  Wide-field imaging of magnetic signals using ensembles of nitrogen-vacancy
(NV) centers in diamond has garnered increasing interest due to its combination
of micron-scale resolution, millimeter-scale field of view, and compatibility
with diverse samples from across the physical and life sciences. Recently,
wide-field NV magnetic imaging based on the Ramsey protocol has achieved
uniform and enhanced sensitivity compared to conventional measurements. Here,
we integrate the Ramsey-based protocol with spin-bath driving to extend the NV
spin dephasing time and improve magnetic sensitivity. We also employ a
high-speed camera to enable dynamic wide-field magnetic imaging. We benchmark
the utility of this quantum diamond microscope (QDM) by imaging magnetic fields
produced from a fabricated wire phantom. Over a $270\times270
\hspace{0.08333em} \mu\mathrm{m}$$^2$ field of view, a median per-pixel
magnetic sensitivity of
$4.1(1)\hspace{0.08333em}\mathrm{nT}$$/\sqrt{\mathrm{Hz}}$ is realized with a
spatial resolution
$\lesssim\hspace{0.08333em}10\hspace{0.08333em}\mu\mathrm{m}$ and
sub-millisecond temporal resolution. Importantly, the spatial magnetic noise
floor can be reduced to the picotesla scale by time-averaging and signal
modulation, which enables imaging of a magnetic-field pattern with a
peak-to-peak amplitude difference of about $300\hspace{0.08333em}\mathrm{pT}$.
Finally, we discuss potential new applications of this dynamic QDM in studying
biomineralization and electrically-active cells.
