Abstract:
An electronic x-ray imaging sensor that flexibly fits within a patient&#39;s mouth includes a flexible portion and a rigid portion. The flexible portion includes an array of detection devices, and the rigid portion includes complementary circuitry for controlling and/or obtaining image data from the array. The flexible portion may be detachable from the rigid portion, which allows the flexible portion to be disposable while the detachable portion is reusable.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a filmless intra-oral dental device for detecting or sensing x-rays. More particularly, the present invention relates to a flexible electronic x-ray sensing device that fits inside a patient&#39;s mouth. 
     2. Related Art 
     Dentists and oral surgeons typically use x-ray radiation to obtain images of intra-oral regions, which aid in diagnosis and treatment of dental disorders. Most conventional x-ray detection techniques use photosensitive film (“x-ray film”) to register an image. For example, in conventional x-ray detection, a film cartridge is inserted in a patient&#39;s mouth and, when the cartridge is exposed to x-rays, the x-ray film is exposed and captures an image of an intra-oral region, such as the patient&#39;s teeth and/or gums. The x-ray film subsequently undergoes chemical development to make the image on the exposed x-ray film readily visible. 
     In digital or electronic dental radiography, an electronic detector or sensor is utilized in place of x-ray film, and the sensor converts x-rays into an electrical signal. This type of radiography offers a variety of advantages over film-based x-ray techniques. Firstly, electronic sensors are more sensitive to x-rays than is x-ray film. This allows the dosage or quantity of x-ray radiation that a patient receives, in order to obtain an intra-oral image, to be reduced by as much as 90%. Secondly, the image can be generated by a computer instantaneously, thus eliminating the time-consuming development process and the use of potentially harmful chemicals. Thirdly, digital images can be stored as an electronic file in a computer-readable memory, which enables them to be easily sent to specialists for consultation, such as via the Internet. 
     A conventional electronic x-ray sensor unit typically is enclosed in a hard, rigid material, which houses and protects a charge-coupled device (CCD) or a complementary metal-oxide-semiconductor (CMOS) imaging array. An example or a CMOS Active Pixel Sensor (APS) array is set forth in U.S. Pat. No. 5,912,942 to Schick et al. (“the Schick &#39;942 patent”), which is assigned to the assignee of the present invention and incorporated herein by reference. The sensors described therein are excellent for their intended applications, in terms of image quality, power consumption, and other characteristics. However, the sensors of the &#39;942 patent and other conventional sensors utilize single-crystal silicon-based technologies, which produce fragile and rigid imaging devices, thus necessitating the use of rigid housing materials. Therefore, conventional sensor units usually are non-compliant or unbendable, which may cause discomfort for certain patients and limit a dental practitioner&#39;s ability to correctly position such a sensor unit in a patient&#39;s mouth. In contrast, even though film cartridges may also be uncomfortable, as they often are made from stiff cardboard, when a patient bites down for an x-ray “shot” or exposure, the film cartridge can bend a bit in response to the biting action, thus providing the patient with some amount of relief from the discomfort. 
     Another problem with current electronic sensing systems is their high cost. Solid-state devices such as CCDs have imperfect manufacturing yields and require nearly perfect charge generation efficiency to achieve a good image comparable in quality those achievable with x-ray film. Usually, CCDs are manufactured in boutique foundries and often have distinct manufacturing requirements that are unlike those of typical semiconductor processes. CMOS APS technology is an alternative solid-state imaging technology that takes advantage of the comparatively less expensive CMOS manufacturing processes, which have been optimized for the high-volume computer-chip industry. However, CCDs and CMOS imaging devices for x-ray sensor applications utilize extremely sophisticated equipment and processing procedures, and these imaging devices are inherently expensive to develop and manufacture. 
     Thin-film transistor (TFT) technology has gained interest from the display industry for its capabilities in producing flat-panel displays, among other things. Conventional TFT displays are manufactured onto rigid glass substrates in a process that involves baking the glass substrates at temperatures exceeding 600° C. This technology also is utilized to manufacture TFT-based amorphous-silicon detectors for the medical imaging industry. The conventional TFT process, however, is much too hot to be used with plastics, and CMOS and CCD processes are similarly unsuitable. 
     Recently, significant advances have been made in the development of flexible, plastic substrates for the display industry. With these advances, processing techniques have been developed that are compatible with such substrates. For example, U.S. Pat. No. 6,808,972 to Sirringhaus et al. (“the Sirringhaus &#39;972 patent”), which is incorporated herein by reference, describes a solution-based method for forming polymeric TFTs on flexible, plastic substrates. Also, in an article entitled “Printed active-matrix TFT arrays for x-ray imaging” (Proceedings of SPIE Vol. 5745, pp. 7-17, Bellingham, Wash., 2005) by Street et al. (“the Street article”), which is incorporated herein by reference, a jet-printing method is described that is used for forming TFTs on flexible substrates, for use as active-matrix backplanes in medical imaging systems. The Street article discusses the fabrication of an amorphous silicon p-i-n sensor that includes a photodiode layer for x-ray imaging applications. 
     Dental sensors usually require a variety of component circuitry in order to operate. For example, as schematically illustrated in  FIG. 1  and discussed in U.S. Pat. No. 6,134,298 to Schick et al. (“Schick &#39;298 patent”), which is assigned to the assignee of the present invention and incorporated herein by reference, a dental sensing system  10  includes an electronic sensor unit  1  and a remote board  2  connected via a wired interface  3  to a computer  4  through a Universal Serial Bus (USB) port  4   a . That is, the dental sensing system  10  includes not only an imaging portion (i.e., the electronic sensor  1 ), but also includes electronic circuitry to run the imaging portion and to convey information from the imaging portion to an image processing unit (i.e., the computer  4 ). 
     More specifically, depending upon the particular design of the electronic sensor unit  1  (e.g., CCD, CMOS APS array, and the like), the sensor unit  1  may include electronic circuitry for generating biasing voltages used to operate the sensing devices, as well as circuitry for generating clocking signals and readout circuitry used to read out image data from the sensing devices. Preferably, the sensor unit  1  includes interface electronics  1   a  for communicating with, for instance, the remote board  2 . Optionally, the sensor unit  1  may include a memory and conditioning circuitry for conditioning a sensed signal (i.e., the image data). For example, U.S. Patent Application Publication No. 2004/0066898 to Schick et al. (“the Schick &#39;898 application”), which is assigned to the assignee of the present invention and incorporated herein by reference, describes a wireless sensor that transmits data for an entire full-mouth series of images, from inside the mouth. For such a wireless sensor, RF transmission circuitry as well as a battery may need to be included within the packaging of the sensor. 
     U.S. Patent Application Publication No. 2003/0031296 to Hoheisel (“the Hoheisel &#39;296 application”), which is incorporated herein by reference, purportedly describes an x-ray detector that includes a flexible housing, a flexible substrate, a matrix of TFTs, and a flexible x-ray converter. However, as pointed out in paragraph [0024] of the Hoheisel &#39;296 application, “the drive circuits, which are usually composed of crystalline silicon, are not bendable.” The Hoheisel &#39;296 application then suggests that it would be advantageous to “secure these circuits to small, rigid circuit boards and to electrically conductively connect these circuit boards to the detector substrate  11  with flexible interconnects.” It is alternatively suggested in the Hoheisel &#39;296 application to glue the circuits onto the substrate  11  “with a soft adhesive that can compensate for the bending.” The schemes proposed in the Hoheisel &#39;296 application, however, may not be possible if the sensor components are large, or undergo a substantial amount of strain. 
     In U.S. Patent Application Publication No. 2004/0016886 to Ringermacher et al. (“the Ringermacher &#39;886 application”), which is incorporated herein by reference, a flexible imager is described, which includes a flexible substrate. The Ringermacher &#39;886 application also describes, at paragraph [0021], a read and reset circuit  210  that is “electrically coupled to photosensor array  110  to receive the electrical signals generated in response to incident radiation  75 .” Presumably, the electrical coupling is a wire connection to a remote module housing the array, as shown in FIG. 1 of the Ringermacher &#39;886 application. This strategy, however, may be unsuitable for a sensor whose entire electronic packaging must fit within a patient&#39;s mouth. Moreover, this strategy may be unsuitable if the sensor is to operate as a wireless sensor. 
     A further consideration for digital x-ray sensors is that they typically include a variety of nonflexible imaging layers that serve to enable the effective capture of x-ray photons. In one approach, a digital x-ray sensor receives a signal indirectly through an intermediary portion that converts x-ray photons impinging thereon to visible light photons, which are detected by a detection portion and provide the electrical imaging signal. The intermediary portion commonly includes a scintillator and a rigid fiber-optic plate (“FOP”) usually made from glass. As described in the Schick &#39;942 patent, for example, the glass FOP is positioned between the scintillator and the detection portion, thus allowing the converted visible light to pass onto the detection portion but attenuating unconverted x-rays. Without the FOP, any unconverted x-rays that pass through the scintillator can be received by the detection portion and registered as noise. 
     An alternative approach to digital x-ray imaging, discussed in U.S. Pat. No. 5,886,353 to Spivey et al. (“the Spivey &#39;353 patent”) and incorporated herein by reference, foregoes use of a scintillator and an FOP. Instead, a photoconductor directly converts incident x-rays to charge carriers, which are collected by proximate capacitive nodes. This approach, however, utilizes conventional semiconductor processing techniques and, therefore, is unsuitable for use with plastic materials. 
     As evident from the above discussion, a number of technical hurdles limit the development of a flexible intra-oral dental sensor. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the deficiencies in the prior art discussed above, by providing a flexible, electronic x-ray imaging device that fits partially or wholly within a patient&#39;s mouth. The imaging device or sensor includes a flexible portion, which advantageously reduces the level of discomfort for the patient, and a rigid portion, which includes complementary circuitry. 
     According to an embodiment of the present invention, the flexible portion includes a sensor array manufactured with flexible TFTs formed from plastic or polymeric materials. The sensor array may be designed to be indirectly sensitive to x-rays, through incorporation of a scintillator and a plastic or polymeric FOP. Alternatively, the sensor array may be designed to be directly sensitive to x-rays, through incorporation of a photoconductor. 
     The rigid portion of the imaging device includes rigid support circuitry that is fabricated using standard semiconductor manufacturing techniques. This portion is suitable for complementary or peripheral circuitry, such as circuitry required to clock and read out information from the sensor array, as well as circuitry required to convey information to an image processing unit through a wired or wireless interface. For a wireless connection, a flexible battery may be incorporated in the flexible portion. 
     According to an aspect of the embodiment, the rigid and flexible portions mate through a common connector. Preferably, the connector is flexible. 
     According to another aspect of the embodiment, the flexible portion is disposable. 
     According to yet another aspect of the embodiment, the rigid portion incorporates a positioning portion, which is utilized to orient the x-ray imaging device with respect to an x-ray source. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features and advantages of the present invention will become more apparent from the detailed description set forth below when considered in conjunction with the attached drawings, in which like reference numbers indicate identical or functionally similar elements, of which: 
         FIG. 1  is a block diagram schematically showing components of an electronic dental sensing system; 
         FIG. 2  is a block diagram schematically showing components of an intra-oral x-ray sensor according to an embodiment of the present invention; 
         FIG. 3  schematically illustrates an arrangement of a flexible TFT array, a flexible FOP, and a flexible scintillator, according to an embodiment of the present invention; 
         FIG. 4  schematically illustrates an arrangement of a flexible portion of an electronic x-ray sensor, according to an embodiment of the present invention; 
         FIG. 5  schematically illustrates an arrangement of a rigid portion of an electronic x-ray sensor, according to an embodiment of the present invention; 
         FIG. 6  schematically illustrates an arrangement of a rigid portion of a wireless electronic x-ray sensor, according to an embodiment of the present invention; 
         FIG. 7  schematically depicts a connector adapted to connect with a flexible portion of an electronic x-ray sensor, according to an embodiment of the present invention; 
         FIG. 8  schematically depicts a connection arrangement between a flexible portion and a connector, according to an embodiment of the present invention; and 
         FIG. 9  schematically depicts an arrangement of circuits bonded on a flexible portion of an electronic x-ray sensor, according to an embodiment of the present invention. 
     
    
    
     It is to be understood that the attached drawings are provided for illustrative purposes and the present invention is not limited to the details shown therein. Further, the illustrative drawings may not be shown to scale. 
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 2  schematically shows components of an intra-oral x-ray sensor  100  according to the present invention. The sensor  100  includes two functional systems: an imaging portion  102  and a supporting-circuitry portion  104 . During operation, the imaging portion  102  is positioned inside a patient&#39;s mouth and oriented to receive incident x-ray radiation. Preferably, the imaging portion  102  is flexible, compliant, and constructed of component circuitry such as an array of flexible TFTs  106 . Preferably, each TFT in the array  106  corresponds to a pixel of a captured image. Optionally, the supporting-circuitry portion  104  also fits within the patient&#39;s mouth during an image-capturing operation. The imaging portion  102  and the supporting-circuitry portion  104  are interconnected by a connector  130 , which may be rigid or flexible. Other connection arrangements are discussed below. 
     The TFT array  106  may be fabricated using any known technique for low-temperature deposition of thin films, including jet printing, evaporative deposition, laser ablation, and the like, for example. The jet printing technique, as mentioned above, is described in some detail in the Street article. Flexible substrates suitable for the array  106  include, for example, polyimide and polyethylenenapthalate. The array  106  may include any number of TFTs each corresponding to a pixel of the image. For example, the array  106  might have a 853×1200 pixel format with a pixel size of about 30 μm, which corresponds to the present standard for a size 2 dental sensor. 
     Preferably, the imaging portion  102  is contained in a flexible, protective housing (not shown), which is impervious to liquids (e.g., water and saliva) but is transparent to x-rays. Suitable housing materials include synthetic polymers, such as polyvinylchloride, polyethylene, polypropylene, and the like. Optionally, both the imaging portion  102  and the supporting-circuitry portion  104  are contained in the flexible protective housing. 
     According to an embodiment of the present invention, the sensor  100  detects x-rays indirectly and includes a flexible FOP  106 A and a flexible scintillator  106 B in addition to the TFT array  106 , as schematically shown in the “exploded” view of  FIG. 3 . The scintillator  106 B is formed of gadolinium oxysulfide or cesium iodide or any scintillating material that functions to convert x-ray energy to visible light energy. The FOP  106 A is constructed from a flexible plastic or polymeric material that functions to attenuate or absorb x-ray energy that passes through the scintillator  106 B unconverted. Presently, fiber-optic bundles suitable for use as flexible FOPs  106 A are available from SCHOTT North America, Inc. (Southbridge, Mass.). Such bundles have a bend radius of 2.0 inches, which is acceptable for use in flexible dental sensors. 
     According to another embodiment of the present invention, the sensor detects x-rays indirectly and includes a flexible FOP that is doped with a scintillating material such as cesium iodide, for example. Scintillating fiber-optic fibers, in fact, provide a good physical resistance to radiation, as discussed in an article entitled “Plastic Optical Fibers: A Introduction To Their Technological Processes and Applications” (J. Optical Fiber Technology, vol. 7, pp. 101-140, 2001) to Arrue (“the Arrue article”). 
     According to yet another embodiment of the present invention, the sensor detects x-rays indirectly and includes a flexible FOP constructed from one or more bundles of optical fibers. In one example, each fiber includes a plastic fiber-optic core, which may be doped with organic flour, and each fiber includes one or more cladding layers of zinc sulphide (ZnS), which is utilized for converting x-ray energy to visible light energy. 
     In both of the above embodiments, use of the flexible FOP  106 A of the flexible doped FOP protects the array  106  from the potentially deleterious effects of unconverted x-rays, including radiation damage and noise generation, for example. 
     According to another embodiment of the present invention, the sensor  100  directly converts incident x-rays to charge carriers. A photoconductive material is used in conjunction with the flexible TFT array  106 , and a FOP is not necessary. Examples of suitable photoconductive materials include selenium, lead oxide, lead iodide, and mercuric iodide. When x-rays impinge upon the photoconductive material, the x-ray energy causes the formation of charge carriers, which are collected by the TFTs in the array  106 . Variations in the quantity of charge collected from pixels of the TFTs correlate with variations in the features of the captured image of the patient&#39;s mouth. Preferably, each TFT includes at least one capacitive node for collecting charge carriers generated for that pixel. 
     For both the direct- and indirect-detection sensors, noise reduction features preferably are incorporated, which absorb or attenuate unconverted x-rays that pass through the scintillator or the photoconductive material. In the case of an indirect-detection sensor, the use of noise reduction features would eliminate the need to incorporate a FOP, thus reducing the thickness of the sensor. 
     According to still another embodiment of the present invention, the sensor  100  includes a battery, which serves as a power source for the sensor  100 , as schematically shown in  FIG. 4 . The battery may be a flexible battery  108  incorporated in the imaging portion  102  of the sensor  100 . The battery  108  may be used to provide temporary power as needed, or to provide permanent power if the sensor  100  is a wireless dental sensor. Currently, flexible batteries are available that are thin and compliant, with some flexible batteries being as thin as 0.5 mm and having a compliancy or bending radius of 25 mm. Such flexible batteries are available from Graphic Solutions International LLC (Burr Ridge, Ill.), including the STD-1, the STD-8, and their 0.375″×0.375″ miniature batteries. Optionally, instead of or in addition to the flexible battery  108 , a flexible or non-flexible battery (not shown) may be incorporated in the supporting-circuitry portion  104  of the sensor  100 . 
     The supporting-circuitry portion  104  houses a variety of components, including: a gate driver and biasing control circuitry component  110 , which is used to control, at least in part, the operation of the TFTs of the array  106 ; a read-out circuitry component  112  for reading out signals from the TFTs of the array  106 ; an interface circuitry component  114  for conveying signals to a port  116 . According to an aspect of the embodiment, schematically shown in  FIG. 5 , the port  116  enables communication with an external device  120  via a cable  118 , in accordance with a known communication standard such as the Universal Serial Bus (USB) Specification, for example. In this case, the cable  118  extends from the supporting-circuitry portion  104  and conveys information to the external device  120 . Preferably, the external device  120  is an information processing unit programmed to process the information to render an image of an area of interest within the patient&#39;s mouth. 
     According to another aspect of the embodiment, schematically shown in  FIG. 6 , the port  116  enables wireless communication with the external device  120  by sending signals to a wireless transmitter  122 , which communicates with the external device  120  in accordance with a known wireless transmission standard. Preferably, the supporting-circuitry portion  104  includes a conditioning circuitry component  124 , which functions to condition the signals to be sent to the external device  120  prior to wireless transmission. 
     Optionally, the supporting-circuitry portion  104  may include a memory unit  130  for storing and/or buffering signals read out from the imaging portion  102 . Additionally, the supporting-circuitry portion  104  may optionally include a microprocessor (not shown) for controlling aspects of the operation of the sensor  100 . 
     A positioning component (not shown) of the sensor  100  enables a dental practitioner to easily align or position the sensor  100  within the patient&#39;s mouth, such that the TFT array  106  is properly positioned with respect to an x-ray source, in order to capture a desired image of an area within the patient&#39;s mouth. 
     According to another embodiment of the present invention, the entire supporting-circuitry portion  104  is formed within a connector  104 A, which is schematically shown in  FIG. 7 . The connector  104 A includes a connection portion  128 , which provides both a mechanical connection with the imaging portion  102  as well as an electrical connection for signal communication with the imaging portion  102 , as schematically depicted in  FIG. 8 . In this case, the imaging portion  102  may be disposable, such that each patient can be provided with a new imaging portion  102  when intra-oral x-ray images are to be taken. This simplifies patient hygiene. The arrows in  FIG. 8  are intended to show how the imaging portion  102  and the connector  104 A join together, according to an aspect of the embodiment. One of ordinary skill in the art of dental imaging will appreciate that other connection schemes may be used and are within the scope of the present invention. Optionally, the connection portion  128  may be arranged on a flexible cable (not shown) extending from the connector  104 A. In another option, instead of including the cable  118 , the connector  104 A communicates wirelessly with the external device  120  via known wireless-communication standards. 
     According to yet another embodiment of the present invention, the connector  104 A is integral with or attached to a sensor positioning system (not shown), which is used to properly align the imaging portion  102  with a source of x-rays. 
     Although the aforementioned embodiments generally are directed to arrangements in which the supporting-circuitry portion  104  is positioned next to and in the same plane as the imaging portion  102 , those skilled in the relevant art(s) will appreciate that alternative arrangements are possible and within the scope of the present invention. 
     In one such alternative embodiment of the present invention, schematically depicted in  FIG. 9 , component circuitry of the supporting-circuitry portion  104  discussed above are distributed as circuits  132   a ,  132   b , . . . ,  132   n , which are bonded to the underside of the imaging portion  102 . The circuits  132   a ,  132   b , . . . ,  132   n , may be formed as rigid, integrated circuits (ICs), which are fabricated by thin-film processing techniques that are well-known and well established and therefore will not be described further. Bonding may be accomplished by known techniques for bonding electrical circuits, such as the various bump-bonding techniques used in flip-chip technology. 
     In this case, circuits corresponding to any or all of the read-out circuitry component  112 , the control circuitry component  110 , the conditioning circuitry component  124 , the interface circuitry component  114 , and the memory unit  130 , for example, are distributed among the circuits  132   a ,  132   b , . . . ,  132   n  and are electrically connected with printed circuits and/or thin-film metallization (i.e., wiring) interconnections formed on and/or in the flexible substrate supporting the TFT array  106 . Of course, the aforementioned circuits  132   a ,  132   b , . . . ,  132   n , are sized to be sufficiently small so as to accommodate the particular bending radius of the array  106  when bonded to the flexible supporting substrate. A flexible cable (not shown) attached to one or more of the circuits  132   a ,  132   b , . . . ,  132   n  on the underside of the imaging portion  102  communicates with the external device  120 . The flexible cable may be physically integrated with the arrangement shown in  FIG. 9 , or may be a detachable cable, similar to the arrangement shown in  FIGS. 7 and 8  (but without incorporating the supporting-circuitry portion  104 ). 
     While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example, and not limitation. It will be apparent to persons skilled in the relevant arts that various changes in form and detail can be made therein without departing from the spirit and scope of the present invention. Thus, the present invention should not be limited by any of the above described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.