Quantitative evaluation of skin shrinkage associated with non-invasive skin tightening: a simple method for reproducible linear measurement using microtattoos. 
Non-invasive skin-tightening devices can induce thermal denaturation and skin shrinkage via externally applied radiofrequency emissions or high-frequency ultrasound.  Therefore, the purpose of this study is to develop and test a method for measurement of skin reduction associated with application of such energy devices.  Twenty-five healthy participants with mild to moderate skin laxity of the arms were enrolled.  Pinpoint microtattoos were placed at each of the treatment sites to delineate two 6 × 12 cm rectangles per subject.  A non-stretchable filament, tape and marking pen apparatus was used to measure the size of each rectangle before treatment and at follow-up visit by two blinded investigators.  After randomization, one side received a single pass with a radiofrequency device (6.78 MHz), while the contralateral side received multiple passes.  Participants underwent two treatment sessions to each side 2 weeks apart, and returned for follow-up 4 weeks after the second treatment.  Length and area measurement were analyzed to assess precision and accuracy of measurements and to compare efficacy of treatment between pre- and post-treatment.  Concordance correlation coefficients (CCC) demonstrated substantial inter-investigator reliability and precision in length measurements (CCC, 0.94 to 0.98 in pre-treatment; 0.95 to 0.98 in post-treatment).  Measurements at the 6-week post-treatment follow-up demonstrated a statistically significant skin reduction in all six of the measured parameters.  A simple skin measurement method requiring minimal instrumentation can quantitatively evaluate skin shrinkage associated with non-invasive skin-tightening devices.