title: 3 Tesla sodium inversion recovery magnetic resonance imaging allows for improved visualization of intracellular sodium content changes in muscular channelopathies.
abstract: OBJECTIVE
  To implement different sodium (²³Na)-magnetic resonance imaging (MRI) contrasts at 3 Tesla and to evaluate if a weighting toward intracellular sodium can be achieved, using 2 rare muscular channelopathies as model diseases.
  
  
  METHODS
  Both lower legs of 6 patients with hypokalemic periodic paralysis (HypoPP), 5 patients with paramyotonia congenita (PC), and 5 healthy volunteers were examined on a 3 Tesla system with 3 different ²³Na-MRI pulse sequences. HypoPP and PC are rare muscle diseases, which are well characterized by elevated myoplasmic sodium at rest and after cooling, respectively. Intra- and interindividual comparisons were performed before and after provocation of one lower leg muscle. Three different ²³Na-MRI sequences were applied: (i) The total tissue sodium concentration was measured using a spin-density sequence (²³Na-TSC). (ii) A T1-contrast was applied to assess whether the known changes of the intracellular sodium concentration can be visualized by T1-weighting (²³Na-T1). (iii) An inversion recovery (²³Na-IR) sequence was used to utmost suppress the sodium signal from extracellular or vasogenic edema. Furthermore, a potential influence of the temperature dependency of the sodium relaxation times was considered. Additionally, H-MRI was performed to examine potential lipomatous or edematous changes.
  
  
  RESULTS
  In HypoPP, all Na sequences showed significantly (P<0.05) higher signal intensities compared with PC patients and healthy subjects. In muscles of PC patients, provocation induced a significant (P=0.0007) increase (>20%) in the muscular ²³Na-IR signal and a corresponding decrease of muscle strength. Additionally, a tendency to higher ²³Na-T1 (P=0.07) and ²³Na-TSC (P=0.07) signal intensities was observed. Provocation revealed no significant changes in ¹H-MRI. In volunteers and in the contralateral, not cooled lower leg, there were no significant signal intensity changes after provocation. Furthermore, the ²³Na-IR sequence allows for a suppression of signal emanating from intravascular sodium and vasogenic edema.
  
  
  CONCLUSIONS
  Our results indicate that the ²³Na-IR sequence allows for a weighting toward intracellular sodium. The combined application of the ²³Na-TSC and the ²³Na-IR sequence enables an improved analysis of pathophysiological changes that occur in muscles of patients with muscular channelopathies.
authors.affiliation: Department of Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany. a.nagel@dkfz.de
authors.forename: Armin Michael
authors.initials: AM
authors.lastname: Nagel
authors.forename: Erick
authors.initials: E
authors.lastname: Amarteifio
authors.forename: Frank
authors.initials: F
authors.lastname: Lehmann-Horn
authors.forename: Karin
authors.initials: K
authors.lastname: Jurkat-Rott
authors.forename: Wolfhard
authors.initials: W
authors.lastname: Semmler
authors.forename: Lothar R
authors.initials: LR
authors.lastname: Schad
authors.forename: Marc-André
authors.initials: MA
authors.lastname: Weber
mesh_terms: D000328:Adult; D003952:Diagnostic Imaging / Q000379:methods*; D005260:Female; D006801:Humans; D020514:Hypokalemic Periodic Paralysis / Q000175:diagnosis* / Q000473:pathology; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D020967:Myotonic Disorders / Q000175:diagnosis* / Q000473:pathology; D012964:Sodium / Q000737:chemistry*
chemical_list: D012964:Sodium