3D diffusion‐weighted ¹²⁹Xe MRI for whole lung morphometry

Abstract

PurposeTo obtain whole lung morphometry measurements from 129Xe in a single breath‐hold with 3D multiple b‐value 129Xe diffusion‐weighted MRI (DW‐MRI) with an empirically optimized diffusion time and compressed sensing for scan acceleration.MethodsProspective three‐fold undersampled 3D multiple b‐value hyperpolarized 129Xe DW‐MRI datasets were acquired, and the diffusion time (Δ) was iterated so as to provide diffusive length scale (LmD) estimates from the stretched exponential model (SEM) that are comparable to those from 3He. The empirically optimized 129Xe diffusion time was then implemented with a four‐fold undersampling scheme and was prospectively benchmarked against 3He measurements in a cohort of five healthy volunteers, six ex‐smokers, and two chronic obstructive pulmonary disease patients using both SEM‐derived LmD and cylinder model (CM)‐derived mean chord length (Lm).ResultsGood agreement between the mean 129Xe and 3He LmD (mean difference, 2.2%) and Lm (mean difference, 1.1%) values was obtained in all subjects at an empirically optimized 129Xe Δ = 8.5 ms.ConclusionCompressed sensing has facilitated single‐breath 3D multiple b‐value 129Xe DW‐MRI acquisitions, and results at 129Xe Δ = 8.5 ms indicate that 129Xe provides a viable alternative to 3He for whole lung morphometry mapping with either the SEM or CM. Magn Reson Med 79:2986–2995, 2018. © 2017 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Comparison of in vivo lung morphometry models from 3D multiple b‐value 3He and 129Xe diffusion‐weighted MRI

“…The 3D 129 Xe DW‐MRI acquisition parameters were 550 mL hyperpolarized 129 Xe (approximately 30% polarization) (balanced with 450 mL of N 2 ), 4 interleaves (b = 0, 12, 20, 30 s/cm 2 ), FOV = 40 32.5 27 cm 3 , voxel size = 6.25 6.25 15 mm 3 , TE/TR = 14.0/17.3 ms, diffusion time = 8.5 ms (maximum diffusion gradient strength = 32.6 mT/m, ramp = 0.3 ms, plateau = 2.3 ms, gap = 5.6 ms), flip angle = 3.1°, and bandwidth = ±6.97 kHz. The respective diffusion times chosen for the two gases (Δ He = 1.6 ms and Δ Xe = 8.5 ms) were empirically optimized such that comparable mean Lm D and Lm measurements are obtained with both 3 He and 129 Xe …”

“…3 He and 129 Xe DW‐MRI were both acquired on a 1.5T GE HDx scanner using flexible quadrature transmit/receive vest coils (Clinical MR Solutions, Brookfield, WI) following the inhalation of a 1‐L gas mixture from functional residual capacity with 3D spoiled gradient‐echo sequences and compressed sensing (CS) . The 3D 3 He DW‐MRI acquisition parameters were 250 mL hyperpolarized 3 He (approximately 25% polarization) (balanced with 750 mL of N 2 ), 4 interleaves (b = 0, 1.6, 4.2, 7.2 s/cm 2 ), FOV = 40 32.5 28.8 cm 3 , voxel size = 4.17 4.17 12 mm 3 , TE/TR = 4.2/6.0 ms, diffusion time = 1.6 ms (maximum diffusion gradient strength = 30 mT/m, ramp = 0.3 ms, plateau = 1.0 ms), flip angle = 1.9°, and bandwidth = ±31.25 kHz.…”

“…In Sukstanskii et al, new phenomenological expressions were derived for 129 Xe DW‐MRI at Δ = 5 ms; however, it was also noted that when the same theoretical free‐diffusion length is probed with both nuclei (i.e., Δ He = 1.6 ms and Δ Xe = 10 ms), the original 3 He‐based expressions should in theory be valid. However, in our recent work with the derivation of an empirically optimized 129 Xe Δ = 8.5 ms, it was concluded that comparable 3 He and 129 Xe CM Lm can be obtained at this diffusion time using the 3 He‐based CM phenomenological expressions. Therefore, in this work in which 129 Xe Δ = 8.5 ms is implemented, 129 Xe‐derived R and h were related to 129 Xe and coefficients using the same expressions as for the 3 He data (Equations ).…”

“…Much work has been performed in modeling the effects of restricted diffusion inside geometrical models of lung microstructure, including cylindrical geometries, acinar trees, branching structures, alveolar ducts, and porous media models . Alternative strategies have also been proposed that do not rely on geometrical assumptions of acinar structure, such as q‐space transform analysis, diffusion kurtosis, and stretch exponential mathematical models . The cylinder model (CM) and the stretched exponential model (SEM) are two theoretical gas diffusion models that can derive in vivo measurements of acinar length scale on a voxel‐by‐voxel basis.…”

Rapid assessment of pulmonary gas transport with hyperpolarized 129Xe MRI using a 3D radial double golden‐means acquisition with variable flip angles

“…The modality can be coarsely divided into two categories: gas-phase (GP) and dissolved-phase (DP) imaging. GP MRI can provide information about ventilation patterns within the pulmonary airspaces (1–4), the rudimentary geometries of these airspaces as derived from apparent diffusion coefficient measurements (5–8), and regional oxygen concentration (9–11). DP MRI, on the other hand, enables the quantification of gas exchange by the lung parenchyma (12–18), as well as pulmonary circulation at the alveolar level (19–26).…”