Pekka Tapani Sipilä

2H transmit–receive NMR probes for magnetic field monitoring in MRI

Measuring image encoding fields in real time and applying the information in postprocessing offer improved image quality for MRI, particularly for applications that are intrinsically sensitive to gradient imperfections. For this task, a stand‐alone magnetometer system based on multiple 2H transmit–receive NMR probes has been developed. The conceptual advantages of changing to 2H NMR probes for 1H magnetic field monitoring are elucidated here, and the practical design of the probes is described. In comparison to previous 1H NMR probe‐based designs, 2H probes are perfectly decoupled from standard 1H imaging. Utilization of RF shielding or other nonoptimal decoupling schemes is therefore not needed. Probes based on 2H nuclei are also more easily miniaturized for high‐resolution imaging. This is particularly important for diffusion tensor and phase‐contrast imaging, which rely on strong motion‐sensitizing gradients. The presented 2H NMR probes have been shown to fulfill the requirements for accurate 1H imaging down to image resolutions of 0.2 mm. Using susceptibility matching techniques, the probes B0 inhomogeneity‐induced signal dephasing is reduced and monitoring periods beyond 200 msec are achieved. The benefit of real time magnetic field monitoring is highlighted for phase‐contrast and non‐Cartesian multishot imaging. Magn Reson Med, 2011.

Spiral imaging artifact reduction: a comparison of two k-trajectory measurement methods.

To compare an external sensor‐based k‐space calibration technique with a routine precalibration method for quantification of method accuracy and reduction of spiral imaging artifacts to obtain improved image quality.

Robust Susceptibility-Matched NMR Probes for Compensation of Gradient Field Imperfections in Magnetic Resonance Imaging

A sensor system has been implemented to measure magnetic field imperfections in Magnetic Resonance Imaging (MRI). For this purpose, a novel method to manufacture Nuclear Magnetic Resonance (NMR) probes has been developed. Casting the NMR signal source and the sensing coil directly into paramagnetically doped epoxy drastically simplifies the manufacturing process. The design of NMR-probes with long acquisition time, and high signal-to-noise ratio (SNR) is presented and the optimization of the susceptibility for epoxy is described. To verify the functionality of the probe design, experimental results for the sensor-assisted acquisition of MR images are presented.