Blood VolumeRegional Blood FlowMicrospheresCardiac OutputBlood CirculationCerebrovascular CirculationHemodynamicsDogsSplanchnic CirculationCoronary CirculationVascular ResistanceBlood PressureHypovolemiaPlasma VolumeErythrocyte VolumePulmonary CirculationScandiumLiver CirculationOxygenBlood Flow VelocityHeart RateRenal CirculationMagnetic Resonance ImagingBrain