IN-VIVO MEASUREMENT OF REGIONAL BRAIN METABOLIC RESPONSE TO HYPERVENTILATION USING MAGNETIC-RESONANCE - PROTON ECHO-PLANAR SPECTROSCOPIC IMAGING (PEPSI)

A new rapid spectroscopic imaging technique with improved sensitivity and lipid suppression, referred to as Proton Echo Planar Spectroscopic Imaging (PEPSI), has been developed to measure the 2-dimensional dist ribution of brain lactate increases during hyperventilation on a conve ntional clincal scanner equipped with a head surface coil phased array . PEPSI images (nominal voxel size: 1.125 cm(3)) in five healthy subje cts from an axial section approximately 20 mm inferior to the intercom missural line were obtained during an 8.5-min baseline period of normo capnia and during the final 8.5 min of a 10-min period of capnometry-c ontrolled hyperventilation (end-tidal PCO2 of 20 mmHg). The lactate/N- acetyl aspartate signal increased significantly from baseline during h yperventilation for the insular cortex, temporal cortex, and occipital regions of both the right and left hemispheres, but not in the basal ganglia. Regional or hemispheric right-to-left differences were not fo und. The study extends previous work using single-voxel MR spectroscop y to dynamically study hyperventilation effects on brain metabolism.