Respiratory motion-resolved, self-gated 4D-MRI using rotating cartesian k-space (ROCK)

Abstract

Purpose To propose and validate a respiratory motion resolved, self-gated (SG) 4D-MRI technique to assess patient-specific breathing motion of abdominal organs for radiation treatment planning. Methods The proposed 4D-MRI technique was based on the balanced steady-state free-precession (bSSFP) technique and 3D k-space encoding. A novel ROtating Cartesian K-space (ROCK) reordering method was designed that incorporates repeatedly sampled k-space centerline as the SG motion surrogate and allows for retrospective k-space data binning into different respiratory positions based on the amplitude of the surrogate. The multiple respiratory-resolved 3D k-space data were subsequently reconstructed using a joint parallel imaging and compressed sensing method with spatial and temporal regularization. The proposed 4D-MRI technique was validated using a custom-made dynamic motion phantom and was tested in 6 healthy volunteers, in whom quantitative diaphragm and kidney motion measurements based on 4D-MRI images were compared with those based on 2D-CINE images. Results The 5-minute 4D-MRI scan offers high-quality volumetric images in 1.2×1.2×1.6mm3 and 8 respiratory positions, with good soft-tissue contrast. In phantom experiments with triangular motion waveform, the motion amplitude measurements based on 4D-MRI were 11.89% smaller than the ground truth, whereas a −12.5% difference was expected due to data binning effects. In healthy volunteers, the difference between the measurements based on 4D-MRI and the ones based on 2D-CINE were 6.2±4.5% for the diaphragm, 8.2±4.9% and 8.9±5.1% for the right and left kidney. Conclusion The proposed 4D-MRI technique could provide high resolution, high quality, respiratory motion resolved 4D images with good soft-tissue contrast and are free of the “stitching” artifacts usually seen on 4D-CT and 4D-MRI based on resorting 2D-CINE. It could be used to visualize and quantify abdominal organ motion for MRI-based radiation treatment planning.

A retrospective 4D‐MRI based on 2D diaphragm profiles for lung cancer patients

“…One of the limitations of 4D imaging is breathing variation from breathing cycle to cycle. To reduce the effect of the breathing variation in 4D‐MRI, prospective imaging techniques utilize a scan triggering method. However, prospective methods usually require a long total scan time and produce a low contrast resolution .…”

“…To reduce the effect of the breathing variation in 4D‐MRI, prospective imaging techniques utilize a scan triggering method. However, prospective methods usually require a long total scan time and produce a low contrast resolution . In contrast, conventional retrospective 4D‐MRI methods utilize a sorting method based on respiratory surrogate signals thus, requiring much shorter imaging time.…”

Scattering matrix imaging pulse design for real‐time respiration and cardiac motion monitoring

“…Alternative methods estimate cardiac and respiratory motion from surrogate signals that are derived from the continuous acquisition of the k‐space centre, from a region‐of‐interest in the image domain, or from navigator echoes that are added to the imaging sequence. Some of these methods have sequence design constraints; others are limited to a specific k‐space sampling trajectory.…”

Accelerating volumetric cine MRI (VC-MRI) using undersampling for real-time 3D target localization/tracking in radiation therapy: a feasibility study

“…Retrospective 4D MRI usually suffers from long acquisition time (5–30 min) (Tryggestad et al , 2013; Stemkens et al , 2015; Han et al , 2017; Cai et al , 2011). Rank et al 2017 developed a method to generate retrospective 4D MRI with an acquisition time of under 40 seconds, but the reconstruction time varied between 5.5 and 7.5 hours (Rank et al , 2017).…”