MR MICROIMAGING OF THE LUNG USING VOLUME PROJECTION ENCODING

Radial acquisition (RA) techniques have been extended to produce isotr opic, three-dimensional images of lung in live laboratory animals at s patial resolution down to 0.013 mm(3) with a signal-to-noise ratio of 30:1, The pulse sequence and reconstruction algorithm have been adapte d to allow acquisition of image matrices of up to 256(3) in less than 15 min. Scan-synchronous ventilation has been incorporated to limit br eathing motion artifacts, The imaging sequence permits randomizing and /or discarding selected views to minimize the consequences of breathin g motion, The signal in lung parenchyma was measured as a function of flip angle (alpha) for different repetition times and found to follow the predictions for which there is an optimum excitation (Ernst) angle , A single T-1 relaxation value of 780 +/- 54 ms fits all data from si x guinea pigs at 2.0 T, This T-1 value parameterizes the signal and al lows for a priori optimization, such as calculation of the Ernst angle appropriate for lung imaging.