BACKGROUND:Isotropic three-dimensional (3D) cine imaging is an attractive one-stop-shop acquisition for cardiac MRI, as it can be arbitrarily resliced for the assessment of cardiac function and simplifies imaging workflows. Current free-breathing 3D cine approaches are hampered by long reconstruction times, and at lower-field strengths, by relatively long acquisition times. Here, we aim to maximize acquisition efficiency at 0.55T pairing two techniques; using a spiral acquisition with an optimized sampling distribution and a reconstruction incorporating data from all respiratory phases. METHODS:We implemented a 2 mm isotropic 3D cine approach on a prototype 0.55T scanner, using a 6 min stack-of-spiral balanced steady-state free precession (bSSFP) acquisition modified to use tiny-golden-angle in-plane rotations and distribute the kz partition samples to a variable-density. The data were reconstructed with a modified iterative motion compensation reconstruction which resolved cardiac motion (denoted 4D iMoCo) and combined respiratory states using a navigator signal extracted from the acquired data. The proposed technique was compared to reference 2D free-breathing Cartesian volumetry of the left ventricle in 11 human subjects. RESULTS:The 4D iMoCo reconstruction required 20 min. The proposed variable-density sampling distribution reduced image artifacts, compared to a common linear sampling approach, and improved apparent signal-to-noise with relative increase of 221 ± 99%. Measurements had good agreement with the 2D Cartesian reference data with a left-ventricular volume bias of -2.5 ± 6.2% and 2.6 ± 10.4% in diastole and systole, respectively, and an ejection fraction bias of -3.5 ± 8.8%. CONCLUSION:We demonstrate an efficient free-breathing technique to produce 2 mm isotropic 3D cardiac images within a 6 min acquisition time and 20 min reconstruction time at 0.55T. Such a method could be a valuable clinical tool for cardiac imaging.

Objective: Magnetic Resonance Imaging (MRI)-guided robotic catheter interventions offer improved safety, visualization and control. Catheter actuation with current-carrying microcoils offers fast and responsive actuation without friction and backlash. However, actuation of this type of catheter leads to large void artifacts in MR images. We propose an interleaving method to reduce these artifacts without compromising the catheter's actuation capability. Methods: Interleaving is accomplished by synchronizing and interleaving catheter actuation and MR image acquisition at a high switching frequency using a TTL trigger from the MR scanner that triggers an Interrupt Service Routine in the catheter firmware. Reduction in catheter duty cycle is compensated using effective currents. Results: Image artifact analysis showed that there is not a statistically significant difference (at 0.05 significance level) between the artifacts associated with the catheter actuating with the proposed actuation-imaging interleaving and with the catheter at rest. Catheter trajectory tracking experiments showed that the error between pure actuation trajectories and interleaved actuation-imaging trajectories is generally within the error of the tracking algorithm. These results hold for both traditional MR imaging and accelerated imaging suitable for cardiac intervention. Conclusion: The proposed interleaving scheme effectively removes the artifact generated by current-carrying actuation coils while preserving the actuation capability of the catheter. The method can be used with an accelerated imaging sequence that is relevant for interventional imaging. Significance: The proposed scheme enables simultaneous/interleaved MR visualization and catheter actuation during intervention.

This protocol describes the procedures and parameters for magnetic resonance imaging (MRI) of embalmed human cadavers.

Atrial disease or myopathy is a growing concept in cardiovascular medicine, particularly in the context of atrial fibrillation, as well as amyloidosis and heart failure. Among cardiac imaging modalities, cardiovascular magnetic resonance (CMR) is particularly well suited for a comprehensive assessment of atrial myopathy, including tissue characterization and hemodynamics. The goal of this review article is to describe clinical applications and make recommendations on pulse sequences as well as imaging parameters to assess the left atrium and left atrial appendage. Furthermore, we aimed to create an overview of current and promising future emerging applications of left atrium-specific CMR pulse sequences focusing on both electrophysiologic (EP) and non-EP applications.

BACKGROUND:CN III is a pure motor cranial nerve that innervates the majority of the extraocular muscles. CN III palsy is the most common cranial nerve palsy with an incidence of 3-4 cases per 100,000. EVIDENCE ACQUISITION:High-resolution, 3-dimensional, skull base MRI allows for high spatial resolution and high signal-to-noise ratio allowing for optimal evaluation of CN III pathology by segment. RESULTS:A systemic approach is used to describe the segmental anatomy of CN III, its vascular supply, clinical pathologic manifestations, and imaging correlate. CONCLUSIONS:We present a segmental approach to high-resolution 3-dimensional MRI of the oculomotor nerve from nuclear to extraforaminal segments.

BACKGROUND:Pathological extravascular lung water is a facet of decompensated congestive heart failure that current cardiovascular magnetic resonance (CMR) methods fail to quantify. CMR can measure total lung water density, but cannot distinguish between intravascular and extravascular fluid, and thus is not diagnostic. Therefore, we develop and evaluate a novel method to measure extravascular lung water by distinguishing intravascular from extracellular fluid compartments using two different contrast agents, extracellular gadolinium chelates and iron-based intravascular ferumoxytol. METHODS:We created two porcine models of pulmonary edema: reversible catheter-induced mitral regurgitation to induce extravascular lung water (n = 5); intravascular volume overload using rapid colloid infusion (n = 5); and compared to normal controls (n = 8). We sequentially acquired lung T1 maps and lung water density maps at 0.55T with native, gadolinium-based, and ferumoxytol contrast, from which we calculated the extracellular volume fraction (ECV) and blood plasma volume fraction in the pulmonary tissue, respectively. We computed extravascular ECV as the difference in ECV and plasma volume fractions. Extravascular lung water volumes were estimated. RESULTS:In the mitral regurgitation model, baseline vs mitral regurgitation ECVextravascular increased from 27 ± 4.1% to 32 ± 1.9% (p = 0.006), and extravascular lung water volume increased from 105 ± 19 mL to 143 ± 15 mL (p = 0.048). Plasma volume fraction was similar at baseline vs mitral regurgitation (43 ± 4.2% vs 46 ± 5.4%, p = 0.26). Compared to naïve pigs, we measured higher plasma volume fractions in the intravascular volume-loaded model (42 ± 4.7% vs 51 ± 2.7%, p = 0.0054), but no differences in ECVextravascular (21 ± 4.6% vs 21 ± 3.6%, p = 0.99) or extravascular lung water volume (67 ± 13 mL vs 89 ± 24 mL, p = 0.11). Assessing the regional distribution, the plasma volume was higher posteriorly, indicating gravitational dependency, whereas, the extravascular lung water was higher anteriorly. CONCLUSION:Extravascular lung ECV measurements and derived lung water volumes corresponded well with predicted increases in extravascular and intravascular pulmonary fluid in animal models. This method may enable mechanistic studies of lung water in patients with dyspnea.

Background The 12-lead electrocardiogram (ECG) is a standard diagnostic tool for monitoring cardiac ischemia and heart rhythm during cardiac interventional procedures and stress testing. These procedures can benefit from magnetic resonance imaging (MRI) information; however, the MRI scanner magnetic field leads to ECG distortion that limits ECG interpretation. This study evaluated the potential for improved ECG interpretation in a “low field” 0.55T MRI scanner. Methods 12-lead ECGs were recorded inside 0.55T, 1.5T, and 3T MRI scanners, as well as at scanner table “home” position in the fringe field and outside the scanner room (7 pigs). To assess interpretation of ischemic ECG changes in a 0.55T MRI scanner, ECGs were recorded before and after coronary artery occlusion (7 pigs). ECGs was also recorded for 5 healthy human volunteers in the 0.55T scanner. ECG error and variation were assessed over 2-minute recordings for ECG features relevant to clinical interpretation: the PR interval, QRS interval, J point, and ST segment. Results ECG error was lower at 0.55T compared to higher field scanners. Only at 0.55T table home position did the error approach the guideline recommended 0.025mV ceiling for ECG distortion (median 0.03mV). At scanner isocenter, only in the 0.55T scanner did J point error fall within the 0.1mV threshold for detecting myocardial ischemia (median 0.03mV in pigs and 0.06mV in healthy volunteers). Correlation of J point deviation inside versus outside the 0.55T scanner following coronary artery occlusion was excellent at scanner table home position (r2 = 0.97), and strong at scanner isocenter (r2 = 0.92). Conclusions ECG distortion is improved in 0.55T compared to 1.5T and 3T MRI scanners. At scanner home position, ECG distortion at 0.55T is low enough that clinical interpretation appears feasible without need for more cumbersome patient repositioning. At 0.55T scanner isocenter, ST segment changes during coronary artery occlusion appear detectable but distortion is enough to obscure subtle ST segment changes that could be clinically relevant. Reduced ECG distortion in 0.55T scanners may simplify the problem of suppressing residual distortion by ECG cable positioning, averaging, and filtering and could reduce current restrictions on ECG monitoring during interventional MRI procedures.

Background: Quantitative myocardial tissue characterization with T1 and T2 parametric mapping can provide an accurate and complete assessment of tissue abnormalities across a broad range of cardiomyopathies. However, current clinical T1 and T2 mapping tools rely predominantly on two-dimensional (2D) breath-hold sequences. Clinical adoption of three-dimensional (3D) techniques is limited by long scan duration. The aim of this study is to develop and validate a time-efficient 3D free-breathing simultaneous T1 and T2 mapping sequence using multi-parametric SAturation-recovery and Variable-flip-Angle (mSAVA). Methods: mSAVA acquires four volumes for simultaneous whole-heart T1 and T2 mapping. We validated mSAVA using simulations, phantoms, and in-vivo experiments at 3T in 11 healthy subjects and 11 patients with diverse cardiomyopathies. T1 and T2 values by mSAVA were compared with modified Look-Locker inversion recovery (MOLLI) and gradient and spin echo (GraSE), respectively. The clinical performance of mSAVA was evaluated against late gadolinium enhancement (LGE) imaging in patients. Results: Phantom T1 and T2 by mSAVA showed a strong correlation to reference sequences (R2 = 0.98 and 0.99). In-vivo imaging with an imaging resolution of 1.5 x 1.5 x 8 mm3 could be achieved. Myocardial T1 and T2 of healthy subjects by mSAVA were 1310 +/- 46 and 44.6 +/- 2.0 ms, respectively, with T1 standard deviation higher than MOLLI (105 +/- 12 vs 60 +/- 16 ms) and T2 standard deviation lower than GraSE (4.5 +/- 0.8 vs 5.5 +/- 1.0 ms). mSAVA T1 and T2 maps presented consistent findings in patients undergoing LGE. Myocardial T1 and T2 of all patients by mSAVA were 1421 +/- 79 and 47.2 +/- 3.3 ms, respectively. Conclusion: mSAVA is a fast 3D technique promising for clinical whole-heart T1 and T2 mapping.

MR parametric mapping including T1 and T2 enabled quantitative evaluation of changes of myocardium. We previously proposed a time-efficient technique for 3D free-breathing simultaneous T1 and T2 mapping based on multi-parametric SAturation recovery and Variable flip Angle (mSAVA). This study evaluated the accuracy, precision, and reproducibility of mSAVA in comparison with conventional 2D sequences. mSAVA achieved good accuracy, between that of MOLLI and SASHA, and better precision and reproducibility than SASHA for T1 measurements. T2 measured by mSAVA had better precision and reproducibility than both GraSE and bSSFP T2. mSAVA offers a promising option for myocardial tissue characterization.

Background: The 12-lead electrocardiogram (ECG) is a standard diagnostic tool for monitoring cardiac ischemia and heart rhythm during cardiac interventional procedures and stress testing. These procedures can benefit from magnetic resonance imaging (MRI) information; however, the MRI scanner magnetic field leads to ECG distortion that limits ECG interpretation. This study evaluated the potential for improved ECG interpretation in a "low field" 0.55T MRI scanner. Methods: The 12-lead ECGs were recorded inside 0.55T, 1.5T, and 3T MRI scanners, as well as at scanner table "home" position in the fringe field and outside the scanner room (seven pigs). To assess interpretation of ischemic ECG changes in a 0.55T MRI scanner, ECGs were recorded before and after coronary artery occlusion (seven pigs). ECGs was also recorded for five healthy human volunteers in the 0.55T scanner. ECG error and variation were assessed over 2-minute recordings for ECG features relevant to clinical interpretation: the PR interval, QRS interval, J point, and ST segment. Results: ECG error was lower at 0.55T compared to higher field scanners. Only at 0.55T table home position, did the error approach the guideline recommended 0.025 mV ceiling for ECG distortion (median 0.03 mV). At scanner isocenter, only in the 0.55T scanner did J point error fall within the 0.1 mV threshold for detecting myocardial ischemia (median 0.03 mV in pigs and 0.06 mV in healthy volunteers). Correlation of J point deviation inside versus outside the 0.55T scanner following coronary artery occlusion was excellent at scanner table home position (r2 = 0.97), and strong at scanner isocenter (r2 = 0.92). Conclusion: ECG distortion is improved in 0.55T compared to 1.5T and 3T MRI scanners. At scanner home position, ECG distortion at 0.55T is low enough that clinical interpretation appears feasible without need for more cumbersome patient repositioning. At 0.55T scanner isocenter, ST segment changes during coronary artery occlusion appear detectable but distortion is enough to obscure subtle ST segment changes that could be clinically relevant. Reduced ECG distortion in 0.55T scanners may simplify the problem of suppressing residual distortion by ECG cable positioning, averaging, and filtering and could reduce current restrictions on ECG monitoring during interventional MRI procedures.

BACKGROUND Intramyocardial guidewire navigation is a novel technique that allows free transcatheter movement within ventricular muscle. Guidewire radial depth, between endocardial and epicardial surfaces, is ambiguous by x-ray and echocardiography.OBJECTIVES The aim of this study was to develop a simple tool, EDEN (Electrocardiographic Radial Depth Navigation), to indicate radial depth during intramyocardial guidewire navigation. Combined with routine imaging, EDEN facilitates a new family of intramyocardial catheter procedures to slice, reshape, pace, and ablate the heart.METHODS We mapped intramyocardial electrograms of left and right ventricular walls and septum during open-and closed-chest swine procedures (N 1/4 53), including MIRTH (Myocardial Intramural Remodeling by Transvenous Tether) ventriculoplasty. We identified radial depth-dependent features on unipolar electrograms. We developed a machine learning-based classifier to indicate categorical position, and modeled the findings in silico to test understanding of the physiology.RESULTS EDEN signatures distinguished 5 depth zones throughout left and right ventricular free walls and interventricular septum. Relative ST-segment elevation magnitude best discriminated position and was maximum (40.1 & PLUSMN; 6.5 mV) in the midmyocardium. Subendocardial positions exhibited dominant Q waves with lower-amplitude ST segments (16.8 & PLUSMN; 5.8 mV), whereas subepicardial positions exhibited dominant R waves with lower-amplitude ST segments (15.7 & PLUSMN; 4.8 mV). EDEN was unaffected by pacing-induced left bundle branch block. ST-segment elevation declined over minutes and reappeared after submillimeter guidewire manipulation. Modeling recapitulated EDEN features. The machine learning-based classifier was 97% accurate. EDEN successfully guided MIRTH ventriculoplasty.CONCLUSIONS EDEN provides a simple and reproducible real-time reflection of categorical guidewire-tip radial depth during intramyocardial guidewire navigation. Used in tandem with x-ray, EDEN enables novel, transcatheter, intramyocardial therapies such as MIRTH, SESAME (Septal Surfing Along Midline Endocardium), and cerclage ventriculoplasty. (J Am Coll Cardiol EP 2023;9:1741-1754) Published by Elsevier on behalf of the American College of Cardiology Foundation.

Purpose We describe a clinical grade, “active”, monopole antenna‐based metallic guidewire that has a continuous shaft‐to‐tip image profile, a pre‐shaped tip‐curve, standard 0.89 mm (0.035″) outer diameter, and a detachable connector for catheter exchange during cardiovascular catheterization at 0.55T. Methods Electromagnetic simulations were performed to characterize the magnetic field around the antenna whip for continuous tip visibility. The active guidewire was manufactured using medical grade materials in an ISO Class 7 cleanroom. RF‐induced heating of the active guidewire prototype was tested in one gel phantom per ASTM 2182‐19a, alone and in tandem with clinical metal‐braided catheters. Real‐time MRI visibility was tested in one gel phantom and in‐vivo in two swine. Mechanical performance was compared with commercial equivalents. Results The active guidewire provided continuous “profile” shaft and tip visibility in‐vitro and in‐vivo, analogous to guidewire shaft‐and‐tip profiles under X‐ray. The MRI signal signature matched simulation results. Maximum unscaled RF‐induced temperature rise was 5.2°C and 6.5°C (3.47 W/kg local background specific absorption rate), alone and in tandem with a steel‐braided catheter, respectively. Mechanical characteristics matched commercial comparator guidewires. Conclusion The active guidewire was clearly visible via real‐time MRI at 0.55T and exhibits a favorable geometric sensitivity profile depicting the guidewire continuously from shaft‐to‐tip including a unique curved‐tip signature. RF‐induced heating is clinically acceptable. This design allows safe device navigation through luminal structures and heart chambers. The detachable connector allows delivery and exchange of cardiovascular catheters while maintaining guidewire position. This enhanced guidewire design affords the expected performance of X‐ray guidewires during human MRI catheterization.

Background Exercise cardiovascular magnetic resonance (Ex-CMR) myocardial tagging would enable quantification of myocardial deformation after exercise. However, current electrocardiogram (ECG)-segmented sequences are limited for Ex-CMR. Methods We developed a highly accelerated balanced steady-state free-precession real-time tagging technique for 3 T. A 12-fold acceleration was achieved using incoherent sixfold random Cartesian sampling, twofold truncated outer phase encoding, and a deep learning resolution enhancement model. The technique was tested in two prospective studies. In a rest study of 27 patients referred for clinical CMR and 19 healthy subjects, a set of ECG-segmented for comparison and two sets of real-time tagging images for repeatability assessment were collected in 2-chamber and short-axis views with spatiotemporal resolution 2.0 × 2.0 mm 2 and 29 ms. In an Ex-CMR study of 26 patients with known or suspected cardiac disease and 23 healthy subjects, real-time images were collected before and after exercise. Deformation was quantified using measures of short-axis global circumferential strain (GCS). Two experienced CMR readers evaluated the image quality of all real-time data pooled from both studies using a 4-point Likert scale for tagline quality (1-excellent; 2-good; 3-moderate; 4-poor) and artifact level (1-none; 2-minimal; 3-moderate; 4-significant). Statistical evaluation included Pearson correlation coefficient ( r ), intraclass correlation coefficient (ICC), and coefficient of variation (CoV). Results In the rest study, deformation was successfully quantified in 90% of cases. There was a good correlation ( r = 0.71) between ECG-segmented and real-time measures of GCS, and repeatability was good to excellent (ICC = 0.86 [0.71, 0.94]) with a CoV of 4.7%. In the Ex-CMR study, deformation was successfully quantified in 96% of subjects pre-exercise and 84% of subjects post-exercise. Short-axis and 2-chamber tagline quality were 1.6 ± 0.7 and 1.9 ± 0.8 at rest and 1.9 ± 0.7 and 2.5 ± 0.8 after exercise, respectively. Short-axis and 2-chamber artifact level was 1.2 ± 0.5 and 1.4 ± 0.7 at rest and 1.3 ± 0.6 and 1.5 ± 0.8 post-exercise, respectively. Conclusion We developed a highly accelerated real-time tagging technique and demonstrated its potential for Ex-CMR quantification of myocardial deformation. Further studies are needed to assess the clinical utility of our technique.

Background Radiofrequency ablation (RFA) is a widely used treatment for atrial fibrillation, reducing the risk of cardiac arrhythmia. Detailed visualization and quantification of atrial scarring has the potential to improve preprocedural decision-making and postprocedural prognosis. Conventional bright-blood late gadolinium enhancement (LGE) MRI can help detect atrial scars; however, its suboptimal myocardium to blood contrast inhibits accurate scar estimation. Purpose To develop and test a free-breathing LGE cardiac MRI approach that simultaneously provides high-spatial-resolution dark-blood and bright-blood images for improved atrial scar detection and quantification. Materials and Methods A free-breathing, independent navigator-gated, dark-blood phase-sensitive inversion recovery (PSIR) sequence with whole-heart coverage was developed. Two coregistered high-spatial-resolution (1.25 × 1.25 × 3 mm3) three-dimensional (3D) volumes were acquired in an interleaved manner. The first volume combined inversion recovery and T2 preparation to achieve dark-blood imaging. The second volume functioned as the reference for phase-sensitive reconstruction with built-in T2 preparation for improved bright-blood contrast. The proposed sequence was tested in prospectively enrolled participants who had undergone RFA for atrial fibrillation (mean time since RFA, 89 days ± 26 [SD]) from October 2019 to October 2021. Image contrast was compared with conventional 3D bright-blood PSIR images using the relative signal intensity difference. Furthermore, native scar area quantification obtained from both imaging approaches was compared with measurements obtained with electroanatomic mapping (EAM) as the reference standard. Results A total of 20 participants (mean age, 62 years ± 9; 16 male) who underwent RFA for atrial fibrillation were included. The proposed PSIR sequence successfully acquired 3D high-spatial-resolution volumes in all participants, with a mean scan time of 8.3 minutes ± 2.4. The developed PSIR sequence improved scar to blood contrast compared with conventional PSIR sequence (mean contrast, 0.60 arbitrary units [au] ± 0.18 vs 0.20 au ± 0.19, respectively; P < .01) and correlated with EAM regarding scar area quantification (r = 0.66 [P < .01] vs r = 0.13 [P = .63]). Conclusion In participants who had undergone RFA for atrial fibrillation, an independent navigator-gated dark-blood PSIR sequence produced high-spatial-resolution dark-blood and bright-blood images with improved image contrast and native scar quantification compared with conventional bright-blood images. © RSNA, 2023 Supplemental material is available for this article.

Diagnostic-quality neuroimaging methods are vital for widespread clinical adoption of low field MRI. Spiral imaging is an efficient acquisition method that can mitigate the reduced signal-to-noise ratio at lower field strengths. As concomitant field artifacts are worse at lower field, we propose a generalizable quadratic gradient-field nulling as an echo-to-echo compensation and apply it to spiral TSE at 0.55 T. A spiral in–out TSE acquisition was developed with a compensation for concomitant field variation between spiral interleaves, by adding bipolar gradients around each readout to minimize phase differences at each refocusing pulse. Simulations were performed to characterize concomitant field compensation approaches. We demonstrate our proposed compensation method in phantoms and (n = 8) healthy volunteers at 0.55 T. Spiral read-outs with integrated spoiling demonstrated strong concomitant field artifacts but were mitigated using the echo-to-echo compensation. Simulations predicted a decrease of concomitant field phase RMSE between echoes of 42

The purpose of the current study was to develop and evaluate a three-dimensional single Breath-hOLd cardiac T2 mapping sequence (3D BOLT) with low-rank plus sparse (L + S) reconstruction for rapid whole-heart T2 measurement. 3D BOLT collects three highly accelerated electrocardiogram-triggered volumes with whole-heart coverage, all within a single 12-heartbeat breath-hold. Saturation pulses are performed every heartbeat to prepare longitudinal magnetization before T2 preparation (T2 -prep) or readout, and the echo time of T2 -prep is varied per volume for variable T2 weighting. Accelerated volumes are reconstructed jointly by an L + S algorithm. 3D BOLT was optimized and validated against gradient spin echo (GraSE) and a previously published approach (three-dimensional free-breathing cardiac T2 mapping [3DFBT2]) in both phantoms and human subjects (11 healthy subjects and 10 patients). The repeatability of 3D BOLT was validated on healthy subjects. Retrospective experiments indicated that 3D BOLT with 4.2-fold acceleration achieved T2 measurements comparable with those obtained with fully sampled data. T2 measured in phantoms using 3D BOLT demonstrated good accuracy and precision compared with the reference (R2  > 0.99). All in vivo imaging was successful and the average left ventricle T2 s measured by GraSE, 3DFBT2, and 3D BOLT were comparable and consistent for all healthy subjects (47.0 ± 2.3 vs. 47.7 ± 2.7 vs. 48.4 ± 1.8 ms) and patients (50.8 ± 3.0 vs. 48.6 ± 3.9 vs. 49.1 ± 3.7 ms), respectively. Myocardial T2 measured by 3D BOLT had excellent agreement with 3DFBT2 and there was no significant difference in mean, standard deviation, and coefficient of variation. 3D BOLT showed excellent repeatability (intraclass correlation coefficient: 0.938). The proposed 3D BOLT achieved whole-heart T2 mapping in a single breath-hold with good accuracy, precision, and repeatability on T2 measurements.