Ultrasonic Doppler detection of laser-tissue interaction.

Laser therapy for the safe and effective coagulation and ablation of tissues requires precise control of the amount of energy delivered to and absorbed by the volume of tissue of interest. We propose that an ultrasonic transducer pointing in the same direction as the laser fiber could be used to monitor the changes in ultrasonic properties caused by the absorption of light by the tissue. A modified 20 MHz pulsed Doppler was used to evaluate the ultrasonic effects of 35 exposures of beef liver and muscle to a high power diode laser in vitro in real time. We found two distinct levels of acoustic activity in the tissue. Type 1 activity consisted of slow variations in the phase and small changes in the amplitude of the echoes, while type 2 activity consisted of large and rapid fluctuations in amplitude and phase. We found that the residual increase in echogenicity of the tissue and the delay to the onset of type 2 activity were functions of laser power and tissue type and were correlated to lesion severity. We hypothesize that type 1 activity corresponds to motion (thermal expansion and contraction) of the tissue, and that type 2 activity corresponds to the creation of gas bubbles (vaporization) in the tissue. We conclude that the absorption of energy changes the acoustic properties of tissue during and after exposure and that Doppler signal processing can be used to differentiate various levels of laser-tissue interaction in real time.

[1]  A. Steger.  INTERSTITIAL LASER HYPERTHERMIA FOR THE TREATMENT OF HEPATIC AND PANCREATIC TUMOURS , 1991, Photochemistry and photobiology.

[2]  C. Hartley,et al.  Doppler quantification of echo-contrast injections in vivo. , 1993, Ultrasound in medicine & biology.

[3]  C. Hartley,et al.  An ultrasonic method for measuring tissue displacement: technical details and validation for measuring myocardial thickening , 1991, IEEE Transactions on Biomedical Engineering.

[4]  S. Rastegar,et al.  Continuous wave laser ablation of tissue: analysis of thermal and mechanical events , 1993, IEEE Transactions on Biomedical Engineering.

[5]  W R Lees,et al.  Hepatic metastases: interstitial laser photocoagulation with real-time US monitoring and dynamic CT evaluation of treatment. , 1993, Radiology.

[6]  G Godlewski,et al.  Deep localized neodymium (Nd)‐YAG laser photocoagulation in liver using a new water cooled and echoguided handpiece , 1988, Lasers in surgery and medicine.

[7]  T Misaki,et al.  Thermally Controlled Laser Irradiation of the Myocardium with Intraoperative Ultrasound Monitoring , 1990, Pacing and clinical electrophysiology : PACE.

[8]  G Godlewski,et al.  Ultrasonic and histopathological correlations of deep focal hepatic lesions induced by stereotaxic Nd-YAG laser applications. , 1988, Ultrasound in medicine & biology.

[9]  D E MALONE,et al.  Sonographic Changes during Hepatic Interstitial Laser Photocoagulation: An Investigation of Three Optical Fiber Tips , 1992, Investigative radiology.

[10]  D. R. Wyman,et al.  Medical imaging systems for feedback control of interstitial laser photocoagulation , 1992, Proc. IEEE.

[11]  R. van Hillegersberg,et al.  Water‐jet‐cooled Nd:YAG laser coagulation of experimental liver metastases: Correlation between ultrasonography and histology , 1993, Lasers in surgery and medicine.

[12]  S. Torp-Pedersen,et al.  Interstitial hyperthermia of colorectal liver metastases with a US-guided Nd-YAG laser with a diffuser tip: a pilot clinical study. , 1993, Radiology.

[13]  P. Fitzgerald,et al.  Intravascular Ultrasound as a Guiding Modality for Mechanical Atherectomy and Laser Ablation , 1990, Echocardiography.

[14]  A. Dachman,et al.  US-guided percutaneous laser ablation of liver tissue in a chronic pig model. , 1990, Radiology.

[15]  R. Roth,et al.  Transurethral ultrasound-guided laser-induced prostatectomy (TULIP procedure): a canine prostate feasibility study. , 1991, The Journal of urology.