title: Renal blood oxygenation level-dependent imaging: contribution of R2 to R2* values.
abstract: OBJECTIVE
  The aim of this study was to assess the impact of oral water and intravenous furosemide challenges on blood oxygenation level-dependent magnetic resonance imaging measurements in the kidney and to examine the contribution of R2 (=1/T2) to changes in R2* (=1/T2*).
  
  
  METHODS
  This Health Insurance Portability and Accountability Act-compliant study had institutional review board approval, and written informed consent was obtained from all subjects. Nine healthy volunteers were imaged at 3 T on 2 visits. During each visit, a baseline fasting magnetic resonance acquisition was followed by a diuretic challenge: oral water load for the first visit and furosemide for the second. R2* and R2 values in the renal cortex and medulla were measured using multiple gradient echo and multiple spin echo sequences, respectively, and R2' values were computed as R2' = R2* - R2. Timed urinary output was also measured.
  
  
  RESULTS
  Averaged across all subjects, the R2* response to furosemide was greater than to water and greater in the medulla than the cortex. The mean R2 responses exhibited the same trends but were uniformly smaller than the mean R2* responses. The peak changes in R2* and R2 appeared, on average, 10 to 14 minutes before peak urinary output. The median percentage contribution of R2 to R2* changes was 16% in the medulla after both challenges. In the cortex, the median contribution was 48% after water load and 58% after furosemide challenge.
  
  
  CONCLUSIONS
  The contributions of R2 to R2* changes after water load and furosemide challenge are not negligible, especially in the renal cortex. In routine clinical practice, R2* could be used alone as a rough surrogate for R2' in the medulla. However, in the cortex, both R2 and R2* should be measured to obtain accurate values of R2'.
authors: NYU Langone Medical Center, Department of Radiology, New York, NY, USA. pierre-hugues.vivier@chu-rouen.fr
authors: Pierre-Hugues
authors: PH
authors: Vivier
authors: Pippa
authors: P
authors: Storey
authors: Hersh
authors: H
authors: Chandarana
authors: Akira
authors: A
authors: Yamamoto
authors: Kristopher
authors: K
authors: Tantillo
authors: Umer
authors: U
authors: Khan
authors: Jeff L
authors: JL
authors: Zhang
authors: Eric E
authors: EE
authors: Sigmund
authors: Henry
authors: H
authors: Rusinek
authors: James S
authors: JS
authors: Babb
authors: Michael
authors: M
authors: Bubenheim
authors: Vivian S
authors: VS
authors: Lee
mesh_terms: D000284:Administration, Oral; D000328:Adult; D004232:Diuretics / Q000008:administration & dosage; D005260:Female; D005665:Furosemide / Q000008:administration & dosage*; D006801:Humans; D007275:Injections, Intravenous; D007668:Kidney / Q000187:drug effects / Q000378:metabolism*; D007677:Kidney Function Tests / Q000379:methods; D018810:Magnetic Resonance Angiography / Q000379:methods*; D008297:Male; D010092:Oximetry / Q000379:methods*; D010100:Oxygen / Q000097:blood*; D012079:Renal Circulation / Q000187:drug effects / Q000502:physiology*; D014018:Tissue Distribution; D014867:Water / Q000008:administration & dosage*; D055815:Young Adult
chemical_list: D004232:Diuretics; D014867:Water; D005665:Furosemide; D010100:Oxygen
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