Gastric EmptyingStomachGastric AcidGastrinsGastric JuiceVagus NervePepsin AGastroparesisGastrointestinal MotilityGastric MucosaDyspepsiaPentagastrinDuodenumHydrogen-Ion ConcentrationEcho-Planar ImagingEcholocationImage EnhancementMagnetic Resonance ImagingChiropteraPhantoms, ImagingImage Interpretation, Computer-AssistedArtifactsReproducibility of ResultsContrast MediaUltrasonographyEchocardiographySensitivity and SpecificityImaging, Three-Dimensional