Characterization and compensation of f(0) inhomogeneity artifact in spiral hyperpolarized C-13 imaging of the human heart

Purpose: This study aimed to investigate the role of regional f(0) inhomogeneity in spiral hyperpolarized C-13 image quality and to develop measures to alleviate these effects. Methods: Field map correction of hyperpolarized C-13 cardiac imaging using spiral readouts was evaluated in healthy subjects. Spiral readouts with differing duration (26 and 45 ms) but similar resolution were compared with respect to off-resonance performance and image quality. An f(0) map-based image correction based on the multifrequency interpolation (MFI) method was implemented and compared to correction using a global frequency shift alone. Estimation of an unknown frequency shift was performed by maximizing a sharpness objective based on the Sobel variance. The apparent full width half at maximum (FWHM) of the myocardial wall on [C-13]bicarbonate was used to estimate blur. Results: Mean myocardial wall FWHM measurements were unchanged with the short readout pre-correction (14.1 +/- 2.9 mm) and post-MFI correction (14.1 +/- 3.4 mm), but significantly decreased in the long waveform (20.6 +/- 6.6 mm uncorrected, 17.7 +/- 7.0 corrected, P =.007). Bicarbonate signal-to-noise ratio (SNR) of the images acquired with the long waveform were increased by 1.4 +/- 0.3 compared to those acquired with the short waveform (predicted 1.32). Improvement of image quality was observed for all metabolites with f(0) correction. Conclusions: f(0)-map correction reduced blur and recovered signal from dropouts, particularly along the posterior myocardial wall. The low image SNR of [C-13]bicarbonate can be compensated with longer duration readouts but at the expense of increased f(0) artifacts, which can be partially corrected for with the proposed methods.