An absolute measurement of brain water content using magnetic resonance imaging in two focal cerebral ischemic rat models

Magnetic resonance imaging (MRI) was utilized to obtain absolute estimates of regional brain water content (W), and results were compared with those o btained with conventional wet/dry measurements. In total, 31 male Long-Evan s rats were studied and divided into two groups based on the surgical proce dures used to induce cerebral focal ischemia: suture (n = 18) and three-ves sel ligation (TVL; n = 13) groups. Both relative spin density and T1 were e xtracted from the acquired MR images. After correcting for radiofrequency f ield inhomogeneities, T2* signal decay, and temperature effects, in vivo re gional brain water content, in absolute terms, was obtained by normalizing the measured relative brain spin density of animals to that of a water phan tom. A highly linear relationship between MR-estimated brain water content based on the normalized spin density and wet/dry measurements was obtained with slopes of 0.989 and 0.986 for the suture (r = 0.79) and TVL (r = 0.83) groups, respectively. Except for the normal subcortex of the TVL group (P < 0.02) and the normal hemisphere of the suture group (P < 0.003), no signi ficant differences were observed between MR-estimated and wet/dry measureme nts of brain water content. In addition, a highly linear relationship betwe en MR-measured R1 (=1/T1) and 1/W of wet/dry measurements was obtained. How ever, slopes of the linear regression lines in the two groups were signific antly different (P < 0.02), indicating that different R1 values were associ ated with the same water content depending on the model. These results show that an absolute measurement of in vivo regional brain water content can b e obtained with MRI and potentially serves as a noninvasive means to monito r different therapeutic interventions for the management of brain edema sub sequent to stroke and head trauma.