Oxygen tension in a murine tumor: a combined EPR and MRI study.

The effects of fusinite, a new agent for the measurement of the concentration of oxygen in vivo by EPR, on MRI images have been studied. There was little effect on spin-echo T1-weighted images, but the fusinite resulted in large effects on T2-weighted images. Especially large effects could be observed when using spoiled gradient echo sequences (SPGR). The observed measurements of oxygen by EPR corresponded to the relative vascularity at the site of the fusinite both histologically and by MRI studies of vascularity using Gd-DTPA as a contrast agent. We conclude that by using the effects of fusinite on magnetic susceptibility, it can be located accurately and noninvasively with MRI and thereby the value of the use of fusinite to measure concentration of oxygen in vivo is enhanced.