Vascular lesions are one of the most common indications for laser therapy. While first and still commonly used for the treatment of port-wine stains and hemangiomas, this chapter will focus on their use for telangiectasias, facial veins, poikiloderma of Civatte, and leg veins. The most frequently used light devices for vascular lesions are the 532-nm potassium titanyl phosphate (KTP) and, more recently, diode laser; the 595-nm pulsed dye laser (PDL); the 1,064-nm Nd:YAG lasers; and the intense pulsed light (IPL) devices. Table 42.1 outlines the various vascular-specific laser and light-based systems. These systems work through selective photothermolysis with oxyhemoglobin (oxy-hb) as the target chromophore in vascular lesions. The absorption peaks for oxy-hb are 418 nm, 542 nm, and 577 nm. By targeting oxy-hb, pulses of energy are transferred to the surrounding vessel wall to selectively heat and destroy the abnormal blood vessels. The success of vascular lasers depends on their wavelength, pulse duration, and spot size as they relate to vessel depth and diameter:

• The wavelength used needs to have sufficient penetration depth and selectivity for the target vasculature.

• The pulse duration should be less than thermal relaxation time (TRT) to affect the intended target, while sparing surrounding structures. The TRT is the cooling time of the target and is proportional to the square of the vessel diameter. For example, a vessel 0.03 mm in size has a TRT of 0.86 ms, as compared to a 0.1 mm vessel, which has a 9.6-ms TRT. Longer pulse durations allow for slower heating of the target, which prevents rapid temperature spikes, which cause vessel wall rupture and purpura. When pulse durations exceed the TRT of the target structure, more heat diffuses outside the vessels, leading to unwanted thermal damage to surrounding tissue.

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