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

Abstract

Purpose A novel technique for highly sensitive detection of multi-resonant fluorine imaging agents was designed and tested with the use of dual-frequency 19F/1H ultra-short echo times (UTE) sampled with a balanced steady-state free precession (SSFP) pulse sequence and 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 to 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 3T scanner. Conclusion A new dual 19F/1H balanced UTE-SSFP sequence manifests high SNR, with detection sensitivity more than twofold better than traditional techniques, and alleviates imaging problems caused by dephasing in complex spectra.

Characterization of perfluorocarbon relaxation times and their influence on the optimization of fluorine-19 MRI at 3 tesla

“…This value, when normalized as in the present study, resulted in a detection limit of 5 mM, which is comparable to those obtained in the present study for PFCE at 3T. Goette et al recently analyzed a PFOB phantom with a bSSFP UTE pulse sequence at 3T . The T 1 and T 2 relaxation times for the CF 3 (θ) were measured and agreed with those measured in the present study.…”

“…For PFOB, only the CF 3 (u) resonance group was used and therefore only 3 out of 17 19 F nuclei were excited. As reported previously (34), this resulted in a significantly higher detection limit than PFPE and PFCE. In general, imaging performed at 37 C for both pulse sequences resulted in a higher detection limit, most likely due to higher T 1 relaxation times and thus lower T 2 /T 1 ratios.…”

“…However, its complex spectrum causes chemical shift artifacts and signal loss due to homonuclear J‐coupling. As reported in previous studies, this technical hurdle can be overcome through the use of a bSSFP ultrashort echo‐time (UTE) pulse sequence , the use of a multi chemical shift selective (MCSS) TSE pulse sequence , or the use of a SE sequence with a specific BW of the refocusing pulse .…”

Iterative reconstruction of radially-sampled 31 P bSSFP data using prior information from 1 H MRI

“…Radially-sampled sequences have already been utilized for other non-proton MRI applications, especially for isotopes with nuclear spin I N ½, where short echo times are required due to faster relaxation [49]. Similar approaches investigating the densityadaption for 1 H MRI [50], fluorine ( 19 F) bSSFP [51], or 31 P bSSFP [52] have already led to promising results. Although 31 P-containing metabolites feature longer relaxation times, a radial acquisition technique may be advantageous in combination with an iterative reconstruction.…”

An iterative sparse deconvolution method for simultaneous multicolor 19F‐MRI of multiple contrast agents

“…Several strategies have been proposed to avoid or mitigate these. The first is spectrally selective excitation and selective suppression of certain resonances, [10][11][12][13] which can also be used to image multiple different compounds, [14][15][16] at the cost of increased scan times and excluding signal of nonexcited resonances.…”