  A direct $Q_{EC}$-value measurement of the superallowed $\beta^+$ emitter
$^{22}$Mg was performed using TRIUMF's Ion Trap for Atomic and Nuclear science
(TITAN). The direct ground-state to ground-state atomic mass difference between
$^{22}$Mg and $^{22}$Na was determined to be $Q_{EC}=4781.40(22)$~keV,
representing the most precise single measurement of this quantity to date. In a
continued push towards calculating superallowed isospin-symmetry-breaking (ISB)
corrections from first principles, ab-initio shell-model calculations of the
$A=22$ IMME are also presented for the first time using the valence-space
in-medium similarity renormalization group formalism. With particular starting
two- and three-nucleon forces, this approach demonstrates a level of agreement
with the experimental data that suggests reliable ab-initio calculations of
superallowed ISB corrections are now possible.
