I recently had one found. I had an MRI done (without contrast) intially to looke for otherthings as I was concerned with MS or tumors. I was told that they suspected an aneurysm but couldn't see that part of my brain well enough and would need to have another MRI series done with contrast. This was this past weekend and I didn't want to wait till Tuesday for an MRI so I went to the ER where they did 2 CT Scans (one with dye and one without) and I was told that for looking at blood vessels that there is debate over which is better and that both will give really good pictures.
The CT Scan is quicker and less scary (not the problem of enclosed space) than an MRI but my understanding is that both are good options for detecting these.
My friends aneruyism was discovered when she had an MRI done. The doctors did an angiogram to see just how bad it was. She ended up having a stent and 3 coils placed in it. Good luck and good health to you.
As far as I know the MRI and CAT scans are only 90% accurate. If you have a particularly small or well hidden aneurysm, it may not be picked up. An angiogram is 100% accurate and gives a far clearer picture.