Nuclear studies

when a nuclear study is billed, 78452.26, 93018 and the 78452.26 gets paid but not the 93018 because of the diagnosis code, how do we get it paid? I have added a 59 modifier to the 93018 in the past and the claim pays. Is that correct or are we billing incorrectly.

we also have a problem with the stress echo. the 93350.26 gets paid but the 93018 gets denied for diagnosis? what is the problem all of the diagnosis codes are payable.

Can anyone help with this problem. It will be greatly appreciated.

Thanks