An echocardiogram will only show you the part of the aorta that comes off of the heart, and it sounds like your doctor is concerned about your abdominal aorta, so it is reasonable to have a separate test.
There are findings on an abdominal ultrasound that could suggest an etiology of hypertension, if you have hypertension. Typically that involves a problem with the renal arteries, though, not the aorta itself.
Thank you - I've got it scheduled. No hypertension diagnosis yet, but I was admitted to the hospital in late September and it turned out my BP was pretty high. It has since normalized.
With my family history, I am glad my doctor is taking every precaution to make sure I get on medication if needed.