This proposal aims to develop a first non-cryogenic fieldable multichannel system to enable interleaved measurements of magnetic resonance imaging (MRI) in the ultra-low field (ULF) regime (<< 1 T) and magneto- encephalography (MEG) of the human brain. The combination of the two modalities is uniquely capable of linking the sources of biomagnetic brain activity (MEG) to the specific anatomical brain structure (ULF MRI) with both excellent temporal and spatial resolution. In addition, the combination essentially eliminates co-registration errors based on the common MEG-MRI coordinate system. This advanced biomedical technology will enhance understanding of human brain function, aid in diagnosis and treatment of multiple brain disorders such as the epileptic focus, and improve neurosurgical planning. Previously, the MEG-MRI combination was realized only using multiple cryogenic superconducting quantum interference device (SQUID) sensors. However, the demand for cryo-cooling and a shielded room is a major drawback. We will build a more practical device by replacing SQUIDs with a novel type of atomic magnetometers (AMs). Based on lasers and alkali-metal vapor cells, AMs are currently the most sensitive cryogen-free magnetic sensors. Specific aims are to: (1) Develop an original compact 16-channel AM module for MEG. It delivers a large number of sensing channels based on a single large vapor cell and two broad nearly parallel laser beams. This new approach leads to significant cost reduction compared to commercial SQUID-based MEG systems. (2) Construct a wearable full-head MEG helmet. We will produce 15–20 compact AM MEG modules for mounting on a helmet for full-head coverage with up to 320 channels. Due to the laser-to-fiber coupling, the module positions will be adjustable for different head geometries for closer proximity of sensors to the head. This will result in improved localization and sensitivity. We will obtain functional brain maps with the MEG helmet. (3) Construct a new multichannel ULF MRI device based on a single- module multichannel AM coupled to multiple flux transformers (FTs). For MRI, the AM design will be modified to allow orthogonal laser beams, and a bias magnetic field will be applied to tune the AM to target MRI frequencies of ~200 kHz. Each FT will be composed of two connected coils, one located near the human head and the other near the AM vapor cell, to transfer MRI signals to the AM. The FT coils can be flexibly arranged around the human head to enhance an MRI signal. We will demonstrate ULF MRI measurements of the human head with an optimized FT array. (4) Combine the full-head MEG helmet and the ULF MRI device in a single instrument. The combination will be achieved by attaching the MRI FT coils to the MEG helmet. The device will be installed in a shielded room for a proof of feasibility and then in a human-sized cylindrical mu-metal magnetic shield for enabling mobile applications. We will perform interleaved imaging of...