ASSESSMENT OF DERMAL WATER BY HIGH-FREQUENCY ULTRASOUND - COMPARATIVE-STUDIES WITH NUCLEAR-MAGNETIC-RESONANCE

Although a principal constituent of human skin, cutaneous water is dif ficult to study, and little is known about water behaviour in physiolo gical and pathological conditions of the skin. It has been proposed re cently that changes in dermal echogenicity measured by high-frequency ultrasonography reflect changes in dermal water content. To validate s kin ultrasonography for assessment of dermal water changes we have stu died the relationship between dermal echogenicity and skin water conte nt determined by nuclear magnetic resonance technique. Twenty MHz ultr asound scanning of the dorsal and ventral forearm skin was performed i n 59 healthy volunteers (age 18-65) and dermal echogenicity was determ ined by counting low echogenic pixels (LEPs) in skin images. H-1 magne tic resonance spectra were obtained from the same regions and the rati o of areas under the water- and fat-specific peaks (W/F) were calculat ed to measure a relative water content. Acute dermal oedema (histamine weal) was studied in the same way in 40 individuals, Baseline dermal echogenicity correlated significantly with W/F, both in the ventral (r = 0.47) and dorsal (r = 0.57) forearm. Intradermal application of his tamine caused a development of intradermal oedema which could be visua lized by nuclear magnetic resonance imaging. In a corresponding ultras ound image oedema was seen as a low-echogenic area. The proportional i ncreases in LEPs and W/F after histamine application were correlated, but the elevation in LEPs was 25-48% (95% confidence intervals) higher than that for W/F. These results suggest that high-frequency ultrason ography is a sensitive method for assessment of changes in dermal hydr ation. This technique may find important applications in comparative a nd non-invasive evaluations of dermal water in physiological condition s and in skin pathologies associated with oedema formation.