How much water should you drink before an ultrasound?

Answer 1

Ultrasound uses sound, or more accurately, sound waves or vibrations, to travel through a medium of some sort to image what is within that medium. Not unlike radar, some of the sound waves bounce off of things within that medium allowing them to be seen. In example, the dividing line between muscle and bone can be thought of as an interface, something the sound waves can bounce off of. The change in density from muscle to bone, allows the bone to be image.

Most ultrasound systems are designed to work best in water environments. This is because most of the solid parts of a body, including organs, bones, and other things, reside in, or are made up of mostly water. Water can carry sound waves better than air. Therefore, water-favoring ultrasound system can’t image well in air. For a water-based ultrasound system, air can act like a barrier to the sound waves. And, much like a brick wall stops you from seeing what is on the other side of the wall, air can prevent ultrasound from seeing what is there. By drinking water, one reduces the amount of air in the stomach and, therefore, improves the image quality of the ultrasound in that region of your body.

However, there are other systems that use sound to image such things as geologic features underground, or things within the air (like the natural imaging bats do using sound). So, what you want to see or image, determines the type of sound-imaging system used.

Answer 2

Two ultrasound exams that would benefit from drinking water prior to the exam would be a transabdominal pelvic ultrasound (different than a transvaginal pelvic ultrasound) and a transabdominal ultrasound to focus just on the pancreas.

The reasoning behind ingesting water for the pelvic ultrasound is so that the bladder will be full and during the exam the full bladder acts as a window to visualize the pelvic organs which sit behind the bladder. The fluid filled bladder allows the soundwaves from the ultrasound machine to to be enhanced as they travel through to the pelvic organs. A full bladder also pushes intestinal gas out of the field of view as well. The transabdominal exam is typically followed by the transvaginal ultrasound. The patient should empty their bladder after the transabdominal pelvic ultrasound and before the transvaginal ultrasound. A full bladder would actually interfere with a transvaginal ultrasound.

The other exam that would benefit from ingesting water would be a transabdominal scan of the pancreas. Typically the pancreas is imaged within an abdominal ultrasound. However, ingesting water would interfere with imaging the other organs typically seen in this exam. So the pancreas should be visualized last and immediately following the patient drinking 8 oz. of water. The reasoning behind this technique is that the fluid filled stomach acts as a window to visualize the deep pancreas, similar to the reasoning behind having a full bladder for a pelvic ultrasound.

Answer 3

My doc said to drink 1 litre or 32 ounces of water one hour before the appointment time.

Answer 4

32 ounces (4 cups) and finish it about 1 hour before the test without going to the bathroom until after the test.