Patent Publication Number: US-2023148893-A1

Title: Bisymmetric Comparison of Sub-Epidermal Moisture Values

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. Nonprovisional Application 15/887,831 filed Feb. 2, 2018, which claims the benefit of priority of U.S. Provisional Application 62/454,455 filed Feb. 3, 2017, and U.S. Provisional Application 62/521,871 filed Jun. 19, 2017, each of which is herein incorporated by reference in its entirety. 
    
    
     FIELD 
     The present disclosure provides apparatuses and computer readable media for measuring sub-epidermal moisture in patients to identify damaged tissue for clinical intervention. The present disclosure also provides methods for determining damaged tissue. 
     BACKGROUND 
     The skin is the largest organ in the human body. It is readily exposed to different kinds of damages and injuries. When the skin and its surrounding tissues are unable to redistribute external pressure and mechanical forces, ulcers may be formed. Prolonged continuous exposure to even modest pressure, such as the pressure created by the body weight of a supine patient on their posterior skin surfaces, may lead to a pressure ulcer. In the presence of other damage, such as the neuropathy and peripheral tissue weakening that can be induced by diabetes, even periodic exposure to moderate levels of pressure and stress may lead to an ulcer, for example a foot ulcer. 
     Pressure ulcers are developed by approximately 2.5 million people a year in the United States and an equivalent number in the European Union. In long-term and critical-care settings, up to 25% of elderly and immobile patients develop pressure ulcers. Approximately 60,000 U.S. patients die per year due to infection and other complications from pressure ulcers. 
     Detecting tissue damage before the skin breaks and intervening with the appropriate therapy to avoid further deterioration of the underlying tissue is desirable not only for the patient but society. The average cost of treating pressure-induced damage at the earliest visible sign (a Stage 1 ulcer) is only $2,000 but this rises to $129,000 when the ulcer is deep enough to expose muscle or bone (a Stage 4 ulcer.) The current standard to detect pressure ulcers is by visual inspection, which is subjective, unreliable, untimely, and lacks specificity. 
     SUMMARY 
     In an aspect, the present disclosure provides for, and includes, an apparatus for identifying damaged tissue, the apparatus comprising: a first and a second sensors, where the sensors each comprises a first electrode and a second electrode, and where each of the sensors is configured to be placed against a patient’s skin; a circuit electronically coupled to the first and second electrodes and configured to measure an electrical property between the first and second electrodes of each of the sensors and provide information regarding the electrical property; a processor electronically coupled to the circuit and configured to receive the information from the circuit and convert the information into a sub-epidermal moisture (SEM) value; and a non-transitory computer-readable medium electronically coupled to the processor and comprising instructions stored thereon that, when executed on the processor, perform the step of: determining a difference between a first SEM value corresponding to the electrical property as measured by the first sensor at a first location on the patient’s skin and a second SEM value corresponding to the electrical property as measured by the second sensor at a second location on the patient’s skin, where the second location is bisymmetric relative to the first location. 
     In an aspect, an apparatus for identifying damaged tissue is provided by the present disclosure, the apparatus comprising: a substrate configured to be placed against a surface of a patient’s skin; a plurality of sensors that are disposed on the substrate at a respective plurality of positions, where each sensor comprises a pair of electrodes; a circuit electronically coupled to the pair of electrodes of each of the plurality of sensors and configured to measure an electrical property between the pairs of electrodes of a portion of the plurality of sensors and provide information regarding the measured electrical properties; a processor electronically coupled to the circuit and configured to receive the information regarding the electrical properties from the circuit and convert the plurality of electrical properties into a respective plurality of sub-epidermal moisture (SEM) values; and a non-transitory computer-readable medium electronically coupled to the processor and comprising instructions stored thereon that, when executed on the processor, perform the steps of: identifying from the plurality of SEM values a first sensor and a second sensor that are located at first and second positions that are bisymmetric with respect to the patient’s skin, and comparing a first SEM value that is associated with the first sensor with a second SEM value that is associated with the second sensor. 
     In one aspect, an apparatus for identifying damaged tissue is provided by the present disclosure, the apparatus comprising: an apparatus body; two sensors comprising a first sensor and a second sensor, where the two sensors are disposed on the apparatus body to allow simultaneous positioning of the first sensor on a first location on a patient’s skin and the second sensor on a second location bisymmetric relative to the first location; a circuit electronically coupled to each of the two sensors and configured to measure an electrical property from each of the two sensors; a processor electronically coupled to the circuit and is configured to receive a first electrical property measurement from a first location and a second electrical property measurement from a second location, and to convert the first electrical property measurement to a first SEM value and the second electrical property measurement into a second SEM value; a non-transitory computer-readable medium electronically coupled to the processor and contains instructions that, when executed on the processor, perform the step of determining a difference between the first SEM value and the second SEM value. 
     In an aspect, a method for identifying damaged tissue is provided by the present disclosure, the method comprising: obtaining a first sub-epidermal moisture (SEM) value from a first location on a patient’s skin; obtaining a second SEM value from a second location that is bisymmetric relative to the first location; determining a difference between a first SEM value and a second SEM value. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Aspects of the disclosure are herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and are for purposes of illustrative discussion of aspects of the disclosure. In this regard, the description and the drawings, considered alone and together, make apparent to those skilled in the art how aspects of the disclosure may be practiced. 
         FIG.  1 A  is an illustration of a plan view of a toroidal sensor. 
         FIG.  1 B  illustrates a cross-section of the toroidal sensor of  FIG.  1 A . 
         FIG.  1 C  illustrates an idealized field map created by the toroidal sensor of  FIG.  1 A  when activated. 
         FIG.  2 A  provides an example of a pair of bisymmetric locations on a sacral region according to the present disclosure. 
         FIG.  2 B  provides an example of a pair of bisymmetric locations on the bottom side of both feet according to the present disclosure. 
         FIG.  2 C  provides an example of a pair of bisymmetric locations on the lateral sides and soles of both feet according to the present disclosure. 
         FIG.  3    is an illustration of an apparatus comprising one coaxial sensor. 
         FIG.  4 A  is a first exemplary apparatus comprising two sensors according to the present disclosure. 
         FIG.  4 B  is a second exemplary apparatus comprising two sensors and is configured to determine SEM values at bisymmetric locations according to the present disclosure. 
         FIG.  5    is an exemplary apparatus comprising a plurality of sensors according to the present disclosure. 
         FIG.  6    is a first exemplary array of electrodes. 
         FIG.  7    is an exemplary array of electrodes according to the present disclosure. 
         FIG.  8 A  illustrates a first example of how the array of electrodes disclosed in  FIG.  7    is configured to form a sensor according to the present disclosure. 
         FIG.  8 B  illustrates a second example of how the array of electrodes disclosed in  FIG.  7    is configured to form a sensor according to the present disclosure. 
         FIG.  9 A  illustrates an example of a first sensor formed in an array of electrodes according to the present disclosure. 
         FIG.  9 B  illustrates an example of how a second sensor is formed to overlap with the first sensor of  FIG.  9 A  according to the present disclosure. 
         FIG.  10    shows an example of how sensors as shown in  FIG.  8 A  are formed from an array of electrodes that is larger than the portion of the patient’s skin that is being positioned against the array, according to the present disclosure. 
         FIG.  11 A  illustrates locations on the left and right feet for SEM measurements according to the present disclosure. 
         FIG.  11 B  is a plot of SEM values associated with known relative locations for identifying bisymmetric locations according to the present disclosure. 
         FIG.  12 A  shows an exemplary configuration of a substrate shaped to be positioned in a known position on a patient’s skin according to the present disclosure. 
         FIG.  12 B  shows a front view of the exemplary configuration of  FIG.  12 A  according to the present disclosure. 
         FIG.  13    depicts an integrated system for measurement, evaluation, storage, and transfer of SEM values, according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     This description is not intended to be a detailed catalog of all the different ways in which the disclosure may be implemented, or all the features that may be added to the instant disclosure. For example, features illustrated with respect to one embodiment may be incorporated into other embodiment, and features illustrated with respect to a particular embodiment may be deleted from that embodiment. Thus, the disclosure contemplates that in some embodiments of the disclosure, any feature or combination of features set forth herein can be excluded or omitted. In addition, numerous variations and additions to the various embodiments suggested herein will be apparent to those skilled in the art in light of the instant disclosure, which do not depart from the instant disclosure. In other instances, well-known structures, interfaces, and processes have not been shown in detail in order not to unnecessarily obscure the invention. It is intended that no part of this specification be construed to effect a disavowal of any part of the full scope of the invention. Hence, the following descriptions are intended to illustrate some particular embodiments of the disclosure, and not to exhaustively specify all permutations, combinations and variations thereof. 
     Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The terminology used in the description of the disclosure herein is for the purpose of describing particular aspects or embodiments only and is not intended to be limiting of the disclosure. 
     All publications, patent applications, patents and other references cited herein are incorporated by reference in their entireties for the teachings relevant to the sentence and/or paragraph in which the reference is presented. References to techniques employed herein are intended to refer to the techniques as commonly understood in the art, including variations on those techniques or substitutions of equivalent techniques that would be apparent to one of skill in the art. 
     U.S. Pat. Application Serial No. 14/827,375 discloses an apparatus that uses radio frequency (RF) energy to measure the sub-epidermal capacitance using a bipolar sensor similar to the sensor  90  shown in  FIG.  1   , where the sub-epidermal capacitance corresponds to the moisture content of the target region of skin of a patient. The ‘375 application also discloses an array of these bipolar sensors of various sizes. 
     U.S. Pat. Application Serial No. 15/134,110 discloses an apparatus for measuring sub-epidermal moisture (SEM) similar to the device shown in  FIG.  3   , where the device emits and receives an RF signal at a frequency of 32 kHz through a single coaxial sensor and generates a bioimpedance signal, then converts this signal to a SEM value. 
     Both U.S. Pat. Application Serial Nos. 14/827,375 and 15/134,110 are incorporated herein by reference in their entireties. 
     Unless the context indicates otherwise, it is specifically intended that the various features of the disclosure described herein can be used in any combination. Moreover, the present disclosure also contemplates that in some embodiments of the disclosure, any feature or combination of features set forth herein can be excluded or omitted. 
     The methods disclosed herein include and comprise one or more steps or actions for achieving the described method. The method steps and/or actions may be interchanged with one another without departing from the scope of the present invention. In other words, unless a specific order of steps or actions is required for proper operation of the embodiment, the order and/or use of specific steps and/or actions may be modified without departing from the scope of the present invention. 
     As used in the description of the disclosure and the appended claims, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. 
     As used herein, “and/or” refers to and encompasses any and all possible combinations of one or more of the associated listed items, as well as the lack of combinations when interpreted in the alternative (“or”). 
     The terms “about” and “approximately” as used herein when referring to a measurable value such as a length, a frequency, or a SEM value and the like, is meant to encompass variations of ± 20%, ± 10%, ± 5%, ± 1%, ± 0.5%, or even ± 0.1% of the specified amount. 
     As used herein, phrases such as “between X and Y” and “between about X and Y” should be interpreted to include X and Y. As used herein, phrases such as “between about X and Y” mean “between about X and about Y” and phrases such as “from about X to Y” mean “from about X to about Y.” 
     As used herein, the term “sub-epidermal moisture” or “SEM” refers to the increase in tissue fluid and local edema caused by vascular leakiness and other changes that modify the underlying structure of the damaged tissue in the presence of continued pressure on tissue, apoptosis, necrosis, and the inflammatory process. 
     As used herein, a “system” may be a collection of devices in wired or wireless communication with each other. 
     As used herein, “interrogate” refers to the use of radiofrequency energy to penetrate into a patient’s skin. 
     As used herein, a “patient” may be a human or animal subject. 
     As used herein, “bisymmetric” refers to a pair of locations that are approximately equidistant from a line of symmetry. 
     As used herein, “delta” refers to a calculated difference between two SEM values. 
       FIG.  1 A  is a plan view of a toroidal sensor  90  comprising a center electrode  110  and a ring electrode  120 . In an aspect, electrodes  110  and  120  are disposed on a common surface of a substrate  100 , as depicted in the cross-section of sensor  90  shown in  FIG.  1 B . In one aspect, substrate  100  is rigid, for example a sheet of FR4 printed circuit board (PCB). In an aspect, substrate  100  is flexible, for example a sheet of polyimide. In one aspect, substrate  100  is a combination of rigid and flexible elements. In an aspect, electrodes  110  and  120  are covered with a cover layer  130  that is non-conductive so as to isolate electrodes  110  and  120  from each other and/or from external contact. In one aspect, portions of cover layer  130  are directionally conductive, enabling electrodes  110  and  120  to be in electrical contact with an object disposed on cover layer  130  while remaining electrically isolated from adjacent electrodes. In an aspect, cover layer  130  is rigid and planar, thereby providing a flat external surface. In one aspect, cover layer  130  conforms to the underlying electrodes  110  and  120  and substrate  100  such that there is no gap or air space between substrate  100  and cover layer  130 . When an electric voltage is applied across electrodes  110  and  120 , an electric field  140  is generated between electrodes  110  and  120  that extends outward from the plane of electrodes  110  and  120  to a distance  150 , also referred to the depth of field, as shown in  FIG.  1 C . The diameter of center electrode  110 , the inner and outer diameters of ring electrode  120 , and the gap between electrodes  110  and  120  may be varied to change characteristics of field  140 , for example the depth of field  150 . 
       FIG.  2 A  depicts the sacral region of the back of a patient  10 . A line of symmetry  12  can be drawn down the center of the back, dividing the back into left and right mirror images. Locations  14  are approximately the same distance from line of symmetry  12  and approximately at the same height and are, therefore, considered to be bisymmetric locations on the back of patient  10 . 
       FIG.  2 B  depicts left foot  20 L and right foot  20 R of a patient  10 , as seen if patient  10  were lying on the back on a bed (not shown) and an observer were standing at the foot of the bed. With respect to soles  22 L and  22 R of feet  20 L and  20 R, locations  24 L and  24 R are located at approximately equivalent locations, e.g. the same distance from the posterior surface, i.e. the heel, and the same distance from the medial side of respective foot  20 L or  20 R and are considered to be bisymmetric locations. 
       FIG.  2 C  depicts additional exemplary bisymmetric locations  26 L and  26 R located on the lateral sides of feet  20 L and  20 R, and bisymmetric locations  28 L and  28 R located on respective soles  22 L and  22 R of feet  20 L and  20 R. In an aspect, locations  26 R and  30 R are considered bisymmetric with respect to foot  20 R when considered alone without reference to foot  20 L. 
     Without being limited to a particular theory, comparison of SEM measurements taken at bisymmetric locations can compensate for an offset of readings of a particular patient from a population of patients. For example, a patient may be dehydrated on a particular day when measurements are being made. A comparison of the SEM value of healthy tissue from the same patient, while in a dehydrated condition, may be shifted from the SEM value of the same tissue at the same location when the patient is fully hydrated. If the tissue at one location is healthy while the tissue at the bisymmetric location is damaged, a comparison of the readings taken at the bisymmetric locations will exclude the “common mode” effect of dehydration on both locations and provide a more robust indication that tissue is damaged at one location. 
       FIG.  3    depicts exemplary SEM measurement apparatus  170  comprising one toroidal sensor  174  disposed on underside  172  of an apparatus body. Apparatus  170  may be used to take measurements at multiple locations, for example a first measurement at a first location and a second measurement at a second location that is bisymmetric relative to the first location. In an aspect, apparatus  170  comprises a processor that can be configured by instructions stored on a non-transitory computer-readable medium to determine a characteristic of the measurements taken at multiple locations or parameters associated with or derived from the measurements, for example one or more of a difference between, an average of, or a difference of each from a common average of SEM values respectively derived from multiple measurements. In one aspect, apparatus  170  comprises a display configured to show one or more parameters associated with the measurements, for example a delta between SEM values derived from measurements taken at two bisymmetric locations. 
       FIG.  4 A  depicts an exemplary SEM measurement apparatus  180  comprising two sensors  184 A and  184 B located at separate locations on apparatus body  182 , according to the present disclosure. An example usage would be to place apparatus  180  against a patient’s body (not shown) so as to simultaneously position first sensor  184 A at a first location and position second sensor  184 B at a second location, both on the surface of a patient’s skin. In an aspect, apparatus body  182  is rigid and maintains sensors  184 A and  184 B at a fixed separation distance and fixed orientation to each other. In one aspect, sensors  184 A and  184 B are aligned on a common plane, as shown in  FIG.  4 A . In an aspect, apparatus body  182  is flexible such that sensors  184 A and  184 B may be oriented at an angle to each other. In one aspect, one or more of sensors  184 A and  184 B are movable such the angle between a movable sensor and the other sensor may be varied. 
     In use, apparatus  180  can measure an electrical property or parameter that comprises one or more electrical characteristics selected from the group consisting of a resistance, a capacitance, an inductance, an impedance, a reluctance, and other electrical characteristics with one or more sensors  184 A and  184 B. In an aspect, sensors  184 A and  184 B are configured as toroidal sensors such as shown in  FIG.  1 A , with center electrode  110  and ring electrode  120 . In one aspect, sensors  184 A and  184 B are provided in other configurations as discussed in this application. In an aspect, sensors  184 A and  184 B comprise an electrical ground plane (not shown) that is proximate to and separated from a portion of electrodes  110  and  120 . In one aspect, a ground plane shields electrodes  110  and  120  from interference or modifies the shape of the field (similar in concept to field  140  of  FIG.  1 C ) of sensors  184 A and  184 B. In an aspect, a ground plane is disposed on a side of a substrate that is opposite the side on which electrodes  110  and  120  are disposed. In one aspect, apparatus  180  comprises a circuit (not shown) is electronically coupled to electrodes  110  and  120  of each sensor  184 A and  184 B and configured to measure an electrical property between electrodes  110  and  120 . In an aspect, a ground plane is coupled to a ground or an equivalent floating reference of a circuit. In one aspect, a circuit is configured to determine and provide information regarding the measured electrical property. In an aspect, apparatus  180  takes the measurements with sensors  184 A and  184 B essentially simultaneously. In one aspect, apparatus  180  takes the measurements in sequence with a time interval between the measurements that ranges from zero to one second or more. In an aspect, a measurement by apparatus  180  is triggered by actuation of a button (not visible in  FIG.  4 A ) or an actuator. In one aspect, a measurement by apparatus  180  is triggered automatically based on input from a switching element (not shown in  FIG.  4 A ) that is part of apparatus  180 , for example a contact sensor, a pressure sensor, an optical sensor, or other type of proximity-detecting device that is positioned, in an aspect, proximate to one or more of sensors  184 A and  184 B. In one aspect, multiple switching elements have to be simultaneously activated to provide the input to take the measurement. 
     In an aspect, apparatus  180  comprises a processor (not shown) that is coupled to a circuit and receives information about a measured electrical property from the circuit. In one aspect, information is in the form of an analog signal, e.g. an electrical voltage, or a digital signal. In an aspect, a processor is coupled directly to sensors  184 A and  184 B, and is configured to measure the electrical property directly. In one aspect, a processor is configured to convert the received electrical property into an SEM value. In an aspect, a processor is configured by machine-readable instructions that are stored on a non-transitory, computer-readable medium that is electronically coupled to the processor. In one aspect, instructions are loaded from a medium into a processor when apparatus  180  is powered on. 
     In an aspect, a measured electrical parameter is related to the moisture content of the epidermis of a patient at a depth that is determined by the geometry of the electrodes of sensors  184 A and  184 B, the frequency and strength of electrical field  140 , with reference to  FIG.  1 C , that is created by sensors  184 A and  184 B, and other operating characteristics of apparatus  180 . In one aspect, the moisture content is equivalent to the SEM content with a value on a predetermined scale. In an aspect, a predetermined scale may range from 0 to 20, such as from 0 to 1, from 0 to 2, from 0 to 3, from 0 to 4, from 0 to 5, from 0 to 6, from 0 to 7, from 0 to 8, from 0 to 9, from 0 to 10, from 0 to 11, from 0 to 12, from 0 to 13, from 0 to 14, from 0 to 15, from 0 to 16, from 0 to 17, from 0 to 18, from 0 to 19. In one aspect, a predetermined scaled can be scaled by a factor or a multiple based on the values provided herein. In an aspect, multiple measurements are taken while varying one or more of operating characteristics between readings, thereby providing information related to the moisture content at various depths of the skin. 
     In an aspect, measurements of capacitance are taken simultaneously with sensors  184 A and  184 B when contact sensors (not visible in  FIG.  4 A ) determine that sensors  184 A and  184 B are in proper contact with two bisymmetric locations on a patient’s skin. In an aspect, simultaneous capacitance measurements are compared to each other so as to determine whether the tissue under one of the bisymmetric locations is damaged. In one aspect, capacitance measurements are individually converted into SEM values that correspond to the moisture content of the tissue that is proximate to respective sensors  184 A  and  184 B and the SEM values compared. In an aspect, a comparison is performed using equivalent voltages, capacitance values, or other intermediate signals. 
     In one aspect, a difference between SEM values is determined, where a difference that exceeds a predetermined threshold is indicative of tissue damage at one of the locations where the corresponding capacitance measurements were taken. In an aspect, means of SEM values obtained at each bisymmetric locations are determined and compared. In one aspect, medians or modes of SEM values obtained at each bisymmetric locations are determined and compared. In an aspect, the damage is indicated to be at the location associated with the larger of the SEM values. In one aspect, the damage is indicated to be at the location associated with the smaller of the SEM values. In an aspect, determination of whether there is tissue damage comprises one or more of comparison of individual SEM values with one or more predetermined ranges or thresholds and comparison of the difference with one or more predetermined ranges or thresholds. In an aspect, a predetermined range may be from 0.1 to 8.0, such as from 0.1 to 1.0, from 1.1 to 2.0, from 2.1 to 3.0, from 3.1 to 4.0, from 4.1 to 5.0, from 5.1 to 6.0, from 6.1 to 7.0, from 7.1 to 8.0, from 0.1 to 7.5, from 0.5 to 8.0, from 1.0 to 7.0, from 1.5 to 6.5, from 2.0 to 6.0, from 3.0 to 5.5, from 3.5 to 5.0, or from 4.0 to 4.5. In an aspect, a predetermined range may be from 0.1 to 4.0, such as from 0.5 to 4.0, from 0.1 to 3.5, from 1.0 to 3.5, from 1.5 to 4.0, from 1.5 to 3.5, from 2.0 to 4.0, from 2.5 to 3.5, from 2.0 to 3.0, from 2.0 to 2.5, or from 2.5 to 3.0. In one aspect, a predetermined range may be from 4.1 to 8.0, such as from 4.5 to 8.0, from 4.1 to 7.5, from 5.0 to 7.5, from 5.5 to 7.0, from 5.5 to 7.5, from 6.0 to 8.0, from 6.5 to 7.5, from 6.0 to 7.0, from 6.0 to 6.5, or from 6.5 to 7.0. In one aspect, a predetermined threshold may be about 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5.0, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9, 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, 7.0, 7.1, 7.2, 7.3, 7.4, or 7.5. In one aspect, a predetermined threshold may range from 0.1 to 8.0, such as from 0.1 to 1.0, from 1.1 to 2.0, from 2.1 to 3.0, from 3.1 to 4.0, from 4.1 to 5.0, from 5.1 to 6.0, from 6.1 to 7.0, from 7.1 to 8.0, from 0.1 to 7.5, from 0.5 to 8.0, from 1.0 to 7.0, from 1.5 to 6.5, from 2.0 to 6.0, from 3.0 to 5.5, from 3.5 to 5.0, or from 4.0 to 4.5. In an aspect, a predetermined range or threshold can be scaled by a factor or a multiple based on the values provided herein. It will be understood that a predetermined value is not limited by design, but rather, one of ordinary skill in the art would be capable of choosing a predetermined value based on a given unit of SEM. In one aspect, ranges and thresholds of the present disclosure are varied according to the specific bisymmetric locations, the portion of a patient’s body on which measurements are being made, or one or more characteristics of the patient such as age, height, weight, family history, ethnic group, and other physical characteristics or medical conditions. 
     One or more regions may be defined on a body. In an aspect, measurements made within a region are considered comparable to each other. A region may be defined as an area on the skin of the body wherein measurements may be taken at any point within the area. In an aspect, a region corresponds to an anatomical region (e.g., heel, ankle, lower back). In an aspect, a region may be defined as a set of two or more specific points relative to anatomical features wherein measurements are taken only at the specific points. In an aspect, a region may comprise a plurality of non-contiguous areas on the body. In an aspect, the set of specific locations may include points in multiple non-contiguous areas. 
     In an aspect, a region is defined by surface area. In an aspect, a region may be, for example, between 5 and 200 cm 2 , between 5 and 100 cm 2 , between 5 and 50 cm 2 , or between 10 and 50 cm 2 , between 10 and 25 cm 2 , or between 5 and 25 cm 2 . 
     In an aspect, measurements may be made in a specific pattern or portion thereof. In an aspect, the pattern of readings is made in a pattern with the target area of concern in the center. In an aspect, measurements are made in one or more circular patterns of increasing or decreasing size, T-shaped patterns, a set of specific locations, or randomly across a tissue or region. In an aspect, a pattern may be located on the body by defining a first measurement location of the pattern with respect to an anatomical feature with the remaining measurement locations of the pattern defined as offsets from the first measurement position. 
     In an aspect, a plurality of measurements are taken across a tissue or region and the difference between the lowest measurement value and the highest measurement value of the plurality of measurements is recorded as a delta value of that plurality of measurements. In an aspect, 3 or more, 4 or more, 5 or more, 6 or more, 7 or more, 8 or more, 9 or more, or 10 or more measurements are taken across a tissue or region. 
     In an aspect, a threshold may be established for at least one region. In an aspect, a threshold of 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or other value may be established for the at least one region. In an aspect, a delta value is identified as significant when the delta value of a plurality of measurements taken within a region meets or exceeds a threshold associated with that region. In an aspect, each of a plurality of regions has a different threshold. In an aspect, two or more regions may have a common threshold. 
     In an aspect, a threshold has both a delta value component and a chronological component, wherein a delta value is identified as significant when the delta value is greater than a predetermined numerical value for a predetermined portion of a time interval. In an aspect, the predetermined portion of a time interval is defined as a minimum of X days wherein a plurality of measurements taken that day produces a delta value greater than or equal to the predetermined numerical value within a total of Y contiguous days of measurement. In an aspect, the predetermined portion of a time interval may be defined as 1, 2, 3, 4, or 5 consecutive days on which a plurality of measurements taken that day produces a delta value that is greater than or equal to the predetermined numerical value. In an aspect, the predetermined portion of a time interval may be defined as some portion of a different specific time period (weeks, month, hours etc.). 
     In an aspect, a threshold has a trending aspect wherein changes in the delta values of consecutive pluralities of measurements are compared to each other. In an aspect, a trending threshold is defined as a predetermined change in delta value over a predetermined length of time, wherein a determination that the threshold has been met or exceeded is significant. In an aspect, a determination of significance will cause an alert to be issued. In an aspect, a trend line may be computed from a portion of the individual measurements of the consecutive pluralities of measurements. In an aspect, a trend line may be computed from a portion of the delta values of the consecutive pluralities of measurements. 
     In an aspect, the number of measurements taken within a single region may be less than the number of measurement locations defined in a pattern. In an aspect, a delta value will be calculated after a predetermined initial number of readings, which is less than the number of measurement locations defined in a pattern, have been taken in a region and after each additional reading in the same region, wherein additional readings are not taken once the delta value meets or exceeds the threshold associated with that region. 
     In an aspect, the number of measurements taken within a single region may exceed the number of measurement locations defined in a pattern. In an aspect, a delta value will be calculated after each additional reading. 
     In an aspect, a quality metric may be generated for each plurality of measurements. In an aspect, this quality metric is chosen to assess the repeatability of the measurements. In an aspect, this quality metric is chosen to assess the skill of the clinician that took the measurements. In an aspect, the quality metric may include one or more statistical parameters, for example an average, a mean, or a standard deviation. In an aspect, the quality metric may include one or more of a comparison of individual measurements to a predefined range. In an aspect, the quality metric may include comparison of the individual measurements to a pattern of values, for example comparison of the measurement values at predefined locations to ranges associated with each predefined location. In an aspect, the quality metric may include determination of which measurements are made over healthy tissue and one or more evaluations of consistency within this subset of “healthy” measurements, for example a range, a standard deviation, or other parameter. 
     In one aspect, a measurement, for example, a threshold value, is determined by SEM Scanner Model 200 (Bruin Biometrics, LLC, Los Angeles, CA). In another aspect, a measurement is determined by another SEM scanner. 
     In an aspect, a measurement value is based on a capacitance measurement by reference to a reference device. In an aspect, a capacitance measurement can depend on the location and other aspects of any electrode in a device. Such variations can be compared to a reference SEM device such as an SEM Scanner Model 200 (Bruin Biometrics, LLC, Los Angeles, CA). A person of ordinary skill in the art understands that the measurements set forth herein can be adjusted to accommodate a difference capacitance range by reference to a reference device. 
     In an aspect, apparatus  180  is capable of storing multiple measurement and computation results. In one aspect, an apparatus in accordance with the present disclosure may also comprise other components, for example a camera or barcode scanner (not visible in  FIG.  4 A ), and may be capable of storing the output of that component. In an aspect, apparatus  180  comprises components (not visible in  FIG.  4 A ) to transfer the stored data, for example via a Bluetooth, WiFi, or Ethernet connection, to another device, for example a personal computer, server, tablet, or smart phone such as depicted in  FIG.  13   . 
       FIG.  4 B  depicts another aspect of an apparatus  186  that is configured to determine SEM values at bisymmetric locations. In an aspect, apparatus  186  comprises a hinge  188  such the separation distance between sensors  187 A and  187 B may be varied. In one aspect, sensors  184 A and  184 B are aligned with respect to apparatus body elements  186 A and  186 B to achieve a desired relative orientation, for example parallel to each other, at a predetermined separation distance. In an aspect, one or more of sensors  187 A and  187 B are movable such the angle between the movable sensor and the other sensor may vary, for example to match the orientation of the skin under each of sensors  187 A and  187 B as apparatus  185  is closed around an ankle to position sensors  187 A and  187 B over locations  26 R and  30 R shown in  FIG.  2 C . 
       FIG.  5    depicts an exemplary mat assembly  190  comprising array  92  comprising a plurality of sensors  90 , according to the present disclosure. In one aspect, mat assembly  192  comprises a mat  200  on which sensors  90  are disposed. In an aspect, sensors  90  are embedded within mat  200 . In one aspect, sensors  90  are located on the top surface of mat  200 . In an aspect, sensors  90  have a cover layer (not visible in  FIG.  5   ) over them. In one aspect, sensors  90  comprise conductive electrodes that are exposed on their upper surface so as to create an electrical contact with an object proximate to the top of a mat, for example the feet of a patient standing on the mat. In an aspect, sensors  90  are toroidal sensors as shown in  FIG.  1 A . In one aspect, sensors  90  are of a single type and configuration. In an aspect, sensors  90  vary in size and type within array  92 . In one aspect, sensors  90  are of one or more alternate configurations, such as those discussed with respect to  FIGS.  6 ,  7 ,  8 A, and  8 B . In an aspect, mat assembly  190  is coupled to an electronics assembly  192  either directly or through a cable  194 . In one aspect, an electronics assembly  192  comprises a circuit (not visible in  FIG.  4 A ) coupled to electrodes of sensors  90  and a processor (not visible in  FIG.  4 A ) coupled to the circuit, as discussed previously with respect to apparatus  180 . 
     In an aspect, mat assembly  190  comprises one or more of pressure sensors, temperature sensors, optical sensors, and contact sensors (not visible in  FIG.  5   ) disposed at one or more respective locations across mat  200 . In one aspect, one or more measurements using sensors  90  are triggered by input from one or more of the pressure, temperature, optical, and contact sensors. 
     In an aspect, mat assembly  190  is configured as a floor mat and actuation of one or more of the pressure, temperature, optical, and contact sensors, for example detection of a person standing on mat assembly  190  due to detection of the weight of a person by a pressure sensor, initiates a measurement by one or more of sensors  90 . In one aspect, sensors  90  are operated in a “detection mode” that is capable of detecting when a person steps onto mat assembly  190  and transitions into a “measurement mode” upon determination that a person is standing on mat assembly  190 . 
     In an aspect, mat assembly  190  is configured as a portable apparatus that can be placed against a surface of a patient’s skin, for example against a patient’s back or against the soles of one or both of their feet while the patient is lying in bed. In one aspect, mat assembly  190  comprises one or more of a support tray, stiffening element, and conformal pad (not shown in  FIG.  5   ) to aid in placing sensors  90  against a surface of a patient’s skin. 
       FIG.  6    depicts an exemplary electrode array  290 , according to the present disclosure. Array  290  is composed of individual electrodes  300  disposed, in this example, in a regular pattern over a substrate  292 . In an aspect, each electrode  300  is separately coupled (through conductive elements not shown in  FIG.  6    through 8B) to a circuit, such as described with respect to  FIG.  4 A , that is configured to measure an electrical parameter. In one aspect, a “virtual sensor” is created by selective connection of predetermined subsets of electrodes  300  to a common element of a circuit. In this example, a particular electrode  310  is connected as the center electrode, similar to electrode  110  of  FIG.  1 A , and six electrodes  320 A– 320 F are connected together as a “virtual ring” electrode, similar to electrode  120  of  FIG.  1 A . In an aspect, two individual electrodes are individually connected to a circuit to form a virtual sensor, for example electrodes  310  and  320 A are respectively connected as the two electrodes of a sensor. In one aspect, one or more electrodes  300  are connected together to form one or the other of the electrodes of a two-electrode sensor. 
       FIG.  7    depicts another exemplary array  400  of electrodes  410 , according to the present disclosure. In this example, each of electrodes  410  is an approximate hexagon that is separated from each of the surrounding electrodes  410  by a gap  420 . In an aspect, electrodes  410  are one of circles, squares, pentagons, or other regular or irregular shapes. In one aspect, gap  420  is uniform between all electrodes  410 . In an aspect, gap  420  varies between various electrodes. In one aspect, gap  420  has a width that is narrower than the cross-section of each of electrodes  410 . In an aspect, electrodes  410  may be interconnected to form virtual sensors as described below with respect to  FIGS.  8 A and  8 B . 
       FIG.  8 A  depicts an array  400  of electrodes  410  that are configured, e.g. connected to a measurement circuit, to form an exemplary sensor  430 , according to the present disclosure. In one aspect, a single hexagonal electrode  410  that is labeled with a “1” forms a center electrode and a ring of electrodes  410  that are marked with a “2” are interconnected to form a ring electrode. In an aspect, electrodes  410  between the center and ring electrode are electrically “floating.” In one aspect, electrodes  410  between the center and ring electrode are grounded or connected to a floating ground. In an aspect, electrodes  410  that are outside the ring electrode are electrically “floating.” In one aspect, electrodes  410  that are outside the virtual ring electrode are grounded or connected to a floating ground. 
       FIG.  8 B  depicts an alternate aspect where array  400  of electrodes  410  has been configured to form a virtual sensor  440 , according to the present disclosure. In an aspect, multiple electrodes  410 , indicated by a “1,” are interconnected to form a center electrode while a double-wide ring of electrodes, indicated by a “2,” are interconnected to form a ring electrode. In one aspect, various numbers and positions of electrodes  410  are interconnected to form virtual electrodes of a variety of sizes and shapes. 
       FIGS.  9 A and  9 B  depict an exemplary configuration of an electrode array  400  that is capable of forming sensors  430  in multiple overlapping locations, according to the present disclosure. In  FIG.  9 A , a virtual sensor  430 A has been formed with center electrode  432   formed by a single electrode  410 , indicated by a “1,” and a ring electrode  434  formed by a plurality of electrodes  410 , indicated by a “2.” This same array  400  is shown in  FIG.  9 B , where a new virtual sensor  430 B has been formed with a center electrode  436 , indicated by a “3,” and ring electrode  438 , indicated by a “4.” The position of virtual sensor  430 A is shown by a dark outline. It can be seen that virtual sensor  430 B overlaps the position of virtual sensor  430 A, allowing measurements to be made at a finer resolution than the diameter of sensors  430 . 
       FIG.  10    shows how sensors  430  may be formed from an array of electrodes  400  that is larger than the portion of a patient’s skin that is being positioned against the array, according to the present disclosure. In this example, the outline of contact area  450  of sole  22 R of right foot  20 R of a patient  10 , as seen from underneath foot  20 R and with reference to  FIGS.  2 A- 2 C , is shown overlaid on array  400 . In this example, sensor  430 C has been formed in a location where a portion of sensor  430 C extends beyond the edge of contact area  450 . In such a position, capacitance or other electrical parameter measured by sensor  430 C is lower than capacitance measured by sensor  430 D, which is positioned completely within contact area  450 . It can be seen that a sensor  430  may be formed at any point within array  400  and, depending on the position of sensor  430 , may partially overlap the contact area at any level within a range of 0-100%. 
     In an aspect, two sensors may overlap 0-50%, such as 0-10%, 5-15%, 10-20%, 15-25%, 20-30%, 25-35%, 30-40%, 35%-45%, 40-50%, 0-25%, 15-35%, or 25-50%. In one aspect, two sensors may overlap 25-75%, such as 25-35%, 30-40%, 35%-45%, 40-50% 45-55%, 50-60%, 55-65%, 60-70%, 65-75%, 25-50%, 40-55%, or 50-75%. In one aspect, two sensors may overlap 50-100%, such as 50-60%, 55-65%, 60-70%, 65-75%, 70-80%, 75%-85%, 80-90%, 85-95%, 90-100%, 50-75%, 65-85%, or 75-100%. 
     In one aspect, an array of sensors  400  may further comprise a plurality of contact sensors (not shown on  FIG.  10   ) on the same planar surface as, and surrounding, each of the electrodes to ensure complete contact of the one or more virtual sensors to the skin surface. The plurality of contact sensors may be a plurality of pressure sensors, a plurality of light sensors, a plurality of temperature sensors, a plurality of pH sensors, a plurality of perspiration sensors, a plurality of ultrasonic sensors, a plurality of bone growth stimulator sensors, or a plurality of a combination of these sensors. In some embodiments, the plurality of contact sensors may comprise four, five, six, seven, eight, nine, or ten or more contact sensors surrounding each electrode. 
       FIGS.  11 A and  11 B  depict an example of how comparison of SEM values associated with sensors in known relative locations can identify bisymmetric locations, according to the present disclosure. In this example, sensors  430  are formed at nonoverlapping locations, marked “A” to “H” in  FIG.  11 A , across a contact area  450 R of a right foot  20 R. The SEM values measured at each location are plotted in the graph of  FIG.  11 B . In this example, the SEM value of locations “A” and “H” are low or zero, reflecting the non-overlap of sensor  430  with contact area  450  in those locations. The SEM values associated with locations “B” and “G” are higher, as sensor  430  overlaps a portion of contact area  450  in those positions. The SEM values for locations C-D-E-F are higher and, in this example, approximately the same, indicating that sensor  430  is completely within contact area  450  at those locations. In one aspect, an SEM measurement apparatus such as apparatus  180  may determine that certain locations, for example locations “C” and “F,” are bisymmetric with respect to a centerline  452 R of right foot  20 R. In an aspect, where a similar set of measurements is made at locations A′-H′ on left foot  20 L, a location on each foot  20 L and  20 R, for example locations E and E′, may be determined to be approximately bisymmetric. 
       FIGS.  12 A and  12 B  depict an exemplary aspect of a sensor assembly  500  configured to be placed in a known position on a patient’s skin, according to the present disclosure. In this example, sensor assembly  500  has a shaped substrate  510  that is configured to conform to posterior and bottom surfaces of heel of a foot 20. In an aspect, shaped substrate  510  may be suitable for use with both a left foot  20 L and a right foot  20 R. In an aspect, sensor assembly  500  comprises one or more sensors  520  disposed on the inner surface of a shaped substrate  510 . In this example, sensors  520  are configured as toroidal sensors as shown in  FIG.  1 A . In one aspect, the inner surface of a shaped substrate  510  is lined with an array  400  of electrodes  410 , with reference to  FIG.  7   , such that virtual sensors may be formed at any location. In an aspect, sensors of other shapes and configurations are provided on the inner surface of a shaped substrate  510 . In one aspect, shaped substrate  510  is a flexible panel (not shown in  FIG.  12 A ) that can be conformed to a patient’s skin, for example wrapped around the back of an ankle. In an aspect, sensor assembly  500  comprises a cable  530  to connect sensors  520  to one or more of a power source, a circuit configured to measure one or more of capacitance or other electrical property, a processor, a communication subsystem, or other type of electronic assembly (not shown in  FIG.  12 A ). 
       FIG.  12 B  depicts an exemplary configuration of sensor assembly  500  where multiple sensors  520  disposed on shaped substrate  510  such that, for example when sensor assembly  500  is placed against the skin of a patient around the back and bottom of the right heel, sensors  520  will be positioned in locations  26 R,  28 R, and  30 R, with reference to  FIG.  2 C , as well as on the center back of a heel. This enables multiple SEM measurements to be taken in repeatable location on a heel with sensor assembly  500  in a single position. In one aspect (not shown in  FIGS.  12 A and  12 B ), sensor assembly  500  is configured to be placed on a portion of the back of a patient thus providing the capability to make measurements at bisymmetric locations on the back. In an aspect, shaped substrate  510  is configured to match anatomical features of the target area of a patient. In an aspect, a shaped substrate  510  comprises markings or other indicators that can be aligned with features of a patient’s body, so as to enable measurements to be taken at the same location at time intervals over a period of time in the general range of hours to weeks. In one aspect, sensor assembly  500  is integrated into a lining of a garment or shoe or other article of clothing. In one aspect, sensor assembly  500  is integrated into a sheet, blanket, liner, or other type of bed clothing. In an aspect, sensor assembly  500  comprises a wireless communication capability, for example a passive radio frequency identification (RFID) or an inductive coupling, to allow actuation of sensors  520  without physically connecting to sensor assembly  500 . 
       FIG.  13    depicts a schematic depiction of an integrated system  600  for measurement, evaluation, storage, and transfer of SEM values, according to the present disclosure. In this example, system  600  comprises a SEM measurement apparatus  180 , as discussed with respect to  FIG.  4 A , that comprises the capability to wirelessly communicate with a WiFi access point  610 . Apparatus  180  communicates with one or more of a SEM application running on a server  640 , an application running on a laptop computer  620 , a smart phone  630 , or other digital device. In one aspect, laptop computer  620  and smart phone  630  are carried by a user of apparatus  180 , for example a nurse, and an application provides feedback and information to the user. In an aspect, information received from apparatus  180  for a patient is stored in a database  650 . In one aspect, information received from apparatus  180  is transferred over a network  645  to another server  660  that stores a portion of information in an electronic medical record (EMR)  670  of a patient. In one aspect, information from apparatus  180  or retrieved from database  650  or EMR  670  is transferred to an external server  680  and then to a computer  685 , for example a computer at the office of a doctor who is providing care for a patient. 
     From the foregoing, it will be appreciated that the present invention can be embodied in various ways, which include but are not limited to the following:
     Embodiment 1. An apparatus for identifying damaged tissue, the apparatus comprising: a first sensor and a second sensor, where the first and second sensors each comprises a first electrode and a second electrode, and where each of the sensors is configured to be placed against a patient’s skin, a circuit electronically coupled to the first and second electrodes and configured to measure an electrical property between the first and second electrodes of each of the sensors and provide information regarding the electrical property, a processor electronically coupled to the circuit and configured to receive the information from the circuit and convert the information into a sub-epidermal moisture (SEM) value, and a non-transitory computer-readable medium electronically coupled to the processor and comprising instructions stored thereon that, when executed on the processor, perform the step of: determining a difference between a first SEM value corresponding to the electrical property as measured by the first sensor at a first location on the patient’s skin and a second SEM value corresponding to the electrical property as measured by the second sensor at a second location on the patient’s skin, where the second location is bisymmetric relative to the first location.   Embodiment 2. The apparatus according to embodiment 1, where the difference being greater than a predetermined threshold is indicative of damaged tissue at one of the first and second locations.   Embodiment 3. The apparatus according to embodiment 1, where: the circuit is electronically coupled to the first and second electrodes of each of the first and second sensors, and the circuit is configured to convert a first electrical property measured with the first sensor into the first SEM value and convert a second electrical property measured with the second sensor into the second SEM value.   Embodiment 4. The apparatus according to embodiment 2, further comprising: a substrate configured to be placed in a known position on the patient’s skin, and the first and second sensors are disposed on the substrate such that the first and second sensors are positioned at bisymmetric locations on the patient’s skin when the substrate is placed in the known position on the patient’s skin.   Embodiment 5. The apparatus according to embodiment 1, further comprising a gap between the first and second electrodes.   Embodiment 6. The apparatus according to embodiment 1, where the electrical property comprises one or more of an electrical component selected from the group consisting of a resistance, a capacitance, an inductance, an impedance, and a reluctance.   Embodiment 7. An apparatus for identifying damaged tissue, the apparatus comprising: a substrate configured to be placed against a surface of a patient’s skin, a plurality of sensors that are disposed on the substrate at a respective plurality of positions, where each sensor comprises a pair of electrodes, a circuit electronically coupled to the pair of electrodes of each of the plurality of sensors and configured to measure an electrical property between the pairs of electrodes of a portion of the plurality of sensors and provide information regarding the measured electrical properties, a processor electronically coupled to the circuit and configured to receive the information regarding the electrical properties from the circuit and convert the plurality of electrical properties into a respective plurality of sub-epidermal moisture (SEM) values, and a non-transitory computer-readable medium electronically coupled to the processor and comprising instructions stored thereon that, when executed on the processor, perform the steps of: identifying from the plurality of SEM values a first sensor and a second sensor that are located at first and second positions that are bisymmetric with respect to the patient’s skin, and comparing a first SEM value that is associated with the first sensor with a second SEM value that is associated with the second sensor.   Embodiment 8. The apparatus according to embodiment 7, where the instructions further comprise the steps of: determining a difference between the first and second SEM values, and providing an indication that tissue is damaged at one of the first and second locations if the difference is greater than a predetermined threshold.   Embodiment 9. The apparatus according to embodiment 7, where the instructions further comprise the steps of: determining a difference between the first and second SEM values, determining which of the first and second SEM values is larger than the other, and providing an indication that tissue is damaged at the location associated with the larger SEM value if the difference is greater than a predetermined threshold.   Embodiment 10. The apparatus according to embodiment 7, where the electrical property comprises one or more of an electrical component selected from the group consisting of a resistance, a capacitance, an inductance, an impedance, and a reluctance.   Embodiment 11. An apparatus for identifying damaged tissue, the apparatus comprising: an apparatus body; two sensors comprising a first sensor and a second sensor, where the two sensors are disposed on the apparatus body to allow simultaneous positioning of the first sensor on a first location on a patient’s skin and the second sensor on a second location bisymmetric relative to the first location; a circuit electronically coupled to each of the two sensors and configured to measure an electrical property from each of the two sensors; a processor electronically coupled to the circuit and is configured to receive a first electrical property measurement from a first location and a second electrical property measurement from a second location, and to convert the first electrical property measurement to a first sub-epidermal moisture (SEM) value and the second electrical property measurement to a second SEM value; a non-transitory computer-readable medium electronically coupled to the processor and contains instructions that, when executed on the processor, perform the step of determining a difference between the first SEM value and the second SEM value.   Embodiment 12. The apparatus according to embodiment 11, where each of the two sensors are disposed on two ends of the apparatus body while being aligned on a common plane.   Embodiment 13. The apparatus according to embodiment 11, where the apparatus body is rigid and maintains the two sensors at a fixed separation distance and fixed orientation to each other.   Embodiment 14. The apparatus according to embodiment 11, where the apparatus body is flexible and allows the two sensors to be oriented at an angle to each other.   Embodiment 15. The apparatus according to embodiment 14, where the apparatus body comprises a hinge.   Embodiment 16. The apparatus according to embodiment 11, where each of the two sensors comprises a first electrode and a second electrode separated by a gap.   Embodiment 17. The apparatus according to embodiment 16, where the electrical property is measured between the first electrode and the second electrode.   Embodiment 18. The apparatus according to embodiment 11, where each of the two sensors comprises a plurality of electrodes separated by a gap.   Embodiment 19. The apparatus according to embodiment 18, where the plurality of electrodes are selectively activated to form a virtual ring electrode and a virtual central electrode.   Embodiment 20. The apparatus according to embodiment 11, where the electrical property comprises one or more of an electrical characteristic selected from the group consisting of a resistance, a capacitance, an inductance, an impedance, and a reluctance.   Embodiment 21. The apparatus according to embodiment 11, where the first electrical property measurement and the second electrical property measurement are measured simultaneously.   Embodiment 22. The apparatus according to embodiment 21, where the apparatus further comprises a contact sensor positioned proximate to one of the two sensors, and where the simultaneous measurements are triggered by the actuation of the contact sensor.   Embodiment 23. The apparatus according to embodiment 22, where the contact sensor is a pressure sensor or an optical sensor.   Embodiment 24. The apparatus according to embodiment 11, where the instructions further comprise the step of providing an indication that tissue is damaged at one of the first and second locations if the difference is greater than a predetermined threshold.   Embodiment 25. The apparatus according to embodiment 11, where the instructions further comprise the steps of: determining the greater of the first and second SEM values, and providing an indication that tissue is damaged at the location associated with the greater SEM value if the difference exceeds a predetermined threshold.   Embodiment 26. A method for identifying damaged tissue, the method comprising: obtaining a first sub-epidermal moisture (SEM) value from a first location on a patient’s skin; obtaining a second SEM value from a second location that is bisymmetric relative to the first location; determining a difference between the first SEM value and the second SEM value.   Embodiment 27. The method according to embodiment 26, further comprising providing an indication that tissue is damaged at one of the first and second locations if the difference is greater than a predetermined threshold.   Embodiment 28. The method according to embodiment 26, further comprising: determining the greater of the first and second SEM values, and providing an indication that tissue is damaged at the location associated with the greater SEM value if the difference exceeds a predetermined threshold.   

     While the invention has been described with reference to particular aspects, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to a particular situation or material to the teachings of the invention without departing from the scope of the invention. Therefore, it is intended that the invention not be limited to the particular aspects disclosed but that the invention will include all aspects falling within the scope and spirit of the appended claims.