CHARACTERIZATION OF THE SKIN INVIVO BY HIGH-RESOLUTION MAGNETIC-RESONANCE-IMAGING - WATER BEHAVIOR AND AGE-RELATED EFFECTS

The age-related modifications of magnetic resonance imaging parameters in the skin have been studied in vivo. Modification of these paramete rs should provide important information about alterations in water str ucture and content in aged skin. Relaxation times, T1 and T2, and rela tive proton density, which corresponds to the mobile water proton frac tion of tissues, have been measured on people under age 40 and over 70 on a sun-protected area. Results have confirmed in vivo skin layer di fferentiation through relaxation times performed in a previous study. Moreover, relative proton density quantification has shown that epider mal mobile water is at least twice as abundant as dermal mobile water. No significant age-related T1 and T2 modification could be establishe d, basically because of a large dispersion of values. The main result concerns the upper part of dermis (about 200 microns in thickness) whi ch contains significantly more mobile water protons in chronologic age d skin than in young adult skin. This increase has been related both t o an increase of total water content in dermis with age and to an appa rent decrease of collagen and proteoglycan content. Associated with al terations of their structure, this decrease reduces macromolecular-wat er interaction sites. This finding has to be compared with ultrasound evaluation of aged skin, which is characterized by modifications of th e echogenicity, related to collagen bundles size and density, in the o uter part of dermis, too. Both of the imaging techniques tend to consi der the outer part of dermis as one of the privileged sites of skin ag ing.