Reproducibility of tailored and universal nonselective excitation pulses at 7 T for human cardiac MRI: A 3-year and an interday study.

Purpose: Ultrahigh-field (UHF; ≥7 T) MRI is challenging due to spatially heterogeneous B profiles. This longitudinal study evaluates the reproducibility of three parallel-transmission excitation strategies to enable UHF cardiac MRI: vendor-supplied radiofrequency (RF) shim, subject-tailored kT-points pulses (TPs), and universal kT-points pulses (UPs).

Methods: Six healthy subjects underwent 7 T MRI scans performed by different MR operators using a 32-element parallel-transmission body array at four time points over 3 years.

Assessing reliability and comparability of 4D flow CMR whole heart measurements using retrospective valve tracking: A single-vendor study in the Berlin research network.

Introduction: This study investigated intracardiac flow dynamics and assessed the comparability and reliability of 4D flow CMR measurements across multiple sites within the Berlin Research Network for Cardiovascular Magnetic Resonance (BER-CMR) using 3D cine phase-contrast imaging with three-directional velocity encoding in a healthy traveling cohort.

Methods: In a prospective multi-site cohort study, 20 healthy volunteers underwent CMR at different sites. Quantitative assessment of Forward flow Volume (FFV), Peak (PV) and Mean Velocity (MV) across the heart's valves were conducted using retrospective valve tracking.

Improving MRI turbulence quantification by addressing the measurement errors caused by the derivatives of the turbulent velocity field - Sequence development and in-vitro validation.

Purpose: To improve the current method for MRI turbulence quantification which is the intravoxel phase dispersion (IVPD) method. Turbulence is commonly characterized by the Reynolds stress tensor (RST) which describes the velocity covariance matrix. A major source for systematic errors in MRI is the sequence's sensitivity to the variance of the derivatives of velocity, such as the acceleration variance, which can lead to a substantial measurement bias.

Deep learning-based whole-brain B -mapping at 7T.

Purpose: This study investigates the feasibility of using complex-valued neural networks (NNs) to estimate quantitative transmit magnetic RF field (B ) maps from multi-slice localizer scans with different slice orientations in the human head at 7T, aiming to accelerate subject-specific B -calibration using parallel transmission (pTx).

Methods: Datasets containing channel-wise B -maps and corresponding multi-slice localizers were acquired in axial, sagittal, and coronal orientation in 15 healthy subjects utilizing an eight-channel pTx transceiver head coil. Training included five-fold cross-validation for four network configurations: used transversal, sagittal, coronal data, and was trained on all slice orientations.

Hypertrophic obstructive cardiomyopathy-left ventricular outflow tract shapes and their hemodynamic influences applying CMR.

Hypertrophic cardiomyopathy (HCM) is one of the most common genetic cardiac disorders and is characterized by different phenotypes of left ventricular hypertrophy with and without obstruction. The effects of left ventricular outflow tract (LVOT) obstruction based on different anatomies may be hemodynamically relevant and influence therapeutic decision making. Cardiovascular magnetic resonance (CMR) provides anatomical information.

B1-MRF: Large dynamic range MRF-based absolute mapping in the human body at 7T.

Purpose: This study aims to map the transmit magnetic field ( ) in the human body at 7T using MR fingerprinting (MRF), with a focus on achieving high accuracy and precision across a large dynamic range, particularly at low flip angles (FAs).

Methods: A FLASH-based MRF sequence (B1-MRF) with high sensitivity was developed. Phantom and in vivo abdominal imaging were performed at 7T, and the results were compared with established reference methods, including a slow but precise preparation-based method (PEX), saturated TurboFLASH (satTFL), actual flip angle imaging (AFI) and Bloch-Siegert shift (BSS).

Learning carotid vessel wall segmentation in black-blood MRI using sparsely sampled cross-sections from 3D data.

Purpose: Atherosclerosis of the carotid artery is a major risk factor for stroke. Quantitative assessment of the carotid vessel wall can be based on cross-sections of three-dimensional (3D) black-blood magnetic resonance imaging (MRI). To increase reproducibility, a reliable automatic segmentation in these cross-sections is essential.

Accelerated mapping and robust parallel transmit pulse design for heart and prostate imaging at 7 T.

Purpose: To investigate the impact of reduced k-space sampling on mapping and the resulting impact on phase shimming and dynamic/universal parallel transmit (pTx) RF pulse design.

Methods: Channel-wise 3D maps were measured at 7 T in 35 and 23 healthy subjects for the heart and prostate region, respectively. With these maps, universal phase shims optimizing homogeneity and efficiency were designed for heart and prostate imaging.

Free-breathing high-resolution respiratory-gated radial stack-of-stars magnetic resonance imaging of the upper abdomen at 7 T.

Ultrahigh field magnetic resonance imaging (MRI) (≥ 7 T) has the potential to provide superior spatial resolution and unique image contrast. Apart from radiofrequency transmit inhomogeneities in the body at this field strength, imaging of the upper abdomen faces additional challenges associated with motion-induced ghosting artifacts. To address these challenges, the goal of this work was to develop a technique for high-resolution free-breathing upper abdominal MRI at 7 T with a large field of view.

Calibration-free parallel transmission of the cervical, thoracic, and lumbar spinal cord at 7T.

Purpose: To address the limitations of spinal cord imaging at ultra-high field (UHF) due to time-consuming parallel transmit (pTx) adjustments. This study introduces calibration-free offline computed universal shim modes that can be applied seamlessly for different pTx RF coils and spinal cord target regions, substantially enhancing spinal cord imaging efficiency at UHF.

Methods: A library of channel-wise relative maps for the cervical spinal cord (six datasets) and thoracic and lumbar spinal cord (nine datasets) was constructed to optimize transmit homogeneity and efficiency for these regions.

Tailored and universal parallel transmit broadband pulses for homogeneous 3D excitation of the human heart at 7T.

Purpose: To research and evaluate the performance of broadband tailored kT-point pulses (TP) and universal pulses (UP) for homogeneous excitation of the human heart at 7T.

Methods: Relative 3D -maps of the thorax were acquired from 29 healthy volunteers. TP and UP were designed using the small-tip-angle approximation for a different composition of up to seven resonance frequencies.

Toward accurate and fast velocity quantification with 3D ultrashort TE phase-contrast imaging.

Purpose: Traditional phase-contrast MRI is affected by displacement artifacts caused by non-synchronized spatial- and velocity-encoding time points. The resulting inaccurate velocity maps can affect the accuracy of derived hemodynamic parameters. This study proposes and characterizes a 3D radial phase-contrast UTE (PC-UTE) sequence to reduce displacement artifacts.

Investigation of alternative RF power limit control methods for 0.5T, 1.5T, and 3T parallel transmission cardiac imaging: A simulation study.

Purpose: To investigate safety and performance aspects of parallel-transmit (pTx) RF control-modes for a body coil at .

Methods: Electromagnetic simulations of 11 human voxel models in cardiac imaging position were conducted for , and and a body coil with a configurable number of transmit channels (1, 2, 4, 8, 16). Three safety modes were considered: the 'SAR-controlled mode' (SCM), where specific absorption rate (SAR) is limited directly, a 'phase agnostic SAR-controlled mode' (PASCM), where phase information is neglected, and a 'power-controlled mode' (PCM), where the voltage amplitude for each channel is limited.

Germany's journey toward 14 Tesla human magnetic resonance.

Multiple sites within Germany operate human MRI systems with magnetic fields either at 7 Tesla or 9.4 Tesla. In 2013, these sites formed a network to facilitate and harmonize the research being conducted at the different sites and make this technology available to a larger community of researchers and clinicians not only within Germany, but also worldwide.

Radiofrequency antenna concepts for human cardiac MR at 14.0 T.

Objective: To examine the feasibility of human cardiac MR (CMR) at 14.0 T using high-density radiofrequency (RF) dipole transceiver arrays in conjunction with static and dynamic parallel transmission (pTx).

Materials And Methods: RF arrays comprised of self-grounded bow-tie (SGBT) antennas, bow-tie (BT) antennas, or fractionated dipole (FD) antennas were used in this simulation study.

Challenges and Solutions for the Benefit Assessment of Tumor-Agnostic Therapies in Germany.

Objectives: Precision medicine is increasingly important in cancer treatment. Tumor-agnostic therapies are used regardless of tumor entity because they target specific biomarkers in tumors. In Germany, the benefit assessment of oncological pharmaceuticals has traditionally been entity specific.

Towards an integrated radiofrequency safety concept for implant carriers in MRI based on sensor-equipped implants and parallel transmission.

To protect implant carriers in MRI from excessive radiofrequency (RF) heating it has previously been suggested to assess that hazard via sensors on the implant. Other work recommended parallel transmission (pTx) to actively mitigate implant-related heating. Here, both ideas are integrated into one comprehensive safety concept where native pTx safety (without implant) is ensured by state-of-the-art field simulations and the implant-specific hazard is quantified in situ using physical sensors.

Optimisation of data acquisition towards continuous cardiac Magnetic Resonance Fingerprinting applications.

Purpose: Assess and optimise acquisition parameters for continuous cardiac Magnetic Resonance Fingerprinting (MRF).

Methods: Different acquisition schemes (flip angle amplitude, lobe size, T2-preparation pulses) for cardiac MRF were assessed in simulations and phantom and demonstrated in one healthy volunteer. Three different experimental designs were evaluated using central composite and fractional factorial designs.

Rapid estimation of 2D relative -maps from localizers in the human heart at 7T using deep learning.

Purpose: Subject-tailored parallel transmission pulses for ultra-high fields body applications are typically calculated based on subject-specific -maps of all transmit channels, which require lengthy adjustment times. This study investigates the feasibility of using deep learning to estimate complex, channel-wise, relative 2D -maps from a single gradient echo localizer to overcome long calibration times.

Methods: 126 channel-wise, complex, relative 2D -maps of the human heart from 44 subjects were acquired at 7T using a Cartesian, cardiac gradient-echo sequence obtained under breath-hold to create a library for network training and cross-validation.

The impact of respiratory motion on electromagnetic fields and specific absorption rate in cardiac imaging at 7T.

Purpose: To present electromagnetic simulation setups for detailed analyses of respiration's impact on and E-fields, local specific absorption rate (SAR) and associated safety-limits for 7T cardiac imaging.

Methods: Finite-difference time-domain electromagnetic field simulations were performed at five respiratory states using a breathing body model and a 16-element 7T body transceiver RF-coil array. and SAR are analyzed for fixed and moving coil configurations.

Fourier-based decomposition for simultaneous 2-voxel MRS acquisition with 2SPECIAL.

Purpose: To simultaneously acquire spectroscopic signals from two MRS voxels using a multi-banded 2 spin-echo, full-intensity acquired localized (2SPECIAL) sequence, and to decompose the signal to their respective regions by a novel voxel-GRAPPA (vGRAPPA) decomposition approach for in vivo brain applications at 7 T.

Methods: A wideband, uniform rate, smooth truncation (WURST) multi-banded pulse was incorporated into SPECIAL to implement 2SPECIAL for simultaneous multi-voxel spectroscopy (sMVS). To decompose the acquired data, the voxel-GRAPPA decomposition algorithm is introduced, and its performance is compared to the SENSE-based decomposition.