NMR probeheads for in vivo applications

Small-animal MRI: signal-to-noise ratio comparison at 7 and 1.5 T with multiple-animal acquisition strategies

“…However, typical preamplifier noise figure values are lower on clinical systems (0.5 ± 0.1 dB for Siemens; 1.8 ± 0.1 dB from Bruker). This difference could also explain the relatively low performance of the 7-T system compared to the clinical 1.5-T system; the difference in noise figures accounts for 16% degradation in SNR [17]. Today, state-of-theart coils for 1.5-T systems are equipped with preamplifiers with noise figures below 0.4 dB, whereas new small-animal high-field systems (7 up to 11.7 T) are equipped with preamplifiers with a noise figure below 1.2 dB.…”

Progress towards in vivo brain 13C-MRS in mice: Metabolic flux analysis in small tissue volumes

“…All brain regions are virtually close to the coil when compared to a human surface coil, although sensitivity varies substantially along the coil axis due to B 1 inhomogeneity, which can nevertheless be mitigated with the use of adiabatic pulses for excitation. However, it could be expected that inhomogeneities in the B 1 field over the sample are reduced in mice due to the relative size of the coil compared to the brain: the Biot-Savart law dictates that the B 1 field on the loop axis has a penetration depth of approximatively a coil radius, so that theoretically the sensitivity would scale as r À1 when other sources of loss are neglected [89]. Since the 13 C loop diameter is usually comparable with the brain diameter in mice, the B 1 field will penetrate more than in the human brain where the size of the loop (80e100 mm [90]) is much smaller than the diameter of the brain.…”

Automatic tuning of flexible interventional RF receiver coils

“…Here we describe its dependence on the tuning and matching of the probe. Haase et al (27) provided an alternative treatment within the broader context of RF coil design.…”