Optimal wavelengths for vein-selective photothermolysis

Oxyhemoglobin (HbO(2)) has been regarded as the primary target chromophore for selective photothermolysis of vascular malformations. In theory, venous lesions might be better treated with wavelengths preferentially absorbed by deoxyhemoglobin (Hb).

Wavelength-dependent fluence thresholds for photocoagulation of whole human blood were determined in glass capillary samples with measured oxygen saturation levels. Pulsed dye lasers at 585, 590, 595, 600, 633 nm, a 694 nm ruby laser, a 755 nm alexandrite laser, and a 1,064 nm Nd:Yag laser were used, all with 1.5-3 milliseconds pulse width and similar exposure spot size.

Selectivity (a lower fluence threshold) for venous blood was maximal at 694 nm, and significant at 595, 600, 633, and 755 nm. At 633 nm, a wavelength with strong relative absorption by metHb, selectivity for venous blood was much less than expected. The Nd:YAG laser at 1,064 nm showed significant selectivity for arterial blood.

Preferential photocoagulation of venous blood is possible at wavelengths with a high Hb/HbO(2) absorption coefficient ratio. Laser-induced metHb may also affect wavelength-dependent selective photothermolysis. Venular malformations such as port wine stains could potentially be treated more selectively with ~630-780 nm sources. Nd:YAG laser pulses at 1,064 nm tend to affect arterial more than venous blood.