## 2 Materials and Methods
If the dermo-epidermal junction (DEJ) could not be detected by LC-OCT because of excessive acantosis or hyperkeratosis, the highest measurable value was used for statistical analysis (Figure 1a). Figure 1: Cont. The chosen 3D stacks were analyzed with artificial intelligence models developed by Damae Medical (Paris, France). One model was trained for skin layer segmentation, the other model for follicle detection. The segmentation of the skin layers and identification of stratum corneum, epidermis, and dermis were realized through the application of a 2D U-Net model to the LC-OCT stacks. The boundaries of the different skin layers were  
Figure 1: **(a)** V0 SP right elbow: vertical (top) and horizontal (bottom). Line-field confocal optical coherence tomography picture (horizontal image size: 1.2 mm \(\times\) 0.5 mm; vertical image size: 1.2 mm \(\times\) 0.4 mm) of SP before start of therapy (LPSI 7) with hyperkeratosis (yellow line), parkeratosis (red arrows), dilated vessels (yellow arrows) in elongated rete ridges, acanthosis (red line), and bright inflammatory cells in the epidermis (red arrowheads); accompanying dermatoscopic picture (bottom right corner, image size: 1.2 mm \(\times\) 0.5 mm) with scales and dotted vessels (blue arrows). Abbreviations: V0 = visit 0 before start of treatment, SP = study plaque, LPSI = local psoriasis severity index. **(b)** V1 SP: right elbow: vertical (top) and horizontal (bottom). Line-field confocal optical coherence tomography (horizontal image size: 1.2 mm \(\times\) 0.5 mm; vertical image size: 1.2 mm \(\times\) 0.4 mm) of SP after 4 weeks of therapy (LPSI 4), less hyperkeratosis (yellow line) and parkeratosis (red arrows), dilated vessels (yellow arrows) in elongated rete ridges, less acanthosis (red line), and bright inflammatory cells in the epidermis (red arrowheads); accompanying dermatoscopic picture (bottom right corner, image size: 1.2 mm \(\times\) 0.5 mm) with no more scales and only very few dotted vessels (blue arrows). Abbreviations: V1 = visit 1 after 4 weeks of treatment, SP = study plaque, LPSI = local psoriasis severity index. **(c)** V2 SP: right elbow: vertical (top) and horizontal (bottom). Line-field confocal optical coherence tomography (horizontal image size: 1.2 mm \(\times\) 0.5 mm; vertical image size: 1.2 mm \(\times\) 0.4 mm) of SP after 12 weeks of therapy: clinically, skin almost completely cleared (LPSI of 1, only minimal erythema left), no more hyperkeratosis (yellow line indicating stratum corneum) or parkeratosis, dilated vessels (yellow arrows) without elongated rete ridges, no more acanthosis (red line), and a few bright inflammatory cells in the epidermis (red arrowheads) and pigmented keratinocytes around the dermal papillae (blue arrowheads); accompanying dermatoscopic picture (bottom right corner, image size: 1.2 mm \(\times\) 0.5 mm) with no more scales and a few dotted vessels (blue arrows, purple pigment as skin marker particles in between). Abbreviations: V2 = visit 2 after 12 weeks of treatment, SP = study plaque, LPSI = local psoriasis severity index. defined using the interface between two segmented areas; for example, the detection of the DEJ was realized using the pixel boundary between the epidermis and dermis. The AI model was trained on a big and diverse dataset, including acquisitions of healthy skin from different body parts and different extent in the undulation of the DEJ, actinic keratoses, and inflammatory dermatoses like atopic dermatitis and psoriasis. To ensure the highest level of accuracy, all segmentations underwent a meticulous validation process. This involved a comprehensive manual review conducted by a skilled operator, who carefully examined and verified each segmentation output by the model. We used the same U-Net model as described in detail elsewhere [22; 28; 29; 30; 31; 32; 33; 34; 35; 36], especially that by [PERSON] et al.