  Unlike charge and spin, the orbital degree of freedom of electrons in
transition metal oxides is difficult to detect. We present the theoretical
study of a new detection method in metallic orbitally active systems by
analyzing the quasiparticle scattering interference (QPI) pattern of the
spectroscopic imaging scanning tunneling spectroscopy, which is sensitive to
orbital structures and orbital ordering. The QPIs for the $d_{xz}$ and
$d_{yz}$-orbital bands in the $t_{2g}$-orbital systems show a characteristic
stripe-like feature as a consequence of their quasi-one-dimensional nature,
which is robust against orbital hybridization. With the occurrence of orbital
ordering proposed in Sr$_3$Ru$_2$O$_7$ and iron-pnictides, the stripe-like QPI
patterns exhibit nematic distortion breaking the $C_4$-symmetry.
