Dose and pulse sequence considerations for hyperpolarized 129Xe ventilation MRI

PurposeThe aim of this study was to evaluate the effect of hyperpolarized 129Xe dose on image signal-to-noise ratio (SNR) and ventilation defect conspicuity on both multi-slice gradient echo and isotropic 3D-radially acquired ventilation MRI.Materials and methodsTen non-smoking older subjects (ages 60.8 ± 7.9 years) underwent hyperpolarized (HP) 129Xe ventilation MRI using both GRE and 3D-radial acquisitions, each tested using a 71 ml (high) and 24 ml (low) dose equivalent (DE) of fully polarized, fully enriched 129Xe. For all images SNR and ventilation defect percentage (VDP) were calculated.ResultsNormalized SNR (SNRn), obtained by dividing SNR by voxel volume and dose was higher for high-DE GRE acquisitions (SNRn = 1.9 ± 0.8 ml− 2) than low-DE GRE scans (SNRn = 0.8 ± 0.2 ml− 2). Radially acquired images exhibited a more consistent, albeit lower SNRn (High-DE: SNRn = 0.5 ± 0.1 ml− 2, low-DE: SNRn = 0.5 ± 0.2 ml− 2). VDP was indistinguishable across all scans.ConclusionsThese results suggest that images acquired using the high-DE GRE sequence provided the highest SNRn, which was in agreement with previous reports in the literature. 3D-radial images had lower SNRn, but have advantages for visual display, monitoring magnetization dynamics, and visualizing physiological gradients. By evaluating normalized SNR in the context of dose-equivalent formalism, it should be possible to predict 129Xe dose requirements and quantify the benefits of more efficient transmit/receive coils, field strengths, and pulse sequences.