Abstract:
A system and method for analyzing the respiratory tract sounds. The system comprises a plurality of transducers that are placed on the individual&#39;s skin over the thorax. A signal analysis module analyzes sound signals recorded by the transducers and produces a first analysis product. A display device displays an image based upon the first analysis product. The image includes a pattern with an overall shape corresponding to that of the respiratory system. Regions in the image that are suspected of having a pathological condition may be indicated.

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 in order to detect adventitious (i.e. abnormal or unexpected) lung sounds. The identification and classification of adventitious lung sounds often provides important information about pulmonary 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.  
         SUMMARY OF THE INVENTION  
         [0004]    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.  
           [0005]    The present invention provides a system and method for recording and analyzing sounds produced by the respiratory tract in order to produce an image that permits easy analysis of pathological conditions of the respiratory tract. In accordance with the invention, sounds are recorded in a plurality of locations over an individual&#39;s thorax (including locations in one or both of the individual&#39;s chest or back surfaces). The sounds are recorded over a period of time, for example, over at least one respiratory cycle and preferably over several respiratory cycles, and the sounds recorded at each location are analyzed to produce a first analysis product. The plurality of first analysis products are then combined in a manner so as to produce the desired image. The first analysis product may be a function of a signal analysis in one or more of a variety of different parameters of the recorded signal, such as an analysis in the frequency domain, in the time domain, in the power domain or a combination of one or more of these domains. In accordance with the preferred embodiment of the invention, the sounds are analyzed in the tine and frequency domains to produce said first analysis product said image therefrom.  
           [0006]    In accordance with one embodiment of the invention, there is provided a system for analyzing the respiratory tract of an individual, comprising:  
           [0007]    a plurality of transducers for placing in a plurality of a pre-defined locations over the individual&#39;s thorax;  
           [0008]    a signal analysis module for analyzing sound signals recorded by each of said transducers to produce a first analysis product; and  
           [0009]    a display, said display displaying an image produced by the analyzed sound recordings, which image includes a pattern with an overall shape corresponding to that of the respiratory system and an indication on said pattern of regions thereof that are suspected of having a pathological condition.  
           [0010]    The present invention also provides a method for analyzing the condition of a respiratory tract of an individual, comprising:  
           [0011]    (i) placing a plurality of sound transducers in pre-defined locations on one or both of an individual&#39;s chest or back over the thorax;  
           [0012]    (ii) recording sound by each of said transducers over a period of time including at least one respiratory cycle;  
           [0013]    (iii) analyzing the sound recorded at each location to obtain a first analysis product; and  
           [0014]    (iv) Combining the plurality of first analysis products into a display, said display comprising a pattern with an overall shape corresponding to that of the respiratory system and an indication of regions thereof that are suspected of having a pathological condition.  
           [0015]    The term “pathological condition” refers to any deviation from the normal, healthy condition of the respiratory tract. This includes infection, inflammation, tumor, narrowing of the airways, existence of a space occupying lesions in the respiratory tract, etc.  
           [0016]    The first analysis product may be a function of one or more parameters of the recorded signal. The first analysis product may be a function of an analysis made in a variety of different domains of the recorded signal, as pointed out above.  
           [0017]    The transducers are typically embedded in a matrix that permits to affix them easily on 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 individual&#39;s; for different ages, sexes, etc.  
           [0018]    The respiratory tract is displayed in a manner such as to resemble the general shape of the lung, typically shaped similar to that which can be viewed in an x-ray of the lung. The term “similar” in this regard should be understood as meaning that a physician can generally recognize the shape of the lung from such a display although it is clear to any man of the art that the actual display of said image is different than that of an x-ray picture.  
           [0019]    In said display, regions that are suspected to include a pathological condition, each region is identified as such by the existence of wheezes and crackles identified by an allowances of the recorded sound signal in the frequency domain, are identified 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.  
           [0020]    The present invention provides, by another embodiment, a system and method for recording and analyzing respiratory tract sounds produced in the respiratory tract. 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 .  
           [0021]    The N signals P(x i , t) are processed by signal processing circuit. In accordance with the invention, the processing involves determining from the N signals an average acoustic energy, denoted herein by {tilde over (P)}(x,t 1 ,t 2 ), 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.  
           [0022]    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   )                               
 
           [0023]    where x i  is the position of the microphone.  
           [0024]    In a more preferred embodiment, an average acoustic energy {tilde over (P)}(x i ,t 1 ,t 2 ) over a time interval from t 1 , to t 2  is obtained 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.  
           [0025]    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   )                               
 
           [0026]    where g(x,x i ,σ) is a kernal satisfying  
                 ∇   2        g     =       ∂   g       ∂   σ               (   3   )                 ∑     i   =   1     N            g        (     x   ,     x   i     ,   σ     )                     is                 approximately                 equal                 to                 1             (   4   )                               
 
           [0027]    and where x i =(x i   1 ,x i   2 ) is the position of the ith microphone and σ is a selectable parameter.  
           [0028]    For example, the kernal  
               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   )                               
 
           [0029]    may be used.  
           [0030]    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 body region that may be analyzed for the detection of a disorder in the body region similar to the analysis of images obtained by other imaging methods such as X-ray or ultrasound imaging.  
           [0031]    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 and an average acoustic energy {tilde over (P)} determined in accordance with the invention for a plurality of sub intervals over a breathing cycle. 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 lungs over the breathing cycle.  
           [0032]    The signals P(x i ,t) may also be subjected to band pass filtering before being analyzed by the method of the invention, so that an average acoustic energy is produced for one or more frequency bands of interest. The functions may be superimposed on the display device by representing each average acoustic energy function with a different color.  
           [0033]    The present invention provides a system for analyzing sounds in at least a portion of an individual&#39;s respiratory tract comprising:  
           [0034]    (a) a plurality of N transducers, 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 a signal P(xi,t) indicative of pressure waves at the location x i ; for i=l to N; and  
           [0035]    (b) a processor configured to receive the signals P(x i ,t) and determine an average acoustic energy {tilde over (P)}(x,t 1 ,t 2 ) at at least one position x over a time interval from a first time t 1  to a second time t 2 , {tilde over (P)} being determined in an algorithm involving at least one of the signals P(xi, t).  
           [0036]    The present invention further provides a method for analyzing sounds in at least a portion of an individual&#39;s thorax, comprising:  
           [0037]    (a) obtaining N signals P(xi,t) for i=1 to N, the signal P(xi,t) being indicative of pressure waves at the location x i ; on a surface of the body over the thorax;  
           [0038]    (b) determining an average acoustic energy {tilde over (P)}(x,t 1 ,t 2 ) at at least one position x over a time interval from a first time t 1  to a second time t 2 , {tilde over (P)} determined in an algorithm involving at least one of the signals.  
           [0039]    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)} using an algorithm involving at least one signal P(xi,t) indicative of pressure waves at a location x i  on a body surface.  
           [0040]    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 body, the computer program product comprising:  
           [0041]    computer readable program code for causing the computer to determine, for at least one time interval, an acoustic energy function {tilde over (P)}, {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. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0042]    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:  
         [0043]    [0043]FIG. 1 shows a system for obtaining an analyzing body sound in accordance with one embodiment of the invention;  
         [0044]    [0044]FIG. 2 shows a flow chart for carrying out a method of obtaining analyzing body sounds in accordance with one embodiment of the invention;  
         [0045]    [0045]FIG. 3 shows recording and analysis of signals over an inspiratory phase of a respiratory cycle; and  
         [0046]    [0046]FIG. 4 shows recording and analysis of signals over an expiratory phase of a respiratory cycle. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0047]    [0047]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 applied to the subject by any means is 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 such 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 a range of interest are analyzed.  
         [0048]    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 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).  
         [0049]    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.  
         [0050]    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.  
         [0051]    [0051]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(xi,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 detrmined 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.  
         [0052]    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  
       [0053]    The system and method of the invention were used to analyze lower respiratory tract sounds in an individual.  
         [0054]    [0054]FIG. 3 shows recording and analysis of signals over an inspiratory phase of a respiratory cycle in an individual. A two-dimensional coordinate system was defined on the individual&#39;s back. As shown in FIG. 3 a,  48 transducers were placed on the individual&#39;s back over the lungs at the locations indicated by the circles  300 . The curves  305  show the presumed contours of the lungs. As can be seen, the transducers were arranged in a regular orthogonal lattice with a spacing between the transducers in the horizontal and vertical directions of 5 cm. The signals P(xi,t) were then recorded over one inspiratory phase of a breathing cycle (t 1  and t 2  are the beginning and end respectively of the inspiratory phase). Each signal was filtered using a low-pass filter having a cut-off of 150 Hz. The average value of each filtered function P(xi,t) over the inspiratory phase is indicated in FIG. 3 a  by means of gray level shading of each circle  300  with reference to the gray level scale  310 . {tilde over (P)}(x,t 1 ,t 2 ) was obtained using Equations (1) and (2) above with the kernal g of Equation (5) with σ=36 pixels. FIG. 3 b  shows a 512 pixel×512 pixel graphical representation of the function {tilde over (P)}(x,t 1 ,t 2 ) over the inspiratory phase also in reference to the gray level scale  310 . In the graphical representation of the function {tilde over (P)}(x,t 1 ,t 2 ) shown in FIG. 3 b,  the contours of the lungs and heart are easily perceived.  
         [0055]    [0055]FIG. 4 shows recording and analysis of signals over an expiratory phase of a respiratory cycle. As shown in FIG. 4 a,  48 transducers were placed on an individual&#39;s back at the same locations x i  used in FIG. 3, as indicated by the circles  400 . The curves  405  show the presumed contours of the individual&#39;s lungs. The signals P(xi,t) were then recorded over one expiratory phase of a breathing cycle (t 1  and t 2  are the beginning and end respectively of the expiratory phase). Each signal was filtered using a low-pass filter having a cut-off of 150 Hz. The average value of each function P(xi,t) over the expiratory phase is indicated in FIG. 4 a  by means of gray level shading of each circle  400  with reference to the gray level scale  410 . {tilde over (P)}(x,t 1 ,t 2 ) was obtained using Equations (1) and (2) above. FIG. 3 b  shows the function {tilde over (P)}(x,t 1 ,t 2 ) over the expiratory phase also in reference to the gray level scale  410 . Comparison of FIGS. 3 b  and  4   b  shows the volume change in acoustic energy between the inspiratory and expiratory phase of the respiratory cycle.