The objective of this proposed research is to develop a noninvasive, challenge-free and widely accessible, imaging method to map oxygen extraction fraction (OEF) determined by deoxyheme-iron from postprocessing multiecho gradient echo (mGRE) data. There is no clinically-available tool to map OEF that is directly associated with brain oxygen metabolism and highly indicative of cerebrovascular and neurodegenerative disorders. We propose to include the often-discarded mGRE phase signal, which contains the magnetic field generated by deoxyheme iron, for increased sensitivity in estimating OEF through QSM processing. Our project will result in an easily and widely usable tool for quantitative OEF mapping, which can be routinely used on all the extensively-distributed MRI scanners to study brain functions and neurological diseases. In this STTR phase 1 project, we will establish a rapid and robust OEF method for routine clinical use. We will achieve this through 2 specific aims. Aim 1. Develop a rapid and robust OEF mapping from mGRE data. Aim 2. Validate the developed OEF mapping on existing data with 15O PET OEF reference.