Navigator gating and volume tracking for double-triggered cardiac proton spectroscopy at 3 Tesla

Respiratory motion compensation based on navigator echoes for double-triggered cardiac proton spectroscopy at 3.0 T is presented. The navigators measure the displacement of the liver-lung interface during free breathing. This information allows for double triggering on a defined window within the respiratory cycle and on a defined trigger delay after the R-wave based on the ECG. Furthermore, it allows the excitation volume to be shifted by the determined respiratory displacement within the defined window in real-time (volume tracking). Static and motion phantom experiments were performed in this study, and it was demonstrated that volume tracking permits the suppression of signal from tissue next to the localized volume. However, triggering on a defined respiratory position is still necessary to achieve high spectral quality, because shimming and water suppression calibration are only optimal for a small window of the respiratory cycle. Single-volume spectra obtained in the myocardial septum of healthy subjects are presented.