Page 246 - Mike Murphy's Blog Posts
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E20 - Thermal Relaxation Time - what is wrong with it?
The theory which has underpinned many skin-laser treatments since 1981 is called 'Selective Photothermolysis'. It is based on matching the laser wavelength to the absorbing chromophore. It also matches the pulse duration of the laser to the thermal relaxation times of those targets.
However, there is a problem with this approach. The thermal relaxation time is a measure of the cooling rate of an object - small objects cool faster than large objects, and hence, have shorter relaxation times. The original theory attempted to minimise collateral damage to adjacent tissues by restricting the laser energy pulse duration to one thermal relaxation time.
The problem with this idea is that it does not consider the actual heating time of the target tissues. Given that the whole point is to destroy selected tissues using heat, delivered by laser or IPL light, then why do we restrict the heating time according to the cooling time of the target? This does not make sense!
Mike’s Blog Posts 246
