1
|
Diffusion weighted hyperpolarized 129 Xe MRI of the lung with 2D and 3D (FLORET) spiral. Magn Reson Med 2023; 89:1342-1356. [PMID: 36352793 PMCID: PMC9892235 DOI: 10.1002/mrm.29518] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2022] [Revised: 09/21/2022] [Accepted: 10/18/2022] [Indexed: 11/11/2022]
Abstract
PURPOSE To enable efficient hyperpolarized 129 Xe diffusion imaging using 2D and 3D (Fermat Looped, ORthogonally Encoded Trajectories, FLORET) spiral sequences and demonstrate that 129 Xe ADCs obtained using these sequences are comparable to those obtained using a conventional, 2D gradient-recalled echo (GRE) sequence. THEORY AND METHODS Diffusion-weighted 129 Xe MRI (b-values = 0, 7.5, 15 s/cm2 ) was performed in four healthy volunteers and one subject with lymphangioleiomyomatosis using slice-selective 2D-GRE (scan time = 15 s), slice-selective 2D-Spiral (4 s), and 3D-FLORET (16 s) sequences. Experimental SNRs from b-value = 0 images ( SNR 0 EX $$ SNR{0}_{EX} $$ ) and mean ADC values were compared across sequences. In two healthy subjects, a second b = 0 image was acquired using the 2D-Spiral sequence to map flip angle and correct RF-induced, hyperpolarized signal decay at the voxel level, thus improving regional ADC estimates. RESULTS Diffusion-weighted images from spiral sequences displayed image quality comparable to 2D-GRE and produced sufficient SNR 0 EX $$ SNR{0}_{EX} $$ (16.8 ± 3.8 for 2D-GRE, 21.2 ± 3.5 for 2D-Spiral, 20.4 ± 3.5 for FLORET) to accurately calculate ADC. Whole-lung means and SDs of ADC obtained via spiral were not significantly different (P > 0.54) from those obtained via 2D-GRE. Finally, 2D-Spiral images were corrected for signal decay, which resulted in a whole-lung mean ADC decrease of ˜15%, relative to uncorrected images. CONCLUSIONS Relative to GRE, efficient spiral sequences allow 129 Xe diffusion images to be acquired with isotropic lung coverage (3D), higher SNR $$ SNR $$ (2D and 3D), and three-fold faster (2D) within a single breath-hold. In turn, shortened breath-holds enable flip-angle mapping, and thus, allow RF-induced signal decay to be corrected, increasing ADC accuracy.
Collapse
|
2
|
Improving hyperpolarized 129 Xe ADC mapping in pediatric and adult lungs with uncertainty propagation. NMR IN BIOMEDICINE 2022; 35:e4639. [PMID: 34729838 PMCID: PMC8828677 DOI: 10.1002/nbm.4639] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/29/2021] [Revised: 09/30/2021] [Accepted: 10/01/2021] [Indexed: 06/13/2023]
Abstract
RATIONALE Hyperpolarized (HP) 129 Xe-MRI provides non-invasive methods to quantify lung function and structure, with the 129 Xe apparent diffusion coefficient (ADC) being a well validated measure of alveolar airspace size. However, the experimental factors that impact the precision and accuracy of HP 129 Xe ADC measurements have not been rigorously investigated. Here, we introduce an analytical model to predict the experimental uncertainty of 129 Xe ADC estimates. Additionally, we report ADC dependence on age in healthy pediatric volunteers. METHODS An analytical expression for ADC uncertainty was derived from the Stejskal-Tanner equation and simplified Bloch equations appropriate for HP media. Parameters in the model were maximum b-value (bmax ), number of b-values (Nb ), number of phase encoding lines (Nph ), flip angle and the ADC itself. This model was validated by simulations and phantom experiments, and five fitting methods for calculating ADC were investigated. To examine the lower range for 129 Xe ADC, 32 healthy subjects (age 6-40 years) underwent diffusion-weighted 129 Xe MRI. RESULTS The analytical model provides a lower bound on ADC uncertainty and predicts that decreased signal-to-noise ratio yields increases in relative uncertainty (ϵADC) . As such, experimental parameters that impact non-equilibrium 129 Xe magnetization necessarily impact the resulting ϵADC . The values of diffusion encoding parameters (Nb and bmax ) that minimize ϵADC strongly depend on the underlying ADC value, resulting in a global minimum for ϵADC . Bayesian fitting outperformed other methods (error < 5%) for estimating ADC. The whole-lung mean 129 Xe ADC of healthy subjects increased with age at a rate of 1.75 × 10-4 cm2 /s/yr (p = 0.001). CONCLUSIONS HP 129 Xe diffusion MRI can be improved by minimizing the uncertainty of ADC measurements via uncertainty propagation. Doing so will improve experimental accuracy when measuring lung microstructure in vivo and should allow improved monitoring of regional disease progression and assessment of therapy response in a range of lung diseases.
Collapse
|
3
|
Validating in vivo hyperpolarized 129 Xe diffusion MRI and diffusion morphometry in the mouse lung. Magn Reson Med 2021; 85:2160-2173. [PMID: 33017076 PMCID: PMC8544163 DOI: 10.1002/mrm.28539] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2020] [Revised: 08/27/2020] [Accepted: 09/14/2020] [Indexed: 02/03/2023]
Abstract
PURPOSE 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 (dual-gating: ADC = 0.020 cm2 /s, single-gating: ADC = 0.020 cm2 /s; P = .38). Diffusion-morphometry-generated maps of ADC (mean, 0.0165 ± 0.0001 cm2 /s) and acinar dimensions (alveolar sleeve depth [h] = 44 µm, acinar duct radii [R] = 99 µm, mean linear intercept [Lm ] = 74 µm) that agreed well with conventional histology (h = 45 µm, R = 108 µm, Lm = 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 motion is reduced. Hyperpolarized 129 Xe diffusion morphometry accurately and noninvasively maps the dimensions of lung microstructure, suggesting it can quantify the pulmonary microstructure in mouse models of lung disease.
Collapse
|
4
|
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. Magn Reson Med 2021; 86:514-525. [PMID: 33624325 DOI: 10.1002/mrm.28703] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2020] [Revised: 12/07/2020] [Accepted: 01/07/2021] [Indexed: 12/24/2022]
Abstract
PURPOSE This work assesses the accuracy of the stretched exponential (SEM) and cylinder models of lung microstructural length scales that can be derived from hyperpolarized gas DWI. This was achieved by simulating 3 He and 129 Xe DWI signals within two micro-CT-derived realistic acinar airspace meshes that represent healthy and idiopathic pulmonary fibrosis lungs. METHODS The healthy and idiopathic pulmonary fibrosis acinar airway meshes were derived from segmentations of 3D micro-CT images of excised human lungs and meshed for finite element simulations of the Bloch-Torrey equations. 3 He and 129 Xe multiple b value DWI experiments across a range of diffusion times (3 He Δ = 1.6 ms; 129 Xe Δ = 5 to 20 ms) were simulated in each mesh. Global SEM mean diffusive length scale and cylinder model mean chord length value was derived from each finite element simulation and compared against each mesh's mean linear intercept length, calculated from intercept length measurements within micro-CT segmentation masks. RESULTS The SEM-derived mean diffusive length scale was within ±10% of the mean linear intercept length for simulations with both 3 He (Δ = 1.6 ms) and 129 Xe (Δ = 7 to 13 ms) in the healthy mesh, and with 129 Xe (Δ = 13 to 20 ms) for the idiopathic pulmonary fibrosis mesh, whereas for the cylinder model-derived mean chord length the closest agreement with mean linear intercept length (11.7% and 22.6% difference) was at 129 Xe Δ = 20 ms for both healthy and IPF meshes, respectively. CONCLUSION This work validates the use of the SEM for accurate estimation of acinar dimensions and indicates that the SEM is relatively robust across a range of experimental conditions and acinar length scales.
Collapse
|
5
|
Lung microstructure in adolescent idiopathic scoliosis before and after posterior spinal fusion. PLoS One 2020; 15:e0240265. [PMID: 33031412 PMCID: PMC7544066 DOI: 10.1371/journal.pone.0240265] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2020] [Accepted: 09/22/2020] [Indexed: 11/19/2022] Open
Abstract
Adolescent idiopathic scoliosis (AIS) is associated with decreased respiratory quality of life and impaired diaphragm function. Recent hyperpolarized helium (HHe) MRI studies show alveolarization continues throughout adolescence, and mechanical forces are known to impact alveolarization. We therefore hypothesized that patients with AIS would have alterations in alveolar size, alveolar number, or alveolar septal dimensions compared to adolescents without AIS, and that posterior spinal fusion (PSF) might reverse these differences. We conducted a prospective observational trial using HHe MRI to test for changes in alveolar microstructure in control and AIS subjects at baseline and one year. After obtaining written informed consent from subjects’ legal guardians and assent from the subjects, we performed HHe and proton MRI in 14 AIS and 16 control subjects aged 8–21 years. The mean age of control subjects (12.9 years) was significantly less than AIS (14.9 years, p = 0.003). At baseline, there were no significant differences in alveolar size, number, or alveolar duct morphometry between AIS and control subjects or between the concave (compressed) and convex (expanded) lungs of AIS subjects. At one year after PSF AIS subjects had an increase in alveolar density in the formerly convex lung (p = 0.05), likely reflecting a change in thoracic anatomy, but there were no other significant changes in lung microstructure. Modeling of alveolar size over time demonstrated similar rates of alveolar growth in control and AIS subjects in both right and left lungs pre- and post-PSF. Although this study suffered from poor age-matching, we found no evidence that AIS or PSF impacts lung microstructure. Trial registration: Clinical trial registration number NCT03539770.
Collapse
|
6
|
Airway Microstructure in Idiopathic Pulmonary Fibrosis: Assessment at Hyperpolarized 3He Diffusion-weighted MRI. Radiology 2019; 291:223-229. [DOI: 10.1148/radiol.2019181714] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
|
7
|
Advanced pulmonary MRI to quantify alveolar and acinar duct abnormalities: Current status and future clinical applications. J Magn Reson Imaging 2019; 50:28-40. [PMID: 30637857 DOI: 10.1002/jmri.26623] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2018] [Revised: 12/04/2018] [Accepted: 12/05/2018] [Indexed: 12/23/2022] Open
Abstract
There are serious clinical gaps in our understanding of chronic lung disease that require novel, sensitive, and noninvasive in vivo measurements of the lung parenchyma to measure disease pathogenesis and progressive changes over time as well as response to treatment. Until recently, our knowledge and appreciation of the tissue changes that accompany lung disease has depended on ex vivo biopsy and concomitant histological and stereological measurements. These measurements have revealed the underlying pathologies that drive lung disease and have provided important observations about airway occlusion, obliteration of the terminal bronchioles and airspace enlargement, or fibrosis and their roles in disease initiation and progression. ex vivo tissue stereology and histology are the established gold standards and, more recently, micro-computed tomography (CT) measurements of ex vivo tissue samples has also been employed to reveal new mechanistic findings about the progression of obstructive lung disease in patients. While these approaches have provided important understandings using ex vivo analysis of excised samples, recently developed hyperpolarized noble gas MRI methods provide an opportunity to noninvasively measure acinar duct and terminal airway dimensions and geometry in vivo, and, without radiation burden. Therefore, in this review we summarize emerging pulmonary MRI morphometry methods that provide noninvasive in vivo measurements of the lung in patients with bronchopulmonary dysplasia and chronic obstructive pulmonary disease, among others. We discuss new findings, future research directions, as well as clinical opportunities to address current gaps in patient care and for testing of new therapies. Level of Evidence: 5 Technical Efficacy: Stage 5 J. Magn. Reson. Imaging 2019;50:28-40.
Collapse
|
8
|
Lung morphometry using hyperpolarized
129
Xe multi‐
b
diffusion
MRI
with compressed sensing in healthy subjects and patients with
COPD. Med Phys 2018; 45:3097-3108. [DOI: 10.1002/mp.12944] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2017] [Revised: 04/18/2018] [Accepted: 04/19/2018] [Indexed: 12/11/2022] Open
|
9
|
Pulmonary 3He Magnetic Resonance Imaging Biomarkers of Regional Airspace Enlargement in Alpha-1 Antitrypsin Deficiency. Acad Radiol 2017. [PMID: 28645458 DOI: 10.1016/j.acra.2017.05.008] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
RATIONALE AND OBJECTIVES Thoracic x-ray computed tomography (CT) and hyperpolarized 3He magnetic resonance imaging (MRI) provide quantitative measurements of airspace enlargement in patients with emphysema. For patients with panlobular emphysema due to alpha-1 antitrypsin deficiency (AATD), sensitive biomarkers of disease progression and response to therapy have been difficult to develop and exploit, especially those biomarkers that correlate with outcomes like quality of life. Here, our objective was to generate and compare CT and diffusion-weighted inhaled-gas MRI measurements of emphysema including apparent diffusion coefficient (ADC) and MRI-derived mean linear intercept (Lm) in patients with AATD, chronic obstructive pulmonary disease (COPD) ex-smokers, and elderly never-smokers. MATERIALS AND METHODS We enrolled patients with AATD (n = 8; 57 ± 7 years), ex-smokers with COPD (n = 8; 77 ± 6 years), and a control group of never-smokers (n = 5; 64 ± 2 years) who underwent thoracic CT, MRI, spirometry, plethysmography, the St. George's Respiratory Questionnaire, and the 6-minute walk test during a single 2-hour visit. MRI-derived ADC, Lm, surface-to-volume ratio, and ventilation defect percent were generated for the apical, basal, and whole lung as was CT lung area ≤-950 Hounsfield units (RA950), low attenuating clusters, and airway count. RESULTS In patients with AATD, there was a significantly different MRI-derived ADC (P = .03), Lm (P < .0001), and surface-to-volume ratio (P < .0001), but not diffusing capacity of carbon monoxide, residual volume or total lung capacity, or CT RA950 (P > .05) compared to COPD ex-smokers with a significantly different St. George's Respiratory Questionnaire. CONCLUSIONS In this proof-of-concept demonstration, we evaluated CT and MRI lung emphysema measurements and observed significantly worse MRI biomarkers of emphysema in patients with AATD compared to patients with COPD, although CT RA950 and diffusing capacity of carbon monoxide were not significantly different, underscoring the sensitivity of MRI measurements of AATD emphysema.
Collapse
|
10
|
3D diffusion-weighted 129 Xe MRI for whole lung morphometry. Magn Reson Med 2017; 79:2986-2995. [PMID: 29034509 PMCID: PMC5888195 DOI: 10.1002/mrm.26960] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2017] [Revised: 09/14/2017] [Accepted: 09/19/2017] [Indexed: 12/27/2022]
Abstract
Purpose To 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. Methods Prospective 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). Results Good 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. Conclusion Compressed 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.
Collapse
|
11
|
Diffusion lung imaging with hyperpolarized gas MRI. NMR IN BIOMEDICINE 2017; 30:10.1002/nbm.3448. [PMID: 26676342 PMCID: PMC4911335 DOI: 10.1002/nbm.3448] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/30/2015] [Revised: 10/20/2015] [Accepted: 10/22/2015] [Indexed: 05/28/2023]
Abstract
Lung imaging using conventional 1 H MRI presents great challenges because of the low density of lung tissue, lung motion and very fast lung tissue transverse relaxation (typical T2 * is about 1-2 ms). MRI with hyperpolarized gases (3 He and 129 Xe) provides a valuable alternative because of the very strong signal originating from inhaled gas residing in the lung airspaces and relatively slow gas T2 * relaxation (typical T2 * is about 20-30 ms). However, in vivo human experiments should be performed very rapidly - usually during a single breath-hold. In this review, we describe the recent developments in diffusion lung MRI with hyperpolarized gases. We show that a combination of the results of modeling of gas diffusion in lung airspaces and diffusion measurements with variable diffusion-sensitizing gradients allows the extraction of quantitative information on the lung microstructure at the alveolar level. From an MRI scan of less than 15 s, this approach, called in vivo lung morphometry, allows the provision of quantitative values and spatial distributions of the same physiological parameters as measured by means of 'standard' invasive stereology (mean linear intercept, surface-to-volume ratio, density of alveoli, etc.). In addition, the approach makes it possible to evaluate some advanced Weibel parameters characterizing lung microstructure: average radii of alveolar sacs and ducts, as well as the depth of their alveolar sleeves. Such measurements, providing in vivo information on the integrity of pulmonary acinar airways and their changes in different diseases, are of great importance and interest to a broad range of physiologists and clinicians. We also discuss a new type of experiment based on the in vivo lung morphometry technique combined with quantitative computed tomography measurements, as well as with gradient echo MRI measurements of hyperpolarized gas transverse relaxation in the lung airspaces. Such experiments provide additional information on the blood vessel volume fraction, specific gas volume and length of the acinar airways, and allow the evaluation of lung parenchymal and non-parenchymal tissue. Copyright © 2015 John Wiley & Sons, Ltd.
Collapse
|
12
|
Hyperpolarized 129Xe for investigation of mild cystic fibrosis lung disease in pediatric patients. J Cyst Fibros 2016; 16:275-282. [PMID: 27477942 DOI: 10.1016/j.jcf.2016.07.008] [Citation(s) in RCA: 98] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2016] [Revised: 07/15/2016] [Accepted: 07/17/2016] [Indexed: 12/19/2022]
Abstract
BACKGROUND Cystic fibrosis (CF) is a genetic disease which carries high morbidity and mortality from lung-function decline. Monitoring disease progression and treatment response in young patients is desirable, but serial imaging via CT is often considered prohibitive, and detailed functional information cannot be obtained using conventional imaging techniques. Hyperpolarized 129Xe magnetic resonance imaging (MRI) can depict and quantify regional ventilation, but has not been investigated in pediatrics. We hypothesized that 129Xe MRI is feasible and would demonstrate ventilation defects in mild CF lung disease with greater sensitivity than FEV1. METHODS 11 healthy controls (age 6-16years) and 11 patients with mild CF (age 8-16years, Forced Expiratory Volume (FEV1) percent predicted >70%) were recruited for this study. Nine CF patients had an FEV1>85%. Each subject was imaged via hyperpolarized 129Xe MRI, and the ventilation defect percentage (VDP) was measured. FEV1 and VDP were compared between the groups. RESULTS FEV1 for controls was 100.3%±8.5% (mean±sd) and for CF patients was 97.9%±16.0% (p=0.67). VDP was 6.4%±2.8% for controls and 18.3%±8.6% for CF (p<0.001). When considering the 9 CF patients with normal FEV1 (>85%), the mean FEV1 was 103.1%±12.3% (p=0.57 compared to controls) and VDP was 15.4%±6.3% (p=0.002). CONCLUSIONS Hyperpolarized 129Xe MRI demonstrated ventilation defects in CF patients with normal FEV1 and more effectively discriminated CF from controls than FEV1. Thus 129Xe may be a useful outcome measure to detect mild CF lung disease, to investigate regional lung function in pediatric lung diseases, and to follow disease progression.
Collapse
|
13
|
Abstract
Imaging has played a vital role in the clinical assessment of bronchopulmonary dysplasia (BPD) since its first recognition. In this review, how chest radiograph, computerized tomography (CT), nuclear medicine, and MRI have contributed to the understanding of BPD pathology and how emerging advancements in these methods, including low-dose and quantitative CT, sophisticated proton and hyperpolarized-gas MRI, influence the future of BPD imaging are discussed.
Collapse
|
14
|
Microstructural Analysis of Peripheral Lung Tissue through CPMG Inter-Echo Time R2 Dispersion. PLoS One 2015; 10:e0141894. [PMID: 26544068 PMCID: PMC4636373 DOI: 10.1371/journal.pone.0141894] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2015] [Accepted: 10/14/2015] [Indexed: 11/25/2022] Open
Abstract
Since changes in lung microstructure are important indicators for (early stage) lung pathology, there is a need for quantifiable information of diagnostically challenging cases in a clinical setting, e.g. to evaluate early emphysematous changes in peripheral lung tissue. Considering alveoli as spherical air-spaces surrounded by a thin film of lung tissue allows deriving an expression for Carr-Purcell-Meiboom-Gill transverse relaxation rates R2 with a dependence on inter-echo time, local air-tissue volume fraction, diffusion coefficient and alveolar diameter, within a weak field approximation. The model relaxation rate exhibits the same hyperbolic tangent dependency as seen in the Luz-Meiboom model and limiting cases agree with Brooks et al. and Jensen et al. In addition, the model is tested against experimental data for passively deflated rat lungs: the resulting mean alveolar radius of RA = 31.46 ± 13.15 μm is very close to the literature value (∼34 μm). Also, modeled radii obtained from relaxometer measurements of ageing hydrogel foam (that mimics peripheral lung tissue) are in good agreement with those obtained from μCT images of the same foam (mean relative error: 0.06 ± 0.01). The model’s ability to determine the alveolar radius and/or air volume fraction will be useful in quantifying peripheral lung microstructure.
Collapse
|
15
|
Experimental evidence of age-related adaptive changes in human acinar airways. J Appl Physiol (1985) 2015; 120:159-65. [PMID: 26542518 DOI: 10.1152/japplphysiol.00541.2015] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2015] [Accepted: 11/01/2015] [Indexed: 11/22/2022] Open
Abstract
The progressive decline of lung function with aging is associated with changes in lung structure at all levels, from conducting airways to acinar airways (alveolar ducts and sacs). While information on conducting airways is becoming available from computed tomography, in vivo information on the acinar airways is not conventionally available, even though acini occupy 95% of lung volume and serve as major gas exchange units of the lung. The objectives of this study are to measure morphometric parameters of lung acinar airways in living adult humans over a broad range of ages by using an innovative MRI-based technique, in vivo lung morphometry with hyperpolarized (3)He gas, and to determine the influence of age-related differences in acinar airway morphometry on lung function. Pulmonary function tests and MRI with hyperpolarized (3)He gas were performed on 24 healthy nonsmokers aged 19-71 years. The most significant age-related difference across this population was a 27% loss of alveolar depth, h, leading to a 46% increased acinar airway lumen radius, hence, decreased resistance to acinar air transport. Importantly, the data show a negative correlation between h and the pulmonary function measures forced expiratory volume in 1 s and forced vital capacity. In vivo lung morphometry provides unique information on age-related changes in lung microstructure and their influence on lung function. We hypothesize that the observed reduction of alveolar depth in subjects with advanced aging represents a remodeling process that might be a compensatory mechanism, without which the pulmonary functional decline due to other biological factors with advancing age would be significantly larger.
Collapse
|
16
|
Abstract
Diffusion-weighted magnetic resonance imaging (MRI) provides a way to generate in vivo lung images with contrast sensitive to the molecular displacement of inhaled gas at subcellular length scales. Here, we aimed to evaluate hyperpolarized 3He MRI estimates of the alveolar dimensions in 38 healthy elderly never-smokers (73 ± 6 years, 15 males) and 21 elderly ex-smokers (70 ± 10 years, 14 males) with (n = 8, 77 ± 6 years) and without emphysema (n = 13, 65 ± 10 years). The ex-smoker and never-smoker subgroups were significantly different for FEV1/FVC (P = 0.0001) and DLCO (P = 0.009); while ex-smokers with emphysema reported significantly diminished FEV1/FVC (P = 0.02) and a trend toward lower DLCO (P = 0.05) than ex-smokers without emphysema. MRI apparent diffusion coefficients (ADC) and CT measurements of emphysema (relative area–CT density histogram, RA950) were significantly different (P = 0.001 and P = 0.007) for never-smoker and ex-smoker subgroups. In never-smokers, the MRI estimate of mean linear intercept (260 ± 27 μm) was significantly elevated as compared to the results previously reported in younger never-smokers (210 ± 30 μm), and trended smaller than in the age-matched ex-smokers (320 ± 72 μm, P = 0.06) evaluated here. Never-smokers also reported significantly smaller internal (220 ± 24 μm, P = 0.01) acinar radius but greater alveolar sheath thickness (120 ± 4 μm, P < 0.0001) than ex-smokers. Never-smokers were also significantly different than ex-smokers without emphysema for alveolar sheath thickness but not ADC, while ex-smokers with emphysema reported significantly different ADC but not alveolar sheath thickness compared to ex-smokers without CT evidence of emphysema. Differences in alveolar measurements in never- and ex-smokers demonstrate the sensitivity of MRI measurements to the different effects of smoking and aging on acinar morphometry.
Collapse
|
17
|
This
is what
COPD
looks like. Respirology 2015; 21:224-36. [DOI: 10.1111/resp.12611] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2015] [Revised: 06/22/2015] [Accepted: 06/24/2015] [Indexed: 12/14/2022]
|
18
|
In vivo lung morphometry with accelerated hyperpolarized (3) He diffusion MRI: a preliminary study. Magn Reson Med 2015; 73:1609-14. [PMID: 24799044 PMCID: PMC4221580 DOI: 10.1002/mrm.25284] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2013] [Revised: 04/11/2014] [Accepted: 04/15/2014] [Indexed: 12/27/2022]
Abstract
PURPOSE Parallel imaging can be used to reduce imaging time and to increase the spatial coverage in hyperpolarized gas magnetic resonance imaging of the lung. In this proof-of-concept study, we investigate the effects of parallel imaging on the morphometric measurement of lung microstructure using diffusion magnetic resonance imaging with hyperpolarized (3) He. METHODS Fully sampled and under-sampled multi-b diffusion data were acquired from human subjects using an 8-channel (3) He receive coil. A parallel imaging reconstruction technique (generalized autocalibrating partially parallel acquisitions [GRAPPA]) was used to reconstruct under-sampled k-space data. The morphometric results of the generalized autocalibrating partially parallel acquisitions-reconstructed data were compared with the results of fully sampled data for three types of subjects: healthy volunteers, mild, and moderate chronic obstructive pulmonary disease patients. RESULTS Morphometric measurements varied only slightly at mild acceleration factors. The results were largely well preserved compared to fully sampled data for different lung conditions. CONCLUSION Parallel imaging, given sufficient signal-to-noise ratio, provides a reliable means to accelerate hyperpolarized-gas magnetic resonance imaging with no significant difference in the measurement of lung morphometry from the fully sampled images. GRAPPA is a promising technique to significantly reduce imaging time and/or to improve the spatial coverage for the morphometric measurement with hyperpolarized gases.
Collapse
|