Abstract:
A method and device in accordance with the present invention enable detecting changes in mechanical and structural properties of the breast tissue that are indicative of breast cancer development. In one embodiment of the invention, an array of force sensors based on PVDF piezopolymer film, data acquisition circuit, and a microprocessor are mounted in a hand held pad. Detection of nodules is achieved by pressing the sensing pad onto the breast, oscillating it over regions under investigation, and analyzing spectral and phase characteristics of the signal from the sensors in the array. The device is able to objectively detect presence of suspicious lesions in the breast and provide a warning signal.

Description:
[0001] This invention was made with government support under SBIR Grants No. 1 R43 CA65246-01 A1 and No. 2 R44 CA69175-03 awarded by the National Institutes of Health, National Cancer Institute. The government has certain rights in this invention. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Technical Field  
           [0003]    The present invention relates to a method and apparatus for breast self-palpation and detecting changes of mechanical properties in the breast tissue that are indicative of breast cancer and other breast pathologies accompanied by changes in tissue viscoelasticity.  
           [0004]    2. Description of the Related Art  
           [0005]    Breast Cancer is a major source of cancer morbidity and mortality in women. Currently, the most widely used clinical diagnostic method is mammography. Efforts to reduce mortality via screening mammography have been successful with definite improvement in survival, particularly in women over 50 year old.  
           [0006]    An alternative method—Breast Self-Examination (BSE) is the most common method of breast cancer detection. About two-thirds of cancers are detected by palpation. Such sensitivity of BSE is related to significant changes in mechanical properties of tissues in the course of breast cancer development. The BSE is widely advised and taught to women as a means of pre-clinical testing and contributes significantly to early cancer detection. A major fraction of breast cancer is first detected by women themselves, who bring the problem to the attention of their physicians. The usefulness of palpatory self-examination as a pre-clinical test is well proven by a wealth of data. The major drawback of this method is that only large size nodules are detectable by palpation. An average examiner, including women conducting breast self-examinations, does not reliably detect lesions until they approach 2 cm in diameter, which may represent a significantly advanced stage of cancer. Even a highly experienced examiner is able to detect a nodule only over 1 cm in diameter, which still may correspond to a considerably advanced cancer.  
           [0007]    It is apparent, therefore, that further investigation into screening techniques with greater sensitivity is urgently warranted. Availability of an easy to use, hand-held device for a regular home testing will facilitate regular self-examinations conducted by women and lead to vast improvement in lowering the morbidity and mortality of breast cancer.  
           [0008]    There have been many attempts to develop methods and devices for sensing the regions of hardening in tissues and thus, mimicking manual palpation aimed to detect breast cancer. Several authors have proposed various devices for breast palpation using different types of force sensors but all with limited success. For example, proposals by Gentle (Gentle C R, “Mammobarography: a possible method of mass breast screening”, J. Biomed. Eng. 10, 124-126, 1988) was capable of detecting lumps of 6 mm in diameter in breast phantoms but was unable to obtain any quantitative data on lumps in a real breast. Many of the proposed BSE means were related to simple non-computerized mechanical systems enhancing sense of touch such as apparatuses described in U.S. Pat. No. 5,572,995, U.S. Pat. No. 4,657,021, U.S. Pat. No. 4,793,354, and U.S. Pat. No. D348,618  
           [0009]    Various types of devices mimicking palpation to detect tumors using different types of force sensors have been suggested. For example, Frei et al., U.S. Pat. No. 4,250,894, have proposed an instrument for breast examination that uses a plurality of spaced piezoelectric strips which are pressed into the body being examined by a pressure member which applies a given periodic or steady stress to the tissue beneath the strips.  
           [0010]    Another method and devices for breast self-examination is described in U.S. Pat. No. 5,883,634 and U.S. Pat. No. 5,989,199. The sensors used in those devices are based on force sensor array manufactured by Tekscan Inc., Boston, Mass. The array consists of conductive rows and columns whose intersecting points form sensing locations. The rows and columns are separated by a material, which changes its electrical resistance under applied force, and thus each intersection becomes a force sensor.  
         SUMMARY OF THE INVENTION  
         [0011]    The present invention, Self-Palpation Device (SPD), utilizes the same mechanical information as obtained by manual palpation conducted by a skilled physician but objectively and with higher sensitivity and accuracy. The proposed method and device provides detection of tissue heterogeneity and hard inclusions by measuring changes in the surface stress pattern using a force sensing array applied to the tissue in the oscillatory mode. Temporal and spatial changes of the spectral components and phase relationships of oscillatory signals from the sensors contain information on the mechanical properties and geometry of the internal structures of the breast.  
           [0012]    The method and devices in accordance with the present invention enable the user to detect changes in the breast tissue that could be indicative of cancer development. The apparatus of the current invention uses sensors based on piezopolymer PVDF films and comprises mechanical arrangements allowing to increase PVDF signal while providing a good spatial resolution. PVDF film provides inexpensive means for measuring mechanical forces by converting them into an electrical signal. The apparatus also comprises data acquisition circuit, and a microprocessor that are mounted in a hand held pad. Detection of nodules is achieved by analyzing the dynamic and spatial features of the measured signals obtained by pressing the probe to the breast and oscillating it over the area under investigation. The device is able to objectively detect the mechanical changes in a breast that could be an indication of cancer development.  
           [0013]    The present invention provides indications on how elasticity differences in localized areas inside of tissue and respective changes in the spectral components as well as temporal and spatial derivatives of the oscillatory signals from the force sensors on the surface of the tissue are inter-related. The present invention also determines how the above relationship can be used for forming the basis for a method of detecting and quantifying tissue abnormalities.  
           [0014]    A significant new feature of SPD is its learning ability needed for developing individually optimized diagnostic criteria. Learning algorithms implemented in the software of SPD make it possible to significantly increase the sensitivity of SPD by fine tuning the device to specific anatomical and physiologic features of a particular woman.  
           [0015]    The learning ability of a home-use medical diagnostic system, such as the breast Self-Palpation Device of the present invention, is based on the fact that the data collected during extended period of time provides means for defining much more precisely the “normal state” of a particular organ and thus, detecting meaningful deviations from the normal state with greater sensitivity.  
           [0016]    Medical logic for diagnosis is typically based on the principle that healthy state of body is an objective notion and should be defined by “normal” intervals for vital parameters, which are the same for all people. For instance, if there are no palpable nodules in a breast, it is considered appropriate to qualify that breast “normal” from mechanical point of view. At the same time, a particular, seemingly “normal”, breast could have detectable mechanical changes resulting from a cancer development, but these changes are within the range of statistical variation of properties of the breast in general. Such meaningful changes can be detected only if one relates these changes to an individual baseline of a particular patient. The proposed self-palpation device of the present invention is based on a principle of medical diagnosis, by which the ranges of parameters that define the healthy state are determined individually.  
           [0017]    Every human body is a complex dynamic system with a high level of self-adapting mechanisms. The term “normal range” for a parameter of an organism should be linked to its specific environment. In other words, while in one condition a particular range is normal, in another, the same range corresponds to an abnormality in the body.  
           [0018]    The principle of individual normality can be described by using a formal model of a diagnostic process in general. A vector space A of “vital states” of an organ or entire organism can be considered. A single point (a vector a={a 1 , a 2 , . . . , ak} of the space) represents “an elementary temporal” state for a given organ or organism. The elementary state is defined by a set of vital parameters measured over a particular short period of time. Accordingly, the biological life of the investigated organism can be represented as a sequence of elementary states S=&lt;s 1 , s 2 , . . . , sN&gt; based on the sequence of the periods T={1, 2, . . . , N}. Every element from the sequence is a point in A, and the sequence S can be interpreted as a trajectory of “elementary” transformations Ts(i)=s(i+1). The main idea to introduce “individual standard” for “normal” and “abnormal” states is based on the well known fact that if a clinician looks at a single element s(i) from S, he/she often cannot estimate the normality of the state, but if he/she can observe the entire sequence S the estimation of s(i) is not a hard problem in the most of cases.  
           [0019]    The sequence S can be presented by an average state s*(S). Variance v(s*) of the average is a simplest measure of uncertainties of how well s* represents S. If v(s*) is small enough the representation gives a good approximation for S. This state will be referred to as “stable temporally and individually” because of its stability during a long period of life time. If the variance for every vital parameters is small during period T and the average value for each of them belongs to “objective” intervals of norms the s*(S) as will be referred to as “normal” for a given patient for the period of time T. Otherwise, the state of S will be referred to as “abnormal”.  
           [0020]    In the extended sequence of elementary states S′={S, s(N+1)}, the elementary state s(N+1) is called “alarm-state” if the state of S is normal while the state of S′ is abnormal.  
           [0021]    The principle of “individual normality” of the breast proposed in the present invention is based on a predefined choice of concrete values for several parameters (such as N, thresholds on variances for all vital parameters, etc.). The list of parameters which can be considered “relevant” and can be used as state characteristics need to be predefined.  
           [0022]    In general, there are many approaches to represent a set by its members. For example, one can use a simple average representation. Other approaches, such as median representatives, can also be used. 
       
    
    
       [0023]    With the foregoing and other objects, advantages and features of the invention that will become hereinafter apparent, the nature of the invention may be more clearly understood by referencing to the following detailed description of the invention, the appended claims and the several views illustrated in the drawings.  
       BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]    [0024]FIG. 1A is a cross-section of PVDF based force sensor.  
         [0025]    [0025]FIG. 1B is a top view of PVDF based force sensor shown in FIG. 1A.  
         [0026]    [0026]FIG. 2 is a cross-section of another PVDF based force sensor.  
         [0027]    [0027]FIG. 3 is a cross-section of yet another embodiment of PVDF based force sensor.  
         [0028]    [0028]FIG. 4 shows the arrangements to convert PVDF sensor signals to a digital form.  
         [0029]    [0029]FIG. 5 shows a different arrangement to convert PVDF sensor signal to a digital form.  
         [0030]    [0030]FIG. 6 is a general view of an embodiment of a self-palpation device.  
         [0031]    [0031]FIG. 7 represents the self-palpation device shown in FIG. 6 in use.  
         [0032]    [0032]FIG. 8 is across-section side view of another embodiment of self-palpation device.  
         [0033]    [0033]FIG. 9 represents the self-palpation device shown in FIG. 8 in use.  
         [0034]    [0034]FIG. 10 is a schematic diagram of an electronic unit for acquisition, processing and displaying mechanical imaging data from the self-palpation devices shown in FIG. 6 and FIG. 8.  
         [0035]    [0035]FIG. 11 shows a flow chart representative of an algorithm for obtaining diagnostic information on the state of breast from the data obtained by the force sensor array.  
         [0036]    [0036]FIG. 12A shows a sectional view of the force-sensor array pressed against a tissue phantom with hard inclusion.  
         [0037]    [0037]FIG. 12B is a graphical representation of a time dependence of signals from force sensors in one row of the array in the process of the experiment shown in FIG. 12A.  
         [0038]    [0038]FIG. 12C is a graphical representation of a time dependence of signals from force sensors from the entire array in the process of the experiment shown in FIG. 12A.  
         [0039]    [0039]FIG. 13 shows spatial distribution of the amplitude of the first harmonic of the oscillatory signals shown in FIG. 12C.  
         [0040]    [0040]FIG. 14 is a topographic representation of the data shown in FIG. 13.  
         [0041]    [0041]FIG. 15 shows spatial distribution of the amplitude of the second harmonic of the oscillatory signals shown in FIG. 12C.  
         [0042]    [0042]FIG. 16 is a topographic representation of the data shown in FIG. 15.  
         [0043]    [0043]FIG. 17 shows spatial distribution of the phase shift of the first harmonic of the oscillatory signals shown in FIG. 12C.  
         [0044]    [0044]FIG. 18 is a topographic representation of data shown in FIG. 17. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0045]    Referring now to the drawings, like elements are designated by like numerals, FIGS. 1A, 1B show an arrangement to mechanically amplify a PVDF sensor signal by converting a small force into a high tangential tension. PVDF based force sensor  10  comprises sensing elements  11  made of PVDF film and printed circuit board (PCB)  14  with a round opening. Electronic components  15  are mounted at the bottom of PCB  14 . PVDF sensing element  11  has metallization on both surfaces in order to collect a charge. Top metallization layer  19  covers the entire surface and it is connected to the common point of electrical circuit. Bottom metallization layer  20  is a circle slightly larger in diameter than the opening in PCB (see FIG. 1B). PCB  14  has a round contact  13  to get collected charge to electronic components  15 . Top metallization layer  19  of PVDF film  11  also acts as an electric shield to eliminate noise pick up.  
         [0046]    [0046]FIGS. 2 and 3 show other embodiments of PVDF based force sensor arrays with PVDF sensing elements  11  embedded into elastic material  12  covering the surface of PCB  14 . For example, elastic material  12  can be a soft rubber. When a force is applied to PVDF sensor  11  it results in bending, stretching and tangential tension in the PVDF material and generating electrical charge on the electrodes of the sensors. Embodiment shown in FIG. 2 comprises individual PVDF sensors  11  connected by thin elastic wiring  16  with contact points  17  of PCB  14 . The electrodes on the other side of the PVDF sensors, opposite to PCB, are interconnected and grounded. PVDF sensors  22  of the embodiment shown in FIG. 3 are formed by electrodes  18  on surface  23  of a single PVDF sheet  25 . Opposite surface  24  of PVDF sheet is metallized and grounded. This ground electrode layer acts also as an electric shield to eliminate noise pick up.  
         [0047]    [0047]FIG. 4 shows an arrangement for converting PVDF sensor signals into a digital form. Multiple cells  30  are connected to a multiplexer  44 . Each cell  30  has PVDF sensor  41 , external capacitor  42  and high input impedance amplifier  43 . External capacitor  42  increases the time constant. Output of multiplexer  44  goes to analog-to-digital converter  45  to be converted into digital form and fed to a computer.  
         [0048]    [0048]FIG. 5 shows an alternative arrangement  50  of converting PVDF sensor signals into a digital form. Arrangement  50  includes PVDF sensors  41 , external capacitors  42 , and multiplexer  44 , bleeding resistor  53 , high input impedance amplifier  51  and analog-to-digital converter  52 . The use of one amplifier on the output of multiplexer  44  instead of individual amplifiers for each sensor substantially reduces the cost and power consumption.  
         [0049]    Referring to FIG. 6, self-palpation device  70  includes a plurality of force sensing transducers  74 . Force sensing transducers  74  can be similar to arrays shown in FIGS. 1, 2 and FIG. 3. Force sensing transducers  74  generate signals, which vary with the force applied by the contact with the breast tissue and dynamic properties of the force sensors. Device  70  also includes electronic board  75 , housing  73 , electric power supply  72 , such as a battery, and signal light  71 . FIG. 7 represents self-palpation device  70  of FIG. 6 in use. During operation of self-palpation device  70 , it is pressed gently against the breast and then is oscillated over the breast.  
         [0050]    [0050]FIG. 8, shows an alternative self-palpation device  90  that comprises a force sensor array  93  composed of sensors shown in FIGS.  1 - 3 . Device  90  also includes electronic board  75 , housing  92 , electric power supply  72 , display  94 , and belt fastener  91 . FIG. 9 represents the self-palpation device  90  of FIG. 8 in use. During operation of self-palpation device  90 , it is pressed gently against the breast and then is oscillated over the breast.  
         [0051]    [0051]FIG. 10 is a schematic diagram of an electronic unit for providing acquisition, processing and displaying of mechanical imaging data from the self-palpation devices shown in FIG. 6 and FIG. 8. FIG. 10 illustrates a schematic diagram of a preferred embodiment of the electronic unit  75  which is coupled to self-palpation device  70  or self-palpation device  90  (not shown). A plurality of PVDF sensor elements  41  form force sensor assembly  76  of the device. A force sensing circuit is formed of a plurality of amplifiers  43  to amplify respective signals generated by force PVDF sensor elements  41  of force sensor assembly  76 . The amplified signals from amplifiers  43  are applied to the multiplexer  44 . Multiplexed signals are converted into digital signals by analog-to-digital converter  45  and fed to a processor  101 . Display device  94  is connected to the processor  101 , thereby displaying the breast examination process and the results of the examination. Processor  101  communicates with analog-to-digital converter  45  and multiplexer  44  for sending data and control signals. Storage device  102  having PC connector port can store examination data and transfer it to a computer.  
         [0052]    [0052]FIG. 11 shows a flow chart representative of an algorithm for determining diagnostic information from palpation data. Force data  131  from force sensor assembly  76  are acquired in real-time. Analog signals representing the force measured from all the force transducers of the force sensor assembly  76  at time t form force data flow  131 . In box  111 , force data flow  131  are combined over time into acquired data represented by A(p i ,n i ,t). Using force calibration data, the acquired data are combined over a period of time to form force data file P(x,y,t) in box  112 . In box  113 , data file P(x,y,t) is processed by one of the known approximation and filtration method, as described for example by J.-L. Stark, F. Murtagh and A. Bijaouiet,  Image Processing and Data Analysis,  Cambridge University Press (1998). In boxes  114 ,  115 , and  116  the data is further analyzed and phase correlations, spectral composition of the signals, and spatial and temporal derivatives of the signals are evaluated and forwarded to box  117  for evaluating mechanical and geometrical features of the breast. Based on mechanical and geometrical parameters the state of the examined breast is estimated in box  118  and compared to the “normal state” using information from global data base from box  127 . When the deviation of the state of the breast from the “normal state” exceeds a predetermined level, the device produces an alarm signal in box  121 . Information on every particular examination is collected in the personal data base in box  119 . After accumulating sufficient data on the states of the particular breast the system generates an adjusted personalized definition of the “normal state” and subsequently, the detection of the anomalous development significantly improves.  
         [0053]    [0053]FIG. 12A is a sectional view showing the force sensor assembly  76  pressed against a tissue phantom  123  with a hard inclusion  122 . Oscillating the probe over the phantom enables detecting the hidden nodules and evaluating their parameters: the diameter, hardness and depth.  
         [0054]    [0054]FIG. 12B is a graphical representation of time dependence of signals from the force sensors in one row of the array in the process of the experiment shown in FIG. 12A. The difference in the time profiles of signals from the sensors located at different positions with regard to the nodule, as seen in records  125  and  126 , allows detecting and evaluating parameters of nodules.  
         [0055]    [0055]FIG. 12C is a different graphical representation of the data presented in FIG. 12B showing clearly the trace  128  formed by the inclusion on the time dependence of the force pattern. FIGS. 12B and 12C illustrate sensitivity of temporal and spatial derivatives of the force sensor array signals to the presence of mechanical heterogeneity such as a hard nodule in the examined tissue.  
         [0056]    [0056]FIG. 13 is a graphical representation of amplitude of the first harmonic A 1  for the data of FIG. 12C. Presence of the nodule results in the appearance of two distinctly expressed peaks  132  and  133 .  
         [0057]    [0057]FIG. 14 is a topographic representation of amplitude of the first harmonic obtained from the same data as in FIG. 13. The location of the nodule is shown by dotted circle  143 .  
         [0058]    [0058]FIG. 15 shows a spatial distribution of the amplitude of the second harmonic A 2  of the oscillatory signals shown in FIG. 12C. Presence of the nodule is clearly revealed by maximum  152  of the second harmonic with two characteristic shoulders  153  and  154  at the position of the first harmonic maxima shown in FIG. 13.  
         [0059]    [0059]FIG. 16 is a topographic representation of the data shown in FIG. 15. The nodule located in the region shown by the circle  143  is detected without any ambiguity from the pattern of the second harmonic distribution with maximum  153  and shoulders  153  and  154 .  
         [0060]    [0060]FIG. 17 is a graphical representation of the phase shift of the first harmonic for force signals calculated from the data of FIG. 12C. In the vicinity of the location of the nodule the phase of the oscillatory signal experiences significant changes. The phase of the signal changes up to 180° from region  173  to region  174  having the steepest slope at the location of the nodule, as it is seem more clearly in FIG. 18.  
         [0061]    [0061]FIG. 18 is a topographic representation of a phase shift of the first harmonic showing the same data as FIG. 17. Phase inversion is observed while moving along the row of the sensors from region  172  to region  182  located on two opposite sides of the nodule located at the region denoted by the circle  143 . The phase inflection point  183  corresponds to the exact location of the nodule.  
         [0062]    FIGS.  12 - 18  clearly illustrate the possibility to use dynamic features of the oscillatory signals from the force sensor array to detect hard inclusions imbedded in the soft tissue.  
         [0063]    Although certain presently preferred embodiments of the present invention have been specifically described herein, it will be apparent to those skilled in the art to which the invention pertains that variations and modifications of the various embodiments shown and described herein may be made without departing from the spirit and scope of the invention.