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placed in the femoral artery of the groin. The catheter is snaked up to the aorta and then iodine contrast material is injected into the aorta while pictures are taken. Last time I looked these are
2 dimensional pics.. Up down, right left.
With a CT scan the contrast is injected into a vein in the arm and timed just right so the contrast is caught right when it's at the aorta. The CT is two dimensional SLICES. So you can manipulate the images to get a three dimensional look after the scan is done.. The 2 d images are stacked one on top of the other and then soft tissue is digitally removed to view the aorta by it's self.
Think of the chest as a loaf of bread. You slice up the loaf of bread and then put the slices back together to get at the whole thing...Does that make sense?
The Angio and the CT give the MD more information. What I don't understand is why he did the easy, least invasive test last? The CT is easy, quick and relatively inexpensive.... Unless he did the angiogram and made a few bucks for him self...

The one on the left (A)is the angiogram
The candy cane looking thing is the aortic arch with the root being at the end of the candy cane where it attaches to the heart. You can see the pig tail catheter in the arch of the aorta. Yup that's what they call it... Looks like a little oinker tail..
The one on the right (B) is the rendering after the CT angiogram of just the aorta...
I did Angio/CT and MRI before I retired. Hope this helps
m