Low frequency electron paramagnetic resonance imaging is a powerful tool to noninvasively measure the physiological status of tumors. Here, we report on the design and functionality of a rapid scan and pulse tabletop imaging spectrometer based around an arbitrary waveform generator and 25 mm cross-loop resonator operating at 700 MHz. Two and four-dimensional rapid scan spectral-spatial images are presented. This tabletop imager is a prototype for future preclinical imagers.
Recording of data other than MR signals are often of interest during MRI. We present unique, versatile circuitry developed for sampling and real-time processing of such non-MR signals to facilitate recording of these by an MR scanner. The circuitry is capable of acquiring multiple signals at 200 kHz sampling rate, measure RF power correlates, perform fast and flexible signal processing, and transmitting both amplitude and frequency modulated RF signals receivable by MR scanners. As an example of use, an electronic point-source signal is generated by the circuitry, and transmitted wirelessly to the receive coil of an MR scanner during an echo planar imaging sequence.
Next to conventional magnetic resonance imaging (MRI), which utilizes hydrogen nuclei, other nuclei, so-called X-nuclei, are of increasing interest since they can provide additional diagnostic information. However, X-nuclei MRI is challenging due to the lower Signal-to-Noise Ratio (SNR) compared to 1H (35Cl provides approximately 200 000 times lower SNR than 1H). In order to compete with this challenge, the use of high-field strengths and optimized hardware is crucial. In this work, a transmit-only receive-only (TORO) system for 35Cl MRI at a preclinical 9.4 T scanner is presented, composed of a volumetric birdcage coil and a 3 channel Rx array. SNR degradation despite preamplifier decoupling can no longer be neglected since the resonance frequency of 35Cl is low. This paper will prove the SNR degradation due to the coil coupling of the receiver coils for this setup and evaluate three different approaches to mitigate the SNR degradation. The performance of the different approaches is evaluated via single channel and combined SNR maps using phantom measurements. Finally, the SNR maps acquired with the Rx array are compared to the SNR map acquired using the Birdcage coil as a reference.
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