Velocity selective spin labeling using parallel transmission.

PURPOSE: Ultra-high field (UHF) provides improved SNR which greatly benefits SNR starved imaging techniques such as perfusion imaging. However, transmit field (B1 + ) inhomogeneities commonly observed at UHF hinders the excitation uniformity. Here we show how replacing standard excitation pulses with parallel transmit pulses can improve efficiency of velocity selective labeling. METHODS: The standard tip-down and tip-up excitation pulses found in a velocity selective preparation module were replaced with tailored non-selective kT -points pulse solutions. Bloch simulations and experimental validation on a custom-built flow phantom and in vivo was performed to evaluate different pulse configurations in circularly polarized mode (CP-mode) and parallel transmit (pTx) mode. RESULTS: Tailored pTx pulses significantly improved velocity selective labeling fidelity and signal uniformity. The transverse magnetization normalized RMS error was reduced from 0.489 to 0.047 when compared to standard rectangular pulses played in CP-mode. Simulations showed that manipulation of time symmetry in the tailored pTx pulses is vital in minimizing residual magnetization. In addition, in vivo experiments achieved a 44% lower RF power output and a shorter pulse duration when compared to using adiabatic pulses in CP-mode. CONCLUSION: Using tailored pTx pulses for excitation within a velocity selective labeling preparation mitigated transmit field artifacts and improved SNR and contrast fidelity. The improvement in labeling efficiency highlights the potential of using pTx to improve robustness and accessibility of flow-based sequences such as velocity selective spin labeling at ultra-high field.

A custom MR-compatible dataglove for fMRI of the human motor cortex at 7T.

We present a custom-built MR-compatible data glove to capture hand motion during concurrent fMRI experiments at 7 Tesla. Thermal and phantom tests showed our data glove can be used safely and without degradation of image quality. Subject-specific Blood Oxygen Level Dependent (BOLD) signal models, for use in fMRI analysis, were constructed based on recorded kinematic measurements. Experiments revealed the relative fMRI BOLD signal contribution of flexing, extending, and sustained isotonic extension. The ability to evaluate subject performance in real-time and create subject-specific BOLD signal models enables a wide range of experimental paradigms with improved data quality.Clinical Relevance- Using an MR compatible dataglove, subject specific Blood Oxygen Signal Level Dependent (BOLD) signal models can be constructed to study how the brain implements fine motor control.

Feasibility of functional magnetic resonance lung imaging in Australia with long distance transport of hyperpolarized helium from Germany.

BACKGROUND AND OBJECTIVE: MRI of the lung using hyperpolarized helium as an inhaled contrast agent has important research applications and clinical potential. Owing to the limited availability of hyperpolarized helium, this type of imaging has not been performed in the human lung outside of North America or Europe. The objective of this study was to test the feasibility of imaging human lungs in Australia using hyperpolarized helium gas imported from Germany. METHODS: A Bruker 2-Tesla whole-body magnetic resonance scanner located in Brisbane, Australia was adapted with a helium-3 radiofrequency transceiver coil. Helium-3 was hyperpolarized to 72% in Mainz, Germany and airfreighted to Brisbane. The time taken for the journey was 32 h and scanning was performed 36-40 h after departure from Mainz, with an estimated polarization level of 44%. Procedures were developed to transfer 300 mL of the hyperpolarized helium to Tedlar bags filled with 700 mL of nitrogen. Healthy volunteers inhaled the 1 L helium/nitrogen mixture from FRC, and imaging was performed with a 10 s breathhold. RESULTS: Imaging showed very detailed and even ventilation of all regions of the lung with a good signal-to-noise ratio. No adverse effects of inhaling the gas mixture were noted. CONCLUSIONS: This report of MRI of the human lung using hyperpolarized helium demonstrates the feasibility of long distance gas transport from Germany to Australia. This will help to facilitate research and clinical application of this innovative functional lung imaging technique.

High-field magnetic resonance imaging using solenoid radiofrequency coils.

High-resolution magnetic resonance imaging using dedicated high-field radiofrequency micro-coils at 16.4 T (700 MHz) was investigated. Specific solenoid coils primarily using silver and copper as conductors with enamel and polyurethane coatings were built to establish which coil configuration produces the best image. Image quality was quantified using signal-to-noise ratio and signal variation over regions of interest. Benchmarking was conducted using 5-mm diameter coils, as this size is comparable to an established coil of the same size. Our 1.4-mm-diameter coils were compared directly to each other, from which we deduce performance as a function of conductor material and coating. A variety of materials and conductor coatings allowed us to choose an optimal design, which we used to image a kidney section at 10-micron resolution. We applied zero-fill extrapolation to achieve 5-micron resolution.