Authors: Team Iradix R. Nick Bryan[1], MD, PhD Department of Radiology University of Pennsylvania Health System 3400 Civic Center Blvd, Penn Tower Lobby Level Philadelphia, PA 19104 This e-mail address is being protected from spambots. You need JavaScript enabled to view it Summary: As initially reported by Ogawa et al (1), the magnetic resonance (MR) imaging T2* blood oxygen level–dependent (BOLD) signal is sensitive to blood oxygen concentration; however, this signal is also sensitive to a number of other normal and abnormal tissue features. As a result, T2* imaging alone cannot be used to accurately measure vascular oxygenation, much less tissue oxygenation. However, with separate MR imaging measurements of other tissue factors influencing T2*, it might be possible to noninvasively image local tissue oxygen. Such a capability could be of great clinical importance, not only in patients with hypoxic or ischemic disease states, but also in patients with other pathologic conditions that have abnormal respiratory metabolism, such as cancer. The Setting If H2O is the body’s most precious fluid, surely O2 is its most precious gas. Most animals, and all mammals, depend on O2 metabolism for survival, though they may transiently use anaerobic respiration, as in short-term strenuous muscular exercise. States of hypoxia leave tissues at risk, at first functionally and then structurally, ultimately ending in cell death if hypoxia is sufficiently severe or long lasting. Because of its relatively constant high metabolic rate, the brain is particularly sensitive to hypoxia, losing normal function within a few minutes and dying within tens of minutes of anoxia. Hence, as stated by Christen et al in the accompanying article, “a technique with which to image brain hypoxia in vivo is of considerable interest” (2). Christen et al (2) follow the initial work of Ogawa et al (1), who showed sensitivity but not specificity of the BOLD T2* MR imaging signal to blood oxygenation. From the earliest descriptions of the BOLD technique, it was appreciated that the T2*measurement was dependent not only on blood oxygen saturation (SO2), but also on other MR … References^ R. Nick Bryan (radiology.rsna.org)

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