Abstract:
A method and system for analyzing sounds originating in at least a portion of an individual&#39;s cardiovascular system. N transducers, where N is an integer, are fixed on a surface of the individual over the thorax. The ith transducer is fixed at a location x i  and generates an initial signal P(x i ,i) indicative of pressure waves at the location x i , for i=1 to N. the signals P(x i ,t) are processed so as to generate filtered signals in which at least one component of the signals P(x i ,t)not arising from cardiovascular sounds has been removed. The filtered signals may be used for generating an image of the at least portion of the cardiovascular system.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to medical devices and methods, and more particularly to such devices and methods for analyzing body sounds.  
         BACKGROUND OF THE INVENTION  
         [0002]    Body sounds are routinely used by physicians in the diagnosis of various disorders. A physician may place a stethoscope on a person&#39;s chest or back and monitor the patient&#39;s breathing or heartbeat in order to detect adventitious (i.e. abnormal or unexpected) lung or heartsounds. The identification and classification of adventitious lung or heart sounds often provides important information about pulmonary or cardiac abnormalities.  
           [0003]    It is also known to fix one or more microphones onto a subject&#39;s chest or back and to record lung sounds. U.S. Pat. No. 6,139,505 discloses a system in which a plurality of microphones are placed around a patient&#39;s chest. The recordings of the microphones during inhalation and expiration are displayed on a screen, or printed on paper. The recordings are then visually examined by a physician in order to detect a pulmonary disorder in the patent. Kompis et al. (Chest, 120(4), 2001) disclose a system in which M microphones are placed on a patient&#39;s chest, and lung sounds are recorded. The recordings generate M linear equations that are solved using a least-squares fit. The solution of the system is used to determine the location in the lungs of the source of a sound detected in the recordings.  
           [0004]    U.S. Pat. No. 5,285,788 discloses an ultrasound tissue imaging system having an acoustic transducer, and imaging means for producing an image of tissue. The system also includes Doppler imaging means to produce a scanned acoustic image of moving tissue that is displayed superimposed on the ultrasound image.  
         SUMMARY OF THE INVENTION  
         [0005]    In the following description and set of claims, two explicitly described, calculable, or measurable variables are considered equivalent to each other when the two variables are proportional to one another.  
           [0006]    The present invention provides, in one of its embodiments, a system and method for recording and analyzing cardiovascular sounds produced in the cardiovascular system. The system includes a plurality of N transducers (microphones) configured to be attached to an essentially planar region R of the individual&#39;s back or chest over the individual&#39;s thorax. Positions in the region R are indicated by two-dimensional position vectors x=(x 1 ,x 2 ) in a two-dimensional coordinate system defined in the planar region R. The ith transducer, for i=1 to N. is fixed at a position x i  in the region R and generates a signal, denoted herein by P(x i ,t), indicative of pressure waves in the body arriving at x i .  
           [0007]    The transducers are typically embedded in a matrix that permits to affix them easily onto the individual&#39;s skin. Such a matrix may typically be in the form of a vest or garment for easily placing over the individual&#39;s thorax. As may be appreciated, different matrices may be used for differently sized individuals, for different ages, sexes, etc.  
           [0008]    The N signals P(x i ,t) are processed by signal processing circuitry. In accordance with the invention, the signals are filtered so as to remove one or more components of the signals not arising from cardiovascular sounds (e.g. respiratory tract signals). Cardiovascular sounds are typically in the range of 6 to 45 Hz, while respiratory tract sounds are typically in the range of 100 to 400 Hz. Thus, respiratory sounds may be removed from the signals by filtering the signals, for example, with a band pass filter passing between 15 to 45 Hz.  
           [0009]    The N filtered signals (also indicated herein by P(x i ,t)) may be processed in order to diagnose the state of the individual&#39;s cardiovascular system. This may be via an automatic differential diagnosis in which the results of the processing are compared to functions or parameters previously stored in a database that are known to be indicative of various disorders in the body region.  
           [0010]    The filtered signals may also be processed to generate an image of the individual&#39;s cardiovascular system. The results of this processing are displayed on a display device, for example using a gray level scale, as demonstrated in the examples below. In the image, anatomic features of the heart such as the atria, ventricles, septal walls, can be observed. The image may be visually or automatically analyzed for the detection of a disorder in the cardiovascular system similar to the analysis of images obtained by other imaging methods such as X-ray (scintigraphy) or ultrasound imaging (echocardiography).  
           [0011]    A region or regions of the heart or cardiovascular system in a displayed image that are suspected of including a pathological condition, may de identified in the image, and this may be in a number of ways, for example, by different colors, by different patterns, by way of a written text, and many other ways. The term “pathological condition” refers to any deviation from the normal, healthy condition of the cardiovascular system. This includes murmurs and other hemodynamic irregularities, cardiac effusion, narrowing of blood vessel, and other space containing lesions in the cardiovascular system, etc.  
           [0012]    Additionally, a time interval can be divided into a plurality of sub intervals, and each subinterval processed separately. An image of the cardiovascular system for each of these subintervals may then be determined and displayed sequentially on the display device. This generates a movie showing dynamic changes occurring in the cardiovascular system over the time interval. This allows viewing of the systoles and diastoles of the different parts of the heart during the heartbeat.  
           [0013]    In a preferred embodiment, the processing involves determining from the N signals an average acoustic energy arising from cardiovascular sounds, denoted herein by {tilde over (P)}(x,t 1 ,t 2 ), at at least one position x in the region R over a time interval from t 1  to t 2 . The term “acoustic energy” at a location is used herein to refer to a parameter indicative of or approximating the product of the pressure and the mass propagation velocity at that location.  
           [0014]    In one embodiment, an average acoustic energy over a time interval from t 1  to t 2  is obtained at a position of one of the microphones using the algebraic expression  
                 P   ~          (       x   i     ,     t   1     ,     t   2       )       =       ∫     t   1       t   2                P   2          (       x   i     ,   t     )               t                 (   1   )                               
 
           [0015]    where x i  is the position of the microphone.  
           [0016]    In a more preferred embodiment, the processing involves obtaining an average acoustic energy {tilde over (P)}(x i ,t 1 ,t 2 ) over a time interval from t 1  to t 2  at a plurality of positions x i  of the microphones, for example using Equation (1), and then calculating {tilde over (P)}(x,t 1 ,t 2 ) at other locations x by interpolation of the {tilde over (P)}(x i ,t 1 ,t 2 ) using any known interpolation method.  
           [0017]    In a most preferred embodiment, the interpolation is performed to obtain an average acoustic energy {tilde over (P)}(x,t 1 ,t 2 ) at a position x=(x 1 ,x 2 ) in the surface R using the algebraic expression:  
                 P   ~          (     x   ,     t   1     ,     t   2       )       =       ∑     i   =   1     N              P   ~          (       x   i     ,     t   1     ,     t   2       )                       g        (     x   ,     x   i     ,   σ     )                   (   2   )                               
 
           [0018]    where g(x, x i ,σ) is a kernel satisfying  
                 ∇   2        g     =       ∂   g       ∂   σ               (   3   )                               
 
               ∑     i   =   1     N            g        (     x   ,     x   i     ,   σ     )                     is                 approximately                 equal                 to                 1             (   4   )                               
 
           [0019]    and where x i =(x i   1 , x i   2 ) is the position of the ith microphone and σ is a selectable parameter.  
           [0020]    For example, the kernel  
               g        (     x   ,     x   i     ,   σ     )       =     Exp   -       (         (       x   1     -       x   i   1          σ         )     2       2                 σ       )     ·   Exp     -     (         (       x   2     -       x   i   2          σ         )     2       2                 σ       )               (   5   )                               
 
           [0021]    may be used.  
           [0022]    The system may optionally contain a display device for displaying the function {tilde over (P)}. The function {tilde over (P)} may be displayed on the display, for example using a gray level scale, as demonstrated in the examples below. A two dimensional graphical representation of the function {tilde over (P)} produces an image of the cardiovascular system. In the image anatomic features of the heart such as the atria, ventricles, septal walls, can be observed. The image may be analyzed for the detection of a disorder in the cardiovascular system similar to the analysis of images obtained by other imaging methods such as X-ray (scintigraphy) or ultrasound imaging (echocardiography).  
           [0023]    A region or regions of the heart or cardiovascular system in a displayed image that are suspected of including a pathological condition, may de identified in the image, and this may be in a number of ways, for example, by different colors, by different patterns, by way of a written text, and many other ways. The term “pathological condition” refers to any deviation from the normal, healthy condition of the cardiovascular system. This includes murmurs and other hemodynamic irregularities, cardiac effusion, narrowing of blood vessel, and other space containing lesions in the cardiovascular system, etc.  
           [0024]    Additionally, a time interval can be divided into a plurality of sub intervals, and an average acoustic energy {tilde over (P)} determined over the region R for two or more of the sub intervals. An image of {tilde over (P)} for each of these sub intervals may then be determined and displayed sequentially on the display device. This generates a movie showing dynamic changes occurring in the acoustic energy in the body region, over the time interval. For example, transducers may be placed on a person&#39;s chest or back and an average acoustic energy {tilde over (P)} determined in accordance with the invention for a plurality of sub intervals over one or more heartbeats. An image can be obtained for each of these sub intervals and displayed sequentially so as to generate a movie showing changes in the acoustic energy of the heart over the heartbeat. This allows viewing of the systoles and diastoles of the different parts of the hear during the heartbeat.  
           [0025]    The signals P(x i ,t)may also be subjected to additional analysis to detect abnormal heart sounds.  
           [0026]    The present invention also provides a program storage device readable by machine, tangibly embodying a program of instructions executable by the machine to perform method steps for determining for at least one time interval, an average acoustic energy function {tilde over (P)} arising from cardiovascular sounds using an algorithm involving at least one signal P(xi,t) indicative of pressure waves at a location x i  on a body surface.  
           [0027]    The present invention still further provides a computer program product comprising a computer useable medium having computer readable program code embodied therein analyzing sounds in at least a portion of an individual&#39;s cardiovascular system, the computer program product comprising:  
           [0028]    computer readable program code for causing the computer to determine, for at least one time interval, an acoustic energy function {tilde over (P)} arising from the portion of the cardiovascular system, {tilde over (P)} being determined in algorithm involving at least one signal P(xi,t) indicative of pressure waves at a location x i  on a body surface.  
           [0029]    The invention thus provides a system for analyzing sounds originating in at least a portion of an individual&#39;s cardiovascular system comprising:  
           [0030]    (One) N transducers, where N is an integer, each transducer configured to be fixed on a surface of the individual over the thorax, the ith transducer being fixed at a location x i  and generating an initial signal P(x i ,t) indicative of pressure waves at the location x i ; for i=1 to N; and  
           [0031]    (Two) a processor configured to receive the signals P(x i ,t) and to filter the signals P(x i ,t) so as to generate filtered signals in which at least one component of the signals P(x i ,t)not arising from cardiovascular sounds has been removed.  
           [0032]    The invention thus further provides a system for analyzing sounds originating in at least a portion of an individual&#39;s cardiovascular system comprising:  
           [0033]    (a) N transducers, where N is an integer, each transducer configured to be fixed on a surface of the individual over the thorax, the ith transducer being fixed at a location xi and generating an initial signal P(x i ,t) indicative of pressure waves at the location x i ; for i=1 to N; and  
           [0034]    (Two) a processor configured to receive the signals P(x i ,t) and to generate therefrom an image of the at least portion of the cardiovascular system.  
           [0035]    The invention thus further provides a method for analyzing sounds originating in at least a portion of an individual&#39;s cardiovascular system comprising:  
           [0036]    (One) fixing on a surface of the individual over the thorax, N transducers, where N is an integer, the ith transducer being fixed at a location x i  and generating an initial signal P(x i ,t) indicative of pressure waves at the location x i ; for i=1 to N; and  
           [0037]    (Two) processing the signals P(x i ,t) so as to generate filtered signals in which at least one component of the signals P(x i ,t) not arising from cardiovascular sounds has been removed.  
           [0038]    The invention thus further provides a method for analyzing sounds originating in at least a portion of an individual&#39;s cardiovascular system comprising:  
           [0039]    (One) fixing on a surface of the individual over the thorax, N transducers, where N is an integer, the ith transducer being fixed at a location x i  and generating an initial signal P(x i ,t) indicative of pressure waves at the location x i ; for i=1 to N; and  
           [0040]    (Two) processing the signals P(x i ,t) so as to generate therefrom an image of the at least portion of the cardiovascular system.  
           [0041]    The invention thus further provides a program storage device readable by machine, tangibly embodying a program of instructions executable by the machine to perform method steps for analyzing sounds originating in at least a portion of an individual&#39;s cardiovascular system, comprising: processing N initial signals P(x i ,t), where N is an integer, the initial signals being indicative of pressure waves at a location x i ; for i=1 to N, so as to generate filtered signals in which at least one component of the signals P(x i ,t) not arising from cardiovascular sounds has been removed.  
           [0042]    The invention thus further provides a computer program product comprising a computer useable medium having computer readable program code embodied therein for analyzing sounds originating in at least a portion of an individual&#39;s cardiovascular system, comprising: processing N initial signals P(x i ,t), where N is an integer, the initial signals being indicative of pressure waves at a location x i ; for i=1 to N, so as to generate filtered signals in which at least one component of the signals P(x i ,t) not arising from cardiovascular sounds has been removed. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0043]    In order to understand the invention and to see how it may be carried out in practice, a preferred embodiment will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:  
         [0044]    [0044]FIG. 1 shows a system for obtaining an analyzing cardiovascular sounds in accordance with one embodiment of the invention;  
         [0045]    [0045]FIG. 2 shows a flow chart for carrying out a method of analyzing cardiovascular sounds in accordance with one embodiment of the invention;  
         [0046]    [0046]FIG. 3 shows the locations of transducers on an individual&#39;s back for analyzing cardiovascular sounds;  
         [0047]    [0047]FIG. 4 shows successive frames from a movie of the heart of a healthy individual over one heart beat;  
         [0048]    [0048]FIG. 5 shows successive frames from a movie of the heart and lungs of an individual over one respiratory cycle; and 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0049]    [0049]FIG. 1 shows a system generally indicated by  100  for analyzing body sounds in a three-dimensional region of an individual&#39;s body in accordance with one embodiment of the invention. A plurality of N sound transducers  105 , of which four are shown, are applied to a planar region of the chest or back skin of individual  110 . The transducers  105  may be any type of sound transducer, such as a microphone or a Doppler shift detector. The transducers  105  may be applied to the subject by any means known in the art, for example using an adhesive, suction, or fastening straps. Each transducer  105  produces an analog voltage signal  115  indicative of pressure waves arriving to the transducer. The analog signals  115  are digitized by a multichannel analog to digital converter  120 . The digital data signals P(x i ,t)  125 , represent the pressure wave at the location x i  of the ith transducer (i=1 to N) at time t. The data signals  125  are input to a memory  130 . Data input to the memory  130  are accessed by a processor  135  configured to process the data signals  125 . The signals  125  may be denoised by filtering components having frequencies outside of the range of body sounds in the body region, for example, vibrations due to movement of the individual. Each signal  125  may also be subject to band pass filtering so that only components in the signal within the range of cardiovascular sounds are analyzed. The signal may be divided into frequency bands, and each band analyzed separately.  
         [0050]    An input device such as a computer keyboard  140  or mouse  145  is used to input relevant information relating to the examination such as personal details of the individual  110 . The input device  140  may also be used to input values of the times t 1  and t 2 . Alternatively, the times t 1  and t 2 may be determined automatically in a respiratory phase analysis of the signals P(x i ,t) performed by the processor  135 . The processor  135  determines an average acoustic energy {tilde over (P)}(x, t 1 ,t 2 ) over the time interval from t 1  to t 2  at least one location x in the region R in a calculation involving at least one of the signals P(x i ,t).  
         [0051]    The average acoustic energies are stored in the memory  130  and may be displayed on a display device  150  such as a CRT screen for diagnosis by a physician.  
         [0052]    The processor  135  may also perform an automatic differential diagnosis by comparing the function {tilde over (P)} to functions stored in the memory and known to be indicative of various disorders in the body region.  
         [0053]    [0053]FIG. 2 shows a flow chart diagram for carrying out the method of the invention in accordance with one embodiment. In step  200  the signals P(x i ,t) are obtained from N transducers placed at predetermined locations x i  for i from 1 to N in a region R on the body surface. In step  205  values of t 1  and t 2  are either input to the processor  135  using the input devices  140  or  145 , or are determined by the processor. In step  210 , an average acoustic energy {tilde over (P)}(x,t 1 ,t 2 ) is determined at least one location x in the region R over the time interval t 1  to t 2 . In step  220  the average acoustic energy is displayed on the display  150  for at least one value of x. In step  230 , it is determined whether a function {tilde over (P)} is to be determined over another time interval. If yes, the process returns to step  205 . If not, the process terminates.  
         [0054]    It will also be understood that the system according to the invention may be a suitably programmed computer. Likewise, the invention contemplates a computer program being readable by a computer for executing the method of the invention. The invention further contemplates a machine-readable memory tangibly embodying a program of instructions executable by the machine for executing the method of the invention.  
       EXAMPLES  
       [0055]    The system and method of the invention were used to analyze cardiovascular sounds in an individual.  
       Example 1  
       [0056]    [0056]FIG. 3 shows recording of signals over one heartbeat in an individual. A two-dimensional coordinate system was defined on the individual&#39;s back. As shown in FIG. 3, 48 transducers were placed on the individual&#39;s back over the thorax, at the locations indicated by the circles  300 . The curves  305  show the presumed contours of the lungs, and the curve  306  shows the presumed contour of the heart. As can be seen, the transducers were arranged in a regular orthogonal lattice with spacing between the transducers in the horizontal and vertical directions of 2.5 cm. The signals P(x i ,t) from each transducer were then recorded over one heartbeat. Each signal was filtered using a 6-45 Hz band pass filter, in order to remove respiratory tract sounds. The heartbeat was divided into intervals of 0.1 sec duration, and for each interval, {tilde over (P)}(x,t 1 ,t 2 ) was obtained using Equations (1) and (2) above with the kernel g of Equation (5) with σ=36 pixels. FIG. 4 shows the images obtained by representing the obtained functions {tilde over (P)}(x,t 1 ,t 2 ) by gray level shading. The images may be displayed on the display device  150  in rapid succession so as to produce a movie of the heart over a heartbeat. The movie can be analyzed to determine the values of basic parameters of heart function, such as left ventricular end diastolic (LVED) volume, left ventricular end systolic (LVES) volume, right ventricular end diastolic (RVED) volume, right ventricular end systolic (RVES), volume, left atrium end diastolic (LAED) diameter, right atrium end diastolic (LAES) diameter, wall thickness of the inter-ventricular septum (systolic and diastolic), and parameters derivable from these parameters such as left ventricle stroke volume, left ventricular cardiac output, ejection fraction, left ventricular fractional shortening, inter-ventricular septal thickening. The movie can also be analyzed in order to detect heart defects such as valve dysfunction and cardiac arrhythmia.  
       Example 2  
       [0057]    The signals P(x i ,t) were obtained from each transducer as described in Example 1, and were then recorded over one respiratory cycle which includes about 5 heartbeats. Each signal was divided into two sub-signals P 1 (x i ,t) and P 2 (x i ,t) of different frequency bands. The sub-signal P 1 (x i ,t) was obtained by filtering the signal using a 6-40 Hz band pass filter. The sub-signal P 2 (x i ,t) was obtained by filtering the signal using a 100-150 band pass filter. The sub-signal P 1 (x i ,t) consists primarily of heart sounds, while the sub-signal P 2 (x i ,t) consists primarily of lung sounds. The P 1 (x i ,t) sub-signal was analyzed by the method of the invention, and the sub-signal P 2 (x i ,t) was analyzed as disclosed in Applicant&#39;s co-pending U.S. patent application Ser. No. 10/338,742 filed on Jan. 9, 2003. The signal P 2 (x i ,t) was divided into intervals of 0.25 sec duration, and the signal P 1 (x i ,t) was divided into intervals of 0.1 sec duration. For each interval, functions {tilde over (P)}(x,t 1 ,t 2 ) and {tilde over (P)}(x,t 1 ,t 2 ) were obtained from P 1 (x i ,t) and P 2 (x i ,t), respectively, using Equations (1) and (2) above with the kernel g of Equation (5) with σ=36 pixels. The two functions are preferably displayed simultaneously on a display device by intensity shading, using a different color for each function. FIG. 5 shows the images obtained by representing the obtained functions {tilde over (P)}(x,t 1 ,t 2 ) and {tilde over (P)}(x,t 1 ,t 2 ) simultaneously by gray level shading. The images may be displayed on the display device 150 in rapid succession so as to produce a movie of the heart over a heartbeat. The movie can be analyzed to determine the values of parameters of heart function, such as cardiac output and blood ejection fraction. The movie can also be analyzed in order to detect hear defects such as valve dysfunction and cardiac arrhythmia.