3D Ultrasound Validation for Measuring Stomach Volume

The goal is to study the accuracy of 3-dimensional ultrasound (which does not involve radiation) to measure the size of the stomach, comparing it with a previously validated method that involves radiation. This will make it possible to check the stomach function of children without exposing them to radiation. A second goal is to measure the size of the stomach and the effect of a standard meal on stomach volume in adolescent boys and girls.