Oxygen Metabolic Mapping by MRI-BOLD technique

背景资料：急性脑缺血时局部脑氧代谢的评价为半暗区的抢救提供了有用的信息，但PET是目前唯一可行的方法。1：Δ BOLD = M{1-（rCMRO_2）^β（Δ CBF）}^<α-β>其中M取决于组织dHb含量如果CMRO_2不受乙酰唑胺给药的影响，我们可以从以下方程获得rCMRO_2值：rCMRO_2=ΔCBF^<1-α/β>（1-ΔBOLD/M）^<1/β>α和β来自以下方程：CBV=CBF^α，1/T_2^*=C（1-Y）^βCBV_v，其中Y是静脉血氧水平，CBV_v是静脉脑血容量。我们设定α=0.38，β= 1.5。对5例大血管闭塞患者进行了BOLD和CBF测量。我们使用奥斯塔加德的算法^[2]来测量CBF。我们从矢状窦测量静脉输出功能，以校正动脉输入功能（AIF）的部分容积效应。结果：所有患者经BOLD/灌注法获得的rCMRO 2图均具有合理的灰/白色对比。在左侧MCA闭塞的患者中，降低的rCMRO_2区域似乎与PET的区域一致（图）。结论：我们表明，通过CBF和BOLD测量的组合，氧代谢可以在地图上可视化。虽然需要仔细验证，但该技术具有临床应用的潜力。

Background : Evaluation of regional oxygen metabolism of the brain in acute ischemia provides useful information for salvage of penumbral area, but PET is the only available method for this purpose at present We carried out a preliminary study to develop a new approach by using MR imaging.Methods : We used the equations proposed by Davis et al.^1 :Δ BOLD = M{1-(rCMRO_2)^β(Δ CBF)}^<α-β>where M is dependent on tissue dHb content If CMRO_2 is not affected by acetazolamide administration, we can get rCMRO_2 value from the following equation :rCMRO_2=ΔCBF^<1-α/β>(1-ΔBOLD/M)^<1/β>α and β come from the following equations : CBV=CBF^α,1/T_2^*=C(1-Y) ^βCBV_v, where Y is venous blood oxygenation level and CBV_v is venous cerebral blood volume. Here, we set α=0.38 and β=1.5.Pairs of BOLD and CBF measurements were performed in five patients with large vessel occlusion. We used Ostargaad' s algorism ^2 for CBF measurements. We measured venous output function from the sagittal sinus to correct the partial volume effect of arterial input function(AIF). For verification of the results, the patients were also underwent PET study.Results : There was reasonable gray/white contrast in the rCMRO_2 map obtained by BOLD/perfusion methods in all patients. In a patient with left MCA occlusion, the area of lowered rCMRO_2 seemed to be in agreement with that of the PET(Figure).Conclusions : We showed that oxygen metabolism could be visualized on the map by the combination of CBF and BOLD measurements. Although careful verification is necessary, this technique has a potential for clinical use.