title: Two-dimensional semi-LASER correlation spectroscopy with well-maintained cross peaks.
abstract: OBJECTIVE
  To demonstrate that the limited bandwidth of the second 90° radiofrequency (RF) pulse in two-dimensional (2D) localized correlation spectroscopy (L-COSY) induces spatially dependent magnetization transfer that results in attenuated cross-peaks, and to propose a new 2D semi-adiabatically localized COSY sequence to solve this problem.
  A semi-localization by adiabatic selective refocusing (semi-LASER or sLASER) method was incorporated into the COSY sequence with the slice-selective first 90° RF pulse and the non-slice-selective second 90° RF pulse to form a new 2D sLASER localized COSY sequence, named "sLASER-first-COSY," to solve the problem of spatially dependent magnetization transfer. Experiments were performed to verify the feasibility and advantages of sLASER-first-COSY sequence over a recently reported other sLASER COSY sequence with a slice-selective second 90° RF pulse, named "sLASER-last-COSY".
  
  
  RESULTS
  Phantom, ex vivo, and in vivo human brain experiments demonstrated that sLASER-first-COSY yielded stronger cross peaks and higher ratios of cross peak volumes to diagonal peak volumes than sLASER-last-COSY.
  
  
  CONCLUSIONS
  As COSY relies on the cross peaks to obtain larger dispersion of peaks for quantification, the new sLASER-first-COSY sequence yielding well-maintained cross peaks will facilitate more reliable and accurate quantification of metabolites with coupled spin systems.
authors.affiliation: University of Illinois at Chicago, Department of Psychiatry, Chicago, Illinois, USA.
authors.forename: Meijin
authors.initials: M
authors.lastname: Lin
authors.forename: Anand
authors.initials: A
authors.lastname: Kumar
authors.forename: Shaolin
authors.initials: S
authors.lastname: Yang
mesh_terms: D000818:Animals; D001923:Brain Chemistry; D006801:Humans; D066298:In Vitro Techniques; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D019047:Phantoms, Imaging; D011846:Radio Waves; D013552:Swine
keywords: chemical shift displacement error (CSDE); correlation spectroscopy (COSY); cross peak; localization by adiabatic selective refocusing (LASER); magnetization transfer; two-dimensional (2D) magnetic resonance spectroscopy (MRS)