Sometime in the past few million years, collapse at the top of the cave and surface erosion created the natural entrance of Carlsbad Cavern. This opened previously hidden underground cave passageways to the world above for the first time.
The Society of Diagnostic Medical Sonography (SDMS) defines sonography as diagnostic medical procedure that uses high frequency sound waves (ultrasound) to produce dynamic visual images of organs, tissues, or blood flow inside the body. This type of procedure is often referred to as a sonogram or ultrasound scan.
Carotid ultrasound (also called sonography) is the most common test for diagnosing carotid artery disease. It's a painless, harmless test that uses sound waves to create pictures of the insides of your carotid arteries. This test can show whether plaque has narrowed your carotid arteries and how narrow they are.