Retrospective respiratory self‐gating and removal of bulk motion in pulmonary <scp>UTE MRI</scp> of neonates and adults

<jats:sec><jats:title>Purpose</jats:title><jats:p>To implement pulmonary three‐dimensional (3D) radial ultrashort echo‐time (UTE) MRI in non‐sedated, free‐breathing neonates and adults with retrospective motion tracking of respiratory and intermittent bulk motion, to obtain diagnostic‐quality, respiratory‐gated images.</jats:p></jats:sec><jats:sec><jats:title>Methods</jats:title><jats:p>Pulmonary 3D radial UTE MRI was performed at 1.5 tesla (T) during free breathing in neonates and adult volunteers for validation. Motion‐tracking waveforms were obtained from the time course of each free induction decay's initial point (i.e., k‐space center), allowing for respiratory‐gated image reconstructions that excluded data acquired during bulk motion. Tidal volumes were calculated from end‐expiration and end‐inspiration images. Respiratory rates were calculated from the Fourier transform of the motion‐tracking waveform during quiet breathing, with comparison to physiologic prediction in neonates and validation with spirometry in adults.</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p>High‐quality respiratory‐gated anatomic images were obtained at inspiration and expiration, with less respiratory blurring at the expense of signal‐to‐noise for narrower gating windows. Inspiration‐expiration volume differences agreed with physiologic predictions (neonates; Bland‐Altman bias = 6.2 mL) and spirometric values (adults; bias = 0.11 L). MRI‐measured respiratory rates compared well with the observed rates (biases = <jats:italic>−</jats:italic>0.5 and 0.2 breaths/min for neonates and adults, respectively).</jats:p></jats:sec><jats:sec><jats:title>Conclusions</jats:title><jats:p>Three‐dimensional radial pulmonary UTE MRI allows for retrospective respiratory self‐gating and removal of intermittent bulk motion in free‐breathing, non‐sedated neonates and adults. Magn Reson Med 77:1284–1295, 2017. © 2016 International Society for Magnetic Resonance in Medicine</jats:p></jats:sec>