  We investigate properties of the structural physical approximation (SPA) of
the partial transposition map recently introduced by Horodecki and Ekert
[quant-ph/0111064]. We focus on the case of two-qubit states and show that in
this case the map has the structure of a generalized quantum measurement
followed by preparation of a suitable output state. We also introduce SPA for
map that transforms two copies of density matrix of a single qubit onto a
square of that matrix. We prove that also this map is essentially a generalized
quantum measurement.
