Parallel-plate split-conductor surface coil: Analysis and design
ABSTRACT A split-conductor circular parallel-plate resonator with one end shorted to ground can be used to one's advantage as a surface coil for NMR imaging experiments. It can be easily constructed by a printed-circuit method and possesses a relatively high loaded Q with negligible frequency detuning. From the proposed equivalent circuit, an equation was derived that relates the self-resonance frequency of the resonator to the split distance measured from a reference point. An example of a 101-mm-diameter surface coil operating at 26 MHz for 31P in vivo spectroscopy is given to illustrate the concordance between calculated and experimental results. Complementary equations and formulas are also included to assist researchers in designing their own antennas to meet specific requirements.
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ABSTRACT: Surface coils are used widely in magnetic resonance imaging (MRI) application for their ability to operate in receive mode with high signal-to-noise ratio (SNR). In this work we show how the choice of the polygonal geometry and the number of distributed capacitors affects the coil overall performance. Several surface coils, tuned at 297.2 MHz, were designed and built, using different polygonal geometries and different number of the capacitors. Realized coils were tested and characterized by laboratory workbench in order to extract several quality indices. In addition, experiments were done in a whole body MRI scanner to evaluate the SNR. The optimal choice of coil shape and capacitors numbers allows us to obtain high-quality surface coils tuned at frequencies in the ultra-high field. According to the signal to noise ratio images, the circular shaped coil with four capacitors shows the most uniformity of the B1+ RF-field.
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ABSTRACT: Multi-turn split-conductor transmission-line resonators (MSTR) can be designed to operate over a wide range of NMR operating frequencies without lumped tuning capacitors. This architecture constitutes an alternative solution to recent designs proposed for high-Q, thin-film, high-temperature superconducting NMR probes. An advantage is that the resonant frequency can be calculated in a relatively simple manner in terms of coil turns or total coil length, coil width, substrate thickness, and dielectric constant. Analytical calculation of the resonant frequency is provided. Also, a series of MSTRs was constructed on a double copper-clad substrate, and their resonant frequencies are noted. The results obtained were in good agreement with the predicted values.Magnetic Resonance in Medicine 10/1997; 38(4):687-689. DOI:10.1002/mrm.1910380424 · 3.40 Impact Factor
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ABSTRACT: Purpose This paper presents a novel inductive decoupling technique for form-fitting coil arrays of monolithic transmission line resonators (TLR), which target biomedical applications requiring high SNR over a large FOV to image anatomical structures varying in size and shape from patient to patient. Methods Individual TLR elements are mutually decoupled employing magnetic flux sharing by overlapping annexes. This decoupling technique was evaluated by electromagnetic simulations and bench measurements for two- and four-element arrays, comparing single- and double-gap TLR designs, combined either with a basic capacitive matching scheme or inductive pick up loop matching. The best performing array was used in 7T MRI experiments demonstrating its form-fitting ability and parallel imaging potential. Results The inductively matched double-gap TLR array provided the best decoupling efficiency in simulations and bench measurements (< 15 dB). The decoupling and parallel imaging performance proved robust against mechanical deformation of the array. Conclusion The presented decoupling technique combines the robustness of conventional overlap decoupling regarding coil loading and operating frequency with the extended FOV of non-overlapped coils. While demonstrated on four-element arrays, it can be easily expanded in order to fabricate readily decoupled form-fitting 2D arrays with an arbitrary number of elements in a single etching process.Magnetic Resonance in Medicine 04/2014; early view. DOI:10.1002/mrm.25260 · 3.40 Impact Factor