MEASUREMENT OF RADIOMETRIC SURFACE-TEMPERATURE AND INTEGRATED BACKSCATTERED LIGHT-INTENSITY DURING FEEDBACK-CONTROLLED LASER-ASSISTED CARTILAGE RESHAPING

Cartilage undergoes characteristic mechanical stress relaxation follow ing laser irradiation below the ablation threshold. Porcine auricular cartilage (1-2 mm thickness) was irradiated with a Nd:YAG laser (lambd a = 1.32 mu m) at two power levels (W/cm(2)). Surface temperature (S-c (t)(degrees C)) (monitored using a single element HgCdTe infrared dete ctor, 10-14 mu m spectral range), and integrated back scattered light intensity I(t) were measured during laser irradiation. A HeNe laser be am (lambda = 632.8 nm) was incident on the back surface of the cartila ge specimen and fractional integrated backscattered light intensity wa s measured using an integrating sphere and a silicon photodiode. Laser irradiation (5.83 W/cm(2), 50 Hz pulse repetition rate (PRR)) continu ed until surface temperature reached approximately 70 degrees C, durin g which cartilage mechanical stress relaxation was observed. Integrate d back scattered light intensely reached a plateau at about 70 degrees C). At higher laser power (39.45 W/cm(3), 50 Hz PRR), a feedback-cont rolled cryogen spray was used to maintain surface temperature below 50 degrees C. A similar plateau response was noted in integrated backsca ttered light intensity. This signal may be used to optimise the proces s of stress relaxation in laser cartilage reshaping. Several clinical applications involving reconstructive surgery are proposed.