Dose and pulse sequence considerations for hyperpolarized (129)Xe ventilation MRI

Abstract

Purpose: The aim of this study was to evaluate the effect of hyperpolarized (129)Xe 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 methods: Ten non-smoking older subjects (ages 60.8±7.9years) underwent hyperpolarized (HP) (129)Xe ventilation MRI using both GRE and 3D-radial acquisitions, each tested using a 71ml (high) and 24ml (low) dose equivalent (DE) of fully polarized, fully enriched (129)Xe. For all images SNR and ventilation defect percentage (VDP) were calculated.

Results: Normalized SNR (SNRn), obtained by dividing SNR by voxel volume and dose was higher for high-DE GRE acquisitions (SNRn=1.9±0.8ml(-2)) than low-DE GRE scans (SNRn=0.8±0.2ml(-2)). Radially acquired images exhibited a more consistent, albeit lower SNRn (High-DE: SNRn=0.5±0.1ml(-2), low-DE: SNRn=0.5±0.2ml(-2)). VDP was indistinguishable across all scans.

Conclusions: These 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 (129)Xe dose requirements and quantify the benefits of more efficient transmit/receive coils, field strengths, and pulse sequences.

Keywords: Hyperpolarized (129)Xe MRI; Pulse sequence; Signal-to-noise ratio; Ventilation defect.

Copyright © 2015 Elsevier Inc. All rights reserved.

Figures

Figure 1

Representative 1H SSFP and free-breathing 3D-radial 1H anatomical images as well as 129Xe ventilation images acquired with low and high 129Xe dose equivalents using both multi-slice GRE and 3D radial sequences. Features that appear similar across different images are indicated by arrows.

Figure 2

a) SNR for ventilation images acquired using GRE and radial sequences at high and low dose. b) SNR normalized by voxel volume and dose equivalent polarization.

Figure 3

Representative 129Xe ventilation images and associated linear-binning maps for high- and low-dose equivalent images acquired with each acquisition. Note, the 3D-radial acquisition is isotropic and can be reformatted in any view plane. Features that appear similar across different images and binning maps are indicated by arrows.

Figure 4

Comparison of ventilation defect percentage (VDP) derived from both sequences at both high and low 129Xe dose equivalents. No statistically significant differences were observed across any acquisitions. The GRE images, however, tended to exhibit higher VDP than 3D-radial, and high-dose equivalent images tended to have higher VDP than low-dose equivalent. Error bars represent standard error about the mean.

Figure 5

Correlations and Bland-Altman plots of the VDP generated with different acquisition sequences and with different 129Xe dose-equivalents.

Figure 6

Comparison of the SNR variation from the anterior-to-posterior slice positions for both GRE and 3D-radial acquisitions.

Figure 7

Possible benefits of 3D-radial acquisition illustrated in subject with changing right-lung volume. (a) Multi-slice GRE reference image showing homogeneous distribution. (b) 3D-radial 129Xe ventilation image shows a false lung border caused by probable motion in the right basal lung during acquisition. (c) 3D-radial image reconstructed 700 frames (2.3 seconds) at a time showing that the right lung position changed around frame 1400 (4.6 seconds). (d) This artifact of diaphragm movement was corrected by reconstructing only frames 1401 to 4601 (4.6-15.2 seconds).