Rapid single-breath hyperpolarized noble gas MRI-based biomarkers of airspace enlargement.

Background: Multi-b diffusion-weighted hyperpolarized-gas MRI measures pulmonary airspace-enlargement using apparent diffusion coefficients (ADCs) and mean-linear-intercepts (L _m ).
Purpose: To develop single-breath 3D multi-b diffusion-weighted ³ He and ¹²⁹ Xe MRI using k-space undersampling. Rapid, cost-efficient, single-breath acquisitions may facilitate clinical translation.
Study Type: Prospective.
Subjects: We evaluated 12 participants, including nine subjects (mean age = 69 ± 9) who were included in the retrospective experiment and three chronic pulmonary obstruction disease (COPD) patients (mean age = 81 ± 6) who participated in the prospective study.
Field Strength: A whole-body 3 T 2D/3D fast gradient recall echo (FGRE) sequence.
Assessment: Hyperpolarized ³ He/ ¹²⁹ Xe MRI, spirometry, plethysmography computed tomography (CT). We evaluated ¹²⁹ Xe ADC/morphometry estimates by retrospectively undersampling previously acquired fully sampled multibreath, multi-b diffusion-weighted data. Next, we prospectively evaluated the feasibility of accelerated (AF = 7) ³ He MRI static-ventilation/T ₂ * (extra short-TE, b = 0 image) and ADC/morphometry (five b-values) maps using a single gas-dose and 16-second breath-hold. To conservatively evaluate cost-improvement, we compared total costs of single vs. multiple ¹²⁹ Xe doses.
Statistical Tests: Multivariate analysis of variance, independent t-tests and voxel-by-voxel basis difference test.
Results: For the retrospectively undersampled ¹²⁹ Xe data, a nonsignificant mean difference for ADC/L _m of 14%/12%, 12%/8%, and 11%/9% was observed (all, P > 0.4) between the fully sampled and accelerated data for the never-smoker, COPD, and alpha-1 antitrypsin deficiency (AATD) groups, respectively. The control never-smoker group had significantly lower ADC (P < 0.001) and L _m (P < 0.001) than the COPD/AATD group for both fully sampled and accelerated data. For the prospectively acquired ³ He MRI data, static-ventilation, T ₂ *, ADC, and morphometry maps were acquired using a single 16-second breath-hold scan and single gas dose. Accelerated imaging resulted in cost savings of ~$US 1000/patient, a conservative estimate based on ¹²⁹ Xe MRI dose savings (single vs. five doses).
Data Conclusion: This is a proof-of-concept demonstration of accelerated (7×) morphometry that shows that less cost- and time-efficient multibreath methods that lead to variability and patient fatigue may be avoided in the future.
Level of Evidence: 2 Technical Efficacy: Stage 5 J. Magn. Reson. Imaging 2018.
(© 2018 International Society for Magnetic Resonance in Medicine.)