title: Short TE (7) Li-MRS confirms Bi-exponential lithium T2 relaxation in humans and clearly delineates two patient subtypes.
abstract: OBJECTIVE
  (i) To develop an MRS technique to measure (7) Li levels in human brain in a reasonable scan time, (ii) to develop a technique to quantify (7) Li T2 relaxation times as measured from human brain in patients taking lithium for the treatment of their bipolar disorder, and (iii) to confirm or refute the presence of bi-exponential (7) Li T2 relaxation in human brain.
  
  
  METHODS
  We modified a spin-echo MRS pulse sequence to decrease its minimum echo time. With IRB approval, we performed lithium MRS with the modified pulse sequence on 13 euthymic bipolar patients stable on long-term lithium to treat their disease.
  
  
  RESULTS
  We were able to achieve a total scan time per sample of 8:20; total scan time including imaging, calibration and MRS was approximately 1 h 15 min. We observed bi-exponential T2 relaxation in the majority of patients, with an average short decay time of 5.3 ± 1.4 ms and an average long decay time of 68.2 ± 10.2 ms. However, in two patients we observed strongly mono-exponential T2 relaxation with an average decay time of 47.4 ± 1.3 ms.
  
  
  CONCLUSIONS
  (7) Li relaxation patterns may prove useful to distinguish between lithium-responsive and lithium nonresponsive bipolar patients.
authors.affiliation: Department of Radiology, Mayo Clinic, Rochester, Minnesota 55905, USA. port.john@mayo.edu
authors.forename: John D
authors.initials: JD
authors.lastname: Port
authors.forename: Karen E
authors.initials: KE
authors.lastname: Rampton
authors.forename: Yunhong
authors.initials: Y
authors.lastname: Shu
authors.forename: Armando
authors.initials: A
authors.lastname: Manduca
authors.forename: Mark A
authors.initials: MA
authors.lastname: Frye
mesh_terms: D000328:Adult; D018692:Antimanic Agents / Q000493:pharmacokinetics / Q000627:therapeutic use; D001714:Bipolar Disorder / Q000175:diagnosis / Q000188:drug therapy* / Q000378:metabolism*; D001921:Brain / Q000378:metabolism*; D005260:Female; D006801:Humans; D007554:Isotopes / Q000493:pharmacokinetics; D008094:Lithium / Q000493:pharmacokinetics*; D016651:Lithium Carbonate / Q000493:pharmacokinetics* / Q000627:therapeutic use*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008297:Male; D008875:Middle Aged; D014018:Tissue Distribution
chemical_list: D018692:Antimanic Agents; D007554:Isotopes; D016651:Lithium Carbonate; D008094:Lithium