title: Advantages and controversies in the era of intrarenal volumetry.
abstract: OBJECTIVE
  Ultrasound is the preferred imaging modality in nephrology. In many kidney diseases, however, more accurate methods are needed to distinguish between relevant intrarenal structures. MRI could be a solution, although the use of MRI contrast has caused severe complications in some cases, and invasive kidney biopsies may follow, even though such small specimens traditionally provide inaccurate quantitative data. We evaluated the usefulness of MRI volumetry and quantitative kidney biopsies to assess glomerular number and volume as well as cortical volume.
  
  
  METHODS
  We specifically highlight an experimental study in which different MRI scans were performed in healthy pigs as well as pigs with unilateral ureteral obstruction to assess intrarenal volume. Single-kidney glomerular filtration rate (GFR) was measured using ureteral cannulation and (51)Cr-EDTA. Kidney biopsies were taken and evaluated employing stereological techniques to measure number and volume of glomeruli. Pigs were sacrificed and kidneys were removed for stereological analysis. Non-contrast-based MRI intrarenal volumes were - without significant difference to intrarenal volumes - obtained using contrast-enhanced MRI and ex vivo techniques.
  
  
  RESULTS
  Kidney biopsies gave valid estimates regarding quantitative parameters, such as mean number and volume of glomeruli in the cortex. Different structural parameters correlated with kidney GFR with high, although varying, correlation coefficients.
  
  
  CONCLUSIONS
  Non-contrast MRI is suitable for estimating intrarenal volumes in healthy and diseased kidneys. We advocate further research in diagnostic modalities combining MRI and biopsies. Major challenges are the cortical architecture and heterogeneous distribution of glomeruli within the kidney.
authors.affiliation: MR Research Center, Aarhus University Hospital, Skejby, Denmark.
authors.forename: Michael
authors.initials: M
authors.lastname: Pedersen
authors.forename: Kristian
authors.initials: K
authors.lastname: Karstoft
authors.forename: Anders
authors.initials: A
authors.lastname: Lødrup
authors.forename: Bente
authors.initials: B
authors.lastname: Jespersen
authors.forename: Jens R
authors.initials: JR
authors.lastname: Nyengaard
mesh_terms: D000818:Animals; D001706:Biopsy / Q000379:methods; D005919:Glomerular Filtration Rate; D006652:Histological Techniques; D007678:Kidney Glomerulus / Q000033:anatomy & histology* / Q000473:pathology*; D008279:Magnetic Resonance Imaging; D009929:Organ Size; D013552:Swine; D014517:Ureteral Obstruction / Q000150:complications