You really should push for an ApoB test in general - most people are bit by LDL-C and not other atherogenic particles like Lp(a), but it's still common enough to find out. The good news is Lp(a) is largely genetic so if you know you have low levels you likely don't need to test again anytime soon.
A CAC will show calcified build-up, not reversible (or at least not in any appreciable way)
A CTA will show soft plaque buildup, which IS reversible with a low enough atherogenic particle load. This generally means keeping your LDL-C below the 50-70 range, though if Lp(a) is the cause you'll likely need a PKCS9 inhibitor or an upcoming CETP inhibitor to drive it down.
A CAC will show calcified build-up, not reversible (or at least not in any appreciable way)
A CTA will show soft plaque buildup, which IS reversible with a low enough atherogenic particle load. This generally means keeping your LDL-C below the 50-70 range, though if Lp(a) is the cause you'll likely need a PKCS9 inhibitor or an upcoming CETP inhibitor to drive it down.