Application of MR imaging in assessment and follow-up of congenital heart disease in adults

mDixon ECG-gated 3-dimensional cardiovascular magnetic resonance angiography in patients with congenital cardiovascular disease

BACKGROUND

Cardiovascular magnetic resonance (CMR) angiography (CMRA) is an important non-invasive imaging tool for congenital heart disease (CHD) and aortopathy patients. The conventional 3D balanced steady-state free precession (bSSFP) sequence is often confounded by imaging artifacts. We sought to compare the respiratory navigated and electrocardiogram (ECG) gated modified Dixon (mDixon) CMRA sequence to conventional non-gated dynamic multi-phase contrast enhanced CMRA (CE-CMRA) and bSSFP across a variety of diagnoses.

METHODS

We included 24 patients with CHD or aortopathy with CMR performed between September 2017 to December 2017. Each patient had undergone CE-CMRA, followed by a bSSFP and mDixon angiogram. Patients with CMR-incompatible implants or contraindications to contrast were excluded. The studies were rated according to image quality at a scale from 1 (poor) to 4 (excellent) based on diagnostic adequacy, artifact burden, vascular border delineation, myocardium-blood pool contrast, and visualization of pulmonary and systemic veins and coronaries. Contrast-to-noise ratio (CNR), signal-to-noise ratio (SNR) and quantitative vascular measurements were compared between the two gated sequences. Bland-Altman plots were generated to compare paired measures.

RESULTS

All scans were diagnostically adequate. Mean (SD) quality scores were 3.4 (0.7) for the mDixon, 3.2 (0.5) for the bSSFP and 3.4 (0.5) for the CE-CMRA. Qualitatively, the intracardiac anatomy and myocardium-blood pool definition were better in the bSSFP; however, mDixon images showed enhanced vessel wall sharpness with less blurring surrounding the anatomical borders distally. Coronary origins were identified in all cases. Pulmonary veins were visualized in 92% of mDixon sequences, 75% of bSSFP and 96% of CE-CMRA. Similarly, neck veins were identified in 92, 83 and 96% respectively. Artifacts prevented vascular measurement in 6/192 (3%) and 4/192 (2%) of total vascular measurements for the mDixon and bSSFP, respectively. However, the size of signal void and field distortion were significantly worse in the latter, particularly for flow and metal induced artifacts.

CONCLUSION

In patients with congenital heart disease, ECG gated mDixon angiography yields high fidelity vascular images including better delineation of head and neck vasculature and pulmonary veins and fewer artifacts than the comparable bSSFP sequence. It should be considered as the preferred strategy for successful CHD imaging in patients with valve stenosis, vascular stents, or metallic implants.

Right Heart-Pulmonary Circulation Unit in Congenital Heart Diseases

The right ventricle plays a major role in congenital heart disease. This article describes the right ventricular mechanics in some selected congenital heart diseases affecting the right ventricle in different ways: tetralogy of Fallot, Ebstein anomaly, and the systemic right ventricle.

Magnetic resonance imaging for characterizing myocardial diseases

The National Institute of Health defined cardiomyopathy as diseases of the heart muscle. These myocardial diseases have different etiology, structure and treatment. This review highlights the key imaging features of different myocardial diseases. It provides information on myocardial structure/orientation, perfusion, function and viability in diseases related to cardiomyopathy. The standard cardiac magnetic resonance imaging (MRI) sequences can reveal insight on left ventricular (LV) mass, volumes and regional contractile function in all types of cardiomyopathy diseases. Contrast enhanced MRI sequences allow visualization of different infarct patterns and sizes. Enhancement of myocardial inflammation and infarct (location, transmurality and pattern) on contrast enhanced MRI have been used to highlight the key differences in myocardial diseases, predict recovery of function and healing. The common feature in many forms of cardiomyopathy is the presence of diffuse-fibrosis. Currently, imaging sequences generating the most interest in cardiomyopathy include myocardial strain analysis, tissue mapping (T₁, T_2, T₂*) and extracellular volume (ECV) estimation techniques. MRI sequences have the potential to decode the etiology by showing various patterns of infarct and diffuse fibrosis in myocarditis, amyloidosis, sarcoidosis, hypertrophic cardiomyopathy due to aortic stenosis, restrictive cardiomyopathy, arrythmogenic right ventricular dysplasia and hypertension. Integrated PET/MRI system may add in the future more information for the diagnosis and progression of cardiomyopathy diseases. With the promise of high spatial/temporal resolution and 3D coverage, MRI will be an indispensible tool in diagnosis and monitoring the benefits of new therapies designed to treat myocardial diseases.

Use of a semi-automated cardiac segmentation tool improves reproducibility and speed of segmentation of contaminated right heart magnetic resonance angiography

Three-dimensional printing has an increasing number of clinical applications in pediatric cardiology. Time required for dataset segmentation and conversion to stereolithography (STL) format remains a significant limitation. We investigated the impact of semi-automated cardiovascular-specific segmentation software on time and reproducibility of segmentation. Magnetic resonance angiograms (MRAs) of 19 patients undergoing intervention for right ventricular outflow lesions were segmented to demonstrate the right heart. STLs were created by two independent clinicians using semi-automated cardiovascular segmentation (SAS) and traditional manual segmentation (MS). Time was recorded and geometric STL disagreement was determined (0 % = no disagreement, 100 % = complete disagreement). MRA datasets were categorized as clean when only right heart structures were present in the MRA, or contaminated when left heart structures were also present and required removal. Eighteen (seven clean and 11 contaminated) cases were successfully segmented with both methods. Time to STL for clean datasets was faster with MS than SAS [median 209 s (IQR 192-252) vs. 296 s (272-317), p = 0.018] while contaminated datasets were faster with SAS [455 s (384-561) vs. 866 s (310-1429), p = 0.033]. Interobserver STL geometric disagreement was significantly lower using SAS than MS overall (0.70 ± 1.15 % vs. 1.31 ± 1.52 %, p = 0.030), and for the contaminated subset (0.81 ± 1.08 % vs. 1.75 ± 1.57 %, p = 0.036). Most geometric disagreement occurred at areas where left heart contamination was removed. Semi-automated segmentation was faster and more reproducible for contaminated datasets, while MS was faster but equally reproducible for clean datasets. Semi-automated segmentation methods are preferable for contaminated datasets and continued refinement of these tools should be supported.

Cardiac magnetic resonance imaging and the assessment of ebstein anomaly in adults

No published studies have evaluated the role of cardiac magnetic resonance (CMR) imaging for the assessment of Ebstein anomaly. Our objective was to evaluate the right heart characteristics in adults with unrepaired Ebstein anomaly using contemporary CMR imaging techniques. Consecutive patients with unrepaired Ebstein anomaly and complete CMR studies from 2004 to 2009 were identified (n = 32). Volumetric measurements were obtained from the short-axis and axial views, including assessment of the functional right ventricular (RV) end-diastolic volume (EDV) and end-systolic volume. The volume of the atrialized portion of the right ventricle in end-diastole was calculated as the difference between the total RVEDV and the functional RVEDV. The reproducibility of the measurements in the axial and short-axis views was determined within and between observers. The median value derived from the short-axis and axial views was 136 ml/m(2) (range 59 to 347) and 136 ml/m(2) (range 63 to 342) for the functional RVEDV, 153 ml/m(2) (range 64 to 441) and 154 ml/m(2) (range 67 to 436) for the total RVEDV, 49% (range 32% to 46%) and 50% (range 40% to 64%) for the functional RV ejection fraction, respectively. The axial measurements demonstrated lower intraobserver and interobserver variability than the short-axis approach for all values, with the exception of the intraobserver functional RVEDV and interobserver total RVEDV for which the limits of agreement and variance were not significantly different between the 2 views. In conclusion, measurements of right heart size and systolic function in patients with Ebstein anomaly can be reliably achieved using CMR imaging. Axial imaging appeared to provide more reproducible data than that obtained from the short-axis views.

Improved radial GRAPPA calibration for real-time free-breathing cardiac imaging

To generate real-time, nongated, free-breathing cardiac images, the undersampled radial trajectory combined with parallel imaging in the form of radial GRAPPA has shown promise. However, this method starts to fail at high undersampling factors due to the assumptions that must be made for the purposes of calibrating the GRAPPA weight sets. In this manuscript, a novel through-time radial GRAPPA calibration scheme is proposed which greatly improves image quality for the high acceleration factors required for real-time cardiac imaging. This through-time calibration method offers better image quality than standard radial GRAPPA, but it requires many additional calibration frames to be acquired. By combining the through-time calibration method proposed here with the standard through-k-space radial GRAPPA calibration method, images with high acceleration factors can be reconstructed using few calibration frames. Both the through-time and the hybrid through-time/through-k-space methods are investigated to determine the most advantageous calibration parameters for an R = 6 in vivo short-axis cardiac image. Once the calibration parameters have been established, they are then used to reconstruct several in vivo real-time, free-breathing cardiac datasets with temporal resolutions better than 45 msec, including one with a temporal resolution of 35 msec and an in-plane resolution of 1.56 mm(2) .