Abstract:
In a device and a method for data transfer between two parts moving relative to one another while maintaining a slight distance between the parts, a transmission device with at least one transmission antenna (connected with a transmitter) and a reception device with a reception antenna (connected with a receiver are used). The transmission antenna and/or the reception antenna is/are fashioned as radio-frequency conductors and are arranged such that signals fed into the transmission antenna during at least one segment of the relative movement are received by the reception antenna by capacitive or inductive coupling. One or more compensation devices is/are arranged between the transmitter and the receiver. The compensation devices counteract signal distortion caused on the radio-frequency conductor by propagation of the signals. Higher data transfer rates can be realized in a cost-effective manner given the use of radio-frequency strip conductors as transmission and/or reception antennas.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention concerns a device as well as a method for data transfer between two parts moving relative to one another while maintaining a slight distance between the parts.  
         [0003]     2. Description of the Prior Art  
         [0004]     A device of the above type is known that has a transmission device with at least one transmission antenna (connected with a transmitter) on one of the parts moving relative to one another and one receiver device that has at least one reception antenna (connected with a receiver) on the other of the parts moving relative to one another. The transmission antenna and/or the receiver antenna is/are fashioned and arranged as radio-frequency conductors, such that during at least one segment of the relative movement, signals submitted by the transmission antenna are received by the reception antenna by capacitive or inductive coupling.  
         [0005]     The preferred application field of the present invention concerns data transfer between the rotating part and the stationary part of a computed tomography apparatus. In operation of the computed tomography apparatus the data acquired by the x-ray detectors must be transferred from the rotating part to the stationary part of the computed tomography apparatus in order to further process the data. The data quantity to be transferred increases with the continuous development of computed tomography systems.  
         [0006]     In many presently available computed tomography apparatuses a slip ring system as known is, for example, from U.S. Pat. No. 5,140,696 or U.S. Pat. No. 5,530,422 is used for data transfer. This data transfer system has a transmission device on the rotating part as well as a reception device on the stationary part. The transmission device has at least one radio-frequency conductor connected with a transmitter and forming a transmission antenna that is arranged on the periphery of the rotating part of the rotating frame. The reception device has a receiver and at least one reception antenna connected with the receiver, this reception antenna being formed by a short segment of a radio-frequency conductor. In operation of the computed tomography apparatus, the transmission antenna moves past the reception antenna attached on the stationary part at a slight distance, such that the signals propagating on the transmitting radio-frequency conductor are capacitively launched or injected into the reception antenna via the developing wave. The radio-frequency conductors are normally fashioned as microstrip conductors in a PCB (printed circuit board) technique and can be realized cost-effectively.  
         [0007]     This transfer technology, however, due to the steadily increasing data rate (already at multiple gigabits/s (Gbps)) in computed tomography systems, in particular in multi-line computed tomography systems, will lead to problems in the near future since the signals or data to be transferred must be conducted over a larger distance in the transmitting radio-frequency conductor dependent on the current position of the rotating frame. Given increased data rate, strong signal distortions that limit the transferable data rate arise in the data transfer due to frequency-dependent losses, in particular due to dielectric losses and the skin effect. Since a shortening of the radio-frequency conductor used in the transmission device is not possible in computed tomography systems, a higher data rate can be achieved only by the use of special low-loss dielectric materials in the radio-frequency conductor. Such materials are expensive and are not always available for the desired data rates.  
       SUMMARY OF THE INVENTION  
       [0008]     An object of the present invention is to provide a device as well as a method for data transfer between two parts that are moving relative to one another while maintaining a slight distance, in particular between the rotating part and the stationary part of a computed tomography apparatus, which can be realized in an economic manner and enable a higher transferable data rate than the data transfer systems described above.  
         [0009]     The object is achieved in accordance with the invention by a device and a method using, in a known manner, a transmission device that has at least one transmission antenna (connected with a transmitter) on one of the parts moving relative to one another and a reception device that has at least one reception antenna (connected with a receiver) on the other of the parts moving relative to one another. The transmission antenna and/or the reception antenna are each fashioned as a radio-frequency conductor and are arranged such that signals emitted by the transmission antenna during at least one segment of the relative movement are received by the reception antenna via capacitive or inductive coupling. The radio-frequency conductor can be a microstrip conductor or a waveguide. For example, the transmission antenna can be a strip conductor that extends over the entire distance of the relative movement, with the reception antenna being formed only by a short piece of a strip conductor. In accordance with the invention, one or more compensation devices is/are arranged between the transmitter and the receiver, the compensation devices counteracting signal distortion caused on the radio-frequency conductor by propagation of the signals. The one or more compensation devices thus effect a frequency-dependent increase or decrease of frequency amplitudes of the transferred signals that counteracts the frequency characteristic of the frequency-dependent attenuation caused by the signal propagation on the radio-frequency conductor, and thus at least approximately compensates this frequency-dependent attenuation.  
         [0010]     For data rates above 1 Gbps, the signal distortion is caused primarily by dielectric losses on the radio-frequency conductor that exhibit an f-1 characteristic. The signal distortions at the receiver (as occur, for example, along with the transfer of NRZ (non-return to zero)) signals, thus can be avoided or distinctly reduced by the arrangement of suitable compensation devices for compensation of this f-1 characteristic. The device and the associated method in accordance with the invention enable the transfer of higher data rates between two parts moving relative to one another at a slight distance with data transfer systems that operate with capacitive or inductive coupling such as, for example, the slip ring systems used in computed tomography systems. The device furthermore allows the use of cost-effective materials for the radio-frequency conductor as have previously been used in computed tomography systems. The use of particularly low-loss dielectric materials, however, is naturally also possible. In this case, the present invention leads to a an even further increase of the data transfer rate at a given transfer distance.  
         [0011]     The compensation devices can be formed by active or passive components; a combination of active and passive components is also possible. The compensation devices can be used at any point between transmitter and receiver, for example in the transmitter, in the receiver or in the radio-frequency conductor. An arrangement of a compensation device exclusively in the transmitter or exclusively in the receiver is naturally also possible.  
         [0012]     In principle, suitable compensation devices are known from the field of radio-frequency data transfer, but these have conventionally been used with fixed transfer distances and have been exactly adapted to the length of the transfer path. In the case of data transfer between two parts moving relative to one another, however, the transfer distance changes continuously, such that the use of such components has not previously been considered for this application.  
         [0013]     the inventive device and the associated method thus are based on the insight that a signal distortion can also be successfully countered (and thus the data transfer rate can be increased) in such an application by suitable adaptation of the compensation devices.  
         [0014]     In one embodiment this can ensue by adaptation of the respective compensation device for the optimal compensation of a transfer distance that lies in a median range between a minimum transfer distance and a maximum transfer distance that are predetermined by the relative movement.  
         [0015]     In another embodiment, the compensation is continuously adapted dependent on the changing transfer distance that occurs during the relative movement, in order to achieve an optimal compensation of the signal distortions for each transfer distance during the relative movement. For this purpose, the relative position between the two parts moving relative to one another is directly or indirectly detected during the relative movement (in the event that this is not already known from the controller of the relative movement) and is communicated to the one or more compensation devices. These compensation devices then alter the frequency-dependent attenuation and/or amplification of the signals continuously or in steps (advantageously by using a stored table) dependent on the relative position or the transfer distance.  
         [0016]     In a further embodiment an active regulation of at least one of the compensation devices ensues which can be arranged, for example, in the transmitter or in the receiver). For this purpose, the energy distribution within the signals is measured at the output of the receiver in at least two frequency ranges (a high-frequency range and a low-frequency range) and is communicated to the compensation device. The compensation device then regulates the frequency-dependent amplification and/or attenuation such that an optimally uniform energy distribution within the signals in the at least two frequency ranges is obtained at the output of the receiver.  
         [0017]     In the present device and the associated method the compensation devices can be fashioned both as passive components that attenuate the low-frequency signal portions (or at least more significantly attenuate the low-frequency signal portions than the high-frequency signal portions) or as active components that amplify the high-frequency signal portions (or at least more significantly amplify the high-frequency signal portions than the low-frequency signal portions). Given the use of active components, for example, or corresponding compensation device can be provided in the transmitter in order to effect a pre-compensation of the signal distortions, or the compensation device can be provided in the receiver in order to implement a post-compensation of the signal distortions. Suitable compensation devices can be, for example, an equalizer of the type available from the company Maxim Integrated Products, Inc.  
         [0018]     The inventive device for data transfer is advantageously arranged in a computed tomography apparatus in which data must be transferred at high rates between the rotating part and the stationary part. The transmission antenna is advantageously fashioned as a microstrip conductor that extends around the periphery of the rotating part of the rotating frame. The reception antenna on the stationary part is advantageously a short strip conductor segment that exhibits a slight separation from the strip conductor on the rotating part of the rotating frame during the entire rotation. Variations of the transmission and reception antennas can naturally deviate from the preferred embodiment, with any design known in this context from the prior art for capacitive or inductive coupling being possible in principle. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0019]      FIG. 1  is a schematic representation of a computed tomography apparatus showing the basic components of an associated data transfer system.  
         [0020]      FIG. 2  shows an example for a device for data transfer in a computed tomography apparatus according to the prior art, in schematic representation.  
         [0021]      FIG. 3  shows an example for a device for data transfer according to the present invention, in schematic representation.  
         [0022]      FIG. 4  shows an example for a compensation device according to the present invention in the transmitter.  
         [0023]      FIG. 5  illustrates two examples for a variable adaptation of the compensation dependent on the transfer distance.  
         [0024]      FIG. 6  shows an example for a compensation device according to the present invention in the receiver.  
         [0025]      FIG. 7  shows a further example for an embodiment of a compensation device according to the present invention in the receiver.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0026]      FIG. 1  schematically shows a computed tomography apparatus with a device for transfer of measurement data from the rotating part to the stationary part of the rotating frame. A computed tomography apparatus has, among other things, an x-ray tube  3 , x-ray detectors  4  arranged in lines, and a patient positioning table  9 . The x-ray tube  3  and the x-ray detectors  4  are arranged on the rotating part  1  of a rotating frame that rotates around the patient positioning table  9  and an examination axis z running parallel to this patient positioning table  9 . The patient positioning table  9  normally can be displaced along the examination axis  2  relative to the rotating frame. The x-ray tube  3  generates an x-ray beam flared in a fan shape in a slice plane perpendicular to the examination axis  2 . The x-ray beam, for examinations in the slice plane, penetrates a slice of a subject (for example a body slice of a patient who is on the patient positioning table  9 ) and strikes the x-ray detectors  4  situated opposite the x-ray tube  3 . The angle at which the x-ray beam penetrates the body slice of the patient, and possibly the position of the patient positioning table  9  relative to the rotating frame  9 , vary continuously during the image data acquisition with the computed tomography apparatus. During the image apparatus data acquisition the x-ray detectors  4  therefore deliver a large quantity of measurement data that must be evaluated for reconstruction of a two-dimensional slice image or a three-dimensional image of the body of the patient. The evaluation ensues in a stationary computer system  8  that is connected with the computed tomography apparatus. During the measurement data acquisition the rotating part  1  of the rotating frame rotates within the stationary part  2 . The measurement data acquired by the x-ray detectors  4  are transferred with a rotating transmission device  5  (that is mounted on the rotating part  1  of the rotating frame) to a stationary reception device  6  on the stationary part  2  of the computed tomography apparatus. The data are then normally fed via an optical cable connection from the stationary reception device  6  to an image reconstruction module  7  of the computer system  8  for evaluation.  
         [0027]      FIG. 2  exemplarily shows an embodiment of a known data transfer device of the prior art in a schematic representation, as is used in numerous computed tomography systems. With this data transfer device the measurement data are transferred via capacitive coupling from the rotating part  1  to the stationary part  2  of the rotating frame. For this purpose, a circular RF strip conductor  11  is affixed on the rotating part  1  as a transmission antenna into which the measurement data are injected from the data source  10 . The strip conductor  11  is terminated on the side situated opposite the in-feed point by a suitable impedance (termination  12 ). The data bits fed into the strip conductor  11  from the data source  10  propagate in both branches of the strip conductor  11  up to the termination  12 . The selected splitting of the strip conductor  11  into two branches extending in opposite directions enables a continuous data transfer during the rotation of the rotating frame. The arrows in  FIG. 2  show the propagation directions of the data signals in the two branches of the strip conductor  11 . A short segment of an RF strip conductor  13  is arranged at the stationary part  2  of the rotating frame as a reception antenna that is part of the reception device  6  of the stationary part  2 . Given rotation of the rotating part  1  of the rotating frame, the reception antenna (strip conductor  13 ) is located in immediate proximity to the strip conductor  11  (used as a transmission antenna) of the rotating part  1 , such that the data signals fed into the strip conductor  11  are received by the reception antenna via capacitive coupling. However, at higher data rates this type of data transfer runs into problems, as explained above.  
         [0028]     In the inventive device for data transfer, the basic design can be realized in the same manner as this is shown in the computed tomography apparatuses of  FIGS. 1 and 2 , but with the addition of one or more compensation devices. This is shown in  FIG. 3 , which shows the transmission device  5  and the reception device  6  according to the present invention. The transmission device  5  has a transmitter  14  that feeds an incoming signal into the strip conductor  11  serving as a transmission antenna, this strip conductor  11  being terminated with a termination  12 . In the present example a first compensation device  15  is fashioned in the transmitter  14 , this first compensation device  15  being indicated only by the arrow in  FIG. 3 . The reception device  6  is formed by a segment of a strip conductor  13  as well as a receiver  16  that, in the present example, has a compensation device  17  for post-compensation, this compensation device  17  likewise being indicated by an arrow. In the transmitter  14  the incoming signals are modulated on a carrier frequency by suitable modulation circuitry. In the receiver  16 , the incoming signals are extracted again from the received signal by suitable demodulation circuitry. The signals are transferred by capacitive coupling between the two strip conductors  11 ,  13 , which are symmetrical transfer conductors.  
         [0029]     In the embodiment of  FIG. 3 a  passive compensation device  18  is also exemplarily indicated on the strip conductor  11 . This passive compensation device, in the form of a passive equalizer, represents a high-pass RLC filter with a frequency response that is complementary to the frequency-dependent loss of the strip conductor  11  and thus counteracts a signal distortion caused by this frequency-dependent loss. Naturally a number of such passive compensation devices can be provided on the strip conductor  11  or  13  or also in the transmitter  14  or in the receiver  16 . Such passive equalizers, however, lead to an additional loss of signal amplitude, such that in principle active compensation devices as are explained in detail in the following are preferable.  
         [0030]      FIG. 4  shows an example of such an active compensation device for pre-compensation in the transmitter  14 . With this compensation device  15  for pre-compensation (pre-emphasis), the high-frequency components of the signal are amplified before they are fed into the strip conductor  11 . However, the pre-compensation must be specially adapted since the transfer distance over the strip conductor  11  is not constant during the operation of a computed tomography apparatus. During the rotation of the rotating frame, the distance over which the signal propagates on the strip conductor  11  before it launches into the reception antenna depends on the current angle offset between the rotating part and the stationary part of the rotating frame. The distance is shortest for an angle offset of 0 degrees, at which the receiver  16  and the transmitter  14  lie directly opposite one another, and longest for an angle offset of 180°. An optimal pre-compensation for an angle offset of 180° would lead to a widely exaggerated pre-compensation for an angle offset of 0°. Such an exaggerated pre-compensation likewise leads to a worsening of the signal quality and causes a jitter that is not acceptable in terms of level. Different ways can be proposed to avoid this problem.  
         [0031]     For example, a constant pre-compensation can be set at the compensation device  15  that is designed for an average transfer distance between the minimum transfer distance (at an angle offset of 0°) and the maximum transfer distance (at an angle offset of 180°). In the range of this average transfer distance the pre-compensation is set such that an optimally small deterministic jitter is achieved for angle offset of 0° and an optimally good pre-compensation is achieved for an angle offset of 180°. An optimal compensation of the signal distortions is thereby only achieved at a very transfer distance in this median range.  
         [0032]     For further minimization of the jitter, additional devices for clock regeneration as are known from U.S. Pat. No. 6,862,299 can be used in this embodiment, as well as in other embodiments of the present device.  
         [0033]     A second possibility of the use of the compensation device  15  for pre-compensation is to vary the compensation in real time dependent on the changing transfer distance. Given use in a computed tomography apparatus, the level of the pre-compensation is thus varied dependent on the current angle offset between the transmitter  14  and the receiver  16  in order to achieve an optimal compensation of the signal distortion for each transfer distance. The respective current relative position, i.e. the angle offset between the rotating part and the stationary part of a computed tomography apparatus, is already available both at the stationary part and at the rotating part during operation of the computed tomography apparatus, since this information is also required for the later image reconstruction. In the present embodiment this information is also provided to the compensation device  15 , which then varies the level of the pre-compensation corresponding to the current angle position. The adaptation of the pre-compensation to the angle offset can be read from a table in which the different level the pre-compensation dependent on the angle offset is specified.  
         [0034]      FIG. 5  shows such a dependency using two examples. In the first example the level of the pre-compensation is continuously adapted with the angle offset, while a stepped adaptation ensues in the second example. This information required for the compensation device can be stored, for example, in a digital table in which the amplification coefficients dependent on the angle offset are listed. The digital coefficients are then converted via a digital/analog converter (D/A converter) into an analog control signal for controlling the amplification of the signals.  
         [0035]      FIG. 4  shows a compensation device designed in this manner in the transmitter  14  of the present device. The compensation device includes, among other things, a linear amplifier  19  and an HF boost amplifier  23  for frequency-dependent amplification that receives the information about the level of the pre-compensation via a LUT (look-up table)  20  with a downstream D/A converter  21  dependent on the current angle offset  22  between rotating part and stationary part of the rotating frame. The pre-compensated signal is then available at the output of the transmitter  14  to be fed into the strip conductor  11 .  
         [0036]     A compensation device  17  for post-compensation in the receiver  16  can be used in the same manner, as is exemplarily shown in  FIGS. 6 and 7 . In this case high-frequency signal components are also more strongly amplified by the compensation device  17  (here in the embodiment of an equalizer) than low-frequency signal components, in order to compensate the frequency-dependent attenuation of the signals due to the propagation on the strip conductor  11 . The continuously changing transfer distance can be considered in the same manner as was explained in connection with the compensation device  15  for pre-compensation in the transmitter.  
         [0037]      FIG. 6  exemplarily shows a corresponding design of the compensation device  17  using an LUT  20 , but in this case the frequency-dependent amplification is not varied in the RF boost amplifier  23 . Rather, the amplified signals are attenuated in frequency-dependent manner by two variable attenuation elements  26 , dependent on the current angle offset  22  between the rotating part and the stationary part. An output signal compensated with regard to the signal distortion is then available at the output of the receiver  16  after a limit amplifier  27  (also shown in  FIG. 4 ). Other components in  FIG. 6  correspond to those described in connection with  FIGS. 3 and 4 .  
         [0038]     A further possibility of the adaptation of the post-compensation to the continuously changing transfer distance is the realization of an adaptive compensation, as is exemplarily shown in  FIG. 7 . In this example the energy distribution within the signal spectrum is measured at the output of the receiver  16  with two bandpass filters  24 . An analog computer  25  determines the ratio of the energy between the high-frequency and low-frequency signal portions and regulates the compensation device  17  with the two variable attenuation elements  26  such that an optimally uniform distribution of the energy at the high-frequency and low-frequency signal components results at the output. An automatic adaptation of the compensation in the receiver  17  to the changing transfer distance thus ensues via the shown regulatory loop.  
         [0039]     Such a regulation can also be realized for the pre-compensation by the analog computer  25  regulating the compensation device  15  for pre-compensation dependent on the energy distribution at the output of the receiver.  
         [0040]     Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventor to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of his contribution to the art.