title: Quantitative and qualitative (23)Na MR imaging of the human kidneys at 3 T: before and after a water load.
abstract: OBJECTIVE
  To qualitatively and quantitatively assess the corticomedullary sodium 23 ((23)Na) concentration in human kidneys before and after oral administration of a water load by using 3-T magnetic resonance (MR) imaging.
  
  
  METHODS
  Fourteen healthy volunteers (mean age, 28 years; range, 24-34 years) were included in this institutional review board-approved study between July and December 2009. For (23)Na MR imaging, a density-adapted three-dimensional radial gradient echo sequence (echo time, 0.55 msec; repetition time, 120 msec; spatial resolution, 5 × 5 × 5 mm) was used with a dedicated (23)Na-tuned coil. Beforehand, the coil profile was assessed by using phantom measurements, and the volunteer images were mathematically corrected accordingly. Images of the volunteers were obtained before and 30 minutes after oral ingestion of 1 L of water. As internal reference, (23)Na concentration of the cerebrospinal fluid (CSF) was calculated. Well-defined corticomedullary complexes in each kidney were assessed, with (23)Na concentrations in the cortex and medulla assessed at various standardized points. From these values, quantitative (23)Na concentrations were derived, and the slopes of the linear portion of the concentration gradient were calculated. Paired t tests were performed.
  
  
  RESULTS
  Mean calculated (23)Na concentrations of CSF before (135.2 mmol/L ± 10.4) and after water load (135.5 mmol/L ± 11.0) fell within physiologic ranges (P = .95). An increase in average (23)Na concentration from 63.5 mmol/L ± 9.3 in the cortex to 108.0 mmol/L ± 10.9 in the medulla was identified. After the water load, this gradient was preserved, although (23)Na concentrations decreased significantly (P < .0001) to 48.6 mmol/L ± 5.3 in the cortex and 81.9 mmol/L ± 10.1 in the medulla-declines of 23.4% and 24.7%, respectively.
  
  
  CONCLUSIONS
  This study demonstrates the physiologic evaluation of human kidneys with 3-T (23)Na MR imaging. The (23)Na imaging technique used allows the quantification of the corticomedullary (23)Na concentration and the assessment of its change with differing physiologic conditions.
authors.affiliation: Institute of Clinical Radiology and Nuclear Medicine, University Medical Centre Mannheim, Medical Faculty Mannheim, Heidelberg University, Theodor-Kutzer-Ufer 1-3, 68167 Mannheim, Germany. Stefan.Haneder@umm.de
authors.forename: Stefan
authors.initials: S
authors.lastname: Haneder
authors.forename: Simon
authors.initials: S
authors.lastname: Konstandin
authors.forename: John N
authors.initials: JN
authors.lastname: Morelli
authors.forename: Armin M
authors.initials: AM
authors.lastname: Nagel
authors.forename: Frank G
authors.initials: FG
authors.lastname: Zoellner
authors.forename: Lothar R
authors.initials: LR
authors.lastname: Schad
authors.forename: Stefan O
authors.initials: SO
authors.lastname: Schoenberg
authors.forename: Henrik J
authors.initials: HJ
authors.lastname: Michaely
mesh_terms: D000284:Administration, Oral; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D007668:Kidney / Q000378:metabolism*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D012964:Sodium / Q000493:pharmacokinetics*; D014018:Tissue Distribution; D014867:Water / Q000008:administration & dosage* / Q000378:metabolism*; D055815:Young Adult
chemical_list: D014867:Water; D012964:Sodium