Dataset Information

Preclinical hyperpolarized ¹²⁹ Xe MRI: ventilation and T₂ * mapping in mouse lungs at 7 T using multi-echo flyback UTE.

ABSTRACT: Fast apparent transverse relaxation (short T₂ *) is a common obstacle when attempting to perform quantitative ¹ H MRI of the lungs. While T₂ * times are longer for pulmonary hyperpolarized (HP) gas functional imaging (in particular for gaseous ¹²⁹ Xe), T₂ * can still lead to quantitative inaccuracies for sequences requiring longer echo times (such as diffusion weighted images) or longer readout duration (such as spiral sequences). This is especially true in preclinical studies, where high magnetic fields lead to shorter relaxation times than are typically seen in human studies. However, the T₂ * of HP ¹²⁹ Xe in the most common animal model of human disease (mice) has not been reported. Herein, we present a multi-echo radial flyback imaging sequence and use it to measure HP ¹²⁹ Xe T₂ * at 7 T under a variety of respiratory conditions. This sequence mitigates the impact of T₁ relaxation outside the animal by using multiple gradient-refocused echoes to acquire images at a number of effective echo times for each RF excitation. After validating the sequence using a phantom containing water doped with superparamagnetic iron oxide nanoparticles, we measured the ¹²⁹ Xe T₂ * in vivo for 10 healthy C57Bl/6 J mice and found T₂ * ~ 5 ms in the lung airspaces. Interestingly, T₂ * was relatively constant over all experimental conditions, and varied significantly with sex, but not age, mass, or the O₂ content of the inhaled gas mixture. These results are discussed in the context of T₂ * relaxation within porous media.

SUBMITTER: Niedbalski PJ

PROVIDER: S-EPMC7702724 | biostudies-literature | 2020 Jul

REPOSITORIES: biostudies-literature

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Publications

Preclinical hyperpolarized 129 Xe MRI: ventilation and T2 * mapping in mouse lungs at 7 T using multi-echo flyback UTE.

Niedbalski Peter J PJ Cochran Alexander S AS Akinyi Teckla G TG Thomen Robert P RP Fugate Elizabeth M EM Lindquist Diana M DM Pratt Ronald G RG Cleveland Zackary I ZI

NMR in biomedicine 20200414 7

Fast apparent transverse relaxation (short T2 *) is a common obstacle when attempting to perform quantitative 1 H MRI of the lungs. While T2 * times are longer for pulmonary hyperpolarized (HP) gas functional imaging (in particular for gaseous 129 Xe), T2 * can still lead to quantitative inaccuracies for sequences requiring longer echo times (such as diffusion weighted images) or longer readout duration (such as spiral sequences). This is es ...[more]

PMID: 32285574

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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

Preclinical hyperpolarized ¹²⁹ Xe MRI: ventilation and T₂ * mapping in mouse lungs at 7 T using multi-echo flyback UTE.

Publications

Preclinical hyperpolarized <sup>129</sup> Xe MRI: ventilation and T<sub>2</sub> * mapping in mouse lungs at 7 T using multi-echo flyback UTE.

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