Optimization of the measurement procedure during multiphoton tomography of human skin in vivo.

ABSTRACT

BACKGROUND: The in vivo multiphoton tomography has evolved into a useful tool for the non-invasive investigation of morphological and biophysical characteristics of human skin. Until now, changes of skin have been evaluated mainly by clinical and histological techniques. The current study addresses the effects of a changed acquisition time for single scans in a Z-stack on the directly related qualitative and quantitative interpretability of the data. METHODS: A test area of the skin was used for scanning 12 Z-stacks of 10 volunteers aged between 25 and 34 years. The stacks were taken up to a depth of 220 µm at increments of 10 µm at four different times, 1, 3, 7, 13 s, per scan. Subsequently, the second harmonic generation (SHG)-to-autofluorescence aging index of dermis (SAAID) was evaluated at three different measuring depths, i.e. at the maximum of SHG as well as at depths of 60 and 150 µm. RESULTS: The evaluation did not reveal any significant differences in the SAAID behavior between the Z-stacks of each test area scanned at different acquisition times. However, the acquisition time of 1 s/frame increases the measurement stability without influencing the SAAID behavior. The resolution of subcellular structures decreases significantly at scan times ≤3 s, whereas the acquisition time from 7 to 13 s warrants a high image quality. CONCLUSION: The study has shown that there are no significant differences between the scan speeds per scan in a Z-stack and the resulting SAAID. Acquisition times of 7 s are suitable for the morphological evaluation whereas a further extension to 13 s does not result in any benefits. A scan time per image of 1 s is sufficient for the quantitative evaluation of SAAID thus substantially reducing the possible influence of movement artifacts.