Hyperpolarized gas diffusion MRI of biphasic lung inflation in short- and long-term emphysema models

Abstract

During lung inflation, airspace dimensions are affected nonlinearly by both alveolar expansion and recruitment, potentially confounding the identification of emphysematous lung by hyperpolarized helium-3 diffusion magnetic resonance imaging (HP MRI). This study aimed to characterize lung inflation over a broad range of inflation volume and pressure values in two different models of emphysema, as well as in normal lungs. Elastase-treated rats ( = 7) and healthy controls ( = 7) were imaged with HP MRI. Gradual inflation was achieved by incremental changes to both inflation volume and airway pressure. The apparent diffusion coefficient (ADC) was measured at each level of inflation and fitted to the corresponding airway pressures as the second-order response equation, with minimizing residue (χ < 0.001). A biphasic ADC response was detected, with an initial ADC increase followed by a decrease at airway pressures >18 cmHO. Discrimination between treated and control rats was optimal when airway pressure was intermediate (between 10 and 11 cmHO). Similar findings were confirmed in mice following long-term exposure to cigarette smoke, where optimal discrimination between treated and healthy mice occurred at a similar airway pressure as in the rats. We subsequently explored the evolution of ADC measured at the intermediate inflation level in mice after prolonged smoke exposure and found a significant increase ( < 0.01) in ADC over time. Our results demonstrate that measuring ADC at intermediate inflation enhances the distinction between healthy and diseased lungs, thereby establishing a model that may improve the diagnostic accuracy of future HP gas diffusion studies.

In Vivo Endomicroscopy of Lung Injury and Repair in ARDS: Potential Added Value to Current Imaging

“…Magnetic resonance imaging (MRI) is also becoming a more widespread technique for lung imaging, especially since the challenges related to low proton density and tissue inhomogeneity have been tackled [30]. Hyperpolarization of gases, notably 129 Xe, increases their signal by a factor of up to 100,000, thus giving background-free images of these gases [36,37,38]. Movement artefacts of the lung can be attenuated using fast image acquisition techniques, and more complex lung characteristics, can be ascertained by measuring local lung physiology.…”

The Effect of Positive End-Expiratory Pressure on Lung Micromechanics Assessed by Synchrotron Radiation Computed Tomography in an Animal Model of ARDS

“…The poor understanding of this phenomenon derives from the difficulty of imaging the entire lung at high resolution, in vivo, and with an intact chest wall–lung complex. These conditions cannot be fulfilled by conventional imaging methods like CT [24,25], He-hyperpolarized nuclear magnetic resonance [26], or in vivo subpleural microscopy [27,28]. Phase contrast synchrotron radiation computed tomography (PCSRCT) allows us to overcome these limits by using highly coherent monochromatic radiation and exploiting the long sample-to-detector distance; in this configuration it is possible to record the interferences patterns determined by X-rays undergoing different phase changes by passing through the sample (phase contrast).…”

Novel imaging approaches for small animal models of lung disease (2017 Grover Conference series)

“…Other techniques such as hyperpolarized magnetic resonance imaging (HP MRI) and micro-positron emission tomography (micro-PET) imaging can provide unique functional and metabolic information about the state of diseased lungs. Dr. Rizi’s group, for example, used HP MRI to determine the apparent diffusion coefficient in rat models of emphysema as a non-invasive measure of airspace enlargement, 37 as well as to measure lactate-to-pyruvate ratios in a rat model of acute lung injury. 38 Micro-PET, with a resolution of 1–1.4 mm, 26 , 39 has been used in mice to detect lung metastases 26 and to measure glucose uptake in a model of acute lung injury, 40 to name just a few examples.…”