The subsets, comprising each ten A-scans and representing regions of constant axial DEJ position, are averaged laterally (horizontally in image) to accentuate the DEJ from the speckle noise providing three graphs with means and stds (top graphs). A double sigmoid fitting (bottom graphs) is performed for each average to extract DEJ information.

Fig. 9

The palm: Ep thickness values and DEJ edge sharpness values found from the double sigmoid fitting procedure for both C-OCT and UHR-OCT system central B-scans for the palm. A, B and C (K, L and M) denote the three subsets of each of the three high-contrast B-scans denoted 1, 2 and 3 (HP3, HP5 and HP7).

Fig. 10

B-scan zoom-in highlighting skin structures in the palm of the high contrast HPs for C-OCT and UHR-OCT. Stratum corneum (Sc) and stratum spinosum (Ss) and D is marked for HP3. Dermal papillaries and the exact DEJ is marked for HP5. The characteristic two dark bands (DB1 and DB2) seen for OCT signals of glabrous skin are surrounded by oval contours. The scale bars represent 100 μm.

Fig. 11

Zoom-ins on individual dermal papillae of the palm of HP5. (a)-(d) depicts capillaries of the dermal papillae seen in the UHR-OCT images generated from 3–5 averaged B-scans each. Scale bars are 20 μm.

Fig. 12

Imaging of smaller and larger hairs on cheek of HP 4 comparing C-OCT and UHR-OCT systems. In images a–f and g–l hair follicles are located, each with scale bars representing 100 μm. a and g show larger hairs. fz and lz are zoom-ins of f and l, respectively, and pairs of vertical dashed green lines mark hair-to-surroundings bounderies, each pair enclosing three rows of pixels. Scale bars in fz and lz represent 20 μm.

Fig. 13

Histology images of human skin representing the gold standard of histology. (a) is a histology projection of normal skin of the cheek and (b) presents a glabrous skin histology image of the palm with associated adnexal structures including dermal papillae capillaries. Scale bars represent 100 μm. Images by courtesy of R. H. Nielsen, Rigshospitalet, Denmark.

Fig. 14

Sketch of the double sigmoid model curve (MC) with definitions of the dark band (DB) and the edge sharpness (ES). A, B1, B2, C1, C2, and D refer to the parameters in eq. (1)

Fig. 15

Image comparison between commonly logarithmically scaled images and a shadow compensated image. (a)–(c) display the same image using three different 8-bit thresholds on logarithmic scale. (d) shows the same image with shadow compensation and linear scaling.

Fig. 16

Profiles of laterally averaged central B-scans of the cheek for all HPs but HP1 containing severe artefacts. The dashed and solid lines introduced for HP2 mark the respective maximum (D) and minimum (Ep) signal readings applied in determining the DEJ region Ep-D contrast presented in Fig 2(c). All depth-axis are optical distances, i.e. scaled as in free space.

Fig. 17

Profiles of laterally averaged central B-scans of the palm for all HPs but HP2, HP6 and HP9 containing severe artefacts. The dashed and dotted lines introduced for HP1 mark the respective Ep and D maxima signal readings where solid lines mark minima (DB) readings. The data is applied in determining the DEJ region Ep-D contrast presented in Fig 6(c). All depth-axis are optical distances, i.e. scaled as in free space.