Indirect qualitative MRI of pulmonary function is feasible using the paramagnetic effects of oxygen physically dissolved in blood. In this study, a more quantitative oxygen-enhanced pulmonary function test based on the slope of a plot of R 1 vs. oxygen concentration-the oxygen transfer function (OTF)-was developed and tested in a pool of five healthy volunteers and five patients with cystic fibrosis (CF). The lung T 1 relaxation rate, R 1 , under normoxic conditions (room air, 21% O 2 ), and the response to various hyperoxic conditions (40%-100% O 2 ) were studied. Lung T 1 in healthy volunteers showed a relatively homogeneous distribution while they breathed room air, and a homogeneous decrease under hyperoxic conditions. Lung T 1 in CF patients showed an inhomogeneous distribution while they breathed room air, and the observed lung Oxygen plays a critical role in the physiology and pathophysiology of the lung. The ability to detect and characterize altered lung oxygen uptake is of great potential value for clinical diagnoses. Thus, in general, functional studies of the human lung address ventilation and gas exchange processes, particularly those of oxygen. The direct use of oxygen as a contrast agent (CA) in an imaging setting would be an interesting means of assessing pulmonary function.Indirect MRI of pulmonary function based on the paramagnetic effects of oxygen physically dissolved in pulmonary blood was demonstrated for the first time by Edelman et al. (1). This pulmonary function test exploits the fact that the amount of dissolved oxygen in the pulmonary blood increases during breathing pure oxygen, resulting in significant signal enhancement in T 1 -weighted lung images. Since the effect of oxygen on the proton spins of blood water, rather than the oxygen molecules themselves, is detected by this method, the diffusion of oxygen from the alveoli to the capillaries of the lungs can only be indirectly measured. However, the diffusion of oxygen is not the only parameter that specifies the observed MR signal in this method, since ventilation-perfusion inequalities also directly affect the observed signal changes. Thus, it has been proposed (2) that different mechanisms, such as ventilation, perfusion, and diffusion, are potentially responsible for the observed signal changes. The major advantage of this oxygen-enhanced approach is its relatively simple experimental setup, since only standard hardware for proton imaging, a ventilatory mask system, and oxygen (which is widely available) as a paramagnetic CA are required. The main current limitations of this approach are that no signal changes are visible at certain T 1 values (i.e., regions without signal changes could mimic pathology, since T 1 is not homogeneous across the entire lung (3,4)), and a quantitative assessment of the pulmonary function is critical because only relative signal changes in T 1 -weighted images are detected. Therefore, quantitative T 1 measurements of oxygen-enhanced MR images have a higher potential for the diagnosis of lung diseas...

In this contribution, a rapid and robust technique for quantitative T(1) mapping of the human lung is presented. Based on a series of Snapshot FLASH tomograms acquired after a single inversion pulse, high quality and quantitative T(1) parameter maps acquired in under five seconds were obtained from six healthy volunteers. The measured T(1) values are in good agreement with previously reported literature values. T(1) maps were also acquired with the volunteers breathing room air or 100% O(2). The T(1) difference between breathing room air and 100% O(2) is statistically significant at P < 0.0001.

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Magnetic susceptibility gradients caused by tissue/air interfaces lead to very short T 2 * times in the human lung. These susceptibility gradients are dependent on the magnetic susceptibility of the respiratory gas and therefore should influence T 2 * relaxation. In this work, a technique for quantitative T 2 * mapping of the human lung during one breath hold is presented. Using this method, the lung T 2 * relaxation time was measured under normoxic (room air, 21% O 2 ) and hyperoxic (100% O 2 ) conditions to verify this assumption. The mean T 2 * difference between room air and 100% O 2 is about 10% and contains ventilation information, since only ventilated regions contribute to signal change due to different susceptibility gradients.

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