Measurements of laser light attenuation following cryogen spray cooling spurt termination.

Ahmad Edris,Bernard Choi,J Stuart Nelson,Guillermo Aguilar

doi:10.1002/lsm.10151

Abstract

Cryogen spray cooling (CSC) is used to minimize the risk of epidermal damage during laser dermatological surgery. However, while CSC can protect the epidermis from non-specific thermal damage, the cryogen film on the skin surface may pose a potential problem of laser light attenuation due to optical scattering. This study is focused on measuring the light transmittance changes that occur following cryogen spurt termination. The wavelengths studied were chosen for their clinical relevance to treatment of hypervascular skin lesions (594 nm) and laser-assisted hair removal (785 nm). Following delivery of cryogen spurts to the surface of an epoxy skin phantom, continuous records of light transmittance for 594 and 785 nm were obtained using an integrating sphere-based light collection apparatus. Shortly after spurt termination, there was negligible light attenuation by the cryogen film at the two wavelengths studied. For the typical clinical use of a 30 milliseconds spurt duration and 30 milliseconds delay between spurt termination and delivery of the laser pulse, a minimum average transmittance value of approximately 97% was measured.

Highlights

The clinical objective of laser dermatologic surgery is to maximize thermal damage to target chromophores while minimizing injury to overlying skin
While cryogen spray cooling (CSC) can protect the epidermis from non-specific thermal damage, the cryogen film that forms on the skin surface may pose a potential problem of laser light attenuation due to optical scattering
Light attenuation by the liquid cryogen film depends on the interval between spurt termination and laser irradiation

Summary

Introduction

The clinical objective of laser dermatologic surgery is to maximize thermal damage to target chromophores while minimizing injury to overlying skin. The novel method of achieving selective epidermal protection with ‘‘dynamic’’ or cryogen spray cooling (CSC) is well established and in current use for laser treatment of selected dermatoses [1,2,3,4,5,6,7,8]. While CSC can protect the epidermis from non-specific thermal damage, the cryogen film that forms on the skin surface may pose a potential problem of laser light attenuation due to optical scattering. Light attenuation by the liquid cryogen film depends on the interval between spurt termination and laser irradiation. While CSC can protect the epidermis from non-specific thermal damage, the cryogen film on the skin surface may pose a potential problem of laser light attenuation due to optical scattering.

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