Analysis of Nd:YAG laser-mediated thermal damage in rabbit nasal septal cartilage.
OBJECTIVE
Laser cartilage reshaping (LCR) involves the use of photo-thermal heating to reshape cartilage. Its clinical relevance depends on the ability to minimize thermal injury in irradiated regions. The present study seeks to understand the safety of LCR by determining shape change and resultant tissue viability as a function of laser dosimetry.


METHODS
Rabbit nasal septal cartilage were irradiated using a Nd:YAG laser (lambda = 1.32 microm, 5.4 mm spot diameter) with different exposure times of 4, 6, 8, 10, 12, and 16 seconds and powers of 4, 6, and 8 W. Temperature on the cartilage surface in the laser-irradiated region was collected using infrared thermography, this data was then used to predict tissue damage via a rate process model. A Live/Dead viability assay combined with fluorescent confocal microscopy was used to measure the amount of thermal damage generated in the irradiated specimens.


RESULTS
Considerable thermal injury occurred at and below the laser-reshaping parameters that produced clinically relevant shape change using the present Nd:YAG laser. Confocal microscopy identified dead cells spanning the entire cross-sectional thickness of the cartilage specimen (about 500 microm thick) at laser power density and exposure times above 4 W and 6 seconds; damage increased with time and irradiance. The damage predictions made by the rate process model compared favorably with measured data.


CONCLUSIONS
These results demonstrate that significant thermal damage is concurrent with clinically relevant shape change. This contradicts previous notions that there is a privileged laser dosimetry parameter where clinically relevant shape change and tissue viability coexist.
Li
Chao
C
Beckman Laser Institute and Medical Clinic, University of California Irvine, 1002 Health Sciences Road east, Irvine, California 92612, USA.
Protsenko
Dmitry E
DE
Zemek
Allison
A
Chae
Yong-Seok
YS
Wong
Brian
B
D000818:Animals; D002356:Cartilage / Q000293:injuries* / Q000528:radiation effects*; D016923:Cell Death; D002470:Cell Survival; D004307:Dose-Response Relationship, Radiation; D007834:Lasers / Q000009:adverse effects*; D018613:Microscopy, Confocal; D009300:Nasal Septum / Q000528:radiation effects*; D011817:Rabbits; D013817:Thermography