My understanding is the CT-A is an angiogram - but non-invasive (except for the injection of the contrast dye). Otherwise I'd need two of the invasive types of angiograms (one for the LAD artery and another for the RCA artery). Also, apparently, carotid arteries can also calcify, and the CT CAC test doesn't measure them. They are the two that carry blood to your brain (e.g. if obstructed then you get a stroke). The CT Angiogram with dye might be able to observe narrowing spots of all of the above. Then I'd get the catheter to pinpoint areas for widening. I hope that makes some sense.