Patent Publication Number: US-10772523-B2

Title: Non-invasive system and method of spatial localization of specific electrocardiac elements

Description:
RELATED APPLICATIONS 
     This is a continuation-in-part of International Application PCT/US16/36478 titled Non-Invasive System and Method of Spatial Localization of Specific Electrocardiac Elements, with an international filing date of Jun. 8, 2016, which claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application Ser. No. 62/172,565 titled Non-Invasive System and Method of Spatial Localization of Specific Electrocardiac Elements filed Jun. 8, 2015, the entire contents of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the field of atrial ablation and, more specifically, to systems and methods for locating and ablating foci of arrhythmia. 
     BACKGROUND 
     Much work is being done to develop a system which is capable of accurately locating arrhythmogenic foci within the electrical system of the heart. Existing systems with the purpose of mapping the electrical potential distribution throughout the cardiac system maintain relatively low resolutions, and are unable to provide any clinically significant data. Currently, invasive catheter-based systems are used to locate these problematic cardiac foci, which cause arrhythmias like atrial fibrillation. The existing catheter procedures are generally done as a prelude to ablation after the faulty components within the hearts chambers have been located and identified. 
     While some research has been done in the area of using anatomic imaging methods like CT and MRI in conjunction with external or superficial body surface potential mapping to correlate both cardiac anatomy and electrophysiology, a significant problem facing the development of a device with functionality worthy of a clinical setting lies within the mathematical principles of reconstructing an electromagnetic field source using collected field data after it has been subject to a volume conductor (the human body). Due to the nature of the problem, many different valid mathematical solutions can be reached using the same field data. This leads to the inability of a system to accurately describe the source(s) which produced the resulting field experienced by the sensor arrays. The following proposed system looks to address these issues. 
     SUMMARY OF THE INVENTION 
     With the above in mind, embodiments of the present invention are related to a patch including a fiducial layer and adhesive. The fiducial layer may have a surface adapted to secure to a portion of skin on a patient. The fiducial layer may further include a plurality of fiducial markers, which may have at least one of acoustic properties, material density, and proton content different from those of human tissue. The adhesive may be disposed along the surface of the fiducial layer. 
     The fiducial layer may wrap from an anterior to a posterial aspect of a torso of the patient. 
     The plurality of fiducial markers may be non-magnetic. 
     The plurality of fiducial markers may be configured in an array. 
     The array may further include a first and second plurality of parallel, elongate fiducial markers. Each of the first plurality of fiducial markers may have a unique row width. The second plurality of fiducial markers may be orthogonal to the first plurality fiducial markers. Each of the second plurality of fiducial markers may have a unique column width. 
     None of the unique row widths may be equal to any unique column width. 
     The first plurality of fiducial markers may be positioned within the same plane as the second plurality fiducial markers. 
     The array may further include a third plurality of parallel, elongate fiducial markers orthogonal to the first plurality of fiducial markers and orthogonal to the second plurality of fiducial markers. 
     Each of the third plurality of fiducial markers may be of uniform dimensions. 
     The patch may further include a sensor layer removably secured to a side of the fiducial layer positionable distal the skin of the patient. The sensor layer may further include a plurality of sensors evenly spaced from one another and adapted be in electrical communication with the skin of the patient. Each sensor may be adapted to measure at least one of the group consisting of an electric field and impedance. 
     The fiducial layer may further include a plurality of conductive areas. 
     The patch may further include a sensor layer removably secured to the fiducial layer. The sensor layer may include a plurality of sensors, each having a corresponding contact point. Each of the contact points may correlate spatially with a respective one of the plurality of conductive areas. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top plan view of a sensing patch according to an embodiment of the present invention. 
         FIG. 2  is an exploded perspective view of the sensing patch illustrated in  FIG. 1 . 
         FIG. 3  is perspective view of an array of high-sensitivity unidirectional field sensors to be used in connection with the sensing patch according to an embodiment of the present invention. 
         FIG. 4  depicts field sensing directions of the high-sensitivity unidirectional field sensors illustrated in  FIG. 3 . 
         FIG. 5  is a top plan view of a fiducial layer of the sensing patch illustrated in  FIG. 1 . 
         FIG. 6  is a top plan view of a sensor layer of the sensing patch illustrated in  FIG. 1 . 
         FIG. 7  is an environmental view of the sensing patch illustrated in  FIG. 1  affixed to a patient. 
         FIG. 8  is a perspective view of an array of fiducial markers to be used in connection with the sensing patch according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Those of ordinary skill in the art realize that the following descriptions of the embodiments of the present invention are illustrative and are not intended to be limiting in any way. Other embodiments of the present invention will readily suggest themselves to such skilled persons having the benefit of this disclosure. Like numbers refer to like elements throughout. 
     Although the following detailed description contains many specifics for the purposes of illustration, anyone of ordinary skill in the art will appreciate that many variations and alterations to the following details are within the scope of the invention. Accordingly, the following embodiments of the invention are set forth without any loss of generality to, and without imposing limitations upon, the invention. 
     In this detailed description of the present invention, a person skilled in the art should note that directional terms, such as “above,” “below,” “upper,” “lower,” and other like terms are used for the convenience of the reader in reference to the drawings. Also, a person skilled in the art should notice this description may contain other terminology to convey position, orientation, and direction without departing from the principles of the present invention. 
     Furthermore, in this detailed description, a person skilled in the art should note that quantitative qualifying terms such as “generally,” “substantially,” “mostly,” and other terms are used, in general, to mean that the referred to object, characteristic, or quality constitutes a majority of the subject of the reference. The meaning of any of these terms is dependent upon the context within which it is used, and the meaning may be expressly modified. 
     An embodiment of the invention, as shown and described by the various figures and accompanying text provides apparatus, systems, and methods that may introduce additional mathematical constraints on available mathematic solutions to create an electromagnetic field map of a patient. The constrained solutions used to create an electromagnetic field map may combine anatomic imaging methods, by way of example and not as a limitation, such as CT, MRI, or the like, in conjunction with external or superficial body surface potential mapping. The use of anatomic imaging, body surface potential mapping, or both may be used to correlate cardiac anatomy with electrophysiology. Additionally, relevant probabilistic evaluation techniques may be incorporated to weigh, compare, or otherwise determine the viability of those possible mathematic solutions that remain viable. 
     The inventive system may comprise several parts that may work together with a common goal of non-invasive spatial location of arrhythmogenic foci. Through the implementation of different detection devices, a variety of independent data types may be analyzed and co-referenced to enhance the mathematical ability of the system to isolate the location of likely sources of arrhythmia, etc. 
     Referring initially to  FIG. 2 , an exploded view of an embodiment of the sensing patch  30  according to the present invention is depicted. The sensing patch  30  may include a plurality of layers. In one embodiment, the sensing patch  30  may have a sensor layer  33 , a fiducial layer  32 , a control layer  37 , and a protective layer. Other embodiments may have a control layer  37  incorporated into or disbursed throughout a sensor layer  33 . Any combination of these layers is possible within the scope of this invention. 
     As perhaps best illustrated in  FIG. 7 , the sensing patch  30  may be affixed to a patient&#39;s skin. Returning to  FIG. 2 , the fiducial layer  32  may be proximate to the patient&#39;s skin. The fiducial layer  32  may have biocompatible adhesives disposed along the surface contacting the patient&#39;s skin. The biocompatible adhesive may be used to secure the sensing patch  30  to the patient&#39;s skin. The fiducial layer  32  may firmly attach to a patient&#39;s skin on one side and be removably secured to the sensor layer  33  on the other side. In other embodiments, the fiducial layer  32  may firmly attach to a patient&#39;s skin on one side and be surrounded by, surround, border, or otherwise be proximate to the sensor layer  33 . The fiducial layer  32  may include fiducial markers  35  disposed on a fiducial layer surface  36 . The fiducial markers  35  may be compatible with imaging systems, such as, but not limited to, magnetic resonance imaging (MRI), ultrasound (US), and x-ray computed tomography (CT), and remain affixed to a patient while MRI, US, or CT imaging is performed. 
     In embodiments intended for use with US imaging, the material used to create the fiducial markers  35  may be any material that has acoustic properties different from those of human tissue. The greater the difference, the more the signal from the fiducial markers  35  will be evident. In embodiments intended for use with imaging systems other than US imaging, the fiducial marker  35  material density or proton content may provide the properties necessary to differentiate the fiducial markers  35  from the native tissue. The fiducial markers  35  may be plastic, metal, or the like. However, for a system compatible with all imaging modalities, including MRI, it may be desirable to utilize a non-magnetic material. 
     The fiducial markers  35  may be configured in an array such that the image of the fiducial markers  35  allows the system to identify where the imaging device is place and how it is oriented at any given time. Specifically, when the fiducial markers  35  are imaged using US technology, the arrangement of the fiducial markers  35 , or their appearance in a US image, may allow the system to determine the location and orientation of the US wand. This orientation may either be directly detected or interpreted by the US system, or may be derived from the signal data obtained from the sensing patch  30  or imaging device, including the US wand itself. The fiducial layer  32  may comprise an array of a plurality of unique fiducials, a dual-axis barcode system, a tri-axis barcode system, or the like. The dual-axis barcode system may be a 2-dimensional (M×N) matrix or arrangement of fiducial markers  35 . The fiducial markers  35  may be oriented in such a way that for any given probe location the US system is able to extract fiducial data at that point, and correlate that data with a spatial location on the patch. For this barcode system, there may be multiple strips of fiducial markers  35  arranged in rows. Each fiducial marker  35  that makes up one of these rows may have a unique width. There may also be multiple strips of fiducial markers  35  arranged in columns orthogonal to the rows. Each fiducial marker  35  that makes up one of these columns may have a unique width. The US system may identify the unique width associated with a given row and the unique width associated with a given column at locations where the rows and columns intersect. The US system may then be able to correlate those two measurements with a specific point on the sensing patch  30 . This dual-axis-type barcode system may be most efficient with the US probe oriented at a 90° angle in relation to the surface of the sensing patch  30 . 
     In embodiments utilizing a third axis, a tri-axis barcode system, the fiducial markers  35  may be arranged in a 3-dimensional (M×N×P) matrix. Such an arrangement may provide the system with more data to determine the current angle of the probe and allow for more accurate and flexible image reconstruction. For this tri-axis barcode system, fiducial markers  35  may be arranged as rows, with each fiducial marker  35  in the row having a unique width, fiducial markers  35  may be arranged as columns orthogonal to the rows, with each fiducial marker  35  in the column having a unique width. The US system may identify the unique width associated with a given row and the unique width associated with a given column. The fiducial markers  35  arranged in the third dimension may all be of uniform dimensions. The US system may then be able to correlate those three measurements with a specific point on the sensing patch  30 . 
       FIG. 8  depicts an exemplary dual-axis barcode system. The black bars depict the fiducial markers  35  and the white circles indicate the identifiable points. For the tri-axis fiducial matrix, an additional set of fiducials markers  35 , similar to those shown in  FIG. 8  may be arranged at another point along the layer axis. The fiducial markers  35  in the additional set of fiducial markers may be of uniform dimensions. Such a configuration may provide the system with a reference for the angle of US probe. 
     The unique widths of the fiducial markers  35  used in rows may be different from the set of unique widths of the fiducial markers  35  used in columns. This may assist in orienting the system and provide a reference for horizontal versus vertical direction. 
     The fiducial markers  35  may be of a uniform size and distribution. Such a configuration may allow for simple trigonometric calculations to be used to determine probe angle. The fiducial markers  35  may also be within the same plane, and be made of a material with easily differentiable acoustic impedances so as not to be confused with other materials. 
       FIG. 5  depicts a top view of the fiducial layer  32 . Conductive areas  42  may be disposed on the fiducial layer  32 . The conductive areas  42  may be openings, apertures, isolated conductive substances, by way of example, but not as a limitation, Ag/AgCl gel, or the like. The conductive areas  42  may correlate spatially with contact points of the sensor layer. The fiducial layer  32  may consist primarily of a material that has poor conductivity so as not to diminish the measurable electrical potential signals across each sensor contact point. However, the conductive areas  42  of the fiducial layer  32  correlating to the contact points on the sensor layer may have high conductivity. The fiducial layer  32  may also be made from materials that are compatible with the various types of medical imaging systems, by way of example, but not as a limitation, X-ray, CT, MRI, positron emission tomography (PET), single-photon emission computed tomography (SPECT), or the like. The materials of the fiducial layer  32  may also be compatible with different combinations of medical imaging systems. The fiducial layer  32  may be designed in such a way that it is easily or readily disposable. Other layers of the sensing patch may be easily reprocessed and reused. 
       FIG. 1  depicts the sensor layer  33  along with the control layer  37 . These layers may not be compatible with imaging systems and may be removable from the fiducial layer  32  without affecting the attachment of the fiducial layer  32  to the patient&#39;s skin. 
     The sensor layer is depicted alone in  FIG. 6 . The sensor layer  33  may be comprised of a plurality of sensors  31  forming an array of sensors  31 . The sensors  31  may be spaced evenly from one another and disposed on a sensor layer surface  34 . The inventive system may consist of one or more arrays of one or more sensors  31 . The sensors  31  may include, but are not limited to, sensors capable of detecting magnetic field changes on the nanotesla (nT) scale, voltmeters, or the like. The sensors  31  may be part of a body surface potential measurement system. The sensors  31  may be integrated with or used in combination with an electrocardiograph. Each sensor  31  may have one or more corresponding contact points  43 . Each sensor  61  may be placed on or proximate to one or more corresponding contact points  43 . At each contact point  43 , the sensor  31  may be in electrical communication or direct contact with the patient&#39;s skin. Each sensor  31  may acquire patient information at or through its corresponding contact point  43 . 
     Referring now back to  FIG. 1 , the sensor array may be a grid that includes a plurality of sensors  31  affixed to a sensor layer surface  34 . The sensor layer  33  may include a plurality of conductive areas that allow for the plurality of sensors  31  to traverse through the patch material and maintain electrical connection with the patient&#39;s skin. In some embodiments, the electrical connection with the patient&#39;s skin may be made through the fiducial layer  32 . 
     Each sensor  31  may have one or more contact point with the patient&#39;s skin and measure patient information at the one or more contact points. In some embodiments, the sensor  31  may be provided by a voltmeter, or the like, which may allow for the voltage level at that contact point may be measured. In other embodiments, the sensor  31  may be provided by an electric field sensor, or the like, in which case, the electric field magnitude or direction at that contact point may be measured. 
     Each sensor  31  may serve as a reference potential for one or more other sensors  31 . Each sensor  31  may be separated by one or more resistive elements to produce a measurable voltage differential between the sensors  31 . The voltage values of specific locations in the patient&#39;s body may then be determined through mathematical operations. 
     The sensor layer  33  portion of the inventive system may further include a specially configured grid of sensors  31 . The sensors  31  may include resistor components and voltmeters. Additionally desired bioinstrumentation amplifier elements, or any such other components necessary to condition the signals being harvested, may be disposed on the sensor layer. These conditioning components may also be located in a control layer  37  affixed to the sensor layer  33  or the fiducial layer. 
     Referring now again to  FIG. 2 , the sensor layer  33  may be attached to the side of the fiducial layer  32  that is distal from the patient&#39;s skin. The sensor layer  33  may carry the components intended to harvest the electrical signals found on the surface of the patient&#39;s skin. The electrode or sensor elements that are contained in the sensor layer  33  may have contact points that are configured to be in direct contact with a patient&#39;s skin, or may be in direct contact with some conductive element that may improve signal detection capability and itself be in direct contact with the patient&#39;s skin. The conductive element may be contained in the sensor layer  33  and have direct contact with the patient&#39;s skin through one or more openings in the fiducial layer  32 . In some embodiments, the conductive element may be contained in the fiducial layer  32  and have direct contact with the patient&#39;s skin due to the adherence of the sensing patch  30  to the patient&#39;s skin. 
     This sensor layer  33  may comprise a network of resistive elements, wires, printed circuitry, a plurality of voltage potential measurement components, a plurality of magnetic field detection elements, or the like. Bioinstrumentation systems may be contained by the sensor layer  33  or control layer  37  as necessary to produce usable results. Terminals may be contained in the sensor layer  33  and configured to allow for numerous voltage samples to be taken using the sensors  31 . Utilizing the measurements of voltage levels at a plurality of contact points, potentials across a plurality of contact points may be calculated. These values may be used to create an electric field map of the patient. 
     The magnetic field produced by the heart has been measured at approximately 12 nT. Most standard sensors are unable to detect changes in a magnetic field of such small magnitude; however, some potential options do exist. Available sensors may be capable of detecting both field magnitude and field direction in three dimensions, but the sensitivities of these devices may be low. Signal conditioning or noise reduction may be performed on the data acquired by the sensors  31 . This post processing may be performed by a control module  37 . Electromagnetic field (EMF) shielding may be incorporated in the design of the sensing patch to reduce noise collected by the sensors. 
     Additionally, micro-magnetic sensors capable of uni-directionally detecting magnetic fields of less than 1 nT in magnitude may be available. Utilizing micro-magnetic sensors may reduce the electronics contained in the control layer  37  or eliminate the need for a control layer  37 . 
     By utilizing varying orientations of high-sensitivity unidirectional field sensors, the system may detect different field magnitudes spatially. Field vectors may be established mathematically once the field magnitudes have been measured by sensors of varying orientation.  FIG. 4  depicts two high-sensitivity unidirectional field sensors  38  and  39 . The resolution of the inventive system, especially in terms of direction, may be entirely dependent upon the number of sensors  38 ,  39  used. In one embodiment, one stack of two unidirectional sensors  38 ,  39  may be placed in such a manner that their respective sensing directions are orthogonal to one another. Such a configuration allows for the computation of the sensed magnetic field direction and magnitude. The respective sensing directions of sensors  38  and  39  are shown by arrows  40  and  41 . 
     The system depicted in  FIG. 3  incorporates an array of high-sensitivity unidirectional field sensors  38  and  39 . The sensors  38  and  39  may be stacked in pairs with sensing directions orthogonal to one another. These pairs may then be arranged in an array, grid, or other configuration. 
     A simplified example of the necessary mathematics to determine field strength and direction in two dimensions is shown below. 
     
       
         
           
             
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     Returning to  FIG. 2 , the sensor layer  33  may carry the necessary components to detect nano-scale magnetic fields. These components may be oriented in such a way that the magnitude and directional orientation of the field can be quantified. With the orientation of each individual sensor  31  known and the output voltage resulting from the affecting fields, vector mathematics can be performed to determine these characteristics. 
     In one embodiment, a change in magnetic field may be detected by one or more sensor  31 , which is caused by the presence of an abnormal amount of or increase in fluid located around the heart. The detection of a changed magnetic field may be indicative congestive heart failure. The electrical field response may change due to the increase of the dielectric change created by fluid increase. This change can be measured by calculating a difference between one or more of the sensors  31 . Calculating and graphically depicting differences in magnetic field between one or more sensors  31  of the sensor layer  33  may create a map the amount of fluid at different locations around the heart. Similarly, impedance changes may be detected by one or more of the sensors  31  to detect and represent fluid located around the heart. 
     A protective layer may comprise protective or shielding elements to improve the accuracy of the electronics or protect the other components of the sensing patch  30 . The protective layer may also incorporate or comprise an outer covering to enhance wearer comfort and reduce device interference with daily activities. The protective layer may be placed above the sensor layer or the control layer. The protective layer may encapsulate, surround, or protect any component of the sensing patch. 
     The sensing patch  30  described here may be used in a system in which a plurality of sensing patches  30  are used in combination with one another in different locations on the body. By way of example, and not as a limitation, a first sensing patch  30  may be placed anterior while a second sensing patch  30  is placed posterior. In another embodiment, two sensing patches may be placed anterior. 
     The sensing patch  30  may also be implemented as a vest system. In such an embodiment, one or more layers of the sensing patch  30  may be incorporated into a vest. The fiducial layer may adhere to the patient&#39;s skin. The sensor layer or control layer may be incorporated into a vest and secured to the fiducial layer to maintain a constant physical relationship between the sensor layer and the fiducial layer. 
     In another embodiment, a single large patch may cover a large amount of surface area on the body. By way of example, and not as a limitation, a sensing patch  30  may wrap around from anterior to posterior aspects of the torso. In some embodiments, the sensing patch may encompass one or more lateral aspects. 
     With the integration of properly compatible fiducial markers, the patch system may be integrated with current medical imaging systems and related applications. The fiducial layer  32  of the sensing patch  30  may be removable from the other layers of the device. The method of removal should allow for the fiducial layer  32  to remain in the same position on the patient&#39;s skin. The fiducial layer  32 , which contains the fiducial markers  35 , should remain affixed to the patient&#39;s skin during any medical imaging procedure that is performed. The fiducial markers  35  will be visible on the resulting images, which allows the data gathered from the sensors  31  to be accurately correlated with the patient&#39;s anatomical character through reference distances, or the like. 
     Not only does this implementation allow for the imposition of mathematical constraints on the spatial localization of different electro-cardiac structures based on patient anatomy, it also allows for ease of transition from the diagnostic phase to the surgical operating phase. The fiducial layer may remain on the patient during surgery, and may be used to provide image-based, or like, guidance of a catheter or other surgical instrument. The system may also utilize data collected from the sensors or other patch components to target problematic areas. 
     The mathematical and computational operations necessary to develop a system which is capable of locating one or more electromagnetic field sources are highly involved. Although the inventive system will provide more constraints on the potential solution to the mapping problems inherent in measuring patent electric and magnetic fields, probabilistic models may also be incorporated to develop a solution. Additionally, the solution may require the ability to isolate and produce models with different numbers of sources. 
     Electric fields and magnetic fields are affected differently by the various structures in the body. Therefore, they provide data independent from one another. Incorporation of electrical and magnetic sensor arrays in a system such as this is not redundant. Each type of sensor will impose different constraints and yield different possible solutions. The integration of imaging data allows for the system to constrain its solution still further to a certain spatial area defined by the image and correlated to the data by the fiducial markers. The use of ECG data may allow for temporal analysis. 
     Each group of data will provide its own set of solutions or constraints when attempting to calculate or otherwise determine the location of the problematic field source (cardiac foci, or the like). By combining the data and analyzing them as whole, the number of constraints increases and the number of possible solutions decreases, allowing for more accurate predictions of where the source in question may be located. This system may be able to provide highly accurate predictions, but it will be impossible to tell without experimentation. 
     In order to obtain more clear and useful data, high sampling frequencies may be used in each system so as to reduce the impact of noise. The high sampling frequencies may help to account for spatial resolution limitations inherent to any system, and will allow for spatial localization of sources with higher levels of confidence. For some applications, a type of selective sampling may be used and may be dependent on the intended application. By way of example, and not as a limitation, when attempting to capture data specifically relevant to atrial fibrillation and the source foci, data may be compared to the corresponding ECG traces and all segments preceding the R-peak may be analyzed. Any one of these segments containing a normal, rhythmic P-wave may be ignored, whereas those segments where either no P-wave or an abnormal P-wave morphology is observed may be recorded and processed. This may help to isolate data specific to the problematic foci, and eliminate data that will be of no use. 
     One or more of the leads used to measure and map these body surface potentials may also double as ECG leads to provide ECG data. Provided there are a sufficient number of suitable leads, multiple ECG channels may be measured. 
     The incorporation of built-in fiducial markers  35  on the fiducial layer  32 , which are compatible with different clinically used medical imaging systems, allows for data collected by the sensors  31 , or otherwise by the inventive device, to be accurately cross-referenced with high-resolution anatomical images of the patient. This ability may be useful in both standard imaging procedures as well as in applications involving real-time image-guided surgery, where continuous scanning (generally CT) takes place as visual aid for the surgeon. Fiducial markers  35  may be used as a reference to aid in various medical or surgical procedures, such as catheter-based guidance or mapping. Data provided by the medical images containing fiducial marker  35  references may be used to impress more mathematical constraints on the calculations to locate different electric field and magnetic field sources within the patient. 
     Many smaller facilities lack the equipment necessary to perform in-house medical imaging procedures like CT or MRI scans. For this reason, the inventive system may be capable of performing similar operations with ultrasound imaging modality (US). US systems utilize the acoustic properties of tissue to form medical images and require that the probe be in contact with the patient to perform the scan. Therefore, the incorporation of fiducial markers  35  in a US application may require a different approach than in the other modalities. In known systems, fiducial markers  35  may work in a passive manner to correlate the US images to fiducial markers only when the fiducial marker  35  is placed invasively within the patient&#39;s body. A standard, relatively large superficially placed fiducial marker may not be of any use, or may be of only limited use, for spatial reference in the US system because the majority of data collected by the US system comes from within the body. At least two potential solutions to this problem are included within the inventive concept. 
     In one solution, the sensing patch  30  may comprise one or more active or semi-active fiducial markers  35  that may be capable of communication with a US probe. Such a configuration utilizing active or semi-active fiducial markers  35  may allow the system to localize where the US probe is with respect to one or more fiducial markers  35  disposed on the sensing patch  30 . This information may allow for correlation with the other data collected by, for example, the sensors  31 . Several possibilities exist to produce a system containing active or semi-active fiducial markers  35 . One possible embodiment may include incorporation of RF or IR communication in one or more of the fiducial markers  35  or US probe. In some embodiments, a device may be attached to the US probe, and a process for calibration may be followed prior to, during, or subsequent to one or more US procedures. A US system incorporating active or semi-active fiducial markers  35  may have no, or only limited, adverse effects on the US image due to fiducial interference, or the like. In many 3D US systems, this type of communication between the probe and the computer system already exists; however, selecting this design could limit potential users to those who have relatively more expensive US systems. The inventive system may include adaptive hardware to upgrade existing US systems to utilize the inventive systems and methods. 
     Another embodiment of a potential solution involves the use of a sheet of very small, but detectable, superficial fiducial markers  35 . A layer of the sensing patch  30  that contacts the patient&#39;s skin, the fiducial layer  32 , may comprise an organized pattern of small fiducial markers  35 , which may be depicted in a US image when the beam of the US probe is directed through the fiducial markers  35 . 
     In such an embodiment, the fiducial layer  32  may be constructed from a material that has acoustic properties similar to human tissue. Additionally, the fiducial markers  35  may be designed or oriented in such a way that the US image of the target area is not substantially affected by the presence of the fiducial markers  35 . By incorporating a variety of unique fiducials within the sensing patch  30 , US data can be correlated spatially to the sensing patch  30  with a theoretically high degree of accuracy even if the sensor layer  33  is removed from the sensing patch  30 . The US probe may need to rapidly alternate between high and low frequency transmission bands in order to simultaneously detect the superficial fiducial markers  35  and the anatomical structures deeper within the body. Frequencies between 10 and 15 MHz may be necessary to image the fiducial markers  35  while a frequency less than 7 MHz may be necessary to image the anatomical structures within the body. Such an embodiment may also provide the added benefits of non-invasive, passive markers, and no extra hardware required to localize the probe itself. 
     Embodiments of the inventive device and methods may require software to interpret the data and reconstruct accurate images which correlate with the sensor  31  data according to the fiducial markers  35 . Benefits from both systems may be experienced in either 2D or 3D US systems. 
     Returning to  FIG. 1 , the spatial resolution of the inventive mapping system may be directly dependent upon the number of sensors  31 , and corresponding contact points, within the array. A plurality of sensors  31  may comprise a voltmeter. The number of sensors  31  may be determined by the number of voltmeters that may be implemented in the system. The spacing of the contact point or points associated with each sensor may be a tunable value. However, it may be beneficial to maintain constant spacing between each contact point. The voltage measurement taken by each sensor  31  at its corresponding contact point may be correlated spatially to other measurements using the relevant formulated equation associated with each contact point. This information may then be used to produce a surface map of the body surface potentials of the patient within the range of the device. A plurality of samples of the measured voltage levels or electric field may be taken over a period of time, using an appropriate sampling frequency, to produce a time-varying map of the body surface potentials (isochrones). 
     Returning to  FIG. 1 , some contact points used by the sensors  31  of the system described above could potentially double as contact points for electrodes to gather electrocardiograph (ECG) signals. The contact points chosen from the inventive mapping system to provide information to an ECG may be organizationally consistent with standard ECG electrode layouts used in a clinical setting. By measuring the ECG signals, data acquired from the sensors  31  or through other systems may be compared isotemporally against known cardiac cycle information. For example, the data acquired at a given time by the inventive sensor system may be matched with its concurrent ECG signal. This would allow for the data acquired by the sensors  31  during atrial contraction to be isolated and processed through the identification of P-wave initiation in the ECG signal trace. The same holds true for any other system used in the inventive device or method, and for any stage of the cardiac cycle. 
     A voltmeter separate from the sensors  31  may be implemented to measure the potentials across the contact points that may be utilized to produce the desired channel of ECG signal. Similarly, data from the sensors  31  may be used to calculate the potentials across those contact points providing ECG data. Such an implementation may reduce the hardware requirements of the system. The total extent of the potential applications of this technology is unknown; however, the main foreseeable impact of this technology would be in the realm of cardiology, both in diagnostic and surgical areas. Current methods may take several hours of invasive surgery just for the identification of problematic areas. Non-invasive identification and spatial localization of problematic electrocardiac components would save patients and doctors considerable time currently spent in surgery to identify these things. Essentially, this system can use image-based guidance provided by the fiducial markers to guide the surgeon to the area which has been identified as problematic by the sensor systems, which at the very least would provide potential areas of where the problem(s) are located with high probability, if not with certainty. 
     Some of the illustrative aspects of the present invention may be advantageous in solving the problems herein described and other problems not discussed which are discoverable by a skilled artisan. 
     While the above description contains much specificity, these should not be construed as limitations on the scope of any embodiment, but as exemplifications of the presented embodiments thereof. Many other ramifications and variations are possible within the teachings of the various embodiments. While the invention has been described with reference to exemplary embodiments, 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 adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best or only mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the description of the invention. Also, in the drawings and the description, there have been disclosed exemplary embodiments of the invention and, although specific terms may have been employed, they are unless otherwise stated used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention therefore not being so limited. Moreover, the use of the terms first, second, etc. do not denote any order or importance, but rather the terms first, second, etc. are used to distinguish one element from another. Furthermore, the use of the terms a, an, etc. do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item.