Iterative motion‐compensation reconstruction ultra‐short TE (iMoCo UTE) for high‐resolution free‐breathing pulmonary MRI

Abstract

Purpose: To develop a high scanning efficiency, motion corrected imaging strategy for free-breathing pulmonary MRI by combining a motion compensation reconstruction with a UTE acquisition, called iMoCo UTE.Methods: An optimized golden angle ordering radial UTE sequence was used to continuously acquire data for 5 minutes. All readouts were grouped to different respiratory motion states based on self-navigator signals, then motion resolved data was reconstructed by XD Golden-angle RAdial Sparse Parallel reconstruction (XD-GRASP). One state from the motion resolved images was selected as a reference, and motion fields from the other states to the reference were derived via non-rigid registration. Finally, all motion resolved data and motion fields were reconstructed by using an iterative motion compensation reconstruction with a total generalized variation sparse constraint. Results:The iMoCo UTE strategy was evaluated in volunteers and non-sedated pediatric patient(4-6 y/o) studies. Images reconstructed with iMoCo UTE provided sharper anatomical lung structures, and higher apparent SNR and CNR, compared to using other motion correction strategies, such as soft-gating, motion resolved reconstruction, and non-rigid motion compensation(MoCo). iMoCo UTE also showed promising results in an infant study. Conclusions:The proposed iMoCo UTE combines self-navigation, motion modeling, and a compressed sensing reconstruction to increase scan efficiency, SNR, and reduce respiratory motion in lung MRI. This proposed strategy shows improvements in free breathing lung MRI scans, especially in very challenging application situations, such as pediatric MRI studies.

Three-dimensional magnetic resonance imaging ultrashort echo-time cones for assessing lung density in pediatric patients

“…Nonetheless MRI is being used increasingly for assessing the lung and airways in children [1][2][3][4]. Newer MRI techniques such as ultrashort echo-time and zero echo-time sequences have recently boosted the clinical MRI application to lung morphology and pathology [5][6][7][8][9][10]. The big advantage of MRI for lung imaging in children would be that it does not involve ionizing radiationwhich poses a substantial risk, especially in young children, who are the most sensitive [11] thus MRI could be used as radiation-free alternative to follow-up CT scans in pediatric patients [12].…”

Free‐breathing radial imaging using a pilot‐tone radiofrequency transmitter for detection of respiratory motion

“…To quantitatively evaluate the improvement in image sharpness achieved with PT, nine volunteer scans were reformatted into coronal orientation (via multi‐planar reformation), which is better suited for this task than the natively acquired axial orientation. Analysis of the image sharpness 12 was then performed on 10 central coronal slices by calculating the relative maximum derivative along the lung‐liver interfaces, defined as the maximum intensity gradient change between lung‐liver interfaces divided by mean intensity in the liver. To further evaluate the image sharpness achieved by self‐gating and PT signals, image sharpness was evaluated by an abdominal radiologist with 10 years of post‐fellowship experience (H.C.), who was blinded to the reconstruction methods.…”

2D Ultrashort Echo‐Time Functional Lung Imaging

“…[1][2][3] Even though fast 3D gradient echo sequences have been successfully applied to lung imaging, ultrashort (UTE) and zero-echo-time (ZTE) techniques have recently gained attention due to their excellent properties for imaging ultrashort T 2 * compounds. 1,2,[4][5][6][7][8][9][10][11][12][13][14][15] UTE techniques use radial center-out kspace sampling, thus enabling echo times only limited by the time required for switching between transmit and receive mode (front-end switching time), 16 while simultaneously showing beneficial motion artifact properties. 17 Where cardiac motion is negligible for anatomic lung imaging, respiratory motion has to be carefully considered to avoid impairment of the resulting image quality.…”

“…21,22 Further self-gating techniques exploit low-resolution images continuously reconstructed during free-breathing with high temporal resolution and follow, eg, the lungliver or lung-heart interface for deriving respective gating signals. 9,11,18 With either technique, images representing different respiratory and, if required, cardiac phases can be reconstructed. However, the application of non-UTE techniques is limited by the intrinsic low signal-to-noise ratio (SNR) and motion sensitivity in case of residual respiratory or cardiac motion.…”

“…Lung MRI is challenging due to both respiratory and cardiac motion, and the intrinsic low MR signal of the lung parenchyma caused by the low proton concentration and the multiple air–tissue interfaces resulting in a short T 2 * 1–3 . Even though fast 3D gradient echo sequences have been successfully applied to lung imaging, ultrashort (UTE) and zero‐echo‐time (ZTE) techniques have recently gained attention due to their excellent properties for imaging ultrashort T 2 * compounds 1,2,4–15 . UTE techniques use radial center‐out k‐ space sampling, thus enabling echo times only limited by the time required for switching between transmit and receive mode (front‐end switching time), 16 while simultaneously showing beneficial motion artifact properties 17 …”