Ring for the transfer of data

Abstract: A computerized tomography system includes a stationary section ( A ) and a rotating section electrically linked by at least one interconnecting slip ring ( E ). On one side the slip ring ( E ) is configured as a series of electrically conductive segments separated by non-conductive interruptions. On the other side a like number of transmitters is in selective electrical contact with the conductive segments depending on a position of the rotating frame. Also included is a de-multiplexer which takes image data from the plurality of receivers and rearranges the image data in a determined sequence. Also provided is an angular encoder for providing angular displacement signals to the de-multiplexer for assistance in reconstructing the data channels in the determined sequence.

Description: The present invention relates to a ring for the transfer of data, especially for electrical signal transfer between a moving part and a stationary part. It finds particular application in conjunction with radiography, especially for computerized tomography (CT) scanners and will be described with particular reference thereto. However, it is to be appreciated that the present invention is also amenable to other like applications. Heretofore, CT scanners have commonly included a floor mounted frame assembly or gantry which remains stationary during an imaging procedure. A radiation generator, such as an x-ray tube, is mounted to a rotatable frame assembly or section which rotates around a patient being imaged. In third generation scanners, a radiation detector array is located within the rotating frame along with the x-ray tube. It is therefore necessary to provide a mechanism to transfer electrical signals to and from the rotating frame. That is, electrical power and control signals are transferred from the stationary frame to the rotating frame to power and control electronics, hardware, and the x-ray tube. Additionally, a communications path is provided to transfer imaging data from the radiation detector array in the rotating frame to the stationary frame for image processing. The rotating gantry rotates rapidly, preferably one (1) revolution per second or less. The detector array includes numerous individual detectors, e.g. hundreds or even thousands. The detectors are sampled rapidly, typically in a fraction of a degree of rotation, to a high resolution, e.g. 32 bits or more. The amount of data to be transferred is so massive, that the data transfer rate is becoming a limiting factor in scanner speed and resolution. Various devices are known for providing the communication path between the rotating frame and the stationary frame. Older CT scanners employed an umbilical cable. Typically, one or more flexible, shielded cables were hardwired to electronics such as the detector array, in the rotating frame. The cables were connected at the other end to stationary side electronics including image processing computers. Unfortunately the umbilical cable is typically capable of +/-360° of rotation. Accordingly, the rotating frame on such umbilical devices is limited to a total of 720° of rotation in one direction before the frame is stopped and rewound in the opposite direction. Such "cycling" type scanners were good for imaging a small number of slices. For larger volumes, continuous rotating scanners are preferred. The subject moves axially to create a spiral scanning pattern. In continuous rotate third generation systems, slip rings are commonly used to transfer power, data, and control signals. However, continuing improvements keep increasing rates of data transfer. On slip ring data links, the time required to propagate data signals around the circular rings effectively limits the maximum data transfer rate. Signals propagating around the ring in opposite directions may arrive at a reception point at offset times causing interference or garbled reception. Similar limitations are observed in slip ring data links employing capacitance-type data transfer. Demands for higher data rates are increasingly being met, not through electrical slip ring configurations, but by optical data transmission links. Such data links typically employ a series of pulsating lights distributed around either the stationary frame or the rotating frame. On the opposing frame, an optical receiver is used to detect the synchronously strobing lights. The received light signals are then translated back into electronic image data for follow-on processing. Unfortunately, optical systems are more costly per channel of image data supplied, and greatly depend on the alignment of the optical transmitters and receivers. Moreover, optical systems are unusually sensitive to dirt and/or dust obscuring the optics. From US patent document US 5,010,254 an imaging system is known that has a rotating part and a stationary part, where on one of the parts a plurality of transmitting elements is disposed and on the other part a plurality of receiving elements is disposed. The transmitting elements and the receiving elements are in selective communication to transmit a single data stream originating from one common source. The vernier principle is used to avoid simultaneous operation of more than one transmit-receive pair and the number of receiving elements is therefore one different than the number of transmitting elements. In accordance with one aspect of the present invention, an imaging system is provided according to claim 1. In accordance with another embodiment of the present invention, a data transfer method is provided according to claim 6. Ways of carrying out the invention will now be described in detail, by way of example, with reference to the accompanying drawings, in which: FIGURE 1 is a diagrammatic illustration of a CT scanner in accordance with the present invention; FIGURE 2A and 2B are exemplary illustrations of single multi-channel segmented slip rings according to the present invention; FIGURE 3 is a time line showing usage of segments, receivers, transmitters, and relative angular locations; FIGURE 4 is an illustration of an angular encoder and image data formatting device in accordance with the present invention; FIGURE 5 is an illustrative diagram of two segmented slip rings angularly offset from one another; FIGURE 6 is an illustrative diagram of an alternate embodiment of the present invention; and FIGURE 7 is an illustrative diagram of another alternate embodiment of the present invention. With reference to FIGURE 1, a CT scanner includes a floor mounted stationary frame portion or section A whose position remains fixed during data collection. An x-ray tube B and x-ray detector array C are mounted on a rotating frame or section D disposed within the stationary frame A . A multi-channel segmented slip ring E is disposed between the stationary frame A and the rotating frame D to provide electrical communication between the frames. With reference now to Figure 2A, the segmented slip ring E includes a plurality of electrically conductive segments 20A-20H configured as a ring. The segments 20 are separated by a like number of non-conductive interruptions 22A-22H . Those skilled in the art will appreciate that the segments 20 can be disposed either on the rotating frame or the stationary frame with no loss of functionality. In the illustrated embodiment, receiving circuitry RxA-RxH is electrically connected to each conductive segment 20 for filtering and amplifying the signal as is known in the art. Additionally, the receiving circuits RxA-RxH route the signal to a de-multiplexer more fully discussed below. The segmented slip ring E also includes a plurality of transmitting elements 26A-26H each in electrical communication with at least a portion of the radiation detector C (Figure 1). As illustrated in Figure 2, the transmitting elements include a brush 28A-28H with at least an electrically conductive tip. As used herein the term 'brush' is understood to refer to any of a single wire, a spring biased electrical element, a group of wires in close physical proximity, or the like. As above, those skilled in the art will recognize that the transmitting elements 26 can be positioned on either the stationary frame or the rotating frame with no loss of functionality. Moreover, artisans will appreciate that a ground path is provided between the stationary frame and the rotating frame via means known in the art such as a dedicated non-segmented slip ring and the like. As is apparent now from combined reference to Figures 2A and 2B, as the rotating frame moves or is angularly offset, the brushes 28 move over the conductive segments 20 uniformly until reaching the non-conductive interruptions 22 . In other words, when the rotating frame is positioned such that the transmitter 26 and the brushes 28 are in contact with a conductive segment 20 , electrical communication is established between the rotating frame C and the stationary frame A . Those skilled in the art can appreciate that dividing the slip ring into a plurality of conductive segments can be seen as effecting a parallel format data transfer. For example, in the illustrated embodiment eight data streams may be transmitted simultaneously one between each brush and conductive segment pair. Additionally, those skilled in the art will appreciate that use of the relatively short conductive segments desirably reduces time delay and/or phase errors within the signals conducted. Referring now to Figure 2B, when the rotating frame urges the brushes through a non-conductive interruption 22 onto a following conductive segment 20 , it can now be appreciated that each transmitter 26 is in electrical communication with a different receiver 24 . For example, in Figure 2A transmitter 26H is in electrical contact with receiver RxH . Figure 2B illustrates a slight angular displacement of the rotating frame which has the effect of placing transmitter 26H in electrical communication with receiver RxG . Thus, as the rotating frame rotates, each transmitter 26 must periodically cease sending data as the brushes approach the non-conductive interruptions 22 . Moreover, positioning information accompanies the data from the receivers Rx to ensure correct processing and association with the originating transmitter. In other words, imaging signals from transmitter 26A are transmitted to the stationary frame A cyclically first through receiver RxA , then through receiver RxH , then RxG , etc. In order to best appreciate the timing required to preferably control transmit sequences to occur only when the transmitters are in electrical communication with the receivers is best illustrated by reference to Figure 3. Information about the relative rotational angle of the rotating frame is preferably provided to both transmitters 26 and receivers Rx . The angular location is graphically depicted on timing graph 30 by the location axis 32. Those skilled in the art will appreciate that by gating the transmission and/or the reception of data on and off as the brushes pass through the non-conductive interruptions 22, data loss and data garble are minimized. In order to gate the transmitters and receivers on and off, the data illustrated on the location axis 32, that is the location of the rotating ring, is preferably provided to both the portion of the slip ring assembly on the rotating frame, and the portion of the slip ring located on the stationary frame. In fact, regardless of the source of the rotational or angular information, a path such as a non-segmented slip ring section or the like is provided to communicate the angular information. It can be appreciated that the channel A data, as seen on the transmit axis 34 sequences through each segment 20 of the segmented slip ring, as illustrated by the segments axis 36 to receivers associated with each segment. The receivers illustrated by the receiver axis 38 route the signals for further processing on the stationary side of the gantry. Those skilled in the art will appreciate that gating individual transmitter and receivers on and off depending on the relative rotational position of the rotating section may be required in certain embodiments, for example single rings or dual aligned rings comprising one signal pair. In other embodiments however, continuous data streams are also envisioned across a multiplicity of concentric parallel slip ring pairs angularly offset from one another. In other words, as the brushes approach gaps on a first slip ring, the transmitting and receiving responsibility for each particular channel may be switched to a second parallel slip ring where the brushes are in communication with the slip ring segments. In an additional embodiment, a single segmented slip ring may provide a signal pair to insure against sporadic signal loss. Such an embodiment is envisioned as dedicating two receivers and two transmitters on each segmented slip ring to any particular channel. In other words the eight segmented slip ring illustrated in Figure 2A, 2B would be capable of channels A-D in duplicate as opposed to a singular path for channels A-H as illustrated. Yet another potential embodiment includes different numbers of brushes and ring segments angularly staggered within one slip ring's assembly. In such a configuration, angular position or rotational information is preferably still provided to both the rotating segment and the stationary segment. The angular offset of brushes and segments will ensure that a number of brush/segment pairs are always in electrical communication. It is now apparent at a variety of configurations of slip ring assemblies, segments within an assembly and brushes within an assembly are possible depending on the particular system requirements needed. Referring now to Figure 4, a de-multiplexer or decoder 40 preferably receives image data 42A-42H from the plurality of receivers Rx in addition to an angular displacement signal 44 from an angular encoder 46 . The de-multiplexer or decoder 40 preferably includes a register 48 controlled by angular displacement signal 44 which reorders data from each of the receivers Rx into a channelized coherent data stream for further processing by an image reconstruction computer F (Figure 1). It should be appreciated that de-multiplexer 40 simultaneously reorders receiver data for each channel depending on the relative position sensed by encoder 46 . In parallel processing reconstruction systems, each detector of the array C is connected with one of the transmitters on the rotating frame. The demultiplexer outputs the signal from each detector, in parallel to a parallel reconstruction processor. In either single or parallel channel systems, a reconstruction processor 50 reconstructs the image data into an electronic image representation that is stored in a memory 52 . A video processor 54 converts selected portions of the electronic image representation into slice images, three-dimensional renderings, projection images, or the like which images are displayed on a human readable monitor 56 . Referring now to Figure 5, an alternate embodiment of a multi-channel segmented slip ring includes a first slip ring 60 similar in most respects to the segmented slip ring of Figure 2. In the embodiment illustrated by Figure 5 however, a capacitive transmitting system 66A-66H is used as opposed to the brush system previously discussed. Such capacitive electrical communication is known in the electrical arts. In addition, a second segmented slip ring is included 62 which includes segments 64 angularly offset from the segments of the first ring 60 . In other words, one of the slip rings 60 , 62 will provide electrical communication between the stationary side and the rotating side at all times. This redundancy can be used for error correction or to increase the data rate over the slip ring. Those skilled in the art will appreciate that a similar angularly offset multi-ring configuration is workable in the brush system discussed above. With reference to Figure 6, in another alternate embodiment, the slip ring has N segments 20 , where N is a plural integer, preferably odd. N-1 brushes 28 contact the segments. In this manner, no two brushes are in the non-conductive interruptions at the same time. By connecting each detector with 2 brushes (and programming the demultiplexer 40 accordingly), a continuous data stream is provided from each detector. In another alternate embodiment there are again N ring segments 20 and N-1 transmitters 26' . Each transmitter 26' has a brush, brush set, or capacitive element which is large enough to span the non-conductive interruption between segments 20 . The brushes, brush sets, or capacitive elements are spaced from each other by more than the arc of the ring segments. Partially overlapping segments, as illustrated in Figure 7, facilitate making communication with two adjacent rings. One advantage of the described embodiments is that they improve data transfer efficiency. Another advantage resides in their simplicity. Another advantage resides in the extremely high data transfer rates. Another advantage is the achievement of higher data transfer rates in CT type scanners which provide continuous rotation and reliable high-speed communications. Yet another advantage resides in the space efficiency. Fewer slip ring assemblies can carry more data.

Claims: An imaging system including a stationary section (A) defining a central opening, an annular rotating section (D) rotatably mounted in the central opening, an interconnecting data link (E) which transmits data therebetween, said interconnecting data link (E) comprising: at least one ring including a plurality of electrically conductive segments (20A-20H) separated by non-conductive interruptions (22A-22H) spaced angularly around one of said sections; and a plurality of signal communication elements (26A-26H) spaced angularly around the other of said sections, the plurality of signal communication elements (26A-26H) being in selective electrical communication with said plurality of electrically conductive ring segments (20A-20H)and the plurality of signal communication elements (26A-26H) being provided for transmitting a plurality of data streams; characterized in that the angular extension of the electrically conductive segments (20A-20H) is larger than the angular extension of the non-conductive interruptions (22A-22H). An imaging system as claimed in claim 1, wherein the signal communication elements (26A-26H) include brushes (28A-28H)in selective physical contact with the electrically conductive ring segments (20A-20H). An imaging system as claimed in claim 1, where the signal communication elements (26A-26H) include capacitive couplers (66A-66H) spaced from the conductive segments (20A-20H). An imaging system as claimed in any one of claims 1 to 3, further comprising: an encoder (46) which generates an angular displacement signal indicative of the rotation of the rotating section (D); and a de-multiplexer (40) which receives the angular displacement signal and the data, and sorts the data in accordance with the angular displacement signals. An imaging system as claimed in any one of claims 1 to 4, where the interconnecting data link further comprises: a second ring (62) including a second plurality of electrically conductive segments (64A-64H) axially spaced from said first plurality of conductive segments (20A-20H); and a second plurality of signal communication elements (68A-68H) in electrical communication with the second ring (62). A data transfer method comprising: generating relative rotational movement between at least a first ring of electrically conductive segments (20A-20H) that are separated by non-conductive interruptions (22A-22H) and a plurality of signal communication elements (26A-26H), where the angular extension of the electrically conductive segments (20A-20H) is larger than the angular extension of the non-conductive interruptions (22A-22H); applying a plurality of data streams to selected signal communication elements (26A-26H); and at selected rotational angles receiving the plurality of data streams, one on each segment of the ring (20A-20H). A data transfer method as claimed in claim 6, wherein the plurality of signal communication elements (26A-26H) include electrically conductive brushes (28A-28H), the receiving step including: establishing physical contact between at least selected brushes and ring segments (20A-20H). A data transfer method as claimed in claim 6, wherein the plurality of signal communication elements (26A-26H) include capacitive couplers (66A-66H), the receiving step including: capacitively coupling at least selected couplers and ring segments (20A-20H). A data transfer method as claimed in any one of claims 1 to 8, further including: monitoring the relative rotational movement; and sorting each of the plurality of data streams in accordance with the monitored relative rotational movement. A data transfer method as claimed in any one of claims 6 to 9, further including: generating relative rotational movement between a second ring (62)of electrically conductive segments (64A-64H) and a plurality of signal communication elements (68A-68H), where the second ring and the first ring are parallel and concentric.

Inventors: HEROLD MARK D, RESNICK THEODORE A, HEROLD, MARK D., RESNICK, THEODORE A.
Applicants: KONINKL PHILIPS ELECTRONICS NV, KONINKLIJKE PHILIPS ELECTRONICS N.V.
Application year: 2000
Main classification: A61B6
IPC codes: A61B6, H01R39