  From Nov. 2019 to May 2020, the red supergiant star Betelgeuse experienced an
unprecedented drop of brightness in the visible domain called the great dimming
event. Large atmospheric dust clouds and large photospheric convective features
are suspected to be responsible for it. To better understand the dimming event,
we used mid-infrared long-baseline spectro-interferometric measurements of
Betelgeuse taken with the VLTI/MATISSE instrument before (Dec. 2018), during
(Feb. 2020), and after (Dec. 2020) the GDE. We present data in the 3.98 to
4.15\,$\mu$m range to cover SiO spectral features molecules as well as adjacent
continuum. We have employed geometrical models, image reconstruction, as well
as radiative transfer models to monitor the spatial distribution of SiO over
the stellar surface. We find a strongly in-homogeneous spatial distribution of
SiO that appears to be looking very different between our observing epochs,
indicative of a vigorous activity in the stellar atmosphere. The contrast of
our images is small in the pseudo-continuum for all epochs, implying that our
MATISSE observations support both cold spot and dust cloud model.
