Self-gated cardiac cine MRI

Abstract

The need for ECG gating presents many difficulties in cardiac magnetic resonance imaging (CMRI). Real-time imaging techniques eliminate the need for ECG gating in cine CMRI, but they cannot offer the spatial and temporal resolution provided by segmented acquisition techniques. Previous MR signal-based techniques have demonstrated an ability to provide cardiac gating information; however, these techniques result in decreased imaging efficiency. The purpose of this work was to develop a new "self-gated" (SG) acquisition technique that eliminates these efficiency deficits by extracting the motion synchronization signal directly from the same MR signals used for image reconstruction. Three separate strategies are proposed for deriving the SG signal from data acquired using radial k-space sampling: echo peak magnitude, kymogram, and 2D correlation. The SG techniques were performed on seven normal volunteers. A comparison of the results showed that they provided cine image series with no significant differences in image quality compared to that obtained with conventional ECG gating techniques. SG techniques represent an important practical advance in clinical MRI because they enable the acquisition of high temporal and spatial resolution cardiac cine images without the need for ECG gating and with no loss in imaging efficiency.

FIG. 1

Relationship between 2D object COM (x_c,y_c) and the 1D projection COM (ξ_c) at five projection orientations (ψ). Note the incremental change in ξ_c relative to the projection angle (θ), in accordance with Eq. [3].

FIG. 2

2D PR TrueFISP sequence (a) and the associated k-space sampling trajectory (b).

FIG. 3

End-systolic images in mid short-axis (top row) and four-chamber long-axis (bottom row) orientations. The images in column a were reconstructed using only the signal acquired with the small loop coil. The low-resolution images (12 views) in column b are representative of those used for ROI correlation mask h(x,y) selection, and the images in column c are the corresponding full-resolution images reconstructed using 144 total views and the signals from five coils.

FIG. 4

Representative SG signals used for gating the retrospective reconstruction while imaging in a cardiac short-axis orientation (◇ = R-wave position as recorded by the scanner ECG monitor ECG(i), dotted = echo peak magnitude, dashed = COM kymogram, solid = ROI correlation) along with the SG trigger positions (x = EPM(i), ■ = KYM(i), ▼ = 2DCOR(i)). Note the similar morphology of these SG signals, which is typical in the short-axis orientation.

FIG. 5

Representative SG signals used for gating the retrospective reconstruction while imaging in a cardiac long-axis orientation (◇ = R-wave position as recorded by the scanner ECG monitor ECG(i), dotted = echo peak magnitude, dashed = COM kymogram, solid = ROI correlation) along with the SG trigger positions (x = EPM(i), ■ = KYM(i), ▼ = 2DCOR(i)). Note the different morphology of these SG signals, which is typical in the long-axis orientation.

FIG. 6

Representative end-diastole (top row) and end-systole (bottom row) short-axis images from a single volunteer reconstructed using ECG gating (a), and echo-peak magnitude (b), COM kymogram (c), and ROI correlation (d) SG techniques. Note the relatively equivalent image quality among the techniques.

FIG. 7

Representative end-diastole (top row) and end-systole (bottom row) long-axis images from a single volunteer reconstructed using ECG gating (a), and echo-peak magnitude (b), COM kymogram (c), and ROI correlation (d) SG techniques. Note the relatively equivalent image quality among the techniques.