PET/MR – simultaneous hybrid imaging with Intragate: freezing PET cardiac and respiratory motion with MRI

Ziel/Aim:

Despite all advances in the last decade in PET/MR imaging hardware, true hybrid imaging would require acquiring MRI and PET data simultaneously to better understand and pinpoint dynamically evolving physiological conditions. Implementations like positron energy range correction, motion correction and plasma activity corrections are even more important and difficult when moving to high magnetic field strength and stronger MR gradients. One of the most challenging applications for simultaneous PET/MR is cardiac imaging. Therefore, we implemented MRI self-gating sequences in PET data reconstruction to advance PET/MR hybrid imaging.

Methodik/Methods:

The MRI self-gating sequences use so-called MR navigator information for the determination of cardiac and respiratory motion [1]. The state of the cardiac and respiratory motion is assigned to every navigator time. The MRI- and PET scanners are synchronized by the navigator events and the cardiac and respiratory motion states are used to retrospectively reconstruct synchronized motion cines or images of specific motion states.

Ergebnisse/Results:

¹⁸F-FDG PET and MRI data have been simultaneously acquired and synchronous respiratory gated cardiac cines were successfully reconstructed retrospectively. Spatially encoded navigators were used to retrieve information out of different regions such as the vena cava, ascending aorta, the heart itself and even multiple hearts in a multiple mouse setting.

Schlussfolgerungen/Conclusions:

Intragate offers a unique, non-invasive tool, providing simultaneously metrics of global heart function (end-diastolic and systolic volume, ejection fraction and cardiac output, pulsatile-flow, aortic function, cardiac motion) and monitoring of respiration motion. Simultaneously acquired PET scans can now be reconstructed implementing this information and this allows for drastically improved PET data analysis and correction.

Literatur/References:

[1] Bovens SM et al., Evaluation of infarcted murine heart function: comparison of prospectively triggered with self-gated MRI; NMR Biomed. 2011; 24: 307 – 315