Ultrashort echo time and zero echo time MRI at 7T.

Objective: Zero echo time (ZTE) and ultrashort echo time (UTE) pulse sequences for MRI offer unique advantages of being able to detect signal from rapidly decaying short-T2 tissue components. In this paper, we applied 3D ZTE and UTE pulse sequences at 7T to assess differences between these methods.

Materials And Methods: We matched the ZTE and UTE pulse sequences closely in terms of readout trajectories and image contrast.

Clinically feasible NODDI characterization of glioma using multiband EPI at 7 T.

Recent technological progress in the multiband echo planer imaging (MB EPI) technique enables accelerated MR diffusion weighted imaging (DWI) and allows whole brain, multi-b-value diffusion imaging to be acquired within a clinically feasible time. However, its applications at 7 T have been limited due to B1 field inhomogeneity and increased susceptibility artifact. It is an ongoing debate whether DWI at 7 T can be performed properly in patients, and a systematic SNR comparison for multiband spin-echo EPI between 3 T and 7 T has not been methodically studied.

Assessment of Silent T1-weighted head imaging at 7 T.

Objectives: This study aimed to assess the performance of a "Silent" zero time of echo (ZTE) sequence for T1-weighted brain imaging using a 7 T MRI system.

Methods: The Silent sequence was evaluated qualitatively by two neuroradiologists, as well as quantitatively in terms of tissue contrast, homogeneity, signal-to-noise ratio (SNR) and acoustic noise. It was compared to conventional T1-weighted imaging (FSPGR).

Tissue Border Enhancement by inversion recovery MRI at 7.0 Tesla.

Introduction: This contribution presents a magnetic resonance imaging (MRI) acquisition technique named Tissue Border Enhancement (TBE), whose purpose is to produce images with enhanced visualization of borders between two tissues of interest without any post-processing.

Methods: The technique is based on an inversion recovery sequence that employs an appropriate inversion time to produce images where the interface between two tissues of interest is hypo-intense; therefore, tissue borders are clearly represented by dark lines. This effect is achieved by setting imaging parameters such that two neighboring tissues of interest have magnetization with equal magnitude but opposite sign; therefore, the voxels containing a mixture of each tissue (that is, the tissue interface) possess minimal net signal.

Ultrashort echo time MRI of cortical bone at 7 tesla field strength: a feasibility study.

Purpose: To implement and examine the feasibility of a three-dimensional (3D) ultrashort TE (UTE) sequence on a 7 Tesla (T) clinical MR scanner in comparison with 3T MRI at high isotropic resolution.

Materials And Methods: Using an in-house built saddle coil at both field strengths we have imaged mid-diaphysial sections of five fresh cadaveric specimens of the distal tibia. An additional in vivo scan was performed at 7 Tesla using a quadrature knee coil.

Reduced field-of-view diffusion-weighted imaging of the brain at 7 T.

Ventral and rostral regions of the brain are of emerging importance for the MRI characterization of early dementia, traumatic brain injury and epilepsy. Unfortunately, standard single-shot echo planar diffusion-weighted imaging of these regions at high fields is contaminated by severe imaging artifacts in the vicinity of air-tissue interfaces. To mitigate these artifacts and improve visualization of the temporal and frontal lobes at 7 T, we applied a reduced field-of-view strategy, enabled by outer volume suppression (OVS) with novel quadratic phase radiofrequency (RF) pulses, combined with partial Fourier and parallel imaging methods.

Shielded microstrip array for 7T human MR imaging.

The high-frequency transceiver array based on the microstrip transmission line design is a promising technique for ultrahigh field magnetic resonance imaging (MRI) signal excitation and reception. However, with the increase of radio-frequency (RF) channels, the size of the ground plane in each microstrip coil element is usually not sufficient to provide a perfect ground. Consequently, the transceiver array may suffer from cable resonance, lower Q-factors, and imaging quality degradations.

Imaging of the musculoskeletal system in vivo using ultra-high field magnetic resonance at 7 T.

Recently, great progress has been made in particularly in the imaging of cartilage and bone structure. Increased interest has focused on high-field (3 Tesla) imaging and more recently on ultra-high field (UHF) magnetic resonance imaging (MRI) at 7 T for in vivo imaging. Because the signal-to-noise ratio (SNR) scales linearly with field strength, a substantial increase in SNR is expected compared with lower field strengths.

Assessment of cartilage-dedicated sequences at ultra-high-field MRI: comparison of imaging performance and diagnostic confidence between 3.0 and 7.0 T with respect to osteoarthritis-induced changes at the knee joint.

Objective: The objectives of the study were to optimize three cartilage-dedicated sequences for in vivo knee imaging at 7.0 T ultra-high-field (UHF) magnetic resonance imaging (MRI) and to compare imaging performance and diagnostic confidence concerning osteoarthritis (OA)-induced changes at 7.0 and 3.

High-resolution phased-array MRI of the human brain at 7 tesla: initial experience in multiple sclerosis patients.

Recent advancement for magnetic resonance imaging (MRI) involves the incorporation of higher-field strengths. Although imagers with higher magnetic field strengths were developed and tested in research labs, the direct application to patient MR studies have been extremely limited. Imaging at 7 Tesla (7T) affords advantages in signal-to-noise ratio and image contrast and resolution; however, these benefits can only be realized if the correct coils exist to capture the images.

GRAPPA-based susceptibility-weighted imaging of normal volunteers and patients with brain tumor at 7 T.

Susceptibility-weighted imaging (SWI) is a valuable technique for high-resolution imaging of brain vasculature that greatly benefits from the emergence of higher field strength MR scanners. Autocalibrating partially parallel imaging techniques can be employed to reduce lengthy acquisition times as long as the decrease in signal-to-noise ratio does not significantly affect the contrast between vessels and brain parenchyma. This study assessed the feasibility of a Generalized Autocalibrating Partially Parallel Acquisition (GRAPPA)-based SWI technique at 7 T in both healthy volunteers and brain tumor patients.

Phased array 3D MR spectroscopic imaging of the brain at 7 T.

Ultra-high-field 7 T magnetic resonance (MR) scanners offer the potential for greatly improved MR spectroscopic imaging due to increased sensitivity and spectral resolution. Prior 7 T human single-voxel MR Spectroscopy (MRS) studies have shown significant increases in signal-to-noise ratio (SNR) and spectral resolution as compared to lower magnetic fields but have not demonstrated the increase in spatial resolution and multivoxel coverage possible with 7 T MR spectroscopic imaging. The goal of this study was to develop specialized radiofrequency (RF) pulses and sequences for three-dimensional (3D) MR spectroscopic imaging (MRSI) at 7 T to address the challenges of increased chemical shift misregistration, B1 power limitations, and increased spectral bandwidth.

Compressed sensing for resolution enhancement of hyperpolarized 13C flyback 3D-MRSI.

High polarization of nuclear spins in liquid state through dynamic nuclear polarization has enabled the direct monitoring of 13C metabolites in vivo at very high signal-to-noise, allowing for rapid assessment of tissue metabolism. The abundant SNR afforded by this hyperpolarization technique makes high-resolution 13C 3D-MRSI feasible. However, the number of phase encodes that can be fit into the short acquisition time for hyperpolarized imaging limits spatial coverage and resolution.

Rapid in vivo musculoskeletal MR with parallel imaging at 7T.

The purpose of this work was to implement autocalibrating GRAPPA-based parallel imaging (PI) for in vivo high-resolution (HR) MRI of cartilage and trabecular bone micro-architecture at 7T and to evaluate its performance based on comparison of MR-derived morphology metrics between accelerated and conventional images and comparison of geometry factor measures between 3T and 7T. Using an eight channel coil array for trabecular MRI at the ankle, a higher maximum feasible acceleration (R) = 6 and lower geometry factor values than that at 3T were observed. The advantages of two-dimensional acceleration were also demonstrated.

Development of a robust method for generating 7.0 T multichannel phase images of the brain with application to normal volunteers and patients with neurological diseases.

The increased susceptibility effects and high signal-to-noise ratio at 7.0 T enable imaging of the brain using the phase of the magnetic resonance signal. This study describes and evaluates a robust method for calculating phase images from gradient-recalled echo (GRE) scans.

In vivo bone and cartilage MRI using fully-balanced steady-state free-precession at 7 tesla.

The purpose of this work was to investigated the feasibility of fully-balanced steady-state free-precession (bSSFP) pulse sequence for trabecular bone and knee cartilage imaging in vivo using ultra-high-field (UHF) MRI at 7T in comparison with pulse sequences previously used at 3T. We showed that bSSFP and spin-echo imaging is possible at higher field strengths within 3.2 W/kg specific absorption rate (SAR) constraints.

Intracranial time-of-flight MR angiography at 7T with comparison to 3T.

Purpose: To establish the feasibility of intracranial time-of-flight (TOF) MR angiography (MRA) at 7T using phased array coils and to compare its performance to 3T.

Materials And Methods: In an initial study, five normal volunteers were scanned at 7T and 3T using eight-channel coils and standard acquisition parameters from a clinical TOF protocol. In a second study three additional studies were performed at 7T and 3T using empirically optimized 7T parameters.

High-speed 3T MR spectroscopic imaging of prostate with flyback echo-planar encoding.

Prostate MR spectroscopic imaging (MRSI) at 3T may provide two-fold higher spatial resolution over 1.5T, but this can result in longer acquisition times to cover the entire gland using conventional phase-encoding. In this study, flyback echo-planar readout trajectories were incorporated into a Malcolm Levitt's composite-pulse decoupling sequence (MLEV)-point-resolved spectroscopy sequence (PRESS) to accelerate the acquisition of large array (16 x 16 x 8), high spatial (0.