  To address the demands in healthcare and industrial settings for spatially
resolved magnetic imaging, we present a modular optically pumped magnetometer
(OPM) system comprising a multi-sensor array of highly sensitive quantum
magnetometers. This system is designed and built to facilitate fast prototyping
and testing of new measurement schemes by enabling quick reconfiguration of the
self-contained laser and sensor modules as well as allowing for the
construction of various array layouts with a shared light source. The
modularity of this system facilitates the development of methods for managing
high-density arrays for magnetic imaging. The magnetometer sensitivity and
bandwidth are first characterised in both individual channel and differential
gradiometer configurations before testing in a real-world
magnetoencephalography environment by measuring alpha rhythms from the brain of
a human participant. We demonstrate the OPM system in a first-order axial
gradiometer configuration with a magnetic field gradient sensitivity of 10
$\mathrm{fT/cm/\sqrt{Hz}}$. Bandwidths exceeding 200 Hz were achieved for two
independent modules. The system's increased temporal resolution allows for the
measurement of spinal cord signals, which we demonstrate by using phantom
signal trials and comparing with an existing commercial sensor.
