REVIEWARTICLE Imaging Brain Oxygenation withMRI Using BloodOxygenation Approaches: Methods, Validation, and Clinical Applications

SUMMARY: In many pathophysiologic situations, including brain neoplasms, neurodegenerative disease, and chronic and acute ischemia, an imbalance exists between oxygen tissue consumption and delivery. Furthermore, oxygenation changes following a stress challenge, such as with carbogen gas or acetazolamide, can yield information about cerebrovascular reactivity. The unique sensitivity of the BOLD effect to the presence of deoxyhemoglobin has led to its widespread use in the field of cognitive neurosciences. However, the high spatial and temporal resolution afforded by BOLD imaging does not need to be limited to the study of healthy brains. While the complex relationship between the MR imaging signal and tissue oxygenation hinders a direct approach, many different methods have been developed during the past decade to obtain specific oxygenation measurements. These include qBOLD, phase- and susceptibility-based imaging, and intravascular T2-based approaches. The aim of this review is to give an overview of the theoretic basis of these methods as well as their application to measure oxygenation in both healthy subjects and those with disease. ABBREVIATIONS: BOLD blood oxygen level–dependent; CMRO2 cerebral metabolic rate of oxygen consumption; OEF oxygen-extraction fraction; pO2 partial pressure of oxygen; qBOLD quantitative BOLD; QUIXOTICQUantitative Imaging of eXtraction of Oxygen and TIssue Consumption; SaO2 arterial oxygen saturation; SO2 blood oxygen saturation; SvO2 venous oxygen saturation; TRUST T2-relaxation under spin-tagging The development of a reliable brain oxygenation mappingtechnique would not only enable a better understanding of normal physiology during rest, sleep, or functional brain tasks bu