Laser pulse duration must match the estimated thermal relaxation time for successful photothermolysis of blood vessels

J Stuart Nelson,Lars O Svaasand,Thomas E Milner,Sol Kimel

doi:10.1007/bf02133157

Abstract

The relationship between photothermal damage to blood vessels of diameter,d, and laser pulse duration,t p, was verified in a series of studies using the chick chorioallantoic membrane (CAM). A total of 879 individual CAM blood vessels (d=50–130μm) was irradiated, using a laser pulse duration of 0.45 or 10 ms. Laser-induced vascular damage was observed in real time, recorded on videotape, and evaluated in a double-blind fashion. Permanent damage was confirmed by inspection 24 h after laser exposure. Under the conditions of this experiment, only when laser pulse durations are approximately equal to the estimated thermal relaxation times (τ) of the CAM microvessels can the critical core intravascular temperature, necessary to destroy vessels irreversibly, be achieved and sustained for sufficient time. Shorter pulse durations are more effective for damaging smaller blood vessels; conversely, longer pulse durations are more effective for damaging larger diameter vessels.

Highlights

The pulse duration of laser exposure governs the spatial confinement of heat and should, in principle, match the thermal relaxation time (T) for the targeted port-wine stain (PWS) blood vessels, x is defined as the time required for the core temperature, produced by the absorbed light energy within the target blood vessel, to cool to one-half of the original value immediately after the laser pulse [1]
PWS blood vessel diameters vary on an individual patient basis and even from site to site on the same patient, over a range of 10-200 ~m [2]
The relationship between photothermal damage to blood vessels of diameter, d, and laser pulse duration, tp, was verified in a series of studies conducted in our laboratory using the chick chorioallantoic membrane (CAM) [3]

Summary

Introduction

The pulse duration of laser exposure (tp) governs the spatial confinement of heat and should, in principle, match the thermal relaxation time (T) for the targeted port-wine stain (PWS) blood vessels, x is defined as the time required for the core temperature, produced by the absorbed light energy within the target blood vessel, to cool to one-half of the original value immediately after the laser pulse [1]. When laser pulse durations are approximately equal to 9 can the critical core intravascular temperature, necessary to destroy large PWS blood vessels irreversibly, be achieved and sustained for sufcient time.

Results

Conclusion