Volume tracking cardiac 31P spectroscopy.

The limited reliability and accuracy of cardiac spectroscopy have been partly attributed to effects from respiratory motion. In this work, we developed a prospective volume tracking method for respiratory motion compensation based on multiple navigator echoes and demonstrated its application in cardiac (31)P spectroscopy. The sequence consists of two 2D selective excitation pulses preceding the spectroscopic experiment to sample respiratory motion components. The navigator information is evaluated in real-time to calculate the shift of the heart from respiration. Based on the displacement information, the spectroscopic volume and/or grid position is prospectively corrected to track the volume of interest. The method was validated with a moving compartment phantom simulating in vivo respiratory motion. With volume tracking, no signal contamination was apparent. Spectra obtained in 14 healthy volunteers were evaluated using time-domain fitting procedures. The fitting accuracy improved consistently with volume tracking compared to data from non-navigated reference acquisitions. Compared to other gating approaches available for spectroscopy, the current technique does not degrade the scan efficiency, thus allowing effective use of scan time.