$L\sp \infty$-BMO boundedness for a singular integral operator

If $K\left( x \right) = \Omega \left( x \right)/\vert x{\vert^n}$ is a Calderón-Zygmund kernel and $b\left( {\vert x\vert} \right)$ is a bounded radial function, we find conditions on $b$ such that the singular operator whose kernel is $b\left( x \right)K\left( x \right)$ is bounded from ${L^\infty }\left( {{R^n}} \right)$ to ${\text{BMO}}\left( {{R^n}} \right)$, or equivalently from ${H^1}\left( {{R^n}} \right)$ into ${L^1}\left( {{R^n}} \right)$.