INTRODUCTION

Chemical Exchange Saturation Transfer (CEST) has been attracting attention as a molecular imaging method to investigate myocardial muscle energetics according to creatine changes. In this study, we proposed a robust CEST imaging technique from cardiac and respiratory motion using golden angle radial readout to achieve CEST imaging at the heart of the rat. We investigated the feasibility of the proposed method for the creatine phantom and a normal rat.

METHODS

As shown in Figure 1, motion-robust radial readout was used to apply CEST images to the heart of small animals. And golden angle radial trajectory was used to enable self-gating to remove the influence of breathing motion from the navigation echo. The train of magnetization transfer (MT) pulses were used for the CEST effect, and the MT pulse using the gaussian pulse had the properties of 270deg flip angle and 200Hz bandwidth. A segmented radial scan was performed in the mid-diastolic phase with CEST pulse for 10 seconds over 50 heart beats to give a sufficient CEST effect. Thereafter, it had a quiescent time of 5 seconds for T1 recovery. To investigate the feasibility of the radial CEST, we experimented with Creatine Phantom and normal Rat. Analysis of CEST was performed at 2 ppm using multiple Lorentzian fittings.²

RESULTS

Figure 2 shows the result of the CEST experiment with Creatine phantom. The Cr sample with a concentration of 100 mM showed a high CEST contrast in the Z-spectrum and the CESTasym in the 2 ppm. Figure 3 shows the result of applying respiratory gating using the navigation echoes in a rat. Figure 4 shows the possibility of a radial CEST method in the heart of a normal rat. Weak CEST contrast was observed in the 2 ppm.

DISCUSSION

We proposed a CEST imaging technique using a radial trajectory to obtain CEST images from the heart of a rat with rapid cardiac and respiratory cycles. As shown in the phantom experiment in Figure 2, the samples with creatine at 2 ppm showed a high CEST contrast but no distilled water (DW). In Figure 4, CEST contrast was also seen at 2 ppm in the heart of the in vivo rat. The navigation echo obtained at the end of a segmented radial scan can be used as a source of respiratory gating because it can detect changes due to breathing. The radial scan itself is robust to the artifacts associated with movement, but the use of respiratory gating has shown that the boundary between the myocardium and the blood becomes clearer.

Acknowledgements

This work was supported by the National Research Foundation of Korea (RF) grant funded by the Korea government (MISP) (No. 2016R1C1B1013837)