Purpose: To improve preamplifier decoupling in a quadrature phased-array coil using a new quadrature combiner configuration. Materials and Methods:A commercial six-element quadrature cervical-thoracic-lumbar (CTL) coil was used on a 1.5 T GE Signa Lx Scanner. The new combiner configuration is designed based on the fact that when one compares the amount of flux linkage of two loops with butterfly elements separated by the same distance, the loop elements have much higher coupling than the butterfly elements. Results:The results are demonstrated using an imagingbased element coupling measurement method. The new quadrature combiner configuration has introduced an approximately -8dB improvement in preamplifier decoupling. Conclusion:One-dimensional quadrature phased arrays can be built even if the preamplifier is not integrated in the coil. If the combiner is placed between the coil and the preamplifiers, the butterflies should be on the high impedance side of the quadrature combiner. The loops should see the low input impedance of the preamplifiers.

High field magnetic resonance offers new opportunities because of its high SNR and better spectral resolution for MRI and MRS. However, new problems also emerge at high field. As the field strength increases, the wavelength in the tissue becomes shorter and comparable with the body dimensions. This perturbs the field and also causes standing waves within the patient as a result of the impedance mismatching at the tissue interfaces. Due to the complexity of the boundary conditions and the solution of Maxwell's equations, an exact analytical calculation for a loaded RF resonator has not been possible. In this paper, we present a birdcage coil simulation study based on a 3D finite element method (FEM) model for the characterization of the field within the tissue. First, the accuracy of the FEM solutions is validated by the 2D analytical solutions at 64 and 223 MHz. In these solutions, the frequency dependence of the conductivity and permittivity is also taken into account. Then, a more realistic 3D model is studied. The results are compared with the experimental measurements. It is shown that the 3D model makes it possible to explore the effects of the end rings in the presence of a tissue sample inside the coil.

Although in the design of transmit RF coils, B 1 homogeneity is crucial for good image quality, discussion of electric field (E-field) distribution in the literature has been mostly limited to specific absorption rate (SAR) and patient loading (dielectric) effects. In this work, we report on a different aspect of E-field: the receive-only surface coil heating resulting from the voltage drop across the blocking (decoupling) networks and cable traps that are used to minimize the transmit field distortion. The results show that the z-component (parallel to the coil cable) of the E-field has a significant effect on the temperature rise in the surface coil. Therefore, in the receive-only coil designs, it is not sufficient to consider only the induced voltage on the coil loop due to the B 1 field, as is generally done in blocking network analysis calculations. The body coil E-field distribution must be considered as well. J. Magn. Reson. Imaging 2001;14:484 -487.