C Mirkes

High-resolution quantitative sodium imaging at 9.4 tesla

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

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. This allows for simultaneous acquisition of tissue sodium concentration weighted as well as triple‐quantum filtered images. Performance of the sequence is shown on phantoms. The method is demonstrated on six healthy informed volunteers and is applied to three cases of brain tumors. A comparison with images from tumor specific O‐(2‐[18F]fluoroethyl)‐L‐tyrosine positron emission tomography and standard MR images is presented. The combined information of the triple‐quantum‐filtered images with single‐quantum images may enable a better understanding of tissue viability. Future studies can benefit from the evaluation of both contrasts with shortened acquisition times. Magn Reson Med, 2013.

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

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

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. The proposed method relies on a recently presented three‐dimensional (3D) triple‐echo steady‐state (TESS) imaging approach that has proven to be suitable for fast intrinsically B1‐insensitive T2 relaxometry of rigid targets. In this work, 3D TESS imaging is adapted for rapid high‐ to ultra‐high‐field two‐dimensional (2D) acquisitions. The achieved short scan times of 2D TESS measurements reduce motion sensitivity and make TESS‐based T2 quantification feasible in the brain. After validation in vitro and in vivo at 3 T, T2 maps of the human brain were obtained at 7 and 9.4 T. Excellent agreement between TESS‐based T2 measurements and reference single‐echo spin‐echo data was found in vitro and in vivo at 3 T, and T2 relaxometry based on TESS imaging was proven to be feasible and reliable in the human brain at 7 and 9.4 T. Although prominent B0 and B1 field variations occur at ultra‐high fields, the T2 maps obtained show no B0‐ or B1‐related degradations. In conclusion, as a result of the observed robustness, TESS T2 may emerge as a valuable measure for the early diagnosis and progression monitoring of brain diseases in high‐resolution 2D acquisitions at high to ultra‐high fields. Copyright

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

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. The aim of this study was to evaluate the performance and suitability of five different MR sequences for quantitative sodium imaging on a whole-body 9.4Tesla MR scanner. Numerical simulations, phantom experiments and in vivo imaging on healthy subjects were carried out. The results demonstrate that, of these five sequences, the Twisted Projection Imaging sequence is optimal for quantitative sodium imaging, as it combines a number of features which are particularly relevant in order to obtain high quality quantitative images of sodium. These include: ultra-short echo times, efficient k-space sampling, and robustness against off-resonance effects. Mapping of sodium in the human brain is a technique not yet fully explored in neuroscience. Ultra-high field sodium MRI may provide new insights into the pathogenesis of neurological disorders, and may help to develop new and disease-specific biomarkers for the early diagnosis and therapeutic intervention before irreversible brain damage has taken place.

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

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 (1.05 × 1.05 × 2 mm3) ASL experiments were performed.

Dynamic B0 shimming of the human brain at 9.4 T with a 16-channel multi-coil shim setup

A 16‐channel multi‐coil shimming setup was developed to mitigate severe B0 field perturbations at ultrahigh field and improve data quality for human brain imaging and spectroscopy.

MRI using 23 Na

Sodium magnetic resonance imaging (MRI) can provide complementary information to proton MRI. However, small in vivo concentrations and the low NMR sensitivity of sodium require an adaptation of the acquisition techniques commonly used for proton MRI. In this article, the physical properties of the sodium nucleus are summarized and an overview of methods and applications of sodium MRI is given.

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

&NA; 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 &mgr;m isotropic resolution. Signal changes as a function of vessel size, blood volume, vessel orientation to the main magnetic field B0 as well as relations of intra‐ and extravascular and of micro‐ and macrovascular contributions have been analyzed. The results show that bSSFP is highly sensitive to extravascular and microvascular components. Furthermore, GE and bSSFP, and to a lesser extent SE, exhibit a strong dependence of their signal change on the orientation of the vessel network to B0. HighlightsThe contribution from capillaries is highest for SE, followed by bSSFP and is much lower for GE.The intravascular contribution of bSSFP and SE is in the range of 5–10%, and negligible for GE at 9.4T.BOLD signal change of GE, SE and bSSFP depend on orientation of cortex to B0.