Abstract
Specifying the distribution of laser energy within a tissue is the first step towards understanding and capitalizing on a variety of laser-tissue interactions. Whether photothermal, photochemical or photomechanical in nature, laser-tissue interactions begin with the absorption of photon energy. The spatial distribution of photon absorption specifies the required laser exposure to be delivered and the extent of subsequent therapeutic action. Using infra-red tomography (IRT), the broad, long-term objective of this research is the development of a tomographic reconstruction algorithm as a means to determine: (1) the depths and physical dimensions of discrete subsurface port-wine-stain (PWS) blood vessels in human skin; and (2) the initial space-dependent temperature increase in PWS blood vessels immediately following pulsed laser exposure. In this report, preliminary studies are described which demonstrate the potential application of IRT in the clinical management of PWS patients.
Highlights
The flashlamp-pumped pulsed dye laser has offered a superior approach in therapy due to its ability to destroy port-winestain (PWS) blood vessels selectively [1,2,3], onty a small proportion oF patients obtain 100% fading of their PWS, even after undergoing multiple laser treatments [4,5,6,7]
Infra-red tomography (IRT)uses a fast infrared focal plane array (IR-FPA) camera to detect temperature rises in a substrate induced by pulsed radiation
The IRT integral equation, Equation l(a), can be written as a multi-dimensional convolution integral that relates the measured time sequence of infra-red emission images, AM(x,y;t) (~ where x,y;t are the tissue surface coordinates and time, respectively, to the initial space-dependent temperature increase, AT~v(~,q,~;t=0) (~ of discrete subsurface PWS blood vessels at position (~,q,0, immediately following pulsed laser exposure: AM(x,y;t) = j'.[Zc(x-x',y-y')dx'dy'j'.fj'KT(X'
Summary
The flashlamp-pumped pulsed dye laser has offered a superior approach in therapy due to its ability to destroy port-winestain (PWS) blood vessels selectively [1,2,3], onty a small proportion oF patients obtain 100% fading of their PWS, even after undergoing multiple laser treatments [4,5,6,7]. That laser systems with userspecified pulse durations and light dosages are available commercially, how will the clinician select the optimal parameters for laser exposure?. The temperature rise, due to the selective optical absorption of pulsed ~aser light, creates an increase in infra-red (blackbody) emission which is measured by a. For the purposes of IRT, chromophores in human skin can be modelled as a three-dimensional distribution of subsur~hce absorbing structures. In this model, when a pulsed laser source is used to irradiate the skin, an immediate increase in infra-red emission ~ill occur due to heating caused by optical absorption in the chromophores. Infra-red emission in later images is distributed more uniformly in space due to thermal diffusion
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