Imaging human skin autograft integration with optical coherence tomography

Abstract

Background: Skin autografting is a common clinical procedure for reconstructive surgery. Despite its widespread use, very few studies have been conducted to non-invasively evaluate and monitor the vascular and structural features of skin grafts. This study, therefore, aims to demonstrate the potential of optical coherence tomography (OCT) alongside OCT-based angiography (OCTA) to non-invasively image and monitor human skin graft health and integration over time.

Methods: An in-house-built clinical prototype OCT system was used to acquire OCT/OCTA images from patients who underwent split-thickness skin graft surgery following severe burn damage to the skin. The OCT imaging was carried out at multiple locations over multiple time points with a field of view of ~9 mm × 9 mm and a penetration depth of ~1.5 mm. In addition to obtaining high-resolution qualitative images, we also quantitatively measured and compared specific structural and vascular parameters, such as identifiable layer thickness and corresponding vascular area density and diameter.

Results: Two patients (patient #1 and #2) were enrolled for this preliminary study. Vascular and structural features were successfully imaged and measured in the graft tissue and integration layer immediately beneath at different time points. Revascularization, healing, and integration were monitored with patient-specific details. Results of the quantitative image analysis from patient #1 indicated that integration layer thickness 16-day post-surgery was significantly less (~50%) than that of 7-day post-surgery. Additionally, with patient #2, significant growth (~20%) was seen with the vascular area density of both the graft and corresponding integration layer beneath between 6 and 14 days post-surgery.

Conclusions: Our preliminary studies show that OCT/OCTA has clinical potential to image and measure numerous features of human skin graft health and integration in the days and weeks following split-thickness surgery. For the first time, we demonstrate the applicability of non-invasive imaging technology for novel clinical uses that could eventually aid in the betterment of surgical practices and clinical outcomes.

Keywords: Optical coherence tomography angiography (OCTA); integration; split-thickness skin graft; structure; vasculature.

Figure 1

Images showing the prototype OCT system alongside a schematic of data processing. (A) The prototype OCT system capable of OCTA data acquisition; (B) original structural cross-section B-frame images; (C) attenuation correction cross-section B-frame images; (D) 3D structure image. Red lines highlight graft layer boundaries (graft layer further highlighted with a red arrow) and green lines highlight integration layer boundaries (integration layer further highlighted with a green arrow). Layer segmentation was carried out using these lines; (E) vascular cross-section B-frame images; (F) original en face projection of 3D blood vessels; (G) binarized vascular image used for the quantification of vascular area density; (H) skeletonized vascular image used for the quantification of vascular diameter. Scale bar represents 1 mm.

Figure 2

En face OCTA imaging of patient #1. (A,F) showing photographs of the grafted forearm 7 and 16 days post-surgery, respectively. Highlighted are approximate scan sites (yellow perforated boxes) labeled G1, G2, G3 and B1. G1–G3 refer to three graft sites, and B1 refers to a burn site adjacent to the graft. The graft boundary is also highlighted (white perforated line). (B,C) demonstrating the graft vasculature 7 days post-surgery from scan site G2. (D,E) showing the vasculature of the normal skin (contralesional forearm) on the same patient. (G,H) showing the graft vasculature 16 days post-surgery from scan site G2. (I,J) showing the vasculature of a burn site adjacent to the graft 23 days after the initially burn injury from scan site B1. (C,E,H,J) Magnified images of the regions highlighted in the dashed rectangles shown in (B,D,G,I). All en face images are maximum intensity projected representing the depth of 0–1 mm. Color bar represents the vessel depth. Scale bar represents 1 mm. Shown are the three segmented slabs representing the depths of (A,B,C,D,E): 265–530 µm (papillary dermis).

Figure 3

Representative cross-sectional B-frames of OCT structure (after attenuation correction processing). Shown are the B-frames acquired at the site indicated by the white dashed lines in Figure 2A,C,E,G. (A) Shows the graft 7 days post-surgery; (B) shows the normal skin (contralesional forearm) on the same patient; (C) shows the graft 16 days post-surgery; (D) shows a burn site adjacent to the graft 23 days after the initial burn injury. Yellow dashed lines highlight the epidermal-dermal junction. Red dashed lines highlight the boundary between graft layer and the integration layer. Green dashed lines highlight the boundary between the integration layer and the recipient tissue. Scale bar represents 1 mm. E, epidermis; D, dermis; G, graft layer; and I, integration layer. Color bar represents OCT intensity after attenuation correction.

Figure 4

En face projected blood vessel and layer thickness maps from patient #1 spanning two imaging sessions. (A,C,E,G) En face projected vasculature maps derived from the graft and integration layers, respectively. (B,D,F,H) Thickness maps derived from the graft and integration layers, respectively. All en face blood vessel images are maximum intensity projected. Color bar presents a depth range of 0–0.5 mm. Scale bar represents 1 mm.

Figure 5

En face OCTA images and structural (after attenuation correction processing) cross-sectional B-frames from patient #2. (A,E) showing photographs of the grafted forearm 6 days and 14 days post-surgery, respectively. Highlighted are three scan sites (red perforated boxes) labeled G1, G2, G3. G1–G3 refer to three graft sites. (B,C,D) showing the graft 6 days post-surgery from scan site G2. (F,G,H) showing the graft 14 days post-surgery from scan site G2. (B,C,F,G) En face projected blood vessel maps with color coded vessel depth. (C,G) Magnified images of the regions highlighted in the dashed rectangles in (B,F). (D,H) Representative cross-sectional B-frames of OCT structure corresponding to the white dashed line in (B,F). All en face images are maximum intensity projected representing the depth of 0–1 mm. Color bar on the left represents vessel depth. Color bar on the right represents OCT intensity after attenuation correction. Scale bar represents 1 mm. Yellow arrow: dark vessel-like structures. E, epidermis; D, dermis; G, graft layer; and I, integration layer.

Figure 6

En face projected blood vessel and layer thickness maps of patient #2 spanning two imaging sessions. (A,C,E,G) En face projected blood vessel maps derived from the graft and integration layers, respectively. (B,D,F,H) Thickness maps are derived from the graft and integration layers, respectively. All en face blood vessel images are maximum intensity projected. Color bar presents a depth range of 0–0.5 mm. Scale bar represents 1 mm.