Sebastian A Seitz

Feasibility of real-time magnetic resonance imaging-guided endomyocardial biopsies: An in-vitro study

AIM To investigate if magnetic resonance (MR)-guided biopsy can improve the performance and safety of such procedures. METHODS A novel MR-compatible bioptome was evaluated in a series of in-vitro experiments in a 1.5T magnetic resonance imaging (MRI) system. The bioptome was inserted into explanted porcine and bovine hearts under real-time MR-guidance employing a steady state free precession sequence. The artifact produced by the metal element at the tip and the signal voids caused by the bioptome were visually tracked for navigation and allowed its constant and precise localization. RESULTS Cardiac structural elements and the target regions for the biopsy were clearly visible. Our method allowed a significantly better spatial visualization of the bioptoms tip compared to conventional X-ray guidance. The specific device design of the bioptome avoided inducible currents and therefore subsequent heating. The novel MR-compatible bioptome provided a superior cardiovascular magnetic resonance (imaging) soft-tissue visualization for MR-guided myocardial biopsies. Not at least the use of MRI guidance for endomyocardial biopsies completely avoided radiation exposure for both patients and interventionalists. CONCLUSION MRI-guided endomyocardial biopsies provide a better than conventional X-ray guided navigation and could therefore improve the specificity and reproducibility of cardiac biopsies in future studies.

Influence of tissue anisotropy on the distribution of defibrillation fields

The development of new devices used for defibrillation and cardioversion is often supported by numerical simulations of the induced electric potentials and current distributions. The commonly used tools incorporate isotropic models of the tissue properties present in the human torso. A comparative study was conducted to characterize the influence of anisotropic compared to isotropic tissue modeling. Defibrillation shocks with amplitudes of 1000 V and 2000 V were simulated and a set of varying conductivity values and anisotropy ratios was examined. The inclusion of tissue anisotropy produced significantly smaller values for current density compared to isotropic calculations especially in the myocardial tissue.

Diffuse myocardial fibrosis in early forms of dilated cardiomyopathy: insights from T1 mapping cardiovascular magnetic resonance

Background The underlying myocardial injury in early forms of dilated cardiomyopathy (DCM) is unclear. Cardiovascular magnetic resonance (CMR) myocardial T1-mapping monitors the enlargement of the cardiac extra-cellular space and thus offers a non-invasive tool of quantitative measurement of myocardial fibrosis. We used T1mapping techniques to explore the hypothesis that diffuse myocardial fibrosis is related to DCM.

Non-invasive measurement of myocardial extracellular volume using T1 mapping as a novel biomarker of diffuse fibrosis in dilated cardiomyopathy

Background Diffuse myocardial fibrosis is frequently observed in histologies of dilated cardiomyopathy (DCM). T1-mapping techniques have the potential to measure fibrosis quantitatively and therefore provide novel cardiac magnetic resonance (CMR) insights into myocardial tissue characterization beyond the presently employed late gadolinium enhanced (LGE) techniques. Fibrosis results in expansion of the myocardial extracellular volume fraction (ECV). Recent reports indicate that T1-mapping calibrated by the blood hematocrit is a promising tool to non-invasively quantify ECV. We explored the clinical utility of this technique in a DCM cohort with different disease stages.

Increase of myocardial infarctions over the years after heart transplantation detected by late gadolinium enhanced MRI

Background Cardiac allograft vasculopathy (CAV) is one of the leading causes of death in patients who survive the first year after heart transplantation (HTX). Coronary angiography detects the presence of vasculopathy in 10% to 20% of transplant recipients at 1-year follow-up whereas CAV is diagnosed in 52% of survivors 10 years after HTX. As recently shown, non-invasive late gadolinium contrast enhanced MRI (LGE-CMR) is able to detect myocardial infarction (MI) typical patterns in patients after HTX. Since the presence of CAV over the years after HTX increases significantly, we hypothesized that MRI could detect MI consistent with the detection of CAV by coronary angiography. Methods 139 patients were divided into 4 groups depending on the time after HTX they were scanned (group I: 0-2 yrs, group II: 2-5 yrs, group III: 5-8 yrs and group IV: 8-10 yrs). Cine MRI with 32 channel image acquisition and vector-ECG gated short axis, two and four chamber cine slices with parallel image acquisition covering the entire left ventricle (LV) were acquired using a regular SSFP sequence on a 1.5T Whole Body MRI scanner (Achieva 1.5T, Philips Medical Systems). LGE-CMR (GadoliniumDTPA:0.2mmol/kg, Magnevist) was performed and analyzed by two experienced blinded observers. Areas of infarct-typical LGE patterns were defined as sub-endocardial LGE patterns of various degrees of transmurality. Data were expressed as percentage and groups were compared using Chi Square or Fisher Exact Test. P-values ≤ 0.05 were considered statistically significant. Results

Magnetic Resonance Imaging on Patients with Implanted Cardiac Pacemakers

Magnetic resonance imaging (MRI) has become an essential means of medical imaging in modern clinical diagnosis. Especially for the analysis of soft tissues it is often superior to other imaging techniques like computed tomography (CT) or X-ray. At the same time, the number of patients carrying a cardiac pacemaker or defibrillator is increasing. When these patients get in need for an MRI examination, their implanted medical device prohibits them now from being admitted to it. The reason for this contraindication are potentially dangerous interactions between RF fields occurring during MRI procedures and the leads and housings of the pacemakers. Besides dislocation and device malfunctions, which are both manageable today, the eventual heating of the tip of the leads is still regarded as an unresolved concern. The aim of this work was to analyze and identify the patterns that might induce heating and to develop strategies to counteract or totally avoid them. Two approaches were taken: a computational one with simulations of the occurring electromagnetic field distributions and an experimental one with in-vitro studies using Plexiglas phantoms in real MRI devices. In compliance with previous results in the literature, a significant correlation between the position and length of the implants and the to be expected heating was found. Furthermore the computer simulations confirmed the in-vitro experiments and vice versa. The most important finding of this work is the superiority of open MRI devices in contrast to the conventional bore-hole devices regarding a possible heating. The different orientation of the RF fields present in the open type reduced the induced currents in the pacemaker leads to a level where effects on the surrounding tissue are substantially less probable and hazardous.

Temperature measurements of pacemaker leads in a 1.0T high field open MRI using various MR sequences: initial results

Magnetic resonance imaging (MRI) is a valuable diagnostic method for many cardiovascular diseases. To date, patients with pacemakers are contra-indicated for cardiac MRI exams due to several effects that can occur during the MRI procedure: a) heating of the lead-tip, and b) less hazardous sensing errors and device malfunctions. Almost all measurements on MRI pacemaker compatibility have been conducted on classic 1.5 or 3T cylindrical whole-body MRI systems. In contrast, this study focused on the use of a high field open MRI (HFO) system due to its advantageous properties of RF fields which are commonly made responsible for the induction of lead heating.

Comparison of temperature measurements of pacemaker leads in a 1.0T high field open MRI and a 1.5T classic cylindrical MRI: initial results

As of today, the use of MRI procedures on patients with implanted cardiac pacemakers is prohibited due to safety issues. The implants can interact with the RF fields of the MRI device. The most hazardous effect is heating at the tip of the lead, less dangerous are sensing errors and malfunctions of the devices, because they disappear completely after the procedure. The majority of the previous studies used classic cylindrical whole-body MRI systems. The influence of different alignments of the pacemaker/lead system and the RF fields were evaluated by comparing temperature changes occurring in a cylindrical device with the effects induced in a high field open MRI (HFO) system.

Influence of body worn wireless mobile devices on implanted cardiac pacemakers

The number of implanted cardiac pacemakers and defibrillators is constantly increasing. At the same time, more and more of those patients use wireless mobile communication devices.

Electromagnetic Fields near Implanted Cardiac Devices during Magnetic Resonance Imaging

Magnetic Resonance Imaging (MRI) is widely used in daily clinical practice for the diagnosis of soft tissue in general and for several cardiac diseases in particular. With the implantation of active devices like pacemakers the patients become unavailable for this means of imaging due to potentially hazardous effects for the patient. Coupling of RF-fields into the device can lead to interference with the electronics and heating of the tissue near to the electrode. Aim of this work was to determine the field distributions inside the patient by means of computer models and numerical field calculation. In a phantom study all examined objects were placed in a saline filled plexiglass phantom which was positioned in the center of a birdcage coil. The frequency of the RF-signal was set to 64 MHz corresponding to 1.5 Tesla MRI systems. The simulations showed that the level of energy absorption near to the metallic object depends on the distance from the center of the phantom as well as the straight length of the wires.