Characterization of an Optically Pumped Magnetometer (OPM) Magnetoencephalography (MEG) Array

Normal Physiology

Imaging, biomagnetism, somatotopy, optically pumped magnetometer, Magnetoencephalography

Background: Brain activity produces magnetic fields. These fields can be measured outside the head. Existing technology, called MEG, measures these fields. Researchers are testing a new type of magnetic field sensor called OPM. They hope it can help pinpoint with very high accuracy where brain activity is generated. Objective: To develop and test a new type of sensor for measuring the magnetic fields produced by brain activity. Eligibility: Healthy people ages 18-70 who had a magnetic resonance imaging (MRI) scan under protocol 17-M-0181. Design: Participants may be asked to complete sessions on both the traditional MEG instrument and the OPM array. For the MEG, 3-6 small coils will be placed on the participant s face with tape. Their head will be positioned inside the MEG device. For the OPM, sensors are housed in a 3d printed array. The sensors will be attached to a cap placed on the participant s head. For both scans, participants will be seated in a chair inside a magnetically shielded room. They may complete several tasks. In one task, plastic cells will be placed on their fingers. Puffs of air will be sent to these cells, which will stimulate the sense of touch. Other tasks may include the following stimuli: visual (such as checkerboards), auditory (such as beeps and tones), or language (words and letters). Researchers may also obtain recordings while they stimulate the nerve in the participant s forearm using electrical current in small electrodes. Participation is expected to last for 1 day. Additional optional scans may be offered for up to 1 year....

Study Description: This protocol is a technical development protocol to characterize an optically pumped magnetometer (OPM) array used for measuring magnetic brain signals. We hypothesize that with our OPM arrays, we can achieve similar or better spatial resolution to that of a conventional MEG system. Objectives: Primary Objective: To fully characterize the performance of an OPM MEG array at all stages of development. Secondary Objective: To demonstrate that the OPM system can produce somatotopic maps, tonotopic maps, retinotopic maps, and/or maps of receptive language fields. Tertiary Objective: To demonstrate the ability of the OPM system to obtain high SNR and high resolution maps of the cardiac cycle. Endpoints: Primary Endpoint: OPM array characterization parameters including signal to noise, sensitivity, bandwidth, and spatial resolution, and comparison to similar parameters acquired on a standard SQUID system. Secondary Endpoint: Somatotopic representations of the digits of the hand, tonotopic mapping of tone frequency, mapping of visual receptive fields, and mapping of the receptive language system.

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