Bernd Foerster

Asymmetrical gradient coil for head imaging.

This work presents a novel approach to develop dedicated transverse gradient coils for head imaging. The proposed coil design is based on the stochastic optimization of an asymmetrical stream function and improves the matching between the region‐of‐interest and the homogeneous gradient volume. Additionally, the electric field produced by these asymmetrical coils is 30% lower than that produced by standard symmetrical designs, which minimizes the risk of magnetostimulation of nerves in fast imaging techniques. A prototype of the asymmetrical gradient coil was built to test the method and magnetic field produced by the prototype was measured. Magnetic field measurements and electrical parameters of coils are in good agreement with theoretical calculations. Magn Reson Med 48:707–714, 2002.

Electromyographic and magnetic resonance imaging evaluations of individuals with patellofemoral pain syndrome

OBJECTIVES To analyze the electrical activity of the vastus medialis obliquus (VMO), vastus lateralis longus (VLL) and vastus lateralis obliquus (VLO) muscles of individuals with patellofemoral pain syndrome (PFPS) during maximum voluntary isometric contraction (MVIC) of lower leg extension with the knee at 30 degrees; to assess pain using a visual analogue scale (VAS); and to assess patellar positioning using magnetic resonance imaging (MRI). METHODS Twelve women with PFPS and 12 clinically normal women were evaluated. They performed five MVICs of lower leg extension at 30 degrees for electromyographic (EMG) analysis. Using MRI, the sulcus angle (SA), congruence angle (CA), patellar tilt angle (PTA) and patellar displacement (PD) were obtained. The following statistical tests were used: analysis of variance (ANOVA) for repeated measurements to assess EMGs; Mann-Whitney U test to analyze MRIs; Pearsons (r) correlation test between EMGs and MRIs; and one-way ANOVA to evaluate pain (p < or = 0.05). RESULTS In the PFPS group, there was greater electrical activity in the VLL than in the VMO. In both groups, there was greater electrical activity in the VMO and VLL than in the VLO. In the PFPS group, the MRI showed higher SA and lower CA values, and there was a negative correlation between the VMO and the PTA. CONCLUSION The data suggest that, in individuals with PFPS, greater electrical activity in the VLL combined with an increased SA and a decreased CA may contribute to patellar instability.

Optimization of gradient coils using the fast simulated annealing method

This work presents a method to design short self-shielded gradient coils of cylindrical geometry using optimized stream functions (SF). The longitudinal and transverse gradient coil layouts presented here are optimized by the fast simulated annealing of the SF to increase the homogeneity of the gradient fields. Efficiency and inductance of coils, and homogeneity of the gradient fields, produced by the optimized geometries, are studied as a function of the coil length. A prototype of transverse coils was made to test the proposed method. The field measurements were carried out using imaging techniques, and they have shown good agreement with the corresponding theoretical values.

Deuterium microimages and microvolume localized spectroscopy at 9.4T

Deuterium (2H) microscopic images with resolution of tens of microns and localized 2H spectra with volumes in the micro liter range have been obtained on a Varian 400 MHz (9.4T) wide bore spectrometer equipped with a 50 G/cm gradient system. In order to realize 2H experiments at 61.4 MHz, a simple RF coil was built. 2H-Microimaging experiments have been carried out with SE and FLASH pulse sequences and localized 2H-spectroscopy has been tested on a phantom, which consists of a 2×2×2 mm3 cube with CD3OD immersed in D2O. Results show that non-invasive investigation of biological samples is possible. As an example for a biological application, the absorption process of D2O in a plant fragment (Mikania Cordifolia) has been monitored by acquiring consecutive SE microimages along various hours.