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A T₂‐relaxation‐under‐spin‐tagging technique was recently developed to estimate cerebral blood oxygenation, providing potentials for noninvasive assessment of the brain's oxygen consumption. A limitation of the current sequence is the need for long repetition time, as shorter repetition time causes an over‐estimation in blood R₂. This study proposes a postsaturation T₂‐relaxation‐under‐spin‐tagging by placing a nonselective 90° pulse after the signal acquisition to reset magnetization in the whole brain. This scheme was found to eliminate estimation bias at a slight cost of precision. To improve the precision, echo time of the sequence was optimized and it was found that a modest echo time shortening of 3.4 ms can reduce the estimation error by 49%. We recommend the use of postsaturation T₂‐relaxation‐under‐spin‐tagging sequence with a repetition time of 3000 ms and a echo time of 3.6 ms, which allows …