Atrial septal defect (ASD) is a heart defect that is present at birth (congenital). While the baby is in the womb, there is normally an opening between the upper chambers of the heart (atria) to allow blood to flow around the lungs. This opening usually closes around the time when the baby is born.
Atherectomy – A nonsurgical technique for treating diseased arteries with a rotating device that cuts or shaves away material that is blocking or narrowing an artery.
Artifacts can be defined as any structure in an ultrasound image that does not have a corresponding anatomic tissue structure.
Artifacts may be classified into four main categories: missing structures, degraded images, falsely perceived objects, and structures with a misregistered location.
Read more here: http://www.scahq.org/sca3/events/2012/echo/fundamentals/submissions/mon/Artifacts%20od%20Ultrasound%20-%20Heller.pdf
Learn more about the physics of ultrasound at Gulfcoast Ultrasound Institute
Arcuate arteries – small arteries that lie at the bases of the renal medullary pyramids. They normally appear as thread-like echogenic structures that should not be confused for calculi.