Fundamentals Of Laser Treatment Of Leg Veins

Theory of Selective Thermolysis: Major Principles and Determinants

The advent of laser technology for treatment of leg veins began with the concept of selective photothermolysis developed in the late 1980s.5 The theory of selective photother-molysis states that selective damage to a tissue structure is achieved by means of a wavelength of light preferentially absorbed by a chromophore in light-absorbing molecules and laser exposure time less than or equal to the object's thermal relaxation time (i.e., the time required for the object to lose 50% of its thermal energy). The thermal relaxation times of leg veins vary depending upon vessel diameter (see Table 16.2).6

A physician employing laser therapy should routinely consider the utility of laser and intense pulsed light (IPL) technologies versus that of sclerotherapy for the treatment of lower extremity vessels.7 The fundamental requirements for a laser or IPL source in the treatment of leg veins are delineated in Box 16.2.

Laser technology and its role in leg vein reduction is rooted in the molecule hemoglobin and its absorption spectrum, which has broad peaks at 410, 540, and 577 nm and smaller peaks at 920 and 940 nm. The spectra of oxy- and deoxyhemoglobin differ, with bluer veins responding to wavelengths targeting the deoxyspectrum; whereas red var-icosities respond more effectively to wavelengths targeting the oxyhemoglobin spectrum (see Figure 16.1). Generally speaking, any vessel that is less than 3 mm in diameter may be treated by laser and IPL technologies. However, sclerotherapy is a more efficient modality for eradicating cannulable vessels, and when small, difficult to cannulate vessels are present microsclerotherapy may be implemented. Microsclerotherapy, however, is plagued by a number of adverse sequelae, increased incidence of bruising and pigment dyschromia, puncture marks from needle use, microulcerations, and inconsistent results (see Table 16.3). Given the adverse aesthetic outcomes of such procedures, the use of lasers has gained momentum in the management of cosmetic veins.

Lasers and intense pulse light (IPL) have not become replacements for sclerotherapy, primarily because hydrostatic pressure considerations are not addressed by light endothelial interactions. It is also more difficult to have sufficient penetration of photons safely through the thick epidermal-dermal wall surrounding the lower extremity vessels when utilizing noninvasive treatment modalities like laser technology; direct injection into the target chro-mophore is intuitively more efficient. Furthermore, an altered pattern of cytokine release may be observed when using laser technology, resulting in injury to the vessel that may lead to increased incidence of postinflammatory hyperpigmentation.

Wavelength, pulse duration, and spot size are the parameters that are most influential during the treatment and management of individual vessels (see Table 16.4). The larger vessels tend to respond to longer wavelengths or the ratio of vessel to epidermal heating increases the probability of achieving complete vessel coagulation.8 Shorter wavelengths, in contrast, partially coagulate the vessel ultimately increasing the incidence of treatment failures, and subsequent epidermal damage including hyperpigmentation.9 Maximum efficiency of vessel clearance is achieved when the penetration depth of the beam equals the vessel diameter.

The spot size should be as large as possible, at least on the order of 4x the optical penetration depth. An adequate spot size minimizes scattering losses in addition to maximizing beam penetration, which increases the probability that pan endothelial destruction will be achieved. The disadvantage to this, however, is that the use of larger spot sizes increases the pain and discomfort subjectively reported by the patient.

These parameters have influenced and spurred the development of a bimodal, dual-wavelength approach for the treatment of both red and blue lower extremity veins (see Figure 16.2). For the treatment of small, reddish telangiec-tasias with a high degree of oxyhemoglobin, short wavelengths (500-600 nm) were found to be most effective; longer wavelengths (800-1100 nm) were found to be most effective for the treatment of deeper, blue telangiectasias and reticular veins.

With continuing advances, laser technology can now address both variations in vessel size and depth with a single long wavelength 1064 nm Nd:Yag laser utilizing a varied pulse width as the monomodal approach (see Table 16.5).

TABLE 16.3 Microtelangiectasia <0.5 mm: Comparison of Microsderotherapy and Laser Technology

TABLE 16.4 Optimal Laser Parameters for the Treatment of Leg Veins

Wavelength

530-1064 nm

Pulse Duration

2-100 ms

Fluence

30-150 J/cm2

Spot Size

1.5-10 mm

Adapted from Sadick 2002.

Adapted from Sadick 2002.

TABLE 16.5 Monomodal Approach to the Treatment of Leg Veins Using the 1064 nm Nd:YAG Laser

Microsclerotherapy Laser

TABLE 16.3 Microtelangiectasia <0.5 mm: Comparison of Microsderotherapy and Laser Technology

Microsclerotherapy Laser

Number of Treatments

0 0

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