Surgery – Diagnostic testing – Detecting brain electric signal
Reexamination Certificate
1999-05-26
2002-04-02
Nasser, Robert L. (Department: 3736)
Surgery
Diagnostic testing
Detecting brain electric signal
C600S345000, C600S588000, C600S559000
Reexamination Certificate
active
06366805
ABSTRACT:
FIELD OF THE INVENTION
The present invention pertains generally to medical monitoring equipment, including equipment for providing a stimulus signal to a subject and for monitoring the response of the subject to the stimulus, and more particularly to methods and devices for synchronizing the time frames of the stimulus and response signals for analysis and display.
BACKGROUND OF THE INVENTION
Medical monitoring involves monitoring the body of a subject to determine the state of health of the subject and to detect, identify, and diagnosis changes or abnormalities in the state of the body which may be indicative of problems. Medical monitoring may involve monitoring, for example, the motion of a subject's body, temperature or chemical changes of the subject's body, and/or audible or electrical signals generated by the subject's body. For example, electroencephalography (EEG) is a form of medical monitoring wherein the electrical potentials of the subject's brain are monitored by attaching electrodes to the subject's scalp. In electromyography (EMG), electrical activity generated in the subject's muscles is monitored using surface and/or needle recording electrodes. Medical monitoring may take place when a subject is at rest, in motion, or during the performance of a medical procedure. In some cases, medical monitoring involves monitoring the response of the subject to a stimulus. For example, EEG monitoring may be used to detect the electrical response of a subject's brain to audible, visual, or electrical stimuli. Medical monitoring involving stimulus and response detection may be used in combination with EMG and various other medical monitoring methods as well.
A typical method of medical monitoring involving stimulus and response detection includes connecting a stimulator, e.g., via electrodes, to a subject, and placing monitoring electrodes, or other sensors, on the subject to detect the subject's response to the stimuli provided by the stimulator. The stimulator is controlled by a stimulation controller, which provides a trigger signal to a stimulus generator to deliver stimuli of a desired magnitude, duration, and pattern to the subject. The electrodes or other sensors used to detect the response of the subject to the stimuli are connected to an amplifier device which amplifies the detected physiological response signals. The amplified response signals are, in turn, processed, analyzed, and displayed, typically using a microprocessor based monitor device.
In displaying and analyzing detected physiological response signals, it is important that accurate time frame synchronization between the stimulus and response signals is achieved. Such synchronization is critical to determining, for example, the delay time between the stimulus and the response. Such synchronization may be achieved where a stimulation controller, physiological signal amplifier, and analysis and display monitor system are contained in a signal device controlled by a single microprocessor, or by multiple microprocessors operating off of the same system clock. However, it is often desirable to employ stimulator, amplifier, and monitor devices which are implemented as separate devices, each having their own microprocessor control and system clock. This allows for modularity and separation of the medical monitoring system components. Modularity allows a variety of different stimulators, providing a variety of different types of stimulation, and a variety of different amplifier devices, for detecting a variety of different physiological response signals, to be used in combination with each other and with a given analysis and display monitor device. Separation allows the components of the medical monitoring system to be located remotely from each other. For example, during a medical procedure, it may be desirable to have the stimulator and amplifier devices separated from each other and from the analysis and display monitor device, which may be located in another room or even further from the site of the procedure. This minimizes the chance that the medical monitoring system will get in the way of the procedure, and allows the various medical monitoring system components to be positioned optimally such that information is made available to the appropriate personnel where required.
Where separate stimulator, amplifier, and display and analysis monitor devices are employed, and particularly where such devices are separated by a distance, synchronization between the stimulus and response signal time frames can be very difficult to maintain. Each such device is typically controlled by its own device controller, which is driven by its own local device clock. Even if the various device clocks are initially synchronized, and operate at the same nominal rate, divergence between the system clocks over time is inevitable. If the time frames in which the stimulus signal is applied and the response signals are detected cannot be synchronized, accurate display and analysis of the relationship between the stimulus and response signals is not possible. Currently, synchronization is achieved between independent stimulator, amplifier, and display and analysis monitor devices, each having its own independent device controller and device clock, by connecting the stimulator device to the display and analysis monitor device by a wire, and providing a signal on the wire when a stimulus signal is provided to a subject by the stimulator device. The distance over which such a wire can be run is limited. What is desired is a system and method for establishing a synchronous time frame between separate stimulator, amplifier, and monitor display and analysis devices in a medical monitoring system, wherein each such device may have its own independent device controller and device clock.
A general structure for a high speed serial bus for connecting together multiple devices, along with a protocol for sending data on the bus and for sharing the bus medium, is specified in IEEE standard 1394. (The official name of the standard is “IEEE 1394-1995 Standard for High Performance Serial Bus”. It is published by the Institute of Electrical and Electronics Engineers (IEEE). IEEE 1394 has been implemented in commercially available products and sold, for example, under the trade name Fire Wire.) A 1394 bus structure is tree-like, having a “root” device, branching out to logical “nodes” in other physical devices. The root is responsible for certain control functions. The root device is chosen during initialization and, once chosen, retains that function as long as it remains connected to the bus. A 1394 network may include up to 63 nodes, with each node specified by a six-bit physical identification number. Multiple networks may be connected by bridges, to a system maximum of 1,023 busses. Combined, IEEE 1394 allows up to 64,449 nodes in a system with a maximum of 256 TB of memory space per node.
The IEEE 1394 bus structure is very flexible. Devices may be plugged into any available port on the bus. Devices can be hot-plugged, i.e., connected or disconnected while energized. The bus configures itself. There is no need to set address switches, and there are no hard wired addresses. Every time a node is added to or removed from the network, the bus's topology is automatically reconfigured by the bus protocol. There can, however, be at most 16 hops between any two nodes, and devices may not be connected in such a way as to form loops. To maintain signal quality, standard IEEE 1394 bus cables should stretch no more than 4.5 meters between nodes. Physically, a 1394 bus cable terminates in a six-pin connector. The six pins are connected to a pair of power wires and two twisted-wire signal pairs. Each twisted pair is shielded, as is the entire cable. The power wires, which carry up to 1.5 A at 8.40 V, keep all parts of the bus alive even when some devices connected to the bus are unenergized. They also eliminate the need for an external power cable in some devices.
An IEEE 1394 bus is capable of transmitting large
Nasser Robert L.
Viasys Healthcare Inc.
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