TY - GEN
T1 - Imaging laser induced thermal fields and effects
AU - Verdaasdonk, Rudolf M.
PY - 1995/5/22
Y1 - 1995/5/22
N2 - Laser light interaction with biological tissues is a combination of optical, thermal and mechanical effects depending on the energy applied per unit ofvolume per unit oftime. Visualization ofthe phenomena with a high temporal and spatial resolution, contributes to a better understanding of the mechanism of action, especially when pulsed lasers are involved. For this goal, setups were developed based on Schlieren techniques to image the interaction of pulsed (CO2, Holmium and Excimer) and CW (CO2, Nd:YAG, Cu-vapor) lasers with physiological media and biological tissues. In a 'fast' Schlieren setup, images of shock waves and fast expanding and imploding vapor bubbles were captured using very short light flashes (10 ns -10 is). These recordings suggest that these explosive vapor bubbles seem to be the main dynamism for tissue ablation. In a 'color' Schlieren setup, very small changes in optical density of the media induced by temperature gradients, were color coded. Calibration of the color images to absolute temperatures were performed by using calculated temperature distributions and by thermocouple measurements. Cameras with high speed shutters (0.1 - 50 ms) enabled the recording of dynamic images of the thermal relaxation and heat diffusion in tissues during variation of pulse length and repetition rate. Despite pulse lengths < ms, heat generation in tissue was considerable already at pulse repetition rates above a few Hz. Similar Schlieren techniques were applied to study the thermal characteristics of laser probes, e.g. for the treatment of Benign Prostatic Hyperplasia (BPH). In combination with thermal modeling an optimal therapy might be predicted. Schlieren techniques, generating high-speed and 'thermal' images, can provide a good understanding of the ablation mechanism and the thermo-dynamics during laser tissue interaction with continuous wave and pulsed lasers.
AB - Laser light interaction with biological tissues is a combination of optical, thermal and mechanical effects depending on the energy applied per unit ofvolume per unit oftime. Visualization ofthe phenomena with a high temporal and spatial resolution, contributes to a better understanding of the mechanism of action, especially when pulsed lasers are involved. For this goal, setups were developed based on Schlieren techniques to image the interaction of pulsed (CO2, Holmium and Excimer) and CW (CO2, Nd:YAG, Cu-vapor) lasers with physiological media and biological tissues. In a 'fast' Schlieren setup, images of shock waves and fast expanding and imploding vapor bubbles were captured using very short light flashes (10 ns -10 is). These recordings suggest that these explosive vapor bubbles seem to be the main dynamism for tissue ablation. In a 'color' Schlieren setup, very small changes in optical density of the media induced by temperature gradients, were color coded. Calibration of the color images to absolute temperatures were performed by using calculated temperature distributions and by thermocouple measurements. Cameras with high speed shutters (0.1 - 50 ms) enabled the recording of dynamic images of the thermal relaxation and heat diffusion in tissues during variation of pulse length and repetition rate. Despite pulse lengths < ms, heat generation in tissue was considerable already at pulse repetition rates above a few Hz. Similar Schlieren techniques were applied to study the thermal characteristics of laser probes, e.g. for the treatment of Benign Prostatic Hyperplasia (BPH). In combination with thermal modeling an optimal therapy might be predicted. Schlieren techniques, generating high-speed and 'thermal' images, can provide a good understanding of the ablation mechanism and the thermo-dynamics during laser tissue interaction with continuous wave and pulsed lasers.
UR - http://www.scopus.com/inward/record.url?scp=85076702598&partnerID=8YFLogxK
U2 - 10.1117/12.209879
DO - 10.1117/12.209879
M3 - Conference contribution
AN - SCOPUS:85076702598
SN - 0-8194-1738-6
T3 - Proceedings of SPIE - the international society for optical engineering
SP - 165
EP - 175
BT - Laser-Tissue Interaction VI
T2 - Laser-Tissue Interaction VI 1995
Y2 - 1 February 1995 through 8 February 1995
ER -