A Four-Channel Broadband MRI Receive Array Coil.

Low-impedance preamplifier decoupling is commonly used in RF coil array construction to minimize coupling between elements through mutual impedance. The trap circuit is an essential component in preamp decoupling techniques, but becomes a limiting factor in constructing multi-tuned, multi-nuclear coil arrays. In principle, it is possible to double-tune or multi-tune the trap circuits, but will add complexity and loss. We present a broadband decoupling approach using high impedance preamplifiers. A dual-tuned prototype four-channel array using this approach which targets 2H and 23 Na at 4.7T, has been previously constructed, evaluated and reported. Without any retuning of the array, the same setup is tested at the 23Na and 31P frequencies for 3T. Initial bench measurements and Chemical Shift Imaging (CSI) results are acquired and presented in this study.Clinical Relevance- This study could reduce the complexity of multi-nuclear array coil design.

A Novel Voltage Controlled Decoupling Method for Transmit Coils in MRI.

Array coils are ubiquitous in MRI and are becoming more widely used in MR spectroscopy. Conventional PIN diode decoupling circuits require significant currents to forward bias the diodes. The approach proposed here does not require significant current and thus reduces concerns for contaminating the B0 homogeneity with the detune current. Additionally, the proposed approach will facilitate the construction of array coils for MRI due to its simplicity.Clinical Relevance- Decoupling is critical for constructing RF coil arrays and enables rapid MR imaging.

Low-cost MRI System for Teaching.

Magnetic resonance imaging instrumentation is taught at Texas A&M University through the ECEN 463 course and its graduate level equivalent. This class guides students through several labs where they design their own desktop MRI system using various hardware components and LabVIEW. Because the system uses professional grade equipment, the cost of each lab station is high. As a result, there are only four lab stations available, which limits the class to 32 students. The equipment also contains parts that have become obsolete, inhibiting the ability to maintain the system long term. This project focuses on using easily accessible and more affordable equipment for the MRI system. It can also potentially provide opportunities for remote learning, where students could work on assignments off-campus. Other projects have aimed to design low-cost MRI systems with an emphasis on clinical applications or which require advanced FPGA programming skills or pre-programmed modules. This project will develop the MRI instrumentation with updated off-the-shelf components. The current equipment will be replaced with two Analog Discovery 2 devices, which are low-cost teaching tools. It will also feature inexpensive transmit and receive chains, off-the-shelf gradient amplifiers suitable for teaching, gradient coils for signal localization, and a lighter-weight Halbach magnet. In this stage of the project, projections and images have been captured using a 0.06T permanent magnet. In addition to validating successful system operation, each lab of the course will be integrated with current materials to comply with the new equipment. Hardware and software resources will also be prepared and scaled to meet classroom needs and ensure a smooth transition. The goal of the project is to use the new system starting in the fall 2023 semester.Clinical Relevance- This project shows that low-cost equipment can be implemented into a working MRI system. The intent for this project may be educationally focused, but it shows that extremely light and low-cost systems can be created. It may be reconstructed to have a deployable system that could be used in the field.

Wideband receive-coil array design using high-impedance amplifiers for broadband decoupling.

PURPOSE: Multinuclear MRI/S is of increasing interest. Currently, most multinuclear receive array coils are constructed by nesting multiple single-tuned array coils or using switching elements to control the operating frequency, in which case more than one set of conventional isolation preamplifiers and associated decoupling circuits is required. These conventional configurations rapidly become complicated when greater numbers of channels or nuclei are needed. In this work, a novel coil decoupling mechanism is proposed to enable broadband decoupling for array coils with one set of preamplifiers. METHODS: Instead of using conventional isolation preamplifiers, a high-input impedance preamplifier is proposed to create broadband decoupling of the array elements. A matching network consisting of a single inductor-capacitor-capacitor multi-tuned network and a wire-wound transformer was used to interface the surface coil to the high-impedance preamplifier. To validate the concept, the proposed configuration was compared to the conventional preamplifier decoupling configuration on both bench and scanner. RESULTS: 2 The approach can provide more than 15dB decoupling over a range of 25MHz, covering the Larmor frequencies of 23 Na and 2 H at 4.7T. This multi-tuned prototype obtained 61% and 76% of the imaging SNR at 2 H and 23 Na respectively, 76 and 89% in a higher loading test phantom, when compared to the conventional single-tuned preamplifier decoupling configuration. CONCLUSION: With the multinuclear array operation and decoupling achieved using only one layer of array coil and preamplifiers, this work provides a simple approach of building high element-count arrays to enable accelerated imaging or SNR improvement from multiple nuclei.

Investigation of Low-Cost Op-Amps as Decoupling Preamplifiers for MRI Array Coils.

The benefits of array coils in MRI and MRS are well known. A key component of essentially all array coils used today is the decoupling preamplifier. Unlike conventional 50 ohm low-noise preamps, decoupling preamps present a reactive impedance to the coil, which can be used to 'block' currents from being induced in the receive coil, reducing the impact of any electromagnetic coupling between array elements. While available from a number of vendors, a lower-cost solution would be advantageous. We investigate the use of conventional operational amplifiers as low-noise decoupling preamplifiers. In this paper the performance of the op-amp preamplifier is compared to conventional 50 Ω. The op-amp preamp design shows promise for use as a decoupling preamplifier with array coils.Clinical Relevance- This work could facilitate the development of array coils for spectroscopy and imaging.