Modeling the Effect of Hyperoxia on the Spin-Lattice Relaxation Rate R1 of Tissues.

Purpose: Inducing hyperoxia in tissues is common practice in several areas of research, including oxygen-enhanced MRI (OE-MRI), which attempts to use the resulting signal changes to detect regions of tumor hypoxia or pulmonary disease. The linear relationship between PO and R1 has been reproduced in phantom solutions and body fluids such as vitreous fluid; however, in tissue and blood experiments, factors such as changes in deoxyhemoglobin levels can also affect the ΔR1.

Theory And Methods: This manuscript proposes a three-compartment model for estimating the hyperoxia-induced changes in R1 of tissues depending on B0, SO , blood volume, hematocrit, oxygen extraction fraction, and changes in blood and tissue PO .

A simplified empirical model to estimate oxygen relaxivity at different magnetic fields.

The change in longitudinal relaxation rate (R ) 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 ) and R is linear and reproducible, and the slope represents the relaxivity of oxygen (r ) in that material. However, there is considerable variability in the values of r reported, and they have been shown to vary by field strength and temperature.