Free‐breathing whole‐heart coronary MRA with 3D radial SSFP and self‐navigated image reconstruction

Abstract

Respiratory motion is a major source of artifacts in cardiac magnetic resonance imaging (MRI). Free-breathing techniques with pencil-beam navigators efficiently suppress respiratory motion and minimize the need for patient cooperation. However, the correlation between the measured navigator position and the actual position of the heart may be adversely affected by hysteretic effects, navigator position, and temporal delays between the navigators and the image acquisition. In addition, irregular breathing patterns during navigator-gated scanning may result in low scan efficiency and prolonged scan time. The purpose of this study was to develop and implement a selfnavigated, free-breathing, whole-heart 3D coronary MRI technique that would overcome these shortcomings and improve the ease-of-use of coronary MRI. A signal synchronous with respiration was extracted directly from the echoes acquired for imaging, and the motion information was used for retrospective, rigid-body, through-plane motion correction. The images obtained from the self-navigated reconstruction were compared with the results from conventional, prospective, pencilbeam navigator tracking. Image quality was improved in phantom studies using self-navigation, while equivalent results were Key words: 3D radial; motion detection; self-navigation; wholeheart MRI; coronary angiography Free-breathing, three-dimensional (3D) cardiac MRI has received considerable attention because it enables highresolution imaging and, in contrast to breath-held imaging, does not require patient cooperation. For data acquisition during free breathing with the use of navigator technology (1), an end-expiratory gating window is defined prior to image acquisition, and data that were acquired outside the predefined respiratory gating window are rejected and remeasured in the next RR interval.However, fluctuations of the breathing pattern during prolonged scans may adversely affect the scan efficiency and prolong the scan time. Furthermore, the correlation between the navigator information and the actual position of the heart may be compromised by temporal delays (2) between the navigator signal and the actual image acquisition, which may arise from magnetization preparation pulses and the startup cycles necessary to approach the steady state. Also, the 2D-selective navigator pulses ("pencil beams") are preferably localized at the dome of the right hemidiaphragm to avoid contamination of the magnetization in the region of interest (ROI). While a stable correlation between the superior-inferior (SI) displacement of the diaphragm and the heart over a large number of subjects has been reported (3), hysteretic effects may occur (4), such as those induced by the difference in relative displacement between the diaphragm and the heart that reduce the precision of the motion estimation. Finally, the localization of the navigator beam requires special attention (5), which may decrease the utility and reproducibility of coronary MRI.To address these shortcomings, a self-navigated, 3D radi...

New respiratory gating technique for whole heart cine imaging: Integration of a navigator slice in steady state free precession sequences

“…The use of a single coil element for signal reception in combination with an angulated slice allowed selecting and positioning a beam-shaped navigator region. To determine the breathing motion, we used a cross-correlation measure rather than the center of mass or the correlation coefficient (10,15), allowing the determination of the diaphragm displacement in mm. Additional dephasing gradients were shown to be efficient in reducing signal from the imaging volume, with minimal effect over the navigator slice projection, making it more sensitive to motion detection.…”

“…This disturbs the steady state resulting in image artifacts. Self-respiratory gating techniques have been proposed (10)(11)(12)(13) to overcome this limitation. A common approach in those techniques is to use a respiratory navigation based on the acquisition of k 0 center points or k 0 profiles (14).…”

“…A common approach in those techniques is to use a respiratory navigation based on the acquisition of k 0 center points or k 0 profiles (14). For this, the breathing information is obtained from the intensity modulation of k 0 center points (11,12), or is detected using projections derived from the k 0 profiles (10,15). However, both approaches could fail in large patients, where the signal of k 0 or of k 0 profiles is strongly influenced by signals arising from static tissue.…”

Cardiac Magnetic Resonance Imaging for the Investigation of Cardiovascular Disorders. Part 2: Emerging Applications

“…Previously described free-breathing respiratory self-gated techniques are particularly useful for improving the efficiency and image quality of coronary MR imaging. 38,39 One of the strengths of coronary MR imaging lies in its high accuracy in the detection of congenital anomalies of the origin and the proximal course of the coronary arteries (Fig. 4).…”

Non-Invasive Coronary Angiography

“…This technique uses a synchronous respiratory signal from the echoes acquired during imaging. The motion information is then retrospectively corrected, improving temporal resolution and producing stiller images (Stehning et al, 2005).…”