Influence of the anagen:telogen ratio on Q-switched Nd:YAG laser hair removal efficacy.

BACKGROUND AND OBJECTIVE: Laser hair removal is believed to affect only anagen hairs. However, proof of this belief in humans is lacking. The objective of this study was to determine the influence of the anagen: telogen ratio on the results of Q-switched Nd:YAG laser hair removal. STUDY DESIGN/MATERIALS AND METHODS: Fifteen subjects had four test sites delineated in one body area. The test sites were chosen by trimming the hair and evaluating the area in 2 weeks. At that time, the anagen hairs were at least twice as long as the nongrowing telogen hairs and, therefore, could be differentiated and counted. Two sites with a low anagen number and two with a high number were chosen for comparison. All sites were then treated with a Q-switched Nd:YAG laser. Follow-up examination was in 1 month. RESULTS: Test sites with a low anagen number demonstrated a low level of hair loss compared with those sites with a high anagen number. A significantly higher percentage of hair loss was noted when comparing the anagen-only with total hair loss. In addition, lasing plus shaving demonstrated more hair loss than lasing alone. These findings indicated that anagen hairs were clearly affected, but the immediate clinical effect on telogen hairs was minimal. CONCLUSION: Q-switched Nd:YAG laser treatment of anagen hairs results in a rapid switch to telogen and a subsequent clinically obvious shedding of the hair shaft. This process causes a greater percentage hair loss at sites with high anagen number. Telogen hairs demonstrate no such effect and remain in their pretreatment phase after lasing.

Feasibility of picosecond laser-Doppler flowmetry provides basis for time-resolved Doppler tomography of biological tissues.

A detectable signal is obtained from a laser Doppler flowmeter operating in the heterodyne mode with nano- and pico-second pulse laser sources. The ultrashort pulse probing may be useful for depth-dependent time-resolved laser Doppler velocity measurements of blood perfusion in biological tissues. © 1998 Society of Photo-Optical Instrumentation Engineers.

On refraction in Monte-Carlo simulations of light transport through biological tissues.

To obtain reliable results from Monte-Carlo simulations of light scattering experiments, a statistically accurate procedure for positioning the photons after refraction between two different scattering media is necessary. Two statistically equivalent algorithms for calculating the position of the photons immediately after crossing an interface are described and justified.

Probabilistic model of multiple light scattering based on rigorous computation of the first and the second moments of photon coordinates.

We consider a concise method based on recurrent relations that permit rigorous computing of the first and the second moments of the components of the vector locating a randomly walking photon in an infinite homogeneous light-scattering medium. On assumption that the components obey a three-dimensional Gaussian distribution a probability density for the photon locations at the Nth scattering event can readily be written down and the light-intensity distribution in the medium may be calculated. The results from theoretical analyses are compared with the solution of a light-diffusion equation and with results of Monte Carlo simulations and show a better fit with simulated data than the diffusion approximation.