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.
What is an ultrasound? A prenatal ultrasound (also called a sonogram) is a noninvasive diagnostic test that uses sound waves to create a visual image of your baby, placenta, and uterus, as well as other pelvic organs. It allows your healthcare practitioner to gather valuable information about the progress of your pregnancy and your baby's health. During the test, an ultrasound technician (sonographer) transmits high-frequency sound waves through your uterus that bounce off your baby. A computer then translates the echoing sounds into video images that reveal your baby's shape, position, and movements.