Lactate detection at 3T: Compensating J coupling effects with BASING

Detection of lactate by in vivo H-1 magnetic resonance spectroscopy may pro vide a means of identifying regions of metabolic stress in brain and other human tissue, potentially identifying regional ischemia in stroke or necros is in tumors, At higher field strengths [3 and 4 T], which have recently be come available for whole-body human studies, the chemical shift difference between the doublet from the methyl protons and the quartet from the methin e proton becomes comparable to the available radiofrequency (RF) pulse band width. In this case "anomalous" J modulation occurs in PRESS [5] and STEAM [1] because the coupling partner of the observed resonance may or may not b e refocused by the RF pulses depending on the position of the molecule with in the voxel and the size of the chemical shift misregistration artifact. T hese anomalies lead to signal cancellation for echo times near odd multiple s of 1/J (often used to highlight the inverted lactate doublet against near by lipid peaks) in single voxel studies, and spatial variation of the doubl et lineshape in chemical shift imaging studies, producing erroneous determi nation of relative lactate concentrations, While increasing the bandwidth o f the RF pulses can reduce this effect by reducing the signal cancellation, some cancellation will always remain. A means of eliminating this effect u sing BASING/MEGA (Mescher M et al. Solvent suppression using selective echo dephasing J Magn Reson A 1996;123:226-229; Star-Lack J et al, Improved wat er and lipid suppression for 3D PRESS CSI using RF band selective inversion with gradient dephasing (BASING). Magn Reson Med 1997;38: 311-321) water s uppression pulses will be described, along with some of its limitations. a 1999 Wiley-Liss, Inc.