Quantitative evaluation of nonablative laser technology

Paul M Friedman, Greg R Skover, Greg Payonk, Roy G Geronemus
Seminars in Cutaneous Medicine and Surgery 2002, 21 (4): 266-73
A new method for treating facial rhytides and acne scars with nonablative laser and light source techniques has recently been introduced. Given the inherent limitations of photographic and clinical evaluation to assess subtle changes in rhytides and surface topography, new noninvasive, objective instruments were used to accurately assess the outcome of these procedures. This study measures and objectively quantifies facial skin by using 2 novel, noninvasive measuring systems after 3 to 5 treatment sessions with the 1,064 nm QS Nd:YAG laser in patients with photodamage and acne scarring. One system measures the skin surface topography and the other characterizes the biomechanical properties of the skin. Patients undergoing facial rejuvenation procedures were analyzed before and after therapy with a 32 x 32 mm in vivo three-dimensional microtopography imaging system (PRIMOS, GFM, Teltow, Germany). The imaging system projects light on to a specific surface of the skin with a Digital Micromirror Device (DMD; Texas Instruments, Irving, TX) and records the image with a CCD camera. Skin Surface microtopography is reconstructed using temporal phase shift algorithms to generate three-dimensional images. Measurements were taken at baseline, at various times during the treatment protocol, and then at 3 and 6 month follow-up visits. Silicone skin replicas (FLEXICO, Herts, England) were also made before and after the laser treatment protocol for comparison to in vivo acquisition. Skin stiffness and compliance were measured with the BTC-2000 (BTC 2000, S.R.L.I. Inc. Nashville, TN). This instrument measures the response of the skin during dynamic stress created by suction. An infrared targeting laser measures the vertical displacement of the skin during the cycle. Pressure and deformation are graphically displayed on the monitor and embedded biomechanical algorithms determine the aforementioned parameters based on the average of 3 repetitive cycles. Four sites on the face were analyzed and compared including the right and left cheek and the right and left forehead. Measurements were taken at baseline and then at 1-, 3- and 6-month follow-up visits. Skin roughness decreased 11% from baseline in the patient with photodamaged skin, while the patients with acne scarring showed a 33% improvement from baseline after 3 treatment sessions. Six-months after the fifth treatment session, a 26% improvement in skin smoothness was documented in the patients with photodamaged skin, while a 61% improvement was recorded in the subject with acne scarring. Biomechanical analysis of the skin showed a 23% decrease in skin stiffness and a 30% increase in skin compliance at the 6-month follow-up in the patients with photodamage. Alternatively, the patient with acne scarring showed a 50% increase in skin stiffness, and a 30% decrease in skin compliance at the 6-month follow-up. Three-dimensional in vivo optical skin imaging provided a rapid and quantitative assessment of surface topography and facial fine lines after multiple treatment sessions with a 1064-nm QS Nd:YAG laser, correlating with clinical and subjective responses. Biomechanical analysis provided technical understanding of structural changes in photodamaged skin and acne scarring following nonablative laser treatment. Future applications of these devices may include comparison of nonablative laser technology, optimization of treatment regimens, and objective evaluation of other aesthetic procedures performed by dermatologists.

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