Guidelines for the Evaluation of Prosthetic Valve Function With Cardiovascular Imaging: A Report From the American Society of Echocardiography Developed in Collaboration With the Society for Cardiovascular Magnetic Resonance and the Society of Cardiovascular Computed Tomography

In patients with significant cardiac valvular disease, intervention with either valve repair or valve replacement may be inevitable. Although valve repair is frequently performed, especially for mitral and tricuspid regurgitation, valve replacement remains common, particularly in adults. Diagnostic methods are often needed to assess the function of the prosthesis. Echocardiography is the first-line method for noninvasive evaluation of prosthetic valve function. The transthoracic approach is complemented with two-dimensional and three-dimensional transesophageal echocardiography for further refinement of valve morphology and function when needed. More recently, advances in computed tomography and cardiac magnetic resonance have enhanced their roles in evaluating valvular heart disease. This document offers a review of the echocardiographic techniques used and provides recommendations and general guidelines for evaluation of prosthetic valve function on the basis of the scientific literature and consensus of a panel of experts. This guideline discusses the role of advanced imaging with transesophageal echocardiography, cardiac computed tomography, and cardiac magnetic resonance in evaluating prosthetic valve structure, function, and regurgitation. It replaces the 2009 American Society of Echocardiography guideline on prosthetic valves and complements the 2019 guideline on the evaluation of valvular regurgitation after percutaneous valve repair or replacement.

Magnetic resonance in patients with cardiovascular devices. SEC-GT CRMTC/SEC-Heart Rhythm Association/SERAM/SEICAT consensus document

Magnetic resonance has become a first-line imaging modality in various clinical scenarios. The number of patients with different cardiovascular devices, including cardiac implantable electronic devices, has increased exponentially. Although there have been reports of risks associated with exposure to magnetic resonance in these patients, the clinical evidence now supports the safety of performing these studies under specific conditions and following recommendations to minimize possible risks. This document was written by the Working Group on Cardiac Magnetic Resonance Imaging and Cardiac Computed Tomography of the Spanish Society of Cardiology (SEC-GT CRMTC), the Heart Rhythm Association of the Spanish Society of Cardiology (SEC-Heart Rhythm Association), the Spanish Society of Medical Radiology (SERAM), and the Spanish Society of Cardiothoracic Imaging (SEICAT). The document reviews the clinical evidence available in this field and establishes a series of recommendations so that patients with cardiovascular devices can safely access this diagnostic tool.

Magnetic resonance in patients with cardiovascular devices. SEC-GT CRMTC/SEC-Heart Rhythm Association/SERAM/SEICAT consensus document

Magnetic resonance has become a first-line imaging modality in various clinical scenarios. The number of patients with different cardiovascular devices, including cardiac implantable electronic devices, has increased exponentially. Although there have been reports of risks associated with exposure to magnetic resonance in these patients, the clinical evidence now supports the safety of performing these studies under specific conditions and following recommendations to minimize possible risks. This document was written by the Working Group on Cardiac Magnetic Resonance Imaging and Cardiac Computed Tomography of the Spanish Society of Cardiology (SEC-GT CRMTC), the Heart Rhythm Association of the Spanish Society of Cardiology (SEC-Heart Rhythm Association), the Spanish Society of Medical Radiology (SERAM), and the Spanish Society of Cardiothoracic Imaging (SEICAT). The document reviews the clinical evidence available in this field and establishes a series of recommendations so that patients with cardiovascular devices can safely access this diagnostic tool.

Magnetic resonance imaging in patients with temporary external pacemakers

AIMS

To describe safety and feasibility of magnetic resonance imaging (MRI) in patients with transvenous temporary external pacemakers and whether artefacts affect the diagnostic image quality during cardiac MRI.

METHODS AND RESULTS

We reviewed records of all patients treated with temporary external pacing between 2016 and 2020 at a tertiary centre. Temporary pacing was established using a transvenous standard active fixation pacing lead inserted percutaneously and connected to a MRI-conditional pacemaker taped to the skin. All patients undergoing cardiac or non-cardiac MRI during temporary transvenous pacing were identified. Before MRI, devices were programmed according to guidelines for permanent pacemakers, and patients were monitored with continuous electrocardiogram during MRI. Of 827 consecutive patients receiving a temporary external pacemaker, a total of 44 (5%) patients underwent MRI (mean age 71 years, 13 [30%] females). Cardiac MRI was performed in 22 (50%) patients, while MRI of cerebrum, spine, and other regions was performed in the remaining patients. Median time from implantation of the temporary device to MRI was 6 (3-11) days. During MRI, we observed no device-related malfunction or arrhythmia. Nor did we detect any change in lead sensing, impedance, or pacing threshold. We observed no artefacts from the lead or pacemaker compromising the diagnostic image quality of cardiac MRI. MRI provided information to guide the clinical management in all cases.

CONCLUSION

MRI is feasible and safe in patients with temporary external pacing established with a regular MRI-conditional pacemaker and a standard active fixation lead. No artefacts compromised the diagnostic image quality.

Cardiac magnetic resonance imaging in patients with left bundle branch block: Patterns of dyssynchrony and implications for late gadolinium enhancement imaging

Background

Left bundle branch block (LBBB) is a ventricular conduction delay with high prevalence. Aim of our study is to identify possible recurring patterns of artefacts in late gadolinium enhancement (LGE) imaging in patients with LBBB who undergo cardiac magnetic resonance imaging (MRI) and to define parameters of mechanical dyssynchrony associated with artefacts in LGE images.

Materials and methods

Fifty-five patients with LBBB and 62 controls were retrospectively included. Inversion time (TI) scout and LGE images were reviewed for artefacts. Dyssynchrony was identified using cardiac MRI by determining left ventricular systolic dyssynchrony indices (global, septal segments, and free wall segments) derived from strain analysis and features of mechanical dyssynchrony (apical rocking and septal flash).

Results

Thirty-seven patients (67%) with LBBB exhibited inhomogeneous myocardial nulling in TI scout images. Among them 25 (68%) patients also showed recurring artefact patterns in the septum or free wall on LGE images and artefacts also persisted in 18 (72%) of those cases when utilising phase sensitive inversion recovery. Only the systolic dyssynchrony index of septal segments allowed differentiation of patient subgroups (artefact/no artefact) and healthy controls (given as median, median ± interquartile range); LBBB with artefact: 10.44% (0.44–20.44%); LBBB without artefact: 6.82% (-2.18–15.83%); controls: 4.38% (1.38–7.38%); p < 0.05 with an area under the curve of 0.863 (81% sensitivity, 89% specificity). Septal flash and apical rocking were more frequent in the LBBB with artefact group than in the LBBB without artefact group (70 and 62% versus 33 and 17%; p < 0.05).

Conclusion

Patients with LBBB show recurring artefact patterns in LGE imaging. Use of strain analysis and evaluation of mechanical dyssynchrony may predict the occurrence of such artefacts already during the examination and counteract misinterpretation.

Assessment of myocardial lipomatous metaplasia using an optimized out-of-phase cine steady-state free-precession sequence: Validation and clinical implementation

Myocardial lipomatous metaplasia, which can serve as substrate for ventricular arrhythmias, is usually composed of regions in which there is an admixture of fat and nonfat tissue. Although dedicated sequences for the detection of fat are available, it would be time-consuming and burdensome to routinely use these techniques to image the entire heart of all patients as part of a typical cardiac MRI exam. Conventional steady-state free-precession (SSFP) cine imaging is insensitive to detecting myocardial regions with partial fatty infiltration. We developed an optimization process for SSFP imaging to set fat signal consistently "out-of-phase" with water throughout the heart, so that intramyocardial regions with partial volume fat would be detected as paradoxically dark regions. The optimized SSFP sequence was evaluated using a fat phantom, through simulations, and in 50 consecutive patients undergoing clinical cardiac MRI. Findings were validated using standard Dixon gradient-recalled-echo (GRE) imaging as the reference. Phantom studies of test tubes with diverse fat concentrations demonstrated good agreement between measured signal intensity and simulated values calculated using Bloch equations. In patients, a line of signal cancellation at the interface between myocardium and epicardial fat was noted in all cases, confirming that SSFP images were consistently out-of-phase throughout the entire heart. Intramyocardial dark regions identified on out-of-phase SSFP images were entirely dark throughout in 33 patients (66%) and displayed an India-ink pattern in 17 (34%). In all cases, dark intramyocardial regions were also seen in the same locations on out-of-phase GRE and were absent on in-phase GRE, confirming that these regions represent areas with partial fat. In conclusion, if appropriately optimized, SSFP cine imaging allows for consistent detection of myocardial fatty metaplasia in patients undergoing routine clinical cardiac MRI without the need for additional image acquisitions using dedicated fat-specific sequences.

Left Ventricular Non-Compaction Cardiomyopathy-Still More Questions than Answers

Left ventricular non-compaction (LVNC) describes the phenotypical phenomena characterized by the presence of excessive trabeculation of the left ventricle which forms a deep recess filled with blood. Considering the lack of a uniform definition of LVNC as well as the "golden standard" it is difficult to estimate the actual incidence of the disease, however, seems to be overdiagnosed, due to unspecific diagnostic criteria. The non-compacted myocardium may appear both as a disease representation or variant of the norm or as an adaptive phenomenon. This article covers different approaches to incidence, pathogenesis, diagnostics, and treatment of LVNC as well as recommendations for patients during follow-up.

Compact pediatric cardiac magnetic resonance imaging protocols

Cardiac MRI is in many respects an ideal modality for pediatric cardiovascular imaging, enabling a complete noninvasive assessment of anatomy, morphology, function and flow in one radiation-free and potentially non-contrast exam. Nonetheless, traditionally lengthy and complex imaging acquisition strategies have often limited its broader use beyond specialized centers. In this review, the author presents practical cardiac MRI imaging protocols to facilitate the performance of succinct yet successful exams that provide the most salient clinical data for the majority of congenital and acquired pediatric cardiac disease. In addition, the author reviews newer and evolving techniques that permit more rapid but similarly diagnostic MRI, including compressed sensing and artificial intelligence/machine learning reconstruction, four-dimensional flow acquisition and blood pool contrast agents. With the modern armamentarium of cardiac MRI methods, the goal of compact yet comprehensive exams in children can now be realized.

Dobutamine stress cardiac MRI is safe and feasible in pediatric patients with anomalous aortic origin of a coronary artery (AAOCA)

BACKGROUND

Risk stratification in anomalous aortic origin of a coronary artery (AAOCA) is challenged by the lack of a reliable method to detect myocardial ischemia. We prospectively studied the safety and feasibility of Dobutamine stress-cardiac magnetic resonance (DSCMR), a test with excellent performance in adults, in pediatric patients with AAOCA.

METHODS

Consecutive DSCMR from 06/2014-12/2019 in patients≤20 years old with AAOCA were included. Hemodynamic response and major/minor events were recorded. Image quality and spatial/temporal resolution were evaluated. Rest and stress first-pass perfusion and wall motion abnormalities (WMA) were assessed. Inter-observer agreement was assessed using kappa coefficient.

RESULTS

A total of 224 DSCMR were performed in 182 patients with AAOCA at a median age of 14 years (IQR 12, 16) and median weight of 58.0 kg (IQR 43.3, 73.0). Examinations were completed in 221/224 (98.9%), all studies were diagnostic. Heart rate and blood pressure increased significantly from baseline (p < 0.001). No patient had major events and 28 (12.5%) had minor events. Inducible hypoperfusion was noted in 31/221 (14%), associated with WMA in 13/31 (42%). Inter-observer agreement for inducible hypoperfusion was very good (Κ = 0.87). Asymptomatic patients with inducible hypoperfusion are considered high-risk and those with a negative test are of standard risk.

CONCLUSIONS

DSCMR is feasible in pediatric patients with AAOCA to assess for inducible hypoperfusion and WMA. It can be performed safely with low incidence of major/minor events. Thus, DSCMR is potentially a valuable test for detection of myocardial ischemia and helpful in the management of this patient population.

Cardiovascular magnetic resonance: What clinicians should know about safety and contraindications

Cardiovascular magnetic resonance (MR) is a multiparametric, non-ionizing, non-invasive imaging technique, which represents the imaging gold standard to study cardiac anatomy, function and tissue characterization. Faced with a wide range of clinical application, in this review we aim to provide a comprehensive guide for clinicians about MR safety, contraindications and image quality. Starting from the physical interactions of the static magnetic fields, gradients and radiofrequencies with the human body, we will describe the most common metal and electronic devices which are allowed (MR-safe), allowed under limited conditions (MR-conditional) or contraindicated (MR-unsafe). Moreover, some conditions potentially affecting image quality and patient comfort will be mentioned, including arrhythmias, claustrophobia, and poor breath-hold capacity. Finally, we will discuss the pharmacodynamics and pharmacokinetics of current gadolinium-based contrast agents, their contraindications and their potential acute and chronic adverse effects, as well as the safety issue concerning the use of vasodilating/inotropic agents in stress cardiac MR.

[Retrospective Study of Image Quality in Pediatric Cardiac Cine MRI]

In pediatric cardiac cine magnetic resonance imaging (MRI), it must overcome several challenges including the patient's size and higher heart rate. The aim of this study was to retrospectively evaluate imaging optimization. Cardiac cine MRI data from 24 patients was analyzed (age range: 3 months-10 years, average age: 5 years, male/female: 11/13, R-R interval: 450±4 to 819±7 ms). About 11 cases out of 24 have good image quality. For small variations in the R-R interval and higher temporal resolution improved image quality with significant difference (P<0.05, Mann-Whitney U-test). In this study, values of temporal resolution <30 ms yielded good image quality for heart rates over 100 bpm. On the other hands, the factors dependent on the patient like heart rate and ejection fraction have no significant difference. The segmentation of data acquisition is more significant than recording small fields of view or thin slices for infantile and pediatric cardiac cine MRI. Similar to adult cases, variations in heart rate affect the image quality; however, we demonstrated that using segmentation of data acquisition results in improved image quality.

Guidelines for Cardiovascular Magnetic Resonance Imaging from the Korean Society of Cardiovascular Imaging-Part 3: Perfusion, Delayed Enhancement, and T1- and T2 Mapping

This document is the third part of the guidelines for the protocol, the interpretation and post-processing of cardiac magnetic resonance (CMR) studies. These consensus recommendations have been developed by the Consensus Committee of the Korean Society of Cardiovascular Imaging to standardize the requirements for image interpretation and post-processing of CMR. This third part of the recommendations describes tissue characterization modules, including perfusion, late gadolinium enhancement, and T1- and T2 mapping. Additionally, this document provides guidance for visual and quantitative assessment consisting of “What-to-See,” “How-To,” and common pitfalls for the analysis of each module. The Consensus Committee hopes that this document will contribute to the standardization of image interpretation and post-processing of CMR studies.

Guideline for Cardiovascular Magnetic Resonance Imaging from the Korean Society of Cardiovascular Imaging-Part 1: Standardized Protocol

Cardiac magnetic resonance (CMR) imaging is widely used in many areas of cardiovascular disease assessment. This is a practical, standard CMR protocol for beginners that is designed to be easy to follow and implement. This protocol guideline is based on previously reported CMR guidelines and includes sequence terminology used by vendors, essential MR physics, imaging planes, field strength considerations, MRI-conditional devices, drugs for stress tests, various CMR modules, and disease/symptom-based protocols based on a survey of cardiologists and various appropriate-use criteria. It will be of considerable help in planning and implementing tests. In addressing CMR usage and creating this protocol guideline, we particularly tried to include useful tips to overcome various practical issues and improve CMR imaging. We hope that this document will continue to standardize and simplify a patient-based approach to clinical CMR and contribute to the promotion of public health.

Clinical Value of Noncontrast-Enhanced Radial Quiescent-Interval Slice-Selective (QISS) Magnetic Resonance Angiography for the Diagnosis of Acute Pulmonary Embolism Compared to Contrast-Enhanced Computed Tomography and Cartesian Balanced Steady-State Free Precession

BACKGROUND

Free-breathing noncontrast-enhanced (non-CE) magnetic resonance angiography (MRA) techniques are of considerable interest for the diagnosis of acute pulmonary embolism (APE), due to the possibility for repeated examinations, avoidance of side effects from iodine-based contrast agents, and the absence of ionizing radiation exposure as compared to CE-computed tomographic angiography (CTA).

PURPOSE

To analyze the clinical performance of free-breathing and electrocardiogram (ECG)-gated radial quiescent-interval slice-selective (QISS)-MRA compared to CE-CTA and to Cartesian balanced steady-state free precession (bSSFP)-MRA.

STUDY TYPE

Prospective.

SUBJECTS

Thirty patients with confirmed APE and 30 healthy volunteers (HVs).

FIELD STRENGTH/SEQUENCE

Radial QISS- and bSSFP-MRA at 1.5T.

ASSESSMENT

Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were computed to compare the pulmonary imaging quality between MRA methods. The pulmonary arterial tree was divided into 25 branches and an ordinal scoring system was used to assess the image quality of each pulmonary branch. The clinical performance of the two MRA techniques in accurately assessing APE was evaluated with respect to CE-CTA as the clinical reference standard.

STATISTICAL TESTS

Wilcoxon signed-rank and Spearman's correlation tests were performed. Sensitivity and specificity of the MRA techniques were determined using CE-CTA as the clinical reference standard.

RESULTS

Thrombus-mimicking artifacts appeared more frequently in lobar and peripheral arteries of patients with Cartesian bSSFP than with radial QISS-MRA (pulmonary trunk: 12.2% vs. 14.0%, P = 0.64; lobar arteries: 35.6% vs. 22.0%, P = 0.005, peripheral arteries: 74.4% vs. 49.0%, P < 0.001). The relative increases in SNR and of CNR provided by radial QISS-MRA with respect to Cartesian bSSFP-MRA were 30-35% (P-values of SNR/CNR, HVs: 0.09/0.09, patients: 0.03/0.02). The image quality of pulmonary arterial branches was considered good to excellent in 77.2% of patients with radial QISS-MRA and in 43.2% with Cartesian bSSFP-MRA (P < 0.0001). The clinical performance of radial QISS-MRA was higher than Cartesian bSSFP-MRA for grading embolism, with a total sensitivity of 86.0% vs. 80.6% and a specificity of 93.3% vs. 84.0%, respectively.

DATA CONCLUSION

Radial QISS-MRA is a reliable and safe non-CE angiographic technique with promising clinical potential compared to Cartesian bSSFP-MRA and as an alternative technique to CE-CTA for the diagnosis of APE.

LEVEL OF EVIDENCE

1 TECHNICAL EFFICACY STAGE: 3.

Diffeomorphic Upsampling of Serially Acquired Sparse 2D Cross-Sections in Cardiac MRI

In this paper, we propose a new technique for interpolating shapes in order to upsample a sparsely acquired serial-section image stack. The method is based on a maximum a posteriori estimation strategy which models neighboring sections as observations of random deformations of an image to be estimated. We show the computation of diffeomorphic trajectories between observed sections and define estimated upsampled image sections as a Jacobian-weighted sum of flowing images at corresponding distances along those trajectories. We apply this methodology to upsample stacks of sparse 2D magnetic resonance cross-sections through live mouse hearts. We show that the proposed method results in smoother and more accurate reconstructions over linear interpolation, and report a Dice coefficient of 0.8727 against ground truth segmentations in our dataset and statistically significant improvements in both left ventricular segmentation accuracy and image intensity estimates.

Variability of MRI Aortic Stiffness Measurements in a Multicenter Clinical Trial Setting: Intraobserver, Interobserver, and Intracenter Variability of Pulse Wave Velocity and Aortic Strain Measurement

PURPOSE

To assess intraobserver, interobserver, and scan-rescan variability of MRI aortic stiffness measurements in a multicenter trial setting.

MATERIALS AND METHODS

This study was a retrospective analysis of prospectively collected data in a multicenter prospective clinical trial (clinicaltrials.gov ID NCT01870739). Forty-five adult patients (31 men; mean age, 58 years ± 12 [standard deviation]; 15 patients per center; three centers) with arterial hypertension underwent standardized 3-T baseline MRI assessments between June and September 2014. Aortic strain was calculated from maximum and minimum aortic area measurements repeated three times by three readers at three aortic levels on three retrospectively gated axial gradient-echo (GRE) data sets. Pulse wave velocity (PWV) was assessed three times by five readers as Δx/Δt: Δx was measured on a parasagittal GRE image of the aortic arch, and Δt was extracted from ascending and descending aortic velocity curves created on three axial phase-contrast acquisitions. Intraobserver, interobserver, and scan-rescan variability was calculated using percentage coefficient of variation (COV).

RESULTS

Aortic strain variability was lowest at the level of the distal descending aorta (DDA) with median COVs of 1.6% for intraobserver variability, 4.0% for interobserver variability, and 10.3% for scan-rescan variability. It was highest at the ascending aorta (AA) with COVs of 3.6% for intraobserver variability, 10.7% for interobserver variability, and 19.8% for scan-rescan variability. Variability of PWV was low: 0.7% for intraobserver variability, 1.5% for interobserver variability, and 8.1% for scan-rescan variability.

CONCLUSION

Low variability can be achieved for aortic strain and PWV measurements in a multicenter trial setting using standardized MRI protocols. Although COV was lower when measuring aortic strain at DDA compared with AA, variability was acceptable at both anatomic locations.Supplemental material is available for this article.© RSNA, 2020.

Standardized image interpretation and post-processing in cardiovascular magnetic resonance - 2020 update : Society for Cardiovascular Magnetic Resonance (SCMR): Board of Trustees Task Force on Standardized Post-Processing

With mounting data on its accuracy and prognostic value, cardiovascular magnetic resonance (CMR) is becoming an increasingly important diagnostic tool with growing utility in clinical routine. Given its versatility and wide range of quantitative parameters, however, agreement on specific standards for the interpretation and post-processing of CMR studies is required to ensure consistent quality and reproducibility of CMR reports. This document addresses this need by providing consensus recommendations developed by the Task Force for Post-Processing of the Society for Cardiovascular Magnetic Resonance (SCMR). The aim of the Task Force is to recommend requirements and standards for image interpretation and post-processing enabling qualitative and quantitative evaluation of CMR images. Furthermore, pitfalls of CMR image analysis are discussed where appropriate. It is an update of the original recommendations published 2013.

Artifacts by Misalignment of Cardiac Magnetic Resonance Phased-array Coil Elements: From Simulation to In vivo Test

BACKGROUND

Cardiac magnetic resonance evaluations generally require a radiofrequency coil setup comprising a transmit whole-body coil and a receive coil. In particular, radiofrequency phased-array coils are employed to pick up the signals emitted by the nuclei with high signal-tonoise ratio and a large region of sensitivity.

METHODS

Literature discussed different technical issues on how to minimize interactions between array elements and how to combine data from such elements to yield optimum Signal-to-Noise Ratio images. However, image quality strongly depends upon the correct coil position over the heart and of one array coil portion with respect to the other.

RESULTS

In particular, simple errors in coil positioning could cause artifacts carrying to an inaccurate interpretation of cardiac magnetic resonance images.

CONCLUSION

This paper describes the effect of array elements misalignment, starting from coil simulation to cardiac magnetic resonance acquisitions with a 1.5 T scanner. Phased-array coil simulation was performed using the magnetostatic approach; moreover, phantom and in vivo experiments with a commercial 8-elements cardiac phased-array receiver coil permitted to estimate signal-to-noise ratio and B1 mapping for aligned and shifted coil.

Sorted Golden-step phase encoding: an improved Golden-step imaging technique for cardiac and respiratory self-gated cine cardiovascular magnetic resonance imaging

BACKGROUND

Numerous self-gated cardiac imaging techniques have been reported in the literature. Most can track either cardiac or respiratory motion, and many incur some overhead to imaging data acquisition. We previously described a Cartesian cine imaging technique, pseudo-projection motion tracking with golden-step phase encoding, capable of tracking both cardiac and respiratory motion at no cost to imaging data acquisition. In this work, we describe improvements to the technique by dramatically reducing its vulnerability to eddy current and flow artifacts and demonstrating its effectiveness in expanded cardiovascular applications.

METHODS

As with our previous golden-step technique, the Cartesian phase encodes over time were arranged based on the integer golden step, and readouts near ky = 0 (pseudo-projections) were used to derive motion. In this work, however, the readouts were divided into equal and consecutive temporal segments, within which the readouts were sorted according to ky. The sorting reduces the phase encode jump between consecutive readouts while maintaining the pseudo-randomness of ky to sample both cardiac and respiratory motion without comprising the ability to retrospectively set the temporal resolution of the original technique. On human volunteers, free-breathing, electrocardiographic (ECG)-free cine scans were acquired for all slices of the short axis stack and the 4-chamber view of the long axis. Retrospectively, cardiac motion and respiratory motion were automatically extracted from the pseudo-projections to guide cine reconstruction. The resultant image quality in terms of sharpness and cardiac functional metrics was compared against breath-hold ECG-gated reference cines.

RESULTS

With sorting, motion tracking of both cardiac and respiratory motion was effective for all slices orientations imaged, and artifact occurrence due to eddy current and flow was efficiently eliminated. The image sharpness derived from the self-gated cines was found to be comparable to the reference cines (mean difference less than 0.05 mm- 1 for short-axis images and 0.075 mm- 1 for long-axis images), and the functional metrics (mean difference < 4 ml) were found not to be statistically different from those from the reference.

CONCLUSIONS

This technique dramatically reduced the eddy current and flow artifacts while preserving the ability of cost-free motion tracking and the flexibility of choosing arbitrary navigator zone width, number of cardiac phases, and duration of scanning. With the restriction of the artifacts removed, the Cartesian golden-step cine imaging can now be applied to cardiac imaging slices of more diverse orientation and anatomy at greater reliability.

Principles and applications of the balanced steady-state free precession sequence in small animal low-field MRI

Magnetic resonance imaging (MRI) in small animal practice is largely based on classic two-dimensional spin-echo, inversion recovery and gradient-echo sequences which are largely limited by low spatial resolution, especially in low-field (LF)-MRI scanners. Nowadays, however, the availability of volumetric sequences can open new perspectives and enhance the diagnostic potential of this imaging modality. Balanced steady-state free precession (bSSFP) is a three-dimensional gradient-echo sequence in which image contrast is given by the ratio of T2 and T1, resulting in low soft-tissue signal, poor cerebral grey/white matter distinction and a bright signal from free fluid and fat. Such properties, along with a high signal-to-noise ratio and a very high spatial resolution deriving from acquisition of contiguous blocks of data, make this sequence perfectly suited for morphologic imaging, particularly for fluid-containing structures. Although bSSFP is widely adopted in human medical imaging, the use of this sequence in veterinary radiology is limited to anatomic studies of the inner ear and quadrigeminal cistern. This review aims to discuss the technical background of the bSSFP sequence and its possible advantageous applications in small animal LF-MRI for different specific disorders of the spine (arachnoid diverticula, small disc herniation, facet joint synovial cysts), brain (supracollicular fluid accumulation, traumatic injuries) and ligaments (complete and partial tears).

Mitigation of near-band balanced steady-state free precession through-plane flow artifacts using partial dephasing

PURPOSE

To mitigate artifacts from through-plane flow at the locations of steady-state stopbands in balanced steady-state free precession (SSFP) using partial dephasing.

METHODS

A 60° range in the phase accrual during a TR was created over the voxel by slightly unbalancing the slice-select dephaser. The spectral profiles of SSFP with partial dephasing for various constant flow rates and during pulsatile flow were simulated to determine if partial dephasing decreases through-plane flow artifacts originating near SSFP dark bands while maintaining on-resonant signal. Simulations were then validated in a flow phantom. Lastly, phase-cycled SSFP cardiac cine images were acquired with and without partial dephasing in six subjects.

RESULTS

Partial dephasing decreased the strength and non-linearity of the dependence of the signal at the stopbands on the through-plane flow rate. It thus mitigated hyper-enhancement from out-of-slice signal contributions and transient-related artifacts caused by variable flow both in the phantom and in vivo. In six volunteers, partial dephasing noticeably decreased artifacts in all of the phase-cycled cardiac cine datasets.

CONCLUSION

Partial dephasing can mitigate the flow artifacts seen at the stopbands in balanced SSFP while maintaining the sequence's desired signal. By mitigating hyper-enhancement and transient-related artifacts originating from the stopbands, partial dephasing facilitates robust multiple-acquisition phase-cycled SSFP in the heart. Magn Reson Med 79:2944-2953, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

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.

Pseudo-projection-driven, self-gated cardiac cine imaging using cartesian golden step phase encoding

PURPOSE

To develop and evaluate a novel two-dimensional self-gated imaging technique for free-breathing cardiac cine MRI that is free of motion-detection overhead and requires minimal planning for motion tracking.

METHODS

Motion along the readout direction was extracted solely from normal Cartesian imaging readouts near ky  = 0. During imaging, the readouts below a certain |ky | threshold were scaled in magnitude and filtered in time to form "pseudo-projections," enabling projection-based motion tracking along readout without frequently acquiring the central phase encode. A discrete golden step phase encode scheme allowed the |ky | threshold to be freely set after the scan while maintaining uniform motion sampling.

RESULTS

The pseudo-projections stream displayed sufficient spatiotemporal resolution for both cardiac and respiratory tracking, allowing retrospective reconstruction of free-breathing non-electrocardiogram (ECG) cines. The technique was tested on healthy subjects, and the resultant image quality, measured by blood-myocardium boundary sharpness, myocardial mass, and single-slice ejection fraction was found to be comparable to standard breath-hold ECG-gated cines.

CONCLUSION

The use of pseudo-projections for motion tracking was found feasible for cardiorespiratory self-gated imaging. Despite some sensitivity to flow and eddy currents, the simplicity of acquisition makes the proposed technique a valuable tool for self-gated cardiac imaging. Magn Reson Med 76:417-429, 2016. © 2015 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

Best practices for cardiac magnetic resonance imaging in common large animal research models

Magnetic resonance imaging has proven to be useful for the study of cardiovascular physiology in health and disease; it provides important data and information about healthy and diseased states in humans and animals, and it facilitates the safe characterization and positioning of medical devices during cardiovascular applications. Looking to the future, magnetic resonance imaging will continue to play a formative role in biomedical research and applications. Here, we discuss how to avoid common pitfalls and provide safe transport, anesthetic support and physiologic support for animals that are used in dedicated or shared cardiovascular imaging facilities.

Cardiac MRI in patients with cardiac pacemakers: practical methods for reducing susceptibility artifacts and optimizing image quality

BACKGROUND

Magnetic resonance imaging (MRI) of pacemaker patients has become available despite of previous contraindications. However, pacing systems containing ferromagnetic material may hamper the diagnostic quality of cardiac MR (CMR) images.

PURPOSE

To study methods for reducing susceptibility-based artifacts in CMR examinations of pacemaker patients.

MATERIAL AND METHODS

Altogether 16 patients were scanned with 1.5T MRI scanner using cine balanced steady-state free-precession (bSSFP) and spoiled gradient echo (SPGR) sequences. The use of frequency-scout was also evaluated. For myocardial late gadolinium-enhanced (LGE) imaging, SPGR or bSSFP readout inversion-recovery prepared gradient echo sequences were used with and without phase-sensitive inversion-recovery (PSIR). Two radiologists subjectively compared the image quality (IQ) and the ranges of susceptibility artifacts were evaluated objectively.

RESULTS

The IQ proved adequate for diagnosing each patient, although in a few patients with a left-side implanted generator, artifacts hampered IQ in the anterior and anteroseptal segments of the myocardium in bSSFP cine and LGE sequences. In bSSFP cine, the use of frequency-scout could often transfer the banding artifacts away from the left ventricular myocardium. In LGE imaging, the artifacts were more pronounced in IR-bSSFP and PSIR than in IR-SPGR sequences. The ranges of generator-based artifacts were greater in bSSFP (10-12 cm) than in SPGR (6 cm) sequences due to banding artifacts.

CONCLUSION

The artifacts caused by pacemakers typically did not compromise the diagnostic IQ. The use of frequency-scout prior to bSSFP cine or the use of SPGR-based sequences could also improve IQ.

QUANTITATIVE PLANAR AND VOLUMETRIC CARDIAC MEASUREMENTS USING 64 MDCT AND 3T MRI VS. STANDARD 2D AND M-MODE ECHOCARDIOGRAPHY: DOES ANESTHETIC PROTOCOL MATTER?

Cross-sectional imaging of the heart utilizing computed tomography and magnetic resonance imaging (MRI) has been shown to be superior for the evaluation of cardiac morphology and systolic function in humans compared to echocardiography. The purpose of this prospective study was to test the effects of two different anesthetic protocols on cardiac measurements in 10 healthy beagle dogs using 64-multidetector row computed tomographic angiography (64-MDCTA), 3T magnetic resonance (MRI) and standard awake echocardiography. Both anesthetic protocols used propofol for induction and isoflourane for anesthetic maintenance. In addition, protocol A used midazolam/fentanyl and protocol B used dexmedetomedine as premedication and constant rate infusion during the procedure. Significant elevations in systolic and mean blood pressure were present when using protocol B. There was overall good agreement between the variables of cardiac size and systolic function generated from the MDCTA and MRI exams and no significant difference was found when comparing the variables acquired using either anesthetic protocol within each modality. Systolic function variables generated using 64-MDCTA and 3T MRI were only able to predict the left ventricular end diastolic volume as measured during awake echocardiogram when using protocol B and 64-MDCTA. For all other systolic function variables, prediction of awake echocardiographic results was not possible (P = 1). Planar variables acquired using MDCTA or MRI did not allow prediction of the corresponding measurements generated using echocardiography in the awake patients (P = 1). Future studies are needed to validate this approach in a more varied population and clinically affected dogs.

Utility of real-time three-dimensional echocardiography for Duchenne muscular dystrophy with echocardiographic limitations

Duchenne muscular dystrophy (DMD) is strongly associated with a unique form of dilated cardiomyopathy. Cardiac complications are the leading cause of death in DMD; thus, longitudinal assessments and early intervention for cardiac dysfunction are necessary to improve prognosis. Two-dimensional echocardiography, which is routinely used for cardiac assessment, has some limitations for quantitative analyses in DMD patients with thoracic deformities and regional wall motion abnormalities in the left ventricle. Recently, real-time three-dimensional echocardiography has emerged as a feasible tool for cardiac assessment in various cardiac diseases. The aim of this study was to examine the utility of this technology in DMD. We evaluated left ventricular ejection fraction (LVEF), a major parameter of left ventricular function, in 17 male DMD patients. LVEF values measured by real-time three-dimensional echocardiography were compared with those determined by two established nuclear cardiology methods: "the first-pass method of radionuclide angiocardiography" and "quantitative electrocardiogram-gated single-photon emission computed tomography". A good correlation was observed for LVEF values, particularly between real-time three-dimensional echocardiography and "the first-pass method of radionuclide angiocardiography" (r=0.90, p<0.05). Thus, real-time three-dimensional echocardiography can provide an accurate measurement of LVEF in DMD patients with echocardiographic limitations.

Impact of 3.0 T Cardiac MR Imaging Using Dual-Source Parallel Radiofrequency Transmission with Patient-Adaptive B1 Shimming

Objectives

To prospectively evaluate the impact of 3.0 T Cardiac MR imaging using dual-source parallel radiofrequency (RF) transmission with patient-adaptive B1 shimming compared with single-source RF transmission in the RF homogeneity, image contrast and image quality.

Methods

The study was approved by the local institutional review board, and all subjects provided written informed consent. Fourteen healthy volunteers were examined at 3.0 T MR, with both the conventional single-source and the new dual-source RF transmission. B1 calibrations (RF shimming) of the heart region were performed to acquire a percent of the prescribed flip angle (FA) of B1 maps, which were used for quantitative assessment of RF homogeneity. Contrast ratios (CRs) between ventricular blood pool and septum were calculated on balanced-turbo field echo (B-TFE) cine images. The off-resonance artifacts of cine images were blindly assessed by two radiologists according to a 4-point grading-scale.

Results

A significantly lower mean coefficients of variance of the achieved FA with dual-source revealed better RF homogeneity compared to single-source (P = 0.0094). Dual-source RF shimming significantly increased the CRs (P<0.05) and reduced the off-resonance artifacts of B-TFE cine images (P<0.05). Inter-observer agreement for the off-resonance artifacts of B-TFE cine images was good to excellent (k >0.65).

Conclusions

Dual-source parallel RF transmission significantly improves the RF homogeneity, increases image contrast and reduces image artifacts of cardiac B-TFE images compared to single-source mode. This may be of value in reducing the observer-dependence of cardiac MR images and enhancing diagnostic confidence for clinical practice using CMR at 3.0 T.

Cardiovascular magnetic resonance artefacts

The multitude of applications offered by CMR make it an increasing popular modality to study the heart and the surrounding vessels. Nevertheless the anatomical complexity of the chest, together with cardiac and respiratory motion, and the fast flowing blood, present many challenges which can possibly translate into imaging artefacts. The literature is wide in terms of papers describing specific MR artefacts in great technical detail. In this review we attempt to summarise, in a language accessible to a clinical readership, some of the most common artefacts found in CMR applications. It begins with an introduction of the most common pulse sequences, and imaging techniques, followed by a brief section on typical cardiovascular applications. This leads to the main section on common CMR artefacts with examples, a short description of the mechanisms behind them, and possible solutions.

Standardized image interpretation and post processing in cardiovascular magnetic resonance: Society for Cardiovascular Magnetic Resonance (SCMR) board of trustees task force on standardized post processing

With mounting data on its accuracy and prognostic value, cardiovascular magnetic resonance (CMR) is becoming an increasingly important diagnostic tool with growing utility in clinical routine. Given its versatility and wide range of quantitative parameters, however, agreement on specific standards for the interpretation and post-processing of CMR studies is required to ensure consistent quality and reproducibility of CMR reports. This document addresses this need by providing consensus recommendations developed by the Task Force for Post Processing of the Society for Cardiovascular MR (SCMR). The aim of the task force is to recommend requirements and standards for image interpretation and post processing enabling qualitative and quantitative evaluation of CMR images. Furthermore, pitfalls of CMR image analysis are discussed where appropriate.

Myocardial edema imaging by cardiovascular magnetic resonance: current status and future potential

Cardiovascular magnetic resonance (CMR) imaging is widely established, free of radioactive material or ionizing radiation, and the accepted noninvasive gold standard for numerous noninvasive cardiac markers. Using a technique called T2-weighted imaging, CMR can be used to assess myocardial edema as a reliable marker for acute, potentially reversible myocardial injury. Contrast agents are not required as the myocardial free water content affects the magnetic properties of the tissue, thus providing inherent image contrast. In this review, we illustrate the utility of T2-weighted techniques in the assessment of myocardial edema in a range of clinical scenarios. The detection of myocardial edema is clinically relevant in many acute settings and may be further helpful to better understand the pathophysiology of many non-acute clinical diseases. Currently, T2-weighted CMR represents the only imaging modality that can accurately depict and quantify the presence of myocardial edema in a noninvasive fashion. Thus, T2-weighted imaging should be included in a comprehensive CMR imaging protocol, especially if an acute injury is suspected.

Cardiac imaging: Part 1, MR pulse sequences, imaging planes, and basic anatomy

OBJECTIVE

MRI is a well-established modality for evaluating congenital and acquired cardiac diseases. This article reviews the latest pulse sequences used for cardiac MRI. In addition, the standard cardiac imaging planes and corresponding anatomy are described and illustrated.

CONCLUSION

Familiarity with the basic pulse sequences, imaging planes, and anatomy pertaining to cardiac MRI is essential to formulate optimal protocols and interpretations.

Cardiovascular magnetic resonance in patients with myocardial infarction: current and emerging applications

In patients with known or suspected myocardial infarction (MI), cardiovascular magnetic resonance (CMR) provides a comprehensive, multifaceted view of the heart. The data, including that from a recent multicenter clinical trial, indicate that delayed-enhancement cardiac magnetic resonance imaging (DE-CMR) is a well-validated, robust technique that can be easily implemented on scanners that are commonly available worldwide, with an effectiveness that clearly rivals the best available imaging techniques for the detection and assessment of acute and chronic MI. When patients present outside the diagnostic window of cardiac troponins, DE-CMR may be especially useful. Moreover, because DE-CMR can uniquely differentiate between ischemic and various nonischemic forms of myocardial injury, it may be helpful in cases of diagnostic uncertainty, such as in patients with classical features of MI in whom coronary angiography does not show a culprit lesion. Even after the diagnosis of MI has been made, CMR provides clinically relevant information by identifying residual viability, microvascular damage, stunning, and right ventricular infarction. In addition, post-MI sequelae, including left ventricular thrombus and pericarditis, are easily identified. Given that quantification of infarct size by DE-CMR is highly reproducible, this technique may provide a useful surrogate end point for clinical trials with appreciable reductions in sample size compared with alternative methods.