System and methods for lesion characterization in blood vessels

A method of laser ablating a target tissue, the method comprising:

• placing a catheter in a patient's vessel, the catheter comprising a plurality of optical fibers configured to transmit laser ablation radiation from a catheter distal end onto a region of a target tissue;
• coupling the catheter to a laser device, the laser device comprising:
• a processor,
• a memory coupled to the processor,
• an acoustic signal interface, and
• wherein the laser device is configured to generate the laser ablation radiation with a power density, wavelength and pulse width selected to directly ablate the target tissue and to generate an acoustic feedback signal within the vessel due to contact with the region of the target tissue;
• coupling an acoustic device to the acoustic signal interface of the laser device, the acoustic device configured to detect acoustic feedback signals generated by the region of the target tissue from the impingement of the laser ablation radiation onto the target tissue;
• initiating laser ablation of the target tissue using the laser ablation radiation from the catheter distal end such that the laser ablation radiation directly contacts the target tissue;
• generating, during the laser ablation, an acoustic feedback signal within the vessel due to the laser ablation radiation from the catheter distal end contacting the region of the target tissue, wherein the acoustic feedback signal is at least partially generated by:
• cavitation bubbles, jet formation and/or shock waves that are created by the initiating of the laser ablation using the laser ablation radiation with the power density, wavelength and pulse width selected to ablate the target tissue and to generate the acoustic feedback signal within the vessel due to contact of the laser ablation radiation with the target tissue;
• applying, by the processor, a tissue classification algorithm to the detected acoustic feedback signal thereby classifying the target tissue into a specific tissue type, wherein the application of the tissue classification algorithm includes:
• determining an efficiency of the ablation of the region of the target tissue;
• and
• applying a machine learning algorithm to compare the detected acoustic feedback signal with a database of stored acoustic signals;
• determining, by the processor, whether the region of target tissue includes the wall of the vessel, based on the received acoustic feedback signal obtained from the acoustic device and the applied tissue classification algorithm;
• and
• temporarily pausing transmission of the laser ablation radiation and, during the pause, adjusting a position of the catheter distal end away from the wall of the vessel based on the region of the target tissue being determined, by the processor, from the detected acoustic feedback signal and applied tissue classification algorithm, to include the wall of the vessel,
• wherein the database of stored acoustic signals comprises received acoustic feedback signals for prior therapy treatments, acoustic feedback analysis for prior treatments, results of acoustic feedback signal processing analysis for noise filtration, results for tissue classification for specific acoustic feedback signals or acoustic fingerprints for different tissue types, results of treatment efficiency analysis;
• user inputs for prior laser treatments;
• post-treatment user classifications;
• and/or warnings or other signals identified to user by the system during previous treatments.

A method of operating a laser ablation system comprising a catheter, a laser device, a processor, and an acoustic device, the method comprising:

• delivering, by the laser device via the catheter placed in a vessel of a patient, laser energy to a target tissue of the patient, the laser energy having a power density of approximately 50 or 60 mJ/mm2, a wavelength of approximately 355 nm and a pulse width less than approximately 25 ns selected to facilitate direct laser ablating of the target tissue and concurrent with the direct laser ablating, to generate an acoustic feedback signal, the acoustic feedback signal being generated within the vessel by direct impingement of the laser energy onto the target tissue;
• receiving, by the acoustic device, the acoustic feedback signal generated by impingement of the laser energy onto the target tissue during the laser ablating of the target tissue;
• determining, based on the received acoustic feedback signal and a tissue classification algorithm performed by the processor on the received acoustic signal, whether the target tissue includes 1) a wall of the vessel or a stent or 2) blood without any lesion present;
• and
• in response to the target tissue being determined, by the processor, to include the wall of the vessel or the stent based on the detected acoustic feedback signal and applied tissue classification algorithm:
• temporarily pausing laser energy delivery and adjusting a position of a distal end of the catheter away from the wall of the vessel or the stent.