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.
For the tactile alphabet called sonography, see Night writing. Medical ultrasound (also known as diagnostic sonography or ultrasonography) is a diagnostic imaging technique based on the application of ultrasound. It is used to see internal body structures such as tendons, muscles, joints, vessels and internal organs.