Photoacoustic removal of occlusions from blood vessels

Abstract

Partial or total occlusions of fluid passages within the human body are removed by positioning an array of optical fibers in the passage and directing treatment radiation pulses along the fibers, one at a time, to generate a shock wave and hydrodynamic flows that strike and emulsify the occlusions. A preferred application is the removal of blood clots (thrombi and emboli) from small cerebral vessels to reverse the effects of an ischemic stroke. The operating parameters and techniques are chosen to minimize the amount of heating of the fragile cerebral vessel walls occurring during this photoacoustic treatment. One such technique is the optical monitoring of the existence of hydrodynamic flow generating vapor bubbles when they are expected to occur and stopping the heat generating pulses propagated along an optical fiber that is not generating such bubbles.

1 . A method of opening to the flow of blood a human cerebral blood vessel that is blocked by a clot, comprising: 
 positioning within said cerebral vessel an array of optical fiber ends adjacent to and extending in a direction across a surface of the clot, said optical fibers individually having a core diameter less than 100 microns,    directing a sequence of one or more pulses of radiation along one of the plurality of optical fibers and out of its end and then repeating directing such a sequence of pulses along individual ones of others of said plurality of optical fibers at a time, said pulses individually containing less than 250 micro-Joules of energy and having a duration less than 100 nanoseconds in order to generate a shock wave followed by a bubble which together cause a portion of the clot to be emulsified,    introducing a flow of liquid into the vessel adjacent the surface of the clot while radiation is being directed out of said optical fibers, and    while so directing the radiation pulses and the liquid, advancing the catheter end through the clot as the clot becomes emulsified until the blockage to the flow of blood through the vessel is removed.    
     
     
         2 . The method according to  claim 1 , wherein repeating directing the sequence of pulses includes directing said pulses in sequence along adjacent ones of said plurality o,f optical fibers.  
     
     
         3 . The method according to  claim 1 , wherein repeating directing the sequence of pulses includes directing said pulses in sequence along said Plurality of optical fibers that are not adjacent to each other.  
     
     
         4 . The method according to  claim 1 , wherein directing the sequence of pulses includes directing said pulses along individual ones of said plurality of optical fibers in an order that, at any instant, directs radiation against a coolest of a plurality of regions across the clot that are illuminated by the individual fibers of the array.  
     
     
         5 . The method according to  claim 1 , wherein directing a sequence of one or more pulses of radiation along individual ones of the optical fibers includes directing a burst of a plurality of pulses along the individual optical fibers with a repetition rate of one kilo-Hertz or more.  
     
     
         6 . The method according to any one of claims  1 - 5 , wherein positioning the array of optical fibers within the cerebral vessel includes inserting a catheter containing the array of optical fibers into a vessel of the human body a distance removed from said cerebral vessel and advancing the catheter through various vessels a distance of at least 50 centimeters to reach the cerebral vessel clot.  
     
     
         7 . The method according to  claim 6 , wherein inserting and advancing the catheter includes using advancing a catheter having an outside diameter of one-half millimeter or less at least for a portion of its length positioned within cerebral vessels.  
     
     
         8 . The method according to  claim 7 , wherein introducing a flow of liquid into the cerebral vessel adjacent the clot includes passing the liquid through a lumen of the catheter that extends along the catheter length for a distance of at least 75 centimeters from the optical fiber ends.  
     
     
         9 . The method according to  claim 8 , wherein introducing a flow of liquid into the cerebral vessel additionally includes passing liquid through the catheter lumen at a rate of at least one-tenth a cubic centimeter per minute.  
     
     
         10 . The method according to  claim 9 , wherein an average power of the radiation directed along the optical fibers to within said cerebral vessel is less than one-half of one watt.  
     
     
         11 . The method according to  claim 10 , wherein positioning the array of optical fiber ends within said cerebral vessel includes positioning optical fibers that individually have a core diameter of 50 microns or less.  
     
     
         12 . The method according to any one of claims  1 - 5 , wherein an average power of the radiation directed along the optical fibers to within said cerebral vessel is less than one-half of one watt.  
     
     
         13 . The method according to any one of claims  1 - 5 , wherein the flow of liquid introduced into the vessel is within a rate of from one-tenth to five cubic centimeters per minute.  
     
     
         14 . The method according to  claim 13 , wherein an average power of the radiation directed along the optical fibers to within said cerebral vessel is less than one-half watt.  
     
     
         15 . The method according to any one of claims  3 - 5 , wherein positioning the array of optical fiber ends within said cerebral vessel includes positioning optical fibers that individually have a core diameter of 50 microns or less.  
     
     
         16 . The method according to any one of claims  1 - 5 , wherein the generation of individual bubbles is optically monitored through the same optical fibers that carry the pulses which generate the bubbles, and, in response to a failure to detect the existence of a bubble being generated by a pulse directed along one of the optical fibers, suppressing subsequent pulses from being directed along said one optical fiber.  
     
     
         17 . The method according to  claim 16 , wherein suppressing subsequent pulses includes suppressing a predetermined number of pulses from being directed along said one optical fiber, after which directing the pulses along said one optical fiber and the monitoring of bubbles resumes.  
     
     
         18 . The method according to  claim 5 , wherein the generation of individual bubbles is optically monitored through the same optical fibers that carry the pulses that generate the bubbles, and, in response to a failure to detect the existence of a bubble being generated by a first pulse of a burst of pulses being directed along one of the optical fibers, suppressing those pulses after the first pulse from being directed along said one optical fiber.  
     
     
         19 . A method of opening to the flow of blood human cerebral blood vessel that is blocked by a clot, comprising: 
 directing electromagnetic radiation through optical fiber transmission media within the cerebral vessel toward said clot at different locations across the clot in time sequence,    simultaneously directing a cooling liquid within the cerebral vessel in the vicinity of the clot, and    maintaining an average power level of the radiation directed within the cerebral vessel at less that one-half of one watt.    
     
     
         20 . The method according  claim 19 , wherein the cooling liquid is directed into the cerebral vessel at a rate of flow within a range of from one-tenth to two cubic centimeters per minute.  
     
     
         21 . The method according to either of claims  19  and  20 , wherein directing electromagnetic radiation includes directing said radiation through a plurality of optical fibers, one at a time, which individually have a core diameter less than 100 microns.  
     
     
         22 . The method according to either of claims  19  and  20 , wherein directing electromagnetic radiation includes directing said radiation in a manner to generate within the cerebral vessel a succession of a combination of a shock wave and vapor bubble that combine to emulsify the clot.  
     
     
         23 . A method of opening to the flow of blood a human cerebral blood vessel that is blocked by a clot, comprising: 
 positioning an end of a catheter into a blood vessel of the human a distance from the cerebral blood vessel and advancing the catheter end at least 75 centimeters through various human vessels to within the cerebral vessel in a manner to position an open end of a lumen and ends of a plurality of optical fibers directed toward or imbedded in the clot, said optical fibers individually having a core diameter within a range of from 20 to 100 microns,    directing radiation along the plurality of optical fibers, one at a time in sequence, against the clot while a liquid is being discharged at a rate within a range of one tenth to five cubic centimeters per minute into the vessel through said lumen open end,    said radiation being directed along each of the plurality of fibers in the form of a plurality of pulses with a repetition rate within a range of from 1 to 20 kilo-Hertz, an amount of energy per pulse within a range of from 10 to 250 micro-Joules, and a duration of the individual pulses within a range of from 1 to 100 nanoseconds, in a manner that the pulses individually generate a shock wave followed by a bubble that together cause a portion of the clot to be emulsified and the average power delivered within the cerebral vessel is less than one-half of one watt, and    advancing the catheter end through the clot as the clot becomes emulsified until the blockage to the flow of blood through the vessel is removed.    
     
     
         24 . A system for the removal of a clot from a blood vessel, comprising: 
 a catheter having a length in excess of 75 centimeters between first and second ends thereof and an outside diameter less than one-half of one millimeter alone at least a portion of the length adjacent the first end, said catheter including a plurality of optical fibers that individually have a core diameter less than 100 microns and a lumen extending along said length, said optical fibers terminating in a spatial array across a first end of the catheter,    a source of liquid connected to supply cooling liquid to the lumen at the second end of the catheter, the lumen having an inside diameter and the source having a capacity such that the liquid is discharged from the lumen at the first end of the catheter with a rate of flow within a range of from one-tenth to five cubic centimeters per minute, and    a source of electromagnetic radiation connected to the optical fibers at the second end of the catheter in a manner to direct individual pulses of said radiation along the optical fibers, one at a time in sequence, with the pulses individually having a duration within a range of from one to 100 nanoseconds and containing an amount of energy within a range of from 10 to 250 micro-Joules of energy, and with a maximum average power of less than one-half of one watt being delivered from the optical fibers at the first end of the catheter.    
     
     
         25 . The system of  claim 24 , wherein said source of electromagnetic radiation directs a burst of a plurality of pulses along one of the optical fibers before switching to another of the optical fibers, the burst of pulses being supplied at a frequency within a range of from one to 50 kilo-Hertz.  
     
     
         26 . The system of either one of claims  24  or  25 , wherein said source of electromagnetic radiation directs said pulses sequentially along individual ones of the plurality of optical fibers across the spatial array that are not adjacent one another.