Figure 3.

Scanned beam thermal therapy. (a) Temperature maximum occurring during the therapy scan in function of depth at the center of the therapy beam, and resulting fractional tissue damage for a fixed wavelength of 1875 nm at two power settings. The 0.95 fractional damage was chosen as criterion for treatment depth, and the width of the transition region between 0.05 and 0.95 to quantify the margin δ of thermal collateral damage. The high power setting is limited by a 100°C threshold, whereas a fractional damage of 0.99 was used to determine the lower bound power setting. (b) The same upper and lower bound criteria, but applied to illumination at two distinct wavelengths increases the available treatment range. (c) Treatment depth in function of both wavelength and power. Only regions between the two thresholds are viable power-wavelength combinations. The contour lines indicate the variation of the margins δ in function of both parameters. (d) Following the upper threshold with a 5°C security margin, indicated by the dashed line in (c) defines the ideal wavelength-power combination for a given treatment depth. To access more shallow depths, the extreme wavelength of 1900 nm is power controlled, before starting the wavelength tuning.