Development and clinical evaluation of UTE sequences for functional lung imaging

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Magnetic resonance imaging (MRI) allows cross-sectional imaging without ionizing radiation, making its use particularly desirable for high-risk groups of medical radiation applications. Pulmonary MRI has been limited by physical conditions in the lung parenchyma, but latest ultrashort echo time (UTE) MRI sequences provide an improved signal-to-noise ratio and thus significantly better image quality in the lung. Studies show comparable performance of UTE MRI and computed tomography for many indications regarding lung morphology. Although the diagnostic potential of modern UTE sequences suggests their use also in functional lung imaging, this field of application was widely unexplored. During the first funding period of the research project, 2D and 3D UTE sequences for functional lung MRI were developed and clinically tested. Developmental work included the elaboration of 3D UTE sequences for measuring lung ventilation and contrast perfusion, and both 2D single-slice and 2D simultaneous multi-slice UTE sequences were developed for contrast-free measurements of lung perfusion via the inflow effect. Exploratory studies have tested and compared respiratory protocols, successfully verified the reproducibility of ventilation measurements and their agreement with pulmonary function testing, and demonstrated the potential application of UTE sequences for functional imaging in patients with cystic fibrosis, among others. Despite these successes, limitations still exist that hinder the widespread clinical use of UTE sequences for functional lung MRI, most notably the dependence of most methods on breath-hold maneuvers. Within the second funding period, the techniques developed will be expanded and improved: Implementation of free-breathing data acquisition will make functional UTE-MRI accessible to all patients regardless of their breathing compliance. Development of sequences with simultaneous excitation of multiple slices will further reduce scan time, and integration of error maps will allow immediate assessment of the reliability of functional measurements. Systematic investigation of the dependencies between inflow-related parenchymal signal changes and acquisition parameters will lead to a non-contrast protocol for quantitative perfusion imaging. The developments will be tested and validated in exploratory studies on representative patient collectives. Among others, target parameters are the image quality and the agreement of the functional measurements with clinically established methods. At the end of the project, a contrast-free lung MRI based on UTE sequences should be available, which allows high-resolution imaging of the lung parenchyma in a short examination time providing quantifiable functional information. Depending on the individual respiratory compliance, it is then possible to choose between data acquisition during breath-hold or free-breathing and to assess the validity of the functional measurements through error indices.