title: Improved quantitative (19) F MR molecular imaging with flip angle calibration and B1 -mapping compensation.
abstract: OBJECTIVE
  To improve (19) F flip angle calibration and compensate for B1 inhomogeneities in quantitative (19) F MRI of sparse molecular epitopes with perfluorocarbon (PFC) nanoparticle (NP) emulsion contrast agents.
  
  
  METHODS
  Flip angle sweep experiments on PFC-NP point source phantoms with three custom-designed (19) F/(1) H dual-tuned coils revealed a difference in required power settings for (19) F and (1) H nuclei, which was used to calculate a calibration ratio specific for each coil. An image-based correction technique was developed using B1 -field mapping on (1) H to correct for (19) F and (1) H images in two phantom experiments.
  
  
  RESULTS
  Optimized (19) F peak power differed significantly from that of (1) H power for each coil (P < 0.05). A ratio of (19) F/(1) H power settings yielded a coil-specific and spatially independent calibration value (surface: 1.48 ± 0.06; semicylindrical: 1.71 ± 0.02, single-turn-solenoid: 1.92 ± 0.03). (1) H-image-based B1 correction equalized the signal intensity of (19) F images for two identical (19) F PFC-NP samples placed in different parts of the field, which were offset significantly by ~66% (P < 0.001), before correction.
  
  
  CONCLUSIONS
  (19) F flip angle calibration and B1 -mapping compensations to the (19) F images employing the more abundant (1) H signal as a basis for correction resulted in a significant change in the quantification of sparse (19) F MR signals from targeted PFC NP emulsions.
authors.affiliation: Department of Biomedical Engineering, Washington University in St. Louis, Missouri, USA.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Goette
authors.affiliation: Department of Biomedical Engineering, Washington University in St. Louis, Missouri, USA.|Department of Medicine, Washington University in St. Louis, Missouri, USA.
authors.forename: Gregory M
authors.initials: GM
authors.lastname: Lanza
authors.affiliation: Department of Biomedical Engineering, Washington University in St. Louis, Missouri, USA.|Philips Healthcare, Cleveland, Ohio, USA.
authors.forename: Shelton D
authors.initials: SD
authors.lastname: Caruthers
authors.affiliation: Department of Biomedical Engineering, Washington University in St. Louis, Missouri, USA.|Department of Medicine, Washington University in St. Louis, Missouri, USA.
authors.forename: Samuel A
authors.initials: SA
authors.lastname: Wickline
mesh_terms: D000465:Algorithms; D016477:Artifacts; D002138:Calibration; D004867:Equipment Design; D019544:Equipment Failure Analysis; D008279:Magnetic Resonance Imaging / Q000295:instrumentation* / Q000379:methods; D009682:Magnetic Resonance Spectroscopy / Q000295:instrumentation* / Q000379:methods; D057054:Molecular Imaging / Q000379:methods*; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
keywords: B1 correction; RF power settings; flip angle calibration; molecular imaging; perfluorocarbon nanoparticles; quantitative 19F MRI