Abstract:
An intraoral x-ray sensor with embedded standard computer interface. The sensor includes a data transfer cable with improved mechanical strength and heat transferring properties. In one embodiment, the cable is quad-twisted USB cable and includes two data lines, a ground line, and fillers twisted within a metallic sheath, e.g., a metal braided shield. The cable is symmetrically organized about a centerline. The symmetric cable has an improved life due to the ability to withstand mechanical stress (e.g., rotational stress). The sensor includes a processor and a housing with an inner metallization layer. The sheath is coupled to the inner metallization layer to transfer heat generated by the processor from the inner metallization layer to the sheath.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a continuation application of U.S. application Ser. No. 12/796,251 (the “&#39;251 Application”). The &#39;251 Application claims priority to U.S. Provisional Patent Application Ser. No. 61/226,556, filed Jul. 17, 2009, the entire contents of which is hereby incorporated by reference. This application is also related to U.S. patent application Ser. No. 12/605,624, filed Oct. 26, 2009, U.S. Provisional Patent Application Ser. No. 61/108,552, filed Oct. 27, 2008, and U.S. Provisional Patent Application Ser. No. 61/226,533, filed Jul. 17, 2009, the entire contents of which are hereby incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    The present invention relates to x-ray imaging, including dental x-ray imaging. More particularly, embodiments of the invention relate to a data transfer cable for an intraoral sensor with improved mechanical strength and heat transfer properties 
         [0003]    X-rays have been used in dentistry to image teeth and parts of the mouth for many years. In general, the process involves generating x-rays and directing the x-rays at the patient&#39;s mouth. The x-rays are attenuated differently by different parts of the mouth (e.g., bone versus tissue) and this difference in attenuation is used to create an image, such as on film or by using electronic image sensor. 
       SUMMARY 
       [0004]    One challenge associated with electronic intraoral x-ray systems relates to the mechanical stress on a cable coupling the sensor capturing images and an output device, such as a computer. To capture dental x-ray images, the intraoral sensor is positioned within the oral cavity of each patient, which often includes twisting and tugging forces being exerted on the cable. The repeated and continuous positioning of the intraoral sensor for each patient results in increased mechanical stress, which wears the cable. With increased use and wear, the cable can malfunction and become unusable. 
         [0005]    An additional challenge relates to the environment in which the intraoral sensor operates: the oral cavity of a patient. The electronics within the intraoral sensor generate heat and, if left unchecked, can result in injury to the patient. Certain governmental regulations or other standards apply to devices, such as intraoral sensors, that limit the maximum operating temperature. For instance, safety standard 60601-1 2 nd  edition from the International Electrotechnical Commission (IEC) limits the outside temperature of such intraoral sensors to 41 degrees Celsius. 
         [0006]    Embodiments of the invention provide, among other things, an intraoral sensor including a sensor housing having a top portion and a bottom portion. The sensor further includes a twisted-quad universal serial bus (USB) cable coupled to the top portion. The twisted-quad USB cable includes an outer sheath and, within the outer sheath, a first data line, a second data line, a ground line, a power line, and four fillers that are twisted together to form a single bundle. The sensor also includes circuitry within the sensor housing. The circuitry converts x-rays received through the bottom portion into x-ray data and outputs the x-ray data along the twisted-quad USB cable. 
         [0007]    In some embodiments, the first data line, the second data line, the ground line, the power line, and the four fillers are symmetrically organized about a centerline of the twisted-quad USB cable. Additionally, in some embodiments, the four fillers includes a first filler, a second filler, a third filler, and a fourth filler. The first filler abuts the ground line and the first data line; the second filler abuts the ground line and the second data line; the third filler abuts the power line and the first data line; and the fourth filler abuts the power line and the second data line. In some embodiments, the four fillers are made of a plastic, electrically insulating material. 
         [0008]    In some embodiments, the outer sheath includes a braided shield and is coupled via a heat-conducting wire to a metallic layer substantially covering an inner surface of the top portion. In some embodiments, the outer sheath further comprises a jacket layer outside of the braided shield and a tape layer inside of the braided shield. Additionally, in some embodiments, the sensor includes an isolation layer within the sensor housing. The isolation layer is between the circuitry and the top portion and wherein the isolation layer is electrically insulating and heat conducting. In some embodiments, the isolation layer is coupled to one of the metallic layer and the braided shield via one of a second heat-conducting wire and direct contact to provide heat transfer from within the sensor housing to the twisted-quad USB cable. 
         [0009]    Additionally, embodiments of the invention provide an intraoral x-ray sensor including a housing and circuitry within the housing. The housing includes a top portion and a bottom portion. The top portion has a first inner surface and a first thermal resistance. The first inner surface is substantially covered by a metallic layer with a second thermal resistance that is lower than the first thermal resistance. The circuitry converts x-rays received through the bottom portion into x-ray data and outputs the x-ray data along a data cable. The data cable includes wires within a metallic shield. The metallic shield is coupled to the metallic layer by a thermally conductive path that has a thermal resistance that is less than the thermal resistance of air. 
         [0010]    In some embodiments, the bottom portion includes a second inner surface substantially covered by a second metallic layer that is coupled to the metallic layer either directly or via another thermally conductive path. The circuitry is contained on a printed circuit board (PCB) that is isolated from the metallic layer by an isolation layer. The isolation layer is thermally conductive and electrically insulating, and includes (in some implementations) an opening through which the circuitry and the wires are connected. Additionally, in some embodiments, the circuitry includes an array of pixels on a first side of the PCB and, on a second side of the PCB, a processor and an input/output module. The sensor includes x-ray attenuation components between the second side and a surface of the bottom portion through which x-rays are received. The x-ray attenuation components may include: a lead layer, a fiber optic covered by a scintillating layer, and copper planes. The top portion includes a dome (with the shape of a partial, elliptical paraboloid) having a face with a circular opening. The circular opening receives the data cable. 
         [0011]    Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a schematic illustration of a dental x-ray system including an x-ray source, an intraoral sensor located in a patient&#39;s mouth, and a computer connected to the intraoral sensor. 
           [0013]      FIG. 1   a  is a schematic illustration of the intraoral sensor shown in  FIG. 1  showing internal components of the sensor. 
           [0014]      FIG. 2  depicts an exploded view of the intraoral sensor shown in  FIG. 1 . 
           [0015]      FIG. 3  depicts a cross section along line A of  FIG. 4 . 
           [0016]      FIG. 4  depicts a top view of the intraoral sensor shown in  FIG. 1  and a cable connector. 
           [0017]      FIG. 5   a  depicts a cross section of a prior-art universal serial bus (USB) cable. 
           [0018]      FIG. 5   b  depicts a wiring diagram of a prior-art universal serial bus (USB) cable. 
           [0019]      FIG. 6   a  depicts a cross section of a cable according to embodiments of the invention. 
           [0020]      FIG. 6   b  depicts a wiring diagram of a cable according to embodiments of the invention. 
           [0021]      FIG. 7  depicts the underside of the top cover of the intraoral sensor of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. 
         [0023]      FIG. 1  illustrates a dental x-ray system  10 . The system includes an x-ray source  12 . In the embodiment shown, the source is located on an end  13  of a mechanical arm  15 . When activated, the x-ray source  12  generates an x-ray stream  16  that has a generally circular cross-section. (Of course, x-rays are generally invisible, but a representation of a stream is illustrated to facilitate understanding of the invention.) In many applications, a collimator is used to reduce the size of the stream and generate a smaller x-ray stream having a rectangular cross-section. A collimator may be used with a mechanical positioning device to help align the x-ray stream with an x-ray sensor. As shown in  FIG. 1 , x-ray source  12  is positioned (e.g., by an operator) so that the x-ray stream  16  is directed to an intraoral sensor  20 . The intraoral sensor  20  is shown located in the mouth of a patient  21 . In some embodiments, the intraoral sensor  20  includes a scintillator that coverts x-ray radiation to visible light. In other embodiments, the sensor  20  is configured to convert x-rays into electric charge without a scintillator. Unless otherwise specified, the term pixel refers both to a pixel in the array of pixels that converts x-rays to electrons without a scintillator and a pixel in the array of pixels and its associated scintillator or portion of a scintillator. 
         [0024]    As best seen by reference to  FIG. 1   a,  the sensor  20  also includes an array of pixels  22 . The components of  FIG. 1   a,  including the array of pixels  22 , are not drawn to scale relative to the outline of the sensor  20 . Each pixel produces an electric signal in response to light (from the scintillator) or x-ray radiation impinged upon it. In one embodiment, the sensor  20  includes one or more “on-board” analog-to-digital converters to covert analog signals generated by the pixels to digital signals. These signals are provided to a processor  23  (such as a programmable, electronic microprocessor, field programmable gate array, erasable programmable logic device(s), or similar device(s)). In the embodiment shown, the processor  23  is connected to memory  24  (ROM and RAM) and an input-output interface  25 . The sensor  20  also includes one or more electronic circuits for power supply, driving the array of pixels, and driving the output (e.g., circuits located in the I/O interface  25 ). In some embodiments, the I/O interface  25  is a universal serial bus (“USB”) interface. 
         [0025]    In some embodiments, the processor  23  controls image capture or triggering of the sensor  20 . In other embodiments, the x-ray source  12  is coupled to the sensor  20 , e.g., via computer  30 , such that when the x-ray source  12  is activated, a command is sent (simultaneously or nearly simultaneously) to the sensor  20  to perform an image capture. Thus, it is possible to generate a burst of x-ray radiation and be assured that an image will be captured by the sensor  20  during the relatively short period of x-ray exposure either through automatic triggering or via a specific capture command sent to the intraoral sensor  20 . 
         [0026]    Referring back to  FIG. 1 , a wire, cable, or similar connecter  27  of the sensor  20  connects the sensor  20  to a computer  30 . The computer  30  includes various components, including a processor or similar electronic device  32 , an input/output interface  34 , and memory  36  (e.g., RAM and ROM). In some embodiments, the input/output interface  34  is a USB connection and the cable  27  is a USB cable.  FIG. 1  illustrates that image data captured by the sensor  20  and processed by the computer  30  is sent to a display  38  and viewed as image  40 . (Image  40  is drawn more distinctly than an x-ray image would typically appear.) 
         [0027]    The location of the intraoral sensor  20  in the patient&#39;s mouth determines what part of the patient&#39;s anatomy can be imaged (e.g., the upper jaw versus the lower jaw or the incisors versus the molars.) An x-ray operator places (or assists the patient in placing) the intraoral sensor  20  at a desired location with the patient&#39;s mouth. Various sensor holders (including those that are used with or that include a collimator) may be used to keep the sensor  20  in the desired location until an image is created or captured. For example, some holders are designed so that the patient bites the holder with his or her teeth and maintain the position of the sensor  20  by maintaining a bite on the holder. After the sensor  20  is positioned behind the desired anatomical structure, and the x-ray field to be generated by the x-ray source  12  is aligned with the sensor  20 , it is possible that the source  12  and sensor  20  will, nevertheless, become misaligned. Misalignment can be caused by the patient moving his or her head, moving the intraoral sensor  20  (by re-biting the holder, moving his or her tongue, etc.), and other causes. 
         [0028]      FIG. 2  depicts an exploded view of the intraoral sensor  20 . The sensor  20  includes a housing  45 . The housing  45  has a top portion  50  and a bottom portion  55 . Within the housing  45  is an insulator  60 , a printed circuit board (“PCB”)  65 , a silicon detecting layer  67 , an x-ray converter  70 , and a cushioning layer  71 , which protects against mechanical shocks. Some embodiments of the sensor  20  do not include the cushioning layer  71 . 
         [0029]    The top portion  50  includes a dome  75  that receives cable  27 . The dome  75  has a shape that approximates an elliptical paraboloid divided in half by the surface  76  of the top portion  50  (a partial, elliptical paraboloid shape). Other dome shapes are contemplated for use in embodiments of the invention. The dome  75  includes a face with an approximately circular opening through which the cable  27  passes. The cable  27  includes connectors (e.g., wires), a portion of which pass through an opening  79  of the insulator  60  to connect to the PCB  65 . In some embodiments, a ribbon or other connector passes through the opening  79  to couple the wires of cable  27  to the PCB  65 . The insulator  60  provide electrical isolation between the PCB  65  and the housing  45  of the sensor  20 . In some embodiments, the insulator  60  also secures the PCB  65  and x-ray converter  70  in position and protects each against mechanical shocks. Although the insulator  60  resists conducting electricity it is a conductor of heat, which assists in transferring heat away from the PCB  65 . 
         [0030]    The PCB  65 , silicon detecting layer  67 , and converter  70  include the components of the sensor  20  illustrated in  FIG. 1   a,  namely the array of pixels  22 , the processor  23 , the memory  24 , and I/O interface  25 . In the embodiment depicted in  FIG. 2 , the array of pixels  22  includes a plurality of pixels, each pixel including a converting portion (i.e., a portion of converter  70 ) and a detecting portion (i.e., a portion of silicon detecting layer  67 ). The PCB  65  supports the silicon detecting layer  67  (e.g., a CMOS die) and converter  70 , with the silicon detecting layer  67  being secured, e.g., using a glue or epoxy, to the PCB  65 . The converter  70  converts x-rays received through the bottom portion  55  into light. The light travels to the silicon detecting layer  67 , which converts the received light into charge. The charge is integrated at each pixel and the quantity of charge integrated represents the amount of x-rays received (although some of the integrated charge is attributable to noise and dark current). During a read-out of the array of pixels  22 , the processor  23  determines the quantity of charge integrated at each pixel in the array of pixels  22 . In some embodiments, the converter  70  and silicon detecting layer  67  include a fiber optic with scintillator. In some embodiments, the array of pixels  22  converts x-rays directly to charge without an intermediate step of converting x-ray to light. In such embodiments, among other possible alterations, an additional insulator (similar to insulator  60 ) is positioned in place of converter  70 , and is used to provide electrical isolation between the housing  45  and the PCB  65  and help transfer heat away from the PCB  65 . 
         [0031]      FIG. 3  depicts a cross section of the sensor  20  along line A as shown in  FIG. 4 . The top portion  50  is secured to the bottom portion  55  for instance, using ultrasonic welding and machining The welding bonds the top portion  50  to the bottom portion  55 , and machining smoothes the surface. Additionally, the top portion  50  and bottom portion  55  include interlocking portions  56 . The converter  70 , PCB  65 , silicon detecting layer  67 , and insulator  60  are shown within the housing  45 . Also depicted is the cable  27  including stress relief portion  77 . The stress relief portion  77  is secured to the cable  27 , for instance, using an adhesive. Additionally, the stress relief portion  77  includes a circumferential notch  80  that matches up with ridge  85  on the dome  75 . The stress relief portion  77  is secured to the dome  75  using the interlocking notch  80  and ridge  85 . An adhesive may also be used to secure stress relief portion  77  to the dome  75 . The stress relief portion  77  alleviates mechanical stress on the cable-to-housing coupling  81  created from twisting, pulling, and other forces on cable  27  and housing  45 . Thus, the stress relief portion  77  extends the life of the cable-to-housing coupling  81 , preventing or delaying malfunction of the sensor  20  caused by breaking the connection between the cable  27  and the housing  45 .  FIG. 4  depicts a top view of the sensor  20  and a USB connector  82  at the end of cable  27 . 
         [0032]      FIG. 5   a  depicts a cross section of a standard universal serial bus (USB) cable  100  capable of high speed USB version  2 . 0  communication. The standard USB cable  100  includes four main wires: data line  105  (D+), data line  110  (D−), power line  115 , and ground line  120 . Additionally, surrounding the four main wires is an isolating jacket  125 , an outer shield  130  made of 65% interwoven tinned copper braid, and an inner shield  135  made of aluminum metallized polyester. The isolating jacket  125  is made of polyvinyl chloride (PVC) in some embodiments. Running lengthwise along with wire between the inner shield  135  and the outer shield  130  is a copper drain wire  140 . The standard USB cable  100  is not symmetrical. Rather, the standard USB cable  100  has an internal, non-circular, oval structure, although fillers and plastic (not shown) may be used to create an external, circular shape of the cable. The external, circular shape can be approximately 4 mm in diameter. 
         [0033]      FIG. 5   b  depicts a wiring diagram of the standard USB cable  100 . As illustrated, the standard USB cable  100  has one twisted signaling pair including the data line  105  (D+) and data line  110  (D−). In some implementations, the power line  115  and ground line  120  are twisted (possibly to a lesser extent) or, as shown in  FIG. 5   b , not twisted at all. 
         [0034]      FIG. 6   a  depicts a cross section of a cable  150  according to embodiments of the invention. The cable  150  includes four main wires  210  and four fillers  175   a - d.  The four main wires  210  include data line  155  (D+), data line  160  (D−), power line  165 , and ground line  170 , which provide data transmission, power transmission, and grounding, respectively. The data line  155  (D+), data line  160  (D−), power line  165 , and ground line  170  each include a metal conductor encapsulated by a co-axial insulator. The four fillers  175   a - d  are made of plastic and are twisted along with the four main wires  210  to form a twisted quad cable. The four mains wires  210  and four fillers  175   a - d  are surrounded by three layers that run the length of the cable  150 . The three layers include polytetrafluoroethylene (“PTFE”) tape  180 , a braided shield  185 , and a polyurethane jacket  190 . In some embodiments, other materials are used for the jacket  190  and the tape  180  (e.g., another material similar to PTFE with a low surface roughness). The braided shield  185  is made up of, for instance, tinned copper wires with 0.08 mm diameter (40 AWG). As will be discussed further below, in some embodiments, the braided shield  185  is a heat conductor. In some embodiments, the polyurethane jacket  190  is approximately 0.432 mm thick. The total diameter of the cable  150  is less than 3.0 mm. In some embodiments, additional or fewer layers surround the four main wires  210  and fillers  175   a - d  used within cable  27 . 
         [0035]    The wiring diagram of  FIG. 6   b  illustrates the main wires  210  and fillers  175   a - d  twisted together to form a single bundle  195 . Although not shown in  FIG. 6   b , the (“PTFE”) tape  180 , a braided shield  185 , and a polyurethane jacket  190  encapsulate the single bundle  195  as shown in  FIG. 6   a . The twisted quad cable is symmetrical about center line  197 , as shown in  FIG. 6   a . The symmetrical characteristic of the cable  150  provides increased strength and resistance to mechanical stress with a lower outside diameter, relative to the standard USB cable. That is, the cable  150  is less susceptible to damage from twisting, pulling, and other forces on the cable  150 , despite the reduced diameter of the cable  150 . In particular, the cable  150  is less susceptible to damage due to rotational mechanical stress, which is often present during use of an intraoral sensor cable. 
         [0036]      FIG. 7  depicts the inside  200  of the top portion  50 . The inside  200  includes a metallization layer  205 . The cable  27  is shown inserted into the dome  75 . The four main wires  210  (i.e., the data line  155  (D+), data line  160  (D−), power line  165 , and ground line  170 ) are attached to a PCB connector  215 , which is connected to the PCB  65 . In some embodiments, the four main wires  210  are coupled or soldered directly to the PCB  65 . The braided shield  185  is coupled to the metallization layer  205  via a heat conducting wire  220 . The heat conducting wire  220  is coupled to the braided shield  185  and metallization layer  205  by, for instance, soldering. 
         [0037]    As the PCB  65  generates heat while in operation, a substantial portion of the generated heat is transferred through the insulator  60  to the metallization layer  205 . The portion of generated heat is then transferred to the braided shield  185  via the heat conducting wire  220 . The level of thermal resistance may vary by application. For instance, the more heat the PCB  65  generates in a particular embodiment, the lower the thermal resistances are of the materials chosen for the metallization layer  205 , heat conducting wire  220 , and insulator  60 . In general, however, the insulator  60  and heat conducting wire  220  have a thermal resistance that is lower than the thermal resistance of air (which is approximately 1/0.025 W/(mK) at 20 degrees Celsius). Additionally, the metallization layer  205  has a thermal resistance that is less than the thermal resistance of the top portion  50  of the housing  45  and less than the thermal resistance of air. Thus, the sensor  20  provides improved heat transfer away from the sensor  20  along the cable  27 . 
         [0038]    Although not shown, in some embodiments the inside of the bottom portion  55  also includes a metallization layer, which is similar to the metallization layer  205  in form and function. The bottom metallization layer is coupled to the braided shield  185  as well. In some embodiments, the coupling is provided by an additional heat conductor connection between the bottom metallization layer and either the braided shield  185  or the metallization layer  205 . In other embodiments, the coupling is provided by direct contact between the bottom metallization layer and the metallization layer  205 . 
         [0039]    Thus, the invention provides, among other things, an intraoral sensor with a cable providing greater resistance to mechanical stress. Additionally, the invention provides an intraoral sensor with improved heat transfer. Various features and advantages of the invention are set forth in the following claims.