@countryliving, good choice between two excellent choices. I like bone markers CTX and P1NP to determine spine improvement. Partly because it takes longer for the pth drugs to manifest with bone mineral. But also because, for the very few, the medications aren't effective. And who wants to spend two years on a drug, (hopefully, not) tolerating side effects if the medication isn't effective for them.
You might be procure the new biometric CT, covered by Medicare starting in October in lieu of dexa. https://ondiagnostics.com/about-on-diagnostics/about-on-diagnostics/
Otherwise they will compare the bone mineral content with your last dexa in the areas last measured including L3 and L4. You might find this video interesting https://www.youtube.com/watch.