Volumetric quantification of brain swelling after hypobaric hypoxia exposure

We applied a novel MR imaging technique to investigate the effect of acute mountain sickness on cerebral tissue water. Nine volunteers were exposed to hypobaric hypoxia corresponding to 4572 m altitude for 32 h. Such an expos ure may cause acute mountain sickness. We imaged the brains of the voluntee rs before and at 32 h of hypobaric exposure with two different MRI techniqu es with subsequent data processing. (1) Brain volumes were calculated from 3D MRI data sets by applying a computerized brain segmentation algorithm. F or this specific purpose a novel adaptive 3D segmentation program was used with an automatic correction algorithm for RF field inhomogeneity. (2) T-2 decay rates were analyzed in the white matter. The results demonstrated tha t a significant brain swelling of 36.2 +/- 19.6 mi (2.77 +/- 1.47%, n = 9, P < 0.001) developed after the 32-h hypobaric hypoxia exposure with a maxim al observed volume increase of 5.8% (71.3 mi). These volume changes were si gnificant only for the gray matter structures in contrast to the unremarkab le changes seen in the white matter. The same study repeated 3 weeks later in 6 of 9 original subjects demonstrated that the brains recovered and retu rned approximately to the initially determined sea-level brain volume while hypobaric hypoxia exposure once again led to a significant new brain swell ing (24.1 +/- 12.1 mi, 1.92 +/- 0.96%, n = 6, P < 0.005). On the contrary, the T-2 mapping technique did not reveal any significant effect of hypobari a on white matter. We present here a technique which is able to detect reve rsible brain volume changes as they may occur in patients with diffuse brai n edema or increased cerebral blood volume, and which may represent a usefu l noninvasive tool for future evaluations of antiedematous drugs, (C) 2001 Academic Press.