Changes in the proton T 2 relaxation times of cerebral water and metabolites during forebrain ischemia in rat at 9.4 T

Proton T 2 relaxation times of cerebral water and metabolites were measured before, during, and after transient forebrain ischemia in rat at 9.4 T using localized proton magnetic resonance spectroscopy ( 1 H‐MRS) with Hahn echoes formed at different echo times (TEs). It was found that the T 2 values of water and N‐acetyl aspartate (NAA) methyl, but not total creatine (tCr) methyl, decrease significantly (∼10%) during ischemia, and this T 2 reduction is reversed by reperfusion. The T 2 reduction observed for NAA was most likely caused by the extravascular component of the blood oxygenation level‐dependent (BOLD) effect induced by a drastically increased deoxyhemoglobin content during ischemia. The absence of T 2 changes for tCr can probably be explained by the fact that the BOLD‐related T 2 decrease was counterbalanced by the conversion of phosphocreatine (PCr) to creatine (Cr), which has a longer T 2 than PCr, during ischemia. The changes in T 2 should be taken into account for the quantification of metabolite concentrations during ischemia. Magn Reson Med 49:979–984, 2003. © 2003 Wiley‐Liss, Inc.