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.
Extremely low-wavelength sound waves are applied to the body and the reflections from the sound waves are measured to create an internal image of the scanned area. Sonography technicians, sometimes called ultrasound technicians or diagnostic sonographers, are the health care professionals who perform sonographies.