Whole‐heart coronary MR angiography with 2D self‐navigated image reconstruction

Abstract

Several self-navigation techniques have been proposed to improve respiratory motion compensation in coronary MR angiography. In this work, we implemented a 2D self-navigation method by using the startup profiles of a whole-heart balanced Steady-state free precession sequence, which are primarily used to catalyze the magnetization towards the steady-state. To create 2D self-navigation images (2DSN), we added phase encoding gradients to the startup profiles. With this approach we calculated foot-head and left-right motion and performed retrospective translational motion correction. The 2DSN images were reconstructed from 10 startup profiles acquired at the beginning of each shot. Nine healthy subjects were scanned, and the proposed method was compared to a 1D self-navigation (1DSN) method with foot-head correction only. Foot-head correction was also performed with the diaphragmatic 1D pencil beam navigator (1Dnav) using a tracking factor of 0.6. 2DSN shows improved motion correction compared to 1DSN and 1Dnav for all coronary arteries and all subjects for the investigated diaphragmatic gating window of 10 mm. The visualized vessel length of the right coronary artery could be significantly improved with a multiple targeted 2D self-navigation approach, compared to 2DSN method. Magn Reson Med 67:437-445, 2012. V C 2011 Wiley Periodicals, Inc.Key words: respiratory motion correction; whole-heart CMRA; 2D self-navigation Despite ongoing advances in MR sequence development respiratory motion remains a major impediment in coronary MR angiography (CMRA) (1). Early motion correction work focused on diaphragmatic 1D navigators (2), whereby motion models of different complexity, from foot-head (FH) translation (3) to affine 3D models (4), were used to relate diaphragmatic to cardiac motion. Recently, several self-navigation techniques have been proposed to improve respiratory motion correction and improve ease of use in CMRA (5-7). Compared to diaphragmatic navigators self-navigation methods do not require the use of a heart-diaphragm motion model, as they allow direct measurement of respiration-induced bulk cardiac motion. The direct measurement of cardiac motion also circumvents the problem of hysteresis between diaphragmatic and heart motion (8). The previously mentioned self-navigation approaches measure motion from 1D projections in one or more directions which means that motion could be impeded by static structures within the excited volume (9). Image based approaches have been proposed to improve motion estimation, by spatially encoding in 2D (10-12) or 3D (13), which allows for separation of the static chest wall and the moving heart. In this work, we create 2D self-navigation (2DSN) images by encoding the startup profiles of a balanced steady-state free precession sequence, similar to Yui et al. (12), which are primarily used to catalyze the magnetization towards the steady-state. This allows for spatial separation of static and moving structures, as well as translational correction in frequency and the phase encodi...

Motion Compensation Strategies in Magnetic Resonance Imaging

“…73 In coronary MRA, low-resolution images were used for respiratory motion compensation in two dimensions (SI and AP). 74 Another method to obtain motion information from the original MR data consists of reconstructing data segments that belong to the final image. A series of aliased images that are heavily undersampled are thus obtained, but these can be used for motion detection by applying a motion-tracking method such as image coregistration or cross-correlation.…”

Cardiac MR Assessment of Coronary Arteries

“…The technique was further developed to iterative self-navigation that does not require the choice of a respiratory reference position [44]. The image-based navigator technique is another method that uses a spatially encoded, low-resolution, 2D image acquired just before the acquisition of k-space data to correct the high-resolution data [45,46]. Fig.…”

Highly efficient motion-corrected simultaneous cardiac PET-MR imaging

“…A low-resolution 2D image navigator (iNav) is acquired at each heartbeat before the CMRA acquisition ( Fig. 1), by spatially encoding low flip angle start-up echoes of the acquisition [4].…”