Estimating oxygen saturation of blood in vivo with MR imaging at 1.5 T

The use of magnetic resonance (MR) imaging is investigated for noninvasively estimating the oxygen saturation of human blood (%HbO 2 ) in vivo by means of relaxation characteristics identified in earlier MR spectrometry studies. To this end, a sequence is presented for determining the T 2 of vascular blood in regions in which motions of the body and of the blood itself present a major challenge. With use of this sequence on a commercial 1.5‐T whole‐body imager, the relationship between the T 2 and %HbO 2 of blood is calibrated in vitro for the conditions expected in vivo. T 2 varies predictably from about 30 to 250 msec as %HbO 2 varies from 30% to 96%. T 2 values measured in situ for vascular blood in the mediastinum of several healthy subjects qualitatively reflected the behavior observed in vitro. Estimates of %HbO 2 for these vessels obtained with the in vitro calibration appear reasonable, particularly for venous blood, although difficulties arise in selecting the appropriate calibration factors. These encouraging initial results support a more systematic study of potential sources of error and an examination of the accuracy of in vivo measurements by comparison with direct measurements of %HbO 2 in vessels.