Spatiotemporal closure of fractional laser-ablated channels imaged by optical coherence tomography and reflectance confocal microscopy.
OBJECTIVE
Optical coherence tomography (OCT) and reflectance confocal microscopy (RCM) offer high-resolution optical imaging of the skin, which may provide benefit in the context of laser-assisted drug delivery. We aimed to characterize postoperative healing of ablative fractional laser (AFXL)-induced channels and dynamics in their spatiotemporal closure using in vivo OCT and RCM techniques.


METHODS
The inner forearm of healthy subjects (n = 6) was exposed to 10,600 nm fractional CO2 laser using 5 and 25% densities, 120 μm beam diameter, 5, 15, and 25 mJ/microbeam. Treatment sites were scanned with OCT to evaluate closure of AFXL-channels and RCM to evaluate subsequent re-epithelialization.


RESULTS
OCT and RCM identified laser channels in epidermis and upper dermis as black, ablated tissue defects surrounded by characteristic hyper-and hyporeflective zones. OCT imaged individual laser channels of the entire laser grid, and RCM imaged epidermal cellular and structural changes around a single laser channel to the depth of the dermoepidermal junction (DEJ) and upper papillary dermis. OCT images visualized a heterogeneous material in the lower part of open laser channels, indicating tissue fluid. By OCT the median percentage of open channels was evaluated at several time points within the first 24 hours and laser channels were found to gradually close, depending on the used energy level. Thus, at 5 mJ/microbeam, 87% (range 73-100%) of channels were open one hour after laser exposure, which declined to 27% (range 20-100%) and 20% (range 7-93%) at 12 and 24 hours after laser exposure, respectively. At 25 mJ/microbeam, 100% (range 100-100%) of channels were open 1 hour after laser exposure while 53% (range 33-100%) and 40% (range 0-100%) remained open at 12 and 24 hours after exposure. Median depth and width of open channels decreased over time depending of applied energy. RCM verified initial re-epithelialization from day 2 for all energy levels used. Morphology of ablation defects by OCT and RCM corresponded to histological assessments.


CONCLUSIONS
OCT and RCM enabled imaging of AFXL-channels and their spatiotemporal closure. Laser channels remained open up to 24 hours post laser, which may be important for the time perspective to deliver topical substances through AFXL channels.
Department of Dermatology, Bispebjerg Hospital, University of Copenhagen, Copenhagen, Denmark.
Christina A
CA
Banzhaf
Department of Dermatology, Academic Medical Centre, University of Amsterdam, Amsterdam, the Netherlands.
Bas S
BS
Wind
Department of Dermatology, Bispebjerg Hospital, University of Copenhagen, Copenhagen, Denmark.
Mette
M
Mogensen
Department of Dermatology, Academic Medical Centre, University of Amsterdam, Amsterdam, the Netherlands.
Arne A
AA
Meesters
Department of Dermatology, Venereology and Allergology, University of Leipzig, Leipzig, Germany.
Uwe
U
Paasch
Department of Dermatology, Academic Medical Centre, University of Amsterdam, Amsterdam, the Netherlands.
Albert
A
Wolkerstorfer
Department of Dermatology, Bispebjerg Hospital, University of Copenhagen, Copenhagen, Denmark.
Merete
M
Haedersdal
D000328:Adult; D020405:Dermis / Q000000981:diagnostic imaging* / Q000502:physiology / Q000601:surgery*; D004817:Epidermis / Q000000981:diagnostic imaging* / Q000502:physiology / Q000601:surgery*; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D054020:Lasers, Gas; D008297:Male; D018613:Microscopy, Confocal / Q000379:methods; D008875:Middle Aged; D013997:Time Factors; D041623:Tomography, Optical Coherence; D014945:Wound Healing / Q000502:physiology*
ablation defect; ablative fractional laser; diagnostic imaging; micro ablation zone; optical coherence tomography; reflectance confocal microscopy; wound healing