WO2007149402A2

WO2007149402A2 - Positioning system for dental intra-oral x-ray apparatus

Info

Publication number: WO2007149402A2
Application number: PCT/US2007/014211
Authority: WO
Inventors: Giuseppe Rotondo; Gerardo Rinaldi; Stylianos Kokkaliaris; Gianfranco Venturino
Original assignee: Gendex Corporation
Priority date: 2006-06-16
Filing date: 2007-06-14
Publication date: 2007-12-27
Also published as: WO2007149402A3

Abstract

An x-ray apparatus for intra-oral radiography has an x-ray source (60); an x-ray detector (20); and an alignment system for aligning the x-ray source (60) and the x-ray detector (20). The alignment system includes a generator of a variable electromagnetic field and an electromagnetic field detector (40) for detecting the variable electromagnetic field. The alignment system further includes an intra-oral device (30) with the x-ray detector (20), wherein the generator of a variable electromagnetic field is connected to the intra-oral device (30) and the electromagnetic field detector (40) is connected to the x-ray source (60), or the generator of a variable electromagnetic field is connected to the x-ray source (60) and the electromagnetic field detector (40) is connected to the intra-oral device (30).

Description

POSITIONING SYSTEM FOR DENTAL INTRA-ORAL X-RAY APPARATUS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No. 60/804,984 filed June 16, 2006 and U.S. Provisional Application No. 60/826,611 filed on September 22, 2006, both of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] The invention relates to an x-ray apparatus for intraoral radiography and to an alignment system therefore. The invention further relates to a method of aligning an x-ray generator and an x-ray detector. Further, an x-ray detector for the method, apparatus, and alignment system of the invention is provided.

[0003] In traditional oral and dental radiography, a cartridge containing a radiographic film is placed in the patient's mouth, for example behind a patient's tooth, and an x-ray beam is projected through the tooth and onto the film. The film, after being exposed in this manner, is developed in a dark room or a closed processor using special chemicals to obtain a radiographic image of the tooth.

[0004] In filmless dental radiography, an x-ray beam is projected through the patient's tooth similar to the film based methods, but no x-ray sensitive film is used. Instead, an electronic sensor is placed in the patient's mouth behind the tooth to be examined. The electronic sensor may include a charge-coupled device (CCD)₁ a complementary metal oxide semi-conductor (CMOS), or any other filmless radiation sensor. The x-rays pass through the tooth and impinge on the electronic sensor, which converts the x-rays into an electrical signal. The electrical signal is often transmitted over a wire to a computer, either directly or through a module containing intermediate processing circuitry. The computer then processes the signal to produce an image on an associated output device, such as a monitor or a printer.

[0005] Filmless dental radiography offers several advantages over traditional film-based radiography. First, the electronic sensor is much more sensitive to x-rays than is film, allowing the dosage of x-rays to the patient to be lowered. Also, the image of the tooth is generated by the computer almost instantaneously, thus eliminating the film developing process. The operator can quickly determine in real time if the image is the one required for proper diagnosis of the patient or if further imaging is required. In addition, because the images are generated electronically, they can be stored electronically in a computer memory or database. These systems can be generally referred to as digital dental x-ray devices.

[0006] When a dentist or dental technician takes an x-ray of a patient's tooth, there can be a problem that the x-ray source and the detector are not properly aligned, thereby causing geometric distortion of the radiographic image and potential loss of diagnostic value. For these reasons, in the common practice, paralleling devices are often used.

[0007] In taking x-rays of all of a patient's teeth, also known as a "Complete Mouth Series", typically three different x-ray film holders are employed. In addition, the holder for taking periapical films of the upper right and lower left teeth is disassembled and then reassembled in a different configuration to take films of the upper left and lower right teeth. Further, in order to take an x-ray of a tooth undergoing root canal treatment, an additional x-ray holder is used. Furthermore, in some situations the paralleling technique is not possible or practical. Consequently, up to seven different holders are currently used to take dental intra-oral x-rays. This approach can be uncomfortable for the patient and can be difficult to manage for the dentist.

[0008] One apparatus for taking x-rays for dental substraction radiography includes a robotic system allowing an x-ray source to automatically follow and correct for motions of a patient. This system uses magnetic source means mounted at a fixed position in a room. A variable magnetic field is used for performing real-time analysis of the motion of the patient.

[0009] Another dental x-ray alignment system has a permanent magnet attached to an intra- oral x-ray sensor and a plurality of magnetoresistance detectors connected to an x-ray detector. The magnetic field strength of the magnet is measured at various locations by the magnetoresistance detectors, and a misalignment of the x-ray source and the intra-oral x-ray detector is calculated and can be corrected. For the alignment system, certain measures are undertaken to reduce the disturbing influence of the magnetic field of the earth. However, this alignment system is vulnerable to disturbances from magnetic fields in the environment of the alignment system such as those produced by electrical devices like the x-ray apparatus. Further, this system requires a duplex array of magnetic detectors and circuitry to correct for the magnetic field of the earth. [0010] Therefore, what is needed is an alignment system for dental intra-oral radiography that allows convenient alignment of an x-ray source and an x-ray detector, and is essentially not affected by electromagnetic fields in the environment of the alignment system.

[0011] Intended advantages of the systems and/or methods satisfy one or more of these needs or provide other advantageous features. Other features and advantages will be made apparent from the present specification. The teachings disclosed extend to those embodiments that fall within the scope of the claims, regardless of whether they accomplish one or more of the aforementioned needs.

SUMMARY OF THE INVENTION

[0012] The present invention provides an alignment system for dental intra-oral radiography, including: an intra-oral device having a generator of a variable electromagnetic field; and an electromagnetic field detector for detecting the variable electromagnetic field generated by the generator.

[0013] The invention further provides an alignment system for dental intra-oral radiography, including: a generator of a variable electromagnetic field, the generator being adapted to be attached to an x-ray source; and an intra-oral device having an electromagnetic field detector for detecting the variable electromagnetic field generated by the generator.

[0014] Further, an x-ray apparatus for intra-oral radiography is provided, including: an x-ray source; an x-ray detector; and an alignment system for aligning the x-ray source and the x-ray detector, the alignment system has a generator of a variable electromagnetic field and an electromagnetic field detector for detecting the variable electromagnetic field, the alignment system further includes an intra-oral device incorporating the x-ray detector, wherein the generator of a variable electromagnetic field is connected to the intra-oral device and the electromagnetic field detector is connected to the x-ray source, or the generator of a variable electromagnetic field is connected to the x-ray source and the electromagnetic field detector is connected to the intra-oral device.

[0015] The invention also provides a process of aligning an x-ray source and an x-ray detector of an x-ray apparatus for dental intra-oral radiography, the method includes the following steps: providing an x-ray apparatus for dental intra-oral radiography, the apparatus includes: an x-ray source; an x-ray detector; and an alignment system for aligning the x-ray source and the x-ray detector, the alignment system includes: an intra-oral device to which the x-ray detector is attached; a generator of a variable electromagnetic field and an electromagnetic field detector for detecting the variable electromagnetic field, the generator is attached in fixed spatial relationship to one member selected from the group consisting of the x- ray source and the intra-oral device, the electromagnetic field detector being attached in fixed spatial relationship to the other member of the group consisting of the x-ray source and the intra-oral device; a control unit for controlling the variable electromagnetic field to be generated by the generator; and processing means for determining the orientation and position of the x-ray detector relative to the x-ray source; the method further includes: placing the intra-oral device at a predetermined position in the oral cavity of a patient behind a tooth to be examined; moving the x-ray source near the jaw of the patient such that an x-ray beam generated by the x-ray source projects approximately towards the x-ray detector located in the patient's oral cavity; generating a variable electromagnetic field using the control unit and the generator; detecting the variable electromagnetic field by the electromagnetic field detector; determining the orientation and position of the x-ray detector relative to the x-ray source using the variable electromagnetic field detected by the electromagnetic field detector using the processing means; and moving the x-ray source or the x-ray detector until the detected electromagnetic field indicates a desired alignment of the x-ray source and the x-ray detector.

[0016] In the present invention, an x-ray source and an intra-oral x-ray detector are aligned using a variable electromagnetic field generated by a generator of a variable electromagnetic field (also referred to herein as "field generator"). The variable electromagnetic field can be detected by an electromagnetic field detector (also referred to herein as "field detector") and can be analyzed using a processor or processing system to determine the relative position and orientation of the field generator and the field detector. If the field generator is attached in fixed spatial relationship to the x-ray detector, and the field detector is attached in fixed spatial relationship to the x-ray source, or vice versa, the relative position and orientation of the x-ray detector and the x-ray source can be determined. Any deviation from a predefined or desired relative position and/or orientation may be corrected by moving either the x-ray source or the x- ray detector. The determination of the relative position and orientation of the x-ray detector and the x-ray source may be repeated and any further mis-alignment can be corrected until a desired alignment is achieved. By using a variable electromagnetic field, it is possible to distinguish the variable electromagnetic field detected by the field detectors from other disturbing electromagnetic fields including variable electromagnetic fields produced by electrical equipment.

[0017] The variable electromagnetic field used in the alignment process may be a periodic electromagnetic field such as a sinusoidally modulated field of a predetermined frequency.

[0018] There are several embodiments of the alignment process of the present invention. In a first embodiment, the field generator is attached in fixed spatial relationship to the intra-oral device and the field detector is attached in fixed spatial relationship to an x-ray source. In a second embodiment, the field generator is attached in fixed spatial relationship to an x-ray source and the field detector is attached in fixed spatial relationship to the intra-oral device. Accordingly, the intra-oral device of the alignment system may, in one embodiment, include the field generator, and in an alternate embodiment, include the field detector.

[0019] When the x-ray apparatus is used for taking intra-oral x-rays of a patient, an x-ray detector is placed inside the oral cavity of a patient, such as behind a tooth to be examined. In addition, the intra-oral device of the alignment system to be operated inside the oral cavity of a patient, e.g., one of the field generator or the field detector, may incorporate or may be adapted to be connected to the x-ray detector. An x-ray detector may be releasably connected to the intra-oral device to permit the use of x-ray detectors from various manufacturers with the alignment system of the invention. It is also possible to produce the intra-oral device by fixedly connecting the x-ray detector to the field generator or the field detector such that no easy separation of the components is possible. In the latter embodiment, the x-ray detector and either the field generator or the field detector may be integrally contained in one casing of the intra-oral device.

[0020] To align the x-ray detector connected to the intra-oral device, the intra-oral device is positioned at a desired position in the oral cavity of a patient such that the desired position can be maintained during the alignment process and the subsequent x-ray procedure. For maintaining the desired position, the intra-oral device can include a projecting tab on which the patient can bite to secure the position of the intra-oral device. In another embodiment, a tab on which a patient can bite can be connected to a hygienic protection cover for the intra-oral device. Once the hygienic protection cover is placed on the intra-oral device, the intra-oral device can be inserted into the oral cavity of a patient and secured by biting on the tab of the protection cover.

[0021] The field generator of the invention may include one or more coils of an electro- conductive material to which a current can be applied for producing a variable electromagnetic field. The current may be modulated or may be an alternating current. The current can be applied to the generator from a power supply that is controlled by a control unit. The field generator may be powered directly via wires from the power supply. In another embodiment, the field generator may be powered indirectly by magnetic induction from an induction source. The latter embodiment is particularly useful if the field generator is used as the intra-oral device, since wires do not have to be supplied into the oral cavity of a patient during the alignment process to power the field generator.

[0022] The induction source may include at least one induction coil that is adapted for use in powering the field generator. The induction coil may be powered by a power supply that can be controlled by the control unit. During the alignment process, the induction source has to be located close enough to the field generator such that the field generator can be powered by magnetic induction. If the field generator is part of the intra-oral device, the induction coil may be part of the field detector that may be connected to the x-ray source. An induction coil of the induction source may also be used by the field detector for detecting a component of the variable electromagnetic field. In an alternative embodiment, one or more coils of the field detector may be used as the induction coil(s).

[0023] The field detector may have one or more coils of an electro-conductive material for detecting the variable electromagnetic field generated by the field generator. These coils are also referred to herein as detection coils. The field detector may include at least two detection coils in different orientations for detecting at least two vector components of the variable electromagnetic field. The field detector may include multiple sets of the at least two coils, with each set of the at least two coils having a similar or the same orientation, for detecting a vector component of the variable electromagnetic field at two or more different spatial positions of the field detector. In a further embodiment, the field detector has at least three coils in different orientations for detecting three vector components of the electromagnetic field. A set of the at least three coils having a given orientation may be used at two or more different positions in the field detector to detect different field strengths of each vector component at the two or more positions.

[0024] The alignment system may include a processing system for determining the orientation and position of the x-ray detector relative to the x-ray source from the variable electromagnetic field detected by the detection coils of the field detector. The processing system permits filtering of the magnetic field detected by the field detector for electromagnetic field components generated by the field generator, since the properties of the variable electromagnetic field generated by the field generator are known.

[0025] The alignment system may include a control unit for controlling the field generator of the variable electromagnetic field. If the field generator is powered by the induction source, the control unit may control the induction source. The control unit may include a digital to analog converter as a modulator of the power supply to the field generator or the induction source. The control unit and the processing system may be operated in order to eliminate from the detected electromagnetic field contributions from undesired or ambient electromagnetic fields not generated by the field generator. The induction source and the field detector(s) may be operated in an alternating fashion by the control unit.

[0026] The control unit and the processing system are typically connected to a computer or microcontroller that can control the control unit and analyze data received from the processing system.

[0027] The alignment system may further include a display to indicate to an operator of an x-ray apparatus any misalignment of an x-ray detector and an x-ray source. The display can also indicate to an operator the appropriate directions and/or orientations to move an x-ray detector or an x-ray source to achieve alignment. The display can further indicate to an operator when the x-ray source is located sufficiently close to the x-ray detector so that the electromagnetic field generated by the field generator is detected by the field detector. The display may have one or more arrays of LEDs indicating to an operator the directions or orientations to move an x-ray detector or an x-ray source to achieve alignment.

[0028] The present invention provides a hygienic protection cover for the intraoral device. The protection cover may be a thin film that may be made of a natural or synthetic rubber, a latex, or a polythene. The protection cover may be pulled over the intra-oral device before the intra-oral device is inserted into the oral cavity of a patient. The protection cover may have a tab that can project perpendicularly from the surface of the protection cover. Alternatively, such tab may be attached at a desired position on the outer surface of the protection cover after the protection cover has been pulled over the intra-oral device. The intra-oral device covered by the protection cover may then be fixed at a desired location inside the oral cavity of a patient by the patient biting on the tab. The protection cover may have cushions for cushioning the intra-oral device when inside the oral cavity of the patient to provide patient comfort. The cushions may be formed of foamed polyurethane and may be positioned between the intra-oral device and the protection cover. In one embodiment, the cushions can be made of the same material as the protection cover. In another embodiment the cushions can be embedded in the protection cover or in one of at least two layers of the protection cover, e.g., in the form of a layer of foamed material.

[0029] One advantage of the present invention is a reproducible and ergonomic alignment system for dental intra-oral radiography.

[0030] A further advantage of the present invention is hygienic operation of a dental intraoral apparatus.

[0031] Another advantage of the present invention is improved patient comfort during dental intra-oral radiography.

[0032] Still another advantage of the present invention is that disturbances to the alignment system caused by static or variable electromagnetic fields are minimized.

[0033] Alternative exemplary embodiments relate to other features and combinations of features as may be generally recited in the claims.

BRIEF DESCRIPTION OF THE FIGURES

[0034] Figure 1 depicts a magnetic field flux (represented by lines with arrows) generated by a coil oriented horizontally.

[0035] Figure 2 illustrates the output signal from the detector coil relative to the signal driving the generator coil for two embodiments. [0036] Figure 3 is a block diagram of one embodiment of the alignment system.

[0037] Figures 4A and 4B show the bottom side and the top side of a frame for an intra-oral device, respectively.

[0038] Figures 4C and 4D show the bottom side and the top side of an x-ray sensor, respectively.

[0039] Figure 4E show a perspective view of an assembled intra-oral device.

[0040] Figure 5A shows a perspective view of a relative orientation of the coils of a field detector and an intra-oral device.

[0041] Figure 5B shows the bottom side of the intra-oral device of Figure 5A.

[0042] Figure 6A shows a side view of an arrangement of an intra-oral device oriented in parallel to a field detector with an induction coil.

[0043] Figure 6B shows a top view of the arrangement of Figure 6A.

[0044] Figure 7 depicts a field detector in the form of a collar that can be put on a collimating cone of an x-ray source.

[0045] Figure 8 shows a display comprising a plurality of LEDs for indicating to an operator directions and/or orientations to move the x-ray source for achieving alignment with an intra-oral device.

[0046] Figure 9 is a view of a patient having an intra-oral device according to the invention inserted into the oral cavity and an x-ray source having a field detector around the collimating cone.

[0047] Figure 10 shows a hygienic protection cover that can be pulled over an intra-oral device.

[0048] Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. DETAILED DESCRIPTION OF THE INVENTION

[0049] The alignment process and system of the present invention can identify the relative position and orientation of an x-ray sensor and an x-ray source by using a variable electromagnetic field. The variable electromagnetic field can be detected by electromagnetic field detectors that are suitably arranged with respect to a generator of the variable electromagnetic field. The x-ray detector and the x-ray source may be placed in a fixed spatial relationship using the variable magnetic field source or generator and the corresponding detectors.

[0050] Figure 1 represents the flux lines of the generated magnetic field for a circularly shaped field generating coil. In any point of the space, the electromagnetic field is represented by a vector tangent to the respective flux line. The electromagnetic field vector has the same direction as the flux line, and an amplitude H0(x, y, z) that is graphically represented by the density of the flux lines. The amplitude of the electromagnetic field vector, in a first approximation, is inversely proportional to the square of the distance from the field generator (MGM).

[0051] In the case of a variable electromagnetic field generated by a coil excited by a sinusoidal wave, the amplitude of the electromagnetic field associated to a spatial position (x,y,z) has the form:

H(X, y, z, t) = HO(X, y, z)sin(2πft),

where x, y, and z stand for cartesian coordinates, t stands for the time, H0(x, y, z) is the maximum amplitude for the electromagnetic field, and f stands for frequency. In general, the sinusoidal waveform may be replaced by any periodic waveform.

[0052] The right-hand side of Figure 2 represents the output signal(s) generated by an electromagnetic field detector coil when placed in any point of the generated electromagnetic field (H). The left-hand side of Figure 2 shows the corresponding configuration of the electromagnetic field and the detector coil generating the output signal. In general, one detecting coil of an electromagnetic field detector generates an output signal that is proportional to the area of the detector coil and is highly influenced by the relative orientation of the same detector coil versus the flux lines of the generated field. [0053] A first method to determine the position of the x-ray source and x-ray detector is based on the acquisition of the output signals from multiple sets of detection coils and their relevant spatial geometry, in order to reconstruct a complete model of the generated electromagnetic field and identify the relative position and orientation of the electromagnetic source and detectors. A complete simulation of the generated electromagnetic field may be realized using finite elements analysis (FEΞA) tools, such as available in standard mathematic libraries, and the output signals from the detection coils.

[0054] The detection of the actual electromagnetic field vector in a predefined spatial position can be performed by at least three coils arranged in an orthogonal orientation. At least three sets of three coils are necessary for a complete identification of the electromagnetic source position and orientation. This approach requires a complex construction, high computation power and processing time. This method also requires a high accuracy in the acquisition of the detector output.

[0055] A second method to determine the position of the x-ray source and x-ray detector is based on utilizing predetermined configurations where multiple sets of detectors are symmetrically placed on the same plane orthogonal to the central axis of the electromagnetic source coil (such as shown in Figure 5A). The differences between the output signals of the detector coils are analyzed in order to derive relative displacements in position and orientation between the detector plane and the source axis. This method does not involve complex calculations and is particularly efficient when compared to the previous method for limited distances between the electromagnetic source and detectors like those that may be present in dental intra-oral radiography applications.

[0056] In a first embodiment, at least three pairs of detection coils are used, each pair having a predefined angle between the two coils. The first set of three coils with the same orientation produce output signals whose difference is mainly correlated with the displacement of the source axis from its central position. The second set of three coils with the same orientation at an angle from the first set produce output signals whose difference is mainly correlated with the angular displacement of the source axis from its orthogonal orientation. The ratio between output signals from the two sets of coils is mainly correlated with the distance between the source and the detectors plane.

[0057] A second embodiment with four pairs of detection coils can be utilized when the source coil is rectangularly shaped, such as around the package of an x-ray detector as commonly available in dental practice. In this configuration, the four pairs of detector coils produce a more accurate correlation with the biaxial symmetry geometry of the electro-magnetic source.

[0058] In one embodiment, the intraoral device has a generator of a variable electromagnetic field that can be powered by an induction source. In Figs. 4A and 4B, a frame 10 of an intra-oral device is shown to which a field generator and an x-ray detector may be attached. Frame 10 has an approximately rectangular shape with rounded edges. Frame 10 essentially determines the size of the intra-oral device, which may for example be about 2.5 cm by about 3.5 cm (2.5 cm x 3.5 cm) or about 3.5 cm by about 4.5 cm (3.5 cm x 4.5 cm). The thickness of the intra-oral device may for example be in the range of from about 0.5 cm to about 1 cm, preferably from about 0.5 cm to about 0.8 cm. However, the invention is not limited with respect to the size of the intra-oral device. A field generator MGM that can be powered by an induction source may include a resonant circuit having a coil or inductor L and a capacitor or capacitance C, as schematically depicted in Figure 3. The coil L can be located within a hollow portion of frame 10 or may be embedded in the material of a non-hollow frame 10. In a further alternative, the coil L may extend along inner side wall 12 of frame 10. The maximum size of the coil L may be determined by the size of the frame 10. The capacitance C (not shown in Figures 4A and 4B) may be integrated into a hollow part of the frame 10. When the field generator MGM is powered by a variable electromagnetic field, such as by a burst of predefined frequency of the induction source, the electric circuit formed from the coil L and capacitance C is energized and resonates. Thereby, the field generator MGM generates a variable electromagnetic field. It is to be understood that the field generator can have any suitable circuit configuration that can generate an electromagnetic field detectable by the field detector.

[0059] Frame 10 can have a bridge 14 and clips 16 that permits insertion of an x-ray detector 20 (shown in Figures 4C and 4D) within the free space enclosed by the frame 10 such that the x-ray detector 20 is connected in a fixed spatial relationship with both the frame 10 and with the field generator MGM. X-ray detector 20 has a casing 22 having an x-ray transparent wall at its top side, i.e., the side turned towards the x-ray source in an x-ray procedure. X-ray detector 20 has a shape corresponding to that of frame 10, such that x-ray detector 20 can be inserted into the frame 10 for achieving a fixed position of the x-ray detector 20 relative to the frame 10. At the bottom side of the casing 22, i.e., the rear side with respect to the x-ray source in an x-ray procedure, cables 24 exit the casing 22 to supply power to the x-ray detector 20 and to transfer data collected by the x-ray detector 20 to the processing system. Conventional digital x-ray detectors such as CCD or CMOS detectors may be used in the x-ray detector 20. Alternatively, it is also possible to use conventional x-ray sensitive film in the x-ray detector 20.

[0060] Figure 4E shows an assembled intra-oral device 30 comprising frame 10, a field generator MGM and an x-ray detector 20. In the assembled intra-oral device 30, the x-ray detector 20 of Figures 4C and 4D has been inserted into the frame 10 of Figures 4A and 4B. These components of the intra-oral device 30 are fixed in position to prevent a relative movement of these components during the alignment process of the invention.

[0061] Figure 5A depicts an electromagnetic field detector 40 to be used in the alignment system of the present invention together with the intra-oral device 30. The intra-oral device 30 is shown diminished in size within the field detector 40 to indicate that the intra-oral device 30 is in the background. The relative orientation of the field detector 40 and the intra-oral device 30 may occur during the alignment step of the invention, whereby the intra-oral device 30 is located in the oral cavity of a patient (see e.g., Figure 9). A support for the field detector 40 and its components is not shown in Figure 5A. The overall arrangement of field detector 40 and its components is generally circular, such that the field detector 40 can be mounted around a collimating cone of an x-ray source. Preferably, the components of the field detector 40 are mounted in a ring-shaped casing. A field detector 40 having a ring-shaped casing is shown in Figure 7 as the field detector 40 is about to be moved onto a collimating cone of an x-ray source 60. Field detector 40 may be adjusted to the diameter of a collimating cone of a given x-ray source 60 by using an adaptor that permits the mounting of the field detector 40 on the collimating cone in a fixed spatial relationship with the x-ray source 60.

[0062] The field detector 40 can include an induction source for powering the field generator MGM of intraoral device 30. The induction source has an induction coil 42 (also referred to herein as power coil (PC)) and power supply cables 44 for the induction coil 42. Power supply cables 44 can be connected to the control unit. Induction coil 42 is arranged in the field detector 40 to be oriented essentially parallel to the field generator MGM of the electromagnetic field as a result of the alignment process. The intra-oral device 30 illustrated in Figures 5A and 5B includes the coil 18 (L) of the field generator MGM. Coil 18 extends along the inside of frame 10.

[0063] Field detector 40 further has eight detection coils arranged in four pairs of two detection coils. The pairs of coils are distributed along induction coil 42. The four pairs are labeled DC1 to DC4. The coils of each pair are further labeled with letters a and b. The diameters of the detection coils are smaller than that of induction coil 42. One coil of each pair of coils is oriented essentially parallel to induction coil 42 and, as a result of the alignment process, is essentially parallel to the coil L of the field generator MGM. The other coil of each pair of coils is oriented essentially perpendicular to the induction coil 42. The present invention is, however, not limited to the above configuration and other arrangements, orientations and numbers of the detection coils can be used. The detection coils of field detector 40 allow detection of the amplitudes and phases of the variable electromagnetic field generated by the field generator MGM at four spatial positions. The detection coils are connected to the processing system via an analog to digital converter ADC. The amplitudes and phases of the signals derived by the detection coils allow determination of the relative position and orientation of the intra-oral device 30 and an x-ray source 60 to which said field detector 40 is attached.

[0064] Figure 6A is a side view of an arrangement of intra-oral device 30 oriented substantially parallel to field detector 40. Figure 6B shows the same arrangement as in Figure 6A, but viewed in a top view. The relative position of device 30 to detector 40 as shown in Figures 6A and 6B may occur when a desired alignment, i.e., the central axis of the device 30 (or field generator) and the central axis of the detector 40 are substantially coaxial, has nearly been achieved in the alignment process. [0065] Figure 7 depicts mounting of a field detector 40 on a collimating cone of an x-ray source 60 such that the collar surrounds the collimating cone of an x-ray source 60. The x-ray source 60 of the x-ray apparatus may be any conventional x-ray source. The x-ray source 60 may be mounted on a movable arm that holds the x-ray source 60 and allows the x-ray source 60 to be moved close to the head of a patient and to align the x-ray source 60 and the intraoral device 30 by moving the x-ray source 60. The movement of the movable arm may be done by hand by an operator of the x-ray apparatus or automatically by mechanical devices or motors incoφorated in the x-ray source 60.

[0066] Figure 8 shows the display system. The display system includes a plurality of LEDs to indicate to an operator the directions and/or orientations to move the x-ray source 60 in order to achieve alignment with an intra-oral device 30 (not shown) placed in the oral cavity of a patient. The display system may be integrated into the casing of field detector 40. Figure 9 indicates a field detector 40 attached to a collimating cone of an x-ray source 60. The field detector 40 shown in Figure 9 has a display system, such as the one shown in Figure 8, integrated into an outer side wall of the casing of the field detector 40. The display system has 8 LEDs. LEDs 52, if activated, indicate to an operator of the alignment process a movement to be carried out on the x-ray source 60 for achieving alignment with an intra-oral device 30. The movement may be essentially in a plane perpendicular to the x-ray beam direction of the x-ray source 60 during radiography. It is, however, also possible that the display system includes LEDs or other devices for producing an audible signal that indicates to an operator a movement essentially along the x-ray beam axis of the x-ray source 60 for varying the distance between the intra-oral detector 30 and the x-ray source 60. LEDs 54, if activated, indicate to an operator of the alignment process of the invention a rotational movement to be carried out on the x-ray source 60 for achieving alignment with an intra-oral device 30. "T in "T-DOWN" or "T-UP" etc. stands for "tilt". The four LEDs 54 indicate rotations around a vertical axis and around a horizontal axis that may be approximately normal to the direction of the x-ray beam projecting towards the x-ray detector 20 positioned in an oral cavity of a patient. The LEDs of the display are controlled by the processing system when the alignment process is performed.

[0067] Figure 3 is a block diagram of one embodiment of the invention. MGM stands for the field generator of the variable electromagnetic field. DAC stands for digital to analog converter. ADC stands for analog to digital converter. PU stands for processing unit. DC stands for detection coil. DC1a to DC4b indicate the eight detection coils shown in Figure 5A. PC stands for power coil (induction coil). CHSEL stands for channel select. SHORTSEL stands for short select. The display has the eight LEDs described above and a device to generate an audible signal. The processing unit PU may incorporate the processing system and the control unit discussed above. However, the processing unit PU may only incorporate one of the processing system and the control unit with the other device being a separate component in communication with the processing unit PU.

[0068] The processing unit PU can be made of commercially available integrated circuits IC and central processing units CPU or processors assembled in a circuit board mounted on a support. In addition, the processing unit PU may comprise or be connected to a digital to analog converter DAC to drive the induction coil 42 with a periodic signal, e.g., a sinusoidal signal, at the resonant frequency of the field generator MGM. The resonant frequency is preferably a predetermined fixed frequency, however, the field generator MGM can be configured to provide different frequencies selectable by the field generator. A channel select CHSEL multiplexer is provided to select the specific detection coil DCXa/b with which the amplitude and phase of the electromagnetic field generated by the field generator MGM is to be detected. Further, a short select SHORTSEL multiplexer is provided to short the channels of the field detector 40 or of the induction coil 42, respectively, in order to avoid reciprocal influence during the phases of induction and detection in the alignment process. An analog to digital converter ADC may perform the above measurements.

[0069] The alignment method may have the following steps: A patient enters the patient area of an x-ray apparatus. The intra-oral device 30 is placed at a predetermined position in the oral cavity of the patient behind a tooth to be examined. The patient bites on the tab of the intraoral device 30 or the hygienic protection cover for the intra-oral device 30 that serves as a biting element. Thus, the position of the intra-oral device is fixed in a predetermined position in the oral cavity of the patient. Then, the x-ray source 60 is moved near the jaw of the patient using the movable arm on which the x-ray source 60 is mounted such that an x-ray beam generated by the x-ray source 60 projects approximately towards the x-ray detector of the intra-oral device 30. An electromagnetic field may be generated by the field detector 40 with the induction coil 42. The field strength determined by the field detector 40 can be used as an indicator of the distance between intra-oral device 30 and x-ray source 60. When the distance is sufficiently small so that the field detector 40 detects a electromagnetic field, an audible signal may be produced for an operator of the x-ray apparatus to indicate the sufficiently close distance between the x-ray detector 20 and the x-ray source 60.

[0070] Then, a variable electromagnetic field is generated. PU drives the SHORTSEL multiplexer in order to short the eight detection coils DCXa/b while opening the induction coil 42. CPU drives the Digital to Analog Converter (DAC) to generate a sequence of pulses at a predetermined frequency in the induction coil 42. The LC circuit of the field generator MGM resonates and produces the variable electromagnetic field. PU drives the SHORTSEL multiplexer in order to short the induction coil and open the first of the eight detection coils DC1a while maintaining the others shorted. PU acquires the amplitude and the phase of the electromagnetic field generated by the field generator MGM and detected by the detection coil DC1a. The steps given above in this paragraph are repeated for each of the eight detection coils DCXa/b consecutively. It is noted that the invention is not limited to the use of multiplexers and could include any suitable device that can selectively communicate with the detection coils. The detection coils can be polled consecutively, in any pattern synchronized with the induction coils. The detection coils could also be polled simultaneously with the incorporation of additional hardware.

[0071] Next, the orientation and position of the x-ray detector 20 relative to the x-ray source 60 are determined using the variable electromagnetic field detected by the field detector 40 using the processing system. For this purpose, the PU compares the detected values of amplitude and phase of the electromagnetic field, in order to evaluate the correct position and tilt of the intraoral device 30 with respect to the x-ray source 60. The PU gives an indication to the operator of the movement that the x-ray source 60 has to perform in order to reach the correct positioning using the LEDs of the display. If an automated arm is used for the x-ray source 60 is used, the processing unit could move the x-ray source automatically based on the positions determined by the processing unit. After having moved the x-ray source 60, the relative position of the intra-oral device 30 to the x-ray source 60 may be determined again. If a mis-alignment is detected, the PU gives again indications to the operator of the movement that the x-ray source 60 has to perform in order to reach the correct positioning using the LEDs of the display. This sequence of steps is repeated until a correct alignment within predetermined level of accuracy is reached. Translational and rotational (tilt) movements of the x-ray source may be performed for achieving alignment.

[0072] The alignment system is essentially free of disturbances from environmental electromagnetic fields, since the processing system may be set on a frequency of the electromagnetic field that is generated by the field generator MGM. Other frequencies or static magnetic fields may be filtered out. A further advantage of the invention is that it can be used with any commercial x-ray sensor for intra-oral radiography for which the frame of the intra-oral device 30 is customized. In an embodiment where induction source are used, safety is increased, maintenance such as cleaning of the intra-oral device is facilitated, and patient comfort is improved, since no wires for powering the field generator MGM have to go into the oral cavity of the patient. Furthermore, the reduced dimension of the field generator MGM (a simple LC resonant circuit may be sufficient) allows reduction in the size of the intra-oral device 30. If multiplexing is used, the cost of the overall circuitry is reduced to a single channel sampling.

[0073] Figure 9 is a view of a patient having an intra-oral device 30 according to the invention inserted into the oral cavity and an x-ray source 60 having a field detector 40 around the collimating cone. The collar shaped field detector 40 further has integrated therein a display system to indicate movements to be carried out for achieving alignment of the x-ray source 60 and an x-ray detector 20.

[0074] Figure 10 shows a hygienic protection cover in the form of an elastic film that can be pulled over an intra-oral device 30. The protection cover may be a thin film that may be made of a natural or synthetic rubber, a latex, a polythene or any other suitable material. The protection cover may be pulled over the intra-oral device 30 before the intra-oral device 30 is inserted into the oral cavity of a patient. The protection cover may have a tab that can project perpendicularly from the surface of the protection cover. Alternatively, such tab may be attached at a desired position on the outer surface of the protection cover after the protection cover has been pulled over the intra-oral device. The intra-oral device 30 covered by the protection cover may then be fixed at a desired location inside the oral cavity of a patient by the patient biting on the tab.

[0075] The protection cover may have cushions for cushioning the intra-oral device when inside the oral cavity of the patient to provide patient comfort. The cushions may be formed of foamed polyurethane and may be positioned between the intra-oral device and the protection cover. However, the cushions can be made of the same material as the protection cover. Furthermore, the cushions may be embedded in the protection cover or in one of at least two layers of the protection cover, e.g. in the form of a layer of foamed material.

[0076] It should be understood that the application is not limited to the details or methodology set forth in the description or illustrated in the figures. It should also be understood that the phraseology and terminology employed herein is for the purpose of description only and should not be regarded as limiting.

[0077] While the exemplary embodiments illustrated in the figures and described are presently preferred, it should be understood that these embodiments are offered by way of example only. Accordingly, the present application is not limited to a particular embodiment, but extends to various modifications that nevertheless fall within the scope of the appended claims. The order or sequence of any processes or method steps may be varied or re-sequenced according to alternative embodiments.

[0078] The present application contemplates methods, systems and program products on any machine-readable media for accomplishing its operations. The embodiments of the present application may be implemented using an existing computer processors, or by a special purpose computer processor for an appropriate system, incorporated for this or another purpose or by a hardwired system.

[0079] It is important to note that the construction and arrangement of the systems as shown in the various exemplary embodiments is illustrative only. Although only a few embodiments have been described in detail in this disclosure, those skilled in the art who review this disclosure will readily appreciate that many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter recited in the claims. For example, elements shown as integrally formed may be constructed of multiple parts or elements, the position of elements may be reversed or otherwise varied, and the nature or number of discrete elements or positions may be altered or varied. Accordingly, all such modifications are intended to be included within the scope of the present application. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. In the claims, any means-plus-function clause is intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures. Other substitutions, modifications, changes and omissions may be made in the design, operating conditions and arrangement of the exemplary embodiments without departing from the scope of the present application.

[0080] As noted above, embodiments within the scope of the present application include program products comprising machine-readable media for carrying or having machine- executable instructions or data structures stored thereon. Such machine-readable media can be any available media which can be accessed by a general purpose or special purpose computer or other machine with a processor. By way of example, such machine-readable media can comprise RAM, ROM, EPROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to carry or store desired program code in the form of machine-executable instructions or data structures and which can be accessed by a general purpose or special purpose computer or other machine with a processor. When information is transferred or provided over a network or another communications connection (either hardwired, wireless, or a combination of hardwired or wireless) to a machine, the machine properly views the connection as a machine- readable medium. Thus, any such connection is properly termed a machine-readable medium. Combinations of the above are also included within the scope of machine-readable media. Machine-executable instructions comprise, for example, instructions and data which cause a general purpose computer, special purpose computer, or special purpose processing machines to perform a certain function or group of functions.

[0081] It should be noted that although the figures herein may show a specific order of method steps, it is understood that the order of these steps may differ from what is depicted. Also two or more steps may be performed concurrently or with partial concurrence. Such variation will depend on the software and hardware systems chosen and on designer choice. It is understood that all such variations are within the scope of the application. Likewise, software implementations could be accomplished with standard programming techniques with rule based logic and other logic to accomplish the various connection steps, processing steps, comparison steps and decision steps.

Claims

What is claimed is:

1. An alignment system for dental intra-oral radiography, comprising: an intra-oral device comprising a generator of a variable electromagnetic field; and an electromagnetic field detector for detecting said variable electromagnetic field generated by said generator.

2. An alignment system for dental intra-oral radiography, comprising: a generator of a variable electromagnetic field, said generator being adapted to be attached to an x-ray source; and an intra-oral device comprising an electromagnetic field detector for detecting said variable electromagnetic field generated by said generator.

3. The alignment system according to claim 1 wherein said generator of said variable electromagnetic field and said intra-oral device are adapted to be attached in fixed spatial relationship to one another and said electromagnetic field detector is adapted to be attached in fixed spatial relationship to an x-ray source.

4. The alignment system according to claim 1 further comprising an induction source to power said generator of said variable electromagnetic field by induction.

5. The alignment system according to claim 4 wherein said induction source comprises at least one induction coil adapted to power said generator of said variable electromagnetic field and to detect a component of said variable electromagnetic field, said electromagnetic field detector including said at least one induction coil.

6. The alignment system according to claim 1 wherein said electromagnetic field detector comprises at least two coils in different orientations for detecting at least two vector components of said variable electromagnetic field.

7. The alignment system according to claim 1 wherein said electromagnetic field detector comprises at least two coils in similar orientations for detecting a vector component of said variable electromagnetic field at two different spatial positions of said electromagnetic field detector.

8. The alignment system according to claim 1 further comprising a control unit to control the variable electromagnetic field to be generated by said generator.

9. The alignment system according to claim 1 wherein said electromagnetic field detector is adapted to be attached to the collimating cone of an x-ray source.

10. The alignment system according to claim 9 wherein said intra-oral device comprises an x-ray detector.

11. The alignment system according to claim 10 further comprising a processing system configured to determine an orientation and position of said x-ray detector relative to said x-ray source from the electromagnetic field detected by said electromagnetic field detector.

12. The alignment system according to claim 11 wherein said processing system is configured to filter ambient electromagnetic field contributions from said detected variable electromagnetic field, the ambient electromagnetic field contributions being generated by sources other than said generator.

13. The alignment system according to claim 10 further comprising a display, the display being configured to indicate to an operator of an x-ray system at least one of any misalignment of said x-ray detector and said x-ray source, directions or orientations to move said x-ray detector or said x-ray source to achieve alignment, or when said variable electromagnetic field generated by said generator is detected by said electromagnetic field detector.

14. The alignment system according to claim 1 further comprises an x-ray transparent hygienic protection cover covering said intra-oral device.

15. The alignment system according to claim 14 wherein said hygienic protection cover comprises at least one cushion to cushion said intra-oral device for patient comfort.

16. The alignment system according to claim 14 wherein said hygienic protection cover comprises a tab as a bite element for fixing the position of said intra-oral device in an oral cavity of a patient.

17. An x-ray apparatus for intra-oral radiography comprising: an x-ray source; an x-ray detector; and an alignment system for aligning the x-ray source, and the x-ray detector, the alignment system comprising: a generator of a variable electromagnetic field; an electromagnetic field detector for detecting the variable electromagnetic field; an intra-oral device, the intra-oral device including the x-ray detector; and wherein the generator of a variable electromagnetic field being connected to one of the intra-oral device or the x-ray source and the electromagnetic field detector being connected to the other one of said one of the intra-oral device or the x-ray source.

18. The x-ray apparatus of claim 17 wherein the generator is attached in fixed spatial relationship to the intra-oral device and the electromagnetic field detector is attached in fixed spatial relationship to the x-ray source.

19. The x-ray apparatus of claim 17 further comprising: a control unit for controlling the variable electromagnetic field to be generated by said generator; and processing means for determining an orientation and position of the x-ray detector relative to the x-ray source.

20. A method of aligning an x-ray source and an x-ray detector of an x-ray apparatus for dental intra-oral radiography, said method comprising: placing an intra-oral device with said x-ray detector at a predetermined position in the oral cavity of a patient; moving said x-ray source near the jaw of the patient such that an x-ray beam to be generated by said x-ray source projects approximately towards said x-ray detector located in the patient's oral cavity; generating a variable electromagnetic field using a generator; detecting said variable electromagnetic field with an electromagnetic field detector; determining the orientation and position of said x-ray detector relative to said x- ray source using the variable electromagnetic field detected by said electromagnetic field detector; and moving said x-ray source or said x-ray detector until the detected electromagnetic field indicates a desired alignment of said x-ray source and said x-ray detector.

21. The method according to claim 20, further comprising the step of indicating to an operator of said x-ray apparatus a misalignment of said x-ray source and said x-ray detector.

22. The method according to claim 21, wherein the step of moving said x-ray source or said x-ray detector includes adjusting a position of said x-ray source or said x-ray detector in response to indications of misalignment on a display.

23. The method according to claim 20 wherein the step of generating a variable electromagnetic field includes energizing an electric circuit in said generator to resonate said variable electromagnetic field at a predetermined frequency, said electric circuit including an inductor and a capacitor configured to generate the predetermined frequency.