Patent Document

TECHNICAL FIELD OF INVENTION 
     The present invention relates to an assembly for securely mounting a sensor to an image-acquisition device capable of pivoting, and, in particular for securely mounting a sensor to a C-arm or some other C-shaped fluoroscope. 
     BACKGROUND OF INVENTION 
     Referring to FIG. 1, an image-acquisition device  100  can be used for simultaneous real-time image acquisition and intrabody navigation of a probe, such as a catheter  105 . Catheters may be employed for diagnostic purposes, e.g., by retrieving samples of tissue, or for therapeutic purposes, e.g., ablation by radiofrequency waves emitted by at least one electrode contained in the catheter. In either case, tracking of the catheter  105  as it is navigated through the body of a patient is of great importance. 
     To this end, the image-acquisition device  100  comprises a C-arm fluoroscope  110  that may pivot about three orthogonal axes to allow imaging of a patient from several different angles. Typically, such a fluoroscope  110  includes an X-ray source  115  and an image acquisition module  120  mounted on opposite ends of a C-arm  125 , as well as a table  130  where the patient lies. The portion of the patient&#39;s body being imaged, typically the chest, is positioned between the ends of the C-arm  125 . The image-acquisition module  120  converts x-rays that transit through the patient on the table  130  into electronic signals representative of 2-D images of the patient. The pivotable feature provides images from various perspectives, thereby allowing the reconstruction of a 3-D image of the patient from a series of successive 2-D images. This function is performed by a controller/processor  135 , which is coupled to the image-acquisition module  120 . 
     Tracking of the catheter  105  is accomplished by using a fixed transmitter  140  to transmit to a sensor  145  located on the catheter  105 , thereby locating the catheter  105  relative to the transmitter  140 . Optionally, a reference sensor can be placed on the patient, preferably the chest, to create a “fixed” space in combination with the transmitter  140  relative to other moving sensors. In this manner, the device  100  compensates for any movement of the patient, such as chest movement during the respiratory cycle. The sensor  145  typically comprises a housing that contains three pairs of electromagnetic sensing elements for the three orthogonal axes. In any event, the continuously changing position and orientation of the catheter  105  can be inferred from the electromagnetic signals transmitted by the transmitter  140  and received by the sensor  145 . This tracking function is performed by driving circuitry  150  and reception circuitry  155 , which are respectively coupled to the transmitter  140  and sensor  145 , and the controller/processor  135 , which controls the driving circuitry  150  and processes the signals received by the reception circuitry  155 . 
     Thus, by determining the position and orientation of the catheter  105  relative to the frame of reference defined by the transmitter  140  and the optional reference sensor, the controller/processor  135  determines the position and orientation of the catheter  105  relative to the 2-D image acquired by the fluoroscope  110 . The controller/processor  135  then synthesizes a combined image that includes both the 3-D image of the patient and an icon representing the catheter  105  positioned and oriented with respect to the 3-D image, and then displays this combined image on a monitor  158 . In order to synchronize the acquired location of the catheter  105  with each 2-D image, the orientation of which changes as the C-arm  125  is rotated around the patient, another sensor  160 , which is similar to the sensor  145  located in the catheter  105 , is mounted on the C-arm  125 . Electromagnetic signals received by the sensor  160  from the transmitter  140  are sent to reception circuitry  165 , which is identical to the reception circuitry  155 . The controller/processor  135  is coupled to this reception circuitry  155  and acquires the data therefrom to determine the orientation of the C-arm  125 , and thus the orientation of the 2-D image, at any given time, so as to provide a means to synchronize the image of the catheter  105  with that of each 2-D image. Further details on the image-acquisition device  105  are described in PCT publication WO 00/10456, entitled “Intrabody Navigation System for Medical Applications,” and published on Mar. 2, 2000, which publication is fully and expressly incorporated herein by reference. 
     In order to securely mount the sensor  160  to the C-arm  125 , certain constraints must be considered. First, as the sensor  160  serves as a fixed point of reference, it must be sufficiently secured to the C-arm  125 , such that it does not move relative to the C-arm  125  when the C-arm  125  pivots. The sensor  160 , however, should be easily engageable and disengageable from the C-arm  125  in order to replace the sensor  160  if desired. Secondly, as the sensor  160  functions by the reception of electromagnetic waves, it must not contact or be placed in proximity to any ferromagnetic material, such as steel or any other material or alloy containing iron, which would disrupt the magnetic field of the sensor  160 . 
     Thus, an objective of this invention is to provide for a sensor assembly that detachably secures the sensor onto a C-arm, or some other pivotable image-acquisition device, without disrupting the sensor&#39;s magnetic field. 
     SUMMARY OF THE INVENTION 
     The present inventions are directed to medical sensor assemblies that include sensors that can be detachably mounted onto a fluoroscopic mount, such as a C-arm. In accordance with a general aspect of the present inventions, a medical sensor assembly for use with a fluoroscopic mount comprises an electromagnetic sensor that is configured for outputting positional data relating to the fluoroscopic mount. The sensor includes a mount engaging element, and the sensor mount includes a sensor engaging element, both of which are configured to be removably mounted in an interference relationship with each other. The mount engaging element of the sensor can be a sensor housing, or alternatively, an element that is separate from the sensor housing. The sensor mount, which is composed of a non-ferromagnetic material, further includes a spacer for maintaining the sensor at a prescribed distance from the ferromagnetic fluoroscopic mount, thereby minimizing any adverse ferromagnetic effects on the sensor. 
     The sensor mount may be configured, e.g., in a front-mount arrangement, such that the sensor is mounted to the sensor mount in a direction perpendicular to the plane in which the sensor mount is mounted to the fluoroscopic mount. Alternatively, the sensor mount may be configured, e.g., in a side-mount arrangement, such that the sensor is mounted to the sensor mount in a direction parallel to the plane in which the sensor mount is mounted to the fluoroscopic mount. 
     The spacer can be configured to be permanently mounted to the fluoroscopic mount, e.g., by bonding or welding thereto. In this case, the sensor engaging element of the sensor mount can be permanently mounted to the spacer. For example, the sensor engaging element can be bonded or welded thereto, or can be formed with the spacer as a unibody structure. Thus, the sensor with the mount engaging element can be repeatedly attached to and detached from the fluoroscopic mount. Alternatively, the sensor engaging element, rather than the spacer, is configured to be permanently mounted to the fluoroscopic mount, e.g., by bonding or welding thereto. In this case, the spacer acts as the mount engaging element, in that it is configured to be removably mounted to the sensor engaging element, e.g., by using a hook-in-loop material, such as Velcro®. The mount engaging element of the sensor can be permanently mounted to the spacer, e.g., by bonding or welding thereto. Thus, the sensor with the spacer can be repeatedly attached to and detached from the fluoroscopic mount. 
     In accordance with particular aspects of the present inventions, the sensor engaging element and mount engaging element may be variously designed. For example, the sensor engaging element of the sensor mount may comprise a pair of arms, and the mount engaging element of the sensor may comprise the sensor housing, which is received between the pair of arms in a snug relationship. As another example, the sensor engaging element may comprise a pair of arms, and the mount engaging may comprise a T-shaped housing that has a shaft configured to be inserted between the pair of arms and a pair of oppositely-extending sensor arms that are configured to be respectively disposed on the pair of arms. As still another example, the sensor engaging element may be an open cavity, and the mount engaging element may be a sensor housing or other member that can be received within the cavity in a direction perpendicular to a plane in which the sensor mount is mounted. As still another example, the sensor engaging element may be a conical cavity, and the mount engaging element may be a conical sensor housing that is received by the conical cavity. As still another example, the sensor engaging element may comprise means for receiving a clip, and the mount engaging element may comprise a clip that is received by the clip receiving means. As still another example, the sensor engaging element may comprise one of a cavity and member, and the mount engaging element may comprise the other of the cavity and member, with the cavity and member having substantially uniform and matching cross-sections, such that they can slidingly engage each other. As still another example, the sensor engaging element may comprise one of a snap protuberance and hole, and the mount engaging element may comprise the other of the snap protuberance and hole, with the protuberance and hole being capable of engaging each other in a snap-fit arrangement. As still another example, the sensor engaging element may comprise a flexible planar member, e.g., a hook-in-loop material, and the mount engaging element may comprise a rigid planar member, with the flexible planar member being configured to mount the rigid planar member to the sensor mount. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order to better appreciate how the above-recited and other advantages and objects of the present inventions are obtained, a more particular description of the present inventions briefly described above will be rendered by reference to specific embodiments thereof, which are illustrated in the accompanying drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings. 
     FIG. 1 depicts a lateral elevation view of a C-arm with the sensor assembly of the present invention secured thereto. 
     FIG. 2 depicts a conceptual drawing of a sensor assembly of the present invention. 
     FIG. 3 depicts one embodiment of the sensor assembly of the present invention. In particular, FIG. 3A depicts an elevation view of a sensor; FIG. 3B depicts a perspective view of a preferred sensor mount for use with the sensor of FIG. 3A; FIG. 3C depicts an elevation view of the sensor of FIG. 3A mounted in the sensor mount of FIG. 3B; and FIGS. 3D and 3E are perspective views of alternative sensor mounts for use with the sensor of FIG.  3 A. 
     FIG. 4 depicts another embodiment of the sensor assembly of the present invention. In particular, FIG. 4A depicts an elevation view of a sensor; FIG. 4B depicts a perspective view of a sensor mount for use with the sensor of FIG. 4A; and FIG. 4C depicts an elevation view of the sensor of FIG. 4A mounted in the sensor mount of FIG.  4 B. 
     FIG. 5 depicts still another embodiment of the sensor assembly of the present invention. In particular, FIG. 5A depicts a lateral elevation view of a sensor; FIG. 5B depicts a perspective view of a sensor mount for use with the sensor of FIG. 5A; and FIG. 5C depicts a perspective view of the sensor of FIG. 5A mounted in the sensor mount of FIG.  5 B. 
     FIG. 6 depicts another embodiment of the sensor assembly of the present invention. In particular, FIG. 6A depicts a perspective view of a sensor; FIG. 6B depicts a perspective view of a sensor mount for use with the sensor of FIG. 6A; and FIG. 6C depicts a perspective view of the sensor of FIG. 6A mounted in the sensor mount of FIG.  6 B. 
     FIG. 7 depicts another embodiment of the sensor assembly of the present invention. In particular, FIG. 7A depicts a perspective view of a sensor; FIG. 7B depicts a perspective view of a sensor mount for use with the sensor of FIG. 7A; FIG. 7C depicts a perspective view of the sensor of FIG. 7A mounted in the sensor mount of FIG. 7B; and FIGS. 7D-71 depict perspective views of alternate sensor mounts for use with the sensor of FIG.  7 A. 
     FIG. 8 depicts still another embodiment of the sensor assembly of the present invention. In particular, FIG. 8A depicts a perspective view of a sensor; FIG. 8B depicts a perspective view of a sensor mount for use with the sensor of FIG. 8A; and FIG. 8C depicts a perspective view of the sensor of FIG. 8A mounted in the sensor mount of FIG.  8 B. 
     FIG. 9 depicts another embodiment of the sensor assembly of the present invention. In particular, FIG. 9A depicts an elevation view of a sensor; FIG. 9B depicts an elevation view of a portion of a sensor mount in which the sensor of FIG. 9A is mounted; FIG. 9C depicts an elevation view of the other portion of the sensor mount for use with the sensor of FIG. 9A; and FIG. 9D depicts an elevation view of the sensor of FIG. 9A mounted in the sensor mount of FIGS. 9B and 9C. 
     FIG. 10 depicts still another embodiment of the sensor assembly of the present invention. In particular, FIG. 10A depicts a perspective view of a sensor; FIG. 10B depicts a perspective view of a sensor mount for use with the sensor of FIG. 10A; and FIG. 10C depicts a perspective view of the sensor of FIG. 10A mounted in the sensor mount of FIG.  10 B. 
     FIG. 11 depicts still another embodiment of the sensor assembly of the present invention. In particular, FIG. 11A depicts a perspective view of a sensor; FIG. 11B depicts a perspective view of a sensor mount for use with the sensor of FIG. 11A; and FIG. 11C depicts a perspective view of the sensor of FIG. 11A mounted in the sensor mount of FIG.  11 B. 
     FIG. 12 depicts still another embodiment of the sensor assembly of the present invention. In particular, FIG. 12A depicts a perspective view of a sensor; FIG. 12B depicts a perspective view of a sensor mount for use with the sensor of FIG. 12A; and FIG. 12C depicts a perspective view of the sensor of FIG. 12A mounted in the sensor mount of FIG.  12 B. 
     FIG. 13 depicts still another embodiment of the sensor assembly of the present invention. In particular, FIG. 13A depicts a perspective view of a sensor; FIG. 13B depicts a perspective view of a sensor mount for use with the sensor of FIG. 13A; and FIG. 13C depicts a perspective view of the sensor of FIG. 13A mounted in the sensor mount of FIG.  13 B. 
     FIG. 14 depicts still another embodiment of the sensor assembly of the present invention. In particular, FIG. 14A depicts a perspective view of a sensor; FIG. 14B depicts a perspective view of a sensor mount for use with the sensor of FIG. 14A; and FIG. 14C depicts a perspective view of the sensor of FIG. 14A mounted in the sensor mount of FIG.  14 B. 
     FIG. 15 depicts still another embodiment of the sensor assembly of the present invention. In particular, FIG. 15A depicts a perspective view of a sensor; FIG. 15B depicts a perspective view of a sensor mount for use with the sensor of FIG. 15A; and FIG. 15C depicts a perspective view of the sensor of FIG. 15A mounted in the sensor mount of FIG.  15 B. 
     FIG. 16 depicts still another embodiment of the sensor assembly of the present invention. In particular, FIG. 16A depicts a perspective view of a sensor; FIG. 16B depicts a perspective view of a sensor mount; and FIG. 16C depicts a perspective view of the sensor of FIG. 16A mounted in the sensor mount of FIG.  16 B. 
     FIG. 17 depicts still another embodiment of the sensor assembly of the present invention. In particular, FIG. 17A depicts a perspective view of a sensor; FIG. 17B depicts a perspective view of a sensor mount for use with the sensor of FIG. 17A; and FIG. 17C depicts a perspective view of the sensor of FIG. 17A mounted in the sensor mount of FIG.  17 B. 
     FIG. 18 depicts still another embodiment of the sensor assembly of the present invention. In particular, FIG. 18A depicts a perspective view of a sensor; FIG. 18B depicts a perspective view of a sensor mount for use with the sensor of FIG. 18A; and FIG. 18C depicts a perspective view of the sensor of FIG. 18A mounted in the sensor mount of FIG.  18 B. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present inventions provide for a removable sensor assembly for tracking a movable object, such as a catheter, within a patient&#39;s body. As illustrated in FIG. 2, a sensor assembly  170  constructed in accordance with the present inventions is used with the afore-described image acquisition device  105  to facilitate synchronization of the catheter icon with the 2D fluoroscopic images while the C-arm  125  rotates about the patient. The sensor assembly  170  is shown mounted on a lateral surface  175  of the C-arm  125  near the upper end thereof. The sensor assembly  170 , however, may be mounted at alternative positions along the lateral surface, or any surface, of the C-arm  125 , as long as it is provides a reference point that accurately represents the relative position and orientation of the C-Arm  125 . 
     As illustrated in FIG. 2, the sensor assembly  170  comprises a sensor mount  180 , which is permanently attached to C-arm  125 , and a sensor  185 , which is removably attached to the sensor mount  180 . In the illustrated embodiment, the sensor  185  comprises a housing that contains three pairs of sensing elements (not depicted), which orthogonally sense electromagnetic energy in three axes. The sensor  185  also includes an outlet (not depicted) for the leads or wires that connect to the reception circuitry  155  and controller/processor  135  (depicted in FIG.  1 ). 
     The sensor mount  180  is permanently attached to a mounting surface  175  of the C-arm  125  by known means, such as by being welded, bonded, or even screwed on. The sensor mount  180  is made of non-ferromagnetic material, i.e., anything other than steel or a natural or synthetic material containing iron, and acts to separate and provide an appropriate, prescribed distance between the sensor  185  and the mounting surface  175  of the ferromagnetic C-arm  125 , thereby preventing an adverse magnetic effect on the sensor  185 . To this end, the sensor mount  180  includes a spacer  190 , the thickness of which defines the distance between the sensor  185  and the mounting surface of the C-arm  125 . The sensor mount  180  further comprises a sensor engaging element  195  with which the sensor  185  mates and is secured by an interference fit. The element of the sensor  185  that the sensor engaging element  195  of the sensor mount  80  engages is, for the purposes of this specification, a mount engaging element, which may be a sensor housing or other element. For the purposes of this specification, an interference fit refers to any fit or contact between mating parts having prescribed limits of size, material, and shape, so that a reversible mechanical hold between the mating parts is established. 
     As will be understood by the following description and reference to the respective drawings, the present inventors have developed a variety of innovative sensor mount assemblies with removably attached sensors that are maintained at the required distance from the surface of the C-arm  125 . 
     Referring now to FIG. 3C, a preferred embodiment of a sensor assembly  200  is depicted. The sensor assembly  200  comprises a sensor mount  202  (shown separately in FIG. 3B) and a sensor  204  (shown separately in FIG.  3 A), which is removably attached to the sensor mount  202 . The sensor  204  comprises a sensor housing  206 , which contains sensing elements (not depicted). The sensor housing  206  has a substantially tubular shaft  208  that includes an outlet  212  at one end from which sensor wires  214  extend, and an oppositely-disposed rounded end  210 . As can be seen, the diameter of the rounded end  210  is greater than the diameter of the shaft  208 . 
     The sensor mount  202  comprises a planar spacer flange  216 , which spaces the mounted sensor  204  the required distance away from the C-arm  125 . To this end, the spacer flange  216  comprises a first planar mounting surface  218 , which is the surface used to permanently attach the sensor mount  202  to the C-arm  125  via suitable means, such as welding or bonding, and an oppositely-disposed second planar mounting surface  220  from which a pair of sensor holding arms  222  extend. The ends  224  of the arms  222  curve towards each other to define an aperture  226  that has a cross-section that substantially matches that of the shaft  208  of the sensor housing  206 , such that the sensor  204  is disposed within the aperture  226  in a snap-fit arrangement with the arms  222 . Thus, as best illustrated in FIG. 3C, the shaft  208  of the sensor housing  206  fits snugly within the aperture  226 , with the round end  210  of the sensor housing  206  abutting the tops of the arms  222 . It should be noted that the sensor mount  202  can be considered a front mount in that the sensor  204  is inserted therein in a direction perpendicular to the first planar mounting surface  220 . 
     The ends  224  of the arms  222  comprise beveled edges  228 , which guide and facilitate the insertion of the sensor housing shaft  208  between the ends  224  of the arms  222  and into aperture  226 . Moreover, the beveled edges  228  allow the arms  222  to almost completely enclose the sensor housing shaft  208 , thereby providing a more secure fit between the sensor mount  202  and sensor  204 . Preferably, the arms  222  are composed of a firm material having an elastic property, such as an elastomer, so that their shape may be distorted as the shaft  208  is being inserted therebetween, yet at least partially restored once inserted. 
     FIGS. 3D and 3E depict alternative embodiments of sensor mounts that are similar to the afore-described sensor mount  202 , with the exception that they include spacer flanges that are coextensive with the pair of sensor holding arms, i.e., the pair of sensor holding arms has the same profile as the spacer flange when viewing the mount at an angle perpendicular to the mounting surface of the mount. In particular, FIG. 3D depicts a front sensor mount  230  that comprises a spacer flange  232  (set off by dashed lines) that includes a mounting surface  234  for mounting of the sensor mount  230  to the C-arm  125 , and a pair of arms  236  that extend from the flange  232  in a direction perpendicular to the mounting surface  234 . As can be seen, the arms  236  have the same profile as the spacer flange  232  when viewing it at an angle perpendicular to the mounting surface  234 . FIG. 3E depicts a side sensor mount  240  that comprises a spacer flange  242  (set off by dashed lines) that includes a mounting surface  244  for mounting of the sensor mount  240  to the C-arm  125 , and a pair of arms  246  that extend from the flange  242  in a direction parallel to the mounting surface  244 . As can be seen, the arms  246  have the same profile as the spacer flange  242  when viewing it at an angle perpendicular to the mounting surface  244 . 
     Referring to FIGS. 4A-4C, another preferred embodiment of a sensor assembly  250  is depicted. The sensor assembly  250  comprises a sensor mount  252  (shown separately in FIG. 4B) and a sensor  254  (shown separately in FIG.  4 A), which is removably attached to the sensor mount  252 . The sensor  254  comprises a T-shaped sensor housing  256 , which contains sensing elements (not depicted). The sensor housing  256  has a substantially tubular shaft  258  that includes an outlet  260  at one end from which sensor wires  262  extend, and a pair of sensor arms  264  at the other end. As illustrated, the pair of sensor arms  264  extend perpendicularly from the shaft  258  in opposite directions and in a coplanar relationship with the shaft  258 . The sensor arms  264  also include ends  278  that curve towards the shaft  258  for reasons that will further be described below. 
     The sensor mount  252  comprises a planar spacer flange  266 , which spaces the mounted sensor  254  the required distance away from the C-arm  125 . To this end, the spacer flange  266  comprises a first planar mounting surface  268 , which is the surface used to permanently attach the sensor mount  252  to the C-arm  125  via suitable means, such as welding or bonding, and an oppositely-disposed second planar mounting surface  270  from which a pair of sensor holding arms  272  perpendicularly extend. 
     The sensor arms  264  can be removably attached to the sensor holding arms  272  in a snap-fit arrangement. To this end, the sensor arms  264  each includes a ridge  274 , and the sensor holding arms  272  each includes an indentation  276 . Alternatively, the sensor arms  264  can each include an indentation, and the sensor holding arms  272  can each include a ridge. In any event, the sensor arms  264  and sensor holding arms  272  include features that facilitate the snap-fit arrangement. Thus, when the sensor shaft  258  is disposed between the sensor holding arms  272 , and the sensor arms  264  are disposed on the sensor holding arms  272  as illustrated in FIG. 4C, the ridges  274  snap into the indentations  276  to provide a secure fit between the sensor  254  and the sensor mount  252 . Additionally, the respective ends  278  of the sensor arms  264  engage the sensor holding arms  272  to more securely fit the sensor  254  and sensor mount  252 . 
     Referring to FIGS. 5A-5C, still another preferred embodiment of a sensor assembly  300  is depicted. The sensor assembly  300  comprises a sensor mount  302  (shown separately in FIG. 5B) and a sensor  304  (shown separately in FIG.  5 A), which is removably attached to the sensor mount  302 . The sensor  304  comprises an oblong sensor housing  306 , which contains sensing elements (not depicted). The sensor housing  306  has an outlet  308  at one end from which sensor wires  310  extend. The sensor housing  306  further comprises a barb  312  that extends perpendicularly from its center. Alternatively, the barb  312  may extend from any longitudinal point on the sensor housing  306 . 
     The sensor mount  302  comprises a planar spacer flange  314 , which spaces the mounted sensor  304  the required distance away from the C-arm  125 . To this end, the spacer flange  314  comprises a first planar mounting surface  316 , which is the surface used to permanently attach the sensor mount  302  to the C-arm  125  via suitable means, such as welding or bonding, and an oppositely-disposed second planar mounting surface  318 , in which an open oblong cavity  320  is formed for receiving the sensor housing  306 . The open cavity  320  includes a hole  322  along its midpoint for receiving the barb  312  of the sensor housing  306 . In this regard, the sensor housing  306  can be removably mounted within the open cavity  320  in a direction perpendicular to the first planar mounting surface  316  by disposing the barb  312  within the hole  322 , as illustrated in FIG.  5 C. To further facilitate the mounting of the sensor  304  on the sensor mount  302 , the shape and size of the sensor housing  306  and open cavity  320  are similar, such that the sensor housing  306  is securely fit within the open cavity  320 . Alternatively, the spacer flange  314  may be composed of an elastic material, and the size of the cavity  320  may be slightly smaller than the size of the housing  306 , such that the cavity  320  expands in a gripping relationship with the inserted housing  306 . Furthermore, a channel  324  is formed within the second planar mounting surface  318  of the spacer flange  314  to receive the sensor wires  310 . 
     Referring to FIGS. 6A-6C, still another preferred embodiment of a sensor assembly  350  is depicted. The sensor assembly  350  comprises a sensor mount  352  (shown separately in FIG. 6B) and a sensor  354  (shown separately in FIG.  6 A), which is removably attached to the sensor mount  352 . The sensor  354  comprises a conical sensor housing  356 , which contains sensing elements (not depicted). The sensor housing  356  has an outlet  358  at one end from which sensor wires  360  extend. The sensor mount  352  comprises a spacer flange, which spaces the mounted sensor  354  the required distance away from the C-arm  125 . To this end, the spacer flange  362  comprises a mounting surface  364 , which is the surface used to permanently attach the sensor mount  352  to the C-arm  125  via suitable means, such as welding or bonding. The spacer flange  362  further comprises a conical cavity  366  for receiving the conical sensor housing  356 . 
     In this regard, the conical sensor housing  356  can be removably mounted within the conical cavity  366  in a parallel direction to the mounting surface  364 , as illustrated in FIG.  6 C. To ensure a tight fit between the sensor  354  and the sensor mount  352 , the spacer flange  362  is preferably composed of an elastic material, and the size of the conical cavity  366  is slightly smaller than the size of the conical housing  356 , such that the conical cavity  366  expands in a gripping relationship with the inserted conical housing  356 . The spacer flange  362  further includes a slit  368  for receiving the sensor wires  360 . As illustrated, the slit  368  extends from the conical cavity  364  to the exterior of the spacer flange  362 , and is oriented in a direction parallel to the axis of the open cavity  364 . 
     Referring now to FIGS. 7A-7C, still another preferred embodiment of a sensor assembly  400  is depicted. The sensor assembly  400  comprises a sensor mount  402  (shown separately in FIG. 7B) and a sensor  404  (shown separately in FIG.  7 A), which is removably attached to the sensor mount  402 . The sensor  404  comprises a sensor housing  406 , which contains sensing elements (not depicted). The sensor housing  406  has a substantially tubular shaft  408  that includes an outlet  410  at one end from which sensor wires  412  extend, and a clip  414  at the opposite end. The clip  414  exhibits a non-circular cross-section, which in the illustrated embodiment, is generally D-shaped. 
     The sensor mount  402  comprises a spacer flange  416 , which spaces the mounted sensor  404  the required distance away from the C-arm  125 . To this end, the spacer flange  416  comprises a planar mounting surface  418 , which is the surface used to permanently attach the sensor mount  402  to the C-arm  125  via suitable means, such as welding or bonding. The sensor mount  402  also comprises clip-receiving means  420 , and specifically a cavity that exhibits a non-circular cross section, which in the illustrated embodiment, is D-shaped. As illustrated in FIG. 7C, the cavity  420  snugly receives the clip  414  in a direction parallel to the planar mounting surface  418 . 
     FIGS. 7D-7F depict alternative embodiments of sensor mounts that are similar to the afore-described sensor mount  402 , with the exception that the means for receiving the clip  414  comprises a handle that is formed on the spacer flange. Specifically referring to FIG. 7D, a sensor mount  422  comprises a spacer flange  424  that includes a first planar mounting surface  426  for permanently mounting the sensor mount  422  to the C-arm  125 , and a second planar mounting surface  428  from which a handle  430  extends. The handle  430  forms an aperture  431  between it and the second planar surface  428  for receiving the clip  414  of the sensor housing  406  in a direction parallel to the first planar mounting surface  426 . In the illustrated embodiment, the aperture  431  exhibits a cross-section substantially matching that of clip  414 , and in this case a D-shaped cross-section, so that the handle  430  snugly holds the clip  414 . The length of the spacer flange  424  preferably approximately matches that of the clip  414 . 
     Specifically referring to FIG. 7E, a sensor mount  432  comprises a spacer flange  434  that includes a first planar mounting surface  436  for permanently mounting the sensor mount  432  to the C-arm  125 , and a second planar mounting surface  438  from which a handle  440  extends. The handle  440  forms an aperture  441  between it and the second planar surface  438  for receiving the clip  414  of the sensor housing  406  in a direction parallel to the first planar mounting surface  436 . In the illustrated embodiment, the aperture  441  exhibits a cross-section substantially dissimilar to that of the clip  414 , and in this case a semi-circular cross-section, so that the handle  440  snugly holds the clip  414 . The length of the spacer flange  434  is substantially shorter than that of the clip  414 . 
     Specifically referring to FIG. 7F, a sensor mount  442  comprises a spacer flange  444  that includes a first planar mounting surface  446  for permanently mounting the sensor mount  442  to the C-arm  125 , and a second planar mounting surface  448  from which a handle  450  extends. The handle  450  forms an aperture  452  between it and the second planar surface  448  for receiving the clip  414  of the sensor housing  406  in a direction parallel to the first planar mounting surface  446 . In the illustrated embodiment, the aperture  452  exhibits a cross-section substantially dissimilar to that of the clip  414 , and in this case a rectangular cross-section, so that the handle  450  snugly holds the clip  414 . The length of the spacer flange  444  is substantially the same as that of the clip  414 . To further ensure a tight fit between the sensor housing  406  and the sensor mount  442 , a pair of sensor receiving arms  454  extend from the second planar surface  448  of the spacer flange  442 . The pair of arms  454  includes ends  456 , which curve towards each other to define an aperture  458  having a cross-section that substantially matches that of the shaft  408  of the sensor housing  406 , thereby allowing the arms  454  to grip the shaft  408  of the mounted sensor housing  406 . 
     FIG. 7G depicts an alternative embodiment of sensor mount  462  that is similar to the afore-described sensor mount  402 , with the exception that the means for receiving the clip  414  comprises a slit that is formed in the spacer flange. Specifically, the sensor mount  462  comprises a spacer flange  464  that includes a planar mounting surface  466  for permanently mounting the sensor mount  462  to the C-arm  125 . The sensor mount  462  further includes an elastomer slit  468  formed within the spacer flange  464  to receive the clip  414  of the sensor housing  406  in a direction parallel to the planar mounting surface  466 . Preferably, the size of the slit  468  is slightly smaller than the size of the clip  414 , such that the slit  414  expands in a gripping relationship with the inserted clip  414  to snugly engage the sensor  404  with the sensor mount  462 . 
     FIG. 7H depicts an alternative embodiment of sensor mount  472  that is similar to the afore-described sensor mount  402 , with the exception that the means for receiving the clip  414  comprises an L-shaped flange that extends from the spacer flange. Specifically, the sensor mount  472  comprises a spacer flange  474  that includes a first planar mounting surface  476  for permanently mounting the sensor mount  472  to the C-arm  125 , and a second planar mounting surface  478  from which an L-shaped flange  480  extends. The L-shaped flange  480  forms an open slot  481  between it and the second planar surface  478  for receiving the clip  414  of the sensor housing  406  in a direction parallel to the first planar mounting surface  476 . 
     FIG. 71 depicts an alternative embodiment of sensor mount  482  that is similar to the afore-described sensor mount  402 , with the exception that the means for receiving the clip  414  comprises a spring clip that extends from the spacer flange. Specifically, the sensor mount  482  comprises a spacer flange  484  that includes a first planar mounting surface  486  for permanently mounting the sensor mount  482  to the C-arm  125 , and a second planar mounting surface  488  from which a spring clip  490  extends. The spring clip  490  forms an open slot  494  between it and the second planar surface  488  for receiving the shaft  408  of the sensor housing  406  in a direction parallel to the first planar mounting surface  486 . The spring action of the clip  490  compresses the mounted sensor  404  against the spacer flange  484  in a snug relationship. The spring clip  490  also includes a cutout  494  that receives and accommodates the shaft  408  of the sensor housing  406  when the sensor  404  is mounted. 
     Referring now to FIGS. 8A-8C, still another preferred embodiment of a sensor assembly  500  is depicted. The sensor assembly  500  comprises a sensor mount  502  (shown separately in FIG. 8B) and a sensor  554  (shown separately in FIG.  8 A), which is removably attached to the sensor mount  502 . The sensor  504  comprises a sensor housing  506 , which contains sensing elements (not depicted) and an outlet  508  at one end from which sensor wires  510  extend. The sensor housing  506  may be of any shape, e.g., hexagonal, that has at least two lateral edges  512  and  514 . In fact, any shape other than a circle is contemplated to prevent rotation of the sensor housing  506  when mounted in the sensor mount  502 . 
     The sensor mount  502  comprises a planar spacer flange  516 , which spaces the mounted sensor  504  the required distance away from the C-arm  125 . To this end, the spacer flange  516  comprises a first planar mounting surface  518 , which is the surface used to permanently attach the sensor mount  502  to the C-arm  125  via suitable means, such as welding or bonding, and an oppositely-disposed second planar mounting surface  520  in which an open cavity  522  is formed for receiving the sensor housing  506  in a direction perpendicular to the first planar mounting surface  520 . The shape and size of the sensor housing  506  and open cavity  522  are substantially the same, such that the sensor housing  506  is snugly disposed within the open cavity  522  in a snap-fit arrangement. Thus, the open cavity  522  is defined by at least two lateral edges  524  and  526  that engage the at least two lateral edges  512  and  514  of the sensor housing  506  when the sensor  504  is mounted in the open cavity  522 . To further enhance the secure fit between the sensor mount  502  and the sensor  504 , the lateral edges  512  and  514  of the sensor  504  preferably each include at least one ridge  528 , and the lateral edges  524  and  526  of the open cavity  522  each include at least one mating indentation  530 . Alternatively, the lateral edges  512  and  514  of the sensor  504  include at least one indentation, and the lateral edges  524  and  526  of the open cavity  522  each include at least one mating ridge. 
     Referring now to FIGS. 9A-9D, still another preferred embodiment of a sensor assembly  550  is depicted. As illustrated in FIG. 9D, the sensor assembly  550  comprises a sensor mount  552  and a sensor  554 . Referring specifically to FIG. 9A, the sensor  554  comprises a sensor housing  556 , which contains sensing elements (not depicted). The sensor housing  556  has a substantially tubular shaft  558  that includes an outlet  560  at one end from which sensor wires  562  extend. Referring specifically to FIG. 9B, the sensor mount  552  comprises a planar spacer flange  564 , which spaces the mounted sensor  554  the required distance away from the C-arm  125 . The spacer flange  564  comprises a circular cavity  566  in which the sensor  554  is mounted, e.g., by bonding, with the tubular shaft  558  being disposed along the diameter of the circular cavity  566 , and the opposite ends thereof being in contact with a wall  568  of the cavity  566 . The spacer flange  564  further comprises a planar mounting surface  570 , which as will be described below, is the surface used to removably attach the spacer flange  564  to a patch  572  of the sensor mount  552 . 
     Referring specifically to FIG. 9C, the patch  572  comprises a first planar mounting surface  574 , which is the surface used to permanently attach the sensor mount  552  to the C-arm  125  via suitable means, such as welding or bonding, and an oppositely-disposed second planar mounting surface  576 , which is configured, such that the spacer flange  564  can be removably mounted thereto, as illustrated in FIG.  9 D. In the illustrated embodiment, a hook-in-loop material  578 , the hook portion of which is permanently disposed on the planar surface  570  of the spacer flange  564 , and the loop portion of which is permanently disposed on the second planar surface  576  of the patch  572 , is used to removably mount the spacer flange  564  to the patch  572 . 
     Referring now to FIGS. 10A-10C, still another preferred embodiment of a sensor assembly  600  is depicted. The sensor assembly  600  comprises a sensor mount  602  (shown separately in FIG. 10B) and a sensor  604  (shown separately in FIG.  10 A), which is removably attached to the sensor mount  602 . The sensor  604  comprises a cylindrical sensor housing  606 , which contains sensing elements (not depicted) and an outlet  608  at one end, from which sensor wires  610  extend. The sensor  604  further includes a member  612  that extends the length of the sensor housing  606 . 
     The sensor mount  602  comprises a planar spacer flange  614 , which spaces the mounted sensor  604  the required distance away from the C-arm  125 . To this end, the spacer flange  614  comprises a first planar mounting surface  616 , which is the surface used to permanently attach the sensor mount  602  to the C-arm  125  via suitable means, such as welding or bonding, and an oppositely-disposed second planar mounting surface  618 , from which a member  620  extends. A cavity  622  is formed in the member  620 , and extends the length of the spacer flange  614 . 
     The member  612  of the sensor  604  and the cavity  622  of the sensor mount  602  have substantially uniform and complementary cross-sections, and in this case T-shaped cross-sections, such that they are configured to slidingly engage each other in a direction parallel to the first planar mounting surface  616  of the sensor mount  602 . To further ensure a secure fit between the sensor  604  and the sensor mount  602 , the T-shaped member  612  includes a protuberance  624 , and the T-shaped cavity  622  comprises an indentation  626  that engage each other in a snap-fit arrangement when the T-shaped member  612  is fully engaged with the T-shaped cavity  622 , as illustrated in FIG.  10 C. 
     Referring now to FIGS.  11 A 1 - 11 C, still another preferred embodiment of a sensor assembly  650  is depicted. The sensor assembly  650  is similar to the previously described sensor assembly  600 , with the exception that a trapezoidal-shaped member and cavity arrangement is used. Specifically, the sensor assembly  650  comprises a sensor mount  652  (shown separately in FIG. 11B) and a sensor  654  (shown separately in FIG.  11 A), which is removably attached to the sensor mount  652 . The sensor  654  comprises a sensor housing  656 , which contains sensing elements (not depicted) and an outlet  658  at one end from which sensor wires  660  extend. The sensor  654  further includes a member  662  that extends the length of the sensor housing  656 . 
     The sensor mount  652  comprises a planar spacer flange  664 , which spaces the mounted sensor  654  the required distance away from the C-arm  125 . To this end, the spacer flange  664  comprises a planar mounting surface  666 , which is the surface used to permanently attach the sensor mount  652  to the C-arm  125  via suitable means, such as welding or bonding. The spacer flange  664  further comprises a cavity  668  formed therein that extends the length of the sensor housing  656 . 
     The member  662  of the sensor  654  and the cavity  668  of the sensor mount  652  have substantially uniform and complementary cross-sections, and in this case, trapezoidal-shaped cross-sections, such that they are configured to slidingly engage each other in a direction parallel to the planar mounting surface  666  of the sensor mount  652 . To further ensure a secure fit between the sensor  654  and the sensor mount  652 , the trapezoidal-shaped member  662  includes a protuberance  670 , and the trapezoidal-shaped cavity  668  comprises an indentation  672  that engage each other in a snap-fit arrangement when the trapezoidal-shaped member  662  is fully engaged with the trapezoidal-shaped cavity  672 , as illustrated in FIG.  11 C. The sensor  654  conveniently includes a finger handle  674 , which can be grasped by the user to slide the member  662  of the sensor  654  into and out of the cavity  668  of the sensor mount  652 . 
     Referring now to FIGS. 12A-12C, still another preferred embodiment of a sensor assembly  700  is depicted. The sensor assembly  700  comprises a sensor mount  702  (shown separately in FIG. 12B) and a sensor  704  (shown separately in FIG.  11 A), which is removably attached to the sensor mount  702 . The sensor  704  comprises a sensor housing  706 , which contains sensing elements (not depicted) and an outlet  708  at one end from which sensor wires  710  extend. The sensor  704  further includes a member  712  that forms a cavity  714  that extends the length of the sensor housing  706 . 
     The sensor mount  702  comprises a planar spacer flange  716 , which spaces the mounted sensor  704  the required distance away from the C-arm  125 . To this end, the spacer flange  716  comprises a first planar mounting surface  718 , which is the surface used to permanently attach the sensor mount  702  to the C-arm  125  via suitable means, such as welding or bonding, and an oppositely-disposed second planar mounting surface  720  from which a member  722  extends along the length of the spacer flange  716 . 
     The cavity  714  of the sensor  704  and the member  722  of the sensor mount  702  have substantially uniform and complementary cross-sections, and in this case, rectangular-shaped cross-sections, such that they are configured to slidingly engage each other in a direction parallel to the first planar mounting surface  718  of the sensor mount  702 . To further ensure a secure fit between the sensor  704  and the sensor mount  702 , the rectangular-shaped cavity  714  includes opposing sidewalls  724 , each with a ridge  726  that extends the length thereof, and the rectangular-shaped member  722  includes opposing sidewalls  728 , each with a slot  730  that extends the length thereof. The ridges  726  and slots  730  engage each other in a friction fit, as the rectangular member  722  is engaged with the rectangular cavity  714 , as illustrated in FIG.  12 C. 
     Referring now to FIGS. 13A-13C, still another preferred embodiment of a sensor assembly  750  is depicted. The sensor assembly  750  comprises a sensor mount  752  (shown separately in FIG. 13B) and a sensor  754  (shown separately in FIG.  13 A), which is removably attached to the sensor mount  752 . The sensor  754  comprises a cylindrical sensor housing  756 , which contains sensing elements (not depicted) and an outlet  758  at one end, from which sensor wires  760  extend. For purposes that will be described below, the sensor housing  756  further includes a key  762  that extends along the length thereof. 
     The sensor mount  752  comprises a planar spacer flange  764 , which spaces the mounted sensor  754  the required distance away from the C-arm  125 . To this end, the spacer flange  764  comprises a first planar mounting surface  766 , which is the surface used to permanently attach the sensor mount  752  to the C-arm  125  via suitable means, such as welding or bonding, and an oppositely-disposed second planar mounting surface  768 , from which a member  770  extends. The member  770  comprises a cylindrical cavity  772  formed therein that extends along the length of the spacer flange  764 . The cylindrical cavity  772  comprises a key slot  774  that extends along the length thereof. 
     The sensor housing  756  and the cavity  772  of the sensor mount  752  havesubstantially uniform and complementary cross-sections, and in this case, elliposidal-shaped cross-sections, and specifically circular-shaped cross-sections, such that they are configured to slidingly engage each other in a direction parallel to the first planar mounting surface  766  of the sensor mount  752 . Additionally, the key  762  of the sensor housing  756  fits in and engages with the key slot  774  of the cylindrical cavity  772 , such that the cylindrical sensor housing  756  does not rotate along the axis of the cylindrical cavity  772 . To further ensure a secure fit between the sensor  754  and the sensor mount  752 , the cylindrical sensor housing  756  includes a detent  776 , and the cylindrical cavity  772  includes an aperture  778  that engage each other when the cylindrical sensor housing  756  is fully engaged with the cylindrical cavity  772 , as illustrated in FIG.  13 C. 
     Referring now to FIGS. 14A-14C, still another preferred embodiment of a sensor assembly  800  is depicted. The sensor assembly  800  is similar to the previously described sensor assembly  750 , with the exception that opposing extensions, rather than a key, is used to prevent rotation of the sensor housing. Specifically, the sensor assembly  800  comprises a sensor mount  802  (shown separately in FIG. 14B) and a sensor  804  (shown separately in FIG.  14 A), which is removably attached to the sensor mount  802 . The sensor  804  comprises a generally cylindrical sensor housing  806 , which contains sensing elements (not depicted) and an outlet  808  at one end, from which sensor wires  810  extend. For purposes that will be described below, the sensor housing  806  further includes a pair of lateral opposing extensions  812 . 
     The sensor mount  802  comprises a spacer flange  814 , which spaces the mounted sensor  804  the required distance away from the C-arm  125 . To this end, the spacer flange  814  comprises a planar mounting surface  816 , which is the surface used to permanently attach the sensor mount  802  to the C-arm  125  via suitable means, such as welding or bonding. The sensor mount  802  further comprises a cylindrical cavity  822  that is formed within the spacer flange  814  extends along the length of the spacer flange  814 . The cylindrical cavity  822  comprises a pair of lateral opposing extensions  824  that extends along the length thereof. 
     The sensor housing  806  and the cavity  822  of the sensor mount  802  have substantially uniform and complementary cross-sections, and in this case, elliposidal-shaped cross-sections, and specifically circular-shaped cross-sections, such that they are configured to slidingly engage each other in a direction parallel to the planar mounting surface  816  of the sensor mount  802 . Additionally, the pair of opposing lateral extensions  812  of the sensor housing  806  fits in and engages with the pair of opposing lateral extensions  824  of the cylindrical cavity  822 , such that the cylindrical sensor housing  806  does not rotate along the axis of the cylindrical cavity  822 . To further ensure a secure fit between the sensor  804  and the sensor mount  802 , the cylindrical sensor housing  806  includes a detent  826 , and the cylindrical cavity  822  includes an aperture  828  that engage each other when the cylindrical sensor housing  806  is fully engaged with the cylindrical cavity  822 , as illustrated in FIG.  14 C. 
     Referring now to FIGS. 15A-15C, still another preferred embodiment of a sensor assembly  850  is depicted. The sensor assembly  850  comprises a sensor mount  852  (shown separately in FIG. 15B) and a sensor  854  (shown separately in FIG.  15 A), which is removably attached to the sensor mount  852 . The sensor  854  comprises a cylindrical sensor housing  856 , which contains sensing elements (not depicted) and an outlet  858  at one end, from which sensor wires  860  extend. The sensor  854  further includes a rigid planar member  862 , which includes a first planar surface  864  and an oppositely-disposed second planar surface  866 , from which the sensor housing  856  extends. 
     The sensor mount  852  comprises a planar spacer flange  868 , which spaces the mounted sensor  854  the required distance away from the C-arm  125 . To this end, the spacer flange  868  comprises a first planar mounting surface  870 , which is the surface used to permanently attach the sensor mount  852  to the C-arm  125  via suitable means, such as welding or bonding, and an oppositely-disposed second planar mounting surface  872 . The sensor mount  852  further includes a flexible planar member  874  that is configured to be removably attached to the second planar mounting surface  872  of the spacer flange  868 . The flexible planar member  874  comprises an aperture  876 , through which the sensor housing  856  can fit through, but through which the rigid planar member  862  cannot. 
     Thus, the spacer flange  868 , with the sensor housing  856 , can be inserted between the flexible planar member  874  and the spacer flange  868  when removably attaching the flexible planar member  874  to the spacer flange  868 , thereby removably mounting the sensor  854  to the sensor mount  852 , as illustrated in FIG.  15 C. In the illustrated embodiment, a hook-in-loop material (not illustrated), the hook portion of which forms the flexible planar member  874 , and the loop portion of which is permanently disposed on the second planar surface  872  of the spacer flange  868 , is used to removably mount the rigid planar member  862 , and thus, the sensor  854 , to the sensor mount  852 . 
     Referring now to FIGS. 16A-16C, still another preferred embodiment of a sensor assembly  900  is depicted. The sensor assembly  900  comprises a sensor mount  902  (shown separately in FIG. 16B) and a sensor  904  (shown separately in FIG.  16 A), which is removably attached to the sensor mount  902 . The sensor  904  comprises a cylindrical sensor housing  906 , which contains sensing elements (not depicted) and an outlet  908  at one end, from which sensor wires  910  extend. The sensor  904  further includes a pair of axially aligned snap holes  912  that is formed within the sensor housing  906 . 
     The sensor mount  902  comprises a planar spacer flange  914 , which spaces the mounted sensor  904  the required distance away from the C-arm  125 . To this end, the spacer flange  914  comprises a first planar mounting surface  916 , which is the surface used to permanently attach the sensor mount  902  to the C-arm  125  via suitable means, such as welding or bonding, and an oppositely-disposed second planar mounting surface  918 , from which a pair of axially aligned snap protuberances  920  extend. The spacing between, and size of, the pair of snap holes  912  and the spacing between, and size of, the pair of snap protuberances  920  match, such that they are configured to snap together to mount the sensor  904  on the sensor mount  902 , as illustrated in FIG.  16 C. 
     Referring now to FIGS. 17A-17C, still another preferred embodiment of a sensor assembly  950  is depicted. The sensor assembly  950  comprises a sensor mount  952  (shown separately in FIG. 17B) and a sensor  954  (shown separately in FIG.  17 A), which is removably attached to the sensor mount  952 . The sensor  954  comprises a cylindrical sensor housing  956 , which contains sensing elements (not depicted) and an outlet  958  at one end, from which sensor wires  960  extend. The sensor housing  956  includes two oppositely-disposed cutouts  962 , which are preferably provided at or near the midpoint of the sensor housing  956 . 
     The sensor mount  952  comprises a spacer flange  964 , which spaces the mounted sensor  954  the required distance away from the C-arm  125 . To this end, the spacer flange  964  comprises a planar mounting surface  966 , which is the surface used to permanently attach the sensor mount  952  to the C-arm  125  via suitable means, such as welding or bonding, and an oppositely-disposed concave surface  968  that is sized and shaped to receive the sensor housing  956 . A pair of sensor holding arms  970  extends from the concave surface  968  of the spacer flange  964 , and includes opposing concave surfaces  972  that define an aperture  974  between the arms  970 . The holding arms  970  are configured to grip the sensor housing  956  therebetween in a snap-fit arrangement when the concave surfaces  972  are coincident with the cutouts  962  of the sensor housing  956 , as illustrated in FIG.  17 C. The concave surface  968  of the spacer flange  964  receives the sensor housing  956 , thereby further ensuring a secure fit between the sensor  954  and the sensor mount  952 . Each of the pair of sensor arms  970  comprises a beveled edge  976 , which guides and facilitates the insertion of the sensor housing  956  between the arms  970  and into the aperture  974 . Preferably, the sensor holding arms  970  are composed of a resilient material having an elastic property, such as an elastomer, so that their shape may be distorted as the sensor housing  956  is inserted therebetween, yet at least partially restored once inserted. 
     Referring to FIGS. 18A-18C, still another preferred embodiment of a sensor assembly  1000  is depicted. The sensor assembly  1000  comprises a sensor mount  1002  (shown separately in FIG. 18B) and a sensor  1004  (shown separately in FIG.  18 A), which is removably attached to the sensor mount  1002 . The sensor  1004  comprises a generally cylindrical sensor housing  1006 , which contains sensing elements (not depicted). For purposes that will be described in further detail below, the cross-section of the cylindrical sensor housing  1006  forms a semi-circle that exhibits an arc of greater than 180 degrees. The sensor housing  1006  has an outlet  1008  at one end, from which sensor wires  1010  extend. The sensor housing  1006  further comprises extensions  1012  that extend perpendicularly from the sensor housing  1006  in opposite directions. The sensor  1004  further includes a planar flange  1014  that has a planar surface  1016 , from which the sensor housing  1006  extends. 
     The sensor mount  1002  comprises a planar spacer flange  1016 , which spaces the mounted sensor  1004  the required distance away from the C-arm  125 . To this end, the spacer flange  1004  comprises a first planar mounting surface  1018 , which is the surface used to permanently attach the sensor mount  1002  to the C-arm  125  via suitable means, such as welding or bonding, and an oppositely-disposed second planar mounting surface  1020 , in which a generally cylindrical open cavity  1022  is formed for receiving the sensor housing  1006 . The cross-section of the generally cylindrical cavity  1022  forms a semi-circle that exhibits an arc of greater than 180 degrees, such that it receives the generally cylindrical housing  1006  in a snap-fit arrangement, as illustrated in FIG.  18 C. The coincidence between the planar surface  1016  of the sensor  1004  and the second planar mounting surface  1020  of the spacer flange  1016  prevents the sensor housing  1006  from rotating relative to the axis of the cavity  1022 . Additionally, the cavity  1022  further comprises extensions  1024  that extend perpendicularly therefrom, in opposite directions, to receive the lateral extensions  1012  of the sensor housing  1006 , thereby ensuring that the sensor housing  1006  does not rotate within the cavity  1022 . 
     Although particular embodiments of the present inventions have been shown and described, it will be understood that it is not intended to limit the present inventions to the preferred embodiments, and it will be obvious to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the present inventions. Thus, the present inventions are intended to cover alternatives, modifications, and equivalents, which may be included within the spirit and scope of the present inventions as defined by the claims. All publications, patents, and patent applications cited herein are hereby incorporated by reference in their entirety for all purposes.

Technology Category: a