title: (39) K and (23) Na relaxation times and MRI of rat head at 21.1 T.
abstract: At ultrahigh magnetic field strengths (B0  ≥ 7.0 T), potassium ((39) K) MRI might evolve into an interesting tool for biomedical research. However, (39) K MRI is still challenging because of the low NMR sensitivity and short relaxation times. In this work, we demonstrated the feasibility of (39) K MRI at 21.1 T, determined in vivo relaxation times of the rat head at 21.1 T, and compared (39) K and sodium ((23) Na) relaxation times of model solutions containing different agarose gel concentrations at 7.0 and 21.1 T. (39) K relaxation times were markedly shorter than those of (23) Na. Compared with the lower field strength, (39) K relaxation times were up to 1.9- (T1 ), 1.4- (T2S ) and 1.9-fold (T2L ) longer at 21.1 T. The increase in the (23) Na relaxation times was less pronounced (up to 1.2-fold). Mono-exponential fits of the (39) K longitudinal relaxation time at 21.1 T revealed T1  = 14.2 ± 0.1 ms for the healthy rat head. The (39) K transverse relaxation times were 1.8 ± 0.2 ms and 14.3 ± 0.3 ms for the short (T2S ) and long (T2L ) components, respectively. (23) Na relaxation times were markedly longer (T1  = 41.6 ± 0.4 ms; T2S  = 4.9 ± 0.2 ms; T2L  = 33.2 ± 0.2 ms). (39) K MRI of the healthy rat head could be performed with a nominal spatial resolution of 1 × 1 × 1 mm(3) within an acquisition time of 75 min. The increase in the relaxation times with magnetic field strength is beneficial for (23) Na and (39) K MRI at ultrahigh magnetic field strength. Our results demonstrate that (39) K MRI at 21.1 T enables acceptable image quality for preclinical research. Copyright © 2016 John Wiley & Sons, Ltd.
authors.affiliation: German Cancer Research Center (DKFZ), Division of Medical Physics in Radiology, Heidelberg, Germany.|University Medical Center Ulm, Department of Diagnostic and Interventional Radiology, Ulm, Germany.
authors.forename: Armin M
authors.initials: AM
authors.lastname: Nagel
authors.affiliation: German Cancer Research Center (DKFZ), Division of Medical Physics in Radiology, Heidelberg, Germany.
authors.forename: Reiner
authors.initials: R
authors.lastname: Umathum
authors.affiliation: German Cancer Research Center (DKFZ), Division of Medical Physics in Radiology, Heidelberg, Germany.
authors.forename: Manuela B
authors.initials: MB
authors.lastname: Rösler
authors.affiliation: German Cancer Research Center (DKFZ), Division of Medical Physics in Radiology, Heidelberg, Germany.
authors.forename: Mark E
authors.initials: ME
authors.lastname: Ladd
authors.affiliation: National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL, USA.
authors.forename: Ilya
authors.initials: I
authors.lastname: Litvak
authors.affiliation: National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL, USA.
authors.forename: Peter L
authors.initials: PL
authors.lastname: Gor'kov
authors.affiliation: National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL, USA.
authors.forename: William W
authors.initials: WW
authors.lastname: Brey
authors.affiliation: National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL, USA.
authors.forename: Victor D
authors.initials: VD
authors.lastname: Schepkin
mesh_terms: D000818:Animals; D001921:Brain / Q000000981:diagnostic imaging* / Q000378:metabolism*; D005240:Feasibility Studies; D008279:Magnetic Resonance Imaging / Q000379:methods*; D057054:Molecular Imaging / Q000379:methods*; D011188:Potassium / Q000493:pharmacokinetics*; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D051381:Rats; D011916:Rats, Inbred F344; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012975:Sodium Isotopes / Q000493:pharmacokinetics*; D014018:Tissue Distribution
chemical_list: D019275:Radiopharmaceuticals; D012975:Sodium Isotopes; D011188:Potassium
keywords: 21 T; 7 T; high-field MRI; non-proton MRI; potassium (39K); relaxation times; sodium (23Na)