Balanced UTE-SSFP for ¹⁹F MR imaging of complex spectra

Purpose A novel technique for highly sensitive detection of multiresonant fluorine imaging agents was designed and tested with the use of dual-frequency ¹⁹F/¹H ultrashort echo times (UTE) sampled with a balanced steady-state free precession (SSFP) pulse sequence and three-dimensional (3D) radial readout. Methods Feasibility of 3D radial balanced UTE-SSFP imaging was demonstrated for a phantom comprising liquid perfluorooctyl bromide (PFOB). Sensitivity of the pulse sequence was measured and compared with other sequences imaging the PFOB (CF₂)₆ line group including UTE radial gradient-echo (GRE) at α = 30°, as well as Cartesian GRE, balanced SSFP, and fast spin-echo (FSE). The PFOB CF₃ peak was also sampled with FSE. Results The proposed balanced UTE-SSFP technique exhibited a relative detection sensitivity of 51 μmolPFOB-1min^-1/2 (α = 30°), at least twice that of other sequence types with either 3D radial (UTE GRE: 20 μmolPFOB-1min^-1/2) or Cartesian k-space filling (GRE: 12 μmolPFOB-1min^-1/2; FSE: 16 μmolPFOB-1min^-1/2; balanced SSFP: 23 μmolPFOB-1min^-1/2). In vivo imaging of angiogenesis-targeted PFOB nanoparticles was demonstrated in a rabbit model of cancer on a clinical 3 Tesla scanner. Conclusion A new dual ¹⁹F/¹H balanced UTE-SSFP sequence manifests high SNR, with detection sensitivity more than two-fold better than traditional techniques, and alleviates imaging problems caused by dephasing in complex spectra. Magn Reson Med 74:537-543, 2015.