Using a fiber-optic pulse sensor in magnetic resonance imaging

摘要

Abstract: Fiber-optic sensors are very useful in areas that are hostile to conventional sensors. One of these hostile areas is found in the Magnetic Resonance Imaging (MRI) environment. The primary advantage of using fiber-optic sensors in the MRI environment is the elimination of the hazards associated with wire. Currently there are no completely safe and reliable means to monitor the heart rate of a patient being scanned by MRI equipment. Conventional electrocardiograph (EKG) equipment subjects the patient to burn hazards due to RF coupling in the wires that connect the EKG sensor to the EKG monitor. Simple pulse monitoring is important to the patient's health, but the monitoring of movement is also important for sharp high quality images. Although the EKG measures electrical activity of the heart, it does not necessarily provide a true reflection of organ movement associated with the pulse. Because the EKG monitors only electrical activity, it will never be suited to measure a patient's respiration movement during an MR imaging session. The dielectric fiber-optic sensor can be used safely to monitor a patient's heart rate and to trigger the MRI on the ventricular heartbeat. Additionally, future fiber-optic sensor enhancements will provide the ability to detect respiration movement that affects heart position in the chest and to eliminate that detractor from high quality MR images. Sperry Marine has developed a non-metallic all-optical fiber-optic sensor that can be attached to a patient's pulse point for both monitoring the patient and triggering the MRI equipment. Because the sensor and leads are completely dielectric, this fiber-optic sensor presents no danger of electric shock or burns to the patient. Fiber-optic coupler sensors are optically powered by light traveling through a single mode optical fiber which is later split between two output fibers at the coupler. The return light signal travels through the two output fibers and it ultimately monitored by photodiodes. The photodiodes are connected to the inputs of a differential amplifier where the optical signals are converted to conventional electrical signals, which are interpreted by a PC based analog to digital converter. The pulse data from the sensor is displayed in real time on the PC screen and is used to trigger the MRI on the rising edge of the conducted heartbeat. This signal is then used by the MRI equipment to take a series of pulse-gated snapshots. The MR processor uses 128 sets of data which are Fourier transformed to produce the MR images. The MR images produced using the fiber-optic sensor are equivalent to the images obtained when using the EKG function of the MR equipment. The advantage of the fiber-optic sensor is that it is completely safe for the patient.!