Rainer Schneider

Automated slice-specific simultaneous z-shim method for reducing B1 inhomogeneity and susceptibility-induced signal loss with parallel transmission at 3T

Through‐plane susceptibility‐induced signal loss in gradient recalled echo (GRE)‐based sequences can considerably impair both the clinical diagnosis and functional analysis of certain brain areas. In this work, a fully automated simultaneous z‐shim approach is proposed on the basis of parallel transmit (pTX) to reduce those signal dropouts at 3T.

B0-informed variable density trajectory design for enhanced correction of off-resonance effects in parallel transmission

To improve B1 and B0 inhomogeneity mitigation performance of spatially selective radio‐frequency (RF) pulses in parallel transmission while decreasing RF pulse power. Further enhancement of off‐resonance correction for rectilinear spoke‐trajectory‐based RF pulses with known residual geometric distortions after optimization.

Epicardial electroanatomical mapping, radiofrequency ablation, and lesion imaging in the porcine left ventricle under real-time magnetic resonance imaging guidance-an in vivo feasibility study

Abstract Aims Magnetic resonance imaging (MRI) is the gold standard for defining myocardial substrate in 3D and can be used to guide ventricular tachycardia ablation. We describe the feasibility of using a prototype magnetic resonance-guided electrophysiology (MR-EP) system in a pre-clinical model to perform real-time MRI-guided epicardial mapping, ablation, and lesion imaging with active catheter tracking. Methods and results Experiments were performed in vivo in pigs (n = 6) using an MR-EP guidance system research prototype (Siemens Healthcare) with an irrigated ablation catheter (Vision-MR, Imricor) and a dedicated electrophysiology recording system (Advantage-MR, Imricor). Following epicardial access, local activation and voltage maps were acquired, and targeted radiofrequency (RF) ablation lesions were delivered. Ablation lesions were visualized in real time during RF delivery using MR-thermometry and dosimetry. Hyper-acute and acute assessment of ablation lesions was also performed using native T1 mapping and late-gadolinium enhancement (LGE), respectively. High-quality epicardial bipolar electrograms were recorded with a signal-to-noise ratio of greater than 10:1 for a signal of 1.5 mV. During epicardial ablation, localized temperature elevation could be visualized with a maximum temperature rise of 35 °C within 2 mm of the catheter tip relative to remote myocardium. Decreased native T1 times were observed (882 ± 107 ms) in the lesion core 3–5 min after lesion delivery and relative location of lesions matched well to LGE. There was a good correlation between ablation lesion site on the iCMR platform and autopsy. Conclusion The MR-EP system was able to successfully acquire epicardial voltage and activation maps in swine, deliver, and visualize ablation lesions, demonstrating feasibility for intraprocedural guidance and real-time assessment of ablation injury.

Shaped saturation with inherent radiofrequency‐power‐efficient trajectory design in parallel transmission

A target‐pattern‐driven (TD) trajectory design is introduced in combination with parallel transmit (pTX) radiofrequency (RF) pulses to provide localized suppression of unwanted signals. The design incorporates target‐pattern and B1+ information to adjust denser sampling and coverage in k‐space regions where the main pattern information lies. Based on this approach, two‐dimensional RF spiral saturation pulses sensitive to RF power limits were applied in vivo for the first time.