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. Author manuscript; available in PMC: 2017 Mar 22.
Published in final edited form as: Phys Med Biol. 2016 Apr 6;61(9):3500–3526. doi: 10.1088/0031-9155/61/9/3500

Figure 4.

Figure 4

Measured reflection coefficient (S11, magnitude) as a function of frequency for the birdcage resonator. The resonance spectrum includes resonance modes at which an energy transmission to the RF resonator is highly efficient. The mode that provides a homogeneous RF field distribution and is therefore used for spin excitation is highlighted with a grey-shaded area. In contrast, the modes at lower frequencies do not provide a homogeneous field distribution and are therefore not of interest for MRI applications. Hence, a band-pass filter (also indicated by the grey-shaded area) is applied around the Larmor frequency at 3 T. To avoid noise coupling, the sensor die clock frequency is shifted in such a way that as little energy as possible is emitted in the frequency region of the band-pass filter.