  We study supersymmetric (SUSY) effects on $C_7(\mu_b)$ and $C'_7(\mu_b)$
which are the Wilson coefficients (WCs) for $b \to s \gamma$ at b-quark mass
scale $\mu_b$ and are closely related to radiative $B$-meson decays. The
SUSY-loop contributions to $C_7(\mu_b)$ and $C'_7(\mu_b)$ are calculated at
leading order (LO) in the Minimal Supersymmetric Standard Model (MSSM) with
general quark-flavour violation (QFV). For the first time we perform a
systematic MSSM parameter scan for the WCs $C_7(\mu_b)$ and $C'_7(\mu_b)$
respecting all the relevant constraints, i.e. the theoretical constraints from
vacuum stability conditions and the experimental constraints, such as those
from $K$- and $B$-meson data and electroweak precision data, as well as recent
limits on SUSY particle masses and the 125 GeV Higgs boson data from LHC
experiments. From the parameter scan we find the following: (1) The MSSM
contribution to Re($C_7(\mu_b)$) can be as large as $\sim \pm 0.05$, which
could correspond to about 3$\sigma$ significance of New Physics (NP) signal in
the future LHCb and Belle II experiments. (2) The MSSM contribution to
Re($C'_7(\mu_b)$) can be as large as $\sim -0.08$, which could correspond to
about 4$\sigma$ significance of NP signal in the future LHCb and Belle II
experiments. (3) These large MSSM contributions to the WCs are mainly due to
(i) large scharm-stop mixing and large scharm/stop involved trilinear
couplings, (ii) large sstrange-sbottom mixing and large sstrange-sbottom
involved trilinear couplings and (iii) large bottom Yukawa coupling $Y_b$ for
large $\tan\beta$ and large top Yukawa coupling $Y_t$. In case such large NP
contributions to the WCs are really observed in the future experiments at Belle
II and LHCb Upgrade, this could be the imprint of QFV SUSY (the MSSM with
general QFV).
