title: Intravoxel incoherent motion (IVIM) imaging at different magnetic field strengths: what is feasible?
abstract: BACKGROUND
  Due to limited SNR the cerebral applications of the intravoxel incoherent motion (IVIM) concept have been sparse. MRI hardware developments have resulted in improved SNR and this may justify a reassessment of IVIM imaging for non-invasive quantification of the cerebral blood volume (CBV) as a first step toward determining the optimal field strength.
  
  
  OBJECTIVE
  To investigate intravoxel incoherent motion imaging for its potential to assess cerebral blood volume (CBV) at three different MRI field strengths.
  
  
  METHODS
  Four volunteers were scanned twice at 1.5 T, 3 T as well as 7 T. By correcting for field-strength-dependent effects of relaxation, estimates of corrected CBV (cCBV) were obtained in deep gray matter (DGM), frontal gray matter (FGM) and frontal white matter (FWM), using Bayesian analysis. In addition, simulations were performed to facilitate the interpretation of experimental data.
  
  
  RESULTS
  In DGM, FGM and FWM we obtained cCBV estimates of 2.2 ml/100 ml, 2.7 ml/100 ml, 1.4 ml/100 ml at 1.5 T; 3.7 ml/100 ml, 5.0 ml/100 ml, 3.2 ml/100 ml at 3 T and 15.5 ml/100 ml, 20.3 ml/100 ml, 7.0 ml/100 ml at 7 T.
  
  
  CONCLUSIONS
  Quantitative cCBV values obtained at 1.5 T and 3 T corresponded better to physiological reference values, while 7 T showed the largest deviation from expected values. Simulations of synthetic tissue voxels indicated that the discrepancy at 7 T can partly be explained by SNR issues. Results were generally more repeatable at 7 T (intraclass correlation coefficient, ICC=0.84) than at 1.5 T (ICC=0.68) and 3 T (ICC=0.46).
authors.affiliation: Department of Medical Radiation Physics, Lund University, Lund, Sweden. Electronic address: Anna.Rydhog@med.lu.se.
authors.forename: Anna S
authors.initials: AS
authors.lastname: Rydhög
authors.affiliation: C. J. Gorter Center for High Field MRI, Department of Radiology, LUMC, Leiden, The Netherlands.
authors.forename: Matthias J P
authors.initials: MJ
authors.lastname: van Osch
authors.affiliation: Department of Medical Radiation Physics, Lund University, Lund, Sweden.
authors.forename: Emelie
authors.initials: E
authors.lastname: Lindgren
authors.affiliation: Department of Medical Radiation Physics, Lund University, Lund, Sweden; Lund University Bioimaging Center (LBIC), Lund University, Lund, Sweden.
authors.forename: Markus
authors.initials: M
authors.lastname: Nilsson
authors.affiliation: Center for Medical Imaging and Physiology, Skåne University Hospital, Lund, Sweden.
authors.forename: Jimmy
authors.initials: J
authors.lastname: Lätt
authors.affiliation: Department of Medical Radiation Physics, Lund University, Lund, Sweden; Lund University Bioimaging Center (LBIC), Lund University, Lund, Sweden; Department of Diagnostic Radiology, Lund University, Lund, Sweden.
authors.forename: Freddy
authors.initials: F
authors.lastname: Ståhlberg
authors.affiliation: Department of Medical Radiation Physics, Lund University, Lund, Sweden.
authors.forename: Ronnie
authors.initials: R
authors.lastname: Wirestam
authors.affiliation: Department of Medical Radiation Physics, Lund University, Lund, Sweden.
authors.forename: Linda
authors.initials: L
authors.lastname: Knutsson
mesh_terms: D000328:Adult; D000465:Algorithms; D016477:Artifacts; D001499:Bayes Theorem; D001921:Brain / Q000098:blood supply; D002560:Cerebrovascular Circulation / Q000502:physiology*; D003198:Computer Simulation; D005260:Female; D006801:Humans; D007089:Image Enhancement; D007091:Image Processing, Computer-Assisted; D060526:Magnetic Fields; D008279:Magnetic Resonance Imaging; D008297:Male; D009038:Motion; D012016:Reference Values; D015203:Reproducibility of Results; D059629:Signal-To-Noise Ratio
keywords: 7 Tesla; Cerebral blood volume; IVIM; Intravoxel incoherent motion