MR Technology

MRzero - Automated Discovery of MRI Sequences Using Supervised Learning

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]

Autofocusing-Based Phase Correction

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.
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Unshielded Bent Folded-End Dipole 9.4 T Human Head Transceiver Array Decoupled Using Modified Passive Dipoles

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]

A 32-Channel Multi-Coil Setup Optimized for Human Brain Shimming at 9.4 T

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]

Bent Folded-End Dipole Head Array for Ultra-High-Field Magnetic Resonance Imaging Turns “Dielectric Resonance” from an Enemy to a Friend.

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]

Decoupling of Folded-End Dipole Antenna Elements of a 9.4 T Human Head Array Using an RF Shield

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]

Design of a Shim Coil Array Matched to the Human Brain Anatomy

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]

Dynamic B0 Shimming of the Motor Cortex and Cerebellum with a Multicoil Shim Setup for BOLD fMRI at 9.4T

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]

The Orthogonal Shim Coil for 3T Brain Imaging

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]

Comparison of Prospective Head Motion Correction with NMR Field Probes and an Optical Tracking System

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]

Feasibility of Functional MRI at Ultralow Magnetic Field via Changes in Cerebral Blood Volume

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]

Multiple Quantum Coherences Hyperpolarized at Ultra-Low Fields

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]

Spread-Spectrum Magnetic Resonance Imaging

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]

Autofocusing-Based Phase Correction

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]

Dynamic B0 Shimming of the Human Brain at 9.4 T with a 16-Channel Multi-Coil Shim Setup

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]

Human in-vivo Brain Magnetic Resonance Current Density Imaging (MRCDI)

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]

Ultralow-Field NMR and MRI for the Investigation of Hyperpolarization Techniques

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]

Parahydrogen Based Hyperpolarization for Multinuclear NMR Spectroscopy in Ultra-Low Magnetic Fields

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]

Safety Testing and Operational Procedures for Self-Developed Radiofrequency Coils

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]

Signal-to-Noise Ratio and MR Tissue Parameters in Human Brain Imaging at 3, 7, and 9.4 Tesla Using Current Receive Coil Arrays

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]

Investigation of the Optimal Transmit Only/Receive Only (ToRo) RF Coil for Brain Imaging at 9.4T

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]