System and Method for Characterizing Vascular Tissue

Abstract

A system and method is provided for using ultrasound data backscattered from vascular tissue to estimate the transfer function of a catheter and/or substantially synchronizing the acquisition of blood-vessel data to an identifiable portion of heartbeat data. The backscattered ultrasound data is used, together with an algorithm, to estimate at least one transfer function. The transfer function(s) can then be used (at least in a preferred embodiment) to calculate response data for the vascular tissue (i.e., the tissue component of the backscattered ultrasound data). The response data and histology data are then used to characterize at least a portion of the vascular tissue (e.g., identify tissue type, etc.). In some embodiments, the backscattered data is acquired during a cyclical portion of the heartbeat data so that the blood vessel can be analyzed or imaged as if it were standing still, or not expanding and relaxing.

What is claimed is: 
     
         1 . A method of acquiring ultrasound response data for vascular tissue, comprising:
 inserting at least a portion of a catheter into a vascular structure;   activating a transducer portion of said catheter, said activation of said transducer portion resulting in at least two ultrasound signals being transmitted toward vascular tissue;   acquiring at least a first and second set of backscattered ultrasound data from said vascular tissue;   using at least a portion of said first set of backscattered ultrasound data and an algorithm to estimate a first transfer function of said catheter while said catheter is inside said vascular structure;   using at least a portion of said second set of backscattered ultrasound data and said algorithm to estimate a second transfer function of said catheter while said catheter is inside said vascular structure; and   using at least said first and second transfer function to calculate ultrasound response data for said vascular tissue, wherein said ultrasound response data is (i) indicative of data that is backscattered from said vascular tissue and (ii) substantially independent from ultrasound data modifications resulting from said catheter.   
     
     
         2 . The method of  claim 1 , wherein said step of using at least said first and second transfer function to calculate ultrasound response data for said vascular tissue, further comprises:
 using said first transfer function to calculate a first set of ultrasound response data for said vascular tissue, wherein said first set of ultrasound response data corresponds to said first set of backscattered ultrasound data; and   using said second transfer function to calculate a second set of ultrasound response data for said vascular tissue, wherein said second set of ultrasound response data corresponds to said second set of backscattered ultrasound data.   
     
     
         3 . The method of  claim 1 , wherein said step of using at least said first and second transfer function to calculate ultrasound response data for said vascular tissue, further comprises:
 using at least said first transfer function, said second transfer function and a second algorithm to calculate a third transfer function; and   using said third transfer function to calculate said ultrasound response data for said vascular tissue.   
     
     
         4 . The method of  claim 3 , wherein said second algorithm is a weighted-average algorithm. 
     
     
         5 . The method of  claim 1 , wherein said set of using at least said first and second transfer function to calculate ultrasound response data for said vascular tissue, further comprises:
 using at least said first transfer function, said second transfer function and a second algorithm to modify said first transfer function; and   using said modified first transfer function to calculate said ultrasound response data for said vascular tissue.   
     
     
         6 . The method of  claim 1 , further comprising the step of filtering noise from said at least two sets of backscattered ultrasound data. 
     
     
         7 . The method of  claim 1 , wherein said algorithm is an iterative algorithm that considers said first and second set of backscattered ultrasound data as being time-invariant over small intervals. 
     
     
         8 . The method of  claim 1 , wherein said step of using at least a portion of a first set of backscatter ultrasound data and an algorithm to estimate a first transfer function of said catheter, further comprises the step of using an error-criteria algorithm and a least-squares-fit algorithm to estimate at least a first set of said ultrasound response data for said vascular tissue and said first transfer function of said catheter, respectively. 
     
     
         9 . The method of  claim 8 , further comprising the step of using said estimated first set of ultrasound response data and a calculated first set of ultrasound response data to calculate a final first set of ultrasound response data for said vascular tissue. 
     
     
         10 . The method of  claim 1 , further comprising the step of using at least said ultrasound response data to produce an ultrasound image of at least said vascular tissue. 
     
     
         11 . The method of  claim 1 , further comprising the steps of:
 identifying a plurality of parameters of said ultrasound response data; and   using said plurality of parameters and previously stored histology data to characterize at least a portion of said vascular tissue.   
     
     
         12 . The method of  claim 11 , further comprising the steps of:
 transforming said ultrasound response data from the time domain into the frequency domain; and   identifying at least two of said plurality of parameters from the frequency spectrum of said ultrasound response data.   
     
     
         13 . The method of  claim 12 , wherein said step of identifying said at least two of said plurality of parameters further comprises said at least two parameters being selected from a group consisting of maximum power, minimum power, frequency at maximum power, frequency at minimum power, y intercept, slope, mid-band fit, and integrated backscatter. 
     
     
         14 . The method of  claim 11 , wherein said step of using said plurality of parameters and previously stored histology data to characterize at least a portion of said vascular tissue further comprises using said plurality of parameters and said previously stored histology data to identify a tissue type of at least a portion of said vascular tissue, said tissue type being selected from a group consisting of blood, fibrous tissues, fibrous caps, fibro-lipidic tissues, calcified necrotic tissues, calcific tissues, collagen, cholesterol and thrombus. 
     
     
         15 . The method of  claim 14 , further comprising the step of using at least said identified tissue type to produce a tissue-characterization image of at least said portion of said vascular tissue on a display. 
     
     
         16 . An intravascular-ultrasound (IVUS) data-acquisition system, comprising
 a catheter comprising at least one transducer and adapted to transmit a plurality of ultrasound signals and to receive ultrasound data, said ultrasound data being backscattered from vascular tissue; and   a computing device electrically connected to said catheter and comprising a transfer-function application adapted to:
 receive said ultrasound data; 
 use said ultrasound data to estimate a plurality of transfer functions of said catheter; and 
 determine ultrasound response data for said vascular tissue, said ultrasound response data being a function of at least said plurality of transfer functions and said ultrasound data. 
   
     
     
         17 . The IVUS-data-acquisition system of  claim 16 , wherein said transfer-function application is further adapted to determine a first and a second set of ultrasound response data for said vascular tissue, said first set of ultrasound response data being a function of a first one of said plurality of transfer functions and a first set of said ultrasound data, and said second set of ultrasound response data being a function of a second one of said plurality of transfer functions and a second set of said ultrasound data. 
     
     
         18 . The IVUS-data-acquisition system of  claim 16 , wherein said transfer-function application is further adapted to use said plurality of transfer functions and an algorithm to calculate a transfer function of said catheter, wherein said ultrasound response data is a function of at least said transfer function and at least a portion of said ultrasound data. 
     
     
         19 . The IVUS-data-acquisition system of  claim 18 , wherein said transfer-function application is further adapted to used said plurality of transfer functions and a weighted average algorithm to calculate a transfer function of said catheter. 
     
     
         20 . The IVUS-data-acquisition system of  claim 16 , wherein said transfer-function application is further adapted to filter noise from said ultrasound data, said ultrasound response data being a function of at least said plurality of transfer functions, said ultrasound data and said noise. 
     
     
         21 . The IVUS-data-acquisition system of  claim 16 , wherein said transfer-function application is further adapted to use an iterative algorithm that considers said ultrasound data as being time-invariant over small intervals to estimate said plurality of transfer functions. 
     
     
         22 . The IVUS-data-acquisition system of  claim 21 , wherein said transfer function application is further adapted to use at least one algorithm to estimate said plurality of transfer functions of said catheter, said at least one algorithm being selected from a list consisting of an error-criteria algorithm and a least-squares-fit algorithm. 
     
     
         23 . The IVUS-data-acquisition system of  claim 16 , wherein said computing device further comprises:
 a database adapted to store a plurality of parameters corresponding to a plurality of vascular tissue types; and   a characterization application electrically connected to said database and said transfer-function application and adapted to:
 receive said ultrasound response data; 
 transform said ultrasound response data into the frequency domain; 
 analyze said transformed signal for a plurality of identifiable parameters; and 
 use said plurality of identifiable parameters and at least a portion of said plurality of parameters stored in said database to characterize at least a portion of said vascular tissue. 
   
     
     
         24 . The IVUS-data-acquisition system of  claim 23 , wherein said database is further adapted to store at least two parameters corresponding to said plurality of vascular tissue types, said at least two parameters being selected from a group consisting of maximum power, minimum power, frequency at maximum power, frequency at minimum power, y intercept, slope, mid-band fit, and integrated backscatter. 
     
     
         25 . The IVUS-data-acquisition system of  claim 23 , wherein said characterization application is further adapted to use said plurality of identifiable parameters and said at least a portion of said plurality of parameters stored in said database to identify the tissue type of said at least a portion of said vascular tissue, said tissue types being selected from a group consisting of blood, fibrous tissues, fibrous caps, fibro-lipidic tissues, calcified necrotic tissues, calcific tissues, collagen, cholesterol and thrombus. 
     
     
         26 . The IVUS-data-acquisition system of  claim 25 , wherein said computing device further comprises a display for imaging said at least a portion of said vascular tissue in a color corresponding to said tissue type. 
     
     
         27 . A vascular-tissue-characterization system, comprising:
 a catheter comprising at least one transducer and adapted to transmit ultrasound signals toward vascular tissue and to receive backscatters of said ultrasound signals from said vascular tissue;   an intravascular ultrasound (IVUS) console electrically connected to said catheter and adapted to receive said backscatters of said ultrasound signals from said vascular tissue, said backscatters of said ultrasound signals comprising ultrasound data;   a transfer-function application adapted to:
 use the ultrasound data backscattered from said vascular tissue to estimate at least two transfer functions of said catheter; and 
 use at least said at least two transfer functions to calculate a response-data portion of said ultrasound data; and 
   a computing device electrically connected to said IVUS console, comprising:
 a database adapted to store a plurality of parameters corresponding to a plurality of vascular tissue types; and 
 a characterization application electrically connected to said database and adapted to:
 analyze said response-data portion of said ultrasound data for a plurality of identifiable parameters; and 
 use said plurality of identifiable parameters and at least a portion of said plurality of parameters stored in said database to characterize at least a portion of said vascular tissue. 
 
   
     
     
         28 . The vascular-tissue-characterization system of  claim 27 , wherein said transfer-function application is operating on said computing device. 
     
     
         29 . The vascular-tissue-characterization system of  claim 27 , wherein said transfer-function application is operating on said IVUS console. 
     
     
         30 . The vascular-tissue-characterization system of  claim 27 , wherein said transfer-function application is further adapted to filter noise from said ultrasound data. 
     
     
         31 . The vascular-tissue-characterization system of  claim 27 , wherein said transfer-function application is further adapted to use a first one of said at least two transfer functions to calculate a first response-data portion of said ultrasound data and a second one of said at least two transfer functions to calculate a second response-data portion of said ultrasound data. 
     
     
         32 . The vascular-tissue-characterization system of  claim 27 , wherein said transfer-function application is further adapted to:
 use an algorithm and said at least two transfer functions to calculate a transfer function for said catheter; and   use at least said transfer function of said catheter to calculate said response-data portion of said ultrasound data.   
     
     
         33 . The vascular-tissue-characterization system of  claim 27 , wherein said transfer-function application is further adapted to:
 use an algorithm and said at least two transfer functions to modify a first one of said at least two transfer functions; and   use at least said first one of said at least two transfer functions, as modified, to calculate said response-data portion of said ultrasound data.   
     
     
         34 . The vascular-tissue-characterization system of  claim 27 , wherein said characterization application is further adapted to transform said response-data portion of said ultrasound data into the frequency domain. 
     
     
         35 . The vascular-tissue-characterization system of  claim 27 , wherein said computing device further comprises a display and said characterization application is further adapted to produce an image of said at least a portion of said vascular tissue on said display.