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Removal of hyperpolarized 129 Xe gas-phase contamination in spectroscopic imaging of the lungs.

ABSTRACT: PURPOSE:A novel technique is presented for retrospective estimation and removal of gas-phase hyperpolarized Xenon-129 (HP 129 Xe) from images of HP 129 Xe dissolved in the barrier (comprised of parenchymal lung tissue and blood plasma) and red blood cell (RBC) phases. The primary aim is mitigating RF pulse performance limitations on measures of gas exchange (e.g., barrier-gas and RBC-gas ratios). Correction for gas contamination would simplify technical dissemination of HP 129 Xe applications across sites with varying hardware performance, scanner vendors, and models. METHODS:Digital lung phantom and human subject experiments (N?=?8 healthy; N?=?1 with idiopathic pulmonary fibrosis) were acquired with 3D radial trajectory and 1-point Dixon spectroscopic imaging to assess the correction method for mitigating barrier and RBC imaging artifacts. Dependence of performance on TE, image SNR, and gas contamination level were characterized. Inter- and intra-subject variation in the dissolved-phase ratios were quantified and compared to human subject experiments before and after correction. RESULTS:Gas contamination resulted in image artifacts similar to those in disease that were mitigated after correction in both simulated and human subject data; for simulation experiments performance varied with TE, but was independent of image SNR and the amount of gas contamination. Artifacts and variation of barrier and RBC components were reduced after correction in both simulation and healthy human lungs (barrier, P?=?0.01; RBC, P?=?0.045). CONCLUSION:The proposed technique significantly reduced regional variations in barrier and RBC ratios, separated using a 1-point Dixon approach, with improved accuracy of dissolved-phase HP 129 Xe images confirmed in simulation experiments.

SUBMITTER: Hahn AD

PROVIDER: S-EPMC6291357 | biostudies-literature | 2018 Dec

REPOSITORIES: biostudies-literature

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Removal of hyperpolarized <sup>129</sup> Xe gas-phase contamination in spectroscopic imaging of the lungs.

Hahn Andrew D AD Kammerman Jeff J Fain Sean B SB

Magnetic resonance in medicine 20180612 6

<h4>Purpose</h4>A novel technique is presented for retrospective estimation and removal of gas-phase hyperpolarized Xenon-129 (HP <sup>129</sup> Xe) from images of HP <sup>129</sup> Xe dissolved in the barrier (comprised of parenchymal lung tissue and blood plasma) and red blood cell (RBC) phases. The primary aim is mitigating RF pulse performance limitations on measures of gas exchange (e.g., barrier-gas and RBC-gas ratios). Correction for gas contamination would simplify technical disseminatio ...[more]

PMID: 29893992

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Project description:BACKGROUND:MRI of hyperpolarized 129 Xenon (HP 129 Xe) is increasingly utilized for investigating pulmonary function. The solubility of HP 129 Xe in lung tissue, blood plasma (Barrier), and red blood cells (RBC), with unique chemical shifts, enables spectroscopic imaging of potential imaging biomarkers of gas exchange and microstructural pulmonary physiology. PURPOSE:To quantify global average and regional repeatability of Barrier:gas, RBC:gas, and RBC:Barrier ratios derived from dissolved-phase 129 Xe imaging and their dependence on intervisit changes in lung inflation volume. STUDY TYPE:Prospective. POPULATION:Fourteen healthy volunteers. One subject was unable to complete the study resulting in 13 subjects for analysis (eight female, five male, ages 24-69, 53.8 ± 13.9). FIELD STRENGTH:1.5T. ASSESSMENT:Subjects were imaged using a 3D radial 1-point Dixon method to separate Barrier and RBC component signals, at two different timepoints, with ~1 month between visits. RBC:Gas, Barrier:Gas, and RBC:Barrier measures were compared across time and with pulmonary function tests (PFTs). STATISTICAL TESTS:Repeatablilty was quantified using Bland-Altman plots, coefficient of repeatability, coefficient of variation (CV), and intraclass correlation coefficients (ICCs). Dependence of imaging measures on PFTs and lung volume was evaluated using Spearman and Pearson correlation coefficients, respectively. Statistical significance was determined by F-test for intraclass correlations, and t-test for Spearman correlations and regression. RESULTS:Mean RBC:Gas, Barrier:Gas, and RBC:Barrier had CVs of 19.2%, 20.0%, and 11.5%, respectively, and had significant ICCs, equal to 0.78, 0.79, and 0.92, respectively. Intervisit differences in RBC:Barrier were significantly correlated with intervisit differences in DLCO (r = 0.93, P = 0.007). Significant correlations with intervisit lung volume differences and intervisit differences in mean RBC:Gas (r = -0.73, P = 0.005) and Barrier:Gas (r = -0.69, P = 0.009) were found. DATA CONCLUSION:Three commonly used 129 Xe MRI-based measures of gas-exchange show good repeatability, particularly the Barrier:RBC ratio, which did not depend on lung inflation volume and was strongly associated with intervisit changes in DLCO . LEVEL OF EVIDENCE:1 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019;50:1182-1190.

Project description:Magnetic resonance (MR) imaging and spectroscopy using dissolved hyperpolarized (HP) 129Xe have expanded the ability to probe lung function regionally and noninvasively. In particular, HP 129Xe imaging has been used to quantify impaired gas uptake by the pulmonary tissues. Whole-lung spectroscopy has also been used to assess global cardiogenic oscillations in the MR signal intensity originating from 129Xe dissolved in the red blood cells of pulmonary capillaries. Herein, we show that the magnitude of these cardiogenic dynamics can be mapped three dimensionally using radial MRI, because dissolved 129Xe dynamics are encoded directly in the raw imaging data. Specifically, 1-point Dixon imaging is combined with postacquisition keyhole image reconstruction to assess regional blood volume fluctuations within the pulmonary microvasculature throughout the cardiac cycle. This "oscillation mapping" was applied in healthy subjects (mean amplitude 9% of total RBC signal) and patients with pulmonary arterial hypertension (PAH; mean 4%) and idiopathic pulmonary fibrosis (IPF; mean 14%). Whole-lung mean values from these oscillation maps correlated strongly with spectroscopy and clinical pulmonary function testing, but exhibited significant regional heterogeneity, including gravitationally dependent gradients in healthy subjects. Moreover, regional oscillations were found to be sensitive to disease state. Greater percentages of the lungs exhibit low-amplitude oscillations in PAH patients, and longitudinal imaging shows high-amplitude oscillations increase significantly over time (4-14 mo, P = 0.02) in IPF patients. This technique enables regional dynamics within the pulmonary capillary bed to be measured, and in doing so, provides insight into the origin and progression of pathophysiology within the lung microvasculature.NEW & NOTEWORTHY Spatially heterogeneous abnormalities within the lung microvasculature contribute to pathology in various cardiopulmonary diseases but are difficult to assess noninvasively. Hyperpolarized 129Xe MRI is a noninvasive method to probe lung function, including regional gas exchange between pulmonary air spaces and capillaries. We show that cardiogenic oscillations in the raw dissolved 129Xe MRI signal from pulmonary capillary red blood cells can be imaged using a postacquisition reconstruction technique, providing a new means of assessing regional lung microvasculature function and disease state.

Dataset Information

Removal of hyperpolarized 129 Xe gas-phase contamination in spectroscopic imaging of the lungs.

Publications

Removal of hyperpolarized <sup>129</sup> Xe gas-phase contamination in spectroscopic imaging of the lungs.

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