Figure 1
Acoustic Spectrogram obtained at 7.0 T. Spectrogram obtained from a subject positioned at the 7.0 T magnet's isocenter during 2D CINE FLASH acquisitions (TE = 2.0 ms, TR = 4.0 ms). The graphs show signal contributions from gradient switching superimposed on the cardiac signals. The gradient switching manifests itself by several very sharp harmonic components at 1/TR, 2/TR, 3/TR and 1/TE with maximum sound pressure level close to 120 dB. The spectrogram also shows the 1st and the 2nd heart tone which are of low-frequency nature. Acoustic signal-to-noise ratio, which is defined as the ratio between the sound pressure level due to cardiac activity and the gradient switching induced sound pressure level is approximately 30 dB for the frequency range between 10 Hz and 70 Hz.