The surface-coil NMR receiver in the presence of homogeneous B1 excitation

MR spectroscopy using multi-ring surface coils

“…Instead, the intrinsic SNR was calculated using Eq. [9] with R C ϭ 0. This gives a reasonable approximation of the true SNR as found by experiment when sample losses dominate (R S ϾϾ R C ).…”

“…Another problem in using separate transmit/receive coils for spectroscopy is that, in general, the relative B 1 -field direction of the transmit-and-receive coils at a particular point in the sample is different, resulting in irretrievable loss of signal and a sample-dependent signal phase (9,15,20). This effect may also degrade the efficacy of shimming procedures used in MR (15).…”

“…Strategies to overcome surface coil B 1 inhomogeneity include the use of separate transmit-and-receive coils (8)(9)(10) or adiabatic RF pulses. Drawbacks associated with a larger, more homogeneous transmit coil include increased RF power requirements and specific absorption rate (SAR), RF penetration effects (11)(12)(13), and coil decoupling requirements (10,(14)(15)(16), described in more detail previously (17).…”

Performance of a high-temperature superconducting probe for in vivo microscopy at 2.0 T

“…However, decoupling is difficult to achieve in practice (4) since surface coils produce a B 1 that varies its orientation depending on position. Other schemes for decoupling have been shown to degrade the SNR by introducing active or passive elements into the electrical circuit (3,5). Such noise contributions become even more intolerable in the context of the low HTS coil noise.…”

“…The challenge with HTS probes is to decouple the coils while preserving the SNR of the probe. One technique for decoupling the coils is orienting the B 1 fields (the alternating magnetic field produced by the RF coil) orthogonal to each other (3). However, decoupling is difficult to achieve in practice (4) since surface coils produce a B 1 that varies its orientation depending on position.…”