fig1 illustrates a mr compatible patient monitoring system 10 . a patient monitor 12 is mounted at one end of a patient transporter 14 . the patient transporter 14 has a patient tray 16 which slides into a bore of a magnet 18 . a system interconnect 20 connects between the patient transporter 14 and the magnet 18 . fig2 illustrates a functional block diagram for the mr compatible patient monitoring system 10 shown in fig1 . a processor / memory block 22 is connected to a magnetic field sensor 24 , a lcd display 26 , a control panel 28 , physio module block 30 , power supply 32 , and a fiber optic data link 34 . the magnetic field sensor 24 is further connected to the power supply 32 . the power supply 32 and the fiber optic link 34 are connected to a system interconnect 20 . all of the aforementioned components are contained within a shielded enclosure 36 . the processor / memory block 22 provides the central computing and control function required for the monitoring system 10 . this includes the acquisition and processing of the patient &# 39 ; s physiological signals , the control and verification of the various subsystems as well as the display 26 and user control panel 28 . in this embodiment , this block is based on a high performance 32 bit microprocessor . the associated program and data memory requirements are provided by the processor / memory block &# 39 ; s ram and eeprom memory arrays . the magnetic field sensor 24 senses the ambient magnetic field that the patient monitor is operating in . it calculates the absolute magnitude of the ambient field by using a cartesian coordinate field sensor . the absolute magnitude of the ambient field is then compared against three threshold values . as the patient transporter 14 is moved through the mr scanner room , the patient monitor may be subject to magnetic field levels which would adversely affect its operation . the magnetic field sensor 24 warns the user by visual and audio indicators if the ambient field strength is approaching the level ( the first threshold ) at which operation of the monitor would be affected . if the field continues to increase and then exceeds the second threshold , the magnetic field sensor 24 will disable the operation of the patient monitor until the field level falls below a preset value ( the third threshold ). the sensor 24 continues to provide the user with an indication of the ambient field level even when the monitor is disabled . the power supply 32 provides the power requirements for the patient monitor . in this embodiment , the power supply 32 consists of a dc - to - dc converter , battery charger , and rechargeable battery . the dc - to - dc converter converts the battery voltage into the various voltages required by the patient monitor . the battery charger maintains the battery &# 39 ; s charge when the monitor is connected to either the mr scanner or to an external charging port . the fiber optic data link block 34 provides the data and control link between the patient monitor and the mr scanner . the fiber optic data link block 34 supports remote displays and control of the patient monitor , as well as the exchange of data , control and status information between the mr scanner and the patient monitor . the block features a high speed , duplex long wavelength fiber optic transceiver . the interface between the fiber optic transceiver and the processor subsystem is handled by a set of specialized receive and transmit integrated circuits . this chip set provides the parallel - to - serial and serial - to - parallel data conversion , data formatting , clock recovery , and link control logic . the system interconnect 20 provides the connection between the patient monitor and the mr scanner . it consists of an umbilical cable 20a and a connector 20b featuring both electrical and optical contacts . the cable 20a is routed through the patient transporter 14 where it is then mated to the matching receptacle on the mr scanner 18 . the umbilical cable 20a consists of a duplex fiber optic cable pair and a pair of electrical conductors surrounded by a common pvc outer jacket . each of the fiber optic cables has a core diameter of 62 . 5 micrometers and a cladding diameter of 125 micrometers . these fiber optic cables are used to support the duplex data and control link between the patient monitor and the mr system . the electrical conductors are used to supply the patient monitor &# 39 ; s dc to dc converter / battery charger . the connector 20b features a pair of fiber optic contacts . these contacts are capable of repeated mate / demate cycles while maintaining the required optical performance . the connector body is made of a structural plastic , i . e . peek , to minimize the production of particulate during the mate / demate cycle . these particulates and environmental factors , such as dirt , dust , and smoke , could reduce or obscure the transmission of light through the connector . to safeguard against the environment factors , the connector uses a sealing cap that retracts during the mating cycle . the matching receptacle on the mr scanner uses a set of shutter doors which prevent degradation of the contacts due to environmental factors . the shutter doors swing aside during the mating cycle . in one embodiment , the system connector 20b is a cable / connector assembly that the user can plug into a matching receptacle on the mr scanner once the patient transporter has &# 34 ; docked &# 34 ; with the mr scanner . the user will unplug the cable when the transporter has been &# 34 ; undocked &# 34 ;. the cable is managed by a cable retraction system on the patient transporter to prevent the cable from damage when not in use . alternately , the system connector can be part of a docking mechanism which automatically makes and breaks contact as the transporter is &# 34 ; docked &# 34 ; and &# 34 ; undocked &# 34 ; with the mr scanner . the lcd display 26 presents the patient parameter data to the clinicians . an lcd type display was selected because the strong magnetic fields in proximity of the mr scanner make use of a crt type difficult . the control panel 28 allows the user to control the operation of the patient monitor . it contains an array of keys and indicator leds . the shielded enclosure 36 serves two major functions . the first is to reduce the radiated emissions from the patient monitor internal circuits to a level where they will not cause any interference to the operation of the mr scanner . the second function that it serves is to reduce the internal level of the ambient electrical fields . fig3 is a system diagram of the physio - module block 30 shown in fig2 . the physiomodules support the acquisition and conditioning of several patient parameters . three such modules , such as 30a - c , are shown by way of illustration . the ecg physio - module 30a handles the patient &# 39 ; s ecg signal . it contains isolation amplifiers , filter states , analog to digital convertors , and adaptive filtering stages . the adaptive filters use knowledge of the operation of the mr scanner to filter the gradient noise components from the ecg signal . the pulse oximeter block 30b handles the patient pulse oximeter parameter . it uses a transducer which uses fiber optic cables to send the light from a set of visible and infrared light sources to the measuring site and to return the transmitted component to a photo detector . this transducer is usually applied to a finger and the ratio of transmission of the visible and infrared light sources to the finger is measured . this ratio is used to calculate the percentage of oxygenated hemoglobin for the patient . the block contains a light source driver stage , photo detector amplifier , and filter stages , and analog to digital convertors . the non - invasive sphygmomanometer 30c handles the measurement of the patient &# 39 ; s blood pressure . it uses an inflatable cuff which is applied to the patient &# 39 ; s arm or leg . the cuff is connected to the monitor via a non - conductive air tube . the block contains the cuff pump , pressure sensor , and analog to digital convertor . the cables which are used to connect the patient to the three parameter blocks are integrated into the patient transporter with a cable management system . this system protects the cables during transport to and from the mr scanner and while the patient table is sliding in and out of the magnet . fig4 illustrates the fiber optic data link 34 shown in fig1 . an electrical / optical ( eo ) block 38 is connected to a serial - to - parallel block 40 and a parallel - to - serial block 42 . a link control block 44 is connected to the serial - to - parallel block 40 and the parallel - to - serial block 42 . the link control block 44 is further connected to a microprocessor interface controller 46 . the microprocessor interface controller 46 is further connected to a receive data demultiplexor 48 , a transmit data multiplexor 50 , and a voltage level translator block 52 . the voltage level translator block 52 is further connected to the receive data demultiplexor 48 and the transmit data multiplexor 50 . the receive data demultiplexor 48 is further connected to an analog - to - digital converter block 54 . the eo block 38 converts the incoming optical signal to a serial electrical signal and conversely , the serial electrical signal into an optical output signal . the optical signals are coupled to and from a duplex fiber optic cable . in this embodiment , this block is comprised of an hewlett - packard hfbr 5205 multi - mode fiber transceiver that operates at a wavelength of 1300 nm . the serial - to - parallel block 40 converts the serial electrical output signal from the eo block into a parallel digital signal . this block contains the clock recovery , signal detect , and framing circuits . the link control block 44 controls the operation of the fiber link . upon being connected to the fiber optic link cable through the system interconnect , it outputs a series of unique data packets which are designed to facilitate synchronization with the matching fiber link subsystem at the other end of the fiber cable . it also initiates a search for these synchronization packets on the incoming optical path via examining the eo serial output . upon detection of the synchronization packets , it enables data to be sent to and received from the link . the link control block 44 monitors the operation of the operation of the link and flags any data errors . for non - recoverable errors , it disables local use of the link and periodically attempts to re - establish connection . in this embodiment , the serial - to - parallel 40 , parallel - to - serial 42 , and the link control 44 blocks were implemented using the hewlett - packard hdmp1012 and hdmp1014 integrated circuit chipset . the voltage level translator block 52 bidirectionally translates the data , control , and status signals from one set of logic levels to another . in this embodiment , the logic voltage levels are ttl and pecl . the transmit data multiplexor 50 organizes the parallel data which is to be sent as output on the fiber link . there are several sources for this data . these include the remote display video data , physio data , and monitor status data . the receive data demultiplexor 48 inputs the received and translated parallel data from the serial - to - parallel block 40 . the data is demultiplexed and sent to a number of outputs . the outputs include video update data , remote keyboard and system control data and external data . the analog - to - digital converter block 54 converts the externally received digital data via the link into an analog signal . this signal is output to an analog multiplexor and it can be used by the patient monitor to provide local audio annunciation , as well as an analog source useful for signal injection and system verification . the microprocessor interface controller block 46 provides two major functions . the first function is to support the patient monitor interface to the fiber data link . it contains several state machine logic circuits which in conjunction with the control logic of the link control block 44 , determine the operation of the fiber link . it coordinates the synchronization of the operation of the transmit data multiplexor 50 and the receive data demultiplexor 48 to ensure the correct data position in the multiplexing cycle . the second function of this block is to support access to the fiber link and it &# 39 ; s operation by the patient monitor resident microprocessor . it provides an interface that appears to the microprocessor as a series of registers . read and write cycles to these registers allow the microprocessor to send and receive data , control the mode of operation as well as to examine the status of the fiber data link .
a mr compatible monitoring system has a fiber optic data link between the patient monitor and the control room display / keyboard in a magnetic resonance imaging suite to allow for continuous monitoring of a patient &# 39 ; s vital signs and provides critical care patients with the same diagnostic options as stable patients . the patient monitor is mounted on the far end of a magnetic resonance compatible patient transporter . the patient transporter sends video data and receives control data from the control room . during the imaging , the patient monitor is located within the magnet room . magnetic resonance imaging systems are very sensitive to radio frequency interference from other equipment and may produce image artifacts because of this interference . using a fiber optic data link between the patient monitor near the magnet and the control room will minimize the potential rfi .