Just to clarify for others (to Susan_Jane), there is no probe. CT Angiogram is a high-powered x-ray with contrast. They release contrast and as it flows through the brain they take amazing images.
Some people (including myself) see flashes of light in their eyes as the contrast is released, it looks like lightning. But it is a painless procedure. Afterward, you have to lie still for 3-4 hours so your femoral artery (where they put in the catheter) can heal. That was the hardest part for me because I have to urinate a lot. But it was not a bad procedure at all.