Your experience with measurements match my own. Mine was found on a Calcium CT. Then I got a chest CT with contrast and it was a few tenths of a centimeter smaller. I've had a couple of measurements since then, and each one was with and without contrast. They do the scan once, then inject the contrast and do it again. The measurements are always a few tenths of a centimeter different and the one w/o contrast is always larger. I'm not really sure why they do the one without contrast, except perhaps a sanity check of some kind? I've recently learned too that there are gated and non-gated CT scans. A gated scan can account for where your heart is in its cycle. It should be more accurate than non-gated. If you're going to Vanderbilt, I'd guess it's a gated CT. I'm in a rural area and our CT machine is non-gated.

I'd guess whether you can get surgery depends on your other medical conditions and how conservative your surgeon is. I think it's unusual to ever get surgery under 5cm unless you have a rare genetic condition, and usually it's 5.5 unless there are other factors. Here's a link to the relevant guidelines I think, if you want to dig into it: https://www.ahajournals.org/doi/10.1161/CIR.0000000000001106. They wait until the probability of a bad outcome without surgery is greater than the probability of a bad outcome with surgery. Everyone thinks they're going to be the one without a bad outcome and almost everyone is. Once in a while, though, there will be someone on these boards that had a bad outcome from an elective surgery. It does happen, though rarely.

So I've decided my approach is to find a surgeon I trust that has lots of experience (the most important step), and then trust they have far more expertise than I do, have more experience than I do, are more impartial than I am and, hopefully, has my best interests at heart.

Totally get why you'd be concerned. You are going to be fine. You know you have a problem at that's 95% of the solution. It’s actually pretty common to see slight differences in measurements, especially between a scan with contrast and one without. The contrast helps define things more clearly, so the cardiologist is probably right that the 4.8 cm measurement is more accurate. That said, I understand wanting to be extra cautious. If waiting six months feels too long, there’s no harm in asking for an earlier scan—lots of people do it for peace of mind. Or, if you're still uneasy, maybe even get a second opinion just to feel more confident in the plan. It’s not unusual for people in this situation to get slightly different readings and end up with everything being okay. But, if getting a re-check sooner helps you sleep better, it's worth the ask! I suddenly and completely dissected in 2015. It was a nightmare and you don't want that, so listen to your doctors. Peace.