Accelerated fractional ventilation imaging with hyperpolarized Gas MRI

Purpose To investigate the utility of accelerated imaging to enhance multibreath fractional ventilation ( r ) measurement accuracy using hyperpolarized gas MRI. Undersampling shortens the breath‐hold time, thereby reducing the O 2 ‐induced signal decay and allows subjects to maintain a more physiologically relevant breathing pattern. Additionally, it may improve r estimation accuracy by reducing radiofrequency destruction of hyperpolarized gas. Methods Image acceleration was achieved using an eight‐channel phased array coil. Undersampled image acquisition was simulated in a series of ventilation images and data was reconstructed for various matrix sizes (48–128) using generalized auto‐calibrating partially parallel acquisition. Parallel accelerated r imaging was also performed on five mechanically ventilated pigs. Results Optimal acceleration factor was fairly invariable (2.0–2.2×) over the range of simulated resolutions. Estimation accuracy progressively improved with higher resolutions (39–51% error reduction). In vivo r values were not significantly different between the two methods: 0.27 ± 0.09, 0.35 ± 0.06, 0.40 ± 0.04 (standard) versus 0.23 ± 0.05, 0.34 ± 0.03, 0.37 ± 0.02 (accelerated); for anterior, medial, and posterior slices, respectively, whereas the corresponding vertical r gradients were significant ( P < 0.001): 0.021 ± 0.007 (standard) versus 0.019 ± 0.005 (accelerated) (cm −1 ). Conclusion Quadruple phased array coil simulations resulted in an optimal acceleration factor of ∼2× independent of imaging resolution. Results advocate undersampled image acceleration to improve accuracy of fractional ventilation measurement with hyperpolarized gas MRI. Magn Reson Med 70:1353–1359, 2013. © 2013 Wiley Periodicals, Inc.