The concept can be compared to the use of circular polarized receive coils which employ two quadrature coil elements and combines these into a single receive signal. These make use of the fact that the majority of the receive signal’s power is contained in a small number of RF modes. in spine imaging and moving table acquisitions.Īn early commercial solution to the problem was the incorporation of mode matrices in the receiver coil array. The problem is aggravated when large fields-of-view are to be covered and multiple coil arrays are used during a scan, e.g. Thus, the number of receive antennas (coils)–or at least the number of physical connection points in the patient table –present in an MRI examination frequently exceeds the number of receivers available in the system. Unfortunately, this has a significant negative impact in terms of machine cost due to the requirement for additional receiver units and a technologically complex patient table, on patient comfort and operator workflow arising from the bulky cable bundles on the local RF coils, and on the large amounts of data that require handling prior to final image reconstruction. With the increase in the number of elements in phased array coils, more and more parallel receive channels are required per MRI system. These include, but are not limited to, imaging the beating heart, fast functional/diffusion imaging and correcting unwanted artifacts, e.g. In fact, several applications would not be feasible at all without parallel imaging techniques. Moreover, reducing the scan time brings about further benefits in terms of increasing patient compliance (shorter scan times are more comfortable for the patient) and enables an increased workload of expensive MRI machinery (patient throughput can be increased). in multi-nuclear or multi-parametric measurements) within a given time frame. Currently, they are routinely employed to improve image quality, to reduce the scan time or to obtain more information (e.g. Modern magnetic resonance imaging (MRI) systems rely heavily on parallel imaging techniques using multi-channel, phased array coils. For a matrix with 128 inputs and 64 outputs a realization is proposed that displays a worst-case insertion loss of 3.8 dB. Here, we demonstrate the use of metaheuristic approaches to optimize the circuit design of these matrices that additionally carry out the optimization of distances between the parallel transmission lines. The selection of a limited number of lumped element reactance values to compensate for the for the effect of transmission line stubs in large-scale switch matrices capable of supporting multi-nuclear operation is non-trivial and is a combinatorial problem of high order. Thus, especially for high-field systems compensation mechanisms are required to remove the effects of open-ended transmission line stubs.
However, in this configuration, long open-ended transmission lines can potentially remain connected to the signal path leading to high transmission losses. A highly flexible implementation is a crossbar topology that allows to any one input to be routed to any one output and can use single PIN diodes as active elements. These exist in a variety of topologies and differ in routing flexibility and technological implementation. This is usually accomplished with the use of switch matrices. However, for a number of practical, economic and safety reasons, it is better to only route a subset of the connectors. Given that the MR system is equipped with a limited number of digitizing receivers and in order to support operation of multinuclear coil arrays, these connectors need to be flexibly routed to the receiver outside the RF shielded examination room. Modern magnetic resonance imaging systems are equipped with a large number of receive connectors in order to optimally support a large field-of-view and/or high acceleration in parallel imaging using high-channel count, phased array coils.
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