A simplified empirical model to estimate oxygen relaxivity at different magnetic fields
Emma Bluemke, Eleanor Stride, Daniel P. Bulte
Abstract
The change in longitudinal relaxation rate ( R 1 ) produced by oxygen has been used as a means of inferring oxygenation levels in magnetic resonance imaging in numerous applications. The relationship between oxygen partial pressure (pO 2 ) and R 1 is linear and reproducible, and the slope represents the relaxivity of oxygen ( r 1Ox ) in that material. However, there is considerable variability in the values of r 1Ox reported, and they have been shown to vary by field strength and temperature. Therefore, we have compiled 28 reported empirical values of the relaxivity of oxygen as a resource for researchers. Furthermore, we provide an empirical model for estimating the relaxivity of oxygen in water, saline, plasma, and vitreous fluids, accounting for magnetic field strength and temperature. The model agrees well ( R 2 = 0.93) with the data gathered from the literature for fields ranging from 0.011 to 8.45 T and temperatures of 21‐40 °C. This provides a useful resource for researchers seeking to quantify pO 2 in simple fluids in their studies, such as water and saline phantoms, or bodily fluids such as vitreous fluids, cerebrospinal fluids, and amniotic fluids.