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Abstract
Purpose
To develop a two-dimensional (2D) image-based respiratory motion correction technique for free-breathing coronary magnetic resonance angiography (MRA).
Materials and Methods
The proposed respiratory navigator obtained aliased a 2D sagittal image from under-sampled k-space data and utilized motion correlation between the aliased images. The proposed navigator was incorporated into the conventional coronary MRA sequence including the diaphragm navigator and tested in three healthy subjects.
References
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Fig. 1.
Illustration of the proposed 2D motion estimation. (a) Six-fold aliased image of the resolution phantom (a): at a reference position, (b) Shifted 16 mm along the SI direction. (c) Correlation between the reference aliased image and the second aliased image shifted over 2D search space. Due to the same translations of the six replicas, a local maximum is yielded at the true displacement (black arrow), and also at increments of (n·FOV/R) (gray arrow) away from the true solution (n = integer, R = under-sampling rate).
Fig. 2.
Timing diagram of coronary MRA with diaphragm navigator and 2D image-based navigator. The sequence consisted of a T2-preparation pulse, diaphragm navigator acquisition, fat saturation pulse, coronary acquisition, notched saturation pulse, and 2D image-based navigator acquisition, sequentially.
Fig. 3.
(a) Full-FOV sagittal image was acquired prior to coronary MRA scan and used to specify an ROI for motion estimation (yellow box). (b) Six-fold aliased image acquired during an MRA scan clearly shows image features to be used for motion estimation.
Fig. 4.
(a) Estimated motion in the S/I and A/P directions (in millimeters) and bellows signal (in arbitrary unit denoted as ‘a.u.’). In the top row, blue solid curve and black dotted curve represents the estimates by the proposed image-based navigator and the diaphragm navigator, respectively. (b) Trajectory of estimated motion in the SI-AP plane.
Fig. 5.
Representative coronary MRA images obtained using no correction (left column), 1D correction (S/I) based on the diaphragm navigator (middle row) and 2D correction (S/I + A/P) based on the proposed image-based navigator (right column). The delineation of the arterial tree progressively improves with the 1D and 2D corrections (arrows).
Table 1.
Motion Estimation Errors of Phantom Experiments
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