Improved quantitative 19 F MR molecular imaging with flip angle calibration and B 1 ‐mapping compensation

Purpose To improve 19 F flip angle calibration and compensate for B 1 inhomogeneities in quantitative 19 F MRI of sparse molecular epitopes with perfluorocarbon (PFC) nanoparticle (NP) emulsion contrast agents. Materials and 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 B 1 ‐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 B 1 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. Conclusion 19 F flip angle calibration and B 1 ‐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. J. Magn. Reson. Imaging 2015;42:488–494.