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

Purpose Multi‐b diffusion‐weighted hyperpolarized inhaled‐gas MRI provides imaging biomarkers of terminal airspace enlargement including ADC and mean linear intercept (Lm), but clinical translation has been limited because image acquisition requires relatively long or multiple breath‐holds that are not well‐tolerated by patients. Therefore, we aimed to accelerate single breath‐hold 3D multi‐b diffusion‐weighted 129Xe MRI, using k‐space undersampling in imaging direction using a different undersampling pattern for different b‐values combined with the stretched exponential model to generate maps of ventilation, apparent transverse relaxation time constant (T2∗), ADC, and Lm values in a single, short breath‐hold; accelerated and non‐accelerated measurements were directly compared. Methods We evaluated multi‐b (0, 12, 20, 30, and 45.5 s/cm2) diffusion‐weighted 129Xe T2∗/ADC/morphometry estimates using acceleration factor (AF = 1 and 7) and multi‐breath sampling in 3 volunteers (HV), and 6 participants with alpha‐1 antitrypsin deficiency (AATD). Results For the HV subgroup, mean differences of 5%, 2%, and 8% were observed between fully sampled and undersampled k‐space for ADC, Lm, and T2∗ values, respectively. For the AATD subgroup, mean differences were 9%, 6%, and 12% between fully sampled and undersampled k‐space for ADC, Lm and T2∗ values, respectively. Although mean differences of 1% and 4.5% were observed between accelerated and multi‐breath sampled ADC and Lm values, respectively, mean ADC/Lm estimates were not significantly different from corresponding mean ADCM/LmM or mean ADCA/LmA estimates (all P > 0.60 , A = undersampled and M = multi‐breath sampled). Conclusions Accelerated multi‐b diffusion‐weighted 129Xe MRI is feasible at AF = 7 for generating pulmonary ADC and Lm in AATD and normal lung.

{Lm}_{D}^{He}

and

{Lm}_{D}^{xe}

estimates was previously observed for a small group of COPD patients, where longer Δ Xe (8.5 ms) was used for inhaled 129 Xe/N 2 gas mixture …”

Section: Discussionsupporting

confidence: 61%

Section: Discussionmentioning

confidence: 99%

Accelerated ¹²⁹Xe MRI morphometry of terminal airspace enlargement: Feasibility in volunteers and those with alpha‐1 antitrypsin deficiency

Ouriadov

Guo

McCormack

et al. 2019

“…FE simulations of 3 He and 129 Xe multiple b value DWI at the commonly reported in vivo diffusion times of 3 He Δ = 1.6 ms 13,15,22,38 and 129 Xe Δ = 8.5 ms 16,29 were performed. The global diffusion metrics, derived from both the SEM and CM, from the healthy acinar airway mesh were in agreement with those acquired from healthy volunteers with the same 3 He and 129 Xe DWI acquisition parameters.…”

Section: Validation Of In Vivo Diffusion Timesmentioning

confidence: 99%

“…Recently, the SEM-derived mean diffusive length scale (Lm D ) was indirectly validated with comparisons against CM-derived measurements in the same subjects across a range of acinar length scales. 29 However, the Lm D has not yet been directly validated against histology or known acinar geometries. Therefore, this work aims to validate the SEM Lm D , alongside CM-derived parameters, with FE simulations of hyperpolarized 3 He and 129 Xe DWI in realistic models of acinar airway geometry-derived from micro-CT images.…”

Section: Introductionmentioning

confidence: 99%

Finite element simulations of hyperpolarized gas DWI in micro‐CT meshes of acinar airways: validating the cylinder and stretched exponential models of lung microstructural length scales

Chan

Collier

Parra‐Robles

et al. 2021

Self Cite

“…Using the same diffusion-encoding techniques, it is possible to directly estimate airspace dimensions by acquiring multiple images with different diffusion weightings and using either an analytical model of the airspace geometry [12][13][14] or a mathematical model of diffusion behavior. 15,16 These analytic methods, collectively known as diffusion morphometry, use Bayesian probability theory alongside a simplified acinar model to calculate standard lung morphometry parameters such as mean linear intercept (L m ), surface-tovolume (SV) ratio, and alveolar number density (N a ), alongside detailed estimates of acinar dimensions including alveolar sleeve depth (h) and acinar duct radii (R). These quantitative measures of lung microstructure are obtained noninvasively, thereby allowing subtle changes in acinar morphology to be measured longitudinally during both normal development and disease progression.…”

Section: Introductionmentioning

confidence: 99%

Validating in vivo hyperpolarized ¹²⁹Xe diffusion MRI and diffusion morphometry in the mouse lung

Niedbalski

Cochran

Freeman

et al. 2020

Diffusion and lung morphometry imaging using hyperpolarized gases are promising tools to quantify pulmonary microstructure noninvasively in humans and in animal models. These techniques assume the motion encoded is exclusively diffusive gas displacement, but the impact of cardiac motion on measurements has never been explored. Furthermore, although diffusion morphometry has been validated against histology in humans and mice using 3 He, it has never been validated in mice for 129 Xe. Here, we examine the effect of cardiac motion on diffusion imaging and validate 129 Xe diffusion morphometry in mice. Theory and Methods: Mice were imaged using gradient-echo-based diffusion imaging, and apparent diffusion-coefficient (ADC) maps were generated with and without cardiac gating. Diffusion-weighted images were fit to a previously developed theoretical model using Bayesian probability theory, producing morphometric parameters that were compared with conventional histology. Results: Cardiac gating had no significant impact on ADC measurements (dualgating: ADC = 0.020 cm 2 /s, single-gating: ADC = 0.020 cm 2 /s; P = .38). Diffusion-morphometry-generated maps of ADC (mean, 0.0165 ± 0.0001 cm 2 /s) and acinar dimensions (alveolar sleeve depth [h] = 44 µm, acinar duct radii [R] = 99 µm, mean linear intercept [L m ] = 74 µm) that agreed well with conventional histology (h = 45 µm, R = 108 µm, L m = 63 µm). Conclusion: Cardiac motion has negligible impact on 129 Xe ADC measurements in mice, arguing its impact will be similarly minimal in humans, where relative cardiac