MR Technology

MRI at extremely high fields requires a major effort in technical developments. A significant part of our research is thus devoted to capture as much as possible of the tiny magnetic waves emitted from the excited brain. We develop highly dedicated radio-frequency multi-channel transmit and receive arrays with optimized efficiency, receive performance and coverage. Further projects include local shim arrays, parallel transmit technology and ultra-low field MR with hyperpolarization.

Magnetic resonance (MR) images can be created noninvasively using only static and dynamic magnetic fields, and radio frequency pulses. MR imaging provides fast image acquisitions which have been clinically feasible only since the discovery of efficient MR sequences, ie. time-efficient application of two building blocks: radio frequency pulses and spatial magnetic field gradients. [more]
Effective use of the transcranial electrical stimulation (TES) against neuropsychiatric disorders requires accurate mapping of the currents in the brain. Magnetic resonance current density imaging (MRCDI) combines MRI with low-intensity TES (1-2 mA) to map current flow in the brain. However, the utility of MRCDI is still hampered by low measurement sensitivity and image quality.
Common decoupling methods, which require electrical connections, are difficult to use for decoupling of distantly located adjacent transmit (Tx) dipoles. Alternatively, neighboring dipoles can be decoupled using passive dipole antennas placed between them. This decoupling practice should be used with care since passive dipoles may interact destructively with the RF field, B1+, produced by the Tx array. In this work, we developed a novel decoupling method of adjacent Tx dipoles by using modified passive dipole antennas. [more]
System instabilities and physiological motion such as breathing and cardiac pulsation can cause signal fluctuations in gradient-echo scans. In spin-warp imaging (standard Cartesian acquisition), different phase offsets for each line of k-space can lead to severe ghosting in the image domain. [more]
Clinical application of ultra-high field (UHF, >7T) MRI, is still hindered due to technical hurdles associated with imaging of large human objects (body, head). Resulting issues include a significant increase of the local tissue heating (peak SAR (pSAR)), and a strong inhomogeneity of the transmit (Tx) RF magnetic field, B1+. Improvement of the B1+ homogeneity and coverage can be achieved by using multi-loop Tx-arrays. However, an adequate whole-brain coverage was demonstrated only by using multi-row arrays capable of 3D RF shimming. [more]
Due to the substantially smaller size of the sample, dipoles must be shorter than /2. In addition, head arrays are commonly placed on the surface of rigid helmets made sufficiently large to accommodate various heads. As a result, dipoles are not well loaded and are often poorly decoupled, which compromises the transmit (Tx) performance. [more]
This study introduces a novel design method of a shim coil array specifically optimized for whole brain shimming and to compare the performance of the resulting coils to conventional spherical harmonic shimming. [more]
Improved B0 homogeneity leads to higher tSNR and enhances the detection of BOLD signal. We assessed how improved static magnetic field (B0) homogeneity with a dynamic multicoil shimming can influence the blood oxygen level dependent (BOLD) contrast to noise when echo planar imaging (EPI) sequence is used for a motor task functional MRI study. [more]
We designed and implemented an orthogonal shim array consisting of shim coils with their planes perpendicular to the planes of neighboring RF coils. This shim coil improves the magnetic field homogeneity by minimizing the interference to RF coils. [more]
Subject motion is a major problem in functional and anatomical head MRI. The resulting artifacts such as ghosting and blurring may complicate image interpretation, or in the worst case, render acquired images useless. Thus, measurements have to be repeated or entire patient populations, such as elderly or pediatric patients, have to be excluded from certain studies. [more]
Up to now, no successful functional MRI was performed at ultralow magnetic fields (ULF). Therefore we tried to estimate the feasibility of such experiments with a simplified brain model. For a highly optimized ULF system we predict that functional MRI with a contrast to noise ratio of up to ≈ 7 is feasible with a measurement time of 30 minutes. [more]
We used a home-made ultralow-field (ULF) NMR system for measuring multiple quantum coherences up to the third order via heteronuclear correlated spectroscopy (COSY). The multiple spin orders were generated using signal amplification by reversible exchange (SABE). [more]
In conventional imaging, the scan of k-space (which is the Fourier transformed image space) is achieved by applying linear gradients along the principal axes. In most applications, k-space is acquired line by line on a Cartesian grid, or in some implementations along projections or spirals, to name just a few. [more]
System instabilities and physiological motion such as breathing and cardiac pulsation can cause signal fluctuations in gradient-echo scans. In spin-warp imaging (standard Cartesian acquisition), different phase offsets for each line of k-space can lead to severe ghosting in the image domain. [more]
We have developed a multi-coil (MC) shimming array with 16 independent circular loops for dynamic shimming of brain at the 9.4T. In this work, we demonstrate the feasibility of a hybrid method for dynamic shimming by combining scanner’s spherical harmonics (SH) system with our MC shimming array. [more]
Magnetic resonance current density imaging (MRCDI) and MR electrical impedance tomography (MREIT) are two emerging modalities, which combine weak time-varying currents injected via surface electrodes with magnetic resonance imaging (MRI) to acquire information about the current flow and ohmic conductivity distribution at high spatial resolution. [more]
We built a home-made ultralow-field (ULF) NMR and MRI system for the investigation of hyperpolarization techniques such as Overhauser dynamic nuclear polarization (ODNP) and parahydrogen (pH2) based hyperpolarization. [more]
We used a superconducting quantum interference device (SQUID) as broadband detector and signal amplification by reversible exchange (SABRE) to measure hyperpolarized NMR spectra of 1H and 19F simultaneously, highlighting the complexity of the underlying coupling mechanisms. [more]
Any RF coil must meet the strict requirements for safe application on humans with respect to mechanical and electrical safety, as well as the SAR limits. For this purpose, vendor-suggested test specifications for third party coils and custom-developed test procedures exist. [more]
In recent years, available field strengths for MRI instruments have increased rapidly, both for human and animal applications. While 7 Tesla (T) has developed into a standard field strength for ultra-high field MR in humans, the interest in even stronger magnets remains high, causing a slow but steady increase in scanners operating at 9.4T or above. [more]
In this work we investigate the optimal design of the Transmit only/Receive only (ToRo) head coil for 9.4T. The developing coil is inspired by another unshielded ToRo design consisting of 16 transmit only loops in the two rows and 31 receive only tight-fit helmet. In addition, it was observed previously that enlarging coil length may improve the transmit efficiency in the superior part of the brain. [more]
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