Whole-heart cine MRI using real-time respiratory self-gating.

Two-dimensional (2D) breath-hold cine MRI is used to assess cardiac anatomy and function. However, this technique requires cooperation from the patient, and in some cases the scan planning is complicated. Isotropic nonangulated three-dimensional (3D) cardiac MR can overcome some of these problems because it requires minimal planning and can be reformatted in any plane. However, current methods, even those that use undersampling techniques, involve breath-holding for periods that are too long for many patients. Free-breathing respiratory gating sequences represent a possible solution for realizing 3D cine imaging. A real-time respiratory self-gating technique for whole-heart cine MRI is presented. The technique enables assessment of cardiac anatomy and function with minimum planning or patient cooperation. Nonangulated isotropic 3D data were acquired from five healthy volunteers and then reformatted into 2D clinical views. The respiratory self-gating technique is shown to improve image quality in free-breathing scanning. In addition, ventricular volumetric data obtained using the 3D approach were comparable to those acquired with the conventional multislice 2D approach.     

Free‐breathing cardiac MR with a fixed navigator efficiency using adaptive gating window size

A respiratory navigator with a fixed acceptance gating window is commonly used to reduce respiratory motion artifacts in cardiac MR. This approach prolongs the scan time and occasionally yields an incomplete dataset due to respiratory drifts. To address this issue, we propose an adaptive gating window approach in which the size and position of the gating window are changed adaptively during the acquisition based on the individual's breathing pattern. The adaptive gating window tracks the breathing pattern of the subject throughout the scan and adapts the size and position of the gating window such that the gating efficiency is always fixed at a constant value. To investigate the image quality and acquisition time, free breathing cardiac MRI, including both targeted coronary MRI and late gadolinium enhancement imaging, was performed in 67 subjects using the proposed navigator technique. Targeted coronary MRI was acquired from eleven healthy adult subjects using both the conventional and proposed adaptive gating window techniques. Fifty‐six patients referred for cardiac MRI were also imaged using late gadolinium enhancement with the proposed adaptive gating window technique. Subjective and objective image assessments were used to evaluate the proposed method. The results demonstrate that the proposed technique allows free‐breathing cardiac MRI in a relatively fixed time without compromising imaging quality due to respiratory motion artifacts. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.     

Motion correction using coil arrays (MOCCA) for free‐breathing cardiac cine MRI

In this study, we present a motion correction technique using coil arrays (MOCCA) and evaluate its application in free‐breathing respiratory self‐gated cine MRI. Motion correction technique using coil arrays takes advantages of the fact that motion‐induced changes in k‐space signal are modulated by individual coil sensitivity profiles. In the proposed implementation of motion correction technique using coil arrays self‐gating for free‐breathing cine MRI, the k‐space center line is acquired at the beginning of each k‐space segment for each cardiac cycle with 4 repetitions. For each k‐space segment, the k‐space center line acquired immediately before was used to select one of the 4 acquired repetitions to be included in the final self‐gated cine image by calculating the cross correlation between the k‐space center line with a reference line. The proposed method was tested on a cohort of healthy adult subjects for subjective image quality and objective blood‐myocardium border sharpness. The method was also tested on a cohort of patients to compare the left and right ventricular volumes and ejection fraction measurements with that of standard breath‐hold cine MRI. Our data indicate that the proposed motion correction technique using coil arrays method provides significantly improved image quality and sharpness compared with free‐breathing cine without respiratory self‐gating and provides similar volume measurements compared with breath‐hold cine MRI. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

Reconstruction from free‐breathing cardiac MRI data using reproducing kernel Hilbert spaces

This paper describes a rigorous framework for reconstructing MR images of the heart, acquired continuously over the cardiac and respiratory cycle. The framework generalizes existing techniques, commonly referred to as retrospective gating, and is based on the properties of reproducing kernel Hilbert spaces. The reconstruction problem is formulated as a moment problem in a multidimensional reproducing kernel Hilbert spaces (a two‐dimensional space for cardiac and respiratory resolved imaging). Several reproducing kernel Hilbert spaces were tested and compared, including those corresponding to commonly used interpolation techniques (sinc‐based and splines kernels) and a more specific kernel allowed by the framework (based on a first‐order Sobolev RKHS). The Sobolev reproducing kernel Hilbert spaces was shown to allow improved reconstructions in both simulated and real data from healthy volunteers, acquired in free breathing. Magn Reson Med, 2010. © 2009 Wiley‐Liss, Inc.     

Self-gated cardiac cine MRI.

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.     

Comparison of self-gated cine MRI retrospective cardiac synchronization algorithms

PURPOSE: To determine whether improved self-gating (SG) algorithms can provide superior synchronization accuracy for retrospectively gated cine MRI. MATERIALS AND METHODS: First difference, template matching, and polynomial fitting algorithms were implemented to improve the synchronization of MRI data using cardiac SG signals. Cine datasets were acquired during short-axis, two-, three-, and four-chamber cardiac MRI scans. The root-mean-square (RMS) error of SG synchronization positions compared to detected R-wave positions were calculated along with the mean square error (MSE) and peak signal-to-noise ratio (PSNR) comparing SG to electrocardiogram (ECG)-gated images. Overall image quality was also compared by two expert reviewers. RESULTS: RMS errors were highest for the first difference method for all orientations. Improvements for both template matching and cubic polynomial fitting methods were significant for two-, three-, and four-chamber scans. MSE values were lower and PSNR were significantly higher for the cubic method compared to the first difference method for all orientations. Reviewers scored the images to be of comparable quality. CONCLUSION: Template matching and polynomial fitting improved the accuracy of cardiac cycle synchronization for two-, three-, and four-chamber scans; improvements in SG synchronization accuracy were reflected in improvements in analytical image quality. Implementation of robust postprocessing algorithms may bring SG approaches closer to clinical utilization.     

Respiratory and cardiac self‐gated free‐breathing cardiac CINE imaging with multiecho 3D hybrid radial SSFP acquisition

A respiratory and cardiac self‐gated free‐breathing three‐dimensional cine steady‐state free precession imaging method using multiecho hybrid radial sampling is presented. Cartesian mapping of the k‐space center along the slice encoding direction provides intensity‐weighted position information, from which both respiratory and cardiac motions are derived. With in plan radial sampling acquired at every pulse repetition time, no extra scan time is required for sampling the k‐space center. Temporal filtering based on density compensation is used for radial reconstruction to achieve high signal‐to‐noise ratio and contrast‐to‐noise ratio. High correlation between the self‐gating signals and external gating signals is demonstrated. This respiratory and cardiac self‐gated, free‐breathing, three‐dimensional, radial cardiac cine imaging technique provides image quality comparable to that acquired with the multiple breath‐hold two‐dimensional Cartesian steady‐state free precession technique in short‐axis, four‐chamber, and two‐chamber orientations. Functional measurements from the three‐dimensional cardiac short axis cine images are found to be comparable to those obtained using the standard two‐dimensional technique. Magn Reson Med 63:1230–1237, 2010. © 2010 Wiley‐Liss, Inc.     

Wireless self-gated multiple-mouse cardiac cine MRI.

Despite the excellent image-contrast capability of MRI and the ability to synchronize MRI with the murine cardiac cycle, this technique is underused for assessing mouse models of cardiovascular disease because of its perceived cost and complexity. This perception stems, in part, from complications associated with the placement and adjustment of electrocardiographic leads that may interact with gradient pulses and the relatively long acquisition times required with traditional gating schemes. To improve the efficiency and reduce the cost and complexity of using cardiac MRI in mice, we combined wireless self-gating techniques (with which we derived cardiac synchronization signals from acquired data) with an imaging technique that acquires multislice cardiac cine images from four mice simultaneously. As a result, the wireless self-gated acquisitions minimized animal preparation time and improved image quality. The simultaneous acquisition of cardiac cine data from multiple animals greatly increased throughput and reduced costs associated with instrument access.     

Highly accelerated real‐time cardiac cine MRI using k–t SPARSE‐SENSE

For patients with impaired breath‐hold capacity and/or arrhythmias, real‐time cine MRI may be more clinically useful than breath‐hold cine MRI. However, commercially available real‐time cine MRI methods using parallel imaging typically yield relatively poor spatio‐temporal resolution due to their low image acquisition speed. We sought to achieve relatively high spatial resolution (～2.5 × 2.5 mm²) and temporal resolution (～40 ms), to produce high‐quality real‐time cine MR images that could be applied clinically for wall motion assessment and measurement of left ventricular function. In this work, we present an eightfold accelerated real‐time cardiac cine MRI pulse sequence using a combination of compressed sensing and parallel imaging (k‐t SPARSE‐SENSE). Compared with reference, breath‐hold cine MRI, our eightfold accelerated real‐time cine MRI produced significantly worse qualitative grades (1–5 scale), but its image quality and temporal fidelity scores were above 3.0 (adequate) and artifacts and noise scores were below 3.0 (moderate), suggesting that acceptable diagnostic image quality can be achieved. Additionally, both eightfold accelerated real‐time cine and breath‐hold cine MRI yielded comparable left ventricular function measurements, with coefficient of variation <10% for left ventricular volumes. Our proposed eightfold accelerated real‐time cine MRI with k–t SPARSE‐SENSE is a promising modality for rapid imaging of myocardial function. J. Magn. Reson. Imaging 2013. © 2012 Wiley Periodicals, Inc.     

Correction of left ventricular wall thickening from short-axis cine MRI for basal-descent through-plane motion

Purpose

To solve the problem of the basal descent movement in quantification of the regional left ventricular (LV) myocardial wall thickness (WTh) and wall thickening (%WT) in short‐axis (SA) cine MRI for effectively assessing the regional wall motion of LV myocardium.

Materials and Methods

LV long‐axis tagged MRI and SA cine MRI were performed to calculate the longitudinal translation and circumferential WTh of LV myocardium in eight normal volunteers. The new SA end‐systolic thickness (EST) data were reconstructed from the original EST data, based on the quantified longitudinal translation of LV myocardium.

Results

The mean %WT of six segments in the basal section after correction was significantly different from that before correction in both intra‐ and inter‐operator experiments. The polar map also showed the significant improvement of the variability of regional %WT and lack of quantification of %WT in the most basal SA slices after correction.

Conclusion

The proposed technique demonstrated an important advantage to calculate the %WT in the most basal SA myocardial tissue, which was considered difficult to be achieved using cine MRI. J. Magn. Reson. Imaging 2011;33:464–473. © 2011 Wiley‐Liss, Inc.