Abstract:
The present invention is, in one embodiment, a method for efficiently and reliably communicating button presses electronically on a network from one or more push button nodes each having at least one push button, to a master node. This method includes steps of: generating status messages indicative of a push button states at each of push button node; communicating the status messages to the master node via the network; determining, at the master node, the state of the push buttons at each of the push button nodes from the communicated status messages; and triggering a response of the master node, in accordance with the statuses of the push buttons determined from the communicated status messages.

Description:
BACKGROUND OF THE INVENTION 
     This inventions relates to methods and apparatus for interfacing a device to a set of push button inputs, and more particularly to methods and apparatus for interfacing a CT scanner to a network to create a safe and efficient user interface for accepting push button inputs. 
     In at least one known computed tomography (CT) imaging system configuration, an x-ray source projects a fan-shaped beam which is collimated to lie within an X-Y plane of a Cartesian coordinate system and generally referred to as the “imaging plane”. The x-ray beam passes through the object being imaged, such as a patient. The beam, after being attenuated by the object, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is dependent upon the attenuation of the x-ray beam by the object. Each detector element of the array produces a separate electrical signal that is a measurement of the beam attenuation at the detector location. The attenuation measurements from all the detectors are acquired separately to produce a transmission profile. 
     In known third generation CT systems, the x-ray source and the detector array are rotated with a gantry within the imaging plane and around the object to be imaged so that the angle at which the x-ray beam intersects the object constantly changes. A group of x-ray attenuation measurements, i.e., projection data, from the detector array at one gantry angle is referred to as a “view”. A “scan” of the object comprises a set of views made at different gantry angles, or view angles, during one revolution of the x-ray source and detector. In an axial scan, the projection data is processed to construct an image that corresponds to a two dimensional slice taken through the object. One method for reconstructing an image from a set of projection data is referred to in the art as the filtered back projection technique. This process converts the attenuation measurements from a scan into integers called “CT numbers” or “Hounsfield units”, which are used to control the brightness of a corresponding pixel on a cathode ray tube display. 
     Additional operator inputs to CT systems have been provided as CT systems become more and more flexible. The provision of additional push buttons on the gantry of the CT system to accommodate new functions has resulted in an increased number of cables. Although hard-wired connections to push buttons provide both speed and safety in operation, increased cabling requirements pose additional construction and material costs. In addition, cable routing problems occur due to the size of the required cables. 
     It would therefore be desirable to provide methods and apparatus to accommodate the need for additional push buttons on CT scanning systems without requiring large, costly cables, without compromising the safety and speed of a hard-wired connection. 
     BRIEF SUMMARY OF THE INVENTION 
     There is therefore provided, in one embodiment, a method for efficiently and reliably communicating button presses electronically on a network from one or more push button nodes each having at least one push button, to a master node. This method includes steps of: generating status messages indicative of a push button states at each of push button node; communicating the status messages to the master node via the network; determining, at the master node, the state of the push buttons at each of the push button nodes from the communicated status messages; and triggering a response of the master node, in accordance with the statuses of the push buttons determined from the communicated status messages. 
     The above described method accommodates the need for additional push buttons on CT scanning systems without requiring large, costly cables, without compromising the safety and speed of a hard-wired connection. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a pictorial view of a CT imaging system. 
     FIG. 2 is a block schematic diagram of the system illustrated in FIG.  1 . 
     FIG. 3 is a block schematic diagram of one embodiment of a system for detecting and responding to push button presses. 
     FIG. 4 is a block schematic diagram of another, series-connected embodiment, showing a separate circuit for a critical button. 
     FIG. 5 is a block schematic diagram of a parallel-connected embodiment, also showing a separate circuit for a critical button. 
     FIG. 6 is a block schematic diagram of another embodiment in which a display node is present. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIGS. 1 and 2, a computed tomograph (CT) imaging system  10  is shown as including a gantry  12  representative of a “third generation” CT scanner. Gantry  12  has an x-ray source  14  that projects a beam of x-rays  16  toward a detector array  18  on the opposite side of gantry  12 . Detector array  18  is formed by detector elements  20  which together sense the projected x-rays that pass through an object  22 , for example a medical patient. Detector array  18  may be fabricated in a single slice or multi-slice configuration. Each detector element  20  produces an electrical signal that represents the intensity of an impinging x-ray beam and hence the attenuation of the beam as it passes through patient  22 . During a scan to acquire x-ray projection data, gantry  12  and the components mounted thereon rotate about a center of rotation  24 . 
     Rotation of gantry  12  and the operation of x-ray source  14  are governed by a control mechanism  26  of CT system  10 . Control mechanism  26  includes an x-ray controller  28  that provides power and timing signals to x-ray source  14  and a gantry motor controller  30  that controls the rotational speed and position of gantry  12 . A data acquisition system (DAS)  32  in control mechanism  26  samples analog data from detector elements  20  and converts the data to digital signals for subsequent processing. An image reconstructor  34  receives sampled and digitized x-ray data from DAS  32  and performs high speed image reconstruction. The reconstructed image is applied as an input to a computer  36  which stores the image in a mass storage device  38 . 
     Computer  36  also receives commands and scanning parameters from an operator via console  40  that has a keyboard. An associated cathode ray tube display  42  allows the operator to observe the reconstructed image and other data from computer  36 . The operator supplied commands and parameters are used by computer  36  to provide control signals and information to DAS  32 , x-ray controller  28  and gantry motor controller  30 . In addition, computer  36  operates a table motor controller  44  which controls a motorized table  46  to position patient  22  in gantry  12 . Particularly, table  46  moves portions of patient  22  through gantry opening  48 . 
     In one embodiment and referring to FIG. 3, computer  36  is responsive to button presses of push buttons  50  to control table motor controller  46 , for example, among other things. When a button is pressed, a message is output over a controller area network (CAN)  52 . CAN  52  includes a master node  54 , which is incorporated in the hardware and software of computer  36  in one embodiment, or in a separate unit in another embodiment. For flexibility, CAN  52  also includes as many push button nodes  56  as required by an application such as CT scanner or imaging system  10 . (Push button nodes  56 , in one embodiment, include push buttons  50  mounted on gantry  12  of CT imaging system  10 .) Master node  54  is responsive to push buttons to detect any valid pressed button  50  in network  52 . Master node  54  also, on a periodic basis, outputs a status message of buttons  50  (to computer  36  in this embodiment), thus mirroring an output of a corresponding hard-wired implementation. Master node  54  also senses faults in CAN  52  such as a faulty push button node  56 . 
     In one embodiment, push button node  56  initiates communication of messages to master node  54  on a periodic basis over CAN  52 , which comprises a high speed-serial bus  58 , also referred to as Controller Area Network Bus. In one embodiment, these messages are sent over a period that is half of the time specified for master node  54  to be informed of a button  50  press. When a button  50  is pressed, the message includes an indication of, the button press. Because of the timed, repetitive messages sent by push button node  56 , each button  50  press that occurs will be reported to master node  54  in a time less than that specified for master node  54  to be informed of a button press. In still other embodiments, messages are sent sufficiently often by push button node  56  so that, no matter when a button  50  press .occurs, master node  54  receives a message from the affected push button node  56  in sufficient time to ensure an appropriate system response. In these embodiments, a “sufficient time to respond” depends, for example, on the “appropriate system response.” An “appropriate system response” depends, for example, on the functions that the various buttons  50  operate and control. Master node  54  determines the state of each push button  50  from the communicated status messages, and triggers a response of the master node in accordance with the statuses determined from the communicated status messages. This response is a further communication of push button states to computer  36  in this embodiment. In other embodiments, master node  54  provides I/O ports that mimic or mirror push button states. In one embodiment, each I/O port corresponds to a different push button  50 . 
     Master node  54  checks all push button nodes  56  to ensure that the expected periodic messages from each push button node  56  are received. Each push button node  56  is allotted a pre-determined number of wake-up cycles (i.e., a wake-up cycle of master node  54  during which it outputs a status of buttons  50 , for example, via I/O ports) without changing the last button status sent by that push button node  56 . Master node  54  “defaults” the status of that push button node  56  to a known safe state by triggering a response corresponding to the known safe state. The allowance of an extra missed wake-up cycle helps to create a “jitter-free” system. The setting of the status of a push button node  56  also helps guard against stuck buttons  50 . As a further safety measure, in one embodiment, each CAN  52  packet containing push button  50  status also contains a checksum value generated by the push button node  56 . The checksum is used by master node  54  to validate packets from push button nodes  56 . 
     In one embodiment, for further security and safety, each master node  54  and push button node  56  is equipped with a CPU watchdog timer to guard against firmware errors. Also, all buttons  50  are wired so as to be active-high to guard against unintentional grounding, such as that which may cause a stuck button  50  indication. Also in one embodiment, each monitored button  50  in a push button node  56  creates two signals, one unique to that particular pressed push button  50 , and another logically ORed with all other push buttons  50  of that push button node  56 . The logically ORed output and the unique output signal are read by push button node  56 , which performs a redundancy check using these signals for any pressed button  50 . If an inconsistency is encountered, push button node  56  communicates an error indication to master node  54 . 
     Push button nodes  56  are connected to master node  54  by a series connection in one embodiment, as exemplified by the diagram of FIG. 4, and by a parallel connection in another, as exemplified by the diagram of FIG.  5 . (Although not illustrated, combinations of serial and parallel connections are used in some embodiments. For example, in one embodiment, one of push button nodes  54  in FIG. 5 is replaced by a series connection of push button nodes  54 .) Parallel or series bus  58  include at least a CAN high wire  60  and a CAN low wire  62 . Thus, only two conductors are needed for bus  58  for communicating status messages from push button nodes  54  to master node  56 . However, in at least one embodiment, one or more “critical” buttons  64  are provided that control features of scanning device  10  requiring immediate action. A separate, hard-wired circuit  66  is provided for each critical button  64 . Each hard-wired circuit  66  needs only one additional conductor, because one bus  58  line (for example, CAN low wire  62 ) is shared for this purpose in one embodiment. However, in another embodiment, each hard-wired circuit  66  comprises a pair of conductors and does not share any conductors with buttons  50 . Depending on a location of a critical button  64 , in a series connection such as that exemplified in FIG. 5, a dedicated, hard-wired circuit  68  may pass directly through one or more push button nodes  56  on its way to master node  54 . In a parallel connection embodiment such as that represented in FIG. 5, each push button node  56  is directly connected to master node  54 , so there is no need for a “pass through” for a dedicated circuit  66 . When a critical button  64  is pressed, a signal is immediately communicated to master node  54 , separately and independently of status messages concerning push buttons  50 . A response of master node  54  is then immediately triggered in response to the immediately communicated signal. The total time from a critical button  64  press to the triggering of the response is thus small or negligible. In any case, this time is less than a period time of the periodic status messages 
     In one embodiment and referring to FIG. 6, CAN  52  is a two-way network having one or more display or indicator nodes  70 , each having associated controlling circuitry (not shown) that is addressable by master node  54 . Display nodes  70  are responsive to CAN display messages sent by master node  54  for displaying indications, values, alarms, alphanumeric symbols, or types of messages to a user. In one embodiment, for critical messages or indications that are to be displayed, master node  54  selectively includes a checksum with the CAN display message. A displaying push button node  56  includes circuitry for verify the checksum as well as for displaying the message. In one embodiment, each message is sent over CAN  52 , a high-speed serial bus configured for sending messages to specific nodes. Each message is provided with a message header identifying its destination and/or source, and master node  54  and/or display nodes  70  are provided with integral ID filters so that, as required, messages are identified as to source and/or destination. Display nodes  70  need not be incorporated into separate units. In one embodiment, displays or indicators and their associated controlling circuitry are built or incorporated into push button nodes  56 . 
     In one embodiment and again referring to FIG. 6, I/O ports  72  are provided to interconnect with a device such as computer  36  of CT imaging system  10 . I/O ports  72  are under control of master node  54  and are configured to mimic outputs of a corresponding hard-wired implementation. Exemplary configurations include, but are not limited, to those in which I/O ports  72  are configured to appear as switch closures and/or reduced resistance between contacts, with each I/O port  72  corresponding to a different push button  50 . 
     From the preceding description of various embodiments of the present invention, it is evident that CAN  52  provides a push button detection system with both safety and efficiency. Safety is provided both through redundancy (for example, checksums), watchdog timers, and safe default conditions. Polled modes of operation are avoided to provide a system fast enough to handle time-critical medical applications, as well as other applications requiring push button networks having similar characteristics. Predictability is achieved as a result of assignments of particular time periods in which each push button is to transmit its status. A transmitter time can be dedicated to display nodes (if any), and receiver time dedicated to push button nodes, thereby increasing the efficiency of CAN  52 . In one embodiment, master node  54  and CAN  52  are configured so that master node  54  addresses specific push button nodes  56 . If and when master node  54  detects an error on one of push button nodes  56 , a message is sent to the push button node  56  to signal the error and to cause master node  54  to default to a safe state for the faulty push button node  56  without disturbing the integrity of the remainder of the network. In addition, because nodes are wired in a network, the complexity and size of cables required to accommodate large numbers of buttons is reduced, and routing of cables is simplified. 
     Although particular embodiments of the invention have been described and illustrated in detail, it is to be clearly understood that the same is intended by way of illustration and example only and is not to be taken by way of limitation. In addition, the CT system described herein is a “third generation” system in which both the x-ray source and detector rotate with the gantry. The present invention is applicable to many other CT systems, including “fourth generation” systems wherein the detector is a full-ring stationary detector and only the x-ray source rotates with the gantry, and to other applications and devices requiring push button switches. Accordingly, the spirit and scope of the invention are to be limited only by the terms of the appended claims and legal equivalents.