Measuring radiofrequency field-induced temperature variations in brain MRI exams with motion compensated MR thermometry and field monitoring.

Purpose: An MR thermometry (MRT) method with motion and field fluctuation compensation is proposed to measure non-invasively sub-degree brain temperature variations occurring through radiofrequency (RF) power deposition during MR exams.

Methods: MRT at 7T with a multi-slice echo planar imaging (EPI) sequence and concurrent field monitoring was first tested in vitro to assess accuracy in the presence of external field perturbations, an optical probe being used for ground truth. In vivo, this strategy was complemented by a motion compensation scheme based on a dictionary pre-scan, as reported in some previous work, and was adapted to the human brain.

RF heating measurement using MR thermometry and field monitoring: Methodological considerations and first in vivo results.

Purpose: A MR thermometry (MRT) method with field monitoring is proposed to improve the measurement of small temperature variations induced in brain MRI exams.

Methods: MR thermometry experiments were performed at 7 Tesla with concurrent field monitoring and RF heating. Images were reconstructed with nominal k-space trajectories and with first-order spherical harmonics correction.

Dynamic B shimming of the human brain at 9.4 T with a 16-channel multi-coil shim setup.

Purpose: A 16-channel multi-coil shimming setup was developed to mitigate severe B field perturbations at ultrahigh field and improve data quality for human brain imaging and spectroscopy.

Methods: The shimming setup consisted of 16 circular B coils that were positioned symmetrically on a cylinder with a diameter of 370 mm. The latter was large enough to house a shielded 18/32-channel RF transceiver array.

The impact of vessel size, orientation and intravascular contribution on the neurovascular fingerprint of BOLD bSSFP fMRI.

Monte Carlo simulations have been used to analyze oxygenation-related signal changes in pass-band balanced steady state free precession (bSSFP) as well as in gradient echo (GE) and spin echo (SE) sequences. Signal changes were calculated for artificial cylinders and neurovascular networks acquired from the mouse parietal cortex by two-photon laser scanning microscopy at 1 μm isotropic resolution. Signal changes as a function of vessel size, blood volume, vessel orientation to the main magnetic field B as well as relations of intra- and extravascular and of micro- and macrovascular contributions have been analyzed.

Paramagnetic lanthanide chelates for multicontrast MRI.

The preparation of a paramagnetic chelator that serves as a platform for multicontrast MRI, and can be utilized either as a T1-weighted, paraCEST or (19)F MRI contrast agent is reported. Its europium(iii) complex exhibits an extremely slow water exchange rate which is optimal for the use in CEST MRI. The potential of this platform was demonstrated through a series of MRI studies on tube phantoms and animals.

Volumetric imaging with homogenised excitation and static field at 9.4 T.

Objectives: To overcome the challenges of B0 and RF excitation inhomogeneity at ultra-high field MRI, a workflow for volumetric B0 and flip-angle homogenisation was implemented on a human 9.4 T scanner.

Materials And Methods: Imaging was performed with a 9.

(31)P CSI of the human brain in healthy subjects and tumor patients at 9.4 T with a three-layered multi-nuclear coil: initial results.

Objective: Investigation of the feasibility and performance of phosphorus ((31)P) magnetic resonance spectroscopic imaging (MRSI) at 9.4 T with a three-layered phosphorus/proton coil in human normal brain tissue and tumor.

Materials And Methods: A multi-channel (31)P coil was designed to enable MRSI of the entire human brain.

Quantitative and functional pulsed arterial spin labeling in the human brain at 9.4 T.

Purpose: The feasibility of multislice pulsed arterial spin labeling (PASL) of the human brain at 9.4 T was investigated. To demonstrate the potential of arterial spin labeling (ASL) at this field strength, quantitative, functional, and high-resolution (1.

Triple-quantum-filtered sodium imaging at 9.4 Tesla.

Purpose: Efficient acquisition of triple-quantum-filtered (TQF) sodium images at ultra-high field (UHF) strength.

Methods: A three-pulse preparation and a stack of double-spirals were used for the acquisition of TQF images at 9.4 Tesla.

Three-layered radio frequency coil arrangement for sodium MRI of the human brain at 9.4 Tesla.

Purpose: A multinuclei imaging setup with the capability to acquire both sodium ((23) Na) and proton ((1) H) signals at 9.4 Tesla is presented. The main objective was to optimize coil performance at the (23) Na frequency while still having the ability to acquire satisfactory (1) H images.

Combination of a multimode antenna and TIAMO for traveling-wave imaging at 9.4 Tesla.

Purpose: To investigate the performance of a multimode antenna combined with time-interleaved acquisition of modes (TIAMO) for improved (1)H image homogeneity as compared to conventional traveling-wave imaging in the human brain at 9.4 Tesla (T).

Methods: An adjustable three-port antenna was built to stimulate the propagation of three basic waveguide modes within a 9.

Triple-echo steady-state T2 relaxometry of the human brain at high to ultra-high fields.

Quantitative MRI techniques, such as T2 relaxometry, have demonstrated the potential to detect changes in the tissue microstructure of the human brain with higher specificity to the underlying pathology than in conventional morphological imaging. At high to ultra-high field strengths, quantitative MR-based tissue characterization benefits from the higher signal-to-noise ratio traded for either improved resolution or reduced scan time, but is impaired by severe static (B0 ) and transmit (B1 ) field heterogeneities. The objective of this study was to derive a robust relaxometry technique for fast T2 mapping of the human brain at high to ultra-high fields, which is highly insensitive to B0 and B1 field variations.

Mapping tissue sodium concentration in the human brain: a comparison of MR sequences at 9.4Tesla.

Sodium is the second most abundant MR-active nucleus in the human body and is of fundamental importance for the function of cells. Previous studies have shown that many pathophysiological conditions induce an increase of the average tissue sodium concentration. To date, several MR sequences have been used to measure sodium.

High-resolution quantitative sodium imaging at 9.4 Tesla.

Purpose: Investigation of the feasibility to perform high-resolution quantitative sodium imaging at 9.4 Tesla (T).

Methods: A proton patch antenna was combined with a sodium birdcage coil to provide a proton signal without compromising the efficiency of the X-nucleus coil.

Simultaneous single-quantum and triple-quantum-filtered MRI of 23Na (SISTINA).

The low MR sensitivity of the sodium nucleus and its low concentration in the human body constrain acquisition time. The use of both single-quantum and triple-quantum sodium imaging is, therefore, restricted. In this work, we present a novel MRI sequence that interleaves an ultra-short echo time radial projection readout into the three-pulse triple-quantum preparation.