title: Implementation of multi-echo-based correlated spectroscopic imaging and pilot findings in human brain and calf muscle.
abstract: OBJECTIVE
  To implement a spatially encoded correlated spectroscopic imaging (COSI) sequence on 3 Tesla (T) MRI/MR spectroscopy scanners incorporating four echoes to collect four phase-encoded acquisitions per repetition time (TR), and to evaluate the performance and reliability of this four-dimensional (4D) multi-echo COSI (ME-COSI) sequence in brain and calf muscle.
  
  
  METHODS
  Typical scan parameters for the 4D datasets were as follows: repetition time = 1500 ms, 2000 Hz bandwidth, 8 × 8 spatial encoding, one average, 64 Δt(1) increments and the scan duration was 25 min. The performance and test-retest reliability of ME-COSI were evaluated with phantoms and in the occipitoparietal brain tissues and calf of six healthy volunteers (mean age = 32 years old).
  
  
  RESULTS
  Regional differences in concentrations of lipids, creatine (Cr), choline (Ch), and carnosine (Car) were observed between spectra from voxels located in tibial marrow, tibialis anterior, and soleus muscle. Diagonal and cross-peak resonances were identified from several brain metabolites including N-acetyl aspartate (NAA), Ch, Cr, lactate (Lac), aspartate (Asp), glutathione (GSH), and glutamine\glutamate (Glx). Coefficients of variation (CV) in metabolite ratios across repeated measurements were <15% for diagonal and <25% for cross-peaks observed in vivo.
  
  
  CONCLUSIONS
  The ME-COSI sequence reliably acquired spatially resolved 2D Correlated Spectroscopy (COSY) spectra demonstrating the feasibility of differentiating spatial variation of metabolites in different tissues. Multi-echo acquisition shortens scan duration to clinically feasible times.
authors.affiliation: Department of Bioengineering, University of California, Los Angeles, California 90095-1721, USA.
authors.forename: Gaurav
authors.initials: G
authors.lastname: Verma
authors.forename: Scott
authors.initials: S
authors.lastname: Lipnick
authors.forename: Saadallah
authors.initials: S
authors.lastname: Ramadan
authors.forename: Rajakumar
authors.initials: R
authors.lastname: Nagarajan
authors.forename: M Albert
authors.initials: MA
authors.lastname: Thomas
mesh_terms: D000328:Adult; D001853:Bone Marrow / Q000378:metabolism; D001921:Brain / Q000473:pathology*; D002336:Carnosine / Q000378:metabolism; D002794:Choline / Q000378:metabolism; D003401:Creatine / Q000378:metabolism; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D018482:Muscle, Skeletal / Q000473:pathology*; D019047:Phantoms, Imaging; D013053:Spectrophotometry / Q000379:methods*; D013977:Tibia / Q000473:pathology; D013997:Time Factors
chemical_list: D002336:Carnosine; D003401:Creatine; D002794:Choline