title: Assessment of renal artery stenosis using intravoxel incoherent motion diffusion-weighted magnetic resonance imaging analysis.
abstract: OBJECTIVE
  Diffusion-weighted magnetic resonance imaging is a powerful tool to assess renal morphology. However, its quantitative index, apparent diffusion coefficient (ADC), derived from a conventional monoexponential model can vary with both functional and structural alterations as well as the choice of b values. In contrast, the intravoxel incoherent motion (IVIM) biexponential model provides independent parameters that may represent broader aspects of renal pathophysiology. We hypothesized that IVIM analysis is capable of detecting early morphological and functional changes in the swine kidney distal to renal artery stenosis (RAS).
  
  
  METHODS
  Domestic pigs divided into 3 groups (n = 6-7 each) were studied for 16 weeks. Unilateral RAS was induced in 2 groups, of which 1 group was fed with a high-cholesterol diet to induce early atherosclerosis (ARAS), whereas the other (RAS) consumed regular diet. The third group included healthy pigs that served as control sham. Renal function, hemodynamics, tubular function, and morphology were assessed using multidetector computed tomography and histology. Diffusion-weighted magnetic resonance images were acquired at 3T and analyzed using monoexponential and biexponential models. Parameters of ADC and IVIM (diffusivity [D(t)], flow-dependent pseudodiffusivity [D(p)], and fluid fraction [f(p)]) were calculated in the cortex and medulla of the stenotic (STK) and contralateral kidneys (CLKs). Results were analyzed using analysis of variance, Student t test, and regression analysis.
  
  
  RESULTS
  In both RAS and ARAS, the STK shrank and the CLK underwent hypertrophy. Glomerular filtration rate and renal blood flow declined in STKs, and CLKs manifested hyperfiltration. In addition, ARAS kidneys showed reduced mean transit time in distal tubular segments. Apparent diffusion coefficient and diffusivity both decreased in STK of RAS and ARAS. D(p) and f(p) were elevated in both the STK and CLK of RAS and more prominently in ARAS. The STK cortical ADC and D(t) correlated inversely with the degree of fibrosis and directly with glomerular filtration rate. Furthermore, D(p) correlated with tubular injury score in all kidneys.
  
  
  CONCLUSIONS
  Apparent diffusion constant and D(t) both correlated with cortical and medullary fibrosis; however, IVIM-derived parameters can detect subtle functional and structural changes in the post-STK and may also serve as markers for tubular injury.
authors.affiliation: From the Division of Nephrology and Hypertension, Mayo Clinic, Rochester, MN.
authors.forename: Behzad
authors.initials: B
authors.lastname: Ebrahimi
authors.forename: Naveen
authors.initials: N
authors.lastname: Rihal
authors.forename: John R
authors.initials: JR
authors.lastname: Woollard
authors.forename: James D
authors.initials: JD
authors.lastname: Krier
authors.forename: Alfonso
authors.initials: A
authors.lastname: Eirin
authors.forename: Lilach O
authors.initials: LO
authors.lastname: Lerman
mesh_terms: D000818:Animals; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D004195:Disease Models, Animal; D005260:Female; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D012077:Renal Artery / Q000473:pathology*; D012078:Renal Artery Obstruction / Q000175:diagnosis*; D012079:Renal Circulation
references.citation: Kidney Int. 2001 Mar;59(3):932-40
references.pmid: 11231348
references.citation: Radiology. 1991 Feb;178(2):543-8
references.pmid: 1987621
references.citation: Radiology. 2010 Mar;254(3):783-92
references.pmid: 20089719
references.citation: Invest Radiol. 2013 Mar;48(3):140-4
references.pmid: 23249648
references.citation: Arterioscler Thromb Vasc Biol. 2003 Jul 1;23(7):1295-301
references.pmid: 12750121
references.citation: Am J Med. 2007 Jul;120(7):561-2
references.pmid: 17602923
references.citation: PLoS One. 2013 Jul 03;8(7):e67474
references.pmid: 23844014
references.citation: Am J Physiol Renal Physiol. 2001 Oct;281(4):F630-8
references.pmid: 11553509
references.citation: Eur J Radiol. 1998 Feb;26(3):297-303
references.pmid: 9587760
references.citation: N Engl J Med. 2001 Feb 8;344(6):431-42
references.pmid: 11172181
references.citation: Magn Reson Med. 2003 Feb;49(2):288-98
references.pmid: 12541249
references.citation: Radiology. 2007 May;243(2):405-12
references.pmid: 17456868
references.citation: J Clin Invest. 2004 Jul;114(1):5-14
references.pmid: 15232604
references.citation: J Am Soc Nephrol. 1999 Jul;10(7):1455-65
references.pmid: 10405201
references.citation: Radiology. 1997 Oct;205(1):128-36
references.pmid: 9314974
references.citation: Radiology. 2004 Jun;231(3):702-9
references.pmid: 15163810
references.citation: Invest Radiol. 2013 Dec;48(12):834-42
references.pmid: 23907103
references.citation: Radiology. 2010 Jun;255(3):772-80
references.pmid: 20406881
references.citation: Radiology. 2012 Jun;263(3):758-69
references.pmid: 22523327
references.citation: Radiology. 2005 Jun;235(3):911-7
references.pmid: 15845792
references.citation: AJR Am J Roentgenol. 2011 Jun;196(6):1351-61
references.pmid: 21606299
references.citation: Eur J Radiol. 2008 Jan;65(1):148-53
references.pmid: 17537606
references.citation: Am J Physiol Renal Physiol. 2010 Jul;299(1):F135-40
references.pmid: 20462971
references.citation: Hum Brain Mapp. 1999;8(2-3):80-5
references.pmid: 10524596
references.citation: Kidney Int. 1984 May;25(5):824-9
references.pmid: 6236324
references.citation: Radiology. 1997 Apr;203(1):45-53
references.pmid: 9122415
references.citation: J Magn Reson Imaging. 2007 Sep;26(3):678-81
references.pmid: 17729335
references.citation: Invest Radiol. 2012 Dec;47(12):688-96
references.pmid: 22996315
references.citation: Circulation. 2002 Aug 27;106(9):1165-71
references.pmid: 12196346
references.citation: Invest Radiol. 2011 May;46(5):285-91
references.pmid: 21102345
references.citation: Radiology. 1988 Aug;168(2):497-505
references.pmid: 3393671