Irreducible polynomial $\; (x^2-2)^4-2$

Question

I need to proof that $\; f(x)=(x^2-2)^4-2=x^8-8x^6+24x4-32x^2+14\;$ is irreducibel.

I only know the eisenstein criterion and have no idea how to proof that this polynomial is irreducible. Any help would be appreciated