Photothermal tomography (PTT) is applied to characterize diameter and depth of subcutaneous chromophores such as blood vessels that comprise port wine stain (PWS) birthmarks. PTT uses a fast infrared detector array to measure temperature rises in a PWS induced by pulsed laser radiation. A PTT record of PWS in response to pulsed laser exposure is composed of a sequence of infrared emission frames, each consisting of elevated temperature regions indicative of subcutaneous blood vessel heating. An analytic expression for recorded infrared emission frames is derived as a convolution integral of a PTT point spread function and the 3-D temperature distribution in the PWS immediately following laser exposure. Diameters of blood vessels comprising the PWS are best resolved in early infrared emission frames when radial heat diffusion is relatively small.
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