Influence of proton T 1 on oxymetry using Overhauser enhanced magnetic resonance imaging

In Overhauser enhanced magnetic resonance imaging (OMRI) for in vivo measurement of oxygen partial pressure ( p O 2 ), a paramagnetic contrast agent is introduced to enhance the proton signal through dynamic nuclear polarization. A uniform proton T 1 is generally assumed for the entire region of interest for the computation of p O 2 using OMRI. It is demonstrated here, by both phantom and in vivo (mice) imaging, that such an assumption may cause erroneous estimate of p O 2 . A direct estimate of pixel‐wise T 1 is hampered by the poor native MR intensities, owing to the very low Zeeman field (15–20 mT) in OMRI. To circumvent this problem, a simple method for the pixel‐wise mapping of proton T 1 using the OMRI scanner is described. A proton T 1 image of a slice through the center of an SCC tumor in a mouse clearly shows a range of T 1 distribution (0.2∼1.6 s). Computation of p O 2 images using pixel‐wise T 1 values promises oximetry with minimal artifacts by OMRI. Magn Reson Med 54:213–217, 2005. Published 2005 Wiley‐Liss, Inc.