ABSTRACT
In this article, we evaluated the performance of radiofrequency (RF) coils in terms of the signal-to-noise ratio (S/N) and homogeneity of magnetic resonance images when used for ultrahigh-frequency (UHF) 7T magnetic resonance imaging (MRI). Highquality MRI can be obtained when these two basic requirements are met. However, because of the dielectric effect, 7T magnetic resonance imaging still produces essentially a non-uniform magnetic flux (|B1 |) density distribution. In general, heterogeneous and homogeneous RF coils may be designed using electromagnetic (EM) modeling. Heterogeneous coils, which are surface coils, are used in consideration of scalability in the |B1 | region with a high S/N as multichannel loop coils rather than selecting a single loop. Loop coils are considered state of the art for their simplicity yet effective |B1 |-field distribution and intensity. In addition, combining multiple loop coils allows phase arrays (PA). PA coils have gained great interest for use in receiving signals because of parallel imaging (PI) techniques, such as sensitivity encoding (SENSE) and generalized autocalibrating partial parallel acquisition (GRAPPA), which drastically reduce the acquisition time. With the introduction of a parallel transmit coil (pTx) system, a form of transceiver loop arrays has also been proposed. In this article, we discussed the applications and proposed designs of loop coils. RF homogeneous coils for volume imaging include Alderman-Grant resonators, birdcage coils, saddle coils, traveling wave coils, transmission line arrays, composite right-/left-handed arrays, and fusion coils. In this article, we also discussed the basic operation, design, and applications of these coils.
ABSTRACT
Aims: To inhibit the mycelia growth inhibition and reproductive capacity of important phyto-pathogen fungus: Fusarium oxysporum by cell-extracts from submerged cultures of Trichoderma. Study Design: A complete randomized experimental design with factorial fix was used. Place and Duration of Study: Laboratory of plant-pathology, Department of Agricultural Parasitology, Universidad Autónoma Agraria Antonio Narro (UAAAN), Mexico, between August 2012 and March 2012. Methodology: Metabolic extract of Trichoderma asperellum produced in liquid medium and Trichoderma dual cultures on F. oxysporum isolated infected plant pepper was evaluated; both strains were subsequently activated in PDA and tested in dual culture and poisoned culture with Trichoderma strains and metabolic extracts against F. oxysporum to determine their growth inhibition potential. Results: Strains Trichoderma were able to inhibit the growth of the plant pathogen, demonstrating to be an attractive alternative for biological control assays. Similar results were obtained with metabolic extracts, where the inhibition was affected up to 29%, the conidiogenesis by 30% and spore viability by 60% at the highest concentration tested. Conclusions: Metabolites produced have the power to reduce the reproductive capacity of F. oxysporum, decreasing sporulation and inhibit the germination of conidia, and this is extremely important, as reducing the quantity and viability of conidia, it is reducing the secondary inoculum of the pathogen.
ABSTRACT
PURPOSE: To efficiently evaluate phased array coil performance using a software tool box with which we can make visual comparison of the sensitivity of every coil element between the real experiment and EM simulation. MATERIALS AND METHODS: We have developed a C++- and MATLAB-based software tool called Phased Array Coil Evaluator (PACE). PACE has the following functions: Building 3D models of the coil elements, importing the FDTD simulation results, and visualizing the coil sensitivity of each coil element on the ordinary Cartesian coordinate and the relative coil position coordinate. To build a 3D model of the phased array coil, we used an electromagnetic 3D tracker in a stylus form. After making the 3D model, we imported the 3D model into the FDTD electromagnetic field simulation tool. RESULTS: An accurate comparison between the coil sensitivity simulation and real experiment on the tool box platform has been made through fine matching of the simulation and real experiment with aids of the 3D tracker. In the simulation and experiment, we used a 36-channel helmet-style phased array coil. At the 3D MRI data acquisition using the spoiled gradient echo sequence, we used the uniform cylindrical phantom that had the same geometry as the one in the FDTD simulation. In the tool box, we can conveniently choose the coil element of interest and we can compare the coil sensitivities element-by-element of the phased array coil. CONCLUSION: We expect the tool box can be greatly used for developing phased array coils of new geometry or for periodic maintenance of phased array coils in a more accurate and consistent manner.