Klaas P. Prüssmann

Ultrafast bold fMRI using single-shot spin-echo echo planar imaging.

The choice of imaging parameters for functional MRI can have an impact on the accuracy of functional localization by affecting the image quality and the degree of blood oxygenation-dependent (BOLD) contrast achieved. By improving sampling efficiency, parallel acquisition techniques such as sensitivity encoding (SENSE) have been used to shorten readout trains in single-shot (SS) echo planar imaging (EPI). This has been applied to susceptibility artifact reduction and improving spatial resolution. SENSE together with single-shot spin-echo (SS-SE) imaging may also reduce off-resonance artifacts. The goal of this work was to investigate the BOLD response of a SENSE-adapted SE-EPI on a three Tesla scanner. Whole-brain fMRI studies of seven healthy right hand-dominant volunteers were carried out in a three Tesla scanner. fMRI was performed using an SS-SE EPI sequence with SENSE. The data was processed using statistical parametric mapping. Both, group and individual subject data analyses were performed. Individual average percentage and maximal percentage signal changes attributed to the BOLD effect in M1 were calculated for all the subjects as a function of echo time. Corresponding activation maps and the sizes of the activated clusters were also calculated. Our results show that susceptibility artifacts were reduced with the use of SENSE; and the acquired BOLD images were free of the typical quadrature artifacts of SS-EPI. Such measures are crucial at high field strengths. SS SE-EPI with SENSE offers further benefits in this regard and is more specific for oxygenation changes in the microvasculature bed. Functional brain activity can be investigated with the help of single-shot spin echo EPI using SENSE at high magnetic fields.

27.4 A sub-1dB NF dual-channel on-coil CMOS receiver for Magnetic Resonance Imaging

Magnetic Resonance Imaging (MRI) is a widely used medical imaging technique. It employs a strong static magnetic field (1.5 to 10.5T for human imaging) to split the spin states of the 1H nuclei in the body, and RF excitation to induce transitions and coherence among them. Gradient fields are superimposed to modulate the 1H resonance frequency, which enables spatially distinguishable signals to be picked up by RF receive coils. A high-field MRI provides better sensitivity and resolution but requires better receivers (RX), as signal DR and 1H resonance increase (128MHz for 3T, 300MHz for 7T). Overall sensitivity and imaging speed can be enhanced by closely surrounding the target anatomy with tens of RX coils (as in MIMO) [1], at the expense of as many shielded RF cables to carry the information out of the field. Progress in PCB size has allowed multi-channel RX to be placed inside the magnetic field (in-bore), reducing the RF cable length to less than 1m [2,3]. Ultimately, the RX should be placed directly on-coil to avoid bulky coaxial cables and improve patient comfort and safety by acquiring data in-bore and sending them digitally to the MRI scanner via an optical fiber link. The latter is cheap, flexible and insensitive to magnetic fields. The immediate vicinity of the coils and the patient is, however, a hostile as well as sensitive electromagnetic environment, which tolerates only the smallest of PCBs and virtually no magnetic material in its components. Integration of the full RX chain in a CMOS chip, which is small, non-magnetic and low power, holds the key to the next wave of compact MRI coil arrays for advanced medical imaging. This paper presents a fully integrated dual-receiver RFIC for coil arrays intended for (ultra-) high field (1.5 to 10.5T and 64 to 450MHz) scanners for clinical MRI, where requirements are considerably stricter than previously reported transceiver ICs [4,5] on palm-held NMR devices for spectroscopy or lab-on-chip applications.

Magnetic resonance imaging (MRI) study of jet height hysteresis in packed beds

The jet-spout transition in fluidized beds can show hysteretic behavior. In this study the jet-spout transition was studied as a function of orifice velocity for particles of different size and shape using Magnetic Resonance Imaging (MRI). The measurements showed that the particle shape primarily affect to the width of the hysteresis loop whereas particle size governs the position of the hysteresis loop with regards to the orifice velocity.

Computational Analysis and Validation of Coil Arrays for Whole-Brain MR-Imaging at 7 T

The performance of two different head coil designs, an asymmetrically fed microstrip and a microstrip dipole, for whole-brain MRI at 7 T were analyzed regarding the B1 +-field and SAR distributions. The simulated electromagnetic behavior of the single elements are validated by bench measurements. The microstrip dipole design turned out to exhibit an almost similar B1 + -field distribution along with a significantly lower SAR. Preliminary measurement results confirm the simulations of the realized prototype array exciting one single element. The design of the prototype could be substantially supported by numerical simulations.