Psoriasis RSOM imaging.

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. Raster-scanning optoacoustic mesoscopy (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.

(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.

[1] Nestle F.O. et al., Psoriasis, N. Engl. J. Med. 2009 Jul 30; 361(5): 496–509.
[2] Omar M. et al., Pushing the optical imaging limits of cancer with multi-frequency-band raster-scan optoacoustic mesoscopy (RSOM), Neoplasia. 2015 Feb;17(2):208-14.
[3] Aguirre J et al., Precision assessment of label-free psoriasis biomarkers with ultra-broadband optoacoustic mesoscopy, Nat. Biomed. Eng. 1, 0068 (2017).

  • 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.
  • Application Note: Psoriasis RSOM
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