UV Irradiation of Nevi: Impact on Performance of Electrical Impedance Spectroscopy and a Convolution Neural Network

Abstract

Introduction: UV irradiation of nevi induces transient melanocytic activation with dermoscopic and histological changes.

Objectives: We investigated whether UV irradiation of nevi may influence electrical impedance spectroscopy (EIS) or convolution neural networks (CNN).

Methods: Prospective, controlled trial in 50 patients undergoing phototherapy (selective UV phototherapy (SUP), UVA1, SUP/UVA1, or PUVA). EIS (Nevisense, SciBase AB) and CNN scores (Moleanalyzer-Pro, FotoFinder Systems) of nevi were assessed before (V1) and after UV irradiation (V2). One nevus (nevus_irr) was exposed to UV light, another UV-shielded (nevus_non-_irr).

Results: There were no significant differences in EIS scores of nevus_irr before (2.99 [2.51-3.47]) and after irradiation (3.32 [2.86-3.78]; P = 0.163), which was on average 13.28 (range 4-47) days later. Similarly, UV-shielded nevus_non-_irr did not show significant changes of EIS scores (V1: 2.65 [2.19-3.11]), V2: 2.92 [2.50-3.34]; P = 0.094). Subgroup analysis by irradiation revealed a significant increase of EIS scores of nevus_irr (V1: 2.69 [2.21-3.16], V2: 3.23 [2.72-3.73]; P = 0.044) and nevus_non-_irr (V1: 2.57 [2.07-3.07], V2: 3.03 [2.48-3.57]; P = 0.033) for patients receiving SUP. In contrast, CNN scores of nevus_irr (P = 0.995) and nevus_non-_irr (P = 0.352) showed no significant differences before and after phototherapy.

Conclusions: For the tested EIS system increased EIS scores were found in nevi exposed to SUP. In contrast, CNN results were more robust against UV exposure.

Keywords: UV irradiation; convolution neural network; dermoscopy; electrical impedance spectroscopy.

Figure 1

Nevus1 and nevus2 of a participating patient at all 3 study visits (V1–3) are depicted. From V1 to V2 nevus_irr was irradiated with SUP during 10 appointments (cumulative dosage UVA 14.54 J/cm², UVB 0.29 J/cm²), whereas nevus_non-_irr was UV-shielded. Corresponding electrical impedance spectroscopy (EIS) scores (0–10, top row) and convolution neural networks malignancy scores (0-1, bottom row) are depicted, scores marked in red illustrate a change in the diagnostic class, ie scores increased above the threshold for a malignant classification.

Figure 2

Boxplots show electrical impedance spectroscopy (EIS) scores of irradiated nevus_irr and UV-shielded nevus_non-_irr at all 3 study visits (V1-before UV irradiation; V2-after UV irradiation; V3-not earlier than 4 weeks following the last irradiation). The upper and lower bounds of boxes represent the 25^th and 75^th percentiles while the median is given by the line intersecting both boxes. Whiskers present the full range of malignancy scores. The a priori cut-off for a malignant classification is indicated by dotted lines (EIS score ≥ 4).

Figure 3

Figure shows dermoscopic images of two nevi_irr from V1 and V2 with corresponding electrical impedance spectroscopy (EIS) scores. For both lesions and timepoints measurements were repeated and mean values used to define a negative/benign or positive/malignant result. For both lesions mean EIS scores increased from V1 to V2 and lesions were assessed negative/benign at V1 versus positive/malignant at V2.

Figure 4

Boxplots show convolution neural networks (CNN) scores of irradiated nevus_irr and UV-shielded nevus_non-_irr at all 3 study visits (V1-before UV irradiation; V2-after UV irradiation; V3-not earlier than 4 weeks following the last irradiation). The upper and lower bounds of boxes represent the 25^th and 75^th percentiles while the median is given by the line intersecting both boxes. Whiskers present the full range of malignancy scores. The a priori cut-off for a malignant classification is indicated by dotted lines (CNN score > 0.5).

Figure 5

Boxplots show electrical impedance spectroscopy (EIS) scores of nevis_irr and nevis_non-_irr at all 3 study visits (V1–3) for the subgroup of patients receiving SUP. The upper and lower bounds of boxes represent the 25^th and 75^th percentiles while the median is given by the line intersecting both boxes. The a priori cut-off for a diagnosis of malignancy is indicated by a dotted line (EIS score ≥ 4).