MR Technology

To improve whole-brain SNR at 7 T, a novel 32-element hybrid human head array coil was developed, constructed and tested. Our general design strategy was based on two major ideas. Firstly, following suggestions of previous theoretical works, we combined loops and dipoles for improvement of SNR near the head center. Secondly, we minimized the total number of array elements by using a hybrid combination of transceive (TxRx) and receive (Rx) elements. [more]

We designed an 8-channel local B0 coil array, with a 16-transmit/32-receive RF coil within its support, to investigate the ultimate image acceleration by nearly arbitrary spatial-temporal gradient modulations, as a more general technique than wave-CAIPI and FRONSAC. [more]

Parallel imaging (PI) is one of the most successful techniques for accelerating MRI acquisition. Based on the phased array concept, it exploits the spatial information provided by the different sensitivities of multiple local RF receive coils to complement the gradient-based Fourier encoding, thus speeding up the acquisition process.  [more]

Parahydrogen (pH2) is a convenient and cost-efficient source for magnetic resonance signal enhancement. Previous work showed that transient interaction of pH2 with a metal organic complex in a signal amplification by reversible exchange (SABRE) experiment enabled more than 10% polarization for some ¹⁵N molecules. [more]

Homogeneity and longitudinal coverage of transmit (Tx) human head RF coils at ultra-high field (UHF, >7T) can be improved by 3D RF shimming, which requires using multi-row Tx-arrays. Examples of 3D RF shimming using double-row UHF loop transceiver (TxRx) and Tx-arrays have been described previously. [more]

Important issues in designing radiofrequency (RF) coils for human head imaging at ultra-high field (UHF, > 7T) are the inhomogeneity and longitudinal coverage (along the magnet axis) of the transmit (Tx) RF field. Both the homogeneity and coverage produced by Tx volume coils can be improved by means of 3D RF shimming, which requires use of multi-row Tx-arrays. [more]

The aim of this work was to evaluate a new 8-channel transceiver (TxRx) coaxial dipole array for imaging of the human head at 9.4T developed to improve SAR-performance and provide for a more compact and robust alternative to the existing state-of-the art dipole arrays. [more]

Nuclear spin hyperpolarization enables real-time observation of metabolism and intermolecular interactions in vivo. 1-¹³C-Pyruvate is the leading hyperpolarized tracer currently under evaluation in several clinical trials as a promising molecular imaging agent. Still, the quest for a simple, fast, and efficient hyperpolarization technique is ongoing. Here, we describe that continuous, weak irradiation in the audio-frequency range of the ¹³C spin at 121 μT magnetic field (~twice Earth’s field) enables spin order transfer from parahydrogen to ¹³C magnetization of 1-¹³C-pyruvate.  [more]

Traditionally, the discovery of new MRI contrasts was often a trial-and-error process, typically involving laborious human interaction with the MR scanner or sophisticated simulations. For the latter, a theoretical description of the underlying MR physics is required to capture the desired contrast effects. In this context, a framework for MR sequence parameter optimization based on differentiable Bloch simulations has recently been introduced as "MRzero". [more]

Prediction of motion induced magnetic fields In MRI, B0 field inhomogeneity maps are frequently employed to enhance image quality. These inhomogeneities are influenced by the location of the head within the static magnetic field. Subject head movements, which are prevalent in lengthy experiments like fMRI, can disrupt the inhomogeneity distribution. [more]

Accelerating imaging speed has been one of the most important and challenging goals in MRI over the past three decades. About two decades ago, the landscape for rapid MRI changed dramatically with the invention of parallel imaging (PI) techniques, which allow significantly accelerated acquisitions. A fundamental problem of all PI techniques is the decrease in signal-to-noise ratio with increasing imaging acceleration. [more]

The efficacy in ¹H Overhauser dynamic nuclear polarization in liquids at ultralow magnetic field (ULF, B0 = 92 ± 0.8 μT) and polarization field (Bp = 1–10 mT) was studied for a broad variety of 26 different spin probes. [more]

Radiofrequency (RF) coils with multiple transmit elements, so-called array coils, are commonly used in ultrahigh field MRI. When using them for parallel transmit (pTx) applications, it is important to have accurate knowledge of the RF field distribution (B1+-Field) generated by each individual element. [more]

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]

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]

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 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]

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]