Apparatus and Method for Recording an Electroencephalogram During Magnetic Resonance Imaging

This invention relates to the recording of an electroencephalogram (EEG) during magnetic resonance imaging (MRI). The activity of the EEG can be used to acquire MRI images and thus correlate neurophysiological phenomena with the results.

An EEG machine permits the recording of specific brain wave patterns in a patient. An MRI machine can provide metabolic and anatomical information regarding a portion of a patient, including a portion of the patient's brain. However, in the prior art, it has not been possible to record an EEG pattern at the same time that MRI is conducted. This prevents the obtaining of metabolic and anatomical information that is correlated to particular neurophysiological waveforms being studied. By obtaining such a correlation, it would be possible to obtain increased information regarding abnormal as well as normal brain activity and to obtain a better understanding of the functioning of the brain.

The nature of the MRI and EEG severely restrict the ability to record the EEG during magnetic resonance imaging. For example, the strong and rapidly changing radio frequency fields present during MRI, coupled with the large static magnetic field, may induce significant current flow in electrodes and wires located within the magnetic field. When conducting an EEG, the electrodes are connected to a patient's scalp, where the current may produce localized heating or burns.

Also, the equipment necessary to obtain the EEG can interfere with the diagnostic quality of the MRI images. This occurs both because the electrodes produce artifacts on the MRI images and because any radio frequency sources associated with the EEG equipment will interfere with the MRI images.

In addition, the radio frequency and magnetic fields can compromise the quality of the EEG or even make it impossible to obtain.

Currently, patients receiving an MRI who also are having their EEG recorded generally will have the EEG electrodes removed before there are placed in the MRI machine. In some cases, the electrodes are left in place during an MRI, but those electrodes have caused artifacts on the MRI image and it has not been possible to record the EEG during the MRI process.

It is therefore an object of the present invention to provide a method and apparatus for obtaining an EEG during magnetic resonance imaging.

It is another object of the present invention to provide a method and apparatus for triggering an MRI image in response to specific EEG signal patterns.

By reducing the amount of magnetic metal and radio frequency generating equipment associated with the recording of the EEG that is within the bore of the MRI magnet, and moving all significant radio frequency generating equipment outside the MRI room, EEG signals can be recorded and MRI images can be obtained simultaneously.

According to the present invention, the above and other objects and advantages are achieved by positioning a plurality of nonmagnetic electrodes on a patient's head so as to be able to record the patient's EEG. In a preferred embodiment, these can include, surface electrodes having a surface of gold or silver, and sphenoidal electrodes made of Teflon-coated silver wire. A plurality of EEG signals from the electrodes are transmitted to an amplifier that is positioned sufficiently away from the patient's head so as to prevent distortion of the MRI. Preferably, this distance is at least five centimeters. In a preferred embodiment, electrode extension cables are used so as to position the amplifier outside the bore of the MRI magnet. In a preferred embodiment, the plurality of EEG signals are also multiplexed. This can be done with a combined amplifier/multiplexor unit.

The amplified EEG signals are transmitted to an EEG machine or a personal computer, where they are recorded. In a preferred embodiment the amplified, multiplexed signals are first sent through a signal splitter. One output of the signal splitter is fed to a demultiplexor and into the EEG machine, and another output of the signal splitter is fed to the personal computer. The EEG machine can be either within or outside the MRI room. The personal computer is located outside the MRI room.

In a preferred embodiment, the personal computer can be used to analyze the signals and, in response to appropriate EEG patterns, trigger the MRI. Alternatively, the MRI may be triggered manually in response to a visual inspection of the EEG patterns.

For a better understanding of the present invention, together with other and further objects, advantages, and capabilities thereof, reference is made to the accompanying drawings which are incorporated herein by reference and in which:

FIG. 1 is a schematic diagram of the method for obtaining an EEG during magnetic resonance imaging in accordance with the invention;

FIG. 2 is a schematic diagram of an alternative method for obtaining an EEG during magnetic resonance imaging in accordance with the invention;

FIG. 3 is a schematic diagram of another alternative method for obtaining an EEG during magnetic resonance imaging in accordance with the invention; and

FIG. 4 is a graph of experimental data obtained by monitoring EEG signals of a patient during magnetic resonance imaging in accordance with one embodiment of the invention.

In FIGS. 1-3, like elements have the same reference numbers.

With reference to FIG. 1, an MRI room 20 contains an MRI machine 22 in which extends a bore of MRI magnet 24. MRI room 20 also contains a moving table 26 on which a patient 28 rests. In a preferred embodiment, the MRI machine 22 is a Siemens 1.5 T whole body scanner with hardware modifications to provide echo planar capabilities.

Surface electrodes 30 and sphenoidal electrodes 32 are positioned on the patient so as to permit the recording of the signals that make up the patient's EEG. In a preferred embodiment, the surface electrodes 30 are either Grass gold or silver electrodes, model numbers E5GH or E5SH, respectively; and the sphenoidal electrodes 32 are multi-stranded, Teflon-coated pure silver wire, such as Medwire part number AG 7/40T. Alternatively, only surface electrodes or only sphenoidal electrodes may be used, as appropriate. The surface electrodes 30 and sphenoidal electrodes 32 are connected to ribbon cabling 34, which is connected to a harness 36. Surface electrodes 30 and sphenoidal electrodes 32 are nonmagnetic. Preferably, ribbon cabling 34 also is nonmagnetic. Alternatively, the electrodes can be connected to the harness 36 by a length of wire, such as 25 mm standard Grass wire, or other electrode extension cables. The electrodes and cabling should be securely bandaged to the patient's head to minimize movement of the electrodes and cabling. The patient's head also should be secured as much as possible. Even slight movements due to pulsatile blood flow (ballistocardiogram) or movements of the head can cause artifacts to appear on the EEG. The harness 36 plugs into the inputs of a multiplexor 38, which multiplexes the multiple EEG signals onto a single line. Preferably, multiplexor 38 provides 18 channels and a sampling rate of 200 samples per second per channel. The output of multiplexor 38 is fed to amplifier 40. Multiplexor 38 and amplifier 40 can be situated in a single multiplexor/amplifier assembly. In a preferred embodiment, ribbon cabling 34 is at least five centimeters long, so the multiplexor 38 and amplifier 40 can be placed away from the head of the patient and avoid distortion of the MRI images. Preferably, ribbon cabling 34 is sufficiently long that multiplexor 38 and amplifier 40 can be positioned outside the bore of the MRI magnet 24 (FIG. 2).

As seen in FIG. 1, the output of amplifier 40 is transmitted along cable 42 to junction box 44, and from there along cable 46, to power pack 48. Power pack 48 is located outside the bore of the MRI magnet 24. Power pack 48 buffers the multiplexed EEG signals and supplies power and logic signals to multiplexor 38 and amplifier 40 through cable 46 and cable 42. Alternatively, cable 42 can be connected directly to power pack 48 (FIG. 2). This will occur where multiplexor 38 and amplifier 40 are located outside the bore of the MRI magnet 24, or where cable 42 has sufficient length. In such situations, junction box 44 and cable 46 can be omitted. Cable 50 connects power pack 48 to wall unit 52, which is located outside MRI room 20. Wall unit 52 further buffers the multiplexed EEG signals and supplies power to the power pack.

Alternatively, other suitable means can be used to transmit the amplified and multiplexed EEG signals from amplifier 40 to a point outside MRI room 20, and to provide the necessary power and logic signals to multiplexor 38 and amplifier 40.

Cable 54 is used to relay the EEG signals from wall unit 52 to demultiplexor 56, the output of which is connected to EEG machine 58 (FIG. 1). While in a preferred embodiment, EEG machine 58 is located outside MRI room 20, EEG machine 58 also can be located within MRI room 20, as shown in FIG. 3. Successful results with an EEG machine located within the MRI room were obtained with a Grass EEG machine model 8, which relies on analog technology. With this machine, unlike many machines based on digital technology, radio frequency fields that interfere with the operation of the MRI machine were not propagated.

In an alternative embodiment shown in FIG. 2, cable 54 can be connected to signal splitter 60. One output of signal splitter 60 is then fed through demultiplexor 56 to EEG machine 58, and a second output is fed to personal computer 62. Personal computer 62 utilizes an interface board 64 to translate the multiplexed EEG signal to digital signals that can be input into the computer. Personal computer 62 also records the patient's electrocardiogram (EKG), by receiving signals from EKG electrodes placed on the patient (not shown).

Personal computer 62 is used to analyze and store the EEG signals and the EKG signals, and to determine when to trigger MRI machine 22. Interface board 64 is used to generate MRI triggering signal 66. Alternatively, other signal processing equipment can be used instead of personal computer 62. Or, the EEG signals as viewed on a paper read-out or on a computer screen can be used to trigger manually the taking of an MRI image.

In operation, the plurality of EEG signals from patient 28 are picked up by surface electrodes 30 and sphenoidal electrodes 32. The EEG signals are transmitted by ribbon cabling 34 to harness 36, from where they are input into multiplexor 38. The output of multiplexor 38 is amplified by amplifier 40 and then transmitted to EEG machine 58 and/or personal computer 62. Personal computer 62 records the EEG data, as well as the patient's EKG, and also determines when to trigger MRI machine 22. Personal computer 62 causes interface board 64 to generate MRI triggering signal 66.

Recorded EEG data and EKG data are shown in FIG. 4. Although a momentary artifact is generated during acquisition of the echo planar scan by MRI machine 22, as can be seen at 68 in FIG. 4, the EEG data remains readable except during continuous spin echo scanning.

By repeatedly triggering on the same EEG pattern (as recognized by the personal computer or manually), numerous MRI slices can be obtained that correspond to the same brain wave pattern. By linking the MRI slices to a patient's cardiac cycle (by monitoring the patient's EKG), interference caused by background metabolic or anatomical changes associated with the cardiac cycle can be reduced. The use of nonmagnetic electrodes reduces injuries and discomfort to the patient and the appearance of artifacts on the MRI images,

While there have been shown and described what are at present considered the preferred embodiments of the present invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.