Psoriasis RSOM imaging.

In a recent clinical study, vascular patterns in the epidermis and dermis of psoriasis patients were assessed using an RSOM imaging system for explorative clinical use. In RSOM images several features were quantified and showed a good correlation with histology and the clinical reference score. These results suggest that analyzing changes in the microvasculature using RSOM could in the future improve the assessment of a variety of skin conditions.

Psoriasis is a chronic inflammatory skin disease affecting 2-4 percent of the world population. Psoriatic skin shows increased vascularization and an increase of tortuous capillaries in the upper dermis [1]. Clinical presentation of psoriasis is variable, and diagnosis relies on clinical assessment only. RSOM can visualize microvasculature with a resolution of 10-20 µm resolution, at several millimeters depth [2], without the need for contrast agents, providing depth information and also quantitative metrics that could potentially supplement clinical assessments related to diagnosis and therapy monitoring.

RSOM imaging of psoriatic and adjacent healthy skin

(a/b) RSOM cross-sectional images: High frequency content (small structures, green) are overlaid on low frequency content (large structures, red). The epidermal structure (EP) and the dermis (DR) are seen. In the psoriatic skin in (a), acanthosis, i.e. the thickening of the epidermis, elongated capillary loops (blue arrow) and the dilated and dense vascular structure of the dermis (DR) are seen. Scale bars, 200 μm.

In a recent study [3], an RSOM imaging system was used to compare affected skin of psoriasis patients with healthy skin. Visually, psoriatic skin shows epidermal thickening, larger vascular structures in deeper regions and elongated and dilated capillary loops climbing almost to the skin surface. Quantification of epidermal thickness and diameters of deep vascular structures in RSOM images correlated well with histology.

Several quantitative RSOM metrics showed statistically significant differences between healthy and affected skin areas, including blood volume per skin surface (vascularity), a fractal number assessing structure and epidermal thickness. An optoacoustic score (OPIND) based on vascularity and epidermal thickness was defined using a test data set and applied to a validation data set, showing a good correlation to the clinical gold standard, the PASI score.

Future studies will show if RSOM metrics that are quantitative and include information over several millimeters of depths are superior to clinical scoring in terms of staging, assessment of therapy response or can provide more insight into disease progression for research purposes.

(a) Measurements of the total blood volume (TBV), fractal number as a metric of branching and vascular complexity, and epidermal thickness for psoriatic and adjacent healthy skin. For each of the metrics, there were statistically significant differences between healthy and the psoriatic skin. Error bars, s.d. (b) OPIND (optoacoustic index) versus PASI (clinical index) for the validation dataset and the test dataset.

In conclusion, a recent study has shown that RSOM has the potential to be a valuable tool for quantification of microvasculature changes associated with psoriasis or other skin diseases, providing high-resolution, intrinsic, vascular contrast at several millimeters depth. In the future, RSOM might enable more objective, and potentially better or earlier detection of a broad range of skin conditions, thereby reducing the need for biopsies.

  • Aguirre J et al.,
    Precision assessment of label-free psoriasis biomarkers with ultra-broadband optoacoustic mesoscopy,
    Nat. Biomed. Eng. 1, 0068 (2017). DOI:10.1038/s41551-017-0068.
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