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Ventilation Defects (ventilation + defect)
Selected AbstractsEffects of ozone exposure in rat lungs investigated with hyperpolarized 3He MRIJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 4 2008Yannick Crémillieux PhD Abstract Purpose To investigate the effects of subchronic ozone exposure on rat lung ventilation using hyperpolarized (HP) 3He MRI. Materials and Methods A total of 24 Sprague-Dawley rats, distributed in one control group and four groups exposed to 0.5 ppm ozone concentration for two days or six days, either continuously (22 hours/day) or alternatingly (12 hours/day). A three-step MRI protocol was designed and applied to each animal, including: 1) 3He gas distribution images acquired at inspiratory capacity, 2) measurements of intrapulmonary 3He diffusion coefficients, and 3) dynamic ventilation acquisitions performed during lung filling with 3He. Results No differentiation between animals exposed to ozone and control animals was observed from the ventilation images obtained at inspiratory capacity. The 3He diffusion coefficients were not statistically different from one group to another. Ventilation defects, appearing as delayed lung filling regions and heterogeneous lung filling, were observed in the dynamic lung ventilation image series. The percentage of animals with ventilation defects in the control, two-day, and six-day exposed groups were equal to 20%, 43% and 75%, respectively. In the subgroup of the animals exposed six days for 12 hours per day, the percentage of animals exhibiting ventilation defects was equal to 85%. Conclusion Heterogeneous obstructive patterns in an experimental animal model of subchronic ozone exposure were observed using HP 3He MRI. J. Magn. Reson. Imaging 2008;27:771,776. © 2008 Wiley-Liss, Inc. [source] Oxygen-enhanced MR imaging of mice lungsMAGNETIC RESONANCE IN MEDICINE, Issue 6 2008K.N. Watt Abstract Inhaled molecular oxygen has been widely used in humans to evaluate pulmonary ventilation using MRI. MR imaging has recently played a greater role in examining the morphologic and physiologic characteristics of mouse models of lung disease where structural changes are highly correlated to abnormalities in respiratory function. The motivation of this work is to develop oxygen-enhanced MR imaging for mice. Conventional human MR techniques cannot be directly applied to mouse imaging due to smaller dimensions and faster cardiac and respiratory physiology. This study examines the development of oxygen-enhanced MR as a noninvasive tool to assess regional ventilation in spontaneously breathing mice. An optimized cardiac-triggered, respiratory-gated fast spin-echo imaging sequence was developed to address demands of attaining adequate signal from the parenchyma, maintaining practical acquisition times, and compensating for rapid physiological motion. On average, a 20% T1 -shortening effect was observed in mice breathing 100% oxygen as compared to air. The effect of ventilation was shown as a significant signal intensity increase of 11% to 16% in the mouse parenchyma with 100% oxygen inhalation. This work demonstrates that adequate contrast and resolution can be achieved using oxygen-enhanced MR to visualize ventilation, providing an effective technique to study ventilation defects in mice. Magn Reson Med, 2008. © 2008 Wiley-Liss, Inc. [source] Elucidation of structure,function relationships in the lung: contributions from hyperpolarized 3helium MRICLINICAL PHYSIOLOGY AND FUNCTIONAL IMAGING, Issue 6 2002Hans-Ulrich Kauczor Summary Magnetic resonance imaging (MRI) using hyperpolarized 3helium (He) gas as the source of signal provides new physiological insights into the structure,function relationships of the lung. Traditionally, lung morphology has been visualized by chest radiography and computed tomography, whereas lung function was assessed by using nuclear medicine. As all these techniques rely on ionizing radiation, MRI has some inherent advantages. 3He MRI is based on ,optical pumping' of the 3He gas which increases the nuclear spin polarization by four to five orders of magnitude translating into a massive gain in signal. Hyperpolarized 3He gas is administered as an inhaled ,contrast agent' and allows for selective visualization of airways and airspaces. Straightforward gas density images demonstrate the homogeneity of ventilation with high spatial resolution. In patients with lung diseases 3He MRI has shown a high sensitivity to depict ventilation defects. As 3He has some more exciting properties, a comprehensive four-step functional imaging protocol has been established. The dynamic distribution of ventilation during continuous breathing can be visualized after inhalation of a single breath of 3He gas using magnetic resonance (MR) sequences with high temporal resolution. Diffusion weighted 3He MRI provides a new measure for pulmonary microstructure because the degree of restriction of the Brownian motion of the 3He atoms reflects lung structure. Since the decay of 3He hyperpolarization is dependent on the ambient oxygen concentration, regional and temporal analysis of intrapulmonary pO2 becomes feasible. Thus, pulmonary perfusion, ventilation,/perfusion ratio and oxygen uptake can be indirectly assessed. Further research will determine the significance of the functional information with regard to physiology and patient management. [source] |