On improving the speed and reliability of T2-relaxation-under-spin-tagging (TRUST) MRI.

A T(2) -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 R(2). This study proposes a postsaturation T(2)-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 T(2)-relaxation-under-spin-tagging sequence with a repetition time of 3000 ms and a echo time of 3.6 ms, which allows the determination of global venous oxygenation with scan duration of 1 min 12 s and an estimation precision of ± 1% (in units of oxygen saturation percentage).