Patent Publication Number: US-2022231419-A1

Title: Method and Apparatus to Mount a Medical Imaging Antenna to a Flexible Substrate

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of and claims priority to U.S. application Ser. No. 16/247,971, filed Jan. 15, 2019, which, in turn, claims priority to U.S. Provisional Application Ser. No. 62/653,923, filed Apr. 6, 2018, the entire contents of each application is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The subject matter disclosed herein relates to a flexible antenna array for medical imaging and, more specifically, to a system for mounting multiple antennas to a flexible substrate to form the flexible antenna array. 
     As is known to those skilled in the art, a magnetic resonance imaging (MRI) system alternately generates a strong magnetic field which aligns nuclei in the presence of the magnetic field and then detects the faint nuclear magnetic resonance (NMR) signals given off by nuclei returning to a normal state in the absence of the magnetic field. The NMR signals vary as a function of the type of organ, bone, tissue, etc. . . . present within the magnetic field. The NMR signals are received by antennas, also referred to as local coils, and transmitted to the MR scanner for reconstruction into an MR image. Specifically, an anatomical region of a patient is located within the magnetic field and proximate to the antennas. The MR scanner reconstructs the NMR signals into an MR image corresponding to the anatomical region of the patient being imaged. 
     An antenna loop is configured to detect and send the NMR signals to the host MRI scanner such that trained practitioners make appropriate diagnoses of an anatomical region of interest. Often multiple antenna loops are arranged together, forming an antenna array, to obtain NMR signals from a larger anatomical region. Each antenna loop in the antenna array typically includes a signal conditioning circuit. The signal conditioning circuit is an electronic circuit which receives the NMR signals from the corresponding antenna loop and transmits the NMR signals to the MRI scanner. The signal conditioning circuit may amplify the magnitude of the NMR signals to a suitable level for transmission, perform filtering of the NMR signal to remove unwanted signal components, or perform additional processing of the NMR signal prior to transmitting the NMR signal to the MRI scanner. Each antenna loop and signal conditioning circuit are commonly referred to as a channel for the MRI scanner. 
     When multiple antenna loops are arranged in an antenna array, it is often desirable to overlap the antenna loops to detect NMR signals from the entire region to be imaged. However, when antenna loops overlap, cross-coupling occurs between overlapping antenna loops, such that a signal detected by one loop may generate an artifact on another loop. Techniques have been developed to arrange the loops and to process the signals with the signal conditioning circuit to minimize or eliminate the artifacts due to the cross-coupling. These techniques typically rely on consistent positioning of the antenna loops with respect to each other. Once the antenna loops have been positioned, the antenna loops must maintain the relationship with respect to the other loops during use and, in particular, with respect to an overlapping relationship between loops. 
     To facilitate imaging with multiple antenna loops in an antenna array, the antenna arrays have commonly been mounted within a rigid housing. The rigid housing allows the antenna arrays to be precisely positioned within the housing, and during use the rigid housing protects the antenna arrays and retains the consistent positioning of the antenna loops in their original relationship with each other. The housings may take on different shapes corresponding to the shape of the anatomical region of interest. The shape of a housing to fit, for example, over a shoulder is necessarily different than the shape of a housing used to image a foot. Similarly, the antenna arrays and housings need to adapt for variations in the size of a particular anatomical region. The same housing sized to fit a pediatric torso will not fit the torso of a large adult. As a result, the antenna arrays and their corresponding housings (also referred to as a coil) must be designed to accommodate a broad range of anatomical regions of varying sizes, and imaging centers are required to invest in a significant number of coils to cover all imaging applications. 
     In order to reduce the number of coils an imaging center requires, developments have been made in manufacturing flexible antenna coils. However, the flexible antenna coil must similarly be able to maintain the consistent positioning of individual antenna loops with respect to each other in order to avoid introducing unwanted artifacts in an image. Typically, a flexible antenna coil includes multiple antenna loops made from a flexible material mounted to a flexible, thin film substrate, such as KAPTON®. The antenna loops are securely mounted, for example, with an adhesive material or other bonding technique to maintain the desired positioning of each antenna loop with respect to the other on the flexible substrate. The signal conditioning circuits for each antenna loop are similarly mounted to or positioned on the flexible substrate. The antenna loops and flexible substrate are then covered in an interior layer of foam surrounding the antenna and their associated electronic components and an exterior layer made, for example, of a plastic, nylon, rubber, or combination thereof. The foam is included for patient comfort and the external layer is included as a protective layer for the foam and the antennas on the interior to withstand regular contact with the patient, the imaging table, and the like. 
     Serviceability of a coil is another important consideration for selecting an imaging system. If one of the antenna loops or other electronic components in a flexible coil were to fail, typically, the entire flexible substrate must be removed and replaced, including all of the antenna loops. This is due, in part, to the manner in which the antenna loops are secured to the flexible substrate and, in part, to the nature of the flexible substrate. This often results in damage to the flexible substrate if replacing one of the antenna loops is attempted. 
     Thus, it would be desirable to provide a system for mounting antennas to the flexible substrate that facilitates repair and/or replacement of the antennas or other electronic components in a flexible coil, reducing repair time and reducing lost time and revenue of the imaging center. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The subject matter disclosed herein describes a system for mounting antennas to a flexible substrate that facilitates repair and/or replacement of the antennas or other electronic components in a flexible coil. A flexible substrate is provided with a plurality of holes extending through the substrate. Each hole is configured to receive at least a portion of a fastener extending through the hole. Optionally, the flexible substrate may include a pierce point, or small hole, which is smaller than the width of the fastener to be inserted but provides a starting point for insertion of the fastener. As the fastener is inserted through the flexible substrate the opening expands around the fastener. In still another embodiment, the flexible substrate may include markers, or indicia, located on the flexible substrate to identify a location at which a fastener is to be inserted. The fastener may include pins or other sharp points configured to pierce the flexible substrate at the locations identified by the markers. For convenience, the invention will be described herein with respect to holes located in the flexible substrate. However, it is understood that the holes may be replaced by the pierce points or markings according to the desired fastener to be used to secure the antenna loops to the flexible substrate. 
     Each fastener engages the flexible substrate and an antenna loop to positively retain the antenna loop to the flexible substrate. The holes are arranged in the flexible substrate to align each antenna loop with respect to the other antenna loops mounted to the flexible substrate. The fasteners are removably mounted to the flexible substrate such that the fastener positively retains the antenna loop to the flexible substrate when mounted to the flexible substrate but allows individual antenna loops to be removed from the flexible substrate when removed from the flexible substrate. A plurality of fasteners are provided for each antenna loop and are spaced apart from each other and positioned along the length of the loop. 
     According to one embodiment of the invention, a system for assembling a flexible antenna array for medical imaging is disclosed. The system includes a flexible substrate, multiple antennas, and multiple fasteners. The flexible substrate has a plurality of holes extending therethrough, and the antennas are operative to receive a signal corresponding to an anatomical region of a patient during medical imaging. Each fastener is removably mounted to the flexible substrate through at least one of the holes in the flexible substrate and is operative to secure one of the antennas to the flexible substrate. 
     According to another aspect of the invention, each fastener extends through a first hole and a second hole in the flexible substrate, and each antenna is positioned between the first hole and the second hole for one of the fasteners when secured to the flexible substrate. 
     According to still another aspect of the invention, each of the plurality of fasteners may include a first member and a second member. The first member has a first segment, configured to extend through the first hole in the flexible substrate, and a second segment, pivotally mounted to the first segment. The second member is configured to extend through the second hole in the flexible substrate, and the second segment of the first member pivots towards and positively engages the second member to retain one of the plurality of antennas to the flexible substrate. The first member may include a living hinge between the first segment and the second segment. 
     According to yet another aspect of the invention, each fastener may include a first half fastener and a second half fastener. The first half fastener includes a first boss proximate a first end of the first half fastener and a first opening proximate a second end of the first half fastener, where the first boss is configured to extend through the first hole in the flexible substrate from a first side of the flexible substrate. The second half fastener includes a second boss proximate a first end of the second half fastener and a second opening proximate a second end of the second half fastener, where the second boss extends through the second hole in the flexible substrate from a second side of the flexible substrate. The first boss engages the second opening and the second boss engages the first opening to positively retain one of the plurality of antennas to the planar flexible substrate. 
     According to another aspect of the invention, the fastener may include a first side portion, a second side portion, and a middle segment extending between the first and second side portions to positively retain one of the plurality of antennas to the planar flexible substrate. Each of the first and second side portions includes an upper segment configured to be located on a first side of the flexible substrate when the fastener is mounted to the flexible substrate, a lower segment configured to be located on a second side of the flexible substrate when the fastener is mounted to the flexible substrate, and a rear segment configured to extend through one of the plurality of holes in the flexible substrate between the upper and lower segment. The upper segment, the lower segment, and the rear segment define a channel configured to receive the flexible substrate. The lower segment may include at least one resilient member, where the resilient member has a first width greater than a width of each of the plurality of holes when the resilient member is in a first position and a second width less than the width of each of the plurality of holes when the resilient member is in a second position. 
     According to still another aspect of the invention, the system may include a web connected to each of the fasteners operative to secure a first antenna to the flexible substrate. The web is operative to position each of the fasteners proximate to the first hole and the second hole in the flexible substrate through which the fastener extends. In one embodiment, the web may include multiple segments, each segment having a first end and a second end. The first end of each segment is connected to a first fastener and the second end of each segment is connected to a second fastener. In another embodiment, the web may include multiple segments, each segment having a first end and a second end. The first end of each of the segments is connected together at a central point, and the second end of each of the segments is connected to one of the fasteners. In still another embodiment, the web may include multiple first segments and multiple second segments. Each of the first segments includes a first end and a second end, where the first end of each first segment is connected to the second end of another first segment. Each of the second segments includes a first end and a second end, where the first end of each of the second segments is connected to one of the first segments, and the second end of each of the second segments is connected to one of the plurality of fasteners. 
     According to another embodiment of the invention, a method for assembling a flexible antenna array for medical imaging is disclosed. Multiple holes are created through a flexible substrate, and multiple antennas are positioned on the flexible substrate. Each antenna is operative to receive a signal corresponding to an anatomical region of a patient during medical imaging. Multiple fasteners are inserted through the holes in the flexible substrate, and each fastener is removably mounted to the flexible substrate. Each fastener extends through at least one of the holes in the flexible substrate, and each fastener is operative to secure one of the antennas to the flexible substrate. 
     According to another aspect of the invention, each of the plurality of fasteners may include at least one piercing member to cut a hole through the flexible substrate and the step of creating the holes is done by the at least one piercing member as each fastener is inserted through the flexible substrate. 
     According to yet another embodiment of the invention, a system for assembling a flexible antenna array for medical imaging includes a flexible substrate, multiple antennas, and multiple fasteners. The flexible substrate has multiple holes extending therethrough, and the antennas are operative to receive a signal corresponding to an anatomical region of a patient during medical imaging. Each fastener includes a base, a first member, and a second member. The first member extends from the base and has a first segment and a second segment pivotally mounted to the first segment. The second member extends from the base in the same direction as the first member, and each of the first and second members are configured to extend through one of the holes in the flexible substrate. The second segment of the first member pivots towards and is removably connected to the second member to retain one of the antennas to the flexible substrate. The first member may also include a living hinge between the first segment and the second segment, where the second segment is pivotally mounted to the first segment via the living hinge. 
     These and other objects, advantages, and features of the invention will become apparent to those skilled in the art from the detailed description and the accompanying drawings. It should be understood, however, that the detailed description and accompanying drawings, while indicating preferred embodiments of the present invention, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING(S) 
       Various exemplary embodiments of the subject matter disclosed herein are illustrated in the accompanying drawings in which like reference numerals represent like parts throughout, and in which: 
         FIG. 1  is an isometric view of a single antenna loop mounted to a flexible substrate according to one embodiment of the present invention; 
         FIG. 2  is an isometric view of the flexible substrate of  FIG. 1 ; 
         FIG. 3  is a partial isometric vies of the antennal loop, a fastener, and the flexible substrate according to another embodiment of the present invention; 
         FIG. 4  is an isometric view of one half of a fastener to secure the antenna loop to the flexible substrate according to the embodiment shown in  FIG. 1 ; 
         FIG. 5  is a top plan view of the fastener of  FIG. 4 ; 
         FIG. 6  is a side elevation view of the fastener of  FIG. 4 ; 
         FIG. 7  is a bottom plan view of the fastener of  FIG. 4 ; 
         FIG. 8  is an elevation view of a first end of the fastener of  FIG. 4 ; 
         FIG. 9  is an elevation view of a second end of the fastener of  FIG. 4 ; 
         FIG. 10  is an isometric view of a fastener to secure the antenna loop to the flexible substrate according to the embodiment shown in  FIG. 3 ; 
         FIG. 11  is a top plan view of the fastener of  FIG. 10 ; 
         FIG. 12  is a rear elevation view of the fastener of  FIG. 10 ; 
         FIG. 13  is a bottom plan view of the fastener of  FIG. 10 ; 
         FIG. 14  is a front elevation view of the fastener of  FIG. 10 ; 
         FIG. 15  is a right elevation view of the fastener of  FIG. 10 ; 
         FIG. 16  is a left elevation view of the fastener of  FIG. 10 ; 
         FIG. 17  is an isometric view of a fastener to secure the antenna loop to the flexible substrate according to another embodiment of the present invention; 
         FIG. 18  is a top plan view of the fastener of  FIG. 17 ; 
         FIG. 19  is a rear elevation view of the fastener of  FIG. 17 ; 
         FIG. 20  is a bottom plan view of the fastener of  FIG. 17 ; 
         FIG. 21  is a front elevation view of the fastener of  FIG. 17 ; 
         FIG. 22  is a right elevation view of the fastener of  FIG. 17 ; 
         FIG. 23  is a left elevation view of the fastener of  FIG. 17 ; 
         FIG. 24  is an isometric view of a single antenna loop mounted to a flexible substrate according to another embodiment of the present invention; 
         FIG. 25  is an isometric view of the flexible substrate of  FIG. 24 ; 
         FIG. 26  is an isometric view of a fastener to secure the antenna loop to the flexible substrate according to the embodiment shown in  FIG. 24 ; 
         FIG. 27  is a front elevation view of the fastener of  FIG. 26 ; 
         FIG. 28  is a top plan view of the fastener of  FIG. 26 ; 
         FIG. 29  is a side elevation view of the fastener of  FIG. 26 ; 
         FIG. 30  is a top plan view of multiple antenna loops secured to the flexible substrate using the fastener of  FIG. 17 ; 
         FIG. 31  is an isometric, partial exploded view of the antenna array of  FIG. 30 ; 
         FIG. 32  is an isometric view of a set of fasteners to secure the antenna loop to the flexible substrate with one embodiment of a connecting member according to another embodiment of the present invention; 
         FIG. 33  is an isometric view of a set of fasteners to secure the antenna loop to the flexible substrate with another embodiment of a connecting member according to another embodiment of the present invention; 
         FIG. 34  is an isometric view of the fastener of  FIG. 32  in an open position; 
         FIG. 35  is a side elevation view of the fastener of  FIG. 32  in an open position; 
         FIG. 36  is a front elevation view of the fastener of  FIG. 32  in an open position; 
         FIG. 37  is a top plan view of the fastener of  FIG. 32  in an open position; 
         FIG. 38  is an isometric view of the fastener of  FIG. 32  in a closed position; 
         FIG. 39  is a side elevation view of the fastener of  FIG. 32  in a closed position; 
         FIG. 40  is a front elevation view of the fastener of  FIG. 32  in a closed position; 
         FIG. 41  is a top plan view of the fastener of  FIG. 32  in a closed position; 
         FIG. 42  is an isometric view of a set of fasteners to secure the antenna loop to the flexible substrate in an open position with another embodiment of a connecting member according to another embodiment of the present invention; 
         FIG. 43  is an isometric view of the set of fasteners and connecting member of  FIG. 42  with the fasteners in a closed position; 
         FIG. 44  is an isometric view of the fastener of  FIG. 42  in a closed position; and 
         FIG. 45  is an isometric view of the fastener of  FIG. 42  in an open position. 
     
    
    
     In describing the preferred embodiments of the invention which are illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, it is not intended that the invention be limited to the specific terms so selected and it is understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose. For example, the word “connected,” “attached,” or terms similar thereto are often used. They are not limited to direct connection but include connection through other elements where such connection is recognized as being equivalent by those skilled in the art. 
     Detailed Description of the Preferred Embodiments 
     The various features and advantageous details of the subject matter disclosed herein are explained more fully with reference to the non-limiting embodiments described in detail in the following description. 
     Turning initially to  FIGS. 1 and 2 , a system for assembling a flexible antenna array according to one embodiment of the invention is illustrated. According to the illustrated embodiment, a flexible substrate  10  is provided to which an antenna loop  30  is mounted. The flexible substrate  10  is made of a material that is invisible to the medical imaging system. In a magnetic resonance imaging (MRI) scanner, therefore, the flexible substrate is made of a material that is not excited by the presence of the magnetic field generated by the MRI scanner. As a result, the flexible substrate  10  does not generate an image artifact and is not observable when an object is being imaged by the MRI scanner. Further, the flexible substrate  10  and objects connected to the flexible substrate, such as the fasteners, as will be described in more detail below, are made from a material that is not susceptible to magnetic fields. In other words, the materials are not affected by the magnetic field gradients generated by the MRI scanner. 
     According to one embodiment of the invention, the flexible substrate  10  is made from a fibrous material. The fibrous material may be a natural or a synthetic fiber. In one embodiment, the flexible substrate  10  is a para-aramid synthetic fiber. Preferably, the synthetic fiber exhibits little elasticity in the plane of the fabric such that its original form factor is retained during use in medical imaging. However, the fibrous material allows the flexible substrate  10  to be positioned on an object to be imaged, for example, by draping the flexible substrate  10  on the object and the flexible substrate  10  conforms to the shape of the object. In other words, the synthetic fiber resists stretching but allows rolling, folding, or other such forces to position the flexible substrate  10 . When the antenna array is affixed to the flexible substrate  10 , the flexible antenna array is positioned on an object, such as a patient or a portion of the patient&#39;s anatomy, to be imaged. The flexible substrate  10  is, therefore, made from a material with an elasticity low enough that the antenna loops  30  affixed to the material maintain a desired relationship with the other antenna loops  30 . In particular, it is desirable for the antenna loops  30  to maintain their relative position to adjacent antenna loops on the flexible substrate  10  as a result of the flexible substrate  10  stretching while positioning the flexible antenna array over the object to be imaged. 
     It is further contemplated that the flexible substrate  10  may be made from a woven material. As also illustrated in  FIGS. 1 and 2 , a series of holes  15 ,  17  are made through the flexible substrate  10 . The holes  15 ,  17  may be cut, for example, by drilling, stamping, die cutting, laser cutting, or the like in the flexible substrate  10 . A first series of holes  15  are provided to receive a fastener  100 ,  200 ,  300 ,  400 , or  500  or a portion of a fastener extending through the hole  15 . A second series of holes  17  are provided for securing a circuit board or housing  20  containing a circuit board on which an electronic circuit for the antenna loop  30  is mounted. The illustrated embodiment shows the housing  20  as a rectangular box. It is contemplated that various other shapes for the housing  20  may be utilized. Optionally, the circuit board may also be mounted directly to the flexible substrate  10 . 
     Turning next to  FIGS. 4-9 , an exemplary embodiment of one half of a fastener  100  to secure an antenna loop  30  to the flexible substrate  10  is illustrated. The fastener  100  includes two halves, where each half is identical. For ease of illustration, only one half is illustrated. A first half of the fastener  100  is inserted through the holes  15  from one side of the flexible substrate  10 , and a second half of the fastener  100  is inserted through the holes  15  from the other side of the flexible substrate  10  such that the two halves of the fastener  100  engage each other to positively retain the two halves of the fastener  100  to the flexible substrate  10 . 
     The fastener  100  includes a generally rectangular portion having a first end  102  and a second end  104 , where the second end  104  is opposite the first and  102 . The generally rectangular portion further includes a first side  106  and a second side  108 , where the second side  108  is opposite the first side  106 . The generally rectangular portion further includes a top surface  110  and a bottom surface  112 , where the bottom surface  112  is opposite the top surface  110 . Each of the edges of the generally rectangular portion is curved between adjacent surfaces. The fastener  100  further includes a boss  120 , protruding from the bottom surface  112  proximate the second end  104  of the generally rectangular portion, and an opening  140 , extending through the generally rectangular portion proximate the first end  102 . The boss  120  of a first half of the fastener  100  is configured to engage the opening  140  of a second half of the fastener  100 . Similarly, the boss  120  of a second half of the fastener  100  is configured to engage the opening  140  of the first half of the fastener  100 . The two halves of the fastener  100  are positioned such that the bottom surface  112  of one half of the fastener faces the bottom surface  112  of the other half of the fastener. The boss  120  of one half of the fastener is aligned with the opening  140  of the other half of the fastener in the two halves of the fasteners are pressed together. The boss  120  on each half of the fastener  100  includes at least one recess  122  configured to receive a tab  142  protruding from an inner periphery of the opening  140 . As the two halves of the faster  100  are inserted into each other, the tab  142  in the opening  140  of one half engages the recess  122  on the boss  120  of the other half to retain the two halves together. Optionally, the boss  120  may include a tab protruding from an outer periphery of the boss and the opening  140  may include a recess on the inner periphery of the opening  140  that is configured to receive the tab protruding from the boss  120 . 
     According to the illustrated embodiment, the faster  100  further includes a channel  160  extending along the bottom surface  112  and between the first side  106  and the second side  108  of the fastener. The channel  160  is configured to receive the antenna loop  30 . The size of the channel  160  is preferably configured to positively retain the antenna loop  30  in a particular alignment on the flexible substrate  10 . Optionally, the periphery of the channel  160  may be larger than the antenna loop  30  to facilitate positioning of the antenna loop  30  after the fastener  100  has been mounted on the flexible substrate  10 . The portion of the fastener including the channel  160  may be configured to be deformed, for example, by heat, vibration, pressure, or other known manufacturing methods to securely form the channel around the antenna loop  30 . Optionally, an external material, such as a solvent, adhesive, or potting material may be applied to the channel  160  to cause the channel  160  to deform, adhere the antenna loop  30  within the channel, or otherwise positively retain the antenna loop  30  at a desired position within the channel  160 . 
     It is noted that where relational terms such as top and bottom, left and right, upper and lower, and the like are utilized to define aspects of the invention, the terms are not intended to be limiting. The terms are intended to identify relationships between surfaces on a component itself and may be reversed, for example, by turning or rotating a component. It is contemplated that the invention disclosed and defined herein extends to all alternative combinations or orientations of two or more of the individual features of the elements mentioned or evident from the text and/or drawings presented herein. 
     Turning next to  FIGS. 10-16 , a second embodiment of a fastener  200  to secure the antenna loop  30  to the flexible substrate  10  is illustrated. The fastener  200  is of single-part, molded construction. The fastener  200  is symmetric about a central plane  201  extending through the fastener  200 . The fastener  200  includes a first side  202  and a second side  204 , where the second side  204  is opposite the first side  202 . The fastener  200  includes a front side  208  and a rear side  206 , where the rear side  206  is opposite the front side  208 . The fastener also includes a top surface  210  and a bottom surface  212 , where the bottom surface  212  is opposite the top surface  210 . 
     The fastener  200  further includes two portions configured to be inserted into the holes  15  in the flexible substrate  10 . A first portion  220  is proximate the first side  202  of the fastener  200  and a second portion  240  is proximate a second side  204  of the fastener  200 . The first portion  220  is identical to, and symmetrical about the central plane  201  with the second portion  240 . When inserted through the holes  15  in the flexible substrate  10 , the first portion  220  and the second portion  240  positively retain the fastener  200  to the flexible substrate  10 . For convenience, one side of the fastener  200  will be described in detail, where the second side is symmetrical about the plane  201  extending through the fastener  200  and is identical to the first side described below. 
     When viewed from the side  202 , the fastener  200  is generally “c-shaped.” The fastener  200  includes an upper segment  207 , which is configured to be positioned on one surface of the flexible substrate  10 , and a lower segment  211 , which is configured to be positioned on the opposite surface of the flexible substrate  10  when the fastener  200  is inserted into the flexible substrate. The upper segment  207  extends generally parallel to the lower segment  211  and is connected by a rear segment  209  extending between the upper and lower segments. A channel  213  is defined between the upper segment  207 , rear segment  209 , and lower segment  211 , where the channel  213  has a width generally equal to or less than the thickness of the flexible substrate  10 . The flexible substrate  10 , therefore, fits within the channel  213  or is slightly compressed as it is inserted into the channel  213  while the fastener  200  is inserted through the holes  15  of the substrate. 
     The lower segment  211  includes a resilient member  222  having a width, W, greater than a width of the hole  15  in the flexible substrate  10 . According to the embodiment illustrated in  FIG. 13 , the resilient member  222  is elongated with a first arcuate side member  224  and a second arcuate side member  226  each extending generally from the rear side  206  to the front side  208  of the fastener  200 . Each arcuate side member  224 ,  226  meets at a first point  223  proximate the rear side  206  and a second point  225  proximate the front side  208  with the arcuate side member extending outward and returning inward between the two points. In order to insert the fastener  200  into the holes  15  of the flexible substrate  10 , the two arcuate side members  224 ,  226  are pressed together such that the width, W, of the resilient member  222  is less than the width of the hole  15  in the substrate  10 . Pressing the two arcuate side members  224 ,  226  together causes the resilient member to pivot at each of the first point  223  and the second point  225  and become more elongated. The front end of the resilient member  222  is inserted through the hole  15  and to the bottom side of the flexible substrate  10 . When the resilient member  222  has passed through the hole  15 , the arcuate side members  224 ,  226  are released and they return to their original position. Each arcuate side member  224 ,  226  expands outward under the bottom side of the flexible substrate  10 , shortening the length of the resilient member, and the width, W, of the resilient member  222  again becomes greater than the width of the hole  15 , preventing the fastener  200  from pulling back through the hole  15 . With the flexible substrate  10  located in the channel  213  of the fastener  200  and the resilient member  222  retaining the fastener  200  in the substrate  10 , the fastener  200  is securely mounted to the flexible substrate  10 . 
     The fastener  200  further includes a middle segment  230  configured to secure the antenna loop  30  to the flexible substrate  10 . The middle segment  230  includes a channel  232  extending from the rear side  206  to the front side  208  of the fastener  200 . The channel  232  starts at a height generally equal to the lower surface of the upper segment  207  and extends upward for a height generally equal to an expected thickness of the antenna loop  30 . Thus, the channel  232  is configured to receive the antenna loop  30  and to positively retain the antenna loop  30  against the flexible substrate  10  and in a particular alignment on the flexible substrate  10 . 
     Turning next to  FIGS. 17-23 , a third embodiment of a fastener  300  to secure the antenna loop  30  to the flexible substrate  10  is illustrated. The fastener  300  is of single-part, molded construction. The fastener  300  is symmetric about a central plane  301  extending through the fastener  300 . The fastener  300  includes a first side  302  and a second side  304 , where the second side  304  is opposite the first side  302 . The fastener  300  includes a front side  308  and a rear side  306 , where the rear side  306  is opposite the front side  308 . The fastener also includes a top surface  310  and a bottom surface  312 , where the bottom surface  312  is opposite the top surface  310 . 
     The fastener  300  further includes two portions configured to be inserted into the holes  15  in the flexible substrate  10 . A first portion  320  is proximate the first side  302  of the fastener  300  and a second portion  340  is proximate a second side  304  of the fastener  300 . The first portion  320  is symmetrical about the central plane  301  with the second portion  340 . When inserted through the holes  15  in the flexible substrate  10 , the first portion  320  and the second portion  340  positively retain the fastener  300  to the flexible substrate  10 . For convenience, one side of the fastener  300  will be described in detail, where the second side is symmetrical about the plane  301  extending through the fastener  300  with respect to the first side described below. 
     When viewed from the side  302 , the fastener  300  is generally “c-shaped.” The fastener  300  includes an upper segment  307 , which is configured to be positioned on one surface of the flexible substrate  10 , and a lower segment  311 , which is configured to be positioned on the opposite surface of the flexible substrate  10  when the fastener  300  is inserted into the flexible substrate. The upper segment  307  extends generally parallel to the lower segment  311  and is connected by a rear segment  309  extending between the upper and lower segments. A channel  313  is defined between the upper segment  307 , rear segment  309 , and lower segment  311 , where the channel  313  has a width generally equal to or less than the thickness of the flexible substrate  10 . The flexible substrate  10 , therefore, fits within the channel  313  or is slightly compressed as it is inserted into the channel  313  while the fastener  300  is inserted through the holes  15  of the substrate. 
     The lower segment  311  includes a resilient member  322  having a width, W, greater than a width of the hole  15  in the flexible substrate  10 . According to the embodiment illustrated in  FIG. 20 , the resilient member  322  is elongated with a first side member  324  that is arcuate and a second side member  326  that includes a first, curved segment  327  and a second, straight segment  329 . The first, arcuate side member  324  extends generally from the rear side  306  to the front side  308  of the fastener  300 . The second side member  326  meets the first side member  324  at a point  325  proximate the front side  308  of the fastener. The second side member  326  extends rearward from the point  325  but protrudes outwards from the first side  302  of the fastener. The first, curved segment  327  arches rearward and outward for a short distance and the second, straight segment  329  then extends at an angle from the side. The point  325  at the front of the resilient member  322  serves as a living hinge such that the straight segment  329  may be compressed toward the first arcuate side member  324  and pivot about the point  325 . The resilient member  322  further includes a seat  323 , or a recess, in which the end  328  of the straight segment  329  of the second side member  326  is received. The seat  323  provides a positive stop against which the second side member  326  may be compressed. 
     In order to insert the fastener  300  into the holes  15  of the flexible substrate  10 , the two side members  324 ,  326  are pressed together such that the width, W, of the resilient member  322  is less than the width of the hole  15  in the substrate  10 . As indicated above, pressing the two side members  324 ,  326  together causes the second side member  326  to pivot at the point  325  on the front of the resilient member and the end  328  of the straight segment  329  to engage the seat  323 . The front end of the resilient member  322  is then inserted through the hole  15  and to the bottom side of the flexible substrate  10 . When the resilient member  322  has passed through the hole  15 , the side members  324 ,  326  are released and the second side member  326  returns to its original position. As a result, the width, W, of the resilient member  322  again becomes greater than the width of the hole  15 , preventing the fastener  300  from pulling back through the hole  15 . With the flexible substrate  10  located in the channel  313  of the fastener  300  and the resilient member  322  retaining the fastener  300  in the substrate  10 , the fastener  300  is securely mounted to the flexible substrate  10 . 
     The fastener  300  further includes a middle segment  330  configured to secure the antenna loop  30  to the flexible substrate  10 . The middle segment  330  includes a channel  332  extending from the rear side  306  to the front side  308  of the fastener  300 . The channel  332  starts at a height generally equal to the lower surface of the upper segment  307  and extends upward for a height generally equal to an expected thickness of the antenna loop  30 . Thus, the channel  332  is configured to receive the antenna loop  30  and to positively retain the antenna loop  30  against the flexible substrate  10  and in a particular alignment on the flexible substrate  10 . 
     Turning next to  FIGS. 24-29 , a fourth embodiment of a fastener  400  to secure the antenna loop  30  to the flexible substrate  10  is illustrated. Similar to the other embodiments, the fastener  400  is configured to secure an antenna loop  30  to a flexible substrate  10 . As shown in  FIG. 25  a series of holes  15 ,  17  are made through the flexible substrate  10 . The holes  15 ,  17  may be cut, for example, by drilling, stamping, die cutting, laser cutting, or the like in the flexible substrate  10 . A first series of holes  15  are provided to receive the fastener  400  or a portion of the fastener extending through the hole  15 . A second series of holes  17  are provided for securing a circuit board or housing  20  containing a circuit board on which an electronic circuit for the antenna loop  30  is mounted. The illustrated embodiment shows the housing  20  as a rectangular box. It is contemplated that various other shapes for the housing  20  may be utilized. Optionally, the circuit board may also be mounted directly to the flexible substrate  10 . Unlike the other embodiments, the fastener  400  is a single continuous member that extends through each of the holes  15  for the fastener  400  rather than providing multiple fasteners at intervals spaced apart along the length of the antenna loop  30 . 
     Referring to  FIGS. 26-29 , the fastener  400  is a single, elongated member configured to be fed through each of the holes  15  and to secure one of the antenna loops  30  to the substrate  10 . The fastener  400  may have, for example, an extruded body  406  having a cylindrical sectional area. Optionally, the fastener  400  may have other sectional areas without deviating from the scope of the invention. The fastener  400  is preferably constructed of a flexible plastic material and may further be formed in a helical, or other spiral, configuration along the length of the fastener  400 . The helical configuration is molded such that the spiral assists in feeding the fastener  400  through each of the holes  15  and around the antenna loop  30  located on the substrate  10 . The fastener  400  may further be formed in a ring-shape, having a diameter corresponding to a diameter of the antenna loop  30 . The material from which the fastener  400  is made is preferably a resilient material, such that the body  406  of the fastener  400  will maintain the helical form along its length and the ring-shape absent a force applied to the fastener  400 . The fastener  400  may deflect axially or radially along the length of the body  406  as it is being inserted into the substrate  10  and return to its original shape when an external force is no longer applied. 
     The body  406  of the fastener  400  extends from a first end  402  to a second end  404 , where each end  402 ,  404  of the fastener is located proximate one side of the housing  20  for the signal conditioning circuit when the fastener is securing an antenna loop  30  to the substrate  10 . A first tab  410  is connected to the first end  402  of the fastener  400 , and a second tab  420  is connected to the second end  404  of the fastener  400 . Each tab  410 ,  420  may be integrally formed with the body  406  of the fastener  400 , for example, through a molding process. Optionally, each tab may be joined to the body via any suitable method, such as applying solvents or adhesives, or using thermal, induction, or vibrational welding of the members. Each tab  410 ,  420  has preferably the same sectional area of the body  406  and a middle portion of the tab  410 ,  420  is joined to the respective end  402 ,  404  of the body  406 . The first tab  410  includes a first end  412  and a second end  414 , and the second tab  420  similarly includes a first end  422  and a second end  424 . When each tab  410 ,  420  is joined to the body  406  it is generally perpendicular to the end of the body. The point at which each tab  410 ,  420  is joined to the body  406  forms a living hinge, such the tab may be pivoted about the connection such that one end of the tab  410 ,  420  may be aligned adjacent to the body  406  and the other end of the tab  410 ,  420  protrudes in an axial direction from the end of the body  406 . The tab is pivoted back such that it is adjacent the body  406  of the fastener  400  as the fastener  400  is inserted through the holes  15  or to remove the fastener  400  from one of the holes  15 . After inserting the fastener  400  through a hole  15  and, in particular, after inserting the fastener through the last hole, the tab is allowed to return to its original position, which is generally perpendicular to the body  406  of the fastener. In its original position, the tab  410 ,  420  prevents the fastener from being pulled through the hole  15 . 
     Turning next to  FIGS. 32-41  a fifth embodiment of a fastener  500  to secure the antenna loop  30  to the flexible substrate  10  is illustrated. The fastener is of single-part, molded construction. The fastener  500  includes a base  510  and two members extending from the base  510 . A first member  520  is longer than the second member  540 , and both members  520 ,  540  are configured to be inserted through one of the holes  15  in the flexible substrate  10 . Optionally, the distal end of each protruding member with respect to the base may have a piercing member to engage the flexible substrate  10  at a piercing point and create a hole  15  in the flexible substrate  10  as the fastener is inserted. 
     According to the illustrated embodiment of the fastener  500 , the base  510  is a generally rectangular member. The base  510  includes a front surface  511 , a rear surface  512  opposite the front surface, a top surface  513 , a bottom surface  514  opposite the top surface, and two side surfaces  515 , where the front surface  511 , rear surface  512 , and the side surfaces  515  extend between the top and bottom surfaces. Although illustrated as a generally rectangular member, it is contemplated that the base  510  may be of any shape that extends between the first member  520  and the second member  540  to establish a spatial relationship between the two members such that each of the two members may be inserted through separate holes  15  in the flexible substrate together. Further, the top surface  513  may be joined to the side surfaces  515 , the front surface  511 , and the rear surface  512  at a square edge, curved edge, or tapered edge. Similarly, each of the side, front, and rear surfaces ( 515 ,  511 , and  512 , respectively) may be oriented perpendicular to the top surface  513  or curved or sloped with respect to the top surface  513  ( FIGS. 44-45 ). 
     The first member  520  includes a first segment  522  and a second segment  532 , where the two segments  522 ,  532  are joined by a living hinge  530 . The first segment  522  extends for a first height which is greater than the thickness of the flexible substrate  10  and an antenna loop  30 . Thus, when the first member  520  is inserted through the flexible substrate  10 , the flexible substrate generally resides around the first segment  522  of the first member  520 . The living hinge  530  extends for a width of the first member  520  between the first segment  522  and the second segment  532 . The living hinge  530  is formed of the same material as the first and second segments, but is of a reduced thickness, such that the second segment  532  of the first member  520  is pivotally moved about the living hinge  530  and may be rotated forward and in a downward direction toward the second member  540  of the fastener  500  to close the fastener. The second segment  532  of the first member  520  includes two side pieces  533  each extending from the living hinge  530  to an end piece  534 . An opening  535  is defined through the second segment  532  of the first member  520  by the living hinge  530 , the two side pieces  533 , and the end piece  534 . The opening  535  is configured to receive the second segment  552  of the second member  540 . 
     The second member  540  also includes a first segment  542  and a second segment  552  where the two segments are rigidly coupled. The first segment  542  extends from the base for a first height which is greater than the thickness of the flexible substrate  10 . Thus, when the second member  540  is inserted through the flexible substrate  10 , the flexible substrate generally resides around the first segment  542  of the second member. The second segment  552  of the second member  540  is configured to receive the second segment  532  of the first member  520 . The upper end of the second segment  552  includes at least one tapered surface  553 . As shown, for example, in  FIGS. 34-37 , the tapered surface  553  forms a partial conical surface extending around the entire periphery of the second segment  552 . According to another embodiment, the tapered surface  553  is located along either side of the second segment  552 . As shown, for example, in  FIGS. 44-45 , a first tapered surface may extend to the front and rear of the second segment  552  and a second tapered surface  553  may extend to either side of the second segment  552 . The width of the second segment  552  of the second member  540  is greater than the width of the first segment  542  of the second member  540  such that tabs  554  are formed that protrude outward from a central axis of the second member  540  at the junction between the second segment  552  and the first segment  542  of the second member  540 . 
     The tabs  554  on the second segment  552  of the second member  540  are configured to positively retain the second segment  532  of the first member  520  to the second segment  552  of the second member  540 . The tapered surface  553  to the sides of the second segment  552  of the second member  540  are configured to engage the inner periphery of the opening  535  of the second segment  532  of the first member  520 . The width of the second segment  552  of the second member  540  at the tabs  554  is greater than the width of the opening  535 . Thus, as the second segment  532  of the first member  520  slides down along the tapered surface  553 , the side pieces  533  are deflected outward allowing the second segment  552  of the second member  540  to fit between the side pieces  533  and through the opening  535 . When the second segment  532  of the first member  520  has rotated downward past the tabs  554  of the second member  540 , the side pieces  533  of the first member  520  return to their original width and are captured below the tabs  554  of the second member  540 . To release the second segment  532  of the first member  520 , a tool may be inserted in the opening  535  to spread the side pieces  533 , allowing the second segment  532  of the first member  520  to be rotated upward past the tabs  554  of the second member  540 . 
     When the second segment  532  of the first member  520  is secured to the second segment  552  of the second member  540  by the tabs  554 , a channel  570  is defined in the fastener  500  that is configured to secure an antenna loop  30  to the flexible substrate  10 . The channel  570  is defined by the top surface  513  of the base  510 , the two sides of the first and second members facing each other, and the lower surface of the second segment  532  of the first member  520  when it is retained by the tabs  554  of the second member  540 . 
     In operation, one embodiment of the fasteners  100 ,  200 ,  300 ,  400 ,  500  described above is used to secure one or more antenna loops  30  to a flexible substrate  10  to form a flexible antenna array. Referring to  FIGS. 30 and 31 , the fastener  300  of  FIGS. 17-23  is illustrated securing multiple antenna loops  30  to a flexible substrate  10 . Each fastener  300  is inserted through a pair of holes  15  such that the channel  332  secures the antenna loop  30  to the flexible substrate  10 . The fasteners  300  are configured to engage the flexible substrate  10  to prevent movement of the fastener  300  with respect to the flexible substrate. For example, the rear segment  309  of the fastener  300  is sized complementary to the size of the hole  15  such that the fastener does not move within the hole  15 . Similarly, the width of the channel  313  is complementary to the width of the flexible substrate  10  to engage both sides of the flexible substrate and to further prevent movement of the fastener with respect to the substrate. The holes  15  are cut in the substrate  10  to position the fastener  400  or fasteners  100 ,  200 ,  300 ,  500  and when multiple antenna loops  30  are mounted to the flexible substrate  10 , the fastener  400  or fasteners  100 ,  200 ,  300 ,  500  maintain the desired alignment of the antenna loops  30  with respect to each other as the flexible substrate  10  is positioned on the object to be imaged. 
     According to another aspect of the invention, the fasteners  500  may be mounted to a web to form a fastener assembly  501 ,  503 ,  600  (see e.g.,  FIGS. 32, 33, and 42 ). The fastener assemblies  501 ,  503 ,  600  include multiple fasteners  500  used to secure a single antenna loop  30 , where the web includes a number of interconnect segments used to align the fasteners  500  with the holes  15  in the flexible substrate  10 . 
     With reference to  FIG. 32 , a first embodiment of a fastener assembly  501  is illustrated. The fastener assembly  501  includes a web formed from a number or arcuate segments  502 . Each arcuate segment  502  has a first end and a second end, where each of the first and second ends are joined to a side surface  515  of the base  510  of one of the fasteners  500 . Each arcuate segment  502  may have a radius equal to the radius of the antenna loop  30  and is joined between side surfaces  515  of two adjacent fasteners  500 . The arcuate segments  502  align each fastener  500  with a set of holes  15  through which the first and second members  520 ,  540  of each fastener  500  may be inserted. After the fasteners  500  are inserted through the holes  15  in the flexible substrate  10  and closed to secure the antenna loop  30 , the arcuate segments  502  may be cut away and removed such that the arcuate segments  502  do not limit the flexibility of the flexible substrate  10  to which the fasteners  500  are mounted. 
     With reference to  FIG. 33 , a second embodiment of a fastener assembly  503  is illustrated. The fastener assembly  503  includes a web formed from a number of straight segments  504 . Each straight segment  504  has a first end and a second end, where the first end of each straight segment  504  is connected at a central point  505  and the second end of each straight segment  504  is joined to a front surface  511  of the base  510  of one of the fasteners  500 . The straight segments  504  are connected in a star configuration and, similar to the arcuate segments  502  discussed above, align the fasteners  500  with a set of holes  15  through which the first and second members  520 ,  540  of each fastener  500  may be inserted. After the fasteners  500  are inserted through the holes  15  in the flexible substrate  10  and closed to secure the antenna loop  30 , the straight segments  504  may be cut away and removed such that the straight segments  504  do not limit the flexibility of the flexible substrate  10  to which the fasteners  500  are mounted. 
     With reference next to  FIGS. 42, 43 , still another embodiment of a fastener assembly  600  is illustrated. The fastener assembly  600  includes a web formed from two sets of straight segments. A first set of straight segments  602  is joined in an end-to-end manner, where a first end of one segment from the first set of straight segments  602  is joined to a second end of another segment from the first set of straight segments  602 . The first set of straight segments  602  may be formed as a single member or formed by joining separate members via any suitable method, such as vibration, heat, or ultrasonic welding. A second set of straight segments  604  is connected between the first set of straight segments  602  and each fastener  500 . A first end of each segment in the second set of straight segments  604  is connected to one of the first segments or, optionally, connected at a junction between two of the first segments, and a second end of each segment in the second set of straight segments  604  is connected to one of the fasteners  500 . It is contemplated that the first and second set of straight segments  602 ,  604  may be integrally formed as a single member, for example, via injection molding. Similarly, the fasteners  500  may also be integrally formed with the web to create the fastener assembly  600 . Optionally, the fasteners  500 , the first set of straight segments  602 , and the second set of straight segments  604  may be formed of various different separate members and joined via any suitable method, such as vibration, heat, or ultrasonic welding. 
     It should be understood that the invention is not limited in its application to the details of construction and arrangements of the components set forth herein. The invention is capable of other embodiments and of being practiced or carried out in various ways. Variations and modifications of the foregoing are within the scope of the present invention. It also being understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text and/or drawings. All of these different combinations constitute various alternative aspects of the present invention. The embodiments described herein explain the best modes known for practicing the invention and will enable others skilled in the art to utilize the invention.