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Objective: Investigate the capacity of MRI to evaluate efficacy of radiofrequency (RF) ablations delivered to MRI-defined arrhythmogenic substrates., Methods: Baseline MRI was performed at 3 T including 3D LGE in a swine model of chronic myocardial infarct (N = 8). MRI-derived maps of scar and heterogeneous tissue channels (HTCs) were generated using ADAS 3D. Animals underwent electroanatomic mapping and ablation of the left ventricle in CARTO3, guided by MRI-derived scar maps. Post-ablation MRI (in vivo at 3 T in 5/8 animals; ex vivo at 1.5 T in 3/8) included 3D native T1-weighted IR-SPGR (TI = 700-800 ms) to visualize RF lesions. T1-derived RF lesions were compared against excised tissue. The locations of T1-derived RF lesions were compared against CARTO ablation tags, and segment-wise sensitivity and specificity of lesion detection were calculated within the AHA 17-segment model., Results: RF lesions were clearly visualized in HTCs, scar, and myocardium. Ablation patterns delivered in CARTO matched T1-derived RF lesion patterns with high sensitivity (88.9%) and specificity (94.7%), and were closely matched in registered MR-EP data sets, with a displacement of 5.4 ±3.8 mm (N = 152 ablation tags)., Conclusion: Integrating MRI into ablative procedures for RF lesion assessment is feasible. Patterns of RF lesions created using a standard 3D EAM system are accurately reflected by MRI visualization in healthy myocardium, scar, and HTCs comprising the MRI-defined arrhythmia substrate., Significance: MRI visualization of RF lesions can provide near-immediate ( 24 h) assessment of ablation, potentially indicating whether critical MRI-defined ventricular tachycardia substrates have been adequately ablated.

Objectives: Peripheral endovascular revascularization procedures often fail due to technical limitations of guidewire support, steering, and visualization. The novel CathPilot catheter aims to address these challenges. This study assesses the safety and feasibility of the CathPilot and compares its performance to conventional catheters for peripheral vascular interventions., Methods: The study compared the CathPilot to non-steerable and steerable catheters. The success rates and access times for a relevant target inside a tortuous vessel phantom model were assessed. The reachable workspace within the vessel and the guidewire's force delivery capabilities were also evaluated. To validate the technology, chronic total occlusion tissue samples were used ex vivo to compare crossing success rates with conventional catheters. Finally, in vivo experiments in a porcine aorta were conducted to evaluate safety and feasibility., Results: The success rates for reaching the set targets were 31%, 69%, and 100% with the non-steerable catheter, the steerable catheter, and the CathPilot, respectively. CathPilot had a significantly larger reachable workspace, and allowed for up to four times higher force delivery and pushability. In crossing of chronic total occlusion samples, the CathPilot achieved a success rate of 83% and 100%, for fresh and fixed lesions respectively, which was also significantly higher than conventional catheters. The device was fully functional in the in vivo study, and there were no signs of coagulation or damage to the vessel wall., Conclusion: This study shows the safety and feasibility of the CathPilot system and its potential to reduce failure and complication rates in peripheral vascular interventions. The novel catheter outperformed conventional catheters in all defined metrics. This technology can potentially improve the success rate and outcome of peripheral endovascular revascularization procedures.

Objective: Radiofrequency (RF) energy delivered to cardiac tissue produces a core ablation lesion with surrounding edema, the latter of which has been implicated in acute procedural failure of Ventricular Tachycardia (VT) ablation and late arrhythmia recurrence. This study sought to investigate the electrophysiological characteristics of acute RF lesions in the left ventricle (LV) visualized with native-contrast Magnetic Resonance Imaging (MRI)., Methods: An MR-guided electrophysiology system was used to deliver RF ablation in the LV of 8 swine (9 RF lesions in total), then perform MRI and electroanatomic mapping. The permanent RF lesions and transient edema were delineated via native-contrast MRI segmentation of T1-weighted images and T2 maps respectively. Bipolar voltage measurements were matched with image characteristics of pixels adjacent to the catheter tip. Native-contrast MR visualization was verified with 3D late gadolinium enhanced MRI and histology., Results: The T2-derived edema was significantly larger than the T1-derived RF lesion (2.1 ±1.5 mL compared to 0.58 ±0.34 mL; p=0.01). Bipolar voltage was significantly reduced in the presence of RF lesion core (p 0.05) and edema (p 0.05), with similar trends suggesting that both the permanent lesion and transient edema contributed to the region of reduced voltage. While bipolar voltage was significantly decreased where RF lesions are present (p 0.05), voltage did not change significantly with lesion transmurality (p 0.05)., Conclusion: Permanent RF lesions and transient edema are distinct in native-contrast MR images, but not differentiable using bipolar voltage., Significance: Intraprocedural native-contrast MRI may provide valuable lesion assessment in MR-guided ablation, whose clinical application is now feasible.

Objective: MRI in the area of cardiovascular catheter-based interventional procedures is an active field. A common intervention-revascularization of chronic total occlusions, requires a conductive guidewire for revascularization. The mechanical properties of guidewires are paramount to the successful execution of such procedures. Furthermore to benefit from MRI techniques, additional conductors are required to transmit signal from the tip of a catheter. Long thin conductors in MRI systems pose a safety risk in the form of RF heating due to induced RF currents on the conductors. Unfortunately many existing techniques to mitigate this risk require physical modification of the conductors, inevitably resulting in detrimental mechanical tradeoffs in the guidewire. This manuscript proposes a novel application and miniaturization of an existing device, the floating RF trap. The RF trap couples strongly to any thin conductor passing through the trap lumen inducing significant series impedance. This results in reduction of induced RF currents, and thus, heating., Methods and Results: This study shows theoretical and experimental analysis of induced impedance as well as theoretical reduction in heating due to various distributions of traps along the length of a catheter. Results of measuring induced current and heating in phantom experiments are also presented. Through comparison with commercial simulation packages and results of phantom experiments, it is shown that miniaturized RF traps can be modeled accurately, including their induced series impedance and effect on induced RF current., Conclusion and Significance: It was demonstrated that floating RF traps present a feasible method to mitigate RF heating while maintaining important mechanical properties of guidewires.

Goal: The purpose of this study is to improve the accuracy of interventional catheter guidance during intracardiac procedures. Specifically, the use of preprocedural magnetic resonance roadmap images for interventional guidance has limited anatomical accuracy due to intraprocedural respiratory motion of the heart. Therefore, we propose to build a novel respiratory motion model to compensate for this motion-induced error during magnetic resonance imaging (MRI)-guided procedures., Methods: We acquire 2-D real-time free-breathing images to characterize the respiratory motion, and build a smooth motion model via registration of 3-D prior roadmap images to the real-time images within a novel principal axes frame of reference. The model is subsequently used to correct the interventional catheter positions with respect to the anatomy of the heart., Results: We demonstrate that the proposed modeling framework can lead to smoother motion models, and potentially lead to more accurate motion estimates. Specifically, MRI-guided intracardiac ablations were performed in six preclinical animal experiments. Then, from retrospective analysis, the proposed motion modeling technique showed the potential to achieve a 27% improvement in ablation targeting accuracy., Conclusion: The feasibility of a respiratory motion model-based correction framework has been successfully demonstrated., Significance: The improvement in ablation accuracy may lead to significant improvements in success rate and patient outcomes for MRI-guided intracardiac procedures.

The substrate of potentially lethal cardiac arrhythmias often resides in the gray zone (GZ), a mixture of viable myocytes and collagen strands found between healthy myocardium and infarct core (IC). The specific aims of this paper are to demonstrate correspondence between regions delineated in T1* (apparent T1) maps and tissue characteristics seen in histopathology and to determine the MR imaging resolution needed to adequately identify GZ-associated substrate in chronic infarct. For this, a novel 3-D multicontrast late enhancement (MCLE) MR method was used to image ex vivo swine hearts with chronic infarction, at high resolution ( 0.6×0.6×1.25 mm). Pixel-wise classified tissue maps were calculated using steady-state and T1* images as input to a fuzzy-clustering algorithm. Quantitative histology based on collagen stains was performed in n = 10 selected slabs and showed very good correlations between histologically-determined areas of heterogeneous and dense fibrosis, and the corresponding GZ ( R2 = 0.96) and IC ( R2 = 0.97 ) in tissue classified maps. Furthermore, in n = 24 slabs, we performed volumetric measurements of GZ and IC, at the original and decreased image resolutions. Our results demonstrated that the IC volume remained relatively unchanged across all resolutions, whereas the GZ volume progressively increased with diminished image resolution, with changes reaching significance at 1×1×5 mm resolution (p < 0.05 ) but not at 1×1×2.5 mm, suggesting that this resolution may be sufficient to adequately identify the GZ from MCLE images, enabling an effective MR probing of remodeled myocardium in late infarct. Future work will focus on translating these findings to optimizing the current in vivo MCLE imaging of the GZ.

Recently, there is a growing interest in using magnetic resonance imaging (MRI) to guide interventional procedures due to its excellent soft tissue contrast and lack of ionizing radiation compared to traditional radiographic guidance. One of these applications is the use of MRI to guide radio frequency ablation of anatomic substrates, within the left ventricle, responsible for ventricular tachycardia. However, different MRI acquisition schemes have significant tradeoffs between image quality and acquisition time. Guidance using high-quality preoperative 3-D MR images is limited in the case of cardiac interventions because the heart moves dynamically during the procedure. On the other hand, 2-D real-time MR images acquired during the intervention sacrifice image quality for shorter image acquisition time, leading to real-time positional updates of cardiac anatomy. Ideally, we wish to combine the advantages of live feedback from real-time images and accurate visualization of anatomical structures from preoperative images. Therefore, to improve the MRI guidance capabilities for cardiac interventions, we describe a novel multiscale rigid registration framework to correct for respiratory motion between the prior and real-time datasets. In the proposed approach, we use a weighted total variation flow algorithm to extract coarse-to-fine features from the input images and subsequently register the corresponding scales in a hierarchical manner. Registration experiments were performed with in vivo human imaging data, and the target registration error achieved was 1.51 mm. Thus, the feasibility of motion correction in an interventional setting has been demonstrated, which may lead to significant improvements in the guidance of cardiac interventions.

Catheter ablation of ventricular tachycardia (VT) is preceded by characterization of the myocardial substrate via electroanatomical voltage mapping (EAVM). The purpose of this study was to characterize the relationship between chronic myocardial fibrotic scar detected by multicontrast late enhancement (MCLE) MRI and by EAVM obtained using an MR-guided electrophysiology system, with a final aim to better understand how these measures may improve identification of potentially arrhythmogenic substrates. Real-time MR-guided EAVM was performed in six chronically infarcted animals in a 1.5T MR system. The MCLE images were analyzed to identify the location and extent of the fibrotic infarct. Voltage maps of the left ventricle (LV) were created with an average of 231 ± 35 points per LV. Correlation analysis was conducted between bipolar voltage and three MR parameters (infarct transmurality, tissue categorization into healthy and scar classes, and normalized relaxation rate R1). In general, tissue regions classified as scar by normalized R1 values were well correlated with locations with low bipolar voltage values. Moreover, our results demonstrate that MRI information (transmurality, tissue classification, and relaxation rate) can accurately predict areas of myocardial fibrosis identified with bipolar voltage mapping, as demonstrated by ROC analysis. MCLE can help overcome limitations of bipolar voltage mapping including long durations and lower spatial discrimination and may help identify the sites within scars, which are commonly believed to trigger arrhythmic events in postinfarction patients.

Computer models of cardiac electrophysiology (EP) can be a very efficient tool to better understand the mechanisms of arrhythmias. Quantitative adjustment of such models to experimental data (personalization) is needed in order to test their realism and predictive power, but it remains challenging at the organ scale. In this paper, we propose a framework for the personalization of a 3-D cardiac EP model, the Mitchell-Schaeffer (MS) model, and evaluate its volumetric predictive power under various pacing scenarios. The personalization was performed on ex vivo large porcine healthy hearts using diffusion tensor MRI (DT-MRI) and optical mapping data. The MS model was simulated on a 3-D mesh incorporating local fiber orientations, built from DT-MRI. The 3-D model parameters were optimized using features such as 2-D epicardial depolarization and repolarization maps, extracted from the optical mapping. We also evaluated the sensitivity of our personalization framework to different pacing locations and showed results on its robustness. Further, we evaluated volumetric model predictions for various epi- and endocardial pacing scenarios. We demonstrated promising results with a mean personalization error around 5 ms and a mean prediction error around 10 ms (5% of the total depolarization time). Finally, we discussed the potential translation of such work to clinical data and pathological hearts.

The aim of this paper was to compare several in-vivo electrophysiological (EP) characteristics measured in a swine model of chronic infarct, with those predicted by simple 3-D MRI-based computer models built from ex-vivo scans (voxel size <1  mm(3)). Specifically, we recorded electroanatomical voltage maps (EAVM) in six animals, and ECG waves during induction of arrhythmia in two of these cases. The infarct heterogeneities (dense scar and border zone) as well as fiber directions were estimated using diffusion weighted DW-MRI. We found a good correspondence (r = 0.9) between scar areas delineated on the EAVM and MRI maps. For theoretical predictions, we used a simple two-variable macroscopic model and computed the propagation of action potential after application of a train of stimuli, with location and timing replicating the stimulation protocol used in the in-vivo EP study. Simulation results are exemplified for two hearts: one with noninducible ventricular tachycardia (VT), and another with a macroreentrant VT (for the latter, the average predicted VT cycle length was 273  ms, compared to a recorded VT of 250  ms).