title: In vivo chemical exchange saturation transfer imaging of creatine (CrCEST) in skeletal muscle at 3T.
abstract: OBJECTIVE
  To characterize the chemical exchange saturation transfer (CEST)-based technique to measure free creatine (Cr), a key component of muscle energy metabolism, distribution in skeletal muscle with high spatial resolution before and after exercise at 3T.
  
  
  METHODS
  CrCEST saturation parameters were empirically optimized for 3T. CEST, T2 , magnetization transfer ratio (MTR), and (31) P magnetic resonance spectroscopy (MRS) acquisitions of the lower leg were performed before and after mild plantar flexion exercise on a 3T whole-body MR scanner on six healthy volunteers.
  
  
  RESULTS
  The feasibility of imaging Cr changes in skeletal muscle following plantar flexion exercise using CrCEST was demonstrated at 3T. This technique exhibited good spatial resolution and was able to differentiate differences in muscle use among subjects. The CrCEST results were compared with (31) P MRS results, showing good agreement in the Cr and PCr recovery kinetics. A relationship of 0.45% CrCESTasym /mM Cr was observed across all subjects.
  
  
  CONCLUSIONS
  It is demonstrated that the CrCEST technique could be applied at 3T to measure dynamic changes in creatine in muscle in vivo. The widespread availability and clinical applicability of 3T scanners has the potential to clinically advance this method.
authors.affiliation: Center for Magnetic Resonance and Optical Imaging, Department of Radiology, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
authors.forename: Feliks
authors.initials: F
authors.lastname: Kogan
authors.forename: Mohammad
authors.initials: M
authors.lastname: Haris
authors.forename: Catherine
authors.initials: C
authors.lastname: Debrosse
authors.forename: Anup
authors.initials: A
authors.lastname: Singh
authors.forename: Ravi P
authors.initials: RP
authors.lastname: Nanga
authors.forename: Kejia
authors.initials: K
authors.lastname: Cai
authors.forename: Hari
authors.initials: H
authors.lastname: Hariharan
authors.forename: Ravinder
authors.initials: R
authors.lastname: Reddy
mesh_terms: D000328:Adult; D003401:Creatine / Q000378:metabolism*; D005240:Feasibility Studies; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D007866:Leg; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism*
chemical_list: D003401:Creatine
keywords: CrCEST; chemical exchange; creatine; endogenous contrast; muscle