title: T1 mapping for myocardial extracellular volume measurement by CMR: bolus only versus primed infusion technique.
abstract: OBJECTIVE
  The aim of this study was to determine the accuracy of the contrast "bolus only" T1 mapping cardiac magnetic resonance (CMR) technique for measuring myocardial extracellular volume fraction (ECV).
  
  
  BACKGROUND
  Myocardial ECV can be measured with T1 mapping before and after contrast agent if the contrast agent distribution between blood/myocardium is at equilibrium. Equilibrium distribution can be achieved with a primed contrast infusion (equilibrium contrast-CMR [EQ-CMR]) or might be approximated by the dynamic equilibration achieved by delayed post-bolus measurement. This bolus only approach is highly attractive, but currently limited data support its use. We compared the bolus only technique with 2 independent standards: collagen volume fraction (CVF) from myocardial biopsy in aortic stenosis (AS); and the infusion technique in 5 representative conditions.
  
  
  METHODS
  One hundred forty-seven subjects were studied: healthy volunteers (n = 50); hypertrophic cardiomyopathy (n = 25); severe AS (n = 22); amyloid (n = 20); and chronic myocardial infarction (n = 30). Bolus only (at 15 min) and infusion ECV measurements were performed and compared. In 18 subjects with severe AS the results were compared with histological CVF.
  
  
  RESULTS
  The ECV by both techniques correlated with histological CVF (n = 18, r² = 0.69, p < 0.01 vs. r² = 0.71, p < 0.01, p = 0.42 for comparison). Across health and disease, there was strong correlation between the techniques (r² = 0.97). However, in diseases of high ECV (amyloid, hypertrophic cardiomyopathy late gadolinium enhancement, and infarction), Bland-Altman analysis indicates the bolus only technique has a consistent and increasing offset, giving a higher value for ECVs above 0.4 (mean difference ± limit of agreement for ECV <0.4 = -0.004 ± 0.037 vs. ECV >0.4 = 0.040 ± 0.075, p < 0.001).
  
  
  CONCLUSIONS
  Bolus only, T1 mapping-derived ECV measurement is sufficient for ECV measurement across a range of cardiac diseases, and this approach is histologically validated in AS. However, when ECV is >0.4, the bolus only technique consistently measures ECV higher compared with infusion.
authors.affiliation: The Heart Hospital, London, United Kingdom; Institute of Cardiovascular Science, University College London, London, United Kingdom; The Hatter Cardiovascular Institute, University College London, London, United Kingdom.
authors.forename: Steven K
authors.initials: SK
authors.lastname: White
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Sado
authors.forename: Marianna
authors.initials: M
authors.lastname: Fontana
authors.forename: Sanjay M
authors.initials: SM
authors.lastname: Banypersad
authors.forename: Viviana
authors.initials: V
authors.lastname: Maestrini
authors.forename: Andrew S
authors.initials: AS
authors.lastname: Flett
authors.forename: Stefan K
authors.initials: SK
authors.lastname: Piechnik
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Robson
authors.forename: Derek J
authors.initials: DJ
authors.lastname: Hausenloy
authors.forename: Amir M
authors.initials: AM
authors.lastname: Sheikh
authors.forename: Philip N
authors.initials: PN
authors.lastname: Hawkins
authors.forename: James C
authors.initials: JC
authors.lastname: Moon
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001706:Biopsy; D002312:Cardiomyopathy, Hypertrophic / Q000175:diagnosis*; D003287:Contrast Media; D005109:Extracellular Matrix / Q000473:pathology*; D005260:Female; D019786:Gadolinium DTPA; D006801:Humans; D019028:Magnetic Resonance Imaging, Cine / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009206:Myocardium / Q000473:pathology*; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D055815:Young Adult
chemical_list: D003287:Contrast Media; D019786:Gadolinium DTPA
keywords: AS; CMR; CVF; ECV; EQ-CMR; HCM; LGE; ROI; ShMOLLI; T1 mapping; aortic stenosis; bolus; cardiac imaging techniques; cardiac magnetic resonance; collagen volume fraction (%); dynamic; equilibrium; equilibrium contrast cardiac magnetic resonance; extracellular space; extracellular volume; extracellular volume fraction; fibrosis; hypertrophic cardiomyopathy; infusion; late gadolinium enhancement; region of interest; shortened modified look-locker inversion recovery