Fig. 1.

Phasor diagram for $\mathbf{O}$, $\mathbf{D}$, and $\mathbf{T}$, with blood flow contributions being non-negligible. It is easy to see that in this case, $[|\mathbf{O}|/(|\mathbf{O}|+|\mathbf{D}|)]<[|\mathbf{O}|/(|\mathbf{O}+\mathbf{D}|)]$ and neither expression yields $S_V$, which is given by $|{\mathbf{O}}_V|/(|{\mathbf{O}}_V+{\mathbf{D}}_V|)$.