title: Phase-based arterial input functions in humans applied to dynamic contrast-enhanced MRI: potential usefulness and limitations.
abstract: OBJECTIVE
  Phase-based arterial input functions (AIFs) provide a promising alternative to standard magnitude-based AIFs, for example, because inflow effects are avoided. The usefulness of phase-based AIFs in clinical dynamic contrast-enhanced MRI (DCE-MRI) was investigated, and relevant pitfalls and sources of uncertainty were identified.
  
  
  METHODS
  AIFs were registered from eight human subjects on, in total, 21 occasions. AIF quality was evaluated by comparing AIFs from right and left internal carotid arteries and by assessing the reliability of blood plasma volume estimates.
  
  
  RESULTS
  Phase-based AIFs yielded an average bolus peak of 3.9 mM and a residual concentration of 0.37 mM after 3 min, (0.033 mmol/kg contrast agent injection). The average blood plasma volume was 2.7% when using the AIF peak in the estimation, but was significantly different (p < 0.0001) and less physiologically reasonable when based on the AIF tail concentration. Motion-induced phase shifts and accumulation of contrast agent in background tissue regions were identified as main sources of uncertainty.
  
  
  CONCLUSIONS
  Phase-based AIFs are a feasible alternative to magnitude AIFs, but sources of errors exist, making quantification difficult, especially of the AIF tail. Improvement of the technique is feasible and also required for the phase-based AIF approach to reach its full potential.
authors.affiliation: Division of Radiation Physics, Department of Radiation Sciences, Umeå University, SE-901 87 Umeå, Sweden. anders.garpebring@radfys.umu.se
authors.forename: Anders
authors.initials: A
authors.lastname: Garpebring
authors.forename: Ronnie
authors.initials: R
authors.lastname: Wirestam
authors.forename: Jun
authors.initials: J
authors.lastname: Yu
authors.forename: Thomas
authors.initials: T
authors.lastname: Asklund
authors.forename: Mikael
authors.initials: M
authors.lastname: Karlsson
mesh_terms: D000368:Aged; D000465:Algorithms; D002339:Carotid Arteries / Q000502:physiology*; D003287:Contrast Media; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D008955:Models, Cardiovascular; D010953:Plasma Volume / Q000502:physiology*; D012044:Regression Analysis; D015203:Reproducibility of Results
chemical_list: D003287:Contrast Media