Vascular Lesion Treatment
Although the YAG's primary applications are in
treatment of dark and red tattoo inks and lesions, the availability of vascular lesion
applications clearly increases the overall practicality of the laser system. Upon
initial examination of its output characteristics, the laser would seem inappropriate for
treating vascular lesions. This initial conclusion could be drawn form a comparison of the pulse
characteristics of the YAG's relative to the theory of selective photothermolysis.
Selective photothermolysis requires that the energy impacting on a vessel be confined
within the vessel, causing coagulation of the blood in the vessel, before the heat has a
chance to dissipate from the vessel to the surrounding fibrous tissue. Consequently, the
thermal relaxation time of the vessel is important. Most vessels posses thermal
relaxation in hundreds of microseconds. The development of the pulsed dye laser and
newly introduced Copper Bromide system were planned with this theory in mind. The
532nm pulse of the laser is approximately 4 nanoseconds in length or 100,000 times
shorter than the Flashlamp Pulsed Dye Laser (FLPD) (i.e. Candela SPTL). Therefore,
the YAG's effect in vascular lesions must be different. It has been established that the
532nm wavelength is very well absorbed by blood. Consequently, the laser's green
light output will be well absorbed by hemoglobin. However, the absorption of this
extremely short pules causes a very different effect. The high peak power pulse causes a
photoacustic effect and literally obliterates the vessel. The most likely
|
scenario is that the
erythrocytes absorb the input pulse,
explode, vaporize and through the rapid expansion of these vaporized erythrocytes , causes the vessel to rupture. If the vessels are too large
(i.e. 1 mm), the input pulse will only puncture a hole in the vessel and then it will reseal.
If the vessel is small enough in diameter (i.e. 0.5 mm) the vessel should be completely
obliterated. The appropriate treatment technique is to trace along a vessel and
completely obliterate the vessel. Although the laser's pulse is not optimal for
treating vascular lesions, an important factor should be noted. There is virtually no
thermal effect on the tissue, consequently the risk of scarring is extremely low. In recent
clinical trials, the YAG's 532nm output was most successful in treating telangiectasia,
angiomas, spider nevi, small port wine stains, and Campbell de Morgan spots. Energy
densities of 3-4 J/cm2 with a 2mm spot size were typical parameters in successfully
treated lesions during the original studies. Often times, more than one treatment is
necessary. Interestingly, some lesions, successfully treated by this laser, had in fact
failed treatment by other lasers. Another pertinent fact is the immediate post treatment
purpuric effect of the YAG's 532nm pulse. This purpura is the same in appearance
as the FLPD laser and clearing is similar, taking approximately one week. Clearly, the
YAG's primary applications are treating tattoos and pigmented lesions. Yet, its role
in treating vascular lesions is not insignificant. It may be best classified as playing an
adjunctive role to other primary vascular lasers such as the Copper Bromide laser.
|
