Characterization and compensation of f0 inhomogeneity artifact in spiral hyperpolarized 13 C imaging of the human heart

Abstract

Purpose: This study aimed to investigate the role of regional $f_0$ inhomogeneity in spiral hyperpolarized ¹³ C image quality and to develop measures to alleviate these effects.

Methods: Field map correction of hyperpolarized ¹³ C 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 [¹³ C]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 [¹³ C]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.

Keywords: $B_0$; $f_0$; artifacts; bicarbonate; cardiac; hyperpolarized; main field inhomogeneity; multifrequency interpolation; myocardium; spiral.