Noble GasesVentilation-Perfusion RatioPulmonary CirculationPulmonary Gas ExchangePerfusionOxygenLungPerfusion ImagingMyocardial Perfusion ImagingTomography, Emission-Computed, Single-PhotonChemotherapy, Cancer, Regional PerfusionCoronary CirculationCerebrovascular CirculationRegional Blood FlowTechnetium Tc 99m SestamibiOrganotechnetium CompoundsContrast MediaHeartMagnetic Resonance AngiographyMicrocirculationLaser-Doppler FlowmetryRadiopharmaceuticalsBlood Flow Velocity