For a knot $K$, let $\Sigma_K$ be the double cyclic branched cover of a knot.

By the classical work of **Casson** and **Gordon**, we know that if $K$ is smoothly slice, then $\Sigma_K$ bounds a rational homology ball.

Is there any well-known counter-example for the reversed direction?

**EDIT** More general statement is true due to the work of Casson & Gordon, just seen in ACP18.

For any prime $p$ and positive integer $r$, the $p^r$-fold cyclic branched cover of a knot $ K$, denoted by $\Sigma_{p^r}(K)$, is a $\mathbb Z_p$-homology sphere.

**Theorem:** If $K$ is smoothly slice, then $\Sigma_{p^r}(K)$ bounds $\mathbb Z_p$-homology ball.