MR microimaging of the lung using volume projection encoding

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Abstract
Radial acquisition (RA) techniques have been extended to produce isotropic, three‐dimensional images of lung in live laboratory animals at spatial resolution down to 0.013 mm3 with a signal‐to‐noise ratio of 30:1. The pulse sequence and reconstruction algorithm have been adapted to allow acquisition of image matrices of up to 2563 in less than 15 min. Scan‐synchronous ventilation has been incorporated to limit breathing motion artifacts. The imaging sequence permits randomizing and/or discarding selected views to minimize the consequences of breathing motion. The signal in lung parenchyma was measured as a function of flip angle (α) for different repetition times and found to follow the predictions for which there is an optimum excitation (Ernst) angle. A single T1, relaxation value of 780 ± 54 ms fits all data from six guinea pigs at 2.0 T. This T1, value parameterizes the signal and allows for a priori optimization, such as calculation of the Ernst angle appropriate for lung imaging.