Using location and force measurements to estimate tissue thickness

Abstract

A method, including pressing a distal end of a medical probe against a wall of a body cavity, and receiving from the probe first measurements of a force exerted by the distal end on the wall. The method also includes receiving from the probe second measurements indicating a displacement of the wall in response to the force. The method further includes estimating a thickness of the wall based on the first and the second measurements.

1 . A method, comprising:
 pressing a distal end of a medical probe against a wall of a body cavity;   receiving from the probe first measurements of a force exerted by the distal end on the wall;   receiving from the probe second measurements indicating a displacement of the wall in response to the force; and   estimating a thickness of the wall based on the first and the second measurements.   
     
     
         2 . The method according to  claim 1 , wherein the probe comprises a catheter. 
     
     
         3 . The method according to  claim 1 , and comprising, prior to pressing the distal end of the probe against the wall, initializing one or more calibration matrices, each of the calibration matrices associated with a type of tissue. 
     
     
         4 . The method according to  claim 3 , wherein the type of tissue is selected from a list comprising artery tissue and endocardial tissue. 
     
     
         5 . The method according to  claim 3 , wherein initializing a given calibration matrix comprises storing a force value, a displacement value, and an associated thickness value to each element of the calibration matrix. 
     
     
         6 . The method according to  claim 5 , wherein estimating the thickness of the wall comprises identifying, in a given calibration matrix, a given element of the calibration matrix having a given force value corresponding to the first measurements and a given displacement value corresponding to the second measurements, and retrieving the thickness value from the identified matrix element. 
     
     
         7 . The method according to  claim 6 , wherein estimating the thickness of the wall comprises interpolating between the thickness values stored in two calibration matrix elements. 
     
     
         8 . The method according to  claim 6 , and comprising, subsequent to initializing the one or more calibration matrices and prior to estimating the thickness of the wall, selecting a given calibration matrix associated with the type of tissue corresponding to the wall of the body cavity. 
     
     
         9 . The method according to  claim 8 , and comprising, prior to selecting the given calibration matrix, identifying the type of tissue based on a location of the distal end. 
     
     
         10 . The method according to  claim 1 , wherein receiving the second measurements indicating the displacement comprises receiving first position measurements from the probe indicating a first location of the probe upon the probe engaging the wall, receiving second position measurements indicating a second location of the probe upon the distal end exerting the force on the wall, and calculating a distance between the first and the second locations. 
     
     
         11 . Medical apparatus, comprising:
 a probe having a distal end configured for insertion into a body cavity having a wall, the probe comprising:   a force sensor in the distal end, configured to generate a first signal indicative of a force exerted by the distal end on the wall; and   a position sensor in the distal end, configured to generate a second signal indicative of a location of the distal end within the body cavity; and   a processor, which is coupled to receive and process the first and second signals from the probe so as to estimate a thickness of the wall.   
     
     
         12 . The apparatus according to  claim 11 , wherein the processor is configured to process the second signal in order to find a displacement of the wall in response to the force, and to estimate the thickness of the wall using the displacement. 
     
     
         13 . The apparatus according to  claim 12 , wherein the processor is configured, prior to generating the first and the second signals, to initialize one or more calibration matrices, each of the calibration matrices associated with a type of tissue. 
     
     
         14 . The apparatus according to  claim 13 , wherein the processor is configured to select the type of tissue from a list comprising artery tissue and endocardial tissue. 
     
     
         15 . The apparatus according to  claim 13 , wherein the processor is configured to initialize a given calibration matrix by storing a force value, a displacement value, and an associated thickness value to each element of the calibration matrix. 
     
     
         16 . The apparatus according to  claim 15 , wherein the processor is configured to estimate the thickness of the wall by identifying, in a given calibration matrix, a given element of the calibration matrix having a given force value corresponding to the first measurements and a given displacement value corresponding to the second measurements, and retrieving the thickness value from the identified matrix element. 
     
     
         17 . The apparatus according to  claim 16 , wherein the processor is configured to estimate the thickness of the wall by interpolating between the thickness values stored in two calibration matrix elements. 
     
     
         18 . The apparatus according to  claim 16 , wherein the processor is configured, subsequent to initializing the one or more calibration matrices and prior to estimating the thickness of the wall, to select a given calibration matrix associated with the type of tissue corresponding to the wall of the body cavity. 
     
     
         19 . The apparatus according to  claim 18 , wherein the processor is configured, prior to selecting the given calibration matrix, to identify the type of tissue based on the location of the distal end. 
     
     
         20 . The apparatus according to  claim 11 , wherein the processor is configured to receive the second measurements indicating the displacement by receiving first position measurements from the probe indicating a first location of the probe upon the probe engaging the wall, receiving second position measurements indicating a second location of the probe upon the distal end exerting the force on the wall, and calculating a distance between the first and the second locations. 
     
     
         21 . The apparatus according to  claim 11 , wherein the probe comprises a catheter. 
     
     
         22 . A computer software product, operated in conjunction with a probe that is configured for insertion into a body cavity of a patient and that includes a position sensor for measuring a position of a distal end of the probe inside the body cavity and a force sensor for measuring a force between the distal end and a wall of the body cavity, the product comprising a non-transitory computer-readable medium, in which program instructions are stored, which instructions, when read by a computer, cause the computer to receive from the probe, while pressing the distal end against the wall, first measurements of a force exerted by the distal end on the wall, to receive from the probe second measurements indicating a displacement of the wall in response to the force, and to estimate a thickness of the wall based on the first and the second measurements.