Abstract
A quality assurance protocol for RF coils is proposed, which can be used for volume (Tx/Rx) and surface (Rx) coils. Following this protocol, a benchmarking of seven coils (from three different MR sites) dedicated to 13C MRI at 3T is reported. Coil performance is particularly important for 3T MRI at the 13C frequency, since the coil-to-sample noise ratio is typically high. The coils are evaluated experimentally using the proposed protocol based on MR spectroscopic imaging performed with two different phantoms: one head-shaped, and one with cylindrical shape and nearly twice the volume of the first one. To achieve an unbiased SNR comparison of volume and array coils, coil combination was done using sensitivity profiles extracted from the data. SNR, noise correlation matrices and example g-factor maps are reported. For globally calibrated, equal excitation angles, the measured SNR shows large differences for the volume coils of up to 115% at the phantom center for a head phantom. The arrays show lower differences in superficial SNR. The sample surface depth at which the volume coils outperform the arrays is estimated to 7 cm, and SNR furthest away from the coil surface is 28% lower for the best array compared to the best volume coil. A broad set of coils for 13C at 3T have been benchmarked. The results reported, and the method used to benchmark them, should guide the 13C community to choose the most suitable coil for a given experiment.
Highlights
The number of magnetic resonance (MR) applications for hyperpolarized 13C compounds using dissolution dynamic nuclear polarization [1,2,3] has grown steadily over the last decade
The inclusion of Coil #7 in this study provides a comparison for surface signal-to-noise ratio (SNR), which is not impaired by mutual coupling to other elements
The SNR distributions are consistent with the coil geometries, and Coil #3 has the least homogenous volume of the three volume coils
Summary
The number of magnetic resonance (MR) applications for hyperpolarized 13C compounds using dissolution dynamic nuclear polarization (dDNP) [1,2,3] has grown steadily over the last decade. One of the challenges of this technique for its clinical use is the need of dedicated radiofrequency (RF) hardware for the lower Larmor frequency of 13C, as opposed to the standard 1H RF hardware. Apart from its cost, transmit amplifiers do not imply a large technological burden, while the RF coils pose a significant challenge due to the lower resonance frequency of the 13C nuclei and combination with existing 1H coils. The lower frequency implies that the coils operate in (or close to) a regime where their electronic noise. Relatively small differences in coil losses will have a direct impact on the signal-to-noise ratio (SNR) of the MR images. The dominating sample noise will often mask the effect of coil conductor losses on SNR
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